WO2023233932A1 - Carbon nanotube layered structure, carbon nanotube dispersion liquid, coating liquid for production of electronic element, carbon nanotube film, and electronic element - Google Patents

Carbon nanotube layered structure, carbon nanotube dispersion liquid, coating liquid for production of electronic element, carbon nanotube film, and electronic element Download PDF

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WO2023233932A1
WO2023233932A1 PCT/JP2023/017316 JP2023017316W WO2023233932A1 WO 2023233932 A1 WO2023233932 A1 WO 2023233932A1 JP 2023017316 W JP2023017316 W JP 2023017316W WO 2023233932 A1 WO2023233932 A1 WO 2023233932A1
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carbon nanotube
carbon nanotubes
catalyst
layer
carbon
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French (fr)
Japanese (ja)
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惠美 村川
広和 高井
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日本ゼオン株式会社
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/15—Nano-sized carbon materials
    • C01B32/158—Carbon nanotubes
    • C01B32/168—After-treatment
    • C01B32/174—Derivatisation; Solubilisation; Dispersion in solvents
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof  ; Multistep manufacturing processes therefor
    • H01L29/02—Semiconductor bodies ; Multistep manufacturing processes therefor
    • H01L29/06—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by their shape; characterised by the shapes, relative sizes, or dispositions of the semiconductor regions ; characterised by the concentration or distribution of impurities within semiconductor regions
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10B—ELECTRONIC MEMORY DEVICES
    • H10B63/00—Resistance change memory devices, e.g. resistive RAM [ReRAM] devices
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N70/00—Solid-state devices without a potential-jump barrier or surface barrier, and specially adapted for rectifying, amplifying, oscillating or switching
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N99/00—Subject matter not provided for in other groups of this subclass

Definitions

  • the present invention relates to a carbon nanotube laminate structure, a carbon nanotube dispersion, a coating liquid for manufacturing electronic devices, a carbon nanotube film, and an electronic device.
  • ReRAM resistance variable memory devices
  • a resistance change memory device has advantages such as low power consumption, high density, and high speed readout.
  • Patent Document 1 describes a variable resistance memory device in which a variable resistance layer constituting a memory cell is made of carbon nanotubes (hereinafter sometimes referred to as CNT).
  • CNT carbon nanotubes
  • the present invention functions as a functional region of an electronic device (e.g., resistance variable layer of a resistance variable memory device), and enables the electronic device to operate at a low switching voltage when used as the functional region of the electronic device.
  • the present invention aims to provide a carbon nanotube layered structure and a carbon nanotube dispersion that can be used to form a carbon nanotube film.
  • the present invention functions as a functional region of an electronic device (e.g., a variable resistance layer of a variable resistance storage device), and when used as a functional region of an electronic device, the electronic device can operate at a low switching voltage.
  • the purpose of the present invention is to provide a carbon nanotube film, a coating liquid for manufacturing electronic devices, and an electronic device that can be operated at a low switching voltage.
  • the present inventors conducted extensive studies to achieve the above object.
  • the present inventors have discovered that when forming a resistance change layer of a resistance change memory device, by using a carbon nanotube stacked structure formed by stacking a plurality of oxidized flat carbon nanotubes with a high single-layer ratio, electronic devices can be fabricated.
  • the present invention was completed based on the discovery that it is possible to lower the switching voltage.
  • a carbon nanotube laminate structure formed by laminating a plurality of oxidized flat carbon nanotubes, in which the ratio of single-walled carbon nanotubes to all carbon nanotubes in the carbon nanotube laminate structure is within 100 carbon nanotubes.
  • a laminated carbon nanotube structure having 51 or more carbon nanotubes.
  • the carbon nanotubes By using high single-wall ratio carbon nanotubes that have been oxidized as carbon nanotubes, by performing ultrasonic dispersion treatment under specified conditions in a solvent, the carbon nanotubes can easily take on a flat shape, and furthermore, the flat carbon nanotubes can be It becomes easier to form a laminated structure formed by laminating a plurality of layers (hereinafter sometimes referred to as "flat carbon nanotube laminated structure").
  • carbon nanotubes have such a flat carbon nanotube stacked structure, and furthermore, due to the high content of single-walled carbon nanotubes, the functional areas of electronic devices (e.g., the resistance change layer of resistance change storage devices) are This contributes to a reduction in switching voltage when used for formation.
  • Evaluation of whether carbon nanotubes are oxidized i.e., measurement of the degree of oxidation
  • measurement of the content ratio of single-walled carbon nanotubes i.e., measurement of the content ratio of single-walled carbon nanotubes
  • evaluation of whether carbon nanotubes have a flat carbon nanotube layered structure can be performed, for example, by This can be done using the methods described in the Examples.
  • the present invention [2] It is preferable to provide the carbon nanotube laminate structure according to [1] above, wherein the diametrical oblateness of the oxidized flat carbon nanotubes is 10% or more and 40% or less. If the flatness of the CNT is 40% or less, the CNT has a sufficiently flat shape, which contributes to a reduction in switching voltage when the carbon nanotube laminated structure is used in a functional area of an electronic device (e.g., variable resistance layer). . On the other hand, since there is an interlayer distance between the graphite structures of the inner wall, it is difficult to make the flatness of CNT less than 10%.
  • the aspect ratio can be determined, for example, by the method described below.
  • the present invention [3] It is preferable to provide the carbon nanotube laminated structure according to [1] or [2] above, wherein the average number of laminated layers is 2 or more and 20 or less.
  • the average number of laminated layers is within the above range, the effect of lowering the switching voltage when used for forming a functional region of an electronic device (eg, a resistance variable layer of a resistance variable memory device) can be enhanced.
  • the average number of laminated layers can be measured, for example, by the method described in Examples.
  • the present invention [4] It is preferable to provide the carbon nanotube laminate structure according to any one of [1] to [3] above, wherein the average length of the carbon nanotube laminate structure is 20 nm or more and 300 nm or less. It is preferable that the average length of the carbon nanotube laminate structure is 20 nm or more, since the properties such as conductivity of the carbon nanotube laminate structure are not impaired. It is preferable that the average length of the carbon nanotube laminate structure is 300 nm or less in order to prevent the carbon nanotube laminate structure from agglomerating and settling in a solvent.
  • the average length of the carbon nanotube stacked structure can be determined, for example, by the method described below.
  • the present invention [5] It is preferable to provide the carbon nanotube laminate structure according to any one of [1] to [4] above, wherein the plurality of carbon nanotube laminate structures intersect with each other. Because multiple carbon nanotube stacked structures intersect with each other, the switching voltage reduction effect is further improved when used to form a functional region of an electronic device (e.g., resistance variable layer of a resistance variable memory device). do.
  • an electronic device e.g., resistance variable layer of a resistance variable memory device.
  • the present invention [6] Provided is a carbon nanotube dispersion containing the carbon nanotube layered structure according to any one of [1] to [5] above and a solvent.
  • the carbon nanotube dispersion liquid of the present invention can be used, for example, as a coating liquid to form a functional region (e.g., a resistance variable layer) of an electronic element (e.g., a variable resistance layer) during the production of an electronic element (e.g., a resistance variable memory device). This makes it possible to provide an electronic device that can operate with a sufficiently low switching voltage.
  • a coating liquid for manufacturing an electronic device which includes the carbon nanotube dispersion liquid according to [6] above.
  • the coating liquid for manufacturing electronic devices of the present invention can be applied, for example, at the time of manufacturing an electronic device (for example, a resistance variable memory device), and the solvent can be dried and removed to form a functional area (for example, a resistance variable layer) of the electronic device. ) can be used to form.
  • a functional area for example, a resistance variable layer
  • the present invention [8] A carbon nanotube film comprising the carbon nanotube layered structure according to any one of [1] to [5] above is provided.
  • the carbon nanotube film of the present invention is, for example, a material for forming a functional region of an electronic device (eg, a variable resistance layer of a variable resistance memory device), and can be operated at a sufficiently low switching voltage.
  • the present invention [9] An electronic device comprising the carbon nanotube film according to [8] above is provided.
  • the electronic device of the present invention can be operated with a sufficiently low switching voltage, and as long as the switching voltage is low, even if the cells in the electronic device are densely integrated, problems such as current leakage to adjacent cells caused by high voltage may occur. Since this suppresses the storage capacity, it becomes possible to manufacture electronic devices such as memory devices in which cells are integrated at high density and performance such as storage capacity is improved.
  • the present invention [10] It is preferable to provide the electronic device according to [9] above, wherein the electronic device is a variable resistance storage device, and the carbon nanotube film functions as a variable resistance layer.
  • a resistance variable memory device can operate with a sufficiently low switching voltage, and if the switching voltage is low, even if the cells in the resistance variable memory device are densely integrated, there will be no damage to adjacent cells caused by high voltage. Since defects such as current leakage are suppressed, it becomes possible to manufacture electronic devices such as resistance variable memory devices in which cells are integrated at high density and performance such as storage capacity is improved.
  • the present invention functions as a functional region of an electronic device (e.g., a variable resistance layer of a variable resistance storage device), and when used as a functional region of an electronic device, the electronic device can operate at a low switching voltage. It is possible to provide a carbon nanotube stacked structure and a carbon nanotube dispersion that can be used to form a carbon nanotube film. Further, according to the present invention, the electronic device functions as a functional region of an electronic device (e.g., a resistance variable layer of a resistance variable memory device), and when used as a functional region of an electronic device, the electronic device can operate at a low switching voltage. It is possible to provide a carbon nanotube film that can be operated, a coating liquid for manufacturing an electronic device, and an electronic device that can be operated at a low switching voltage.
  • an electronic device e.g., a variable resistance layer of a variable resistance storage device
  • FIG. 2 is a schematic diagram of a carbon nanotube stacked structure. It is a transmission electron microscope (TEM) image of a carbon nanotube stacked structure in a carbon nanotube dispersion (A: original image, B: with markings). It is a TEM image of a carbon nanotube laminate structure including a portion where carbon nanotube laminate structures intersect with each other in a carbon nanotube dispersion liquid (A: original image, B: with markings). 1 is a scanning electron microscope (SEM) image of a cross section of a resistance variable memory device including a carbon nanotube stacked structure and a carbon nanotube film functioning as a resistance change layer.
  • SEM scanning electron microscope
  • FIG. 1 is a schematic diagram showing an example of the configuration of a manufacturing apparatus that can be used to manufacture carbon nanotubes used to form a carbon nanotube stacked structure.
  • FIG. 2 is a schematic diagram showing another example of the configuration of a manufacturing apparatus that can be used to manufacture carbon nanotubes used to form a carbon nanotube stacked structure.
  • FIG. 1 is a schematic diagram of an example of a surface wave plasma etching apparatus.
  • FIG. 1 is a schematic diagram of an example of a plasma etching apparatus including a radial line slot antenna. It is a figure showing an example of a radial line slot antenna.
  • FIG. 3 is a diagram showing a flowchart of an example of a method for manufacturing a resistance variable memory device of the present invention.
  • the carbon nanotube film including the carbon nanotube laminate structure according to the present invention can function as a functional region (e.g., resistance change layer of a resistance change memory device) when formed in an electronic device, for example.
  • a functional region e.g., resistance change layer of a resistance change memory device
  • the carbon nanotube dispersion according to the present invention contains the carbon nanotube layered structure according to the present invention and a solvent, and is used, for example, in the functional area of the electronic device (e.g., resistance change) during the manufacture of the electronic device.
  • the coating liquid for manufacturing electronic devices according to the present invention contains the carbon nanotube dispersion liquid according to the present invention, and can be used, for example, to coat functional regions of electronic devices (e.g., resistance change layers of resistance change storage devices). It can be used to form a coating film for manufacturing, thereby providing an electronic device that can be operated at a sufficiently low switching voltage.
  • the carbon nanotube film (e.g., coating film) according to the present invention includes the carbon nanotube laminated structure according to the present invention, and when formed in an electronic device, for example, a functional region (e.g., a resistor) It can be used as a variable resistance layer of a variable memory device, thereby providing an electronic element that can operate with a sufficiently low switching voltage.
  • the electronic device according to the present invention includes the carbon nanotube film according to the present invention as a portion (functional layer) that can function as a functional region (e.g., a resistance change layer of a resistance change storage device) in the electronic device. It can be used as an electronic device (eg, a resistance variable memory device) that can operate with a sufficiently low switching voltage. If the switching voltage is low, even if cells in an electronic device are densely integrated, problems such as current leakage to adjacent cells caused by high voltage can be suppressed. It becomes possible to manufacture electronic devices such as memory devices with improved performance.
  • the carbon nanotube laminate structure of the present invention is a carbon nanotube laminate structure formed by laminating a plurality of oxidized flat carbon nanotubes, and the ratio of single-walled carbon nanotubes to all carbon nanotubes in the carbon nanotube laminate structure is
  • the carbon nanotube layered structure is characterized in that the number of carbon nanotubes is 51 or more out of 100 carbon nanotubes. That is, the carbon nanotube layered structure of the present invention is composed of carbon nanotubes that have a layered structure in which a plurality of flat carbon nanotubes are stacked (hereinafter sometimes referred to as "flat carbon nanotube layered structure").
  • FIG. 2 shows an example of a transmission electron microscope (TEM) image of the carbon nanotube layered structure of the present invention in a carbon nanotube dispersion.
  • TEM transmission electron microscope
  • the ultrasonic dispersion treatment under predetermined conditions is preferably an ultrasonic dispersion treatment at an oscillation frequency of 30 kHz or more, and the oscillation frequency of the ultrasonic wave is more preferably 35 kHz or more, preferably 50 kHz or less, and 45 kHz or less. It is more preferable that it is above.
  • the ultrasonic dispersion treatment is performed at such an oscillation frequency, the vibrational acceleration of the solvent (eg, water molecules) will increase and the target object can be efficiently obtained.
  • the time for the ultrasonic dispersion treatment is preferably 1 hour or more, more preferably 1 hour and 30 minutes or more, preferably 30 hours or less, and more preferably 15 hours or less.
  • the affinity of the inner wall surface increases so that the inner walls of carbon nanotubes adhere to each other, and when subjected to ultrasonic dispersion treatment under specified conditions in a solvent, the carbon nanotubes become easily deformed into a flat shape. It is possible that Next, the following may be considered as a mechanism that makes it easier to form a flat carbon nanotube stacked structure.
  • carbon nanotubes are obtained as CNT aggregates grown with a common orientation on the catalyst base material, and at that time, while maintaining this orientation, the outer wall surfaces of the CNTs are Take the glued state.
  • the carbon nanotubes are subjected to oxidation treatment and ultrasonic dispersion treatment to deform the carbon nanotubes into a flat shape, allowing the bonded carbon nanotubes to form a layered structure.
  • oxidation treatment and ultrasonic dispersion treatment to deform the carbon nanotubes into a flat shape, allowing the bonded carbon nanotubes to form a layered structure.
  • ultrasonic dispersion treatment to deform the carbon nanotubes into a flat shape, allowing the bonded carbon nanotubes to form a layered structure.
  • Another possible mechanism that makes it easier to form a flat carbon nanotube stacked structure is as follows. Carbon nanotubes that have been deformed into a flat shape are attracted to each other by van der Waals forces.
  • the cross section of the carbon nanotube that has been deformed into a flat shape [the cross section perpendicular to the extending direction (axial direction) of the carbon nanotube] takes a dumbbell shape with both ends bulged, and the flat part and end of the flat surface of the carbon nanotube
  • carbon nanotubes have a flat carbon nanotube stacked structure and contain a high proportion of single-walled carbon nanotubes, they can be used to form functional regions of electronic devices (e.g., resistance change layers of resistance change memory devices). contributes to a reduction in switching voltage. Although the specific mechanism by which this happens is unknown, the following mechanism is probably inferred.
  • the resistance state of cylindrical carbon nanotubes hardly changes even when rotated around the tube axis; The change in resistance state is relatively small even when rotated around the tube axis, whereas the resistance state of carbon nanotubes with a flat carbon nanotube stacked structure changes greatly when rotated around the tube axis.
  • Evaluation of whether carbon nanotubes are oxidized i.e., measurement of the degree of oxidation
  • measurement of the content ratio of single-walled carbon nanotubes i.e., measurement of the content ratio of single-walled carbon nanotubes
  • evaluation of whether carbon nanotubes have a flat carbon nanotube layered structure can be performed, for example, by This can be done using the methods described in the Examples.
  • the carbon nanotubes used in the carbon nanotube laminated structure of the present invention are oxidized carbon nanotubes (oxidized carbon nanotubes with a high single-wall ratio) that have a high content of single-wall carbon nanotubes (i.e., 51 or more out of 100 carbon nanotubes). is used.
  • oxidized high single-wall ratio carbon nanotubes include, for example, non-chemically modified carbon nanotubes (herein referred to as "material CNT”) with a similar content of single-wall carbon nanotubes that are oxidized.
  • CNT As the material CNT, for example, carbon nanotubes synthesized using a CNT synthesis catalyst under conditions that provide a high single-wall ratio as described later may be used, or carbon nanotubes that are synthesized under conditions that provide a high single-wall ratio using a known synthesis method. Synthesized carbon nanotubes may be used, or commercially available carbon nanotubes with a high single-wall ratio that are not chemically modified may be used. By performing ultrasonic dispersion treatment under specified conditions on oxidized carbon nanotubes with a high single-wall ratio in a solvent, the carbon nanotubes can easily take on a flat shape, and furthermore, multiple flat carbon nanotubes can be stacked. This makes it easier to obtain a laminated structure consisting of carbon nanotubes (hereinafter sometimes referred to as "flat carbon nanotube laminated structure").
  • the carbon nanotubes used in the carbon nanotube laminate structure of the present invention preferably have a higher content of single-walled carbon nanotubes.
  • the content ratio of single-walled carbon nanotubes needs to be 51 or more out of 100 carbon nanotubes, preferably 60 or more, and more preferably 70 or more. , more preferably 75 or more.
  • the content ratio of single-walled carbon nanotubes may be considered to be approximately the same before and after these treatments.
  • the content ratio of single-walled carbon nanotubes a value measured at any treatment stage may be used.
  • the switching voltage reduction effect increases when The content ratio of single-walled carbon nanotubes can be measured, for example, by the method described in Examples.
  • Oxidized carbon nanotubes are used as the carbon nanotubes used in the carbon nanotube stacked structure of the present invention.
  • the degree of oxidation of carbon nanotubes can be determined by, for example, the oxygen atomic ratio of carbon nanotubes.
  • the oxygen atomic ratio may be, for example, 10 at% or more, preferably 13 at% or more, for example, 30 at% or less, preferably 20 at% or less.
  • the oxygen atomic ratio of carbon nanotubes can be measured, for example, by the method described in Examples.
  • the "flat shape” taken by the carbon nanotube is a shape of the carbon nanotube having a tape-like portion along its entire length in which the inner walls are close to each other or adhered to each other.
  • a specific example of a flat shape and a method of confirming that it is a flat shape will be described.
  • "having a tape-like portion over the entire length” means "60% or more, preferably 80% or more, more preferably 80% or more of the length (total length) in the extending direction (axial direction) of the carbon nanotube.” 100% continuous or intermittently tape-like parts.”
  • the cross-sectional shape of the flat carbon nanotube has a tape-shaped part at the center in the width direction, and a cross section perpendicular to the extending direction (axial direction).
  • the maximum dimension in the direction perpendicular to the longitudinal direction of the cross section near both ends of the longitudinal direction of the cross section is both larger than the maximum dimension in the direction perpendicular to the longitudinal direction of the cross section near the center of the longitudinal direction of the cross section.
  • the shape is more preferable, and the dumbbell shape is particularly preferable.
  • “near the center in the longitudinal direction of the cross-section” refers to It refers to a region within 30% of the width in the direction
  • “near the end in the longitudinal direction of the cross section” refers to a region outside in the longitudinal direction of "near the center in the longitudinal direction of the cross section.”
  • the flatness of carbon nanotubes can be confirmed by determining the "oblateness” as described below and checking the degree of the oblateness. For example, if the oblateness is 40% or less, it can be determined that the carbon nanotube has a flat shape. The method for calculating the "flattening ratio" will be described later.
  • Another way to confirm that the carbon nanotubes are flat is, for example, by sealing CNTs and fullerene (C60) in a quartz tube and heat-treating the tubes under reduced pressure (fullerene insertion treatment).
  • An example of this method is to observe fullerene-inserted CNTs using a transmission electron microscope (TEM) and confirm the presence of portions (tape-like portions) in which fullerenes are not inserted (e.g., Patent No. 6623512). Publication No.).
  • the carbon nanotubes have a flat carbon nanotube laminate structure.
  • the "flat carbon nanotube laminate structure” is a laminate structure in which a plurality of flat carbon nanotubes are stacked, that is, a structure in which a plurality of flat carbon nanotubes are stacked (a laminate structure).
  • a flat carbon nanotube stacked structure is a structure in which a plurality of flat carbon nanotubes form an arrangement in which the outer surfaces of tape-shaped portions (flat surfaces) are close to each other or adhere to each other. Refers to overlapping structures.
  • TEM transmission electron microscope
  • the carbon nanotube laminated structure of the present invention has a plurality of It is preferable that the carbon nanotube stacked structures intersect with each other.
  • FIG. 3 shows an example of a state in which a plurality of carbon nanotube stacked structures intersect with each other.
  • the flat carbon nanotube stacked structure it is preferable that most of the flat carbon nanotubes are stacked aligned in the longitudinal direction of the carbon nanotube cross section.
  • "Stacked in the same direction in the longitudinal direction” does not mean that the flat carbon nanotubes are stacked in a random orientation and arrangement in a laminated structure of flat carbon nanotubes, but that the flat carbon nanotubes are stacked in the same direction and This refers to a state where the ends of the cross sections in the longitudinal direction are almost aligned and stacked.
  • the expression that the flat carbon nanotubes are oriented in the same direction means that the maximum angle of axis deviation between the flat carbon nanotubes is preferably 15° or less, more preferably 10° or less.
  • Carbon nanotubes have a flat carbon nanotube layered structure, for example, when a carbon nanotube layered structure is observed with a transmission electron microscope (TEM), a layered structure corresponding to the flat carbon nanotube layered structure is observed in the obtained TEM image. This can be confirmed by observation.
  • TEM transmission electron microscope
  • the average number of stacked flat carbon nanotubes in the carbon nanotube stacked structure of the present invention is determined to reduce the effect of switching voltage drop when used to form a functional region of an electronic device (e.g., resistance variable layer of a resistance variable memory device). From the viewpoint of increasing the number, the number is preferably 2 or more, more preferably 4 or more, and even more preferably 5 or more. In addition, the average number of flat carbon nanotubes stacked is preferably 20 or less, more preferably 15 or less, from the viewpoint of preventing problems such as agglomeration and sedimentation of the carbon nanotube stacked structure in a solvent. The average number of laminated layers can be measured, for example, by the method described in Examples.
  • the carbon nanotubes used in the carbon nanotube laminate structure of the present invention are preferably subjected to an ultrasonic dispersion treatment in a solvent in an oxidized state in order to easily form a flat carbon nanotube laminate structure.
  • the conditions for the ultrasonic dispersion treatment, the type of solvent, etc. include, for example, those described below.
  • the "diameter (outer diameter)" of a carbon nanotube usually refers to the diameter (maximum diameter) of a carbon nanotube without a stacked structure of flat carbon nanotubes. It is difficult to measure the diameter of a carbon nanotube when it has a stacked structure of flat carbon nanotubes, so we measure the outer circumference of the carbon nanotube and calculate the diameter when converting the outer circumference to the circumference.
  • the diameter of a carbon nanotube It may also be referred to as "the diameter of a carbon nanotube.”
  • the diameter of a cylindrical carbon nanotube before forming a stacked structure of flat carbon nanotubes may be measured and used as the "diameter of a carbon nanotube.”
  • the diameter is the diameter measured on the cylindrical carbon nanotube (material CNT) before oxidation treatment and ultrasonic dispersion treatment. May be used.
  • the diameter or outer circumference length of such a carbon nanotube may be measured based on an image of the carbon nanotube obtained using a transmission electron microscope (TEM) or a scanning electron microscope (SEM). As an example of how to determine such a diameter, the method described in the Examples can be used.
  • TEM transmission electron microscope
  • SEM scanning electron microscope
  • Average diameter refers to the arithmetic mean value of the diameters (outer diameters) of a significant number (eg, 50) of randomly selected CNTs. As an example of how to determine the average diameter, the method described in the Examples can be used.
  • the average diameter can be controlled by adjusting the conditions for carbon nanotube synthesis. For example, by increasing the thickness of the iron thin film (catalyst layer) of the catalyst base material, the average diameter can be increased, and by decreasing the film thickness of the iron thin film (catalyst layer) of the catalyst base material, the average diameter can be increased. The diameter can be reduced.
  • the average diameter is large (that is, the CNTs are thick).
  • the average diameter is preferably 3.7 nm or more, more preferably 4.0 nm or more, preferably 5.0 nm or less, and more preferably 4.7 nm or less. It is preferable that the average diameter of the CNTs is equal to or larger than the above lower limit because the carbon nanotubes are easily crushed into a flat shape. If the average diameter of the CNTs exceeds the above upper limit, there may be a problem that the flat carbon nanotubes become entangled with each other and a stacked structure of flat carbon nanotubes is inhibited.
  • the "oblateness" of a carbon nanotube refers to a value that is an index of the ratio of the thickness of a carbon nanotube in a state where it has a flat carbon nanotube stacked structure to the diameter of a carbon nanotube in a state where it does not have a stacked structure of flat carbon nanotubes.
  • the oblateness is an indicator that the carbon nanotube has a flat shape.
  • the oblateness can be determined by the following procedure, for example, as described in Examples.
  • a portion of the dispersion containing the carbon nanotube layered structure is separated for measurement, and the solvent is removed (eg, filtered, dried).
  • the carbon nanotube stacked structure from which the solvent has been removed is observed with a transmission electron microscope (TEM) to obtain a TEM image.
  • TEM transmission electron microscope
  • the thickness and number of laminated layers of a significant number (eg, 50) of carbon nanotube laminated structures randomly selected from the obtained TEM images are measured, and the arithmetic mean values are taken as the average thickness and the average number of laminated layers.
  • the flattening ratio is calculated using the following formula.
  • Oblateness (%) [(average thickness of carbon nanotube laminate structure/average number of layers of carbon nanotube laminate structure)/average diameter of CNT] x 100
  • the average diameter can be controlled by adjusting the carbon nanotube synthesis conditions, oxidation treatment conditions, ultrasonic dispersion treatment conditions, etc.
  • the flatness of CNT is preferably 10% or more, more preferably 20% or more, and preferably 40% or less. If the flatness of the CNTs is below the above upper limit, the CNTs will have a sufficiently flat shape, contributing to a reduction in switching voltage when the carbon nanotube laminated structure is used in a functional area (e.g., variable resistance layer) of an electronic device. . On the other hand, since there is an interlayer distance between the graphite structures of the inner wall, it is difficult to make the flatness of the CNTs less than the above lower limit.
  • the "length” of the carbon nanotube stacked structure refers to the dimension (tube length) in the extending direction (axial direction) of the carbon nanotubes.
  • “Average length” refers to the arithmetic mean value of the lengths of a significant number (eg, 50 carbon nanotubes) of randomly selected laminated carbon nanotubes.
  • the average length of the carbon nanotube stacked structure can be determined, for example, by the following procedure.
  • a portion of the dispersion containing the carbon nanotube layered structure is separated for measurement, and the solvent is removed (e.g., filtered, dried).
  • the carbon nanotube stacked structure from which the solvent has been removed is observed with a scanning electron microscope (SEM), and the lengths of a significant number (e.g., 50) of the carbon nanotube stacked structures are randomly selected from the obtained SEM image. is measured, and the arithmetic mean value of the lengths of the carbon nanotube laminate structure is determined as the average length of the carbon nanotube laminate structure.
  • SEM scanning electron microscope
  • the average length of the carbon nanotube stacked structure can be controlled by adjusting various conditions such as carbon nanotube synthesis and processing. For example, by increasing the carbon nanotube synthesis time, the average length of the carbon nanotube layered structure can be increased, and by shortening the carbon nanotube synthesis time, the average length of the carbon nanotube layered structure can be increased. Can be shortened.
  • the average length of the carbon nanotube layered structure is determined by the oxidation treatment conditions of the carbon nanotubes (e.g., the type of acidic solution used for oxidation treatment, the pH, the stirring time for preparing the mixed solution, the reflux time of the mixed solution, the reflux time of the mixed solution, etc.) It can also be controlled by adjusting the ultrasonic dispersion treatment conditions (eg, ultrasonic oscillation frequency, time, number of times, etc.).
  • the oxidation treatment conditions of the carbon nanotubes e.g., the type of acidic solution used for oxidation treatment, the pH, the stirring time for preparing the mixed solution, the reflux time of the mixed solution, the reflux time of the mixed solution, etc.
  • the ultrasonic dispersion treatment conditions eg, ultrasonic oscillation frequency, time, number of times, etc.
  • the average length of the carbon nanotube stacked structure is preferably 20 nm or more, more preferably 50 nm or more, preferably 300 nm or less, and more preferably 200 nm or less. It is preferable that the average length of the carbon nanotube laminate structure is equal to or greater than the above-mentioned lower limit, since properties such as conductivity of the carbon nanotube laminate structure are not impaired. It is preferable that the average length of the carbon nanotube laminate structure is equal to or less than the above upper limit in order to prevent the carbon nanotube laminate structure from agglomerating and settling in the solvent.
  • the carbon nanotubes used to form the carbon nanotube stacked structure and the properties of the carbon nanotube stacked structure such as various sizes, shapes, stacking states, and various physical properties are based on the catalyst used to prepare the carbon nanotubes (e.g., material CNT).
  • the catalyst used to prepare the carbon nanotubes e.g., material CNT.
  • Condition of the catalyst layer of the base material e.g., thickness of thin iron film (catalyst layer), etc.
  • synthesis conditions of carbon nanotubes e.g., material CNT
  • oxidation treatment conditions e.g., composition of mixed gas, etc.
  • ultrasonic dispersion It can be controlled by adjusting processing conditions (eg, oscillation frequency of ultrasonic waves, etc.).
  • the carbon nanotube laminate structure of the present invention includes, for example, the following steps: (i) oxidizing carbon nanotubes with a high single-wall ratio to obtain oxidized carbon nanotubes with a high single-wall ratio; (ii) A step of subjecting the oxidized carbon nanotubes with a high single-wall ratio to an ultrasonic dispersion treatment in a solvent under predetermined conditions to form a carbon nanotube laminate structure in which a plurality of oxidized flat carbon nanotubes with a high single-wall ratio are stacked. It can be manufactured using a method including.
  • a high single-walled carbon nanotube ratio means that the content ratio of the single-walled carbon nanotubes mentioned above is sufficiently high, and needs to be 51 or more out of 100 carbon nanotubes.
  • CNT material obtained by the following manufacturing method may be used.
  • the ultrasonic dispersion treatment under predetermined conditions in step (ii) above is preferably an ultrasonic dispersion treatment at an oscillation frequency of 30 kHz or higher, more preferably an oscillation frequency of 35 kHz or higher, and 50 kHz or lower.
  • the frequency is preferably 45 kHz or less, and more preferably 45 kHz or less.
  • the ultrasonic dispersion treatment is performed at such an oscillation frequency, the vibrational acceleration of the solvent (eg, water molecules) will increase and the target object can be efficiently obtained.
  • the time of the ultrasonic dispersion treatment is preferably 1 hour or more, more preferably 1 hour and 30 minutes or more, preferably 30 hours or less, and 15 hours or less. is more preferable.
  • the manufacturing method of the material CNT is a chemical vapor deposition method (CVD method) using a catalyst base material formed by forming a catalyst support layer and a catalyst layer on the base material using a predetermined method and a predetermined mixed gas.
  • CVD method chemical vapor deposition method
  • One of the major features is that by synthesizing carbon nanotubes on a catalyst base material, carbon nanotubes with a high single-wall ratio can be grown on the catalyst base material as material CNT.
  • the method for manufacturing the material CNT is as follows: (1) A step of applying coating liquid A containing an aluminum compound onto a base material, (2) Drying coating liquid A to form an aluminum thin film on the base material, (3) a step of applying coating liquid B containing an iron compound on the aluminum thin film; (4) drying coating liquid B at a temperature of 50° C. or lower to form a thin iron film on the aluminum thin film to obtain a catalyst base material, and (5) High single-wall ratio CNTs that can form high single-wall ratio oxidized flat CNTs as material CNTs on the catalyst base material by supplying a mixed gas of carbon-containing raw material gas and nitrogen gas to the catalyst base material.
  • the process of growing (growth process), Contains at least In the following, the above two steps (1) and (2) will be collectively referred to as the “catalyst support layer forming step”, and the above two steps (3) and (4) will be collectively referred to as the “catalyst layer forming step”. ”.
  • the catalyst base material is produced by a wet process, and the drying temperature when obtaining the catalyst layer by drying is 50°C or less, and furthermore, a mixed gas of raw material gas and nitrogen gas is used. Since carbon nanotubes are grown using the method, it is possible to produce CNTs with a high single-wall ratio that can form oxidized flat CNTs with a high single-wall ratio.
  • the base material used as the catalyst base material is, for example, a flat member, and preferably one that can maintain its shape even at high temperatures of 500° C. or higher.
  • metals such as iron, nickel, chromium, molybdenum, tungsten, titanium, aluminum, manganese, cobalt, copper, silver, gold, platinum, niobium, tantalum, lead, zinc, gallium, indium, germanium and antimony;
  • alloys and oxides containing these metals, nonmetals such as silicon, quartz, glass, mica, graphite, and diamond, and ceramics.
  • Metal materials are preferred because they are lower in cost and easier to process than nonmetals and ceramics, and in particular, Fe-Cr (iron-chromium) alloy, Fe-Ni (iron-nickel) alloy, Fe-Cr-Ni (Iron-Chromium-Nickel) alloy is suitable.
  • the thickness of the base material there is no particular limit to the thickness of the base material, and for example, a thin film of about several ⁇ m to about several cm can be used.
  • the thickness of the base material is 0.05 mm or more and 3 mm or less.
  • the area of the base material is not particularly limited, and is preferably 20 cm 2 or more, more preferably 30 cm 2 or more.
  • the shape of the base material is not particularly limited, but may be rectangular or square.
  • -Coating liquid A- Coating liquid A is an aluminum compound dissolved or dispersed in an organic solvent.
  • the aluminum compound contained in coating liquid A is not particularly limited as long as it contains an aluminum atom, but metal organic compounds and metal salts that can form an alumina thin film as an aluminum thin film are preferred.
  • metal organic compounds that can form an alumina thin film include aluminum trimethoxide, aluminum triethoxide, aluminum tri-n-propoxide, aluminum tri-i-propoxide, aluminum tri-n-butoxide, and aluminum tri-n-propoxide.
  • aluminum alkoxides such as sec-butoxide and aluminum tri-tert-butoxide.
  • Other metal organic compounds containing aluminum include complexes such as tris(acetylacetonato)aluminum(III).
  • metal salts that can form an alumina thin film include aluminum sulfate, aluminum chloride, aluminum nitrate, aluminum bromide, aluminum iodide, aluminum lactate, basic aluminum chloride, and basic aluminum nitrate. These can be used alone or as a mixture.
  • organic solvents such as alcohols, glycols, ketones, ethers, esters, and hydrocarbons can be used as the organic solvent contained in coating liquid A, but since they have good solubility for metal organic compounds and metal salts, , alcohols or glycols are preferably used. These organic solvents may be used alone or in combination of two or more. As the alcohol, methanol, ethanol, isopropyl alcohol, etc. are preferable in terms of ease of handling and storage stability.
  • a stabilizer may be added to the coating liquid A to suppress the condensation polymerization reaction of the metal organic compound and the metal salt.
  • the stabilizer is preferably at least one selected from the group consisting of ⁇ -diketones and alkanolamines.
  • ⁇ -diketones include acetylacetone, methyl acetoacetate, ethyl acetoacetate, benzoylacetone, dibenzoylmethane, benzoyltrifluoroacetone, furoylacetone, and trifluoroacetylacetone, and it is particularly preferable to use acetylacetone and ethyl acetoacetate. .
  • Alkanolamines include monoethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, N,N-dimethylaminoethanol, diisopropanolamine, triisopropanolamine, etc. Preferably, it is a tertiary alkanolamine.
  • the amount of aluminum compound in coating liquid A is not particularly limited, but is preferably 0.1 g or more, more preferably 0.5 g or more, and preferably 30 g or less, more preferably 5 g or less per 100 mL of organic solvent. . Further, the amount of stabilizer in coating liquid A is not particularly limited, but is preferably 0.01 g or more, more preferably 0.1 g or more, and preferably 20 g or less, more preferably 3 g or less per 100 mL of organic solvent. It is.
  • the above-mentioned coating liquid A is applied onto a substrate.
  • the method of applying coating liquid A onto the substrate is not particularly limited, and any method such as spraying, brushing, spin coating, dip coating, etc. may be used, but dip coating is preferable. .
  • the coating liquid A on the base material is dried to form an aluminum thin film (catalyst supporting layer) on the base material.
  • the method of drying the coating liquid A on the substrate is not particularly limited, but examples include air drying at room temperature and heating (baking treatment), with heating being preferred.
  • the heating temperature is preferably approximately 50°C or higher and 400°C or lower, more preferably 350°C or lower.
  • the heating time is preferably 5 minutes or more and 60 minutes or less, more preferably 40 minutes or less.
  • Coating liquid B- Coating liquid B is one in which an iron compound is dissolved or dispersed in an organic solvent.
  • the iron compound contained in coating liquid B is not particularly limited as long as it contains an iron atom, but metal organic compounds and metal salts that can form an iron thin film are preferable.
  • metal organic compounds that can form an iron thin film include iron pentacarbonyl, ferrocene, iron(II) acetylacetone, iron(III) acetylacetone, iron(II) trifluoroacetylacetone, iron(III) trifluoroacetylacetone, and the like. It will be done.
  • metal salts that can form an iron thin film include inorganic iron acids such as iron sulfate, iron nitrate, iron phosphate, iron chloride, iron bromide, iron acetate, iron oxalate, iron citrate, iron lactate, etc.
  • organic acid iron examples include organic acid iron. Among these, it is preferable to use organic acid iron. These can be used alone or as a mixture.
  • the organic solvent contained in the coating liquid B is not particularly limited, and the same organic solvents as those described in the section of the coating liquid A above can be used. Moreover, the coating liquid B may contain the stabilizer described in the section of the above-mentioned coating liquid A.
  • the amount of iron compound in coating liquid B is not particularly limited, but is preferably 0.05 g or more, more preferably 0.1 g or more, and preferably 5 g or less, more preferably 1 g or less per 100 mL of organic solvent. . Further, the amount of stabilizer in coating liquid B is not particularly limited, but is preferably 0.05 g or more, more preferably 0.1 g or more, and preferably 5 g or less, more preferably 1 g or less per 100 mL of organic solvent. It is.
  • the method for applying coating liquid B onto the aluminum thin film is not particularly limited, and a method similar to the method described in the above-mentioned section of the catalyst support layer forming step can be used.
  • the immersion time of the aluminum thin film-coated substrate in coating liquid B is preferably 1 to 30 seconds.
  • the speed at which the substrate is pulled up from coating liquid B after dipping is preferably 1 to 5 mm/sec.
  • the amount of coating liquid B to be dropped onto the substrate with the aluminum thin film is appropriately selected depending on the desired thickness of the iron thin film. Further, the rotational speed during spin coating is preferably 1000 rpm or more and 8000 rpm or less.
  • the coating liquid B on the aluminum thin film is dried to form an iron thin film on the base material.
  • the coating liquid B needs to be dried at 50°C or lower, preferably 40°C or lower, more preferably 30°C or lower. If the drying temperature exceeds 50° C., high single-wall ratio CNTs that can form high single-wall ratio oxidized flat CNTs cannot be synthesized in the subsequent growth step.
  • the lower limit of the drying temperature is not particularly limited, but is usually 10° C. or higher.
  • air drying is usually suitable.
  • the thickness of the iron thin film (catalyst layer) is preferably 1.2 nm or more, more preferably 1.5 nm or more. , 3.8 nm or less is preferable, and 3.5 nm or less is more preferable.
  • the thickness of the iron thin film is less than the above lower limit, the diameter of the obtained CNTs becomes short, and it is considered that flat CNTs cannot be formed.
  • the thickness of the iron thin film exceeds the above lower limit, the multilayer ratio of the obtained CNT increases, and it is considered that CNTs with a high single layer ratio cannot be efficiently synthesized.
  • the thickness of the iron thin film (catalyst layer) can be determined, for example, by the method described in Examples.
  • the formation step is a step in which the environment around the catalyst is made into a reducing gas (reducing gas) environment, and at least one of the catalyst and the reducing gas is heated. This step produces at least one of the following effects: reduction of the catalyst, promotion of fine particle formation of the catalyst in a state suitable for growth of high single-wall ratio CNTs capable of forming high single-wall ratio oxidized flat CNTs, and improvement of catalyst activity.
  • reducing gas reducing gas
  • the catalyst base material includes an alumina-iron thin film consisting of an alumina thin film and an iron thin film
  • the iron catalyst is reduced and becomes fine particles, and many nanometer-sized iron fine particles are formed on the alumina thin film (catalyst support layer). Ru.
  • the iron thin film (catalyst layer) becomes in a state suitable for producing high single-wall ratio CNTs that can form high single-wall ratio oxidized flat CNTs. Even if this step is omitted, it is possible to produce high single-wall ratio CNTs that can form high single-wall ratio oxidized flat CNTs, but by performing this step, it is possible to form high single-wall ratio oxidized flat CNTs. The production amount and quality of high single-wall ratio CNTs can be dramatically improved.
  • the reducing gas used in the formation step hydrogen gas, ammonia, water vapor, and a mixed gas thereof can be used, for example.
  • the reducing gas may be a mixed gas in which hydrogen gas is mixed with an inert gas such as helium gas, argon gas, or nitrogen gas.
  • the reducing gas may be used only in the formation process, or may be used in the growth process as appropriate.
  • the temperature of the catalyst and/or reducing gas in the formation step is preferably 400°C or higher and 1100°C or lower. Further, the time for the formation step is preferably 3 minutes or more and 20 minutes or less, more preferably 3 minutes or more and 10 minutes or less. Thereby, it is possible to suppress the progress of firing of the iron thin film (catalyst layer) during the formation process and the reduction in film thickness.
  • a mixed gas of carbon-containing raw material gas and nitrogen gas is supplied to the catalyst base material obtained through the catalyst support layer forming process and the catalyst layer forming process, and a high monolayer ratio oxidized flat film is formed on the catalyst base material.
  • carbon nanotubes usually grow on a catalyst base material while being arranged (orientated) in a predetermined direction.
  • at least one of the catalyst layer and the mixed gas is usually heated, but from the viewpoint of growing carbon nanotubes with uniform density, it is preferable to heat at least the mixed gas.
  • the heating temperature is preferably 400°C to 1100°C.
  • raw material gas and nitrogen gas and optionally at least one selected from the group consisting of an inert gas other than nitrogen gas, a reducing gas, and a catalyst activating material, are placed in a growth furnace that accommodates the catalyst base material. Implement and do it.
  • a gaseous substance containing a carbon source at a temperature at which carbon nanotubes grow is used.
  • hydrocarbons such as methane, ethane, ethylene, propane, butane, pentane, hexane, heptane, propylene and acetylene are preferred.
  • lower alcohols such as methanol and ethanol, and oxygen-containing compounds with a low carbon number such as acetone and carbon monoxide may be used. Mixtures of these can also be used.
  • the amount of nitrogen gas mixed with the raw material gas is preferably 30% by volume or more, more preferably 50% by volume or more, based on the total amount of gas supplied to the catalyst base material in the growth step. This is because if the amount of nitrogen gas is 30% by volume or more, it is possible to synthesize CNTs with a high single-wall ratio that can form oxidized flat CNTs with a high single-wall ratio. Note that the upper limit of the amount of nitrogen gas is usually 95% by volume.
  • the source gas may be diluted with an inert gas other than nitrogen.
  • the inert gas may be any gas that is inert at the temperature at which carbon nanotubes grow and does not react with the growing carbon nanotubes, and is preferably a gas that does not reduce the activity of the catalyst. Examples include rare gases such as helium, argon, neon, and krypton; hydrogen; and mixed gases thereof.
  • a catalyst activating material may be added.
  • the catalyst activation material used here is generally a material containing oxygen, and is preferably a material that does not cause significant damage to carbon nanotubes at the temperature at which carbon nanotubes grow.
  • oxygen-containing compounds with a low carbon number such as water, oxygen, ozone, acid gases, nitrogen oxide, carbon monoxide and carbon dioxide; alcohols such as ethanol and methanol; ethers such as tetrahydrofuran; ketones such as acetone; Aldehydes; esters; and mixtures thereof are useful.
  • water, oxygen, carbon dioxide, carbon monoxide, and ethers are preferred, and water is particularly preferred.
  • the volume concentration of the catalyst activating material is not particularly limited, but is preferably in a small amount.
  • it is usually 10 to 10,000 ppm, preferably 50 to 1,000 ppm in the gas introduced into the furnace.
  • the pressure inside the reactor and the treatment time in the growth step may be set appropriately taking into account other conditions, but for example, the pressure is 1 ⁇ 10 2 to 1 ⁇ 10 7 Pa, and the treatment time is about 1 to 60 minutes. It can be done.
  • the method for manufacturing the material CNT includes a cooling step after the growth step.
  • the cooling step is a step of cooling the carbon nanotubes and the catalyst substrate under a cooling gas after the growth step. Since the carbon nanotubes and catalyst base material after the growth process are in a high temperature state, there is a risk that they will be oxidized if placed in an oxygen-existing environment. In order to prevent this, the carbon nanotubes and the catalyst base material are cooled to, for example, 400° C. or lower, more preferably 200° C. or lower in a cooling gas environment.
  • the cooling gas an inert gas is preferable, and nitrogen is particularly preferable from the viewpoint of safety and cost.
  • the method for producing material CNT preferably includes a step of peeling off the material CNT aggregate formed on the catalyst base material from the catalyst base material (peeling step).
  • Methods for exfoliating the material CNT aggregate from the catalyst substrate include physical, chemical, or mechanical exfoliation methods, such as exfoliation using an electric field, magnetic field, centrifugal force, or surface tension.
  • a simple method for peeling is to directly pinch the catalyst with tweezers and peel it off from the catalyst base material. More preferably, it can be separated from the catalyst substrate using a thin blade such as a cutter blade.
  • the manufacturing apparatus used in the method for manufacturing carbon nanotube aggregates described above is not particularly limited as long as it is equipped with a growth furnace (reaction chamber) having a catalyst base material and can grow CNTs by CVD method.
  • a growth furnace reaction chamber
  • a continuous type manufacturing apparatus as shown in FIG. 6 can be used.
  • the manufacturing apparatus 10 shown in FIG. 5 includes a growth furnace 13, a heater 14, a gas inlet 15, and a gas outlet 16.
  • the necessary gas is supplied from the gas inlet 15, and the inside of one furnace (growth furnace 13) is A formation process and a growth process are performed.
  • the manufacturing apparatus 100 shown in FIG. It has ⁇ 9. Then, in the manufacturing apparatus 100, while the catalyst base material 20 on which the material CNT aggregate is grown is transported by the transport unit 6, a formation process is performed on the catalyst base material 20 passing through the formation unit 2, and the growth unit 3 is A growth process is performed on the catalyst base material 20 passing through, and a cooling process is performed on the catalyst base material 20 passing through the cooling unit 4.
  • the inlet purge section 1 has a gas curtain structure that injects purge gas from above and below in a shower shape, and prevents external air from entering the formation unit 2 from the inlet.
  • an inert gas can be used as the purge gas.
  • the purge gas is preferably nitrogen.
  • the formation unit 2 also includes a formation furnace 2a for holding reducing gas, a reducing gas injection section 2b for injecting the reducing gas into the formation furnace 2a, and a formation furnace 2b for heating at least one of the catalyst and the reducing gas. It is composed of a heater 2c and an exhaust hood 2d for exhausting gas inside the formation furnace 2a.
  • the growth unit 3 is a set of devices for realizing the growth process, and includes a growth furnace 3a that is a furnace that maintains the environment around the catalyst base material 20 in a mixed gas environment, and a growth furnace 3a that is a furnace that maintains the environment around the catalyst base material 20 in a mixed gas environment.
  • the growth furnace 3a includes a mixed gas injection unit 200 for injecting the gas into the growth furnace 3a, a heater 3b for heating at least one of the catalyst and the mixed gas, and an exhaust hood 3c for exhausting the gas in the growth furnace 3a.
  • the growth unit 3 may include a catalyst activation material injection section (not shown) for supplying the catalyst activation material.
  • the mixed gas injection section 200 may also serve as a catalyst activation material injection section.
  • the total gas flow rate injected from the mixed gas injection section 200 and the total gas flow rate exhausted from the exhaust hood 3c are approximately the same amount or the same amount. By doing so, it is possible to prevent the mixed gas from flowing out of the growth furnace 3a and to prevent the gas outside the growth furnace 3a from flowing into the growth furnace 3a.
  • the transport unit 6 is a set of devices for intermittently transporting a plurality of catalyst base materials 20 into the manufacturing apparatus 100 at predetermined intervals, and includes a mesh belt 6a and a belt drive section 6b.
  • the catalyst base material 20 is transported by the transport unit 6 to the formation unit 2 , the growth unit 3 , and the cooling unit 4 in this order.
  • the connecting parts 7 to 9 spatially connect the furnace interior spaces of each unit and prevent the catalyst base material 20 from being exposed to the outside air when the catalyst base material 20 is transported from unit to unit.
  • Examples of the connecting portions 7 to 9 include a furnace or a chamber that isolates the environment surrounding the catalyst base material 20 from outside air and allows the catalyst base material 20 to pass from unit to unit.
  • the connecting portions 7 to 9 are provided with gas mixture prevention means 101 to 103.
  • the gas mixing prevention means 101 to 103 prevent gases existing in the furnace spaces of each unit from mixing with each other.
  • the gas mixture prevention means 101 to 103 include seal gas injection units 101b to 103b that eject seal gas along the opening surfaces of the inlet and outlet of the catalyst base material 20 in each furnace, and the injected seal gas ( At least one exhaust section 101a to 103a is provided for sucking in (and other nearby gases) so that they do not enter the respective furnaces and exhausting them to the outside of the apparatus.
  • the seal gas is preferably an inert gas, and more preferably nitrogen from the viewpoint of safety and cost.
  • the total gas flow rate injected from the seal gas injection parts 101b to 103b and the total gas flow rate exhausted from the exhaust parts 101a to 103a are approximately the same amount. This makes it possible to prevent the gases from the spaces on both sides of the gas mixing prevention means 101 to 103 from mixing with each other, and also to prevent the seal gas from flowing out into the spaces on both sides.
  • the cooling unit 4 has a function of cooling the material CNT and the catalyst base material 20 after the growth process, and includes a cooling furnace 4a for holding an inert gas, and a cooling gas for injecting the inert gas into the space inside the cooling furnace 4a. It is composed of an injection part 4b and a water-cooled cooling pipe 4c arranged so as to surround the interior space of the cooling furnace 4a.
  • the outlet purge section 5 prevents outside air from entering the cooling furnace 4a from the outlet by injecting purge gas from above and below in a shower pattern.
  • an inert gas can be used as the purge gas.
  • the purge gas is preferably nitrogen.
  • the oxidation treatment means, for example, adding the material CNT to an acidic solution with a pH of 2 or less to obtain a mixed solution, and oxidizing the material CNT. More specifically, in the oxidation treatment, it is preferable to oxidize the material CNT in the mixture by refluxing the mixture under predetermined temperature conditions.
  • acidic solutions include nitric acid, hydrochloric acid, and sulfuric acid.
  • stirring operation by any method can be performed. Further, the stirring time when obtaining the mixed liquid is preferably 0.1 hour or more and 10 hours or less.
  • the temperature conditions when refluxing the mixed liquid are preferably 100°C or more and 150°C or less, and the reflux time is preferably 3 hours or more and 20 hours or less.
  • the solvent of the acidic solution may be the same as the solvent used for the dispersion process, and water is especially preferable.
  • the ultrasonic dispersion treatment is not particularly limited as long as the desired effect can be obtained, and any known ultrasonic dispersion treatment method can be used.
  • an arbitrary neutralizing agent may be added in order to adjust the pH of the solution containing oxidized CNTs to neutrality (about pH 6 to pH 8).
  • Such a neutralizing agent is not particularly limited, and includes an alkaline solution having a pH of 9 or more and 14 or less, more specifically, an aqueous sodium hydroxide solution, an aqueous ammonia solution, and the like.
  • a solvent may be added to the solution containing oxidized CNTs to dilute the solution, if necessary.
  • a solvent may be the same or different between the solvent used in the oxidation treatment and the solvent added in the ultrasonic dispersion treatment, but preferably the same solvent. Examples of the solvent include those described below.
  • the oscillation frequency of the ultrasonic wave is preferably 30 kHz or more, more preferably 35 kHz or more, preferably 50 kHz or less, and more preferably 45 kHz or less.
  • the time for the ultrasonic dispersion treatment is preferably 1 hour or more, more preferably 1 hour and 30 minutes or more, preferably 30 hours or less, and more preferably 15 hours or less.
  • solvent removal treatment of carbon nanotube stacked structure When the carbon nanotube layered structure has been subjected to a dispersion treatment, the carbon nanotube layered structure may be further subjected to a solvent removal treatment.
  • a solvent removal treatment when measuring or evaluating various physical properties or properties of a carbon nanotube laminate structure dispersed in a solvent, a portion of the dispersed carbon nanotube laminate structure is separated for measurement or evaluation, and the separated carbon nanotube The laminated structure is subjected to solvent removal treatment.
  • the solvent removal treatment include filtration and drying. Filtration can be performed using, for example, filter paper. Examples of drying include heat drying, air drying, reduced pressure drying, and the like.
  • Heat drying may be performed, for example, at a temperature of 80°C or higher, preferably at a temperature of 200°C or lower, for example, for 0.5 hours or more, preferably for 2 hours or less. good.
  • air drying may be performed at a temperature of 20°C or higher, 30°C or lower, a humidity of 30% or higher, a humidity of 70% or lower, and 1. It may be carried out for more than 1 hour or less than 12 hours.
  • vacuum drying may be performed at a temperature of 20°C or higher, 100°C or lower, a pressure of 10Pa or higher, a pressure of 1000Pa or lower, and a drying time of 1 hour. It may be carried out for more than 12 hours or less than 12 hours.
  • the carbon nanotube dispersion liquid of the present invention contains the carbon nanotube layered structure of the present invention and a solvent.
  • the carbon nanotube dispersion liquid of the present invention can be used, for example, as a coating liquid to form a functional region (e.g., a resistance variable layer) of an electronic element (e.g., a variable resistance layer) during the production of an electronic element (e.g., a resistance variable memory device). This makes it possible to provide an electronic device that can operate with a sufficiently low switching voltage.
  • the solvent contained in the carbon nanotube dispersion of the present invention include non-halogen solvents and non-aqueous solvents.
  • the above-mentioned solvents include water; methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, t-butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, amyl alcohol, methoxy Alcohols such as propanol, propylene glycol, and ethylene glycol; Ketones such as acetone, methyl ethyl ketone, and cyclohexanone; Esters such as ethyl acetate, butyl acetate, ethyl lactate, esters of ⁇ -hydroxycarboxylic acids, and benzyl benzoate (benzyl benzoate) ; Et
  • Group hydrocarbons examples include salicylaldehyde, dimethyl sulfoxide, 4-methyl-2-pentanone, N-methylpyrrolidone, ⁇ -butyrolactone, and tetramethylammonium hydroxide.
  • water, ethyl lactate, isopropanol, and methyl ethyl ketone are preferred from the viewpoint of particularly excellent dispersibility. These may be used alone or in combination of two or more.
  • the concentration of carbon nanotubes in the carbon nanotube dispersion of the present invention is preferably 1 mg or more, more preferably 100 mg or more, per 1 L of the solvent. Moreover, it is preferable that it is 10000 mg or less. If 1 mg or more of carbon nanotubes is contained in the solvent, a functional region (eg, resistance change layer) with excellent strength can be formed. Further, if the amount of carbon nanotubes contained is 10,000 mg or less, agglomeration of the carbon nanotube stacked structures can be suppressed, and a dispersion liquid with even better dispersibility of the carbon nanotube stacked structures can be obtained.
  • the concentration of carbon nanotubes in the carbon nanotube dispersion of the present invention is preferably 0.005% by mass or more, more preferably 0.01% by mass or more, and preferably 5% by mass or less, More preferably, it is 0.5% by mass or less.
  • concentration of carbon nanotubes is 0.005% by mass or more, a functional region (eg, a variable resistance layer) with excellent strength can be formed.
  • concentration of carbon nanotubes is 5% by mass or less, agglomeration of carbon nanotube stacked structures can be suppressed, and a dispersion liquid with even better dispersibility of carbon nanotube stacked structures can be obtained.
  • the carbon nanotube dispersion liquid of the present invention preferably does not substantially contain a dispersant, since it can form a functional region (eg, a variable resistance layer) of an electronic device with a sufficiently low switching voltage.
  • a dispersant e.g. a dispersant that can form a functional region (eg, a variable resistance layer) of an electronic device with a sufficiently low switching voltage.
  • substantially free of carbon nanotubes means that they are not actively incorporated unless they are unavoidably mixed in, and specifically, it means that the content in the carbon nanotube dispersion is 0. It is preferably less than .05% by weight, more preferably less than 0.01% by weight, even more preferably less than 0.001% by weight.
  • examples of the dispersant include surfactants, synthetic polymers, natural polymers, and the like.
  • the concentration of metal impurities in the carbon nanotube dispersion is 1. It is preferably less than ⁇ 10 18 atoms/cm 3 , more preferably less than 15 ⁇ 10 16 atoms/cm 3 .
  • the carbon nanotube dispersion liquid of the present invention further improves the dispersibility of the carbon nanotube layered structure, and from the viewpoint of forming a uniform functional region (e.g. resistance change layer), carbon nanotube precipitates and carbon nanotube It is preferable that aggregates of laminated structures are not substantially included.
  • a uniform functional region e.g. resistance change layer
  • the carbon nanotube dispersion of the present invention can be obtained in the form of a carbon nanotube laminate structure dispersed in a solvent, for example, according to the method for manufacturing a carbon nanotube laminate structure described above.
  • the coating liquid for manufacturing electronic devices of the present invention contains the carbon nanotube dispersion liquid of the present invention.
  • the coating liquid for manufacturing electronic devices of the present invention can be applied, for example, at the time of manufacturing an electronic device (for example, a resistance variable memory device), and the solvent can be dried and removed to form a functional area (for example, a resistance variable layer) of the electronic device. ) can be used to form.
  • an electronic device for example, a resistance variable memory device
  • the solvent can be dried and removed to form a functional area (for example, a resistance variable layer) of the electronic device. ) can be used to form.
  • the carbon nanotube film of the present invention includes the carbon nanotube laminate structure of the present invention.
  • a “carbon nanotube film” is a portion (functional layer) that includes a carbon nanotube stacked structure as a material and can function as a functional region (eg, a resistance change layer of a resistance change storage device) in an electronic device.
  • the carbon nanotube film can be formed, for example, in the form of a coating film.
  • a plurality of carbon nanotube stacked structures may cross each other. Preferably. FIG.
  • the carbon nanotube film of the present invention can be formed, for example, by applying the carbon nanotube dispersion liquid of the present invention (eg, a coating liquid for manufacturing electronic devices) and removing the solvent. Formation of such a carbon nanotube film can be performed, for example, by a procedure similar to the "method for forming a variable resistance layer" below.
  • the electronic device of the present invention includes the carbon nanotube film of the present invention.
  • the carbon nanotube film exists as a portion (functional layer) that can function as a functional region.
  • the electronic element include a resistance variable memory device, a microprocessor, a field effect transistor, and a thyristor, but a resistance variable memory device (eg, random access memory) is preferable.
  • the functional region include a variable resistance layer, a semiconductor layer, and an electrode, and a variable resistance layer is preferable.
  • the electronic device of the present invention can be operated with a sufficiently low switching voltage, and as long as the switching voltage is low, even if the cells in the electronic device are densely integrated, problems such as current leakage to adjacent cells caused by high voltage may occur. Since this suppresses the storage capacity, it becomes possible to manufacture electronic devices such as memory devices in which cells are integrated at high density and performance such as storage capacity is improved.
  • An example in which the electronic element of the present invention is used as a resistance variable memory device is shown in FIG. 10(k).
  • FIG. 4 shows the lower electrode 352 (TiN layer), resistance change layer 354 (carbon nanotube film of the invention), and upper part of the resistance change memory device when the electronic element of the invention is used as a resistance change memory device.
  • An example of a scanning electron microscope (SEM) image of a cross section of a region including electrode 355 (TiN layer) is shown.
  • a resistance variable memory device including the carbon nanotube film of the present invention as a portion (functional layer) that can function as a resistance variable layer as an example.
  • a resistance variable memory device including the carbon nanotube film of the present invention as a portion (functional layer) that can function as a resistance variable layer as an example.
  • it is not limited to this.
  • a silicon substrate 350 is prepared.
  • a silicon wafer obtained by growing a single crystal silicon ingot by a Czochralski (CZ) method, a floating zone melting (FZ) method, or the like and performing wafer processing on the grown ingot is used. be able to.
  • the diameter, surface orientation, conductivity type, etc. of the silicon substrate 350 can be appropriately set according to the design.
  • the diameter of the silicon substrate 350 can be 200 mm, 300 mm, 450 mm, etc.
  • the plane orientation of the silicon substrate 350 can be (001), (110), (111), or the like.
  • the conductivity type of the silicon substrate 350 can be n-type or p-type using an appropriate dopant, such as boron (B) as the p-type dopant and phosphorus (P) or the like as the n-type dopant. be able to.
  • a semiconductor substrate other than silicon may be used.
  • an insulating film 351 is formed on the silicon substrate 350.
  • the insulating film 351 can be made of silicon oxide (SiO 2 ), silicon nitride (Si 3 N 4 ), or the like. Further, the insulating film 351 can be formed by a CVD method, a sputtering method, or the like.
  • a lower electrode 352 is formed on the insulating film 351.
  • the lower electrode 352 can be made of titanium nitride (TiN), tungsten (W), aluminum (Al), or the like.
  • the lower electrode 352 can be formed by a CVD method, a sputtering method, or the like.
  • the lower electrode 352 is patterned into a pillar shape by electron beam (EB) lithography, dry etching, or the like.
  • EB electron beam
  • an insulating film 353 is deposited on the lower electrode 352 patterned into a pillar shape.
  • the insulating film 353 can be made of silicon oxide (SiO 2 ), silicon nitride (Si 3 N 4 ), or the like, and can be formed by a CVD method, an ALD method, a sputtering method, or the like.
  • the surface of the deposited insulating film 353 is polished using chemical mechanical polishing (CMP) or the like to expose the pillar-shaped lower electrode 352 on the surface.
  • CMP chemical mechanical polishing
  • variable resistance layer 354 is formed entirely on the exposed surface of the pillar-shaped lower electrode 352.
  • the variable resistance layer 354 is composed of the carbon nanotube film of the present invention.
  • variable resistance layer 354 containing CNTs can be formed, for example, by applying the carbon nanotube dispersion of the present invention to the surface where the pillar-shaped lower electrode 352 is exposed. A method for forming the variable resistance layer 354 will be described in detail later.
  • an upper electrode 355 is formed on the variable resistance layer 354.
  • This upper electrode 355 can be made of titanium nitride (TiN), tungsten (W), aluminum (Al), or the like, and can be formed by a CVD method, a sputtering method, or the like.
  • the upper electrode 355 and the variable resistance layer 354 are successively patterned by photolithography and dry etching to separate the elements.
  • the patterning of the upper electrode 355 is performed by etching the upper electrode 355 using an etching method that does not generate a potential difference between the upper electrode 355 and the lower electrode 352 due to charge-up of the upper electrode 355. This can be done, for example, by a microwave-excited surface wave plasma etching method.
  • destruction of the variable resistance layer 354 made of the carbon nanotube film of the present invention can be suppressed, and the yield of manufacturing the memory device can be improved.
  • the method for forming the upper electrode 355 and the apparatus used therefor will be described in detail later.
  • a protective film 356 is formed to cover the element-isolated upper electrode 355 and variable resistance layer 354.
  • the protective film 356 can be made of silicon oxide (SiO 2 ), silicon nitride (Si 3 N 4 ), or the like, and can be formed by a CVD method, a sputtering method, or the like.
  • a through hole 357 is formed above the upper electrode 355 and the variable resistance layer 354 to penetrate the protective film 356 and expose the upper electrode 355.
  • a through hole 358 that penetrates the protective film 356 and the insulating film 353 and exposes the lower electrode 352 is formed in a portion where the variable resistance layer 354 is not present.
  • the manufacturing method according to the above procedure is suitable for suppressing destruction of the resistance change layer 354 and manufacturing a resistance change storage device with a higher yield.
  • variable resistance layer 354 can be formed, for example, by the following procedure.
  • the solvent is removed from the CNT dispersion of the present invention, and the variable resistance layer 354 is formed.
  • the CNT dispersion of the present invention is coated on the lower electrode 352 patterned into a pillar shape, and then the CNT dispersion of the present invention is dried. The solvent is removed from the liquid, and a variable resistance layer 354 is formed.
  • a known application method can be employed as a method for applying the CNT dispersion of the present invention onto the lower electrode 352.
  • coating methods include dipping method, spin coating method, roll coating method, gravure coating method, knife coating method, air knife coating method, roll knife coating method, die coating method, screen printing method, spray coating method, and gravure coating method.
  • An offset method, a mist coating method, etc. can be used.
  • a known drying method can be used to dry the CNT dispersion of the present invention applied onto the lower electrode 352.
  • Examples of the drying method include hot air drying, vacuum drying, hot roll drying, and infrared irradiation.
  • the drying temperature is not particularly limited, but is usually room temperature to 400° C.
  • the drying time is not particularly limited, but is usually 0.1 to 150 minutes.
  • variable resistance layer 354 formed in the film forming step may optionally be pressed to further increase its density.
  • the pressing pressure during press working is preferably less than 3 MPa, and it is more preferable that no press working is performed.
  • the upper electrode 355 can be formed, for example, by the following procedure. Moreover, the method for manufacturing an electronic device of the present invention can be carried out using the following apparatus.
  • FIG. 7 shows surface wave plasma etching using microwave excitation.
  • 1 shows a schematic diagram of an example of a plasma, SWP) device.
  • the SWP apparatus 200 shown in FIG. 7 includes a processing container 201 that accommodates a silicon substrate 250 to be processed, a lid part 202 that has a plurality of microwave radiation holes 202a arranged at the top of the processing container 201, and a lid part 202 that excites plasma.
  • a processing container 201 that accommodates a silicon substrate 250 to be processed
  • a lid part 202 that has a plurality of microwave radiation holes 202a arranged at the top of the processing container 201
  • a lid part 202 that excites plasma.
  • the direction of the electric field is reversed in a shorter time than when it is generated by conventional low frequency radio wave excitation (for example, 13 MHz).
  • the acceleration of the generated electrons can be suppressed and the energy can be reduced.
  • damage to the upper electrode can be suppressed during etching of the upper electrode.
  • the positively charged upper electrode 355 can be neutralized more efficiently.
  • FIG. 8 shows a schematic diagram of an example of a microwave-excited plasma etching apparatus (hereinafter also referred to as "RSLA apparatus") using a radial line slot antenna, which is a type of SWP apparatus 200 shown in FIG.
  • the RLSA apparatus 300 shown in FIG. 8 includes a processing container 301 that accommodates a silicon substrate 350 to be processed, a radial line slot antenna 302 placed on the top of the processing container 301, and a microwave generator that generates microwaves to excite plasma. (For a more detailed device configuration, see, for example, Japanese Patent Laid-Open No. 2000-77335).
  • FIG. 9 shows an example of the radial line slot antenna 302.
  • a radial line slot antenna is a type of planar antenna, and as shown in FIG. 9, a plurality of microwave radiation holes 302b are formed on the surface of an antenna main body 302a made of a conductor disk, for example, in a concentric or spiral shape. , are arranged radially (for example, see Japanese Patent Laid-Open No. 2000-77335).
  • the upper electrode 355 can be neutralized more uniformly.
  • the switching voltage of the electronic element is preferably as low as possible, preferably 5V or less, more preferably 4.8V or less, and even more preferably 4.5V or less.
  • the lower the switching voltage the more cells in an electronic device can be integrated at high density, and problems such as current leakage to adjacent cells caused by high voltage can be suppressed. It becomes possible to manufacture electronic devices such as memory devices with improved performance.
  • the switching voltage of the electronic element should not be too low from the viewpoint of suppressing the influence of noise, and is preferably 0.5 V or more, more preferably 1 V or more, and even more preferably 1.5 V or more.
  • the switching voltage of an electronic device can be measured, for example, by the method described in Examples.
  • the thickness of the iron thin film (catalyst layer) of the catalyst support was determined as follows. The surface from which a part of the iron thin film (catalyst layer) was peeled off was observed using an atomic force microscope (AFM), and the difference in height of the observed step portion was defined as the film thickness.
  • AFM atomic force microscope
  • ⁇ Ratio of the number of single-walled CNTs to the total number of CNTs The material CNT was observed with a transmission electron microscope (TEM), and a TEM image was obtained. The number of layers of 50 CNTs randomly selected from the obtained TEM images was measured. Then, it was converted to the number of single-walled CNTs in 100 material CNTs, and was defined as "the ratio of the number of single-walled CNTs to the total number of CNTs.”
  • ⁇ Average length> The oxidized CNTs that were collected for measurement and from which the solvent had been removed were observed with a scanning electron microscope (SEM) to obtain a SEM image.
  • SEM scanning electron microscope
  • the oxidized flat CNT laminated structure was not present, the lengths of 50 oxidized CNTs were measured instead of the oxidized flat CNT laminated structure, and the arithmetic mean value was taken as the average length.
  • Example 1 Preparation of catalyst support (catalyst for material CNT synthesis)] 1.9 g of aluminum tri-sec-butoxide as an aluminum compound was dissolved in 100 mL of 2-propanol as an organic solvent. Furthermore, 0.9 g of triisopropanolamine as a stabilizer was added and dissolved to prepare a coating liquid A for forming a base layer. Further, 174 mg of iron acetate as an iron compound was dissolved in 100 mL of 2-propanol as an organic solvent. Furthermore, 190 mg of triisopropanolamine as a stabilizer was added and dissolved to prepare a coating liquid B for forming a catalyst layer.
  • the surface of a Fe-Cr alloy SUS430 substrate (manufactured by JFE Steel Corporation, 40 mm x 100 mm, thickness 0.3 mm, Cr 18%, arithmetic mean roughness Ra ⁇ 0.59 ⁇ m) as a base material was coated at a room temperature of 25°C and relative humidity.
  • the above-mentioned coating liquid A was applied by dip coating in a 50% environment. Specifically, the base material was immersed in coating liquid A, held for 20 seconds, and then pulled up at a pulling speed of 10 mm/sec. Thereafter, it was air-dried for 5 minutes, heated in an air environment at 300° C.
  • alumina thin film (base layer) with a thickness of 40 nm on the base material.
  • the above-mentioned coating liquid B was applied by dip coating onto the alumina thin film provided on the base material under an environment of room temperature 25° C. and relative humidity 50%. Specifically, the base material provided with the alumina thin film was immersed in coating liquid B, held for 20 seconds, and the base material provided with the alumina thin film was pulled up at a pulling speed of 3 mm/sec.
  • CNTs material CNTs
  • CVD apparatus reaction chamber size: diameter 30 mm, heating length 360 mm.
  • the catalyst support prepared above was installed in a reaction chamber of a CVD apparatus maintained at a furnace temperature of 750° C. and a furnace pressure of 1.02 ⁇ 10 5 Pa, and 100 sccm of He and 900 sccm of H 2 were introduced for 6 minutes.
  • the catalyst layer (iron) was reduced and the iron was made into fine particles, creating a state suitable for the growth of single-walled CNTs (a state in which many nanometer-sized fine catalyst particles were formed on the base layer). formation process). Note that the density of the catalyst fine particles at this time was adjusted to 1 ⁇ 10 12 to 1 ⁇ 10 14 particles/cm 2 .
  • ultrasonic treatment (oscillation frequency 40 kHz, high frequency output 1200 W) was performed for 2 hours using an ultrasonic irradiator (manufactured by Hyundai Electronics, product name "WTC-1200-40") to obtain an oxidized CNT dispersion.
  • FIGS. 2 and 3 examples of TEM images of the oxidized CNT dispersion obtained by the method of this example are shown in FIGS. 2 and 3.
  • the TEM images in FIGS. 2 and 3 are images obtained by observing with a TEM a CNT film formed by dropping an oxidized CNT dispersion onto a TEM observation grid mesh and drying it into a film.
  • a resistance variable memory device was manufactured according to the flowchart shown in FIG. First, a silicon substrate 350 was prepared (FIG. 10(a)), and a SiO 2 layer was formed as an insulating film 351 on the silicon substrate 350 (FIG. 10(b)). Next, a TiN layer as a lower electrode 352 was formed on the SiO 2 layer (FIG. 10(c)), and the TiN layer was patterned into a pillar shape by EB lithography and dry etching (FIG. 10(d)). The cross-sectional area of the pillar-shaped electrode was 200 nm x 200 nm.
  • a SiO 2 layer as an insulating film 353 was formed on the TiN layer patterned into a pillar shape (FIG. 10(e)).
  • the surface of the SiO 2 layer was polished using a CMP method to expose the pillar-shaped TiN layer on the surface (FIG. 10(f)).
  • the oxidized CNT dispersion obtained above was applied onto the TiN layer to form a carbon nanotube layer as the variable resistance layer 354 (FIG. 10(g)).
  • a TiN layer as an upper electrode 355 was formed on the carbon nanotube layer (FIG. 10(h)).
  • the TiN layer and the carbon nanotube layer as the upper electrode 355 are patterned by microwave-excited (2.45 GHz) plasma using the RLSA apparatus 300 shown in FIG. 8 to separate the elements. (Figure 10(i)).
  • the area of the upper electrode 355 was 120 ⁇ m ⁇ 200 ⁇ m.
  • a SiN x layer was formed as a protective film 356 so as to cover the TiN layer and carbon nanotube layer that were separated into elements (FIG. 10(j)).
  • a through hole 357 is formed above the TiN layer and carbon nanotube layer as the upper electrode 355 to penetrate the SiN x layer and expose the TiN layer as the upper electrode 355, and the TiN layer as the upper electrode 355 is And in a portion where the carbon nanotube layer does not exist, a through hole 358 was formed to penetrate the SiN x layer as the protective film 356 and the SiO 2 layer as the insulating film 353 and expose the TiN layer as the lower electrode 352 (Fig. 10 (k)). In this way, a resistance variable memory device was manufactured.
  • FIG. 10 (k) a resistance variable memory device was manufactured.
  • FIG. 4 shows a region including a lower electrode 352 (TiN layer), a resistance variable layer 354 (carbon nanotube layer), and an upper electrode 355 (TiN layer) of a resistance variable memory device manufactured based on the method of this example.
  • a cross-sectional scanning electron microscope (SEM) image is shown. A layered structure is observed in the entire region of the variable resistance layer 354, and it can be confirmed that the variable resistance layer 354 is entirely composed of a laminated carbon nanotube structure.
  • the current-voltage (IV) curve of the resistance variable memory device was measured by sweeping the voltage from 0V to 7.0V. A change was observed in the value of the current flowing through the variable resistance layer, and the voltage value when switching between two states, a high resistance state and a low resistance state, occurred was defined as the switching voltage.
  • the results are shown in Table 1. In this example, the switching voltage was a low value of 4.2V. This result showed that by using the carbon nanotube stacked structure according to the present invention as a material for forming a variable resistance layer, it was possible to obtain an electronic device that can operate with a low switching voltage.
  • the oxidized CNTs contained in the oxidized CNT dispersion obtained above had the shape of cylindrical single-walled CNTs, and the carbon nanotube laminate structure according to the present invention It was possible to evaluate that this was not the case.
  • the reason why the oxidized CNTs took on such a shape is probably that the degree of oxidation of the CNTs was low, making it difficult for the CNTs to collapse into a flat shape.
  • the switching voltage of the resistance variable memory device was measured, it was found to be a high value of 5.5V.
  • the oxidized CNTs contained in the oxidized CNT dispersion obtained above had the shape of multi-walled CNTs, which corresponds to the carbon nanotube layered structure according to the present invention. I was able to evaluate that there was no such thing. The reason why the oxidized CNTs took on this shape is thought to be that the thicker catalyst layer strengthened the catalytic activity, promoted excessive reaction, and promoted the multilayering of CNTs. . When the switching voltage of the resistance variable memory device was measured, it was found to be a high value of 5.8V.
  • the present invention functions as a functional region of an electronic device (e.g., a variable resistance layer of a variable resistance storage device), and when used as a functional region of an electronic device, the electronic device can operate at a low switching voltage. It is possible to provide a carbon nanotube stacked structure and a carbon nanotube dispersion that can be used to form a carbon nanotube film. Further, according to the present invention, the electronic device functions as a functional region of an electronic device (e.g., a resistance variable layer of a resistance variable memory device), and when used as a functional region of an electronic device, the electronic device can operate at a low switching voltage. It is possible to provide a carbon nanotube film that can be operated, a coating liquid for manufacturing an electronic device, and an electronic device that can be operated at a low switching voltage.
  • an electronic device e.g., a variable resistance layer of a variable resistance storage device

Abstract

The purpose of the present invention is to provide a carbon nanotube layered structure that can be used to form a carbon nanotube film that serves as a functional region of an electronic element, and that allows the electronic element to be actuated by a low switching voltage when the carbon nanotube layered structure is used as the functional region of the electronic element. A carbon nanotube layered structure according to the present invention comprises a plurality of layers of flat oxidized carbon nanotubes. In the carbon nanotube layered structure, the proportion of single-layer carbon nanotubes in all carbon nanotubes is at least 51 with respect to 100 carbon nanotubes.

Description

カーボンナノチューブ積層構造体、カーボンナノチューブ分散液、電子素子製造用塗布液、カーボンナノチューブ膜、および電子素子Carbon nanotube laminate structures, carbon nanotube dispersions, coating liquids for manufacturing electronic devices, carbon nanotube films, and electronic devices
　本発明は、カーボンナノチューブ積層構造体、カーボンナノチューブ分散液、電子素子製造用塗布液、カーボンナノチューブ膜、および電子素子に関するものである。 The present invention relates to a carbon nanotube laminate structure, a carbon nanotube dispersion, a coating liquid for manufacturing electronic devices, a carbon nanotube film, and an electronic device.
　近年、フラッシュメモリに代わる不揮発性記憶装置として、メモリセルの電気抵抗値を高抵抗状態と低抵抗状態とに変化させてデータを記憶する抵抗変化型記憶装置（ＲｅＲＡＭ）が注目されている。抵抗変化型記憶装置は、消費電力が低く、高密度化が可能であり、さらに読み出しが高速である等の利点を有している。 In recent years, resistance variable memory devices (ReRAM), which store data by changing the electrical resistance value of a memory cell between a high resistance state and a low resistance state, have been attracting attention as a nonvolatile memory device that can replace flash memory. A resistance change memory device has advantages such as low power consumption, high density, and high speed readout.
　特許文献１には、メモリセルを構成する抵抗変化層をカーボンナノチューブ（以下、ＣＮＴという場合がある。）で構成した抵抗変化型記憶装置について記載されている。 Patent Document 1 describes a variable resistance memory device in which a variable resistance layer constituting a memory cell is made of carbon nanotubes (hereinafter sometimes referred to as CNT).
特開２０２１－１０８３４２号公報Japanese Patent Application Publication No. 2021-108342
　記憶装置を製造する際にメモリセルを高密度に集積させることができれば、記憶容量等の性能を向上できると考えられる。一方、メモリセルの書換えのために負荷する電圧（スイッチング電圧）が高いと、隣接セルへの電流漏れ等の原因で記憶内容が消去されるリスクが想定され、メモリセルの高密度集積に対する障害になると考えられる。そのため、隣接セルへの電流漏れ等の不具合を抑制しつつメモリセルを高密度に集積させて記憶容量等の性能を向上させるために、スイッチング電圧を低下させる点において、改善の余地があった。 It is believed that performance such as storage capacity can be improved if memory cells can be integrated at high density when manufacturing a memory device. On the other hand, if the voltage (switching voltage) applied to rewrite a memory cell is high, there is a risk that the memory content will be erased due to current leakage to adjacent cells, which may be an obstacle to high-density integration of memory cells. It is considered to be. Therefore, there is room for improvement in reducing the switching voltage in order to improve performance such as storage capacity by integrating memory cells at high density while suppressing problems such as current leakage to adjacent cells.
　そこで、本発明は、電子素子の機能性領域（例、抵抗変化型記憶装置の抵抗変化層）として機能し、かつ、電子素子の機能性領域として用いた時に電子素子が低いスイッチング電圧で作動可能となる、カーボンナノチューブ膜を形成するために用いることが可能な、カーボンナノチューブ積層構造体およびカーボンナノチューブ分散液を提供することを目的とする。
　また、本発明は、電子素子の機能性領域（例、抵抗変化型記憶装置の抵抗変化層）として機能し、かつ、電子素子の機能性領域として用いた時に電子素子が低いスイッチング電圧で作動可能となる、カーボンナノチューブ膜、電子素子製造用塗布液、および低いスイッチング電圧で作動可能な電子素子を提供することを目的とする。 Therefore, the present invention functions as a functional region of an electronic device (e.g., resistance variable layer of a resistance variable memory device), and enables the electronic device to operate at a low switching voltage when used as the functional region of the electronic device. The present invention aims to provide a carbon nanotube layered structure and a carbon nanotube dispersion that can be used to form a carbon nanotube film.
Further, the present invention functions as a functional region of an electronic device (e.g., a variable resistance layer of a variable resistance storage device), and when used as a functional region of an electronic device, the electronic device can operate at a low switching voltage. The purpose of the present invention is to provide a carbon nanotube film, a coating liquid for manufacturing electronic devices, and an electronic device that can be operated at a low switching voltage.
　本発明者らは、上記目的を達成するために鋭意検討を行った。そして、本発明者らは、抵抗変化型記憶装置の抵抗変化層を形成する際、酸化した高単層比率の扁平カーボンナノチューブが複数積層してなるカーボンナノチューブ積層構造体を用いることにより、電子素子のスイッチング電圧を低くできることを見出し、本発明を完成させた。 The present inventors conducted extensive studies to achieve the above object. The present inventors have discovered that when forming a resistance change layer of a resistance change memory device, by using a carbon nanotube stacked structure formed by stacking a plurality of oxidized flat carbon nanotubes with a high single-layer ratio, electronic devices can be fabricated. The present invention was completed based on the discovery that it is possible to lower the switching voltage.
　即ち、この発明は、上記課題を有利に解決することを目的とするものであり、本発明は、
［１］酸化扁平カーボンナノチューブが複数積層してなるカーボンナノチューブ積層構造体であって、カーボンナノチューブ積層構造体中の全てのカーボンナノチューブに対して単層カーボンナノチューブが占める割合が、カーボンナノチューブ１００本中５１本以上である、カーボンナノチューブ積層構造体
　を提供する。
　カーボンナノチューブとして酸化した高単層比率カーボンナノチューブを用いて、溶媒中で所定条件の超音波分散処理を行うことで、カーボンナノチューブが扁平形状を取りやすくなり、更に、扁平形状となったカーボンナノチューブが複数積層してなる積層構造体の構造（以下、「扁平カーボンナノチューブ積層構造」ということがある。）を取りやすくなる。
　また、カーボンナノチューブがこのような扁平カーボンナノチューブ積層構造を取り、更に、単層カーボンナノチューブの含有割合が高いことにより、電子素子の機能性領域（例、抵抗変化型記憶装置の抵抗変化層）の形成に用いた時のスイッチング電圧低下に寄与する。カーボンナノチューブが酸化されているかどうかの評価（即ち、酸化の程度の測定）、単層カーボンナノチューブの含有割合の測定、カーボンナノチューブが扁平カーボンナノチューブ積層構造を取っているかどうかの評価は、例えば、実施例に記載の方法を用いて行うことができる。 That is, the present invention aims to advantageously solve the above problems, and the present invention has the following features:
[1] A carbon nanotube laminate structure formed by laminating a plurality of oxidized flat carbon nanotubes, in which the ratio of single-walled carbon nanotubes to all carbon nanotubes in the carbon nanotube laminate structure is within 100 carbon nanotubes. Provided is a laminated carbon nanotube structure having 51 or more carbon nanotubes.
By using high single-wall ratio carbon nanotubes that have been oxidized as carbon nanotubes, by performing ultrasonic dispersion treatment under specified conditions in a solvent, the carbon nanotubes can easily take on a flat shape, and furthermore, the flat carbon nanotubes can be It becomes easier to form a laminated structure formed by laminating a plurality of layers (hereinafter sometimes referred to as "flat carbon nanotube laminated structure").
In addition, carbon nanotubes have such a flat carbon nanotube stacked structure, and furthermore, due to the high content of single-walled carbon nanotubes, the functional areas of electronic devices (e.g., the resistance change layer of resistance change storage devices) are This contributes to a reduction in switching voltage when used for formation. Evaluation of whether carbon nanotubes are oxidized (i.e., measurement of the degree of oxidation), measurement of the content ratio of single-walled carbon nanotubes, and evaluation of whether carbon nanotubes have a flat carbon nanotube layered structure can be performed, for example, by This can be done using the methods described in the Examples.
　また、本発明は、
［２］酸化扁平カーボンナノチューブの直径方向の扁平率が、１０％以上４０％以下である、上記［１］に記載のカーボンナノチューブ積層構造体
　を提供することが好ましい。ＣＮＴの扁平率が４０％以下であれば、ＣＮＴが十分に扁平形状となり、カーボンナノチューブ積層構造体を電子素子の機能性領域（例、抵抗変化層）に用いた時のスイッチング電圧低下に寄与する。一方、内壁のグラファイト構造同士に層間距離が存在するため、ＣＮＴの扁平率を１０％未満とすることは難しい。扁平率は、例えば、後述の方法で求めることができる。 Moreover, the present invention
[2] It is preferable to provide the carbon nanotube laminate structure according to [1] above, wherein the diametrical oblateness of the oxidized flat carbon nanotubes is 10% or more and 40% or less. If the flatness of the CNT is 40% or less, the CNT has a sufficiently flat shape, which contributes to a reduction in switching voltage when the carbon nanotube laminated structure is used in a functional area of an electronic device (e.g., variable resistance layer). . On the other hand, since there is an interlayer distance between the graphite structures of the inner wall, it is difficult to make the flatness of CNT less than 10%. The aspect ratio can be determined, for example, by the method described below.
　また、本発明は、
［３］平均積層数が、２以上２０以下である、上記［１］または［２］に記載のカーボンナノチューブ積層構造体
　を提供することが好ましい。平均積層数が上記範囲内であれば、電子素子の機能性領域（例、抵抗変化型記憶装置の抵抗変化層）の形成に用いた時のスイッチング電圧低下の効果を高めることができる。平均積層数は、例えば実施例に記載の方法により測定することができる。 Moreover, the present invention
[3] It is preferable to provide the carbon nanotube laminated structure according to [1] or [2] above, wherein the average number of laminated layers is 2 or more and 20 or less. When the average number of laminated layers is within the above range, the effect of lowering the switching voltage when used for forming a functional region of an electronic device (eg, a resistance variable layer of a resistance variable memory device) can be enhanced. The average number of laminated layers can be measured, for example, by the method described in Examples.
　また、本発明は、
［４］カーボンナノチューブ積層構造体の平均長さが、２０ｎｍ以上３００ｎｍ以下である、上記［１］～［３］のいずれかに記載のカーボンナノチューブ積層構造体
　を提供することが好ましい。カーボンナノチューブ積層構造体の平均長さが２０ｎｍ以上であれば、カーボンナノチューブ積層構造体の導電性などの特性を損なわない点で好ましい。カーボンナノチューブ積層構造体の平均長さが３００ｎｍ以下であれば、カーボンナノチューブ積層構造体が溶媒中で凝集して沈降する不具合を防止する点で好ましい。カーボンナノチューブ積層構造体の平均長さは、例えば、後述の方法で求めることができる。 Moreover, the present invention
[4] It is preferable to provide the carbon nanotube laminate structure according to any one of [1] to [3] above, wherein the average length of the carbon nanotube laminate structure is 20 nm or more and 300 nm or less. It is preferable that the average length of the carbon nanotube laminate structure is 20 nm or more, since the properties such as conductivity of the carbon nanotube laminate structure are not impaired. It is preferable that the average length of the carbon nanotube laminate structure is 300 nm or less in order to prevent the carbon nanotube laminate structure from agglomerating and settling in a solvent. The average length of the carbon nanotube stacked structure can be determined, for example, by the method described below.
　また、本発明は、
［５］複数のカーボンナノチューブ積層構造体が、互いに交差している、上記［１］～［４］のいずれかに記載のカーボンナノチューブ積層構造体
　を提供することが好ましい。複数のカーボンナノチューブ積層構造体が互いに交差していることにより、電子素子の機能性領域（例、抵抗変化型記憶装置の抵抗変化層）の形成に用いた時のスイッチング電圧低下効果がより一層向上する。 Moreover, the present invention
[5] It is preferable to provide the carbon nanotube laminate structure according to any one of [1] to [4] above, wherein the plurality of carbon nanotube laminate structures intersect with each other. Because multiple carbon nanotube stacked structures intersect with each other, the switching voltage reduction effect is further improved when used to form a functional region of an electronic device (e.g., resistance variable layer of a resistance variable memory device). do.
　また、本発明は、
［６］上記［１］～［５］のいずれかに記載のカーボンナノチューブ積層構造体と溶媒とを含むカーボンナノチューブ分散液
　を提供する。本発明のカーボンナノチューブ分散液は、例えば、電子素子（例、抵抗変化型記憶装置）の製造時において、電子素子の機能性領域（例、抵抗変化層）の形成に、例えば、塗布液として用いることができ、そのことによって、十分低いスイッチング電圧で作動可能な電子素子を提供できる。 Moreover, the present invention
[6] Provided is a carbon nanotube dispersion containing the carbon nanotube layered structure according to any one of [1] to [5] above and a solvent. The carbon nanotube dispersion liquid of the present invention can be used, for example, as a coating liquid to form a functional region (e.g., a resistance variable layer) of an electronic element (e.g., a variable resistance layer) during the production of an electronic element (e.g., a resistance variable memory device). This makes it possible to provide an electronic device that can operate with a sufficiently low switching voltage.
　また、本発明は、
［７］上記［６］に記載のカーボンナノチューブ分散液を含む電子素子製造用塗布液
　を提供する。本発明の電子素子製造用塗布液は、例えば、電子素子（例、抵抗変化型記憶装置）の製造時に塗布して溶媒を乾燥除去することにより、電子素子の機能性領域（例、抵抗変化層）を形成させるために用いることができる。本発明の電子素子製造用塗布液を用いることで、十分低いスイッチング電圧で作動可能な電子素子を製造できる。 Moreover, the present invention
[7] A coating liquid for manufacturing an electronic device is provided, which includes the carbon nanotube dispersion liquid according to [6] above. The coating liquid for manufacturing electronic devices of the present invention can be applied, for example, at the time of manufacturing an electronic device (for example, a resistance variable memory device), and the solvent can be dried and removed to form a functional area (for example, a resistance variable layer) of the electronic device. ) can be used to form. By using the coating liquid for manufacturing electronic devices of the present invention, electronic devices that can be operated at sufficiently low switching voltages can be manufactured.
　また、本発明は、
［８］上記［１］～［５］のいずれかに記載のカーボンナノチューブ積層構造体を含むカーボンナノチューブ膜
　を提供する。本発明のカーボンナノチューブ膜は、例えば、電子素子の機能性領域（例、抵抗変化型記憶装置の抵抗変化層）の形成材料であり、十分低いスイッチング電圧で作動可能となる。 Moreover, the present invention
[8] A carbon nanotube film comprising the carbon nanotube layered structure according to any one of [1] to [5] above is provided. The carbon nanotube film of the present invention is, for example, a material for forming a functional region of an electronic device (eg, a variable resistance layer of a variable resistance memory device), and can be operated at a sufficiently low switching voltage.
　また、本発明は、
［９］上記［８］に記載のカーボンナノチューブ膜を含む電子素子
　を提供する。本発明の電子素子は、十分低いスイッチング電圧で作動可能であり、スイッチング電圧が低ければ、電子素子中のセルを高密度に集積しても、高電圧によって生じる隣接セルへの電流漏れ等の不具合が抑制されるので、セルを高密度に集積させ、記憶容量等の性能を向上させた記憶装置等の電子素子を製造することが可能となる。 Moreover, the present invention
[9] An electronic device comprising the carbon nanotube film according to [8] above is provided. The electronic device of the present invention can be operated with a sufficiently low switching voltage, and as long as the switching voltage is low, even if the cells in the electronic device are densely integrated, problems such as current leakage to adjacent cells caused by high voltage may occur. Since this suppresses the storage capacity, it becomes possible to manufacture electronic devices such as memory devices in which cells are integrated at high density and performance such as storage capacity is improved.
　また、本発明は、
［１０］前記電子素子が、抵抗変化型記憶装置であり、前記カーボンナノチューブ膜が、抵抗変化層として機能する、上記［９］に記載の電子素子
　を提供することが好ましい。このような抵抗変化型記憶装置は、十分低いスイッチング電圧で作動可能であり、スイッチング電圧が低ければ、抵抗変化型記憶装置中のセルを高密度に集積しても、高電圧によって生じる隣接セルへの電流漏れ等の不具合が抑制されるので、セルを高密度に集積させ、記憶容量等の性能を向上させた抵抗変化型記憶装置等の電子素子を製造することが可能となる。 Moreover, the present invention
[10] It is preferable to provide the electronic device according to [9] above, wherein the electronic device is a variable resistance storage device, and the carbon nanotube film functions as a variable resistance layer. Such a resistance variable memory device can operate with a sufficiently low switching voltage, and if the switching voltage is low, even if the cells in the resistance variable memory device are densely integrated, there will be no damage to adjacent cells caused by high voltage. Since defects such as current leakage are suppressed, it becomes possible to manufacture electronic devices such as resistance variable memory devices in which cells are integrated at high density and performance such as storage capacity is improved.
　本発明によれば、電子素子の機能性領域（例、抵抗変化型記憶装置の抵抗変化層）として機能し、かつ、電子素子の機能性領域として用いた時に電子素子が低いスイッチング電圧で作動可能となる、カーボンナノチューブ膜を形成するために用いることが可能な、カーボンナノチューブ積層構造体およびカーボンナノチューブ分散液を提供することができる。
　また、本発明によれば、電子素子の機能性領域（例、抵抗変化型記憶装置の抵抗変化層）として機能し、かつ、電子素子の機能性領域として用いた時に電子素子が低いスイッチング電圧で作動可能となる、カーボンナノチューブ膜、電子素子製造用塗布液、および低いスイッチング電圧で作動可能な電子素子を提供することができる。 According to the present invention, the present invention functions as a functional region of an electronic device (e.g., a variable resistance layer of a variable resistance storage device), and when used as a functional region of an electronic device, the electronic device can operate at a low switching voltage. It is possible to provide a carbon nanotube stacked structure and a carbon nanotube dispersion that can be used to form a carbon nanotube film.
Further, according to the present invention, the electronic device functions as a functional region of an electronic device (e.g., a resistance variable layer of a resistance variable memory device), and when used as a functional region of an electronic device, the electronic device can operate at a low switching voltage. It is possible to provide a carbon nanotube film that can be operated, a coating liquid for manufacturing an electronic device, and an electronic device that can be operated at a low switching voltage.
カーボンナノチューブ積層構造体の模式図である。FIG. 2 is a schematic diagram of a carbon nanotube stacked structure. カーボンナノチューブ分散液中のカーボンナノチューブ積層構造体の透過型電子顕微鏡（ＴＥＭ）画像である（Ａ：原図、Ｂ：マーキング付き）。It is a transmission electron microscope (TEM) image of a carbon nanotube stacked structure in a carbon nanotube dispersion (A: original image, B: with markings). カーボンナノチューブ分散液中でカーボンナノチューブ積層構造体同士が互いに交差している部分を含むカーボンナノチューブ積層構造体のＴＥＭ画像である（Ａ：原図、Ｂ：マーキング付き）。It is a TEM image of a carbon nanotube laminate structure including a portion where carbon nanotube laminate structures intersect with each other in a carbon nanotube dispersion liquid (A: original image, B: with markings). カーボンナノチューブ積層構造体を含み、かつ、抵抗変化層として機能する、カーボンナノチューブ膜を含む、抵抗変化型記憶装置の断面の走査型電子顕微鏡（ＳＥＭ）画像である。1 is a scanning electron microscope (SEM) image of a cross section of a resistance variable memory device including a carbon nanotube stacked structure and a carbon nanotube film functioning as a resistance change layer. カーボンナノチューブ積層構造体の形成に用いるカーボンナノチューブの製造に使用可能な製造装置の構成の一例を示す模式図である。FIG. 1 is a schematic diagram showing an example of the configuration of a manufacturing apparatus that can be used to manufacture carbon nanotubes used to form a carbon nanotube stacked structure. カーボンナノチューブ積層構造体の形成に用いるカーボンナノチューブの製造に使用可能な製造装置の構成の他の例を示す模式図である。FIG. 2 is a schematic diagram showing another example of the configuration of a manufacturing apparatus that can be used to manufacture carbon nanotubes used to form a carbon nanotube stacked structure. 表面波プラズマエッチング装置の一例の模式図である。FIG. 1 is a schematic diagram of an example of a surface wave plasma etching apparatus. ラジアルラインスロットアンテナを備えるプラズマエッチング装置の一例の模式図である。FIG. 1 is a schematic diagram of an example of a plasma etching apparatus including a radial line slot antenna. ラジアルラインスロットアンテナの一例を示す図である。It is a figure showing an example of a radial line slot antenna. 本発明の抵抗変化型記憶装置を製造する方法の一例のフローチャートを示す図である。FIG. 3 is a diagram showing a flowchart of an example of a method for manufacturing a resistance variable memory device of the present invention.
　以下、本発明の実施の形態について、詳細に説明する。
　ここで、本発明に係るカーボンナノチューブ積層構造体を含むカーボンナノチューブ膜は、例えば、電子素子中に形成させた時に、機能性領域（例、抵抗変化型記憶装置の抵抗変化層）として機能させることができ、そのことによって、十分低いスイッチング電圧で作動可能な電子素子を提供できる。
　また、本発明に係るカーボンナノチューブ分散液は、本発明に係るカーボンナノチューブ積層構造体と溶媒とを含むものであり、例えば、電子素子の製造時において、電子素子の機能性領域（例、抵抗変化型記憶装置の抵抗変化層）の形成に、例えば、塗布液として用いることができ、そのことによって、十分低いスイッチング電圧で作動可能な電子素子を提供できる。
　また、本発明に係る電子素子製造用塗布液は、本発明に係るカーボンナノチューブ分散液を含むものであり、例えば、電子素子の機能性領域（例、抵抗変化型記憶装置の抵抗変化層）を形成するための塗布膜形成のために用いることができ、そのことによって、十分低いスイッチング電圧で作動可能な電子素子を提供できる。
　また、本発明に係るカーボンナノチューブ膜（例、塗布膜）は、本発明に係るカーボンナノチューブ積層構造体を含むものであり、例えば、電子素子中に形成させた時に、機能性領域（例、抵抗変化型記憶装置の抵抗変化層）として用いることができ、そのことによって、十分低いスイッチング電圧で作動可能な電子素子を提供できる。
　また、本発明に係る電子素子は、本発明に係るカーボンナノチューブ膜を、電子素子中で機能性領域（例、抵抗変化型記憶装置の抵抗変化層）として機能し得る部分（機能層）として含むものであり、十分低いスイッチング電圧で作動可能な電子素子（例、抵抗変化型記憶装置）として用いることができる。スイッチング電圧が低ければ、電子素子中のセルを高密度に集積しても、高電圧によって生じる隣接セルへの電流漏れ等の不具合が抑制されるので、セルを高密度に集積させ、記憶容量等の性能を向上させた記憶装置等の電子素子を製造することが可能となる。 Embodiments of the present invention will be described in detail below.
Here, the carbon nanotube film including the carbon nanotube laminate structure according to the present invention can function as a functional region (e.g., resistance change layer of a resistance change memory device) when formed in an electronic device, for example. This makes it possible to provide an electronic device that can operate with a sufficiently low switching voltage.
Further, the carbon nanotube dispersion according to the present invention contains the carbon nanotube layered structure according to the present invention and a solvent, and is used, for example, in the functional area of the electronic device (e.g., resistance change) during the manufacture of the electronic device. It can be used, for example, as a coating liquid to form a variable resistance layer of a memory device, thereby providing an electronic element that can operate with a sufficiently low switching voltage.
Furthermore, the coating liquid for manufacturing electronic devices according to the present invention contains the carbon nanotube dispersion liquid according to the present invention, and can be used, for example, to coat functional regions of electronic devices (e.g., resistance change layers of resistance change storage devices). It can be used to form a coating film for manufacturing, thereby providing an electronic device that can be operated at a sufficiently low switching voltage.
Furthermore, the carbon nanotube film (e.g., coating film) according to the present invention includes the carbon nanotube laminated structure according to the present invention, and when formed in an electronic device, for example, a functional region (e.g., a resistor) It can be used as a variable resistance layer of a variable memory device, thereby providing an electronic element that can operate with a sufficiently low switching voltage.
Further, the electronic device according to the present invention includes the carbon nanotube film according to the present invention as a portion (functional layer) that can function as a functional region (e.g., a resistance change layer of a resistance change storage device) in the electronic device. It can be used as an electronic device (eg, a resistance variable memory device) that can operate with a sufficiently low switching voltage. If the switching voltage is low, even if cells in an electronic device are densely integrated, problems such as current leakage to adjacent cells caused by high voltage can be suppressed. It becomes possible to manufacture electronic devices such as memory devices with improved performance.
（カーボンナノチューブ積層構造体）
　本発明のカーボンナノチューブ積層構造体は、酸化扁平カーボンナノチューブが複数積層してなるカーボンナノチューブ積層構造体であって、カーボンナノチューブ積層構造体中の全てのカーボンナノチューブに対して単層カーボンナノチューブが占める割合が、カーボンナノチューブ１００本中５１本以上である、カーボンナノチューブ積層構造体であること特徴とする。即ち、本発明のカーボンナノチューブ積層構造体は、扁平カーボンナノチューブが複数積層した積層構造体の構造（以下、「扁平カーボンナノチューブ積層構造」ということがある。）を取るカーボンナノチューブから構成される。このような構造の模式図の例を、図１に示す。また、カーボンナノチューブ分散液中の本発明のカーボンナノチューブ積層構造体の透過型電子顕微鏡（ＴＥＭ）画像の例を、図２に示す。 (Carbon nanotube laminate structure)
The carbon nanotube laminate structure of the present invention is a carbon nanotube laminate structure formed by laminating a plurality of oxidized flat carbon nanotubes, and the ratio of single-walled carbon nanotubes to all carbon nanotubes in the carbon nanotube laminate structure is The carbon nanotube layered structure is characterized in that the number of carbon nanotubes is 51 or more out of 100 carbon nanotubes. That is, the carbon nanotube layered structure of the present invention is composed of carbon nanotubes that have a layered structure in which a plurality of flat carbon nanotubes are stacked (hereinafter sometimes referred to as "flat carbon nanotube layered structure"). An example of a schematic diagram of such a structure is shown in FIG. Further, FIG. 2 shows an example of a transmission electron microscope (TEM) image of the carbon nanotube layered structure of the present invention in a carbon nanotube dispersion.
　カーボンナノチューブとして酸化した高単層比率カーボンナノチューブを用いて、溶媒中で所定条件の超音波分散処理を行うことで、カーボンナノチューブが扁平形状を取りやすくなり、更に、扁平カーボンナノチューブ積層構造を取りやすくなる。所定条件での超音波分散処理とは、３０ｋＨｚ以上の発振周波数での超音波分散処理が好ましく、超音波の発振周波数は、３５ｋＨｚ以上であることがより好ましく、５０ｋＨｚ以下であることが好ましく、４５ｋＨｚ以上であることがより好ましい。このような発振周波数で超音波分散処理を行えば、溶媒（例、水分子）の振動加速度が増加して効率的に目的物を得ることができると予想される。また、所定条件での超音波分散処理として、超音波分散処理の時間は、１時間以上が好ましく、１時間３０分以上がより好ましく、３０時間以下が好ましく、１５時間以下がより好ましい。
　このようになる具体的機構は不明であるが、恐らくは、以下の機構が推測される。
　まず、カーボンナノチューブが扁平形状を取りやすくなる機構としては、カーボンナノチューブが単層であることにより、多層カーボンナノチューブに比してカーボンナノチューブの柔軟性が高く、酸化されることで変形しやすくなり、また、カーボンナノチューブの内壁同士が接着するように内壁表面の親和性が増大し、溶媒中で所定条件の超音波分散処理を行うことで刺激を受けて、カーボンナノチューブが扁平形状に変形しやすくなることが考えられる。
　次に、扁平カーボンナノチューブ積層構造を取りやすくなる機構としては、以下が考えられる。材料ＣＮＴ作製時に、カーボンナノチューブが触媒基材上に、共通の配向性を持って成長したＣＮＴ集合体として得られ、その際に、このような配向性を維持したまま、ＣＮＴの外壁表面同士が接着した状態を取る。そして、このような接着状態を維持したまま、カーボンナノチューブに対して酸化処理および超音波分散処理が行われてカーボンナノチューブが扁平形状に変形し、接着したカーボンナノチューブ同士が積層構造を形成することが考えられる。
　扁平カーボンナノチューブ積層構造を取りやすくなる別の機構としては、以下が考えられる。扁平形状に変形したカーボンナノチューブ同士がファンデルワールス力によって誘引される。この時、扁平形状に変形したカーボンナノチューブの断面〔カーボンナノチューブの延在方向（軸線方向）に直交する断面〕が、両端が膨らんだダンベル形状を取り、カーボンナノチューブの扁平面の平面部と端部の膨らみとの間が溝状構造となり、溶媒中で所定条件の超音波分散処理を行った時に刺激を受けて、カーボンナノチューブの端部の膨らみが別のカーボンナノチューブの溝状構造に嵌まるように、カーボンナノチューブ同士が誘引されて積層し、その結果、扁平形状に変形したカーボンナノチューブが積層構造を取りやすくなることが考えられる。 By using oxidized high single-wall ratio carbon nanotubes as carbon nanotubes and performing ultrasonic dispersion treatment under specified conditions in a solvent, the carbon nanotubes can easily take on a flat shape, and furthermore, can easily take on a flat carbon nanotube stacked structure. Become. The ultrasonic dispersion treatment under predetermined conditions is preferably an ultrasonic dispersion treatment at an oscillation frequency of 30 kHz or more, and the oscillation frequency of the ultrasonic wave is more preferably 35 kHz or more, preferably 50 kHz or less, and 45 kHz or less. It is more preferable that it is above. It is expected that if the ultrasonic dispersion treatment is performed at such an oscillation frequency, the vibrational acceleration of the solvent (eg, water molecules) will increase and the target object can be efficiently obtained. Furthermore, as for the ultrasonic dispersion treatment under predetermined conditions, the time for the ultrasonic dispersion treatment is preferably 1 hour or more, more preferably 1 hour and 30 minutes or more, preferably 30 hours or less, and more preferably 15 hours or less.
Although the specific mechanism by which this happens is unknown, the following mechanism is probably inferred.
First, the mechanism by which carbon nanotubes tend to take on a flat shape is that because carbon nanotubes are single-walled, they have greater flexibility than multi-walled carbon nanotubes, making them easier to deform when oxidized. In addition, the affinity of the inner wall surface increases so that the inner walls of carbon nanotubes adhere to each other, and when subjected to ultrasonic dispersion treatment under specified conditions in a solvent, the carbon nanotubes become easily deformed into a flat shape. It is possible that
Next, the following may be considered as a mechanism that makes it easier to form a flat carbon nanotube stacked structure. When producing the CNT material, carbon nanotubes are obtained as CNT aggregates grown with a common orientation on the catalyst base material, and at that time, while maintaining this orientation, the outer wall surfaces of the CNTs are Take the glued state. Then, while maintaining this bonded state, the carbon nanotubes are subjected to oxidation treatment and ultrasonic dispersion treatment to deform the carbon nanotubes into a flat shape, allowing the bonded carbon nanotubes to form a layered structure. Conceivable.
Another possible mechanism that makes it easier to form a flat carbon nanotube stacked structure is as follows. Carbon nanotubes that have been deformed into a flat shape are attracted to each other by van der Waals forces. At this time, the cross section of the carbon nanotube that has been deformed into a flat shape [the cross section perpendicular to the extending direction (axial direction) of the carbon nanotube] takes a dumbbell shape with both ends bulged, and the flat part and end of the flat surface of the carbon nanotube There is a groove-like structure between the bulges of the carbon nanotube and the bulge at the end of the carbon nanotube fits into the groove-like structure of another carbon nanotube when stimulated by ultrasonic dispersion treatment under predetermined conditions in a solvent. It is conceivable that the carbon nanotubes are attracted to each other and stacked, and as a result, the carbon nanotubes that have been deformed into a flat shape tend to form a stacked structure.
　また、カーボンナノチューブが扁平カーボンナノチューブ積層構造を取り、単層カーボンナノチューブの含有割合が高いことにより、電子素子の機能性領域（例、抵抗変化型記憶装置の抵抗変化層）の形成に用いた時のスイッチング電圧低下に寄与する。
　このようになる具体的機構は不明であるが、恐らくは、以下の機構が推測される。扁平カーボンナノチューブ積層構造のカーボンナノチューブと円筒状カーボンナノチューブとを比較した場合に、円筒状カーボンナノチューブはチューブ軸を中心に回転しても抵抗状態がほとんど変化せず、チューブ軸からずれた軸を中心に回転した場合にも抵抗状態の変化が比較的小さくなるのに対して、扁平カーボンナノチューブ積層構造のカーボンナノチューブはチューブ軸を中心に回転すると抵抗状態が大きく変化することから、どのような回転軸で回転しても、円筒状カーボンナノチューブに比して抵抗状態の変化が大きくなる機会が増大し、低電圧でもスイッチング応答性が高まることに寄与すると考えられる。また、単層カーボンナノチューブの導電性が多層カーボンナノチューブより高いことが、低電圧でも抵抗状態変化への応答性が高くなると考えられる。 In addition, because carbon nanotubes have a flat carbon nanotube stacked structure and contain a high proportion of single-walled carbon nanotubes, they can be used to form functional regions of electronic devices (e.g., resistance change layers of resistance change memory devices). contributes to a reduction in switching voltage.
Although the specific mechanism by which this happens is unknown, the following mechanism is probably inferred. When comparing carbon nanotubes with a flat carbon nanotube stacked structure and cylindrical carbon nanotubes, the resistance state of cylindrical carbon nanotubes hardly changes even when rotated around the tube axis; The change in resistance state is relatively small even when rotated around the tube axis, whereas the resistance state of carbon nanotubes with a flat carbon nanotube stacked structure changes greatly when rotated around the tube axis. Even when the carbon nanotube is rotated at a constant speed, there is an increased chance that the change in resistance state will be large compared to a cylindrical carbon nanotube, and this is thought to contribute to increasing the switching response even at low voltages. Furthermore, it is thought that the fact that the conductivity of single-walled carbon nanotubes is higher than that of multi-walled carbon nanotubes increases the responsiveness to changes in resistance state even at low voltages.
　カーボンナノチューブが酸化されているかどうかの評価（即ち、酸化の程度の測定）、単層カーボンナノチューブの含有割合の測定、カーボンナノチューブが扁平カーボンナノチューブ積層構造を取っているかどうかの評価は、例えば、実施例に記載の方法を用いて行うことができる。 Evaluation of whether carbon nanotubes are oxidized (i.e., measurement of the degree of oxidation), measurement of the content ratio of single-walled carbon nanotubes, and evaluation of whether carbon nanotubes have a flat carbon nanotube layered structure can be performed, for example, by This can be done using the methods described in the Examples.
＜カーボンナノチューブ＞
　本発明のカーボンナノチューブ積層構造体に用いるカーボンナノチューブとしては、単層カーボンナノチューブの含有割合が高い（即ち、カーボンナノチューブ１００本中５１本以上の）酸化カーボンナノチューブ（酸化した高単層比率カーボンナノチューブ）が用いられる。このような酸化した高単層比率カーボンナノチューブとしては、例えば、単層カーボンナノチューブの含有割合が同程度の化学修飾されていないカーボンナノチューブ（本明細書において、「材料ＣＮＴ」という。）を酸化処理したものを用いてもよい。材料ＣＮＴとしては、例えば、後述のようにＣＮＴ合成用触媒を用いて高単層比率となる条件で合成されたカーボンナノチューブを用いてもよく、公知の高単層比率となる条件の合成方法によって合成されたカーボンナノチューブを用いてもよく、市販の化学修飾されていない高単層比率カーボンナノチューブを用いてもよい。
　酸化した高単層比率カーボンナノチューブに対して、溶媒中で所定条件の超音波分散処理を行うことで、カーボンナノチューブが扁平形状を取りやすくなり、更に、扁平形状となったカーボンナノチューブが複数積層してなる積層構造体の構造（以下、「扁平カーボンナノチューブ積層構造」ということがある。）を取りやすくなる。 <Carbon nanotubes>
The carbon nanotubes used in the carbon nanotube laminated structure of the present invention are oxidized carbon nanotubes (oxidized carbon nanotubes with a high single-wall ratio) that have a high content of single-wall carbon nanotubes (i.e., 51 or more out of 100 carbon nanotubes). is used. Such oxidized high single-wall ratio carbon nanotubes include, for example, non-chemically modified carbon nanotubes (herein referred to as "material CNT") with a similar content of single-wall carbon nanotubes that are oxidized. You may also use the As the material CNT, for example, carbon nanotubes synthesized using a CNT synthesis catalyst under conditions that provide a high single-wall ratio as described later may be used, or carbon nanotubes that are synthesized under conditions that provide a high single-wall ratio using a known synthesis method. Synthesized carbon nanotubes may be used, or commercially available carbon nanotubes with a high single-wall ratio that are not chemically modified may be used.
By performing ultrasonic dispersion treatment under specified conditions on oxidized carbon nanotubes with a high single-wall ratio in a solvent, the carbon nanotubes can easily take on a flat shape, and furthermore, multiple flat carbon nanotubes can be stacked. This makes it easier to obtain a laminated structure consisting of carbon nanotubes (hereinafter sometimes referred to as "flat carbon nanotube laminated structure").
＜単層カーボンナノチューブの含有割合＞
　本発明のカーボンナノチューブ積層構造体に用いるカーボンナノチューブは、単層カーボンナノチューブの含有割合が高いほど好ましい。単層カーボンナノチューブとしての効果を奏するためには、単層カーボンナノチューブの含有割合は、カーボンナノチューブ１００本中５１本以上であることが必要であり、６０本以上が好ましく、７０本以上がより好ましく、７５本以上が更に好ましい。また、カーボンナノチューブとして、材料ＣＮＴを酸化処理および任意で超音波分散処理したものを用いる場合、単層カーボンナノチューブの含有割合は、これらの処理の前後でほぼ同一であるとみなしてよい。したがって、単層カーボンナノチューブの含有割合は、どの処理段階で測定した値を用いてもよい。単層カーボンナノチューブの含有割合が高いほど、カーボンナノチューブが扁平カーボンナノチューブ積層構造を取りやすくなり、また、電子素子の機能性領域（例、抵抗変化型記憶装置の抵抗変化層）の形成に用いた時のスイッチング電圧低下効果が増大する。単層カーボンナノチューブの含有割合は、例えば、実施例に記載の方法により測定することができる。 <Content ratio of single-walled carbon nanotubes>
The carbon nanotubes used in the carbon nanotube laminate structure of the present invention preferably have a higher content of single-walled carbon nanotubes. In order to exhibit the effect as a single-walled carbon nanotube, the content ratio of single-walled carbon nanotubes needs to be 51 or more out of 100 carbon nanotubes, preferably 60 or more, and more preferably 70 or more. , more preferably 75 or more. Furthermore, when using CNT material subjected to oxidation treatment and optionally ultrasonic dispersion treatment as carbon nanotubes, the content ratio of single-walled carbon nanotubes may be considered to be approximately the same before and after these treatments. Therefore, for the content ratio of single-walled carbon nanotubes, a value measured at any treatment stage may be used. The higher the content of single-walled carbon nanotubes, the easier it is for the carbon nanotubes to form a stacked structure of flat carbon nanotubes, and the higher the content of single-walled carbon nanotubes, the easier it is for the carbon nanotubes to form a stacked structure of flat carbon nanotubes. The switching voltage reduction effect increases when The content ratio of single-walled carbon nanotubes can be measured, for example, by the method described in Examples.
＜カーボンナノチューブの酸化の程度＞
　本発明のカーボンナノチューブ積層構造体に用いるカーボンナノチューブとしては、酸化カーボンナノチューブが用いられる。カーボンナノチューブの酸化の程度は、例えば、カーボンナノチューブの酸素原子比率を指標とすることができる。カーボンナノチューブが酸化カーボンナノチューブである場合、酸素原子比率は、例えば１０ａｔ％以上、好ましくは１３ａｔ％以上、例えば３０ａｔ％以下、好ましくは２０ａｔ％以下であってもよい。酸化カーボンナノチューブを用いることにより、カーボンナノチューブが扁平カーボンナノチューブ積層構造を取りやすくなる。カーボンナノチューブの酸素原子比率は、例えば、実施例に記載の方法により測定することができる。 <Extent of oxidation of carbon nanotubes>
Oxidized carbon nanotubes are used as the carbon nanotubes used in the carbon nanotube stacked structure of the present invention. The degree of oxidation of carbon nanotubes can be determined by, for example, the oxygen atomic ratio of carbon nanotubes. When the carbon nanotubes are oxidized carbon nanotubes, the oxygen atomic ratio may be, for example, 10 at% or more, preferably 13 at% or more, for example, 30 at% or less, preferably 20 at% or less. By using oxidized carbon nanotubes, the carbon nanotubes can easily form a flat carbon nanotube stacked structure. The oxygen atomic ratio of carbon nanotubes can be measured, for example, by the method described in Examples.
＜扁平形状＞
　本発明のカーボンナノチューブ積層構造体において、カーボンナノチューブが取る「扁平形状」とは、内壁同士が近接または接着したテープ状部分を全長に亘って有するカーボンナノチューブの形状である。以下、扁平形状の具体例および扁平形状であることの確認方法について説明する。なお、本発明において「テープ状部分を全長に亘って有する」とは、「カーボンナノチューブの延在方向（軸線方向）の長さ（全長）の６０％以上、好ましくは８０％以上、より好ましくは１００％に亘って連続的にまたは断続的にテープ状部分を有する」ことを指す。 <Flat shape>
In the carbon nanotube laminate structure of the present invention, the "flat shape" taken by the carbon nanotube is a shape of the carbon nanotube having a tape-like portion along its entire length in which the inner walls are close to each other or adhered to each other. Hereinafter, a specific example of a flat shape and a method of confirming that it is a flat shape will be described. In addition, in the present invention, "having a tape-like portion over the entire length" means "60% or more, preferably 80% or more, more preferably 80% or more of the length (total length) in the extending direction (axial direction) of the carbon nanotube." 100% continuous or intermittently tape-like parts."
　扁平カーボンナノチューブに優れた特性を発揮させる観点からは、扁平カーボンナノチューブの断面形状は、幅方向中央部にテープ状部分を有する形状であることが好ましく、延在方向（軸線方向）に直行する断面の形状が、断面長手方向の両端部近傍における、断面長手方向に直交する方向の最大寸法が、いずれも、断面長手方向の中央部近傍における、断面長手方向に直交する方向の最大寸法よりも大きい形状であることがより好ましく、ダンベル状であることが特に好ましい。
　ここで、扁平カーボンナノチューブの断面形状において、「断面長手方向の中央部近傍」とは、断面の長手中心線（断面の長手方向中心を通り、長手方向線に直交する直線）から、断面の長手方向幅の３０％以内の領域をいい、「断面長手方向の端部近傍」とは、「断面長手方向の中央部近傍」の長手方向外側の領域をいう。 From the viewpoint of making the flat carbon nanotube exhibit excellent properties, it is preferable that the cross-sectional shape of the flat carbon nanotube has a tape-shaped part at the center in the width direction, and a cross section perpendicular to the extending direction (axial direction). The maximum dimension in the direction perpendicular to the longitudinal direction of the cross section near both ends of the longitudinal direction of the cross section is both larger than the maximum dimension in the direction perpendicular to the longitudinal direction of the cross section near the center of the longitudinal direction of the cross section. The shape is more preferable, and the dumbbell shape is particularly preferable.
Here, in the cross-sectional shape of a flat carbon nanotube, "near the center in the longitudinal direction of the cross-section" refers to It refers to a region within 30% of the width in the direction, and "near the end in the longitudinal direction of the cross section" refers to a region outside in the longitudinal direction of "near the center in the longitudinal direction of the cross section."
　なお、カーボンナノチューブが扁平形状であることは、後述のように「扁平率」を求め、その扁平率の程度によって確認することができる。例えば、扁平率が４０％以下であれば、カーボンナノチューブが扁平形状であると判断することができる。「扁平率」の算出方法は後述する。 Note that the flatness of carbon nanotubes can be confirmed by determining the "oblateness" as described below and checking the degree of the oblateness. For example, if the oblateness is 40% or less, it can be determined that the carbon nanotube has a flat shape. The method for calculating the "flattening ratio" will be described later.
　また、カーボンナノチューブの形状が扁平形状であることを確認する別の手段としては、例えば、ＣＮＴとフラーレン（Ｃ６０）とを石英管に密封し、減圧下で加熱処理（フラーレン挿入処理）して得られるフラーレン挿入ＣＮＴを透過型電子顕微鏡（ＴＥＭ）で観察し、ＣＮＴ中にフラーレンが挿入されない部分（テープ状部分）が存在していることに基づいて確認することが挙げられる（例、特許第６６２３５１２号公報）。 Another way to confirm that the carbon nanotubes are flat is, for example, by sealing CNTs and fullerene (C60) in a quartz tube and heat-treating the tubes under reduced pressure (fullerene insertion treatment). An example of this method is to observe fullerene-inserted CNTs using a transmission electron microscope (TEM) and confirm the presence of portions (tape-like portions) in which fullerenes are not inserted (e.g., Patent No. 6623512). Publication No.).
＜扁平カーボンナノチューブ積層構造＞
　本発明のカーボンナノチューブ積層構造体において、カーボンナノチューブは、扁平カーボンナノチューブ積層構造を取る。「扁平カーボンナノチューブ積層構造」とは、扁平カーボンナノチューブが複数積層した積層構造体の構造であり、即ち、複数の扁平カーボンナノチューブが積層した構造（積層構造）である。このような扁平カーボンナノチューブ積層構造とは、図１の模式図に示すように、複数の扁平カーボンナノチューブが、テープ状部分（扁平面）の外面同士が近接または接着した配置を形成することによって、重なり合う構造をいう。図２の透過型電子顕微鏡（ＴＥＭ）画像には、このような扁平カーボンナノチューブ積層構造に相当する層状構造が観察される。 <Flat carbon nanotube stacked structure>
In the carbon nanotube laminate structure of the present invention, the carbon nanotubes have a flat carbon nanotube laminate structure. The "flat carbon nanotube laminate structure" is a laminate structure in which a plurality of flat carbon nanotubes are stacked, that is, a structure in which a plurality of flat carbon nanotubes are stacked (a laminate structure). As shown in the schematic diagram of FIG. 1, such a flat carbon nanotube stacked structure is a structure in which a plurality of flat carbon nanotubes form an arrangement in which the outer surfaces of tape-shaped portions (flat surfaces) are close to each other or adhere to each other. Refers to overlapping structures. In the transmission electron microscope (TEM) image of FIG. 2, a layered structure corresponding to such a stacked structure of flat carbon nanotubes is observed.
　本発明のカーボンナノチューブ積層構造体としては、電子素子の機能性領域（例、抵抗変化型記憶装置の抵抗変化層）の形成に用いた時のスイッチング電圧低下効果がより一層向上する観点から、複数のカーボンナノチューブ積層構造体が、互いに交差していることが好ましい。図３は、複数のカーボンナノチューブ積層構造体が互いに交差している状態の例を示す。 The carbon nanotube laminated structure of the present invention has a plurality of It is preferable that the carbon nanotube stacked structures intersect with each other. FIG. 3 shows an example of a state in which a plurality of carbon nanotube stacked structures intersect with each other.
　また、扁平カーボンナノチューブ積層構造中では、扁平カーボンナノチューブの大部分は、カーボンナノチューブ断面の長手方向に揃って積層していることが好ましい。「長手方向に揃って積層している」とは、扁平カーボンナノチューブ積層構造中で扁平カーボンナノチューブ同士がランダムな向きおよび配置で積層しているのではなく、扁平カーボンナノチューブ同士が同じ向きでかつチューブ断面の長手方向の端部がほぼ揃った状態で積層している状態をいう。扁平カーボンナノチューブ同士が同じ向きであるとは、扁平カーボンナノチューブ間の軸のずれの最大角度が、好ましくは１５°以下、より好ましくは１０°以下であることをいう。 Furthermore, in the flat carbon nanotube stacked structure, it is preferable that most of the flat carbon nanotubes are stacked aligned in the longitudinal direction of the carbon nanotube cross section. "Stacked in the same direction in the longitudinal direction" does not mean that the flat carbon nanotubes are stacked in a random orientation and arrangement in a laminated structure of flat carbon nanotubes, but that the flat carbon nanotubes are stacked in the same direction and This refers to a state where the ends of the cross sections in the longitudinal direction are almost aligned and stacked. The expression that the flat carbon nanotubes are oriented in the same direction means that the maximum angle of axis deviation between the flat carbon nanotubes is preferably 15° or less, more preferably 10° or less.
　カーボンナノチューブが扁平カーボンナノチューブ積層構造を取ることは、例えば、カーボンナノチューブ積層構造体を透過型電子顕微鏡（ＴＥＭ）で観察し、得られたＴＥＭ画像中に扁平カーボンナノチューブ積層構造に相当する層状構造が観察されることによって確認することができる。 Carbon nanotubes have a flat carbon nanotube layered structure, for example, when a carbon nanotube layered structure is observed with a transmission electron microscope (TEM), a layered structure corresponding to the flat carbon nanotube layered structure is observed in the obtained TEM image. This can be confirmed by observation.
　本発明のカーボンナノチューブ積層構造体における扁平カーボンナノチューブの平均積層数は、電子素子の機能性領域（例、抵抗変化型記憶装置の抵抗変化層）の形成に用いた時のスイッチング電圧低下の効果を高める観点から、２以上が好ましく、４以上がより好ましく、５以上がさらに好ましい。また、扁平カーボンナノチューブの平均積層数は、溶媒中でカーボンナノチューブ積層構造体が凝集して沈降する不具合を防止する観点から、２０以下が好ましく、１５以下がより好ましい。平均積層数は、例えば実施例に記載の方法により測定することができる。 The average number of stacked flat carbon nanotubes in the carbon nanotube stacked structure of the present invention is determined to reduce the effect of switching voltage drop when used to form a functional region of an electronic device (e.g., resistance variable layer of a resistance variable memory device). From the viewpoint of increasing the number, the number is preferably 2 or more, more preferably 4 or more, and even more preferably 5 or more. In addition, the average number of flat carbon nanotubes stacked is preferably 20 or less, more preferably 15 or less, from the viewpoint of preventing problems such as agglomeration and sedimentation of the carbon nanotube stacked structure in a solvent. The average number of laminated layers can be measured, for example, by the method described in Examples.
　本発明のカーボンナノチューブ積層構造体に用いるカーボンナノチューブは、扁平カーボンナノチューブ積層構造を取りやすくするために、酸化した状態で、溶媒中で超音波分散処理されることが好ましい。超音波分散処理の諸条件および溶媒の種類等は、例えば後述のものが挙げられる。 The carbon nanotubes used in the carbon nanotube laminate structure of the present invention are preferably subjected to an ultrasonic dispersion treatment in a solvent in an oxidized state in order to easily form a flat carbon nanotube laminate structure. The conditions for the ultrasonic dispersion treatment, the type of solvent, etc. include, for example, those described below.
＜各種サイズ＞
―平均直径―
　カーボンナノチューブの「直径（外径）」とは通常、扁平カーボンナノチューブ積層構造を取っていない状態のカーボンナノチューブの直径（最大径）をいう。扁平カーボンナノチューブ積層構造を取った状態では、カーボンナノチューブの直径を測定することが困難であるため、カーボンナノチューブの外周長を測定し、外周長を円周に変換した場合の直径を計算して「カーボンナノチューブの直径」としてもよい。あるいは、扁平カーボンナノチューブ積層構造を取る前の段階の円筒状カーボンナノチューブの直径を測定して「カーボンナノチューブの直径」としてもよい。例えば、カーボンナノチューブとして、材料ＣＮＴを酸化処理および超音波分散処理したものを用いる場合、直径は、酸化処理および超音波分散処理する前の段階の円筒状カーボンナノチューブ（材料ＣＮＴ）で測定した直径を用いてもよい。このようなカーボンナノチューブの直径または外周長は、透過型電子顕微鏡（ＴＥＭ）または走査型電子顕微鏡（ＳＥＭ）を用いて得たカーボンナノチューブの画像に基づいて計測してもよい。このような直径の求め方の例として、実施例に記載された方法を用いることができる。 <Various sizes>
-Average diameter-
The "diameter (outer diameter)" of a carbon nanotube usually refers to the diameter (maximum diameter) of a carbon nanotube without a stacked structure of flat carbon nanotubes. It is difficult to measure the diameter of a carbon nanotube when it has a stacked structure of flat carbon nanotubes, so we measure the outer circumference of the carbon nanotube and calculate the diameter when converting the outer circumference to the circumference. It may also be referred to as "the diameter of a carbon nanotube." Alternatively, the diameter of a cylindrical carbon nanotube before forming a stacked structure of flat carbon nanotubes may be measured and used as the "diameter of a carbon nanotube." For example, when using material CNT that has been subjected to oxidation treatment and ultrasonic dispersion treatment as carbon nanotubes, the diameter is the diameter measured on the cylindrical carbon nanotube (material CNT) before oxidation treatment and ultrasonic dispersion treatment. May be used. The diameter or outer circumference length of such a carbon nanotube may be measured based on an image of the carbon nanotube obtained using a transmission electron microscope (TEM) or a scanning electron microscope (SEM). As an example of how to determine such a diameter, the method described in the Examples can be used.
　「平均直径」とは、無作為に選択された有意な本数（例、５０本）のＣＮＴの直径（外径）の算術平均値をいう。平均直径の求め方の例として、実施例に記載された方法を用いることができる。 "Average diameter" refers to the arithmetic mean value of the diameters (outer diameters) of a significant number (eg, 50) of randomly selected CNTs. As an example of how to determine the average diameter, the method described in the Examples can be used.
　平均直径は、カーボンナノチューブ合成の諸条件を調整することにより制御することができる。例えば、触媒基材の鉄薄膜（触媒層）の膜厚を大きくすることで、平均直径を大きくすることができ、触媒基材の鉄薄膜（触媒層）の膜厚を小さくすることで、平均直径を小さくすることができる。 The average diameter can be controlled by adjusting the conditions for carbon nanotube synthesis. For example, by increasing the thickness of the iron thin film (catalyst layer) of the catalyst base material, the average diameter can be increased, and by decreasing the film thickness of the iron thin film (catalyst layer) of the catalyst base material, the average diameter can be increased. The diameter can be reduced.
　カーボンナノチューブが扁平形状に潰れやすくする観点から、平均直径は大きい（即ち、ＣＮＴが太い）ことが好ましい。平均直径は、３．７ｎｍ以上が好ましく、４．０ｎｍ以上がより好ましく、５．０ｎｍ以下が好ましく、４．７ｎｍ以下がより好ましい。ＣＮＴの平均直径が上記下限以上であれば、カーボンナノチューブが扁平形状に潰れやすくなる点で好ましい。ＣＮＴの平均直径が上記上限を超えると、扁平カーボンナノチューブ同士が絡み合って扁平カーボンナノチューブ積層構造を取ることが阻害される不具合が考えられる。 From the viewpoint of making the carbon nanotubes easily collapse into a flat shape, it is preferable that the average diameter is large (that is, the CNTs are thick). The average diameter is preferably 3.7 nm or more, more preferably 4.0 nm or more, preferably 5.0 nm or less, and more preferably 4.7 nm or less. It is preferable that the average diameter of the CNTs is equal to or larger than the above lower limit because the carbon nanotubes are easily crushed into a flat shape. If the average diameter of the CNTs exceeds the above upper limit, there may be a problem that the flat carbon nanotubes become entangled with each other and a stacked structure of flat carbon nanotubes is inhibited.
―扁平率―
　カーボンナノチューブの「扁平率」とは、扁平カーボンナノチューブ積層構造を取っていない状態のカーボンナノチューブの直径に対する扁平カーボンナノチューブ積層構造を取った状態のカーボンナノチューブの厚みの割合の指標となる値をいう。扁平率は、カーボンナノチューブが扁平形状を取っていることの指標となる。扁平率は、例えば、実施例に記載のように、以下の手順で求めることができる。 -Oblinity-
The "oblateness" of a carbon nanotube refers to a value that is an index of the ratio of the thickness of a carbon nanotube in a state where it has a flat carbon nanotube stacked structure to the diameter of a carbon nanotube in a state where it does not have a stacked structure of flat carbon nanotubes. The oblateness is an indicator that the carbon nanotube has a flat shape. The oblateness can be determined by the following procedure, for example, as described in Examples.
　カーボンナノチューブ積層構造体を含む分散液の一部を測定用に分取し、溶媒を除去（例、ろ取、乾燥）する。溶媒除去したカーボンナノチューブ積層構造体を透過型電子顕微鏡（ＴＥＭ）で観察し、ＴＥＭ画像を得る。得られたＴＥＭ画像から無作為に選択した有意な個数（例、５０個）のカーボンナノチューブ積層構造体について厚みおよび積層数を測定し、算術平均値を平均厚みおよび平均積層数とする。そして、以下の式により扁平率を算出する。
扁平率（％）＝［（カーボンナノチューブ積層構造体の平均厚み／カーボンナノチューブ積層構造体の平均積層数）／ＣＮＴの平均直径］×１００ A portion of the dispersion containing the carbon nanotube layered structure is separated for measurement, and the solvent is removed (eg, filtered, dried). The carbon nanotube stacked structure from which the solvent has been removed is observed with a transmission electron microscope (TEM) to obtain a TEM image. The thickness and number of laminated layers of a significant number (eg, 50) of carbon nanotube laminated structures randomly selected from the obtained TEM images are measured, and the arithmetic mean values are taken as the average thickness and the average number of laminated layers. Then, the flattening ratio is calculated using the following formula.
Oblateness (%) = [(average thickness of carbon nanotube laminate structure/average number of layers of carbon nanotube laminate structure)/average diameter of CNT] x 100
　平均直径は、カーボンナノチューブ合成の諸条件、酸化処理条件、超音波分散処理条件等を調整することにより制御することができる。 The average diameter can be controlled by adjusting the carbon nanotube synthesis conditions, oxidation treatment conditions, ultrasonic dispersion treatment conditions, etc.
　本発明の目的を達成するためには、ＣＮＴの扁平率は、１０％以上が好ましく、２０％以上がより好ましく、４０％以下が好ましい。ＣＮＴの扁平率が上記上限以下であれば、ＣＮＴが十分に扁平形状となり、カーボンナノチューブ積層構造体を電子素子の機能性領域（例、抵抗変化層）に用いた時のスイッチング電圧低下に寄与する。一方、内壁のグラファイト構造同士に層間距離が存在するため、ＣＮＴの扁平率を上記下限未満とすることは難しい。 In order to achieve the object of the present invention, the flatness of CNT is preferably 10% or more, more preferably 20% or more, and preferably 40% or less. If the flatness of the CNTs is below the above upper limit, the CNTs will have a sufficiently flat shape, contributing to a reduction in switching voltage when the carbon nanotube laminated structure is used in a functional area (e.g., variable resistance layer) of an electronic device. . On the other hand, since there is an interlayer distance between the graphite structures of the inner wall, it is difficult to make the flatness of the CNTs less than the above lower limit.
―平均長さ―
　カーボンナノチューブ積層構造体の「長さ」とは、カーボンナノチューブの延在方向（軸線方向）の寸法（チューブ長）をいう。「平均長さ」とは、無作為に選択された有意な本数（例、５０本）のカーボンナノチューブ積層構造体の長さの算術平均値をいう。カーボンナノチューブ積層構造体の平均長さは、例えば、以下の手順で求めることができる。 -Average length-
The "length" of the carbon nanotube stacked structure refers to the dimension (tube length) in the extending direction (axial direction) of the carbon nanotubes. "Average length" refers to the arithmetic mean value of the lengths of a significant number (eg, 50 carbon nanotubes) of randomly selected laminated carbon nanotubes. The average length of the carbon nanotube stacked structure can be determined, for example, by the following procedure.
　カーボンナノチューブ積層構造体を含む分散液の一部を測定用に分取し、溶媒を除去（例、ろ取、乾燥）する。溶媒除去したカーボンナノチューブ積層構造体を走査型電子顕微鏡（ＳＥＭ）で観察し、得られたＳＥＭ画像から無作為に選択された有意な本数（例、５０本）のカーボンナノチューブ積層構造体の長さを測定し、カーボンナノチューブ積層構造体の長さの算術平均値をカーボンナノチューブ積層構造体の平均長さとする。 A portion of the dispersion containing the carbon nanotube layered structure is separated for measurement, and the solvent is removed (e.g., filtered, dried). The carbon nanotube stacked structure from which the solvent has been removed is observed with a scanning electron microscope (SEM), and the lengths of a significant number (e.g., 50) of the carbon nanotube stacked structures are randomly selected from the obtained SEM image. is measured, and the arithmetic mean value of the lengths of the carbon nanotube laminate structure is determined as the average length of the carbon nanotube laminate structure.
　カーボンナノチューブ積層構造体の平均長さは、カーボンナノチューブの合成、処理等の諸条件を調整することにより制御することができる。例えば、カーボンナノチューブ合成の時間を長くすることで、カーボンナノチューブ積層構造体の平均長さを長くすることができ、カーボンナノチューブ合成の時間を短くすることで、カーボンナノチューブ積層構造体の平均長さを短くすることができる。また、カーボンナノチューブ積層構造体の平均長さは、カーボンナノチューブの酸化処理条件（例、酸化処理に用いる酸性溶液の種類、ｐＨ、混合液作製のための撹拌時間、混合液還流時間、混合液還流温度等）、超音波分散処理条件（例、超音波の発振周波数、時間、回数等）を調整することによっても制御することができる。 The average length of the carbon nanotube stacked structure can be controlled by adjusting various conditions such as carbon nanotube synthesis and processing. For example, by increasing the carbon nanotube synthesis time, the average length of the carbon nanotube layered structure can be increased, and by shortening the carbon nanotube synthesis time, the average length of the carbon nanotube layered structure can be increased. Can be shortened. In addition, the average length of the carbon nanotube layered structure is determined by the oxidation treatment conditions of the carbon nanotubes (e.g., the type of acidic solution used for oxidation treatment, the pH, the stirring time for preparing the mixed solution, the reflux time of the mixed solution, the reflux time of the mixed solution, etc.) It can also be controlled by adjusting the ultrasonic dispersion treatment conditions (eg, ultrasonic oscillation frequency, time, number of times, etc.).
　本発明の目的を達成するためには、カーボンナノチューブ積層構造体の平均長さは、２０ｎｍ以上が好ましく、５０ｎｍ以上がより好ましく、３００ｎｍ以下が好ましく、２００ｎｍ以下がより好ましい。カーボンナノチューブ積層構造体の平均長さが上記下限以上であれば、カーボンナノチューブ積層構造体の導電性などの特性を損なわない点で好ましい。カーボンナノチューブ積層構造体の平均長さが上記上限以下であれば、カーボンナノチューブ積層構造体が溶媒中で凝集して沈降する不具合を防止する点で好ましい。 In order to achieve the object of the present invention, the average length of the carbon nanotube stacked structure is preferably 20 nm or more, more preferably 50 nm or more, preferably 300 nm or less, and more preferably 200 nm or less. It is preferable that the average length of the carbon nanotube laminate structure is equal to or greater than the above-mentioned lower limit, since properties such as conductivity of the carbon nanotube laminate structure are not impaired. It is preferable that the average length of the carbon nanotube laminate structure is equal to or less than the above upper limit in order to prevent the carbon nanotube laminate structure from agglomerating and settling in the solvent.
　なお、カーボンナノチューブ積層構造体の形成に用いるカーボンナノチューブおよびカーボンナノチューブ積層構造体の各種サイズ、形状、積層状態、諸物性値等の性状は、カーボンナノチューブ（例、材料ＣＮＴ）の調製に使用する触媒基材の触媒層の状態（例えば、鉄薄膜（触媒層）の膜厚等）、カーボンナノチューブ（例、材料ＣＮＴ）の合成条件（例えば、混合ガスの組成等）、酸化処理条件、超音波分散処理条件（例、超音波の発振周波数等）を調整することにより制御することができる。 The carbon nanotubes used to form the carbon nanotube stacked structure and the properties of the carbon nanotube stacked structure such as various sizes, shapes, stacking states, and various physical properties are based on the catalyst used to prepare the carbon nanotubes (e.g., material CNT). Condition of the catalyst layer of the base material (e.g., thickness of thin iron film (catalyst layer), etc.), synthesis conditions of carbon nanotubes (e.g., material CNT) (e.g., composition of mixed gas, etc.), oxidation treatment conditions, ultrasonic dispersion It can be controlled by adjusting processing conditions (eg, oscillation frequency of ultrasonic waves, etc.).
（カーボンナノチューブ積層構造体の製造方法）
　本発明のカーボンナノチューブ積層構造体は、例えば、以下
（ｉ）高単層比率のカーボンナノチューブを酸化処理して、酸化した高単層比率カーボンナノチューブを得る工程と、
（ｉｉ）酸化した高単層比率カーボンナノチューブを溶媒中で所定条件で超音波分散処理して、高単層比率の酸化扁平カーボンナノチューブが複数積層してなるカーボンナノチューブ積層構造体を形成させる工程と
　を含む方法を用いて製造することができる。
　高単層比率とは、上述した単層カーボンナノチューブの含有割合が十分に高いことであり、カーボンナノチューブ１００本中５１本以上であることが必要である。
　また、上記工程（ｉ）に用いる高単層比率のカーボンナノチューブとしては、例えば、以下の製造方法で得られる材料ＣＮＴを用いてもよい。
　上記工程（ｉｉ）における所定条件での超音波分散処理とは、３０ｋＨｚ以上の発振周波数での超音波分散処理が好ましく、超音波の発振周波数は、３５ｋＨｚ以上であることがより好ましく、５０ｋＨｚ以下であることが好ましく、４５ｋＨｚ以下であることがより好ましい。このような発振周波数で超音波分散処理を行えば、溶媒（例、水分子）の振動加速度が増加して効率的に目的物を得ることができると予想される。また、上記工程（ｉｉ）における所定条件での超音波分散処理として、超音波分散処理の時間は、１時間以上が好ましく、１時間３０分以上がより好ましく、３０時間以下が好ましく、１５時間以下がより好ましい。
　カーボンナノチューブとして酸化した高単層比率カーボンナノチューブを用いて、溶媒中で所定条件の超音波分散処理を行うことで、カーボンナノチューブが扁平形状を取りやすくなり、更に、扁平カーボンナノチューブ積層構造を取りやすくなるので、上記の製造方法によりカーボンナノチューブ積層構造体を得ることができる。 (Method for manufacturing carbon nanotube laminate structure)
The carbon nanotube laminate structure of the present invention includes, for example, the following steps: (i) oxidizing carbon nanotubes with a high single-wall ratio to obtain oxidized carbon nanotubes with a high single-wall ratio;
(ii) A step of subjecting the oxidized carbon nanotubes with a high single-wall ratio to an ultrasonic dispersion treatment in a solvent under predetermined conditions to form a carbon nanotube laminate structure in which a plurality of oxidized flat carbon nanotubes with a high single-wall ratio are stacked. It can be manufactured using a method including.
A high single-walled carbon nanotube ratio means that the content ratio of the single-walled carbon nanotubes mentioned above is sufficiently high, and needs to be 51 or more out of 100 carbon nanotubes.
Furthermore, as the carbon nanotubes with a high single-wall ratio used in the above step (i), for example, CNT material obtained by the following manufacturing method may be used.
The ultrasonic dispersion treatment under predetermined conditions in step (ii) above is preferably an ultrasonic dispersion treatment at an oscillation frequency of 30 kHz or higher, more preferably an oscillation frequency of 35 kHz or higher, and 50 kHz or lower. The frequency is preferably 45 kHz or less, and more preferably 45 kHz or less. It is expected that if the ultrasonic dispersion treatment is performed at such an oscillation frequency, the vibrational acceleration of the solvent (eg, water molecules) will increase and the target object can be efficiently obtained. Further, as the ultrasonic dispersion treatment under the predetermined conditions in step (ii) above, the time of the ultrasonic dispersion treatment is preferably 1 hour or more, more preferably 1 hour and 30 minutes or more, preferably 30 hours or less, and 15 hours or less. is more preferable.
By using oxidized high single-wall ratio carbon nanotubes as carbon nanotubes and performing ultrasonic dispersion treatment under specified conditions in a solvent, the carbon nanotubes can easily take on a flat shape, and furthermore, can easily take on a flat carbon nanotube stacked structure. Therefore, a carbon nanotube laminate structure can be obtained by the above manufacturing method.
（材料ＣＮＴの製造方法）
　材料ＣＮＴの製造方法は、所定の方法を用いて基材上に触媒担持層および触媒層を形成してなる触媒基材と所定の混合ガスとを使用して化学気相成長法（ＣＶＤ法）により触媒基材上にカーボンナノチューブを合成することで触媒基材上に材料ＣＮＴとして、高単層比率のカーボンナノチューブを成長させることを大きな特徴の一つとする。 (Method for producing material CNT)
The manufacturing method of the material CNT is a chemical vapor deposition method (CVD method) using a catalyst base material formed by forming a catalyst support layer and a catalyst layer on the base material using a predetermined method and a predetermined mixed gas. One of the major features is that by synthesizing carbon nanotubes on a catalyst base material, carbon nanotubes with a high single-wall ratio can be grown on the catalyst base material as material CNT.
　具体的には、材料ＣＮＴを製造する方法は、
（１）アルミニウム化合物を含む塗工液Ａを基材上に塗布する工程、
（２）塗工液Ａを乾燥し、基材上にアルミニウム薄膜を形成する工程、
（３）アルミニウム薄膜の上に、鉄化合物を含む塗工液Ｂを塗布する工程、
（４）塗工液Ｂを温度５０℃以下で乾燥し、アルミニウム薄膜上に鉄薄膜を形成することで触媒基材を得る工程、および、
（５）触媒基材に対し、炭素を含む原料ガスと窒素ガスとの混合ガスを供給し、触媒基材上に材料ＣＮＴとして、高単層比率酸化扁平ＣＮＴを形成し得る高単層比率ＣＮＴを成長させる工程（成長工程）、
を少なくとも含む。なお、以下では、上記（１）と（２）の２つの工程を併せて「触媒担持層形成工程」と称し、上記（３）と（４）の２つの工程を併せて「触媒層形成工程」と称する。
　そして、この製造方法によれば、ウェットプロセスにより触媒基材を作製し、且つ、乾燥により触媒層を得る際の乾燥温度が５０℃以下であり、更に、原料ガスと窒素ガスとの混合ガスを用いてカーボンナノチューブを成長させているので、高単層比率酸化扁平ＣＮＴを形成し得る高単層比率ＣＮＴを製造することができる。 Specifically, the method for manufacturing the material CNT is as follows:
(1) A step of applying coating liquid A containing an aluminum compound onto a base material,
(2) Drying coating liquid A to form an aluminum thin film on the base material,
(3) a step of applying coating liquid B containing an iron compound on the aluminum thin film;
(4) drying coating liquid B at a temperature of 50° C. or lower to form a thin iron film on the aluminum thin film to obtain a catalyst base material, and
(5) High single-wall ratio CNTs that can form high single-wall ratio oxidized flat CNTs as material CNTs on the catalyst base material by supplying a mixed gas of carbon-containing raw material gas and nitrogen gas to the catalyst base material. The process of growing (growth process),
Contains at least In the following, the above two steps (1) and (2) will be collectively referred to as the "catalyst support layer forming step", and the above two steps (3) and (4) will be collectively referred to as the "catalyst layer forming step". ”.
According to this manufacturing method, the catalyst base material is produced by a wet process, and the drying temperature when obtaining the catalyst layer by drying is 50°C or less, and furthermore, a mixed gas of raw material gas and nitrogen gas is used. Since carbon nanotubes are grown using the method, it is possible to produce CNTs with a high single-wall ratio that can form oxidized flat CNTs with a high single-wall ratio.
［［触媒担持層形成工程］］
　材料ＣＮＴの製造方法では、まず、アルミニウム化合物を含む塗工液Ａを基材上に塗布し、該塗工液を乾燥することで、基材上にアルミニウム薄膜を形成する。このようにして基材上に形成されたアルミニウム薄膜は、その上に後述の鉄薄膜（触媒層）を担持する、触媒担持層として機能する。 [[Catalyst support layer formation process]]
In the method for producing the material CNT, first, a coating liquid A containing an aluminum compound is applied onto a base material, and the coating liquid is dried to form an aluminum thin film on the base material. The aluminum thin film thus formed on the base material functions as a catalyst supporting layer on which the iron thin film (catalyst layer) described below is supported.
－基材－
　触媒基材に用いる基材は、例えば平板状の部材であり、５００℃以上の高温でも形状を維持できるものが好ましい。具体的には、鉄、ニッケル、クロム、モリブデン、タングステン、チタン、アルミニウム、マンガン、コバルト、銅、銀、金、白金、ニオブ、タンタル、鉛、亜鉛、ガリウム、インジウム、ゲルマニウムおよびアンチモンなどの金属、並びに、これらの金属を含む合金および酸化物、或いは、シリコン、石英、ガラス、マイカ、グラファイトおよびダイヤモンドなどの非金属、並びに、セラミックなどが挙げられる。金属材料は非金属およびセラミックと比較して、低コスト且つ加工が容易であるから好ましく、特に、Ｆｅ－Ｃｒ（鉄－クロム）合金、Ｆｅ－Ｎｉ（鉄－ニッケル）合金、Ｆｅ－Ｃｒ－Ｎｉ（鉄－クロム－ニッケル）合金などは好適である。 -Base material-
The base material used as the catalyst base material is, for example, a flat member, and preferably one that can maintain its shape even at high temperatures of 500° C. or higher. Specifically, metals such as iron, nickel, chromium, molybdenum, tungsten, titanium, aluminum, manganese, cobalt, copper, silver, gold, platinum, niobium, tantalum, lead, zinc, gallium, indium, germanium and antimony; Also included are alloys and oxides containing these metals, nonmetals such as silicon, quartz, glass, mica, graphite, and diamond, and ceramics. Metal materials are preferred because they are lower in cost and easier to process than nonmetals and ceramics, and in particular, Fe-Cr (iron-chromium) alloy, Fe-Ni (iron-nickel) alloy, Fe-Cr-Ni (Iron-Chromium-Nickel) alloy is suitable.
　基材の厚さに特に制限はなく、例えば数μｍ程度の薄膜から数ｃｍ程度までのものを用いることができる。好ましくは、基材の厚さは０．０５ｍｍ以上３ｍｍ以下である。 There is no particular limit to the thickness of the base material, and for example, a thin film of about several μm to about several cm can be used. Preferably, the thickness of the base material is 0.05 mm or more and 3 mm or less.
　基材の面積は特に制限はなく、好ましくは２０ｃｍ２以上、より好ましくは３０ｃｍ２以上である。基材の形状は特に限定されないが、長方形または正方形とすることができる。 The area of the base material is not particularly limited, and is preferably 20 cm 2 or more, more preferably 30 cm 2 or more. The shape of the base material is not particularly limited, but may be rectangular or square.
－塗工液Ａ－
　塗工液Ａは、アルミニウム化合物を有機溶剤に溶解または分散させたものである。塗工液Ａに含まれるアルミニウム化合物は、アルミニウム原子を含む化合物であれば特に限定されないが、アルミニウム薄膜としてアルミナ薄膜を形成しうる金属有機化合物、金属塩が好ましい。 -Coating liquid A-
Coating liquid A is an aluminum compound dissolved or dispersed in an organic solvent. The aluminum compound contained in coating liquid A is not particularly limited as long as it contains an aluminum atom, but metal organic compounds and metal salts that can form an alumina thin film as an aluminum thin film are preferred.
　アルミナ薄膜を形成しうる金属有機化合物としては、例えば、アルミニウムトリメトキシド、アルミニウムトリエトキシド、アルミニウムトリ－ｎ－プロポキシド、アルミニウムトリ－ｉ－プロポキシド、アルミニウムトリ－ｎ－ブトキシド、アルミニウムトリ－ｓｅｃ－ブトキシド、アルミニウムトリ－ｔｅｒｔ－ブトキシド等のアルミニウムアルコキシドが挙げられる。アルミニウムを含む金属有機化合物としては、他に、トリス（アセチルアセトナト）アルミニウム（ＩＩＩ）などの錯体が挙げられる。アルミナ薄膜を形成しうる金属塩としては、例えば、硫酸アルミニウム、塩化アルミニウム、硝酸アルミニウム、臭化アルミニウム、よう化アルミニウム、乳酸アルミニウム、塩基性塩化アルミニウム、塩基性硝酸アルミニウム等が挙げられる。これらは、単独あるいは混合物として用いることができる。 Examples of metal organic compounds that can form an alumina thin film include aluminum trimethoxide, aluminum triethoxide, aluminum tri-n-propoxide, aluminum tri-i-propoxide, aluminum tri-n-butoxide, and aluminum tri-n-propoxide. Examples include aluminum alkoxides such as sec-butoxide and aluminum tri-tert-butoxide. Other metal organic compounds containing aluminum include complexes such as tris(acetylacetonato)aluminum(III). Examples of metal salts that can form an alumina thin film include aluminum sulfate, aluminum chloride, aluminum nitrate, aluminum bromide, aluminum iodide, aluminum lactate, basic aluminum chloride, and basic aluminum nitrate. These can be used alone or as a mixture.
　塗工液Ａに含まれる有機溶剤としては、アルコール、グリコール、ケトン、エーテル、エステル類、炭化水素類等の種々の有機溶剤が使用できるが、金属有機化合物および金属塩の溶解性が良いことから、アルコールまたはグリコールを用いることが好ましい。これらの有機溶剤は単独で用いてもよいし、２種類以上を混合して用いてもよい。アルコールとしては、メタノール、エタノール、イソプロピルアルコールなどが、取り扱い性、保存安定性といった点で好ましい。 Various organic solvents such as alcohols, glycols, ketones, ethers, esters, and hydrocarbons can be used as the organic solvent contained in coating liquid A, but since they have good solubility for metal organic compounds and metal salts, , alcohols or glycols are preferably used. These organic solvents may be used alone or in combination of two or more. As the alcohol, methanol, ethanol, isopropyl alcohol, etc. are preferable in terms of ease of handling and storage stability.
　塗工液Ａには、金属有機化合物および金属塩の縮合重合反応を抑制するための安定剤を添加してもよい。安定剤は、β－ジケトン類およびアルカノールアミン類からなる群より選ばれる少なくとも一つであることが好ましい。β－ジケトン類ではアセチルアセトン、アセト酢酸メチル、アセト酢酸エチル、ベンゾイルアセトン、ジベンゾイルメタン、ベンゾイルトリフルオルアセトン、フロイルアセトンおよびトリフルオルアセチルアセトンなどがあるが、特にアセチルアセトン、アセト酢酸エチルを用いることが好ましい。アルカノールアミン類ではモノエタノールアミン、ジエタノールアミン、トリエタノールアミン、Ｎ－メチルジエタノ－ルアミン、Ｎ－エチルジエタノールアミン、Ｎ，Ｎ－ジメチルアミノエタノール、ジイソプロパノールアミン、トリイソプロパノールアミンなどがあるが、第２級または第３級アルカノールアミンであることが好ましい。 A stabilizer may be added to the coating liquid A to suppress the condensation polymerization reaction of the metal organic compound and the metal salt. The stabilizer is preferably at least one selected from the group consisting of β-diketones and alkanolamines. β-diketones include acetylacetone, methyl acetoacetate, ethyl acetoacetate, benzoylacetone, dibenzoylmethane, benzoyltrifluoroacetone, furoylacetone, and trifluoroacetylacetone, and it is particularly preferable to use acetylacetone and ethyl acetoacetate. . Alkanolamines include monoethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, N,N-dimethylaminoethanol, diisopropanolamine, triisopropanolamine, etc. Preferably, it is a tertiary alkanolamine.
　塗工液Ａ中のアルミニウム化合物の量は特に限定されないが、有機溶剤１００ｍＬ当たり、好ましくは０．１ｇ以上、より好ましくは０．５ｇ以上であり、好ましくは３０ｇ以下、より好ましくは５ｇ以下である。
　また、塗工液Ａ中の安定剤の量は特に限定されないが、有機溶剤１００ｍＬ当たり、好ましくは０．０１ｇ以上、より好ましくは０．１ｇ以上であり、好ましくは２０ｇ以下、より好ましくは３ｇ以下である。 The amount of aluminum compound in coating liquid A is not particularly limited, but is preferably 0.1 g or more, more preferably 0.5 g or more, and preferably 30 g or less, more preferably 5 g or less per 100 mL of organic solvent. .
Further, the amount of stabilizer in coating liquid A is not particularly limited, but is preferably 0.01 g or more, more preferably 0.1 g or more, and preferably 20 g or less, more preferably 3 g or less per 100 mL of organic solvent. It is.
－塗布－
　上述の塗工液Ａを、基材上に塗布する。塗工液Ａを基材上に塗布する方法は、特に限定されず、スプレー、ハケ塗り等により塗布する方法、スピンコーティング、ディップコーティング等、いずれの方法を用いてもよいが、ディップコーティングが好ましい。 -Application-
The above-mentioned coating liquid A is applied onto a substrate. The method of applying coating liquid A onto the substrate is not particularly limited, and any method such as spraying, brushing, spin coating, dip coating, etc. may be used, but dip coating is preferable. .
－乾燥－
　そして、基材上の塗工液Ａを乾燥し、基材上にアルミニウム薄膜（触媒担持層）を形成する。基材上の塗工液Ａを乾燥する方法は特に限定されないが、室温での風乾、加熱（焼成処理）などが挙げられ、加熱が好ましい。加熱温度はおよそ５０℃以上４００℃以下が好ましく、３５０℃以下がより好ましい。加熱時間は５分以上６０分以下が好ましく、４０分以下がより好ましい。 -Drying-
Then, the coating liquid A on the base material is dried to form an aluminum thin film (catalyst supporting layer) on the base material. The method of drying the coating liquid A on the substrate is not particularly limited, but examples include air drying at room temperature and heating (baking treatment), with heating being preferred. The heating temperature is preferably approximately 50°C or higher and 400°C or lower, more preferably 350°C or lower. The heating time is preferably 5 minutes or more and 60 minutes or less, more preferably 40 minutes or less.
［［触媒層形成工程］］
　次に、触媒担持層形成工程で形成されたアルミニウム薄膜上に、鉄化合物を含む塗工液Ｂを塗布し、該塗工液を温度５０℃以下で乾燥させ、アルミニウム薄膜上に鉄薄膜を形成する。この工程により、アルミニウム薄膜（触媒担持層）と鉄薄膜（触媒層）とを基材上に備えた触媒基材を得ることができる。 [[Catalyst layer formation process]]
Next, coating liquid B containing an iron compound is applied onto the aluminum thin film formed in the catalyst support layer forming step, and the coating liquid is dried at a temperature of 50°C or less to form an iron thin film on the aluminum thin film. do. Through this step, it is possible to obtain a catalyst base material having an aluminum thin film (catalyst supporting layer) and an iron thin film (catalyst layer) on the base material.
－塗工液Ｂ－
　塗工液Ｂは、鉄化合物を有機溶剤に溶解または分散させたものである。塗工液Ｂに含まれる鉄化合物は、鉄原子を含む化合物であれば特に限定されないが、鉄薄膜を形成しうる金属有機化合物、金属塩が好ましい。 -Coating liquid B-
Coating liquid B is one in which an iron compound is dissolved or dispersed in an organic solvent. The iron compound contained in coating liquid B is not particularly limited as long as it contains an iron atom, but metal organic compounds and metal salts that can form an iron thin film are preferable.
　鉄薄膜を形成しうる金属有機化合物としては、例えば、鉄ペンタカルボニル、フェロセン、アセチルアセトン鉄（ＩＩ）、アセチルアセトン鉄（ＩＩＩ）、トリフルオロアセチルアセトン鉄（ＩＩ）、トリフルオロアセチルアセトン鉄（ＩＩＩ）等が挙げられる。鉄薄膜を形成しうる金属塩としては、例えば、硫酸鉄、硝酸鉄、リン酸鉄、塩化鉄、臭化鉄等の無機酸鉄、酢酸鉄、シュウ酸鉄、クエン酸鉄、乳酸鉄等の有機酸鉄等が挙げられる。これらのなかでも、有機酸鉄を用いることが好ましい。これらは、単独で或いは混合物として用いることができる。
　なお、塗工液Ｂに含まれる有機溶剤は、特に限定されず、上述の塗工液Ａの項に記載した有機溶剤と同様のものを用いることができる。また、塗工液Ｂには、上述の塗工液Ａの項に記載した安定剤が含まれていてもよい。 Examples of metal organic compounds that can form an iron thin film include iron pentacarbonyl, ferrocene, iron(II) acetylacetone, iron(III) acetylacetone, iron(II) trifluoroacetylacetone, iron(III) trifluoroacetylacetone, and the like. It will be done. Examples of metal salts that can form an iron thin film include inorganic iron acids such as iron sulfate, iron nitrate, iron phosphate, iron chloride, iron bromide, iron acetate, iron oxalate, iron citrate, iron lactate, etc. Examples include organic acid iron. Among these, it is preferable to use organic acid iron. These can be used alone or as a mixture.
The organic solvent contained in the coating liquid B is not particularly limited, and the same organic solvents as those described in the section of the coating liquid A above can be used. Moreover, the coating liquid B may contain the stabilizer described in the section of the above-mentioned coating liquid A.
　塗工液Ｂ中の鉄化合物の量は特に限定されないが、有機溶剤１００ｍＬ当たり、好ましくは０．０５ｇ以上、より好ましくは０．１ｇ以上であり、好ましくは５ｇ以下、より好ましくは１ｇ以下である。
　また、塗工液Ｂ中の安定剤の量は特に限定されないが、有機溶剤１００ｍＬ当たり、好ましくは０．０５ｇ以上、より好ましくは０．１ｇ以上であり、好ましくは５ｇ以下、より好ましくは１ｇ以下である。 The amount of iron compound in coating liquid B is not particularly limited, but is preferably 0.05 g or more, more preferably 0.1 g or more, and preferably 5 g or less, more preferably 1 g or less per 100 mL of organic solvent. .
Further, the amount of stabilizer in coating liquid B is not particularly limited, but is preferably 0.05 g or more, more preferably 0.1 g or more, and preferably 5 g or less, more preferably 1 g or less per 100 mL of organic solvent. It is.
－塗布－
　塗工液Ｂをアルミニウム薄膜上に塗布する方法は特に限定されず、上述の触媒担持層形成工程の項に記載した方法と同様のものを用いることができる。
　上述の触媒担持層形成工程における塗工液Ａの塗布と同様に、塗工液Ｂの塗布方法としてはディップコーティングを用いることが好ましい。
　なお、塗工液Ｂの塗布方法としてディップコーティングを採用する場合、塗工液Ｂへのアルミニウム薄膜付き基材の浸漬時間は、１～３０秒間が好ましい。加えて、浸漬後、該基材を塗工液Ｂから引き上げる速度は、１～５ｍｍ／秒が好ましい。引き上げ速度が５ｍｍ／秒超であると、基材への塗工液Ｂの付着が過剰となり、得られる材料ＣＮＴが多層となる虞がある。引き上げ速度が１ｍ／秒未満であると、基材への塗工液Ｂの付着が十分でなく、得られる材料ＣＮＴの直径が短くなり、扁平ＣＮＴを形成できなくなる虞がある。
　また、スピンコーディングを採用する場合、アルミニウム薄膜付き基材への塗工液Ｂの滴下量は所望の鉄薄膜の厚みに応じて適宜選択される。また、スピンコーティング時の回転速度は、１０００ｒｐｍ以上８０００ｒｐｍ以下であることが好ましい。 -Application-
The method for applying coating liquid B onto the aluminum thin film is not particularly limited, and a method similar to the method described in the above-mentioned section of the catalyst support layer forming step can be used.
As with the application of coating liquid A in the above-mentioned catalyst-supported layer forming step, it is preferable to use dip coating as the method of applying coating liquid B.
Note that when dip coating is employed as the coating method for coating liquid B, the immersion time of the aluminum thin film-coated substrate in coating liquid B is preferably 1 to 30 seconds. In addition, the speed at which the substrate is pulled up from coating liquid B after dipping is preferably 1 to 5 mm/sec. If the pulling speed exceeds 5 mm/sec, there is a possibility that the coating liquid B will adhere excessively to the base material, and the resulting material CNT will have multiple layers. If the pulling speed is less than 1 m/sec, there is a possibility that the coating liquid B will not adhere to the base material sufficiently, and the diameter of the obtained material CNT will become short, making it impossible to form flat CNTs.
Further, when employing spin coating, the amount of coating liquid B to be dropped onto the substrate with the aluminum thin film is appropriately selected depending on the desired thickness of the iron thin film. Further, the rotational speed during spin coating is preferably 1000 rpm or more and 8000 rpm or less.
－乾燥－
　そして、アルミニウム薄膜上の塗工液Ｂを乾燥し、基材上に鉄薄膜を形成する。ここで、塗工液Ｂは、５０℃以下で乾燥する必要があり、好ましくは４０℃以下、より好ましくは３０℃以下で乾燥する。乾燥温度が５０℃超であると、続く成長工程において、高単層比率酸化扁平ＣＮＴを形成し得る高単層比率ＣＮＴを合成することができない。なお、乾燥温度の下限は特に限定されないが、通常１０℃以上である。乾燥方法としては、通常、風乾が好適である。 -Drying-
Then, the coating liquid B on the aluminum thin film is dried to form an iron thin film on the base material. Here, the coating liquid B needs to be dried at 50°C or lower, preferably 40°C or lower, more preferably 30°C or lower. If the drying temperature exceeds 50° C., high single-wall ratio CNTs that can form high single-wall ratio oxidized flat CNTs cannot be synthesized in the subsequent growth step. Note that the lower limit of the drying temperature is not particularly limited, but is usually 10° C. or higher. As a drying method, air drying is usually suitable.
　高単層比率酸化扁平ＣＮＴを形成し得る高単層比率ＣＮＴを効率的に合成する観点から、鉄薄膜（触媒層）の膜厚は、１．２ｎｍ以上が好ましく、１．５ｎｍ以上がより好ましく、３．８ｎｍ以下が好ましく、３．５ｎｍ以下がより好ましい。鉄薄膜の膜厚が上記下限未満になると、得られるＣＮＴの直径が短くなり、扁平ＣＮＴを形成できなくなると考えられる。また、鉄薄膜の膜厚が上記下限超になると、得られるＣＮＴの多層比率が上昇し、高単層比率ＣＮＴを効率的に合成できなくなると考えられる。鉄薄膜（触媒層）の膜厚は、例えば、実施例に記載の方法で求めることができる。 From the viewpoint of efficiently synthesizing high single-wall ratio CNTs that can form high single-wall ratio oxidized flat CNTs, the thickness of the iron thin film (catalyst layer) is preferably 1.2 nm or more, more preferably 1.5 nm or more. , 3.8 nm or less is preferable, and 3.5 nm or less is more preferable. When the thickness of the iron thin film is less than the above lower limit, the diameter of the obtained CNTs becomes short, and it is considered that flat CNTs cannot be formed. Moreover, when the thickness of the iron thin film exceeds the above lower limit, the multilayer ratio of the obtained CNT increases, and it is considered that CNTs with a high single layer ratio cannot be efficiently synthesized. The thickness of the iron thin film (catalyst layer) can be determined, for example, by the method described in Examples.
［［フォーメーション工程］］
　材料ＣＮＴの製造方法においては、成長工程の前にフォーメーション工程を行なうことが好ましい。フォーメーション工程とは、触媒の周囲環境を還元ガス（還元性を有するガス）環境とすると共に、触媒および還元ガスの少なくとも一方を加熱する工程である。この工程により、触媒の還元、高単層比率酸化扁平ＣＮＴを形成し得る高単層比率ＣＮＴの成長に適した状態としての触媒の微粒子化促進、触媒の活性向上の少なくとも一つの効果が現れる。例えば、触媒基材が、アルミナ薄膜と鉄薄膜からなるアルミナ－鉄薄膜を備える場合、鉄触媒は還元されて微粒子化し、アルミナ薄膜（触媒担持層）上にナノメートルサイズの鉄微粒子が多数形成される。これにより鉄薄膜（触媒層）は高単層比率酸化扁平ＣＮＴを形成し得る高単層比率ＣＮＴの製造に好適な状態となる。この工程を省略しても高単層比率酸化扁平ＣＮＴを形成し得る高単層比率ＣＮＴを製造することは可能であるが、この工程を行うことで高単層比率酸化扁平ＣＮＴを形成し得る高単層比率ＣＮＴの製造量および品質を飛躍的に向上させることができる。 [[Formation process]]
In the method for producing material CNT, it is preferable to perform a formation step before the growth step. The formation step is a step in which the environment around the catalyst is made into a reducing gas (reducing gas) environment, and at least one of the catalyst and the reducing gas is heated. This step produces at least one of the following effects: reduction of the catalyst, promotion of fine particle formation of the catalyst in a state suitable for growth of high single-wall ratio CNTs capable of forming high single-wall ratio oxidized flat CNTs, and improvement of catalyst activity. For example, when the catalyst base material includes an alumina-iron thin film consisting of an alumina thin film and an iron thin film, the iron catalyst is reduced and becomes fine particles, and many nanometer-sized iron fine particles are formed on the alumina thin film (catalyst support layer). Ru. As a result, the iron thin film (catalyst layer) becomes in a state suitable for producing high single-wall ratio CNTs that can form high single-wall ratio oxidized flat CNTs. Even if this step is omitted, it is possible to produce high single-wall ratio CNTs that can form high single-wall ratio oxidized flat CNTs, but by performing this step, it is possible to form high single-wall ratio oxidized flat CNTs. The production amount and quality of high single-wall ratio CNTs can be dramatically improved.
－還元ガス－
　フォーメーション工程に用いる還元ガスとしては、例えば水素ガス、アンモニア、水蒸気およびそれらの混合ガスを用いることができる。また、還元ガスは、水素ガスをヘリウムガス、アルゴンガス、窒素ガスなどの不活性ガスと混合した混合ガスでもよい。還元ガスは、フォーメーション工程のみで用いてもよく、適宜成長工程に用いてもよい。 -Reducing gas-
As the reducing gas used in the formation step, hydrogen gas, ammonia, water vapor, and a mixed gas thereof can be used, for example. Further, the reducing gas may be a mixed gas in which hydrogen gas is mixed with an inert gas such as helium gas, argon gas, or nitrogen gas. The reducing gas may be used only in the formation process, or may be used in the growth process as appropriate.
　フォーメーション工程における触媒および／または還元ガスの温度は、好ましくは４００℃以上１１００℃以下である。またフォーメーション工程の時間は、３分以上２０分以下が好ましく、３分以上１０分以下がより好ましい。これにより、フォーメーション工程中に鉄薄膜（触媒層）の焼成が進行して膜厚が減少するのを抑えることができる。 The temperature of the catalyst and/or reducing gas in the formation step is preferably 400°C or higher and 1100°C or lower. Further, the time for the formation step is preferably 3 minutes or more and 20 minutes or less, more preferably 3 minutes or more and 10 minutes or less. Thereby, it is possible to suppress the progress of firing of the iron thin film (catalyst layer) during the formation process and the reduction in film thickness.
［［成長工程］］
　次に、触媒担持層形成工程および触媒層形成工程を経て得られた触媒基材に、炭素を含む原料ガスと窒素ガスとの混合ガスを供給し、触媒基材上に高単層比率酸化扁平ＣＮＴを形成し得る高単層比率ＣＮＴを成長させる。なお、カーボンナノチューブは、通常、触媒基材上に所定の方向に配列（配向）した状態で成長する。
　そして、成長工程においては、通常、触媒層および混合ガスの少なくとも一方を加熱するが、均一な密度でカーボンナノチューブを成長させる観点からは、少なくとも混合ガスを加熱することが好ましい。加熱の温度は、４００℃～１１００℃が好ましい。成長工程は、触媒基材を収容する成長炉内に、原料ガスおよび窒素ガスと、任意に、窒素ガス以外の不活性ガス、還元ガスおよび触媒賦活物質よりなる群から選択される少なくとも一種とを導入して行う。 [[Growth process]]
Next, a mixed gas of carbon-containing raw material gas and nitrogen gas is supplied to the catalyst base material obtained through the catalyst support layer forming process and the catalyst layer forming process, and a high monolayer ratio oxidized flat film is formed on the catalyst base material. Grow high monolayer ratio CNTs that can form CNTs. Note that carbon nanotubes usually grow on a catalyst base material while being arranged (orientated) in a predetermined direction.
In the growth step, at least one of the catalyst layer and the mixed gas is usually heated, but from the viewpoint of growing carbon nanotubes with uniform density, it is preferable to heat at least the mixed gas. The heating temperature is preferably 400°C to 1100°C. In the growth step, raw material gas and nitrogen gas, and optionally at least one selected from the group consisting of an inert gas other than nitrogen gas, a reducing gas, and a catalyst activating material, are placed in a growth furnace that accommodates the catalyst base material. Implement and do it.
　なお、高単層比率酸化扁平ＣＮＴを形成し得る高単層比率ＣＮＴの製造効率を高める観点からは、混合ガスをガスシャワーによって触媒基材上の触媒に供給するのが好ましい。 Note that from the viewpoint of increasing the production efficiency of high single-wall ratio CNTs that can form high single-wall ratio oxidized flat CNTs, it is preferable to supply the mixed gas to the catalyst on the catalyst base material by a gas shower.
－原料ガス－
　原料ガスとしては、カーボンナノチューブが成長する温度において炭素源を含むガス状物質が用いられる。なかでもメタン、エタン、エチレン、プロパン、ブタン、ペンタン、ヘキサン、ヘプタン、プロピレンおよびアセチレンなどの炭化水素が好適である。この他にも、メタノール、エタノールなどの低級アルコール、アセトン、一酸化炭素などの低炭素数の含酸素化合物でもよい。これらの混合物も使用可能である。 -Raw material gas-
As the source gas, a gaseous substance containing a carbon source at a temperature at which carbon nanotubes grow is used. Among them, hydrocarbons such as methane, ethane, ethylene, propane, butane, pentane, hexane, heptane, propylene and acetylene are preferred. In addition, lower alcohols such as methanol and ethanol, and oxygen-containing compounds with a low carbon number such as acetone and carbon monoxide may be used. Mixtures of these can also be used.
－窒素ガス－
　原料ガスと混合する窒素ガスの量は、成長工程において触媒基材に供給される全ガス量に対し、３０体積％以上であることが好ましく、５０体積％以上であることがより好ましい。窒素ガスの量を３０体積％以上とすれば、高単層比率酸化扁平ＣＮＴを形成し得る高単層比率ＣＮＴを合成することができるからである。なお、窒素ガスの量の上限は、通常、９５体積％である。 -Nitrogen gas-
The amount of nitrogen gas mixed with the raw material gas is preferably 30% by volume or more, more preferably 50% by volume or more, based on the total amount of gas supplied to the catalyst base material in the growth step. This is because if the amount of nitrogen gas is 30% by volume or more, it is possible to synthesize CNTs with a high single-wall ratio that can form oxidized flat CNTs with a high single-wall ratio. Note that the upper limit of the amount of nitrogen gas is usually 95% by volume.
－不活性ガス－
　なお、原料ガスは窒素以外の不活性ガスで希釈されてもよい。不活性ガスとしては、カーボンナノチューブが成長する温度で不活性であり、且つ、成長するカーボンナノチューブと反応しないガスであればよく、触媒の活性を低下させないものが好ましい。例えば、ヘリウム、アルゴン、ネオンおよびクリプトンなどの希ガス；水素；並びにこれらの混合ガスを例示できる。 -Inert gas-
Note that the source gas may be diluted with an inert gas other than nitrogen. The inert gas may be any gas that is inert at the temperature at which carbon nanotubes grow and does not react with the growing carbon nanotubes, and is preferably a gas that does not reduce the activity of the catalyst. Examples include rare gases such as helium, argon, neon, and krypton; hydrogen; and mixed gases thereof.
－触媒賦活物質－
　成長工程では、触媒賦活物質を添加してもよい。触媒賦活物質の添加によって、カーボンナノチューブの生産効率や純度をより一層改善することができる。ここで用いる触媒賦活物質は、一般には酸素を含む物質であり、カーボンナノチューブが成長する温度でカーボンナノチューブに多大なダメージを与えない物質であることが好ましい。例えば、水、酸素、オゾン、酸性ガス、酸化窒素、一酸化炭素および二酸化炭素などの低炭素数の含酸素化合物；エタノール、メタノールなどのアルコール類；テトラヒドロフランなどのエーテル類；アセトンなどのケトン類；アルデヒド類；エステル類；並びにこれらの混合物が有効である。この中でも、水、酸素、二酸化炭素、一酸化炭素、およびエーテル類が好ましく、特に水が好適である。 -Catalyst activation material-
In the growth step, a catalyst activating material may be added. By adding a catalyst activator, the production efficiency and purity of carbon nanotubes can be further improved. The catalyst activation material used here is generally a material containing oxygen, and is preferably a material that does not cause significant damage to carbon nanotubes at the temperature at which carbon nanotubes grow. For example, oxygen-containing compounds with a low carbon number such as water, oxygen, ozone, acid gases, nitrogen oxide, carbon monoxide and carbon dioxide; alcohols such as ethanol and methanol; ethers such as tetrahydrofuran; ketones such as acetone; Aldehydes; esters; and mixtures thereof are useful. Among these, water, oxygen, carbon dioxide, carbon monoxide, and ethers are preferred, and water is particularly preferred.
　触媒賦活物質の体積濃度は、特に限定されないが、微量が好ましく、例えば水の場合、炉内への導入ガスにおいて、通常、１０～１００００ｐｐｍ、好ましくは５０～１０００ｐｐｍとする。 The volume concentration of the catalyst activating material is not particularly limited, but is preferably in a small amount. For example, in the case of water, it is usually 10 to 10,000 ppm, preferably 50 to 1,000 ppm in the gas introduced into the furnace.
－その他の条件－
　成長工程における反応炉内の圧力、処理時間は、他の条件を考慮して適宜設定すればよいが、例えば、圧力は１×１０２～１×１０７Ｐａ、処理時間は１～６０分程度とすることができる。 -Other conditions-
The pressure inside the reactor and the treatment time in the growth step may be set appropriately taking into account other conditions, but for example, the pressure is 1×10 2 to 1×10 7 Pa, and the treatment time is about 1 to 60 minutes. It can be done.
［［冷却工程］］
　材料ＣＮＴの製造方法は、成長工程後に冷却工程を備えることが好ましい。冷却工程とは、成長工程後にカーボンナノチューブおよび触媒基材を冷却ガス下で冷却する工程である。成長工程後のカーボンナノチューブおよび触媒基材は高温状態にあるため、酸素存在環境下に置かれると酸化してしまうおそれがある。それを防ぐために冷却ガス環境下でカーボンナノチューブおよび触媒基材を例えば４００℃以下、さらに好ましくは２００℃以下に冷却する。冷却ガスとしては不活性ガスが好ましく、特に安全性、コストなどの点から窒素であることが好ましい。 [[Cooling process]]
It is preferable that the method for manufacturing the material CNT includes a cooling step after the growth step. The cooling step is a step of cooling the carbon nanotubes and the catalyst substrate under a cooling gas after the growth step. Since the carbon nanotubes and catalyst base material after the growth process are in a high temperature state, there is a risk that they will be oxidized if placed in an oxygen-existing environment. In order to prevent this, the carbon nanotubes and the catalyst base material are cooled to, for example, 400° C. or lower, more preferably 200° C. or lower in a cooling gas environment. As the cooling gas, an inert gas is preferable, and nitrogen is particularly preferable from the viewpoint of safety and cost.
［［剥離工程］］
　また、材料ＣＮＴの製造方法は、触媒基材上に形成された材料ＣＮＴ集合物を、触媒基材から剥離する工程（剥離工程）を備えることが好ましい。材料ＣＮＴ集合物を触媒基材から剥離する方法としては、物理的、化学的あるいは機械的に触媒基材上から剥離する方法があり、たとえば電場、磁場、遠心力、表面張力を用いて剥離する方法；機械的に直接、基材より剥ぎ取る方法；圧力、熱を用いて基材より剥離する方法などが使用可能である。簡単な剥離法としては、ピンセットで直接つまんで触媒基材から剥離させる方法がある。より好適には、カッターブレードなどの薄い刃物を使用して触媒基材より切り離すこともできる。またさらには、真空ポンプ、掃除機を用い、触媒基材上より吸引し、剥ぎ取ることも可能である。なお、材料ＣＮＴ集合物の剥離後、触媒は基材上に残存するので、それを利用して材料ＣＮＴ集合物を新たに成長させることも可能である。 [[Peeling process]]
Further, the method for producing material CNT preferably includes a step of peeling off the material CNT aggregate formed on the catalyst base material from the catalyst base material (peeling step). Methods for exfoliating the material CNT aggregate from the catalyst substrate include physical, chemical, or mechanical exfoliation methods, such as exfoliation using an electric field, magnetic field, centrifugal force, or surface tension. Methods: A method of mechanically directly peeling off from the base material; a method of peeling off from the base material using pressure or heat, etc. can be used. A simple method for peeling is to directly pinch the catalyst with tweezers and peel it off from the catalyst base material. More preferably, it can be separated from the catalyst substrate using a thin blade such as a cutter blade. Furthermore, it is also possible to use a vacuum pump or a vacuum cleaner to suction from above the catalyst base material and strip it off. In addition, since the catalyst remains on the base material after the material CNT aggregate is peeled off, it is also possible to use it to grow a new material CNT aggregate.
［［製造装置］］
　上述したカーボンナノチューブ集合物の製造方法に用いる製造装置としては、触媒基材を有する成長炉（反応チャンバ）を備え、ＣＶＤ法によりＣＮＴを成長させることができるものであれば、特に限定されず、例えば、図５に示すような回分式の製造装置や、図６に示すような連続式の製造装置を用いることができる。 [[Manufacturing equipment]]
The manufacturing apparatus used in the method for manufacturing carbon nanotube aggregates described above is not particularly limited as long as it is equipped with a growth furnace (reaction chamber) having a catalyst base material and can grow CNTs by CVD method. For example, a batch type manufacturing apparatus as shown in FIG. 5 or a continuous type manufacturing apparatus as shown in FIG. 6 can be used.
－材料ＣＮＴの製造装置の一例－
　ここで、図５に示す製造装置１０は、成長炉１３、加熱器１４、ガス導入口１５、および、ガス排出口１６を備えている。そして、製造装置１０では、材料ＣＮＴを成長させる触媒基材１２を成長炉１３内に搬入した後、ガス導入口１５から必要なガスの供給等を行ないつつ、一つの炉（成長炉１３）内でフォーメーション工程および成長工程が実施される。 -Example of manufacturing equipment for material CNT-
Here, the manufacturing apparatus 10 shown in FIG. 5 includes a growth furnace 13, a heater 14, a gas inlet 15, and a gas outlet 16. In the manufacturing apparatus 10, after carrying the catalyst base material 12 for growing the material CNT into the growth furnace 13, the necessary gas is supplied from the gas inlet 15, and the inside of one furnace (growth furnace 13) is A formation process and a growth process are performed.
－材料ＣＮＴの製造装置の他の例－
　また、図６に示す製造装置１００は、入口パージ部１、フォーメーションユニット２、ガス混入防止手段１０１～１０３、成長ユニット３、冷却ユニット４、出口パージ部５、搬送ユニット６、および、接続部７～９を備えている。そして、製造装置１００では、材料ＣＮＴ集合物を成長させる触媒基材２０を搬送ユニット６で搬送しつつ、フォーメーションユニット２を通過する触媒基材２０に対してフォーメーション工程を実施し、成長ユニット３を通過する触媒基材２０に対して成長工程を実施し、冷却ユニット４を通過する触媒基材２０に対して冷却工程を実施する。 -Other examples of manufacturing equipment for material CNT-
Further, the manufacturing apparatus 100 shown in FIG. It has ~9. Then, in the manufacturing apparatus 100, while the catalyst base material 20 on which the material CNT aggregate is grown is transported by the transport unit 6, a formation process is performed on the catalyst base material 20 passing through the formation unit 2, and the growth unit 3 is A growth process is performed on the catalyst base material 20 passing through, and a cooling process is performed on the catalyst base material 20 passing through the cooling unit 4.
　ここで、製造装置１００において、入口パージ部１は、パージガスを上下からシャワー状に噴射するガスカーテン構造を有し、入口からフォーメーションユニット２内に外部の空気が混入することを防止している。なお、パージガスとしては不活性ガスを用いることができる。そして、安全性、コスト、および、パージ性等の点からは、パージガスは窒素であることが好ましい。 Here, in the manufacturing apparatus 100, the inlet purge section 1 has a gas curtain structure that injects purge gas from above and below in a shower shape, and prevents external air from entering the formation unit 2 from the inlet. Note that an inert gas can be used as the purge gas. In terms of safety, cost, purgeability, etc., the purge gas is preferably nitrogen.
　また、フォーメーションユニット２は、還元ガスを保持するためのフォーメーション炉２ａと、還元ガスをフォーメーション炉２ａ内に噴射するための還元ガス噴射部２ｂと、触媒および還元ガスの少なくとも一方を加熱するためのヒーター２ｃと、フォーメーション炉２ａ内のガスを排気するための排気フード２ｄとにより構成されている。 The formation unit 2 also includes a formation furnace 2a for holding reducing gas, a reducing gas injection section 2b for injecting the reducing gas into the formation furnace 2a, and a formation furnace 2b for heating at least one of the catalyst and the reducing gas. It is composed of a heater 2c and an exhaust hood 2d for exhausting gas inside the formation furnace 2a.
　更に、成長ユニット３は、成長工程を実現するための装置一式であり、触媒基材２０の周囲の環境を混合ガス環境に保持する炉である成長炉３ａと、混合ガスを触媒基材２０上に噴射するための混合ガス噴射部２００と、触媒および混合ガスの少なくとも一方を加熱するためのヒーター３ｂと、成長炉３ａ内のガスを排気するための排気フード３ｃとを含んでいる。また、成長ユニット３は、触媒賦活物質を供給するための触媒賦活物質噴射部（図示せず）を有していてもよい。なお、混合ガス噴射部２００は、触媒賦活物質噴射部を兼ねていてもよい。
　ここで、成長ユニット３では、混合ガス噴射部２００から噴射される全ガス流量と、排気フード３ｃから排気される全ガス流量は、ほぼ同量または同量であることが好ましい。このようにすることで、混合ガスが成長炉３ａ外へ流出すること、および、成長炉３ａ外のガスが成長炉３ａ内に流入することを防止できる。 Furthermore, the growth unit 3 is a set of devices for realizing the growth process, and includes a growth furnace 3a that is a furnace that maintains the environment around the catalyst base material 20 in a mixed gas environment, and a growth furnace 3a that is a furnace that maintains the environment around the catalyst base material 20 in a mixed gas environment. The growth furnace 3a includes a mixed gas injection unit 200 for injecting the gas into the growth furnace 3a, a heater 3b for heating at least one of the catalyst and the mixed gas, and an exhaust hood 3c for exhausting the gas in the growth furnace 3a. Furthermore, the growth unit 3 may include a catalyst activation material injection section (not shown) for supplying the catalyst activation material. Note that the mixed gas injection section 200 may also serve as a catalyst activation material injection section.
Here, in the growth unit 3, it is preferable that the total gas flow rate injected from the mixed gas injection section 200 and the total gas flow rate exhausted from the exhaust hood 3c are approximately the same amount or the same amount. By doing so, it is possible to prevent the mixed gas from flowing out of the growth furnace 3a and to prevent the gas outside the growth furnace 3a from flowing into the growth furnace 3a.
　搬送ユニット６は、複数の触媒基材２０を製造装置１００内に所定の間隔を空けて断続的に搬入するための装置一式であり、メッシュベルト６ａとベルト駆動部６ｂとを備えている。触媒基材２０は、搬送ユニット６によって、フォーメーションユニット２、成長ユニット３、および、冷却ユニット４の順に搬送されるようになっている。 The transport unit 6 is a set of devices for intermittently transporting a plurality of catalyst base materials 20 into the manufacturing apparatus 100 at predetermined intervals, and includes a mesh belt 6a and a belt drive section 6b. The catalyst base material 20 is transported by the transport unit 6 to the formation unit 2 , the growth unit 3 , and the cooling unit 4 in this order.
　接続部７～９は、各ユニットの炉内空間を空間的に接続し、触媒基材２０がユニットからユニットへ搬送されるときに、触媒基材２０が外気に曝されることを防ぐ。接続部７～９としては、例えば、触媒基材２０の周囲環境と外気とを遮断し、触媒基材２０をユニットからユニットへ通過させることができる炉またはチャンバなどが挙げられる。 The connecting parts 7 to 9 spatially connect the furnace interior spaces of each unit and prevent the catalyst base material 20 from being exposed to the outside air when the catalyst base material 20 is transported from unit to unit. Examples of the connecting portions 7 to 9 include a furnace or a chamber that isolates the environment surrounding the catalyst base material 20 from outside air and allows the catalyst base material 20 to pass from unit to unit.
　また、接続部７～９には、ガス混入防止手段１０１～１０３が設けられている。そして、ガス混入防止手段１０１～１０３は、各ユニットの炉内空間に存在するガスが、相互に混入することを防ぐ。そして、ガス混入防止手段１０１～１０３は、各炉における触媒基材２０の入口および出口の開口面に沿ってシールガスを噴出するシールガス噴射部１０１ｂ～１０３ｂと、主に噴射されたシールガス（およびその他近傍のガス）を各炉内に入らないように吸引して装置外に排気する排気部１０１ａ～１０３ａとを、それぞれ少なくとも１つ以上備えている。
　なお、シールガスは、不活性ガスであることが好ましく、特に安全性、コストなどの点から窒素であることがより好ましい。また、シールガス噴射部１０１ｂ～１０３ｂから噴射される全ガス流量と排気部１０１ａ～１０３ａから排気される全ガス流量とはほぼ同量であることが好ましい。これによって、ガス混入防止手段１０１～１０３を挟んだ両側の空間からのガスが相互に混入することを防止するとともに、シールガスが両側の空間に流出することも防止することが可能になる。 Further, the connecting portions 7 to 9 are provided with gas mixture prevention means 101 to 103. The gas mixing prevention means 101 to 103 prevent gases existing in the furnace spaces of each unit from mixing with each other. The gas mixture prevention means 101 to 103 include seal gas injection units 101b to 103b that eject seal gas along the opening surfaces of the inlet and outlet of the catalyst base material 20 in each furnace, and the injected seal gas ( At least one exhaust section 101a to 103a is provided for sucking in (and other nearby gases) so that they do not enter the respective furnaces and exhausting them to the outside of the apparatus.
Note that the seal gas is preferably an inert gas, and more preferably nitrogen from the viewpoint of safety and cost. Further, it is preferable that the total gas flow rate injected from the seal gas injection parts 101b to 103b and the total gas flow rate exhausted from the exhaust parts 101a to 103a are approximately the same amount. This makes it possible to prevent the gases from the spaces on both sides of the gas mixing prevention means 101 to 103 from mixing with each other, and also to prevent the seal gas from flowing out into the spaces on both sides.
　冷却ユニット４は、成長工程後の材料ＣＮＴおよび触媒基材２０を冷却する機能を有し、不活性ガスを保持するための冷却炉４ａ、冷却炉４ａ内空間に不活性ガスを噴射する冷却ガス噴射部４ｂ、および、冷却炉４ａ内空間を囲むように配置した水冷冷却管４ｃにより構成されている。 The cooling unit 4 has a function of cooling the material CNT and the catalyst base material 20 after the growth process, and includes a cooling furnace 4a for holding an inert gas, and a cooling gas for injecting the inert gas into the space inside the cooling furnace 4a. It is composed of an injection part 4b and a water-cooled cooling pipe 4c arranged so as to surround the interior space of the cooling furnace 4a.
　出口パージ部５は、パージガスを上下からシャワー状に噴射することで、出口から冷却炉４ａ内に外部の空気が混入することを防止している。なお、パージガスとしては不活性ガスを用いることができる。そして、安全性、コスト、および、パージ性等の点からは、パージガスは窒素であることが好ましい。 The outlet purge section 5 prevents outside air from entering the cooling furnace 4a from the outlet by injecting purge gas from above and below in a shower pattern. Note that an inert gas can be used as the purge gas. In terms of safety, cost, purgeability, etc., the purge gas is preferably nitrogen.
［酸化処理］
　酸化処理とは、例えば、ｐＨ２以下の酸性溶液中に材料ＣＮＴを添加して混合液を得て、材料ＣＮＴを酸化処理することを意味する。より具体的には、酸化処理において、混合液を所定の温度条件下で還流させることにより、混合液中の材料ＣＮＴを酸化処理することが好ましい。酸性溶液としては、例えば、硝酸、塩酸、硫酸等が挙げられる。また、混合液を得る際の混合方法としては、任意の方法による撹拌操作を行い得る。また、混合液を得る際の撹拌時間は、０．１時間以上１０時間以下とすることが好ましい。さらに、混合液を還流させる際の温度条件は、１００℃以上１５０℃以下とすることが好ましく、還流時間は３時間以上２０時間以下とすることが好ましい。
　なお、分散処理を行う場合、酸性溶液の溶媒は、分散処理に用いる溶媒と同じであってもよく、中でも、水が好ましい。 [Oxidation treatment]
The oxidation treatment means, for example, adding the material CNT to an acidic solution with a pH of 2 or less to obtain a mixed solution, and oxidizing the material CNT. More specifically, in the oxidation treatment, it is preferable to oxidize the material CNT in the mixture by refluxing the mixture under predetermined temperature conditions. Examples of acidic solutions include nitric acid, hydrochloric acid, and sulfuric acid. Moreover, as a mixing method when obtaining a liquid mixture, stirring operation by any method can be performed. Further, the stirring time when obtaining the mixed liquid is preferably 0.1 hour or more and 10 hours or less. Furthermore, the temperature conditions when refluxing the mixed liquid are preferably 100°C or more and 150°C or less, and the reflux time is preferably 3 hours or more and 20 hours or less.
In addition, when performing a dispersion process, the solvent of the acidic solution may be the same as the solvent used for the dispersion process, and water is especially preferable.
［超音波分散処理］
　超音波分散処理としては、所望の効果が得られる限り特に限定されることなく、既知の超音波分散処理方法を用いることができる。
　なお、かかる超音波分散処理に際して、酸化ＣＮＴを含む溶液のｐＨを中性（ｐＨ６～ｐＨ８程度）に調節するために、任意の中和剤を添加しても良い。かかる中和剤としては、特に限定されることなく、ｐＨ９以上ｐＨ１４以下のアルカリ性溶液、より具体的には、水酸化ナトリウム水溶液やアンモニア水溶液等が挙げられる。また、超音波分散処理に際して、必要に応じて、酸化ＣＮＴを含む溶液に対して溶媒を添加して希釈しても良い。かかる溶媒は、上記酸化処理で用いる溶媒と、超音波分散処理で添加する溶媒とで同一であっても異なっていても良いが、同じ溶媒であることが好ましい。溶媒としては、例えば、後述のものが挙げられる。
　超音波分散処理において、超音波の発振周波数は、３０ｋＨｚ以上であることが好ましく、３５ｋＨｚ以上であることがより好ましく、５０ｋＨｚ以下であることが好ましく、４５ｋＨｚ以下であることがより好ましい。このような発振周波数で超音波分散処理を行えば、溶媒（例、水分子）の振動加速度が増加して効率的に目的物を得ることができると予想される。
　超音波分散処理の時間は、１時間以上が好ましく、１時間３０分以上がより好ましく、３０時間以下が好ましく、１５時間以下がより好ましい。 [Ultrasonic dispersion treatment]
The ultrasonic dispersion treatment is not particularly limited as long as the desired effect can be obtained, and any known ultrasonic dispersion treatment method can be used.
Note that during such ultrasonic dispersion treatment, an arbitrary neutralizing agent may be added in order to adjust the pH of the solution containing oxidized CNTs to neutrality (about pH 6 to pH 8). Such a neutralizing agent is not particularly limited, and includes an alkaline solution having a pH of 9 or more and 14 or less, more specifically, an aqueous sodium hydroxide solution, an aqueous ammonia solution, and the like. Furthermore, during the ultrasonic dispersion treatment, a solvent may be added to the solution containing oxidized CNTs to dilute the solution, if necessary. Such a solvent may be the same or different between the solvent used in the oxidation treatment and the solvent added in the ultrasonic dispersion treatment, but preferably the same solvent. Examples of the solvent include those described below.
In the ultrasonic dispersion treatment, the oscillation frequency of the ultrasonic wave is preferably 30 kHz or more, more preferably 35 kHz or more, preferably 50 kHz or less, and more preferably 45 kHz or less. It is expected that if the ultrasonic dispersion treatment is performed at such an oscillation frequency, the vibrational acceleration of the solvent (eg, water molecules) will increase and the target object can be efficiently obtained.
The time for the ultrasonic dispersion treatment is preferably 1 hour or more, more preferably 1 hour and 30 minutes or more, preferably 30 hours or less, and more preferably 15 hours or less.
［カーボンナノチューブ積層構造体の溶媒除去処理］
　カーボンナノチューブ積層構造体が分散処理されたものである場合、カーボンナノチューブ積層構造体は、更に溶媒除去処理を施してもよい。特に、溶媒中に分散したカーボンナノチューブ積層構造体の諸物性値または性状を測定または評価する時には、分散したカーボンナノチューブ積層構造体の一部を測定または評価用に分取し、分取したカーボンナノチューブ積層構造体に溶媒除去処理を施す。溶媒除去処理としては、例えば、ろ取、乾燥が挙げられる。ろ取は、例えばろ紙を用いて行うことができる。乾燥としては、例えば、加熱乾燥、風乾、減圧乾燥等が挙げられる。加熱乾燥は、例えば８０℃以上の温度で行ってもよく、好ましくは２００℃以下の温度で行ってもよく、例えば０．５時間以上で行ってもよく、好ましくは２時間以下で行ってもよい。風乾は、例えば、２０℃以上の温度で行ってもよく、３０℃以下の温度で行ってもよく、３０％以上の湿度で行ってもよく、７０％以下の湿度で行ってもよく、１時間以上で行ってもよく、１２時間以下で行ってもよい。減圧乾燥は、例えば、２０℃以上の温度で行ってもよく、１００℃以下の温度で行ってもよく、１０Ｐa以上の気圧で行ってもよく、１０００Ｐa以下の気圧で行ってもよく、１時間以上行ってもよく、１２時間以下で行ってもよい。 [Solvent removal treatment of carbon nanotube stacked structure]
When the carbon nanotube layered structure has been subjected to a dispersion treatment, the carbon nanotube layered structure may be further subjected to a solvent removal treatment. In particular, when measuring or evaluating various physical properties or properties of a carbon nanotube laminate structure dispersed in a solvent, a portion of the dispersed carbon nanotube laminate structure is separated for measurement or evaluation, and the separated carbon nanotube The laminated structure is subjected to solvent removal treatment. Examples of the solvent removal treatment include filtration and drying. Filtration can be performed using, for example, filter paper. Examples of drying include heat drying, air drying, reduced pressure drying, and the like. Heat drying may be performed, for example, at a temperature of 80°C or higher, preferably at a temperature of 200°C or lower, for example, for 0.5 hours or more, preferably for 2 hours or less. good. For example, air drying may be performed at a temperature of 20°C or higher, 30°C or lower, a humidity of 30% or higher, a humidity of 70% or lower, and 1. It may be carried out for more than 1 hour or less than 12 hours. For example, vacuum drying may be performed at a temperature of 20°C or higher, 100°C or lower, a pressure of 10Pa or higher, a pressure of 1000Pa or lower, and a drying time of 1 hour. It may be carried out for more than 12 hours or less than 12 hours.
（カーボンナノチューブ分散液）
　本発明のカーボンナノチューブ分散液は、本発明のカーボンナノチューブ積層構造体と溶媒とを含む。本発明のカーボンナノチューブ分散液は、例えば、電子素子（例、抵抗変化型記憶装置）の製造時において、電子素子の機能性領域（例、抵抗変化層）の形成に、例えば、塗布液として用いることができ、そのことによって、十分低いスイッチング電圧で作動可能な電子素子を提供できる。 (Carbon nanotube dispersion)
The carbon nanotube dispersion liquid of the present invention contains the carbon nanotube layered structure of the present invention and a solvent. The carbon nanotube dispersion liquid of the present invention can be used, for example, as a coating liquid to form a functional region (e.g., a resistance variable layer) of an electronic element (e.g., a variable resistance layer) during the production of an electronic element (e.g., a resistance variable memory device). This makes it possible to provide an electronic device that can operate with a sufficiently low switching voltage.
＜溶媒＞
　本発明のカーボンナノチューブ分散液に含有される溶媒としては、例えば、非ハロゲン系溶媒、及び非水溶媒等が挙げられる。具体的には、上記溶媒としては、水；メタノール、エタノール、ｎ－プロパノール、イソプロパノール、ｎ－ブタノール、イソブタノール、ｔ－ブタノール、ペンタノール、ヘキサノール、ヘプタノール、オクタノール、ノナノール、デカノール、アミルアルコール、メトキシプロパノール、プロピレングリコール、エチレングリコール等のアルコール類；アセトン、メチルエチルケトン、シクロヘキサノン等のケトン類；酢酸エチル、酢酸ブチル、乳酸エチル、α－ヒドロキシカルボン酸のエステル、ベンジルベンゾエート（安息香酸ベンジル）等のエステル類；ジエチルエーテル、ジオキサン、テトラヒドロフラン、モノメチルエーテル等のエーテル類；Ｎ，Ｎ－ジメチルホルムアミド、Ｎ－メチルピロリドン等のアミド系極性有機溶媒；トルエン、キシレン、クロロベンゼン、オルトジクロロベンゼン、パラジクロロベンゼン、等の芳香族炭化水素類；サリチルアルデヒド、ジメチルスルホキシド、４－メチル－２－ペンタノン、Ｎ－メチルピロリドン、γ－ブチロラクトン、テトラメチルアンモニウムヒドロキシド等が挙げられる。中でも、分散性に特に優れる観点から、水、乳酸エチル、イソプロパノール、メチルエチルケトンが好ましい。これらは１種類のみを単独で用いてもよいし、２種類以上を混合して用いてもよい。 <Solvent>
Examples of the solvent contained in the carbon nanotube dispersion of the present invention include non-halogen solvents and non-aqueous solvents. Specifically, the above-mentioned solvents include water; methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, t-butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, amyl alcohol, methoxy Alcohols such as propanol, propylene glycol, and ethylene glycol; Ketones such as acetone, methyl ethyl ketone, and cyclohexanone; Esters such as ethyl acetate, butyl acetate, ethyl lactate, esters of α-hydroxycarboxylic acids, and benzyl benzoate (benzyl benzoate) ; Ethers such as diethyl ether, dioxane, tetrahydrofuran, monomethyl ether; Amide-based polar organic solvents such as N,N-dimethylformamide and N-methylpyrrolidone; Aromatics such as toluene, xylene, chlorobenzene, orthodichlorobenzene, paradichlorobenzene, etc. Group hydrocarbons; examples include salicylaldehyde, dimethyl sulfoxide, 4-methyl-2-pentanone, N-methylpyrrolidone, γ-butyrolactone, and tetramethylammonium hydroxide. Among these, water, ethyl lactate, isopropanol, and methyl ethyl ketone are preferred from the viewpoint of particularly excellent dispersibility. These may be used alone or in combination of two or more.
　本発明のカーボンナノチューブ分散液中のカーボンナノチューブの濃度は、上記溶媒１Ｌに対して、カーボンナノチューブが１ｍｇ以上含まれることが好ましく、１００ｍｇ以上含まれることがより好ましい。また、１００００ｍｇ以下であることが好ましい。溶媒に対してカーボンナノチューブが１ｍｇ以上含まれれば、強度に優れる機能性領域（例、抵抗変化層）を形成することができる。また、含まれるカーボンナノチューブが１００００ｍｇ以下であれば、カーボンナノチューブ積層構造体同士の凝集を抑制して、カーボンナノチューブ積層構造体の分散性に一層優れる分散液を得ることができる。 The concentration of carbon nanotubes in the carbon nanotube dispersion of the present invention is preferably 1 mg or more, more preferably 100 mg or more, per 1 L of the solvent. Moreover, it is preferable that it is 10000 mg or less. If 1 mg or more of carbon nanotubes is contained in the solvent, a functional region (eg, resistance change layer) with excellent strength can be formed. Further, if the amount of carbon nanotubes contained is 10,000 mg or less, agglomeration of the carbon nanotube stacked structures can be suppressed, and a dispersion liquid with even better dispersibility of the carbon nanotube stacked structures can be obtained.
　本発明のカーボンナノチューブ分散液中のカーボンナノチューブの濃度は、０．００５質量％以上であることが好ましく、０．０１質量％以上であることがより好ましく、５質量％以下であることが好ましく、０．５質量％以下であることがより好ましい。カーボンナノチューブの濃度が０．００５質量％以上であれば、強度に優れる機能性領域（例、抵抗変化層）を形成することができる。また、カーボンナノチューブの濃度が５質量％以下であれば、カーボンナノチューブ積層構造体同士の凝集を抑制して、カーボンナノチューブ積層構造体の分散性に一層優れる分散液を得ることができる。 The concentration of carbon nanotubes in the carbon nanotube dispersion of the present invention is preferably 0.005% by mass or more, more preferably 0.01% by mass or more, and preferably 5% by mass or less, More preferably, it is 0.5% by mass or less. When the concentration of carbon nanotubes is 0.005% by mass or more, a functional region (eg, a variable resistance layer) with excellent strength can be formed. Further, if the concentration of carbon nanotubes is 5% by mass or less, agglomeration of carbon nanotube stacked structures can be suppressed, and a dispersion liquid with even better dispersibility of carbon nanotube stacked structures can be obtained.
　本発明のカーボンナノチューブ分散液は、スイッチング電圧が十分低い電子素子の機能性領域（例、抵抗変化層）を形成することができることから、分散剤を実質的に含まないことが好ましい。本明細書において、「実質的に含まない」とは、不可避的に混入する場合を除いて積極的には配合しないことをいい、具体的には、カーボンナノチューブ分散液中の含有量が、０．０５質量％未満であることが好ましく、０．０１質量％未満であることがより好ましく、０．００１質量％未満であることが更に好ましい。
　なお、上記分散剤としては、界面活性剤、合成高分子、天然高分子等が挙げられる。 The carbon nanotube dispersion liquid of the present invention preferably does not substantially contain a dispersant, since it can form a functional region (eg, a variable resistance layer) of an electronic device with a sufficiently low switching voltage. As used herein, the term "substantially free of carbon nanotubes" means that they are not actively incorporated unless they are unavoidably mixed in, and specifically, it means that the content in the carbon nanotube dispersion is 0. It is preferably less than .05% by weight, more preferably less than 0.01% by weight, even more preferably less than 0.001% by weight.
Note that examples of the dispersant include surfactants, synthetic polymers, natural polymers, and the like.
　本発明のカーボンナノチューブ分散液は、カーボンナノチューブ分散液中の不純物が少なくなり、また、特性の安定した長寿命の電子部品を作製できる観点から、カーボンナノチューブ分散液中の金属不純物の濃度が、１×１０１８原子／ｃｍ３未満であることが好ましく、１５×１０１６原子／ｃｍ３未満であることがより好ましい。 In the carbon nanotube dispersion of the present invention, the concentration of metal impurities in the carbon nanotube dispersion is 1. It is preferably less than ×10 18 atoms/cm 3 , more preferably less than 15 × 10 16 atoms/cm 3 .
　本発明のカーボンナノチューブ分散液は、カーボンナノチューブ積層構造体の分散性が一層向上し、また、均一な機能性領域（例、抵抗変化層）を形成できる観点から、カーボンナノチューブの沈殿物及びカーボンナノチューブ積層構造体同士の凝集物が実質的に含まれないことが好ましい。
　なお、本明細書において、沈殿物、凝集物とは、１００００Ｇで２０分間遠心して沈殿するカーボンナノチューブをいう。 The carbon nanotube dispersion liquid of the present invention further improves the dispersibility of the carbon nanotube layered structure, and from the viewpoint of forming a uniform functional region (e.g. resistance change layer), carbon nanotube precipitates and carbon nanotube It is preferable that aggregates of laminated structures are not substantially included.
In this specification, the term "precipitate" or "aggregate" refers to carbon nanotubes that are precipitated by centrifugation at 10,000 G for 20 minutes.
　本発明のカーボンナノチューブ分散液は、例えば、上述したカーボンナノチューブ積層構造体の製造方法に従って、溶媒中に分散したカーボンナノチューブ積層構造体の形態として得ることができる。 The carbon nanotube dispersion of the present invention can be obtained in the form of a carbon nanotube laminate structure dispersed in a solvent, for example, according to the method for manufacturing a carbon nanotube laminate structure described above.
（電子素子製造用塗布液）
　本発明の電子素子製造用塗布液は、本発明のカーボンナノチューブ分散液を含む。本発明の電子素子製造用塗布液は、例えば、電子素子（例、抵抗変化型記憶装置）の製造時に塗布して溶媒を乾燥除去することにより、電子素子の機能性領域（例、抵抗変化層）を形成させるために用いることができる。本発明の電子素子製造用塗布液を用いることで、十分低いスイッチング電圧で作動可能な電子素子を製造できる。 (Coating liquid for electronic device manufacturing)
The coating liquid for manufacturing electronic devices of the present invention contains the carbon nanotube dispersion liquid of the present invention. The coating liquid for manufacturing electronic devices of the present invention can be applied, for example, at the time of manufacturing an electronic device (for example, a resistance variable memory device), and the solvent can be dried and removed to form a functional area (for example, a resistance variable layer) of the electronic device. ) can be used to form. By using the coating liquid for manufacturing electronic devices of the present invention, electronic devices that can be operated at sufficiently low switching voltages can be manufactured.
（カーボンナノチューブ膜）
　本発明のカーボンナノチューブ膜は、本発明のカーボンナノチューブ積層構造体を含む。「カーボンナノチューブ膜」とは、カーボンナノチューブ積層構造体を材料として含み、電子素子中で機能性領域（例、抵抗変化型記憶装置の抵抗変化層）として機能し得る部分（機能層）である。カーボンナノチューブ膜は、例えば、塗布膜等の形態で形成され得る。また、電子素子中で機能性領域として機能させるために形成させた時にスイッチング電圧低下に寄与する観点から、本発明のカーボンナノチューブ膜中で、カーボンナノチューブ積層構造体のうち複数が、互いに交差していることが好ましい。図３は、複数のカーボンナノチューブ積層構造体が互いに交差している状態の例を示す。本発明のカーボンナノチューブ膜は、例えば、本発明のカーボンナノチューブ分散液（例、電子素子製造用塗布液）を塗布して、溶媒を除去することによって形成させることができる。このようなカーボンナノチューブ膜の形成は、例えば、下記の「抵抗変化層の形成方法」に準じた手順で行うことができる。 (carbon nanotube film)
The carbon nanotube film of the present invention includes the carbon nanotube laminate structure of the present invention. A “carbon nanotube film” is a portion (functional layer) that includes a carbon nanotube stacked structure as a material and can function as a functional region (eg, a resistance change layer of a resistance change storage device) in an electronic device. The carbon nanotube film can be formed, for example, in the form of a coating film. In addition, from the viewpoint of contributing to a reduction in switching voltage when formed to function as a functional region in an electronic device, in the carbon nanotube film of the present invention, a plurality of carbon nanotube stacked structures may cross each other. Preferably. FIG. 3 shows an example of a state in which a plurality of carbon nanotube stacked structures intersect with each other. The carbon nanotube film of the present invention can be formed, for example, by applying the carbon nanotube dispersion liquid of the present invention (eg, a coating liquid for manufacturing electronic devices) and removing the solvent. Formation of such a carbon nanotube film can be performed, for example, by a procedure similar to the "method for forming a variable resistance layer" below.
（電子素子）
　本発明の電子素子は、本発明のカーボンナノチューブ膜を含む。本発明の電子素子中で、カーボンナノチューブ膜は、機能性領域として機能し得る部分（機能層）として存在する。電子素子としては、例えば、抵抗変化型記憶装置、マイクロプロセッサ、電界効果トランジスタ、サイリスタが挙げられるが、抵抗変化型記憶装置（例、ランダムアクセスメモリ）が好ましい。機能性領域としては、抵抗変化層、半導体層、電極が挙げられるが、抵抗変化層が好ましい。本発明の電子素子は、十分低いスイッチング電圧で作動可能であり、スイッチング電圧が低ければ、電子素子中のセルを高密度に集積しても、高電圧によって生じる隣接セルへの電流漏れ等の不具合が抑制されるので、セルを高密度に集積させ、記憶容量等の性能を向上させた記憶装置等の電子素子を製造することが可能となる。本発明の電子素子を抵抗変化型記憶装置とした例が、図１０（ｋ）に示される。更に、図４は、本発明の電子素子を抵抗変化型記憶装置とした時の抵抗変化型記憶装置の下部電極３５２（ＴｉＮ層）、抵抗変化層３５４（本発明のカーボンナノチューブ膜）、および上部電極３５５（ＴｉＮ層）を含む領域の断面の走査型電子顕微鏡（ＳＥＭ）画像の例を示す。 (electronic device)
The electronic device of the present invention includes the carbon nanotube film of the present invention. In the electronic device of the present invention, the carbon nanotube film exists as a portion (functional layer) that can function as a functional region. Examples of the electronic element include a resistance variable memory device, a microprocessor, a field effect transistor, and a thyristor, but a resistance variable memory device (eg, random access memory) is preferable. Examples of the functional region include a variable resistance layer, a semiconductor layer, and an electrode, and a variable resistance layer is preferable. The electronic device of the present invention can be operated with a sufficiently low switching voltage, and as long as the switching voltage is low, even if the cells in the electronic device are densely integrated, problems such as current leakage to adjacent cells caused by high voltage may occur. Since this suppresses the storage capacity, it becomes possible to manufacture electronic devices such as memory devices in which cells are integrated at high density and performance such as storage capacity is improved. An example in which the electronic element of the present invention is used as a resistance variable memory device is shown in FIG. 10(k). Further, FIG. 4 shows the lower electrode 352 (TiN layer), resistance change layer 354 (carbon nanotube film of the invention), and upper part of the resistance change memory device when the electronic element of the invention is used as a resistance change memory device. An example of a scanning electron microscope (SEM) image of a cross section of a region including electrode 355 (TiN layer) is shown.
　以下、本発明のカーボンナノチューブ膜を抵抗変化層として機能し得る部分（機能層）として含む抵抗変化型記憶装置を例として、本発明の電子素子を製造するための手順の例を具体的に説明するが、これに限定されない。 Hereinafter, an example of the procedure for manufacturing the electronic device of the present invention will be specifically explained using a resistance variable memory device including the carbon nanotube film of the present invention as a portion (functional layer) that can function as a resistance variable layer as an example. However, it is not limited to this.
　まず、図１０（ａ）に示すように、シリコン基板３５０を用意する。シリコン基板３５０としては、チョクラルスキー（ＣＺ）法や浮遊帯域溶融（ＦＺ）法などによって単結晶シリコンインゴットを育成し、育成したインゴットに対してウェーハ加工処理を施して得られたシリコンウェーハを用いることができる。 First, as shown in FIG. 10(a), a silicon substrate 350 is prepared. As the silicon substrate 350, a silicon wafer obtained by growing a single crystal silicon ingot by a Czochralski (CZ) method, a floating zone melting (FZ) method, or the like and performing wafer processing on the grown ingot is used. be able to.
　シリコン基板３５０の直径、面方位、導電型などは、設計に応じて適宜設定することができる。例えば、シリコン基板３５０の直径は、２００ｍｍ、３００ｍｍ、４５０ｍｍなどとすることができる。また、シリコン基板３５０の面方位は、（００１）、（１１０）、（１１１）などとすることができる。さらに、シリコン基板３５０の導電型は、適切なドーパントを用いてｎ型またはｐ型とすることができ、ｐ型ドーパントとしてはホウ素（Ｂ）など、ｎ型ドーパントとしてはリン（Ｐ）などを用いることができる。また、シリコン以外の半導体基板を用いても構わない。 The diameter, surface orientation, conductivity type, etc. of the silicon substrate 350 can be appropriately set according to the design. For example, the diameter of the silicon substrate 350 can be 200 mm, 300 mm, 450 mm, etc. Further, the plane orientation of the silicon substrate 350 can be (001), (110), (111), or the like. Furthermore, the conductivity type of the silicon substrate 350 can be n-type or p-type using an appropriate dopant, such as boron (B) as the p-type dopant and phosphorus (P) or the like as the n-type dopant. be able to. Further, a semiconductor substrate other than silicon may be used.
　次いで、図１０（ｂ）に示すように、シリコン基板３５０上に絶縁膜３５１を形成する。絶縁膜３５１は、酸化シリコン（ＳｉＯ２）や窒化シリコン（Ｓｉ３Ｎ４）などで構成することができる。また、絶縁膜３５１は、ＣＶＤ法、スパッタリング法などにより形成することができる。 Next, as shown in FIG. 10(b), an insulating film 351 is formed on the silicon substrate 350. The insulating film 351 can be made of silicon oxide (SiO 2 ), silicon nitride (Si 3 N 4 ), or the like. Further, the insulating film 351 can be formed by a CVD method, a sputtering method, or the like.
　続いて、図１０（ｃ）に示すように、絶縁膜３５１上に下部電極３５２を形成する。下部電極３５２は、窒化チタン（ＴｉＮ）、タングステン（Ｗ）、アルミニウム（Ａｌ）などで構成することができる。下部電極３５２は、ＣＶＤ法、スパッタリング法などにより形成することができる。 Subsequently, as shown in FIG. 10(c), a lower electrode 352 is formed on the insulating film 351. The lower electrode 352 can be made of titanium nitride (TiN), tungsten (W), aluminum (Al), or the like. The lower electrode 352 can be formed by a CVD method, a sputtering method, or the like.
　次に、図１０（ｄ）に示すように、電子ビーム（ＥＢ）リソグラフィー法およびドライエッチング法などにより、下部電極３５２をピラー状にパターニングする。 Next, as shown in FIG. 10(d), the lower electrode 352 is patterned into a pillar shape by electron beam (EB) lithography, dry etching, or the like.
　その後、図１０（ｅ）に示すように、ピラー状にパターニングした下部電極３５２上に絶縁膜３５３を堆積させる。絶縁膜３５３は、酸化シリコン（ＳｉＯ２）や窒化シリコン（Ｓｉ３Ｎ４）などで構成することができ、ＣＶＤ法、ＡＬＤ法、スパッタリング法などにより形成することができる。 Thereafter, as shown in FIG. 10E, an insulating film 353 is deposited on the lower electrode 352 patterned into a pillar shape. The insulating film 353 can be made of silicon oxide (SiO 2 ), silicon nitride (Si 3 N 4 ), or the like, and can be formed by a CVD method, an ALD method, a sputtering method, or the like.
　続いて、図１０（ｆ）に示すように、化学機械研磨（ＣＭＰ）法などを用いて、堆積した絶縁膜３５３の表面を研磨して、ピラー状の下部電極３５２を表面に露出させる。 Subsequently, as shown in FIG. 10(f), the surface of the deposited insulating film 353 is polished using chemical mechanical polishing (CMP) or the like to expose the pillar-shaped lower electrode 352 on the surface.
　次に、図１０（ｇ）に示すように、ピラー状の下部電極３５２が露出した表面に、抵抗変化層３５４を全面に形成する。本発明においては、抵抗変化層３５４は、本発明のカーボンナノチューブ膜で構成する。下部電極３５２と、後工程で形成される上部電極３５５との間に電圧を印加すると、抵抗変化層３５４を構成するＣＮＴ間の距離が変化し、相対的に低抵抗となる低抵抗状態と相対的に高抵抗となる高抵抗状態を取らせることができ、データを記憶させることができる。 Next, as shown in FIG. 10(g), a variable resistance layer 354 is formed entirely on the exposed surface of the pillar-shaped lower electrode 352. In the present invention, the variable resistance layer 354 is composed of the carbon nanotube film of the present invention. When a voltage is applied between the lower electrode 352 and the upper electrode 355 that will be formed in a later process, the distance between the CNTs forming the variable resistance layer 354 changes, resulting in a relatively low resistance state and a relatively low resistance state. It can be made to take a high resistance state where the resistance is high, and data can be stored.
　上記ＣＮＴを有する抵抗変化層３５４は、例えば本発明のカーボンナノチューブ分散液をピラー状の下部電極３５２が露出した表面に塗布することにより形成することができる。抵抗変化層３５４の形成方法については、後に詳述する。 The variable resistance layer 354 containing CNTs can be formed, for example, by applying the carbon nanotube dispersion of the present invention to the surface where the pillar-shaped lower electrode 352 is exposed. A method for forming the variable resistance layer 354 will be described in detail later.
　続いて、図１０（ｈ）に示すように、抵抗変化層３５４上に上部電極３５５を形成する。この上部電極３５５は、窒化チタン（ＴｉＮ）や、タングステン（Ｗ）、アルミニウム（Ａｌ）などで構成することができ、ＣＶＤ法やスパッタリング法などにより形成することができる。 Subsequently, as shown in FIG. 10(h), an upper electrode 355 is formed on the variable resistance layer 354. This upper electrode 355 can be made of titanium nitride (TiN), tungsten (W), aluminum (Al), or the like, and can be formed by a CVD method, a sputtering method, or the like.
　次に、図１０（ｉ）に示すように、上部電極３５５および抵抗変化層３５４をフォトリソグラフィー法およびドライエッチング法により連続的にパターニングして、素子分離させる。このとき、上記上部電極３５５のパターニングは、上部電極３５５と下部電極３５２との間に上部電極３５５のチャージアップによる電位差が生じないエッチング方法により上部電極３５５をエッチングすることにより行う。これは、例えばマイクロ波励起表面波プラズマエッチング法により行うことができる。これにより、本発明のカーボンナノチューブ膜で構成された抵抗変化層３５４の破壊を抑制して、記憶装置の製造の歩留まりを向上させることができる。上部電極３５５の形成方法およびそれに用いる装置については、後に詳述する。 Next, as shown in FIG. 10(i), the upper electrode 355 and the variable resistance layer 354 are successively patterned by photolithography and dry etching to separate the elements. At this time, the patterning of the upper electrode 355 is performed by etching the upper electrode 355 using an etching method that does not generate a potential difference between the upper electrode 355 and the lower electrode 352 due to charge-up of the upper electrode 355. This can be done, for example, by a microwave-excited surface wave plasma etching method. Thereby, destruction of the variable resistance layer 354 made of the carbon nanotube film of the present invention can be suppressed, and the yield of manufacturing the memory device can be improved. The method for forming the upper electrode 355 and the apparatus used therefor will be described in detail later.
　続いて、図１０（ｊ）に示すように、素子分離された上部電極３５５および抵抗変化層３５４を覆うように、保護膜３５６を形成する。保護膜３５６は、酸化シリコン（ＳｉＯ２）や窒化シリコン（Ｓｉ３Ｎ４）などで構成することができ、ＣＶＤ法やスパッタリング法などにより形成することができる。 Subsequently, as shown in FIG. 10(j), a protective film 356 is formed to cover the element-isolated upper electrode 355 and variable resistance layer 354. The protective film 356 can be made of silicon oxide (SiO 2 ), silicon nitride (Si 3 N 4 ), or the like, and can be formed by a CVD method, a sputtering method, or the like.
　最後に、図１０（ｋ）に示すように、上部電極３５５および抵抗変化層３５４の上方にて保護膜３５６を貫通して上部電極３５５を露出する貫通孔３５７を形成するとともに、上部電極３５５および抵抗変化層３５４が存在しない部分において、保護膜３５６および絶縁膜３５３を貫通して下部電極３５２を露出する貫通孔３５８を形成する。 Finally, as shown in FIG. 10(k), a through hole 357 is formed above the upper electrode 355 and the variable resistance layer 354 to penetrate the protective film 356 and expose the upper electrode 355. A through hole 358 that penetrates the protective film 356 and the insulating film 353 and exposes the lower electrode 352 is formed in a portion where the variable resistance layer 354 is not present.
　上記手順による製造方法は、抵抗変化層３５４の破壊を抑制して、より高い歩留まりで抵抗変化型記憶装置を製造することに適している。 The manufacturing method according to the above procedure is suitable for suppressing destruction of the resistance change layer 354 and manufacturing a resistance change storage device with a higher yield.
（抵抗変化層の形成方法）
　抵抗変化層３５４の形成は、例えば、以下の手順により行うことができる。 (Method for forming resistance change layer)
The variable resistance layer 354 can be formed, for example, by the following procedure.
＜成膜工程＞
　成膜工程では、本発明のＣＮＴ分散液から溶媒を除去して、抵抗変化層３５４を成膜する。具体的には、成膜工程では、本発明のＣＮＴ分散液をピラー状にパターニングした下部電極３５２上に塗布した後、塗布した本発明のＣＮＴ分散液を乾燥させることにより、本発明のＣＮＴ分散液から溶媒を除去し、抵抗変化層３５４を成膜する。 <Film formation process>
In the film forming step, the solvent is removed from the CNT dispersion of the present invention, and the variable resistance layer 354 is formed. Specifically, in the film-forming process, the CNT dispersion of the present invention is coated on the lower electrode 352 patterned into a pillar shape, and then the CNT dispersion of the present invention is dried. The solvent is removed from the liquid, and a variable resistance layer 354 is formed.
［塗布］
　本発明のＣＮＴ分散液を下部電極３５２上に塗布する方法としては、公知の塗布方法を採用できる。具体的には、塗布方法としては、ディッピング法、スピンコート法、ロールコート法、グラビアコート法、ナイフコート法、エアナイフコート法、ロールナイフコート法、ダイコート法、スクリーン印刷法、スプレーコート法、グラビアオフセット法、ミストコート法などを用いることができる。 [Application]
As a method for applying the CNT dispersion of the present invention onto the lower electrode 352, a known application method can be employed. Specifically, coating methods include dipping method, spin coating method, roll coating method, gravure coating method, knife coating method, air knife coating method, roll knife coating method, die coating method, screen printing method, spray coating method, and gravure coating method. An offset method, a mist coating method, etc. can be used.
［乾燥］
　下部電極３５２上に塗布した本発明のＣＮＴ分散液を乾燥する方法としては、公知の乾燥方法を採用できる。乾燥方法としては、熱風乾燥法、真空乾燥法、熱ロール乾燥法、赤外線照射法等が挙げられる。乾燥温度は、特に限定されないが、通常、室温～４００℃、乾燥時間は、特に限定されないが、通常、０．１～１５０分である。 [Drying]
A known drying method can be used to dry the CNT dispersion of the present invention applied onto the lower electrode 352. Examples of the drying method include hot air drying, vacuum drying, hot roll drying, and infrared irradiation. The drying temperature is not particularly limited, but is usually room temperature to 400° C., and the drying time is not particularly limited, but is usually 0.1 to 150 minutes.
　なお、成膜工程では、上澄み液中の溶媒は完全に除去する必要はなく、溶媒の除去後に残ったＣＮＴが膜状の集合体（抵抗変化層３５４）としてハンドリング可能な状態であれば、多少の溶媒が残留していても問題はない。 Note that in the film forming process, it is not necessary to completely remove the solvent in the supernatant liquid; if the CNTs remaining after the removal of the solvent are in a state that can be handled as a film-like aggregate (resistance change layer 354), the solvent may be removed to some extent. There is no problem even if some solvent remains.
＜抵抗変化層の後処理＞
　また、上記抵抗変化層３５４の形成方法では、任意に、成膜工程において成膜した抵抗変化層３５４をプレス加工して密度を更に高めてもよい。ＣＮＴの損傷または破壊による特性低下を抑制する観点からは、プレス加工する際のプレス圧力は３ＭＰａ未満であることが好ましく、プレス加工を行なわないことがより好ましい。 <Post-treatment of variable resistance layer>
Furthermore, in the above method for forming the variable resistance layer 354, the variable resistance layer 354 formed in the film forming step may optionally be pressed to further increase its density. From the viewpoint of suppressing property deterioration due to damage or destruction of CNTs, the pressing pressure during press working is preferably less than 3 MPa, and it is more preferable that no press working is performed.
（上部電極の形成方法）
　上部電極３５５の形成は、例えば、以下の手順により行うことができる。また、本発明の電子素子を製造する方法は、以下の装置を用いて行うことができる。 (Method of forming upper electrode)
The upper electrode 355 can be formed, for example, by the following procedure. Moreover, the method for manufacturing an electronic device of the present invention can be carried out using the following apparatus.
　図７は、マイクロ波励起による表面波プラズマエッチング（Ｓｕｒｆａｃｅ　Ｗａｖｅ
　Ｐｌａｓｍａ、ＳＷＰ）装置の一例の模式図を示している。図７に示したＳＷＰ装置２００は、処理対象のシリコン基板２５０を収容する処理容器２０１と、処理容器２０１の上部に配置された複数のマイクロ波放射孔２０２ａを有する蓋部２０２と、プラズマを励起するためのマイクロ波を発生させるマイクロ波発生部２０３とを備える（より詳細な装置構成については、例えば特開２０１９－９３０５号公報参照）。 Figure 7 shows surface wave plasma etching using microwave excitation.
1 shows a schematic diagram of an example of a plasma, SWP) device. The SWP apparatus 200 shown in FIG. 7 includes a processing container 201 that accommodates a silicon substrate 250 to be processed, a lid part 202 that has a plurality of microwave radiation holes 202a arranged at the top of the processing container 201, and a lid part 202 that excites plasma. (For a more detailed device configuration, see, for example, Japanese Patent Application Publication No. 2019-9305).
　上記装置１において、プラズマの生成をマイクロ波（例えば、２．４５ＧＨｚ）励起により行うと、従来の低周波数電波の励起（例えば、１３ＭＨｚ）により行う場合に比べて、短時間で電界の向きが反転させて、生成された電子の加速を抑制してエネルギーを小さくすることができる。これにより、上部電極のエッチングの際に、電極に与えるダメージを抑制することができる。 In the above device 1, when plasma is generated by microwave excitation (for example, 2.45 GHz), the direction of the electric field is reversed in a shorter time than when it is generated by conventional low frequency radio wave excitation (for example, 13 MHz). By doing so, the acceleration of the generated electrons can be suppressed and the energy can be reduced. Thereby, damage to the upper electrode can be suppressed during etching of the upper electrode.
　また、マイクロ波励起により高密度のプラズマを生成することができ、生成されるマイナスイオンの量も増加するため、プラスに帯電した上部電極３５５をより効率的に中和することができる。 Further, since high-density plasma can be generated by microwave excitation and the amount of generated negative ions increases, the positively charged upper electrode 355 can be neutralized more efficiently.
　図８は、図７に示したＳＷＰ装置２００の一種であるラジアルラインスロットアンテナを用いたマイクロ波励起プラズマエッチング装置（以下、「ＲＳＬＡ装置」とも言う。）の一例の模式図を示している。図８に示したＲＬＳＡ装置３００は、処理対象のシリコン基板３５０を収容する処理容器３０１と、処理容器３０１の上部に配置されたラジアルラインスロットアンテナ３０２と、プラズマを励起するためのマイクロ波を発生させるマイクロ波発生部３０３とを備える（より詳細な装置構成については、例えば特開２０００－７７３３５号公報参照）。 FIG. 8 shows a schematic diagram of an example of a microwave-excited plasma etching apparatus (hereinafter also referred to as "RSLA apparatus") using a radial line slot antenna, which is a type of SWP apparatus 200 shown in FIG. The RLSA apparatus 300 shown in FIG. 8 includes a processing container 301 that accommodates a silicon substrate 350 to be processed, a radial line slot antenna 302 placed on the top of the processing container 301, and a microwave generator that generates microwaves to excite plasma. (For a more detailed device configuration, see, for example, Japanese Patent Laid-Open No. 2000-77335).
　図９は、ラジアルラインスロットアンテナ３０２の一例を示している。ラジアルラインスロットアンテナは、平面アンテナの一種であり、図９に示すように、例えば導体の円板で構成されたアンテナ本体３０２ａの表面に複数のマイクロ波放射孔３０２ｂが、例えば同心円状、らせん状、放射状に設けられて構成される（例えば、特開２０００－７７３３５号公報参照）。このようなラジアルラインスロットアンテナ３０２を用いてプラズマ励起を行うことにより、アンテナ近傍の電磁界を制御して、大面積で、かつ安定的にプラズマを均一に生成することができ、プラスに帯電した上部電極３５５をより均一に中和することができる。 FIG. 9 shows an example of the radial line slot antenna 302. A radial line slot antenna is a type of planar antenna, and as shown in FIG. 9, a plurality of microwave radiation holes 302b are formed on the surface of an antenna main body 302a made of a conductor disk, for example, in a concentric or spiral shape. , are arranged radially (for example, see Japanese Patent Laid-Open No. 2000-77335). By excitation of plasma using such a radial line slot antenna 302, it is possible to control the electromagnetic field near the antenna and generate plasma stably and uniformly over a large area. The upper electrode 355 can be neutralized more uniformly.
＜電子素子のスイッチング電圧＞
　電子素子のスイッチング電圧は、できるだけ低いほうがよく、５Ｖ以下が好ましく、４．８Ｖ以下がより好ましく、４．５Ｖ以下が更に好ましい。スイッチング電圧が低いほど、電子素子中のセルを高密度に集積しても、高電圧によって生じる隣接セルへの電流漏れ等の不具合が抑制されるので、セルを高密度に集積させ、記憶容量等の性能を向上させた記憶装置等の電子素子を製造することが可能となる。また、電子素子のスイッチング電圧は、ノイズの影響を抑制する観点から低すぎないほうがよく、０．５Ｖ以上が好ましく、１Ｖ以上がより好ましく、１．５Ｖ以上が更に好ましい。電子素子のスイッチング電圧は、例えば、実施例に記載の方法により測定することができる。 <Switching voltage of electronic elements>
The switching voltage of the electronic element is preferably as low as possible, preferably 5V or less, more preferably 4.8V or less, and even more preferably 4.5V or less. The lower the switching voltage, the more cells in an electronic device can be integrated at high density, and problems such as current leakage to adjacent cells caused by high voltage can be suppressed. It becomes possible to manufacture electronic devices such as memory devices with improved performance. Further, the switching voltage of the electronic element should not be too low from the viewpoint of suppressing the influence of noise, and is preferably 0.5 V or more, more preferably 1 V or more, and even more preferably 1.5 V or more. The switching voltage of an electronic device can be measured, for example, by the method described in Examples.
　以下、本発明について実施例に基づき具体的に説明するが、本発明はこれら実施例に限定されるものではない。なお、以下の説明において、量を表す「％」及び「部」は、特に断らない限り、質量基準である。
　なお、実施例および比較例において、各種測定および評価は、以下のとおりに実施した。 EXAMPLES Hereinafter, the present invention will be specifically explained based on Examples, but the present invention is not limited to these Examples. In the following description, "%" and "part" representing amounts are based on mass unless otherwise specified.
In addition, in Examples and Comparative Examples, various measurements and evaluations were carried out as follows.
［触媒担持体の物性値の測定］
＜鉄薄膜（触媒層）の膜厚＞
　触媒担持体の鉄薄膜（触媒層）の膜厚は、以下のようにして求めた。
　鉄薄膜（触媒層）の一部を剥離した面を原子間力顕微鏡（ＡＦＭ）で観察を行い、観察された段差部分の高さの差を膜厚とした。 [Measurement of physical property values of catalyst carrier]
<Thickness of iron thin film (catalyst layer)>
The thickness of the iron thin film (catalyst layer) of the catalyst support was determined as follows.
The surface from which a part of the iron thin film (catalyst layer) was peeled off was observed using an atomic force microscope (AFM), and the difference in height of the observed step portion was defined as the film thickness.
［材料ＣＮＴの評価］
＜平均直径＞
　材料ＣＮＴを透過型電子顕微鏡（ＴＥＭ）で観察し、ＴＥＭ画像を得た。得られたＴＥＭ画像から無作為に選択された５０本のＣＮＴの直径（外径）を測定し、ＣＮＴの直径の算術平均値を材料ＣＮＴの平均直径とした。 [Evaluation of material CNT]
<Average diameter>
The material CNT was observed with a transmission electron microscope (TEM), and a TEM image was obtained. The diameters (outer diameters) of 50 CNTs randomly selected from the obtained TEM images were measured, and the arithmetic mean value of the diameters of the CNTs was taken as the average diameter of the material CNTs.
＜ＣＮＴの全本数に対して単層ＣＮＴの本数が占める割合＞
　材料ＣＮＴを透過型電子顕微鏡（ＴＥＭ）で観察し、ＴＥＭ画像を得た。得られたＴＥＭ画像から無作為に選択した５０本のＣＮＴについて層数を測定した。そして、材料ＣＮＴ１００本中の単層ＣＮＴの本数に換算し、「ＣＮＴの全本数に対して単層ＣＮＴの本数が占める割合」とした。 <Ratio of the number of single-walled CNTs to the total number of CNTs>
The material CNT was observed with a transmission electron microscope (TEM), and a TEM image was obtained. The number of layers of 50 CNTs randomly selected from the obtained TEM images was measured. Then, it was converted to the number of single-walled CNTs in 100 material CNTs, and was defined as "the ratio of the number of single-walled CNTs to the total number of CNTs."
［酸化扁平ＣＮＴ積層構造体の評価］
＜酸素原子比率＞
　測定用に分取し、溶媒除去した酸化ＣＮＴをＸ線光電子分光分析装置（Ｔｈｅｒｍｏ　Ｆｉｓｈｅｒ　Ｓｃｉｅｎｔｉｆｉｃ社製、ＶＧ　Ｔｈｅｔａ　Ｐｒｏｂｅ）で分析した。そして、酸化ＣＮＴについて、Ｏ１ｓのピーク面積と、検出された全ピーク面積とを求め、それらに基づいて、酸化ＣＮＴの表面を構成する全原子量に対する酸素原子（Ｏ）存在量の比（ａｔ％）（＝Ｏ原子存在量／全原子量×１００）を算出し、得られた値を酸化ＣＮＴの酸素原子比率（ａｔ％）とした。 [Evaluation of oxidized flat CNT laminate structure]
<Oxygen atomic ratio>
The oxidized CNTs that were collected for measurement and from which the solvent was removed were analyzed using an X-ray photoelectron spectrometer (manufactured by Thermo Fisher Scientific, VG Theta Probe). Then, for oxidized CNTs, the peak area of O1s and the total detected peak area are determined, and based on these, the ratio of the amount of oxygen atoms (O) present to the total atomic weight constituting the surface of oxidized CNTs (at%) (=O atom abundance/total atomic weight×100) was calculated, and the obtained value was taken as the oxygen atomic ratio (at%) of the oxidized CNTs.
＜平均積層数、扁平率＞
　測定用に分取し、溶媒除去した酸化ＣＮＴを透過型電子顕微鏡（ＴＥＭ）で観察し、ＴＥＭ画像を得た。得られたＴＥＭ画像から無作為に選択した５０個の酸化ＣＮＴ積層構造体について厚みおよび積層数を測定し、算術平均値を平均厚みおよび平均積層数とした。そして、以下の式により扁平率を算出した。
扁平率（％）＝［（酸化ＣＮＴ積層構造体の平均厚み／酸化ＣＮＴ積層構造体の平均積層数）／材料ＣＮＴの平均直径］×１００ <Average number of laminated layers, flatness ratio>
The oxidized CNTs were separated for measurement and the solvent was removed, and the oxidized CNTs were observed with a transmission electron microscope (TEM) to obtain a TEM image. The thickness and number of stacked layers of 50 oxidized CNT stacked structures randomly selected from the obtained TEM images were measured, and the arithmetic mean values were taken as the average thickness and the average number of stacked layers. Then, the flatness was calculated using the following formula.
Oblateness (%) = [(average thickness of oxidized CNT laminated structure/average number of laminated layers of oxidized CNT laminated structure)/average diameter of material CNT] x 100
＜平均長さ＞
　測定用に分取し、溶媒除去した酸化ＣＮＴを走査型電子顕微鏡（ＳＥＭ）で観察し、ＳＥＭ画像を得た。得られたＳＥＭ画像から無作為に選択された５０本の酸化扁平ＣＮＴ積層構造体の長さを測定し、酸化扁平ＣＮＴ積層構造体の長さの算術平均値を酸化扁平ＣＮＴ積層構造体の平均長さとした。酸化扁平ＣＮＴ積層構造体が存在しない場合は、酸化扁平ＣＮＴ積層構造体に代えて５０本の酸化ＣＮＴの長さを測定し、算術平均値を平均長さとした。 <Average length>
The oxidized CNTs that were collected for measurement and from which the solvent had been removed were observed with a scanning electron microscope (SEM) to obtain a SEM image. The lengths of 50 oxidized flat CNT laminated structures randomly selected from the obtained SEM images were measured, and the arithmetic mean value of the lengths of the oxidized flat CNT laminated structures was calculated as the average of the oxidized flat CNT laminated structures. length. When the oxidized flat CNT laminated structure was not present, the lengths of 50 oxidized CNTs were measured instead of the oxidized flat CNT laminated structure, and the arithmetic mean value was taken as the average length.
［抵抗変化型記憶装置の評価］
＜スイッチング電圧＞
　抵抗変化型記憶装置について０Ｖから７．０Ｖまでの電圧スイープにより電流－電圧（ＩＶ）曲線を測定した。抵抗変化層を流れる電流値に変化が見られ、高抵抗状態と低抵抗状態の２つの状態の切り替えが起きたときの電圧値をスイッチング電圧とした。 [Evaluation of resistance variable memory device]
<Switching voltage>
The current-voltage (IV) curve of the resistance variable memory device was measured by sweeping the voltage from 0V to 7.0V. A change was observed in the value of the current flowing through the variable resistance layer, and the voltage value when switching between two states, a high resistance state and a low resistance state, occurred was defined as the switching voltage.
（実施例１）
［触媒担持体（材料ＣＮＴ合成用触媒）の調製］
　アルミニウム化合物としてのアルミニウムトリ－ｓｅｃ－ブトキシド１．９ｇを、有機溶剤としての２－プロパノール１００ｍＬに溶解させた。さらに、安定剤としてのトリイソプロパノールアミン０．９ｇを加えて溶解させて、下地層形成用の塗工液Ａを調製した。また、鉄化合物としての酢酸鉄１７４ｍｇを有機溶剤としての２－プロパノール１００ｍＬに溶解させた。さらに、安定剤としてのトリイソプロパノールアミン１９０ｍｇを加えて溶解させて、触媒層形成用の塗工液Ｂを調製した。 (Example 1)
[Preparation of catalyst support (catalyst for material CNT synthesis)]
1.9 g of aluminum tri-sec-butoxide as an aluminum compound was dissolved in 100 mL of 2-propanol as an organic solvent. Furthermore, 0.9 g of triisopropanolamine as a stabilizer was added and dissolved to prepare a coating liquid A for forming a base layer. Further, 174 mg of iron acetate as an iron compound was dissolved in 100 mL of 2-propanol as an organic solvent. Furthermore, 190 mg of triisopropanolamine as a stabilizer was added and dissolved to prepare a coating liquid B for forming a catalyst layer.
　基材としてのＦｅ－Ｃｒ合金ＳＵＳ４３０基板（ＪＦＥスチール株式会社製、４０ｍｍ×１００ｍｍ、厚さ０．３ｍｍ、Ｃｒ１８％、算術平均粗さＲａ≒０．５９μｍ）の表面に、室温２５℃、相対湿度５０％の環境下でディップコーティングにより、上述の塗工液Ａを塗布した。具体的には、基材を塗工液Ａに浸漬後、２０秒間保持して、１０ｍｍ／ｓｅｃの引き上げ速度で基材を引き上げた。その後、５分間風乾し、３００℃の空気環境下で３０分間加熱後、室温まで冷却することにより、基材上に膜厚４０ｎｍのアルミナ薄膜（下地層）を形成した。次いで、室温２５℃、相対湿度５０％の環境下で、基材に設けられたアルミナ薄膜の上に、ディップコーティングにより上述の塗工液Ｂを塗布した。具体的には、アルミナ薄膜を備える基材を塗工液Ｂに浸漬後、２０秒間保持して、３ｍｍ／秒の引き上げ速度でアルミナ薄膜を備える基材を引き上げた。その後、５分間風乾（乾燥温度４５℃）することにより、膜厚２．０ｎｍの鉄薄膜（触媒層）を形成して材料ＣＮＴ合成用触媒として用いるための触媒担持体を得た（触媒担持体形成工程）。 The surface of a Fe-Cr alloy SUS430 substrate (manufactured by JFE Steel Corporation, 40 mm x 100 mm, thickness 0.3 mm, Cr 18%, arithmetic mean roughness Ra≒0.59 μm) as a base material was coated at a room temperature of 25°C and relative humidity. The above-mentioned coating liquid A was applied by dip coating in a 50% environment. Specifically, the base material was immersed in coating liquid A, held for 20 seconds, and then pulled up at a pulling speed of 10 mm/sec. Thereafter, it was air-dried for 5 minutes, heated in an air environment at 300° C. for 30 minutes, and then cooled to room temperature to form an alumina thin film (base layer) with a thickness of 40 nm on the base material. Next, the above-mentioned coating liquid B was applied by dip coating onto the alumina thin film provided on the base material under an environment of room temperature 25° C. and relative humidity 50%. Specifically, the base material provided with the alumina thin film was immersed in coating liquid B, held for 20 seconds, and the base material provided with the alumina thin film was pulled up at a pulling speed of 3 mm/sec. Thereafter, by air drying for 5 minutes (drying temperature 45°C), a thin iron film (catalyst layer) with a film thickness of 2.0 nm was formed to obtain a catalyst support to be used as a catalyst for material CNT synthesis (catalyst support forming process).
［材料ＣＮＴの合成］
　次に、ＣＶＤ装置（反応チャンバのサイズ：直径３０ｍｍ、加熱長３６０ｍｍ）を用いて触媒担持体の触媒層上にＣＮＴ（材料ＣＮＴ）を形成した。具体的には、上記で作製した触媒担持体を、炉内温度：７５０℃、炉内圧力：１．０２×１０５Ｐａに保持されたＣＶＤ装置の反応チャンバ内に設置し、この反応チャンバ内に、Ｈｅ：１００ｓｃｃｍ、Ｈ２：９００ｓｃｃｍを６分間導入した。これにより、触媒層（鉄）を還元して鉄の微粒子化を促進し、単層ＣＮＴの成長に適した状態（下地層上にナノメートルサイズの触媒微粒子が多数形成された状態）とした（フォーメーション工程）。なお、このときの触媒微粒子の密度は、１×１０１２～１×１０１４個／ｃｍ２に調整した。 [Synthesis of material CNT]
Next, CNTs (material CNTs) were formed on the catalyst layer of the catalyst support using a CVD apparatus (reaction chamber size: diameter 30 mm, heating length 360 mm). Specifically, the catalyst support prepared above was installed in a reaction chamber of a CVD apparatus maintained at a furnace temperature of 750° C. and a furnace pressure of 1.02×10 5 Pa, and 100 sccm of He and 900 sccm of H 2 were introduced for 6 minutes. As a result, the catalyst layer (iron) was reduced and the iron was made into fine particles, creating a state suitable for the growth of single-walled CNTs (a state in which many nanometer-sized fine catalyst particles were formed on the base layer). formation process). Note that the density of the catalyst fine particles at this time was adjusted to 1×10 12 to 1×10 14 particles/cm 2 .
　その後、炉内温度：７５０℃、炉内圧力：１．０２×１０５Ｐａに保持された状態の反応チャンバ内に、Ｈｅ：８５０ｓｃｃｍ、Ｃ２Ｈ４：１５０ｓｃｃｍ、Ｈ２Ｏ：３００ｐｐｍとなる量で炭素源ガスを５分間供給した。これにより、単層ＣＮＴを各触媒微粒子から成長させた（ＣＮＴ成長工程）。そして、ＣＮＴ成長工程の終了後、反応チャンバ内にＨｅ：１０００ｓｃｃｍのみを供給し、残余の原料ガスや触媒賦活剤を排除した。これにより、ＣＮＴ（材料ＣＮＴ）が表面に形成された触媒担持体を得た。 Thereafter, the amounts of He: 850 sccm, C 2 H 4 : 150 sccm, and H 2 O: 300 ppm were placed in the reaction chamber maintained at a furnace temperature of 750° C. and a furnace pressure of 1.02×10 5 Pa. Carbon source gas was supplied for 5 minutes. As a result, single-walled CNTs were grown from each catalyst fine particle (CNT growth step). After the CNT growth step was completed, only 1000 sccm of He was supplied into the reaction chamber, and the remaining raw material gas and catalyst activator were removed. As a result, a catalyst support having CNT (material CNT) formed on the surface was obtained.
＜材料ＣＮＴの回収＞
　その後、上記の触媒担持体の表面から、触媒層上に成長したＣＮＴを剥離した。具体的には、鋭利部を備えたプラスチック製のヘラを使用し、ＣＮＴを剥離した（回収工程）。なお、剥離時には、ヘラの鋭利部をＣＮＴと基材との境界に当て、基材からＣＮＴをそぎ取るように、基材面に沿って鋭利部を動かした。これにより、ＣＮＴを基材から剥ぎ取り、材料ＣＮＴを得た。
　得られた材料ＣＮＴを透過型電子顕微鏡（ＴＥＭ）で観察してＴＥＭ画像を得て、材料ＣＮＴの平均直径および単層ＣＮＴの割合を求めた。結果を表１に示す。 <Recovery of material CNT>
Thereafter, the CNTs grown on the catalyst layer were peeled off from the surface of the catalyst support. Specifically, a plastic spatula with a sharp part was used to peel off the CNTs (recovery step). Note that during peeling, the sharp part of the spatula was applied to the boundary between the CNTs and the base material, and the sharp part was moved along the surface of the base material so as to scrape off the CNTs from the base material. As a result, the CNTs were peeled off from the base material to obtain material CNTs.
The obtained material CNT was observed with a transmission electron microscope (TEM) to obtain a TEM image, and the average diameter of the material CNT and the proportion of single-walled CNT were determined. The results are shown in Table 1.
［酸化処理］
　得られた材料ＣＮＴ０．１ｇを、２５０ｍＬの３９質量％（７．７Ｍ）の硝酸（ＨＮＯ３）水溶液（ｐＨ０以下）中に添加して混合液とした。この混合液を室温（約２５℃）で８時間撹拌した。さらに、マントルヒーターのヒーター温度を１２５℃に昇温して液温が１００℃の状態で６時間還流して、混合液中に含まれる材料ＣＮＴを酸化処理することにより、酸化ＣＮＴを含む混合液（粗分散液）を得た。 [Oxidation treatment]
0.1 g of the obtained material CNT was added to 250 mL of a 39 mass % (7.7 M) nitric acid (HNO 3 ) aqueous solution (pH 0 or less) to prepare a mixed solution. This mixture was stirred at room temperature (approximately 25°C) for 8 hours. Furthermore, by increasing the heater temperature of the mantle heater to 125°C and refluxing the liquid at 100°C for 6 hours to oxidize the CNT material contained in the mixed liquid, a mixed liquid containing oxidized CNT is added. (crude dispersion) was obtained.
［酸化ＣＮＴの分散処理］
　得られた酸化ＣＮＴを含む混合液に対して、脱イオン交換水１８００ｍＬを添加して希釈した。この希釈液を１５分間静置して酸化ＣＮＴを沈殿させた後、上澄み液を除去した。その後、脱イオン交換水を加えて液量を１８００ｍＬとした。得られた液に対して、中和剤として０．１％アンモニア水溶液を添加して液のｐＨを７．１に調整した。そして、超音波照射機（本多電子製、製品名「ＷＴＣ－１２００－４０」）で２時間超音波処理（発振周波数４０ｋＨｚ、高周波出力１２００Ｗ）を行い、酸化ＣＮＴ分散液を得た。 [Dispersion treatment of oxidized CNT]
The obtained mixed solution containing oxidized CNTs was diluted by adding 1800 mL of deionized exchange water. After this diluted solution was allowed to stand for 15 minutes to precipitate oxidized CNTs, the supernatant solution was removed. Thereafter, deionized exchanged water was added to bring the liquid volume to 1800 mL. A 0.1% ammonia aqueous solution was added as a neutralizing agent to the obtained liquid to adjust the pH of the liquid to 7.1. Then, ultrasonic treatment (oscillation frequency 40 kHz, high frequency output 1200 W) was performed for 2 hours using an ultrasonic irradiator (manufactured by Honda Electronics, product name "WTC-1200-40") to obtain an oxidized CNT dispersion.
　得られた酸化ＣＮＴ分散液の一部を測定用に分取した。分取した酸化ＣＮＴ分散液中の酸化ＣＮＴをろ取し、８０℃で１時間乾燥させて、溶媒を除去した。そして、溶媒除去後の酸化ＣＮＴについてＴＥＭ画像およびＳＥＭ画像を得て、酸素原子比率、平均積層数および平均長さを求め、扁平率を算出した。結果を表１に示す。 A portion of the obtained oxidized CNT dispersion was taken for measurement. The oxidized CNTs in the separated oxidized CNT dispersion were collected by filtration and dried at 80° C. for 1 hour to remove the solvent. Then, a TEM image and a SEM image were obtained for the oxidized CNTs after the solvent was removed, and the oxygen atomic ratio, average number of stacked layers, and average length were determined, and the oblateness was calculated. The results are shown in Table 1.
＜ＣＮＴの評価結果＞
　上記の測定値の結果から、上記で得られた酸化ＣＮＴ分散液に含まれる酸化ＣＮＴは、扁平単層カーボンナノチューブ積層構造体の形状を有していたことが示され、本発明に係るカーボンナノチューブ積層構造体に該当していたと評価することができた。なお、本実施例の方法で得られる酸化ＣＮＴ分散液のＴＥＭ画像の例を、図２および３に示す。図２および３のＴＥＭ画像は、酸化ＣＮＴ分散液をＴＥＭ観察用グリッドメッシュ上に滴下し、膜状に乾燥させて形成したＣＮＴ膜を、ＴＥＭで観察することによって得た画像である。図２では、破線の四角で囲った部分に層状構造が観察されるので、カーボンナノチューブ積層構造体が形成されたことを確認することができる。図３では、破線の四角で示される複数の層状構造が互いに交差していること（矢印）が観察されるので、複数のカーボンナノチューブ積層構造体が互いに交差していることを確認することができる。 <CNT evaluation results>
From the results of the above measurement values, it was shown that the oxidized CNTs contained in the oxidized CNT dispersion obtained above had the shape of a flat single-walled carbon nanotube laminate structure, and the carbon nanotubes according to the present invention It was possible to evaluate that it corresponded to a laminated structure. Note that examples of TEM images of the oxidized CNT dispersion obtained by the method of this example are shown in FIGS. 2 and 3. The TEM images in FIGS. 2 and 3 are images obtained by observing with a TEM a CNT film formed by dropping an oxidized CNT dispersion onto a TEM observation grid mesh and drying it into a film. In FIG. 2, a layered structure is observed in the area surrounded by the broken line square, so it can be confirmed that a carbon nanotube stacked structure has been formed. In Figure 3, it can be observed that multiple layered structures indicated by dashed squares intersect with each other (arrows), so it can be confirmed that multiple carbon nanotube stacked structures intersect with each other. .
＜抵抗変化型記憶装置の作製＞
　上記で得られた酸化ＣＮＴ分散液を用いて、図１０に示したフローチャートに従って、抵抗変化型記憶装置を作製した。まず、シリコン基板３５０を用意し（図１０（ａ））、シリコン基板３５０上に絶縁膜３５１としてのＳｉＯ２層を形成した（図１０（ｂ））。次いで、下部電極３５２としてのＴｉＮ層をＳｉＯ２層の上に形成し（図１０（ｃ））、ＥＢリソグラフィー法およびドライエッチング法によってＴｉＮ層をピラー状にパターニングした（図１０（ｄ））。ピラー状の電極の断面積は２００ｎｍ×２００ｎｍとした。続いて、ピラー状にパターニングしたＴｉＮ層上に絶縁膜３５３としてのＳｉＯ２層を形成した（図１０（ｅ））。次に、ＣＭＰ法を用いて、ＳｉＯ２層の表面を研磨して、ピラー状のＴｉＮ層を表面に露出させた（図１０（ｆ））。続いて、上記で得られた酸化ＣＮＴ分散液をＴｉＮ層上に塗布して抵抗変化層３５４としてのカーボンナノチューブ層を形成した（図１０（ｇ））。その後、カーボンナノチューブ層上に上部電極３５５としてのＴｉＮ層を形成した（図１０（ｈ））。そして、ＴｉＮ層およびカーボンナノチューブ層を、図８に示したＲＬＳＡ装置３００を用いたマイクロ波励起（２．４５ＧＨｚ）プラズマにより、上部電極３５５としてのＴｉＮ層およびカーボンナノチューブ層をパターニングして素子分離させた（図１０（ｉ））。上部電極３５５の面積は１２０μｍ×２００μｍとした。続いて、素子分離されたＴｉＮ層およびカーボンナノチューブ層を覆うように、保護膜３５６としてのＳｉＮｘ層を形成した（図１０（ｊ））。最後に、上部電極３５５としてのＴｉＮ層およびカーボンナノチューブ層の上方にてＳｉＮｘ層を貫通して上部電極３５５としてのＴｉＮ層を露出する貫通孔３５７を形成するとともに、上部電極３５５としてのＴｉＮ層およびカーボンナノチューブ層が存在しない部分において、保護膜３５６としてのＳｉＮｘ層および絶縁膜３５３としてのＳｉＯ２層を貫通して下部電極３５２としてのＴｉＮ層を露出する貫通孔３５８を形成した（図１０（ｋ））。こうして、抵抗変化型記憶装置を作製した。図４は、本実施例の方法に基づいて作製した抵抗変化型記憶装置の下部電極３５２（ＴｉＮ層）、抵抗変化層３５４（カーボンナノチューブ層）、および上部電極３５５（ＴｉＮ層）を含む領域の断面の走査型電子顕微鏡（ＳＥＭ）画像の例を示す。抵抗変化層３５４の領域の全体に層状構造物が観察され、抵抗変化層３５４が全体的にカーボンナノチューブ積層構造体から構成されていることが確認できる。 <Production of resistance variable memory device>
Using the oxidized CNT dispersion obtained above, a resistance variable memory device was manufactured according to the flowchart shown in FIG. First, a silicon substrate 350 was prepared (FIG. 10(a)), and a SiO 2 layer was formed as an insulating film 351 on the silicon substrate 350 (FIG. 10(b)). Next, a TiN layer as a lower electrode 352 was formed on the SiO 2 layer (FIG. 10(c)), and the TiN layer was patterned into a pillar shape by EB lithography and dry etching (FIG. 10(d)). The cross-sectional area of the pillar-shaped electrode was 200 nm x 200 nm. Subsequently, a SiO 2 layer as an insulating film 353 was formed on the TiN layer patterned into a pillar shape (FIG. 10(e)). Next, the surface of the SiO 2 layer was polished using a CMP method to expose the pillar-shaped TiN layer on the surface (FIG. 10(f)). Subsequently, the oxidized CNT dispersion obtained above was applied onto the TiN layer to form a carbon nanotube layer as the variable resistance layer 354 (FIG. 10(g)). Thereafter, a TiN layer as an upper electrode 355 was formed on the carbon nanotube layer (FIG. 10(h)). Then, the TiN layer and the carbon nanotube layer as the upper electrode 355 are patterned by microwave-excited (2.45 GHz) plasma using the RLSA apparatus 300 shown in FIG. 8 to separate the elements. (Figure 10(i)). The area of the upper electrode 355 was 120 μm×200 μm. Subsequently, a SiN x layer was formed as a protective film 356 so as to cover the TiN layer and carbon nanotube layer that were separated into elements (FIG. 10(j)). Finally, a through hole 357 is formed above the TiN layer and carbon nanotube layer as the upper electrode 355 to penetrate the SiN x layer and expose the TiN layer as the upper electrode 355, and the TiN layer as the upper electrode 355 is And in a portion where the carbon nanotube layer does not exist, a through hole 358 was formed to penetrate the SiN x layer as the protective film 356 and the SiO 2 layer as the insulating film 353 and expose the TiN layer as the lower electrode 352 (Fig. 10 (k)). In this way, a resistance variable memory device was manufactured. FIG. 4 shows a region including a lower electrode 352 (TiN layer), a resistance variable layer 354 (carbon nanotube layer), and an upper electrode 355 (TiN layer) of a resistance variable memory device manufactured based on the method of this example. An example of a cross-sectional scanning electron microscope (SEM) image is shown. A layered structure is observed in the entire region of the variable resistance layer 354, and it can be confirmed that the variable resistance layer 354 is entirely composed of a laminated carbon nanotube structure.
＜抵抗変化型記憶装置の評価結果＞
　抵抗変化型記憶装置について０Ｖから７．０Ｖまでの電圧スイープにより電流－電圧（ＩＶ）曲線を測定した。抵抗変化層を流れる電流値に変化が見られ、高抵抗状態と低抵抗状態の２つの状態の切り替えが起きたときの電圧値をスイッチング電圧とした。結果を表１に示す。本実施例では、スイッチング電圧は、４．２Ｖという低い値であった。この結果から、本発明に係るカーボンナノチューブ積層構造体を抵抗変化層の形成材料として用いれば、低いスイッチング電圧で作動可能な電子素子を得ることができることが示された。 <Evaluation results of resistance variable memory device>
The current-voltage (IV) curve of the resistance variable memory device was measured by sweeping the voltage from 0V to 7.0V. A change was observed in the value of the current flowing through the variable resistance layer, and the voltage value when switching between two states, a high resistance state and a low resistance state, occurred was defined as the switching voltage. The results are shown in Table 1. In this example, the switching voltage was a low value of 4.2V. This result showed that by using the carbon nanotube stacked structure according to the present invention as a material for forming a variable resistance layer, it was possible to obtain an electronic device that can operate with a low switching voltage.
（比較例１）
　材料ＣＮＴの合成時に、材料ＣＮＴ合成用触媒として鉄薄膜（触媒層）の膜厚が１ｎｍの触媒担持体を用い、材料ＣＮＴの酸化処理における還流時間を２時間とし、酸化ＣＮＴの分散処理時に超音波処理を発振周波数２８ｋＨｚ、高周波出力７００Ｗの条件で行った以外は、実施例１と同様にして、酸化ＣＮＴ分散液の調製および抵抗変化型記憶装置の作製ならびに各種測定および評価を行った。結果を表１に示す。 (Comparative example 1)
During the synthesis of the material CNT, a catalyst support with a thin iron film (catalyst layer) of 1 nm in thickness was used as a catalyst for material CNT synthesis, the reflux time in the oxidation treatment of the material CNT was 2 hours, and the An oxidized CNT dispersion liquid was prepared, a resistance variable memory device was manufactured, and various measurements and evaluations were performed in the same manner as in Example 1, except that the sonication was performed at an oscillation frequency of 28 kHz and a high frequency output of 700 W. The results are shown in Table 1.
　酸化ＣＮＴのＴＥＭ画像に積層構造がほとんど観察されなかったので、得られた酸化ＣＮＴ分散液中で、カーボンナノチューブ積層構造体がほとんど形成されなかったと評価することができた。上記の測定値の結果から、上記で得られた酸化ＣＮＴ分散液に含まれる酸化ＣＮＴは、円筒状単層ＣＮＴの形状を有していたことが示され、本発明に係るカーボンナノチューブ積層構造体に該当しなかったと評価することができた。酸化ＣＮＴがこのような形状を呈した理由としては、恐らくは、ＣＮＴの酸化の程度が低かったことにより、ＣＮＴが扁平に潰れにくくなっていたことが考えられる。抵抗変化型記憶装置のスイッチング電圧を測定したところ、５．５Ｖという高い値であった。 Since almost no stacked structure was observed in the TEM image of the oxidized CNTs, it could be evaluated that almost no carbon nanotube stacked structure was formed in the obtained oxidized CNT dispersion. The results of the above measurement values indicate that the oxidized CNTs contained in the oxidized CNT dispersion obtained above had the shape of cylindrical single-walled CNTs, and the carbon nanotube laminate structure according to the present invention It was possible to evaluate that this was not the case. The reason why the oxidized CNTs took on such a shape is probably that the degree of oxidation of the CNTs was low, making it difficult for the CNTs to collapse into a flat shape. When the switching voltage of the resistance variable memory device was measured, it was found to be a high value of 5.5V.
（比較例２）
　材料ＣＮＴの合成時に、材料ＣＮＴ合成用触媒として鉄薄膜（触媒層）の膜厚が４ｎｍの触媒担持体を用い、酸化ＣＮＴの分散処理時に超音波処理を発振周波数２８ｋＨｚ、高周波出力７００Ｗの条件で行った以外は、実施例１と同様にして、酸化ＣＮＴ分散液の調製および抵抗変化型記憶装置の作製ならびに各種測定および評価を行った。結果を表１に示す。 (Comparative example 2)
During the synthesis of the material CNT, a catalyst support with an iron thin film (catalyst layer) having a thickness of 4 nm was used as a catalyst for material CNT synthesis, and during the dispersion treatment of the oxidized CNTs, ultrasonic treatment was performed at an oscillation frequency of 28 kHz and a high frequency output of 700 W. Except for the above, preparation of an oxidized CNT dispersion liquid, fabrication of a variable resistance memory device, and various measurements and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.
　酸化ＣＮＴのＴＥＭ画像に積層構造がほとんど観察されなかったので、得られた酸化ＣＮＴ分散液中で、カーボンナノチューブ積層構造体がほとんど形成されなかったと評価することができた。上記の測定値の結果から、上記で得られた酸化ＣＮＴ分散液に含まれる酸化ＣＮＴは、多層ＣＮＴの形状を有していたことが示され、本発明に係るカーボンナノチューブ積層構造体に該当しなかったと評価することができた。酸化ＣＮＴがこのような形状を呈した理由としては、触媒層の膜厚が厚かったことにより触媒活性がより強くなって過剰な反応が進行し、ＣＮＴの多層化が促進されたことが考えられる。抵抗変化型記憶装置のスイッチング電圧を測定したところ、５．８Ｖという高い値であった。 Since almost no stacked structure was observed in the TEM image of the oxidized CNTs, it could be evaluated that almost no carbon nanotube stacked structure was formed in the obtained oxidized CNT dispersion. The results of the above measurement values indicate that the oxidized CNTs contained in the oxidized CNT dispersion obtained above had the shape of multi-walled CNTs, which corresponds to the carbon nanotube layered structure according to the present invention. I was able to evaluate that there was no such thing. The reason why the oxidized CNTs took on this shape is thought to be that the thicker catalyst layer strengthened the catalytic activity, promoted excessive reaction, and promoted the multilayering of CNTs. . When the switching voltage of the resistance variable memory device was measured, it was found to be a high value of 5.8V.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
（表の注釈）
　「－」はカーボンナノチューブ積層構造体が観察されなかったことを示す。 (Table notes)
"-" indicates that no carbon nanotube stacked structure was observed.
　表１の結果から、本発明の範囲に属するカーボンナノチューブ積層構造体を抵抗変化層として用いれば、スイッチング電圧が十分低い抵抗変化型記憶装置を製造できることが示された。 The results in Table 1 indicate that by using a carbon nanotube stacked structure within the scope of the present invention as a variable resistance layer, a variable resistance memory device with a sufficiently low switching voltage can be manufactured.
　本発明によれば、電子素子の機能性領域（例、抵抗変化型記憶装置の抵抗変化層）として機能し、かつ、電子素子の機能性領域として用いた時に電子素子が低いスイッチング電圧で作動可能となる、カーボンナノチューブ膜を形成するために用いることが可能な、カーボンナノチューブ積層構造体およびカーボンナノチューブ分散液を提供することができる。
　また、本発明によれば、電子素子の機能性領域（例、抵抗変化型記憶装置の抵抗変化層）として機能し、かつ、電子素子の機能性領域として用いた時に電子素子が低いスイッチング電圧で作動可能となる、カーボンナノチューブ膜、電子素子製造用塗布液、および低いスイッチング電圧で作動可能な電子素子を提供することができる。 According to the present invention, the present invention functions as a functional region of an electronic device (e.g., a variable resistance layer of a variable resistance storage device), and when used as a functional region of an electronic device, the electronic device can operate at a low switching voltage. It is possible to provide a carbon nanotube stacked structure and a carbon nanotube dispersion that can be used to form a carbon nanotube film.
Further, according to the present invention, the electronic device functions as a functional region of an electronic device (e.g., a resistance variable layer of a resistance variable memory device), and when used as a functional region of an electronic device, the electronic device can operate at a low switching voltage. It is possible to provide a carbon nanotube film that can be operated, a coating liquid for manufacturing an electronic device, and an electronic device that can be operated at a low switching voltage.
１　入口パージ部
２　フォーメーションユニット
３　成長ユニット
４　冷却ユニット
５　出口パージ部
６　搬送ユニット
７～９　接続部
１０　製造装置
１２　基材
１３　成長炉
１４　加熱器
１５　ガス導入口
１６　ガス排出口
１００　製造装置
１０１～１０３　ガス混入防止手段
２００　ＳＷＰ装置
３００　ＲＬＳＡ装置
２０１，３０１　処理容器
２０２　蓋部
２０２ａ　マイクロ波放射孔
２０３，３０３　マイクロ波発生部
３０２　ラジアルラインスロットアンテナ
３０２ａ　アンテナ本体
３０２ｂ　マイクロ波放射孔
２５０，３５０　シリコン基板
３５１，３５３　絶縁膜
３５２　下部電極
３５４　抵抗変化層
３５５　上部電極
３５６　保護膜
３５７，３５８　貫通孔 1 Inlet purge section 2 Formation unit 3 Growth unit 4 Cooling unit 5 Outlet purge section 6 Transfer units 7 to 9 Connection section 10 Manufacturing device 12 Base material 13 Growth furnace 14 Heater 15 Gas inlet 16 Gas outlet 100 Manufacturing device 101 to 103 Gas mixing prevention means 200 SWP device 300 RLSA device 201, 301 Processing container 202 Lid 202a Microwave radiation holes 203, 303 Microwave generator 302 Radial line slot antenna 302a Antenna body 302b Microwave radiation holes 250, 350 Silicon substrate 351 , 353 Insulating film 352 Lower electrode 354 Resistance change layer 355 Upper electrode 356 Protective film 357, 358 Through hole

Claims (10)

  1. 　酸化扁平カーボンナノチューブが複数積層してなるカーボンナノチューブ積層構造体であって、カーボンナノチューブ積層構造体中の全てのカーボンナノチューブに対して単層カーボンナノチューブが占める割合が、カーボンナノチューブ１００本中５１本以上である、カーボンナノチューブ積層構造体。 A carbon nanotube laminate structure formed by laminating a plurality of oxidized flat carbon nanotubes, in which the ratio of single-walled carbon nanotubes to all carbon nanotubes in the carbon nanotube laminate structure is 51 or more out of 100 carbon nanotubes. A carbon nanotube stacked structure.
  2. 　酸化扁平カーボンナノチューブの直径方向の扁平率が、１０％以上４０％以下である、請求項１に記載のカーボンナノチューブ積層構造体。 The carbon nanotube laminate structure according to claim 1, wherein the oxidized flat carbon nanotubes have a diametrical oblateness of 10% or more and 40% or less.
  3. 　平均積層数が、２以上２０以下である、請求項１に記載のカーボンナノチューブ積層構造体。 The carbon nanotube layered structure according to claim 1, wherein the average number of layers is 2 or more and 20 or less.
  4. 　カーボンナノチューブ積層構造体の平均長さが、２０ｎｍ以上３００ｎｍ以下である、請求項１に記載のカーボンナノチューブ積層構造体。 The carbon nanotube laminate structure according to claim 1, wherein the average length of the carbon nanotube laminate structure is 20 nm or more and 300 nm or less.
  5. 　複数のカーボンナノチューブ積層構造体が、互いに交差している、請求項１に記載のカーボンナノチューブ積層構造体。 The carbon nanotube laminate structure according to claim 1, wherein the plurality of carbon nanotube laminate structures intersect with each other.
  6. 　請求項１～５のいずれかに記載のカーボンナノチューブ積層構造体と溶媒とを含むカーボンナノチューブ分散液。 A carbon nanotube dispersion comprising the carbon nanotube layered structure according to any one of claims 1 to 5 and a solvent.
  7. 　請求項６に記載のカーボンナノチューブ分散液を含む電子素子製造用塗布液。 A coating liquid for manufacturing electronic devices, comprising the carbon nanotube dispersion liquid according to claim 6.
  8. 　請求項１～５のいずれかに記載のカーボンナノチューブ積層構造体を含むカーボンナノチューブ膜。 A carbon nanotube film comprising the carbon nanotube laminate structure according to any one of claims 1 to 5.
  9. 　請求項８に記載のカーボンナノチューブ膜を含む電子素子。 An electronic device comprising the carbon nanotube film according to claim 8.
  10. 　前記電子素子が、抵抗変化型記憶装置であり、前記カーボンナノチューブ膜が、抵抗変化層として機能する、請求項９に記載の電子素子。
          10. The electronic device according to claim 9, wherein the electronic device is a variable resistance storage device, and the carbon nanotube film functions as a variable resistance layer.
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