WO2012029234A1 - Field effect transistor using carbon nanotubes, and method for producing said field effect transistor - Google Patents

Field effect transistor using carbon nanotubes, and method for producing said field effect transistor Download PDF

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WO2012029234A1
WO2012029234A1 PCT/JP2011/004434 JP2011004434W WO2012029234A1 WO 2012029234 A1 WO2012029234 A1 WO 2012029234A1 JP 2011004434 W JP2011004434 W JP 2011004434W WO 2012029234 A1 WO2012029234 A1 WO 2012029234A1
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carbon nanotube
field effect
effect transistor
carbon nanotubes
thin film
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PCT/JP2011/004434
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French (fr)
Japanese (ja)
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雄高 大野
東明 孫
エスコ カウピネン
マリナ ティメルマンス
アルバート ナシブリン
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国立大学法人名古屋大学
アールトユニバーシティ
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Publication of WO2012029234A1 publication Critical patent/WO2012029234A1/en

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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
    • B82Y10/00—Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K85/00—Organic materials used in the body or electrodes of devices covered by this subclass
    • H10K85/20—Carbon compounds, e.g. carbon nanotubes or fullerenes
    • H10K85/221—Carbon nanotubes
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K10/00—Organic devices specially adapted for rectifying, amplifying, oscillating or switching; Organic capacitors or resistors having a potential-jump barrier or a surface barrier
    • H10K10/40—Organic transistors
    • H10K10/46—Field-effect transistors, e.g. organic thin-film transistors [OTFT]
    • H10K10/462—Insulated gate field-effect transistors [IGFETs]
    • H10K10/484—Insulated gate field-effect transistors [IGFETs] characterised by the channel regions
    • H10K10/486—Insulated gate field-effect transistors [IGFETs] characterised by the channel regions the channel region comprising two or more active layers, e.g. forming pn heterojunctions

Definitions

  • the present invention relates to a field effect transistor in which a channel between a source and a drain is a carbon nanotube, and a manufacturing method thereof.
  • a thin film transistor is an electronic element essential for a flat display or the like, and amorphous silicon or polysilicon is used as a channel.
  • Development of a thin film transistor (CNT-TFT) using carbon nanotubes as a channel is also underway.
  • Patent Document 1 discloses a CNT-TFT having a structure in which a source and a drain are bridged by carbon nanotubes. CNT-TFTs are attracting attention because they can be manufactured on a flexible substrate such as plastic and can be reduced in cost and area.
  • carbon nanotubes are produced in a ratio of metal type and semiconductor type of 1: 2.
  • metal-type carbon nanotube is cross-linked between the source and the drain, it is not possible to obtain FET characteristics that pinch off due to current leakage. Therefore, it is conceivable to reduce the density of the carbon nanotubes and reduce the leakage of current, but there is a problem that the mobility is lowered. That is, the on / off characteristics and mobility of the FET are traded off.
  • an object of the present invention is to realize a field effect transistor using a carbon nanotube having excellent on / off characteristics and high mobility as a channel.
  • the first invention has a structure in which a carbon nanotube thin film chained in a network located in contact with an insulating film has a structure in which the source and the drain are cross-linked and has a length exceeding the channel length Lc between the source and the drain. Carbon nanotubes are substantially absent, and the average length Lcnt of carbon nanotubes is in the range of 1/20 to 1/3 times the channel length Lc.
  • the field effect transistor is characterized in that when the surface density is defined by ⁇ * (Lcnt) 2 where ⁇ is defined as ⁇ , the normalized carbon nanotube coverage is 5 to 15.
  • the average length of the carbon nanotubes can be regarded as a target length at the time of manufacturing, and is an average length after allowing for variations in manufacturing. Even if a carbon nanotube shorter than 1/20 of the channel length Lc is present, the on / off ratio of the field effect transistor is not greatly affected. However, if a carbon nanotube having a length exceeding the channel length Lc is present, a metal type carbon nanotube is present. Since the nanotube bridges the source and the drain, the on / off ratio rapidly decreases. Therefore, when the average length Lcnt of carbon nanotubes is in the range of 1/20 to 1/3 times the channel length Lc, some carbon nanotubes exist outside this range in a range shorter than the channel length Lc. It means you can do it.
  • the carbon nanotube having a length exceeding the channel length Lc between the source and the drain does not substantially exist is such that the on / off ratio of the field effect transistor is not lowered by a short circuit due to the metallic carbon nanotube between the source and the drain.
  • the on / off ratio can be increased without reducing the mobility of the field effect transistor.
  • the average length Lcnt is in the range of 1/20 to 1/5 times the channel length Lc, and the standardized carbon nanotube coverage is 5 to 15 without reducing the mobility. A more desirable range is to increase the on / off ratio.
  • Lcnt / Lc is preferably 1/20 or more and 1/3 or less. In order not to lower the on / off ratio of the field effect transistor, it is more desirable that the average length Lcnt is 1/5 or less of the channel length Lc. Therefore, a range where Lcnt / Lc is 1/20 or more and 1/5 or less is a more desirable range.
  • the relationship between the channel length Lc and the average length Lcnt of the carbon nanotubes only needs to be a relationship that eliminates the connection between the source and the drain due to the connection of only the metallic carbon nanotubes. If at least one semiconductor-type carbon nanotube exists in the connecting chain of the carbon nanotubes connecting the source and the drain, on / off characteristics can be obtained with respect to the connecting chain. Therefore, the ratio between the length Lcnt of the carbon nanotube and the channel length Lc is important. There is an optimum channel length Lc range for a certain carbon nanotube length Lcnt, and conversely there is an optimum average carbon nanotube length Lcnt range for a certain channel length Lc.
  • the channel length Lc is not particularly limited, but the channel length Lc is preferably 10 to 200 ⁇ m. Further, the channel length Lc is preferably 30 to 200 ⁇ m and 40 to 100 ⁇ m. If the channel length Lc is smaller than 10 ⁇ m, it is difficult to manufacture with the current manufacturing technology. If the channel length Lc exceeds 200 ⁇ m, the response speed is lowered and the element becomes larger, which is not desirable.
  • the channel length Lc of 30 to 200 ⁇ m is a desirable range for increasing the mobility and the on / off ratio with respect to the average length Lcnt of easy-to-manufacture carbon nanotubes (for example, 10 ⁇ m).
  • the standardized degree of coverage represents the degree of approach of the carbon nanotubes or the frequency of crossing.
  • the standardized coverage is a value from which the influence of the average length Lcnt of the carbon nanotube is excluded. If the coverage is less than 5, it contributes to the improvement of the on / off ratio, but it is not desirable because the density of the carbon nanotubes constituting the channel becomes too small and the current capacity decreases. On the other hand, if the degree of coverage exceeds 15, the number of intersections of the carbon nanotubes increases, and the on-time mobility decreases, which is not desirable. Therefore, the coverage is preferably 5 or more and 15 or less. A more desirable range of the coverage is in the range of 7 or more and 10 or less.
  • the on / off ratio of the field effect can be increased and the on-time mobility is not lowered.
  • the average length Lcnt of the carbon nanotubes may be in the range of 1/10 to 1/5 times the channel length Lc, and the standardized coverage of the carbon nanotubes may be 7 to 10. In this range, the on / off ratio and the mobility are further increased.
  • the carbon nanotubes may be coated with F 4 TCNQ (2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane).
  • F 4 TCNQ 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane
  • the thickness of the carbon nanotube is preferably 1.1 nm or less.
  • the on / off ratio of the field effect transistor can be increased in a wide range of the drain-source voltage. Therefore, the working voltage range of the field effect transistor can be expanded.
  • the field effect transistor has an element structure formed on a flexible plastic substrate. It can be used as a gate transistor for controlling a pixel of a flexible flat display, and a thin film display can be easily realized.
  • the invention of a manufacturing method is a method of manufacturing a field effect transistor having a structure in which a carbon nanotube thin film chained in a network located in contact with an insulating film bridges a channel between a source and a drain.
  • an element structure consisting of a carbon nanotube thin film that connects the source, drain, and the channel between the source and drain, and an insulating film that insulates and separates the gate and the gate from the carbon nanotube thin film is formed, and carbon nanotubes are generated by the floating catalyst method.
  • the generated carbon nanotubes are collected in a filter to form a thin film, and the carbon nanotube thin film collected in the filter is transferred onto the channel.
  • a gate is formed on a substrate, an insulating film is formed on the gate and a substrate not covered with the gate, and a source is separated from the insulating film by the length of the channel,
  • a method of forming the drain and transferring the carbon nanotube thin film collected by the filter onto the channel on the insulating film can be employed. Further, the carbon nanotube thin film collected by the filter is transferred onto the channel region on the substrate, and the source and drain are formed so as to bridge the carbon nanotubes at the ends separated by the channel length of the carbon nanotube thin film.
  • An insulating film may be formed on the nanotube thin film, the source, and the drain, and a gate may be formed on the insulating film and on the channel.
  • the carbon nanotube thin film collected on the filter is transferred so that the source and drain are formed on the substrate, and the channel between the source and drain is bridged, and the carbon nanotube thin film, the source and the drain are formed on the substrate.
  • an insulating film may be formed, and a gate may be formed on the insulating film and above the channel.
  • Carbon nanotubes are generated by floating catalyst method and collected in a filter, a carbon nanotube thin film is formed on the filter, and the thin film is transferred to the channel region, thereby easily controlling the length and density of the carbon nanotube.
  • a thin film can be used as a channel, and uniform and uniform element characteristics can be obtained.
  • the floating catalyst method is a method in which a raw material gas (for example, CO gas, hydrocarbon gas, etc.) and a catalyst (for example, ferrocene) are flowed into a reaction furnace to grow carbon nanotubes in the space.
  • a raw material gas for example, CO gas, hydrocarbon gas, etc.
  • a catalyst for example, ferrocene
  • the carbon nanotubes grown in this space are accumulated on a filter (for example, a cloth-like object such as nitrocellulose) to form a carbon nanotube thin film on the filter.
  • the carbon nanotube thin film is transferred onto a channel of a transistor element having a source, drain, and gate manufactured separately.
  • the filter can be removed after the transfer of the carbon nanotube thin film or dissolved by an organic solvent (acetone or the like).
  • the average length Lcnt of the carbon nanotube is 1/20 to 1/3 times the channel length Lc.
  • the standardized carbon nanotube coverage is defined as ⁇ * (Lcnt) 2 where ⁇ is the surface density of the carbon nanotube thin film, the standardized carbon nanotube coverage is 5-15. Is desirable.
  • the average length Lcnt of the carbon nanotubes is in the range of 1/20 to 1/5 times the channel length Lc.
  • the surface density of the carbon nanotube thin film can be controlled by the collection time in the filter.
  • a field effect transistor having a high on / off ratio and good characteristics can be uniformly and uniformly manufactured.
  • the average diameter of the carbon nanotubes can be determined by controlling the temperature at the time of forming the carbon nanotubes.
  • a field effect transistor having a large on / off ratio can be easily and uniformly manufactured over a wide range of voltages between the source and drain.
  • the average diameter of the carbon nanotubes can control the ratio of carbon dioxide gas added to the raw material gas added during the formation of the carbon nanotubes.
  • a field effect transistor having a large on / off ratio can be easily and uniformly manufactured over a wide range of voltages between the source and drain.
  • the average diameter of the carbon nanotubes be 1.1 nm or less.
  • a field effect transistor having a large on / off ratio can be easily and uniformly manufactured over a wide range of voltages between the source and drain.
  • the temperature at the time of forming the carbon nanotube is desirably 825 ° C. or lower.
  • the average diameter of the carbon nanotube with which the characteristic of a field effect transistor becomes favorable can be 1.1 nm or less.
  • the channel length Lc, the average length Lcnt of carbon nanotubes, and the coverage of standardized carbon nanotubes are set within the ranges shown in the present invention.
  • the field effect transistor can be realized.
  • a field effect transistor using a carbon nanotube thin film as a channel which has excellent on-off characteristics and high mobility, can be easily and uniformly manufactured.
  • FIG. 4 shows a configuration of a CNT-TFT of Example 1.
  • FIG. 4 is a view showing a manufacturing process of the CNT-TFT of Example 1.
  • FIG. 4 is a view showing a manufacturing process of the CNT-TFT of Example 1.
  • FIG. 4 is a view showing a manufacturing process of the CNT-TFT of Example 1.
  • the SEM image which showed the structure of the carbon nanotube thin film 11 in collection time 10 second.
  • the graph which showed the relationship between the standardized coverage and m. 3 is a graph showing Id-Vgs characteristics of the CNT-TFT of Example 1.
  • 6 is a graph showing Id-Vds characteristics of the CNT-TFT of Example 1.
  • the graph which showed the Id-Vgs characteristic of CNT-TFT The graph which showed the Id-Vgs characteristic of CNT-TFT.
  • the graph which showed the Id-Vgs characteristic of CNT-TFT The graph which showed the Id-Vgs characteristic of CNT-TFT.
  • Wavelength absorption characteristics showing the relationship between the flow rate of carbon dioxide gas and the diameter of carbon nanotubes in the production of CNT-TFTs Wavelength absorption characteristics showing the relationship between carbon nanotube formation temperature and diameter in the production of CNT-TFTs.
  • FIG. 1 is a diagram showing the configuration of a thin film transistor (CNT-TFT) using carbon nanotubes of Example 1.
  • the CNT-TFT has a resin film substrate 21 made of PEN (polyethylene naphthalate) and having a thickness of 125 ⁇ m.
  • a flexible plastic substrate other than PEN may be used as the resin film substrate.
  • a gate electrode 22 made of Ti / Au Ti film thickness 10 nm, Au film thickness 100 nm
  • An insulating film 23 made of Al 2 O 3 and having a thickness of 40 nm is formed continuously on the gate electrode 22 and the resin film 21.
  • a source electrode 24 and a drain electrode 25 are separately formed on the insulating film 23 in a region sandwiching the gate electrode 22 in plan view.
  • the source electrode 24 and the drain electrode 25 are made of Ti / Au (Ti film thickness 10 nm, Au film thickness 150 nm).
  • the carbon nanotube thin film 11 having a structure for bridging the source electrode 24 and the drain electrode 25 is formed.
  • CNT-TFTs having seven types of channel lengths Lc of 5 ⁇ m, 10 ⁇ m, 20 ⁇ m, 30 ⁇ m, 40 ⁇ m, 50 ⁇ m, and 100 ⁇ m were manufactured.
  • the carbon nanotube thin film 11 has a structure in which carbon nanotubes having an average length Lcnt of 10 ⁇ m are chained in a network.
  • the bonding shape of the individual carbon nanotubes the Y-shaped bonding shape is more dominant than the X-shaped bonding.
  • carbon nanotubes were generated using a floating catalyst method and collected using a filter 10 to form a carbon nanotube thin film 11 chained in a network on the filter 10 (FIG. 2.A).
  • the growth temperature was 825 ° C.
  • CO was used as the carbon source
  • ferrocene was used as the catalyst.
  • the flow rate of CO gas was 400 sccm.
  • the filter 10 was a membrane filter made of nitrocellulose having a diameter of 25 mm and a pore diameter of 400 nm.
  • the density of the carbon nanotube thin film 11 can be controlled by the time for collecting the carbon nanotubes by the filter 10.
  • the average length Lcnt of the carbon nanotubes can be controlled by the growth temperature, gas flow rate, and the like.
  • the gate electrode 22, the insulating film 23, the source electrode 24, and the drain electrode 25 were sequentially formed on the resin film substrate 21. These can be formed by vapor deposition, printing, lithography, or the like.
  • the structure in which the gate electrode 22, the insulating film 23, the source electrode 24, and the drain electrode 25 are formed on the resin film substrate 21 is referred to as an element substrate 20 (hereinafter simply referred to as “substrate”). Therefore, the substrate 20 has a structure in which the carbon nanotube thin film 11 is removed from the CNT-TFT shown in FIG.
  • the bonded filter 10 may be simply peeled off.
  • the carbon nanotube thin film 11 can be transferred onto the surface of the substrate 20 on the side where the source electrode 24 and the drain electrode 25 are formed by the action of intermolecular force.
  • the CNT-TFT shown in FIG. 1 is manufactured by removing the carbon nanotube thin film 11 other than the channel region by photolithography and etching.
  • Etching can be performed, for example, by using oxygen plasma when performed in a vacuum, and can be performed by irradiating ultraviolet rays, for example, in an ozone atmosphere when performed at atmospheric pressure.
  • FIG. 3 is an SEM image of the carbon nanotube thin film 11. Each SEM image has a different collection time by the filter 10, and FIG. A is 10 seconds, FIG. B is 7 seconds, FIG. C is 5 seconds, FIG. D is 4 seconds, FIG. E is 3 seconds, FIG. F is 2 seconds. As shown in FIG. 3, it can be seen that the shorter the collection time, the smaller the density of the carbon nanotubes. In addition, it can be seen that the shorter the collection time, the smaller the X-shape and the more the Y-shape in the bonded shape of the carbon nanotubes. When the collection time was 2 seconds, 4 seconds, and 10 seconds, the abundance ratios of Y-shaped carbon nanotubes were 65%, 62%, and 47%, respectively.
  • the contact area between the carbon nanotubes is wider and the contact resistance is lower than in the X-shaped bond, so that the mobility is improved. Therefore, it is desirable that the carbon nanotube thin film constituting the channel is dominated by Y-shaped carbon nanotubes. Therefore, there is an optimal time for collection. From the above, the ratio of carbon nanotubes with Y-shaped bonds is desirably 62% or more or 65% or more.
  • FIG. 4 is a graph showing the relationship between the channel length Lc of the CNT-FET and the on-current and off-current. The plotted point represents the average value of the measured values of a large number of samples. Both the horizontal and vertical axes are logarithmic scales.
  • FIG. A is shown in FIG. 4 when the collection time by the filter 10 is 10 seconds.
  • FIG. C is the case of 2 seconds.
  • the normalized coverage is defined by assuming that the surface density (number of carbon nanotubes contained per unit area) of the carbon nanotube thin film 11 is ⁇ (unit: ⁇ m ⁇ 2 ) and the length of the carbon nanotube is Lcnt (unit: ⁇ m). , ⁇ * (Lcnt) 2 . Since ⁇ is the number of carbon nanotubes per unit area, when ⁇ is the same, the shorter the length Lcnt of the carbon nanotubes, the smaller the degree of approach of the carbon nanotubes (the longer the separation distance). . Therefore, by setting the number of carbon nanotubes per area (Lcnt) 2 as a standardized coverage, the standardized coverage may indicate the degree of approach of the carbon nanotubes or the frequency of crossing. it can.
  • the range of the normalized carbon nanotube coverage of the present invention in the range of 5 to 15 and 7 to 10 is The on / off ratio can be increased regardless of the length of the carbon nanotube and the channel length.
  • M is the slope of the straight line in the graph of FIG.
  • m is a substantially constant small value.
  • the plot points in FIG. 5 are represented so that the measured m in FIG. 4 is located on the theoretical curve in FIG.
  • the slope when the transistor is on and the slope when it is off are different, as shown in FIG. When plotted on the basis, the normalized coverage is different even for the same sample.
  • FIG. 1 In the case of A, the on-current m is 1.05 and the off-current m is 1.3, and there is no significant difference in the value of m.
  • the on-off ratio is about 10 and does not depend much on the channel length Lc.
  • the on-off ratio is approximately when Lc is 10 ⁇ m. When it is 10, 100 ⁇ m, it is about 10 2, which is a low value.
  • the value of m of the off current is small, the on / off ratio is also low. This is because the collection time by the filter 10 is long, so that ⁇ is high, and the standardized coverage is a large value. As a result, m is a small value as shown in FIG.
  • FIG. 1 When the collection time by the filter 10 is short as in C, when the average length Lcnt of the carbon nanotubes is 10 ⁇ m and the channel length Lc is 5 to 20 ⁇ m, the metal-type carbon nanotubes bridge between the source and the drain. As a result, the on / off ratio is about 10 to 10 2, which is worse. Further, when the channel length Lc is 100 ⁇ m or more, the off-current has a limit value generated by the heat conduction of the carbon nanotube, and the off-current cannot be further reduced. Further, when the channel length Lc is 30 to 50 ⁇ m, a value predicted based on the percolation theory is taken.
  • the upper limit of the channel length Lc is 100 ⁇ m, but it is presumed that the on / off ratio is a good value of 10 6 or more even if it is 100 ⁇ m or more.
  • the channel length Lc is larger than 200 ⁇ m, the response speed is lowered or the element size becomes too large.
  • said characteristic is a characteristic when the average length Lcnt of a carbon nanotube is 10 micrometers. The average length Lcnt and the channel length Lc of the carbon nanotubes have a similar relationship that the same characteristics can be obtained if the ratios are the same.
  • the above characteristics can be obtained by shortening the channel length Lc according to the ratio. For this reason, even if the channel length Lc is shortened to the production limit, the above-described characteristics with a large on / off ratio can be obtained by shortening the average length Lcnt of the carbon nanotubes in proportion thereto.
  • the on / off ratio of the CNT-TFT can be improved by the normalized coverage, channel length Lc, and carbon nanotube length Lcnt.
  • the normalized coverage can be achieved by controlling the density ⁇ during the collection time by the filter 10 and controlling the average length Lcnt of the carbon nanotubes by controlling the growth temperature and the gas flow rate when the carbon nanotubes are generated. Specifically, when the normalized coverage is 5 to 15, the average length Lcnt of carbon nanotubes is 10 ⁇ m, the channel length Lc is 30 to 200 ⁇ m, and Lcnt is 1/20 to 1/3 times Lc. Thus, a CNT-TFT having an on / off ratio of 10 3 or more can be realized.
  • Lcnt to 1/20 to 1/3 times Lc prevents a decrease in mobility and reduces the probability that the metal-type carbon nanotube is bridged between the source and the drain, thereby preventing current leakage. Because.
  • the average length Lcnt of the carbon nanotube is 10 ⁇ m
  • the channel length Lc is 30 to 200 ⁇ m
  • Lcnt is 1 / L of Lc. 20 to 1/5 times.
  • the channel length Lc is 40 to 100 ⁇ m
  • Lcnt is 1/10 to 1/5 times Lc.
  • the normalized coverage is 7 to 10
  • the channel length Lc is 40 to 100 ⁇ m
  • Lcnt is 1/10 to 1/5 times Lc.
  • the standardized coverage is 9 to 10
  • the channel length Lc is 90 to 100 ⁇ m
  • Lcnt is 0.1 to 0.15 times Lc.
  • the normalized coverage is a value from which the influence of the average length Lcnt of the carbon nanotubes has been eliminated, and thus the above characteristics are independent of the length of the carbon nanotubes and the channel length. It can be obtained by a standard range of coverage. Accordingly, the range of the coverage of the standardized carbon nanotube of the present invention of 5 to 15 and 7 to 10 is a range in which the on / off ratio can be increased regardless of the length of the carbon nanotube and the channel length.
  • the structure of the TFT is not limited to that of the first embodiment. If the carbon nanotube thin film chained in a network located in contact with the insulating film has a structure in which the source and the drain are bridged, Any structure may be used. For example, a gate is formed on a substrate, an insulating film is formed on the gate and a substrate not covered with the gate, and a source and a drain are formed on the insulating film by a length of a channel, and the filter is formed. The collected carbon nanotube thin film can be transferred onto the channel on the insulating film.
  • the carbon nanotube thin film collected by the filter is transferred onto the channel region on the substrate, and the source and drain are formed so as to bridge the carbon nanotubes at the ends separated by the channel length of the carbon nanotube thin film.
  • An insulating film can be formed on the nanotube thin film, the source, and the drain, and a gate can be formed on the insulating film and above the channel.
  • the carbon nanotube thin film collected on the filter is transferred so that the source and drain are formed on the substrate, and the channel between the source and drain is bridged, and the carbon nanotube thin film, the source and the drain are formed on the substrate.
  • an insulating film may be formed, and a gate may be formed on the insulating film and above the channel.
  • a flexible TFT is realized using PEN as a substrate, but a conventionally used substrate such as a Si substrate may be used.
  • the thickness dependence of the carbon nanotube was considered.
  • the thickness of the carbon nanotube was controlled by adjusting the concentration of carbon dioxide in the carbon nanotube production method using the floating catalyst method shown in Example 1.
  • FIG. 8 is a diagram showing the Ids-Vgs characteristics of the CNT-TFT when the thickness (diameter) of the carbon nanotube is 1.1 nm.
  • FIG. 9 is a diagram showing Ids-Vgs characteristics of the CNT-TFT when the thickness of the carbon nanotube is 1.6 nm.
  • the on / off ratio when Vds is ⁇ 0.5V is on the order of 10 8
  • the on / off ratio when Vds is ⁇ 5V is 10 7 is of the order
  • the difference between the on-off ratio is 10 to 10 2 about.
  • the wavelength absorption characteristics of the carbon nanotubes obtained when the carbon dioxide concentration was changed were measured.
  • the results are shown in FIG.
  • the diameter of the carbon nanotube can be measured from the wavelength of the absorption peak of this wavelength absorption characteristic.
  • the flow rate of CO 2 gas is 0, 1, 2, 3 , 4 cm 3 / min, and the flow rate ratio to CO gas (CO 2 / CO) is 0, 2.5 ⁇ 10 ⁇ 3 , 7.5 ⁇ 10 ⁇ 3 , It can be seen that the diameters of the carbon nanotubes obtained at 1.0 ⁇ 10 ⁇ 2 are 1.1, 1.2, 1.3, 1.6, and 1.9 nm, respectively.
  • the diameter of the carbon nanotubes increases as the CO 2 gas flow rate ratio relative to the CO gas increases.
  • the CO 2 gas flow rate ratio to the CO gas is 2.5 ⁇ 10 ⁇ 3 or less. It is desirable to do.
  • the wavelength absorption characteristics of the carbon nanotubes obtained when the temperature during formation was changed were measured.
  • the results are shown in FIG. From the wavelength of the absorption peak of this wavelength absorption characteristic, the diameter of the carbon nanotube can be measured.
  • the forming temperatures are 800, 825, 850, and 900 ° C.
  • the diameters of the obtained carbon nanotubes are 1.0, 1.1, 1.2, and 1.3 nm, respectively. It is understood that the higher the formation temperature, the larger the diameter of the carbon nanotube.
  • the diameter of the carbon nanotube can be controlled even when the diameter is 1.1 nm or less.
  • the threshold voltage of the CNT-TFT of Example 1 can be controlled by the following means. It spin-coats a solution containing F 4 TCNQ (2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane), so that the carbon nanotubes that are channels of the CNT-TFT are formed with F 4 TCNQ. Coating and spin coating the solution to control the concentration of F 4 TCNQ. F 4 TCNQ acts as a p-type dopant for carbon nanotubes.
  • F 4 TCNQ acts as a p-type dopant for carbon nanotubes.
  • FIG. 10 also shows the case where the F 4 TCNQ solution is not spin-coated. As shown in FIG. 10, the threshold voltage increases as the concentration of F 4 TCNQ is increased.
  • the concentration of F 4 TCNQ is 0.01 to 0.04 mMol / l
  • the CNT-TFT can be quickly turned on and off, whereas when the concentration of F 4 TCNQ is 0.08 mMol / l. It can be seen that the CNT-TFT is not capable of prompt on / off operation. From this, it is considered that the concentration of F 4 TCNQ is desirably controlled in the range of 0.01 mMol / l or more and 0.04 mMol / l or less.
  • the threshold voltage of the CNT-TFT of Example 1 is controlled by controlling the F 4 TCNQ concentration of the carbon nanotube when the carbon nanotube is coated with F 4 TCNQ by spin coating of the F 4 TCNQ solution. Can be done.
  • the present invention can be used as a TFT used in a display or electronic paper.

Abstract

[Problem] To obtain a CNT-TFT having a high ON/OFF ratio and mobility. [Solution] As illustrated in figure 1, a CNT-TFT has, on an insulating film (23), a carbon nanotube thin film (11) formed so as to bridge a source electrode (24) and a drain electrode (25). The carbon nanotube thin film (11) has a structure in which carbon nanotubes are linked in the form of a network. The channel length (Lc) is 30 to 200 µm, the length (Lcnt) of the carbon nanotubes is 1/20 to 1/5 of Lc, and the coverage (ρ*(Lcnt)2) of the standardized carbon nanotube is 5 to 15, wherein ρ represents the surface density of the carbon nanotube thin film (11).

Description

カーボンナノチューブを用いた電界効果トランジスタ及びその製造方法Field effect transistor using carbon nanotube and method for manufacturing the same
　本発明は、ソースとドレイン間のチャネルをカーボンナノチューブとした電界効果トランジスタ及びその製造方法に関する。 The present invention relates to a field effect transistor in which a channel between a source and a drain is a carbon nanotube, and a manufacturing method thereof.
　薄膜トランジスタ（ＴＦＴ）は平面ディスプレイなどに必須の電子素子であり、チャネルとしてアモルファスシリコンやポリシリコンが用いられている。また、チャネルとしてカーボンナノチューブを用いた薄膜トランジスタ（ＣＮＴ－ＴＦＴ）の開発も進められている。たとえば特許文献１には、ソースとドレイン間をカーボンナノチューブによって架橋した構造のＣＮＴ－ＴＦＴが示されている。ＣＮＴ－ＴＦＴは、プラスチックなどのフレキシブルな基板上に作製することができ、低コスト化、大面積化が可能なため注目されている。 A thin film transistor (TFT) is an electronic element essential for a flat display or the like, and amorphous silicon or polysilicon is used as a channel. Development of a thin film transistor (CNT-TFT) using carbon nanotubes as a channel is also underway. For example, Patent Document 1 discloses a CNT-TFT having a structure in which a source and a drain are bridged by carbon nanotubes. CNT-TFTs are attracting attention because they can be manufactured on a flexible substrate such as plastic and can be reduced in cost and area.
特開２００９－２３１６３１JP2009-231631
　現在知られているカーボンナノチューブの製造方法によると、カーボンナノチューブは金属型と半導体型が１：２の割合で生成されることが知られている。しかし、金属型のカーボンナノチューブがソースとドレイン間に架橋されてしまうと、電流のリークのためピンチオフするＦＥＴ特性を得ることができない。そこで、カーボンナノチューブの密度を小さくし、電流のリークを減らすことが考えられるが、それでは移動度が低下してしまうという問題がある。つまり、ＦＥＴのオンオフ特性と移動度とがトレードオフになっている。 According to the currently known carbon nanotube production method, it is known that carbon nanotubes are produced in a ratio of metal type and semiconductor type of 1: 2. However, if the metal-type carbon nanotube is cross-linked between the source and the drain, it is not possible to obtain FET characteristics that pinch off due to current leakage. Therefore, it is conceivable to reduce the density of the carbon nanotubes and reduce the leakage of current, but there is a problem that the mobility is lowered. That is, the on / off characteristics and mobility of the FET are traded off.
　そこで本発明の目的は、オンオフ特性に優れ、かつ移動度の高いカーボンナノチューブをチャネルとして用いた電界効果トランジスタを実現することである。 Therefore, an object of the present invention is to realize a field effect transistor using a carbon nanotube having excellent on / off characteristics and high mobility as a channel.
　第１の発明は、絶縁膜上に接して位置するネットワーク状に連鎖したカーボンナノチューブ薄膜が、ソースとドレインとの間を架橋した構造を有し、ソースとドレイン間のチャネル長Ｌｃを越える長さのカーボンナノチューブが実質上存在せず、カーボンナノチューブの平均長さＬｃｎｔがチャネル長Ｌｃの１／２０～１／３倍の範囲であり、規格化されたカーボンナノチューブの被覆度を、カーボンナノチューブ薄膜の面密度をρとして、ρ＊（Ｌｃｎｔ）2 で定義するとき、規格化されたカーボンナノチューブの被覆度が５～１５である、ことを特徴とする電界効果トランジスタである。 The first invention has a structure in which a carbon nanotube thin film chained in a network located in contact with an insulating film has a structure in which the source and the drain are cross-linked and has a length exceeding the channel length Lc between the source and the drain. Carbon nanotubes are substantially absent, and the average length Lcnt of carbon nanotubes is in the range of 1/20 to 1/3 times the channel length Lc. The field effect transistor is characterized in that when the surface density is defined by ρ * (Lcnt) 2 where ρ is defined as ρ, the normalized carbon nanotube coverage is 5 to 15.
　ここにおいて、カーボンナノチューブの平均長さとは、製造時の目標とする長さと見做すことができ、製造におけるばらつきを許容した上での平均長さである。チャネル長Ｌｃの１／２０よりも短いカーボンナノチューブが存在していても、電界効果トランジスタのオンオフ比に大きく影響を与えないが、チャネル長Ｌｃを越える長さのカーボンナノチューブが存在すると金属型のカーボンナノチューブがソースとドレインとを架橋するために、オンオフ比が急激に低下する。したがって、カーボンナノチューブの平均長さＬｃｎｔがチャネル長Ｌｃの１／２０～１／３倍の範囲に存在するとは、一部のカーボンナノチューブが、チャネル長Ｌｃよりも短い範囲で、この範囲外に存在していても良いことを意味する。また、ソースとドレイン間のチャネル長Ｌｃを越える長さのカーボンナノチューブが実質上存在せずとは、ソース、ドレイン間の金属型のカーボンナノチューブによる短絡により電界効果トランジスタのオンオフ比を低下させない程度には、チャネル長Ｌｃを越える長さのカーボンナノチューブが存在しないことを意味する。この範囲の時に、電界効果トランジスタの移動度を低下させることなく、オンオフ比を大きくすることができる。また、平均長さＬｃｎｔがチャネル長Ｌｃの１／２０～１／５倍の範囲であり、規格化されたカーボンナノチューブの被覆度が５～１５であることも、移動度を低下させることなく、オンオフ比を大きくするのにより望ましい範囲である。平均長さＬｃｎｔがチャネル長Ｌｃの１／２０よりも小さくなると、チャネルにおけるカーボンナノチューブの交差数が多くなり、移動度が低下するので望ましくない。平均長さＬｃｎｔがチャネル長Ｌｃの１／３よりも大きくなると、チャネルにおいてカーボンナノチューブの交差数が少なくなり過ぎて、ソース、ドレイン間を金属型のカーボンナノチューブだけの連鎖で接続する経路が多くなり過ぎて、オンオフ比を低下させるので望ましくない。したがって、Ｌｃｎｔ／Ｌｃは、１／２０以上、１／３以下が望ましい。電界効果トランジスタのオンオフ比を低下させないためには、平均長さＬｃｎｔがチャネル長Ｌｃの１／５以下であることがより望ましい。したがって、Ｌｃｎｔ／Ｌｃが、１／２０以上、１／５以下の範囲は、より望ましい範囲である。 Here, the average length of the carbon nanotubes can be regarded as a target length at the time of manufacturing, and is an average length after allowing for variations in manufacturing. Even if a carbon nanotube shorter than 1/20 of the channel length Lc is present, the on / off ratio of the field effect transistor is not greatly affected. However, if a carbon nanotube having a length exceeding the channel length Lc is present, a metal type carbon nanotube is present. Since the nanotube bridges the source and the drain, the on / off ratio rapidly decreases. Therefore, when the average length Lcnt of carbon nanotubes is in the range of 1/20 to 1/3 times the channel length Lc, some carbon nanotubes exist outside this range in a range shorter than the channel length Lc. It means you can do it. Further, the fact that the carbon nanotube having a length exceeding the channel length Lc between the source and the drain does not substantially exist is such that the on / off ratio of the field effect transistor is not lowered by a short circuit due to the metallic carbon nanotube between the source and the drain. Means that there is no carbon nanotube having a length exceeding the channel length Lc. In this range, the on / off ratio can be increased without reducing the mobility of the field effect transistor. Further, the average length Lcnt is in the range of 1/20 to 1/5 times the channel length Lc, and the standardized carbon nanotube coverage is 5 to 15 without reducing the mobility. A more desirable range is to increase the on / off ratio. If the average length Lcnt is smaller than 1/20 of the channel length Lc, the number of carbon nanotube crossings in the channel increases and the mobility decreases, which is not desirable. When the average length Lcnt is larger than 1/3 of the channel length Lc, the number of carbon nanotube crossings in the channel becomes too small, and there are more paths connecting the source and drain with a chain of only metallic carbon nanotubes. This is undesirable because it reduces the on / off ratio. Therefore, Lcnt / Lc is preferably 1/20 or more and 1/3 or less. In order not to lower the on / off ratio of the field effect transistor, it is more desirable that the average length Lcnt is 1/5 or less of the channel length Lc. Therefore, a range where Lcnt / Lc is 1/20 or more and 1/5 or less is a more desirable range.
　チャネル長Ｌｃとカーボンナノチューブの平均長さＬｃｎｔとの関係は、金属型のカーボンナノチューブだけの連結により、ソース、ドレイン間が接続されることが排除される関係であれば良い。ソースとドレイン間を連結するカーボンナノチューブの連結鎖の中に、一つでも半導体型のカーボンナノチューブが存在すれば、その連結鎖に関してオンオフ特性を得ることができる。したがって、カーボンナノチューブの長さＬｃｎｔとチャネル長Ｌｃとの比率が重要である。あるカーボンナノチューブの長さＬｃｎｔに対して、最適なチャネル長Ｌｃの範囲が存在し、逆に、あるチャネル長Ｌｃに対して、最適なカーボンナノチューブの平均長さＬｃｎｔの範囲が存在する。よって、チャネル長Ｌｃは特に限定される訳ではないが、チャネル長Ｌｃは、１０～２００μｍであることが望ましい。また、チャネル長Ｌｃが３０～２００μｍ、４０～１００μｍも望ましい範囲である。チャネル長Ｌｃが１０μｍより小さい場合は、現在の製造技術では製造が困難であり、２００μｍを越えると、応答速度が低下すると共に、素子が大きくなるので望ましくない。また、チャネル長Ｌｃが３０～２００μｍは、製造し易いカーボンナノチューブの平均長さＬｃｎｔに対して（例えば、１０μｍ）、オンオフ比が大きく、移動度を大きくするのに望ましい範囲である。 The relationship between the channel length Lc and the average length Lcnt of the carbon nanotubes only needs to be a relationship that eliminates the connection between the source and the drain due to the connection of only the metallic carbon nanotubes. If at least one semiconductor-type carbon nanotube exists in the connecting chain of the carbon nanotubes connecting the source and the drain, on / off characteristics can be obtained with respect to the connecting chain. Therefore, the ratio between the length Lcnt of the carbon nanotube and the channel length Lc is important. There is an optimum channel length Lc range for a certain carbon nanotube length Lcnt, and conversely there is an optimum average carbon nanotube length Lcnt range for a certain channel length Lc. Therefore, the channel length Lc is not particularly limited, but the channel length Lc is preferably 10 to 200 μm. Further, the channel length Lc is preferably 30 to 200 μm and 40 to 100 μm. If the channel length Lc is smaller than 10 μm, it is difficult to manufacture with the current manufacturing technology. If the channel length Lc exceeds 200 μm, the response speed is lowered and the element becomes larger, which is not desirable. The channel length Lc of 30 to 200 μm is a desirable range for increasing the mobility and the on / off ratio with respect to the average length Lcnt of easy-to-manufacture carbon nanotubes (for example, 10 μm).
　また、規格化された被覆度は、カーボンナノチューブの接近の程度、又は、交差の頻度を表している。規格化された被覆度は、カーボンナノチューブの平均長さＬｃｎｔによる影響が排除された値である。被覆度が５よりも小さいと、オンオフ比の向上には寄与するが、チャネルを構成するカーボンナノチューブの密度が小さくなり過ぎ、電流容量が低下するので望ましくない。また、被覆度が１５を越えると、カーボンナノチューブの交点数が多くなり、オン時の移動度が低下するので望ましくない。したがって、被覆度は５以上、１５以下が望ましい。被覆度のさらに望ましい範囲は、７以上、１０以下の範囲である。この範囲の時に、電界効果のオンオフ比を大きくでき、オン時の移動度を低下させることがない。
　また、カーボンナノチューブの平均長さＬｃｎｔは、チャネル長Ｌｃの１／１０～１／５倍の範囲であり、規格化されたカーボンナノチューブの被覆度が７～１０であっても良い。この範囲の時に、さらに、オンオフ比、移動度が大きくなる。 Further, the standardized degree of coverage represents the degree of approach of the carbon nanotubes or the frequency of crossing. The standardized coverage is a value from which the influence of the average length Lcnt of the carbon nanotube is excluded. If the coverage is less than 5, it contributes to the improvement of the on / off ratio, but it is not desirable because the density of the carbon nanotubes constituting the channel becomes too small and the current capacity decreases. On the other hand, if the degree of coverage exceeds 15, the number of intersections of the carbon nanotubes increases, and the on-time mobility decreases, which is not desirable. Therefore, the coverage is preferably 5 or more and 15 or less. A more desirable range of the coverage is in the range of 7 or more and 10 or less. In this range, the on / off ratio of the field effect can be increased and the on-time mobility is not lowered.
Further, the average length Lcnt of the carbon nanotubes may be in the range of 1/10 to 1/5 times the channel length Lc, and the standardized coverage of the carbon nanotubes may be 7 to 10. In this range, the on / off ratio and the mobility are further increased.
　上記発明において、カーボンナノチューブは、Ｆ4 ＴＣＮＱ（2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane）で被覆されていても良い。その場合に、Ｆ4 ＴＣＮＱの濃度が０．０１～０．０４ｍＭｏｌ／ｌの溶液を用いて被覆されていることが望ましい。この被覆により電界効果トランジスタのしきい値電圧を大きくすることができ、ゲート電圧が印加されていない時に、トランジスタをオフ状態とする、ノーマリオフを確実に実現することができる。 In the above invention, the carbon nanotubes may be coated with F 4 TCNQ (2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane). In that case, it is desirable to coat with a solution having an F 4 TCNQ concentration of 0.01 to 0.04 mMol / l. By this covering, the threshold voltage of the field effect transistor can be increased, and normally-off in which the transistor is turned off when the gate voltage is not applied can be reliably realized.
　また、カーボンナノチューブの太さは、直径１．１ｎｍ以下が望ましい。この場合には、ドレイン、ソース間電圧の広い範囲において、電界効果トランジスタのオンオフ比を大きくすることができる。したがって、電界効果トランジスタの使用電圧範囲を拡大することができる。
　また、電界効果トランジスタは、フレキシブルなプラスチック基板上に、その素子構造を形成したものとすることが望ましい。屈曲性のある平面ディスプレイのピクセルを制御するゲートトランジスタに用いることができ、薄膜ディスプレイを容易に実現することができる。 The thickness of the carbon nanotube is preferably 1.1 nm or less. In this case, the on / off ratio of the field effect transistor can be increased in a wide range of the drain-source voltage. Therefore, the working voltage range of the field effect transistor can be expanded.
In addition, it is desirable that the field effect transistor has an element structure formed on a flexible plastic substrate. It can be used as a gate transistor for controlling a pixel of a flexible flat display, and a thin film display can be easily realized.
　また、製造方法の発明は、絶縁膜上に接して位置するネットワーク状に連鎖したカーボンナノチューブ薄膜が、ソースとドレインとの間のチャネルを架橋した構造を有する電界効果トランジスタの製造方法において、基板上に、ソース、ドレイン、ソースとドレイン間のチャネルを接続するカーボンナノチューブ薄膜、ゲート、ゲートとカーボンナノチューブ薄膜とを絶縁分離する絶縁膜とから成る素子構造を形成し、浮遊触媒法によりカーボンナノチューブを生成し、生成されたカーボンナノチューブをフィルタに収集して薄膜を生成し、フィルタに収集されたカーボンナノチューブ薄膜を、チャネルの上に転写することを特徴とする。
　素子構造の製造の製法には、基板上にゲートを形成し、そのゲート上及びゲートで覆われていない基板上に絶縁膜を形成し、その絶縁膜上にチャネルの長だけ離間してソース、ドレインを形成し、フィルタに収集されたカーボンナノチューブ薄膜を絶縁膜上のチャネルの上に転写する方法が採用できる。また、基板上に、フィルタに収集されたカーボンナノチューブ薄膜をチャネル領域に転写し、そのカーボンナノチューブ薄膜のチャネルの長だけ離間した端部にカーボンナノチューブを架橋するようにソース、ドレインを形成し、カーボンナノチューブ薄膜、ソース、及び、ドレインの上に、絶縁膜を形成し、その絶縁膜の上であって、チャネルの上部にゲートを形成するようにしても良い。また、基板上に、ソース、ドレインを形成し、ソース、ドレイン間のチャネルに両者を架橋するように、フィルタに収集されたカーボンナノチューブ薄膜を転写し、カーボンナノチューブ薄膜、ソース、及び、ドレインの上に、絶縁膜を形成し、その絶縁膜の上であって、チャネルの上部にゲートを形成するようにしても良い。
　浮遊触媒法によりカーボンナノチューブを生成してフィルタに収集して、フィルタ上にカーボンナノチューブ薄膜を形成して、その薄膜を、チャネル領域に転写することで、容易に長さや密度の制御されたカーボンナノチューブ薄膜をチャネルとすることができ、均質一様な素子特性を得ることができる。
　浮遊触媒法は、原料ガス（例えば、ＣＯガス、炭化水素ガスなど）と、触媒（例えば、フェロセンなど）を、反応炉に流して、カーボンナノチューブを空間中において成長させる方法である。発明では、この空間中に成長したカーボンナノチューブをフィルタ（例えば、ニトロセルロースなどの布状物体）に集積して、フィルタ上にカーボンナノチューブ薄膜を形成する。そして、カーボンナノチューブ薄膜を、別途、製造したソース、ドレイン、ゲートを有するトランジスタ素子のチャネル上に転写している。フィルタは、カーボンナノチューブ薄膜の転写後に剥離させたり、有機溶剤（アセトンなど）で溶解させて除去することができる。 Further, the invention of a manufacturing method is a method of manufacturing a field effect transistor having a structure in which a carbon nanotube thin film chained in a network located in contact with an insulating film bridges a channel between a source and a drain. In addition, an element structure consisting of a carbon nanotube thin film that connects the source, drain, and the channel between the source and drain, and an insulating film that insulates and separates the gate and the gate from the carbon nanotube thin film is formed, and carbon nanotubes are generated by the floating catalyst method. Then, the generated carbon nanotubes are collected in a filter to form a thin film, and the carbon nanotube thin film collected in the filter is transferred onto the channel.
In the manufacturing method of the element structure, a gate is formed on a substrate, an insulating film is formed on the gate and a substrate not covered with the gate, and a source is separated from the insulating film by the length of the channel, A method of forming the drain and transferring the carbon nanotube thin film collected by the filter onto the channel on the insulating film can be employed. Further, the carbon nanotube thin film collected by the filter is transferred onto the channel region on the substrate, and the source and drain are formed so as to bridge the carbon nanotubes at the ends separated by the channel length of the carbon nanotube thin film. An insulating film may be formed on the nanotube thin film, the source, and the drain, and a gate may be formed on the insulating film and on the channel. In addition, the carbon nanotube thin film collected on the filter is transferred so that the source and drain are formed on the substrate, and the channel between the source and drain is bridged, and the carbon nanotube thin film, the source and the drain are formed on the substrate. In addition, an insulating film may be formed, and a gate may be formed on the insulating film and above the channel.
Carbon nanotubes are generated by floating catalyst method and collected in a filter, a carbon nanotube thin film is formed on the filter, and the thin film is transferred to the channel region, thereby easily controlling the length and density of the carbon nanotube. A thin film can be used as a channel, and uniform and uniform element characteristics can be obtained.
The floating catalyst method is a method in which a raw material gas (for example, CO gas, hydrocarbon gas, etc.) and a catalyst (for example, ferrocene) are flowed into a reaction furnace to grow carbon nanotubes in the space. In the invention, the carbon nanotubes grown in this space are accumulated on a filter (for example, a cloth-like object such as nitrocellulose) to form a carbon nanotube thin film on the filter. Then, the carbon nanotube thin film is transferred onto a channel of a transistor element having a source, drain, and gate manufactured separately. The filter can be removed after the transfer of the carbon nanotube thin film or dissolved by an organic solvent (acetone or the like).
　また、製造方法の発明において、ソースとドレイン間のチャネル長Ｌｃを越える長さのカーボンナノチューブが実質上存在せず、カーボンナノチューブの平均長さＬｃｎｔがチャネル長Ｌｃの１／２０～１／３倍の範囲であり、規格化されたカーボンナノチューブの被覆度を、カーボンナノチューブ薄膜の面密度をρとして、ρ＊（Ｌｃｎｔ）2 で定義するとき、規格化されたカーボンナノチューブの被覆度が５～１５とすることが望ましい。電界効果トランジスタの発明で説明した事項が、この製造方法の発明においても適用される。カーボンナノチューブの平均長さＬｃｎｔがチャネル長Ｌｃの１／２０～１／５倍の範囲に存在することはより望ましい。 In the invention of the manufacturing method, there is substantially no carbon nanotube having a length exceeding the channel length Lc between the source and drain, and the average length Lcnt of the carbon nanotube is 1/20 to 1/3 times the channel length Lc. When the standardized carbon nanotube coverage is defined as ρ * (Lcnt) 2 where ρ is the surface density of the carbon nanotube thin film, the standardized carbon nanotube coverage is 5-15. Is desirable. The matters described in the invention of the field effect transistor also apply to the invention of the manufacturing method. More preferably, the average length Lcnt of the carbon nanotubes is in the range of 1/20 to 1/5 times the channel length Lc.
　製造方法の発明において、カーボンナノチューブ薄膜の面密度を、フィルタでの収集時間により制御することができる。これにより、オンオフ比の高い良好な特性の電界効果トランジスタを、均質一様に製造することができる。
　また、カーボンナノチューブの平均直径は、カーボンナノチューブの形成時の温度を制御することにより行うことができる。これにより、ソース、ドレイン間の電圧の広い範囲において、オンオフ比の大きな電界効果トランジスタを、均質一様に容易に製造することができる。
　また、カーボンナノチューブの平均直径は、カーボンナノチューブの形成時に追加する二酸化炭素ガスの原料ガスに対する比率を制御することができる。これにより、ソース、ドレイン間の電圧の広い範囲において、オンオフ比の大きな電界効果トランジスタを、均質一様に容易に製造することができる。 In the invention of the manufacturing method, the surface density of the carbon nanotube thin film can be controlled by the collection time in the filter. Thereby, a field effect transistor having a high on / off ratio and good characteristics can be uniformly and uniformly manufactured.
Further, the average diameter of the carbon nanotubes can be determined by controlling the temperature at the time of forming the carbon nanotubes. Thereby, a field effect transistor having a large on / off ratio can be easily and uniformly manufactured over a wide range of voltages between the source and drain.
Further, the average diameter of the carbon nanotubes can control the ratio of carbon dioxide gas added to the raw material gas added during the formation of the carbon nanotubes. Thereby, a field effect transistor having a large on / off ratio can be easily and uniformly manufactured over a wide range of voltages between the source and drain.
　また、カーボンナノチューブの平均直径を１．１ｎｍ以下とすることが望ましい。これにより、ソース、ドレイン間の電圧の広い範囲において、オンオフ比の大きな電界効果トランジスタを、均質一様に容易に製造することができる。
　また、カーボンナノチューブの形成時の温度は、８２５℃以下であることが望ましい。これにより、電界効果トランジスタの特性が良好となるカーボンナノチューブの平均直径を１．１ｎｍ以下とすることができる。
　また、カーボンナノチューブに、Ｆ4 ＴＣＮＱの濃度が０．０１～０．０４ｍＭｏｌ／ｌの溶液を用いて、被覆することが望ましい。この場合には、しきい値電圧を大きくすることができ、確実に、ノーマリオフとなる電界効果トランジスタを実現することができる。 Moreover, it is desirable that the average diameter of the carbon nanotubes be 1.1 nm or less. Thereby, a field effect transistor having a large on / off ratio can be easily and uniformly manufactured over a wide range of voltages between the source and drain.
Further, the temperature at the time of forming the carbon nanotube is desirably 825 ° C. or lower. Thereby, the average diameter of the carbon nanotube with which the characteristic of a field effect transistor becomes favorable can be 1.1 nm or less.
In addition, it is desirable to coat the carbon nanotubes using a solution having an F 4 TCNQ concentration of 0.01 to 0.04 mMol / l. In this case, the threshold voltage can be increased, and a field effect transistor that is normally off can be realized with certainty.
　チャネル長Ｌｃ、カーボンナノチューブの平均的長さＬｃｎｔ、規格化されたカーボンナノチューブの被覆度をそれぞれ本発明に示した範囲とすることで、オンオフ特性に優れ、かつ移動度の高い、カーボンナノチューブをチャネルとした電界効果トランジスタを実現することができる。また、本発明の製造方法によると、オンオフ特性に優れ、かつ移動度の高い、カーボンナノチューブ薄膜をチャネルとした電界効果トランジスタを、簡単に且つ均質一様に製造することができる。 By setting the channel length Lc, the average length Lcnt of carbon nanotubes, and the coverage of standardized carbon nanotubes within the ranges shown in the present invention, it is possible to channel carbon nanotubes with excellent on-off characteristics and high mobility. The field effect transistor can be realized. In addition, according to the manufacturing method of the present invention, a field effect transistor using a carbon nanotube thin film as a channel, which has excellent on-off characteristics and high mobility, can be easily and uniformly manufactured.
実施例１のＣＮＴ－ＴＦＴの構成を示した図。FIG. 4 shows a configuration of a CNT-TFT of Example 1. 実施例１のＣＮＴ－ＴＦＴの製造工程を示した図。FIG. 4 is a view showing a manufacturing process of the CNT-TFT of Example 1. 実施例１のＣＮＴ－ＴＦＴの製造工程を示した図。FIG. 4 is a view showing a manufacturing process of the CNT-TFT of Example 1. 実施例１のＣＮＴ－ＴＦＴの製造工程を示した図。FIG. 4 is a view showing a manufacturing process of the CNT-TFT of Example 1. 収集時間１０秒でのカーボンナノチューブ薄膜１１の構造を示したＳＥＭ像。The SEM image which showed the structure of the carbon nanotube thin film 11 in collection time 10 second. 収集時間７秒でのカーボンナノチューブ薄膜１１の構造を示したＳＥＭ像。The SEM image which showed the structure of the carbon nanotube thin film 11 in collection time 7 second. 収集時間５秒でのカーボンナノチューブ薄膜１１の構造を示したＳＥＭ像。The SEM image which showed the structure of the carbon nanotube thin film 11 in collection time 5 second. 収集時間４秒でのカーボンナノチューブ薄膜１１の構造を示したＳＥＭ像。The SEM image which showed the structure of the carbon nanotube thin film 11 in collection time 4 seconds. 収集時間３秒でのカーボンナノチューブ薄膜１１の構造を示したＳＥＭ像。The SEM image which showed the structure of the carbon nanotube thin film 11 in collection time 3 second. 収集時間２秒でのカーボンナノチューブ薄膜１１の構造を示したＳＥＭ像。The SEM image which showed the structure of the carbon nanotube thin film 11 in collection time 2 second. 収集時間１０秒でのチャネル長Ｌｃとオン電流、オフ電流との関係を示したグラフ。The graph which showed the relationship between channel length Lc, ON current, and OFF current in collection time 10 second. 収集時間４秒でのチャネル長Ｌｃとオン電流、オフ電流との関係を示したグラフ。The graph which showed the relationship between channel length Lc, ON current, and OFF current in collection time 4 second. 収集時間２秒でのチャネル長Ｌｃとオン電流、オフ電流との関係を示したグラフ。The graph which showed the relationship between channel length Lc, on-current, and off-current in collection time 2 second. 規格化された被覆度とｍとの関係を示したグラフ。The graph which showed the relationship between the standardized coverage and m. 実施例１のＣＮＴ－ＴＦＴのＩｄ－Ｖｇｓ特性を示したグラフ。3 is a graph showing Id-Vgs characteristics of the CNT-TFT of Example 1. 実施例１のＣＮＴ－ＴＦＴのＩｄ－Ｖｄｓ特性を示したグラフ。6 is a graph showing Id-Vds characteristics of the CNT-TFT of Example 1. ＣＮＴ－ＴＦＴのＩｄ－Ｖｇｓ特性を示したグラフ。The graph which showed the Id-Vgs characteristic of CNT-TFT. ＣＮＴ－ＴＦＴのＩｄ－Ｖｇｓ特性を示したグラフ。The graph which showed the Id-Vgs characteristic of CNT-TFT. ＣＮＴ－ＴＦＴのＩｄ－Ｖｇｓ特性を示したグラフ。The graph which showed the Id-Vgs characteristic of CNT-TFT. ＣＮＴ－ＴＦＴを製造において、二酸化炭素ガスの流量とカーボンナノチューブの直径との関係を示した波長吸収特性。Wavelength absorption characteristics showing the relationship between the flow rate of carbon dioxide gas and the diameter of carbon nanotubes in the production of CNT-TFTs. ＣＮＴ－ＴＦＴを製造において、カーボンナノチューブの形成温度、直径との関係を示した波長吸収特性。Wavelength absorption characteristics showing the relationship between carbon nanotube formation temperature and diameter in the production of CNT-TFTs.
　以下、本発明の具体的な実施例について説明するが、本発明は実施例に限定されるものではない。 Hereinafter, specific examples of the present invention will be described, but the present invention is not limited to the examples.
　図１は、実施例１のカーボンナノチューブを用いた薄膜トランジスタ（ＣＮＴ－ＴＦＴ）の構成を示した図である。ＣＮＴ－ＴＦＴは、ＰＥＮ（ポリエチレンナフタレート）からなる厚さ１２５μｍの樹脂フィルム基板２１を有している。樹脂フィルム基板として、ＰＥＮ以外のフレキシブルなプラスチック基板を用いてもよい。樹脂フィルム２１上の一部領域には、Ｔｉ／Ａｕ（Ｔｉ膜の厚さ１０ｎｍ、Ａｕ膜の厚さ１００ｎｍ）からなるゲート電極２２が形成されている。また、ゲート電極２２上および樹脂フィルム２１上に連続して、Ａｌ2 Ｏ3 からなる厚さ４０ｎｍの絶縁膜２３が形成されている。絶縁膜２３上であって、平面視でゲート電極２２を挟む領域に、ソース電極２４とドレイン電極２５とがそれぞれ離間して形成されている。ソース電極２４およびドレイン電極２５は、Ｔｉ／Ａｕ（Ｔｉ膜の厚さ１０ｎｍ、Ａｕ膜の厚さ１５０ｎｍ）からなる。絶縁膜２３上には、ソース電極２４とドレイン電極２５との間を架橋する構造のカーボンナノチューブ薄膜１１が形成されている。チャネル長Ｌｃを、後述するように、５μｍ、１０μｍ、２０μｍ、３０μｍ、４０μｍ、５０μｍ、１００μｍの７種類とするＣＮＴ－ＴＦＴを製造した。 FIG. 1 is a diagram showing the configuration of a thin film transistor (CNT-TFT) using carbon nanotubes of Example 1. FIG. The CNT-TFT has a resin film substrate 21 made of PEN (polyethylene naphthalate) and having a thickness of 125 μm. A flexible plastic substrate other than PEN may be used as the resin film substrate. A gate electrode 22 made of Ti / Au (Ti film thickness 10 nm, Au film thickness 100 nm) is formed in a partial region on the resin film 21. An insulating film 23 made of Al 2 O 3 and having a thickness of 40 nm is formed continuously on the gate electrode 22 and the resin film 21. A source electrode 24 and a drain electrode 25 are separately formed on the insulating film 23 in a region sandwiching the gate electrode 22 in plan view. The source electrode 24 and the drain electrode 25 are made of Ti / Au (Ti film thickness 10 nm, Au film thickness 150 nm). On the insulating film 23, the carbon nanotube thin film 11 having a structure for bridging the source electrode 24 and the drain electrode 25 is formed. As will be described later, CNT-TFTs having seven types of channel lengths Lc of 5 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, and 100 μm were manufactured.
　カーボンナノチューブ薄膜１１は、平均的長さＬｃｎｔが１０μｍのカーボンナノチューブがネットワーク状に連鎖した構造を有している。個々のカーボンナノチューブの結合形状は、Ｘ字型の結合よりもＹ字型に結合した形状が支配的となっている。 The carbon nanotube thin film 11 has a structure in which carbon nanotubes having an average length Lcnt of 10 μm are chained in a network. As for the bonding shape of the individual carbon nanotubes, the Y-shaped bonding shape is more dominant than the X-shaped bonding.
　次に、実施例１のＣＮＴ－ＴＦＴの製造工程について、図２を参照に説明する。 Next, the manufacturing process of the CNT-TFT of Example 1 will be described with reference to FIG.
　まず、浮遊触媒法を用いてカーボンナノチューブを生成し、これをフィルタ１０を用いして収集することで、フィルタ１０上にネットワーク状に連鎖したカーボンナノチューブ薄膜１１を形成した（図２．Ａ）。成長温度は８２５℃とし、カーボンソースとしてＣＯ、触媒としてフェロセンを用いた。ＣＯガスの流量は４００ｓｃｃｍとした。また、フィルタ１０には、ニトロセルロースからなる直径２５ｍｍ、孔径４００ｎｍのメンブレンフィルタを用いた。ここで、カーボンナノチューブ薄膜１１の密度は、フィルタ１０によりカーボンナノチューブを収集する時間によって制御することが可能である。また、カーボンナノチューブの平均的長さＬｃｎｔは、成長温度やガス流量などによって制御することが可能である。 First, carbon nanotubes were generated using a floating catalyst method and collected using a filter 10 to form a carbon nanotube thin film 11 chained in a network on the filter 10 (FIG. 2.A). The growth temperature was 825 ° C., CO was used as the carbon source, and ferrocene was used as the catalyst. The flow rate of CO gas was 400 sccm. The filter 10 was a membrane filter made of nitrocellulose having a diameter of 25 mm and a pore diameter of 400 nm. Here, the density of the carbon nanotube thin film 11 can be controlled by the time for collecting the carbon nanotubes by the filter 10. The average length Lcnt of the carbon nanotubes can be controlled by the growth temperature, gas flow rate, and the like.
　また、一方で、樹脂フィルム基板２１上に、ゲート電極２２、絶縁膜２３、ソース電極２４、およびドレイン電極２５を順次、形成した。これらは、蒸着法や印刷法やリソグラフィなどによって形成することができる。以下、樹脂フィルム基板２１上に、ゲート電極２２、絶縁膜２３、ソース電極２４、およびドレイン電極２５を形成した構造を素子基板２０（以下、単に、「基板」）という。したがって、基板２０は、図１に示したＣＮＴ－ＴＦＴにおいて、カーボンナノチューブ薄膜１１を除いた構造である。 On the other hand, the gate electrode 22, the insulating film 23, the source electrode 24, and the drain electrode 25 were sequentially formed on the resin film substrate 21. These can be formed by vapor deposition, printing, lithography, or the like. Hereinafter, the structure in which the gate electrode 22, the insulating film 23, the source electrode 24, and the drain electrode 25 are formed on the resin film substrate 21 is referred to as an element substrate 20 (hereinafter simply referred to as “substrate”). Therefore, the substrate 20 has a structure in which the carbon nanotube thin film 11 is removed from the CNT-TFT shown in FIG.
　次に、基板２０のソース電極２４およびドレイン電極２５形成側の面と、フィルタ１０のカーボンナノチューブ薄膜１１形成側の面とを貼り合わせた（図２．Ｂ）。そして、フィルタ１０にエタノールを滴下した後、アセトン溶液によってフィルタ１０を除去した（図２．Ｃ）。これにより、基板２０のソース電極２４およびドレイン電極２５形成側の面に、カーボンナノチューブ薄膜１１が転写される。 Next, the surface of the substrate 20 on the source electrode 24 and drain electrode 25 formation side and the surface of the filter 10 on the carbon nanotube thin film 11 formation side were bonded together (FIG. 2.B). And ethanol was dripped at the filter 10, and the filter 10 was removed with the acetone solution (FIG. 2.C). Thereby, the carbon nanotube thin film 11 is transferred to the surface of the substrate 20 on the side where the source electrode 24 and the drain electrode 25 are formed.
　なお、上記図２．Ｃの工程に替えて、単に貼り合わせたフィルタ１０を剥離するだけでもよい。この場合も、分子間力の作用によって、基板２０のソース電極２４およびドレイン電極２５形成側の面にカーボンナノチューブ薄膜１１を転写することができる。 In addition, the above figure 2. Instead of the step C, the bonded filter 10 may be simply peeled off. Also in this case, the carbon nanotube thin film 11 can be transferred onto the surface of the substrate 20 on the side where the source electrode 24 and the drain electrode 25 are formed by the action of intermolecular force.
　次に、フォトリソグラフィとエッチングによって、チャネル領域以外のカーボンナノチューブ薄膜１１を除去することで、図１に示したＣＮＴ－ＴＦＴが製造される。エッチングは、真空中で行う場合は、たとえば酸素プラズマを用いることができ、大気圧下で行う場合は、たとえばオゾン雰囲気下で紫外線を照射することで行うことができる。 Next, the CNT-TFT shown in FIG. 1 is manufactured by removing the carbon nanotube thin film 11 other than the channel region by photolithography and etching. Etching can be performed, for example, by using oxygen plasma when performed in a vacuum, and can be performed by irradiating ultraviolet rays, for example, in an ozone atmosphere when performed at atmospheric pressure.
　図３は、カーボンナノチューブ薄膜１１のＳＥＭ像である。各ＳＥＭ像はフィルタ１０による収集時間が異なっており、図３．Ａは１０秒、図３．Ｂは７秒、図３．Ｃは５秒、図３．Ｄは４秒、図３．Ｅは３秒、図３．Ｆは２秒である。図３のように、収集時間が短いほど、カーボンナノチューブの密度が小さいことがわかる。また、収集時間が短いほど、カーボンナノチューブ同士の接合形状においてＸ字型が減少し、Ｙ字型が増加していることがわかる。収集時間が２秒、４秒、１０秒の時には、Ｙ字型結合のカーボンナノチューブの存在割合は、それぞれ、６５％、６２％、４７％であった。Ｙ字型の結合では、Ｘ字型に比べてカーボンナノチューブ同士の接触面積が広く、コンタクト抵抗が低くなるため、移動度が向上する。したがって、チャネルを構成するカーボンナノチューブ薄膜は、Ｙ字型の結合のカーボンナノチューブが支配的となることが望ましい。そのために収集の最適時間が存在する。Ｙ字型結合のカーボンナノチューブの割合は、上記のことから６２％以上、又は、６５％以上であることが望ましい。 FIG. 3 is an SEM image of the carbon nanotube thin film 11. Each SEM image has a different collection time by the filter 10, and FIG. A is 10 seconds, FIG. B is 7 seconds, FIG. C is 5 seconds, FIG. D is 4 seconds, FIG. E is 3 seconds, FIG. F is 2 seconds. As shown in FIG. 3, it can be seen that the shorter the collection time, the smaller the density of the carbon nanotubes. In addition, it can be seen that the shorter the collection time, the smaller the X-shape and the more the Y-shape in the bonded shape of the carbon nanotubes. When the collection time was 2 seconds, 4 seconds, and 10 seconds, the abundance ratios of Y-shaped carbon nanotubes were 65%, 62%, and 47%, respectively. In the Y-shaped bond, the contact area between the carbon nanotubes is wider and the contact resistance is lower than in the X-shaped bond, so that the mobility is improved. Therefore, it is desirable that the carbon nanotube thin film constituting the channel is dominated by Y-shaped carbon nanotubes. Therefore, there is an optimal time for collection. From the above, the ratio of carbon nanotubes with Y-shaped bonds is desirably 62% or more or 65% or more.
　このように、チャネル長Ｌｃが５μｍ、１０μｍ、２０μｍ、３０μｍ、４０μｍ、５０μｍ、１００μｍの７種類であるＣＮＴ－ＦＥＴを、各種類毎に多数製造した。また、それぞれのチャネル長Ｌｃに対して、カーボンナノチューブの密度を、収集時間２秒、４秒、１０秒の３通りにより、３種類に変化させたＣＮＴ－ＦＥＴを、それぞれ、多数製造した。図４は、ＣＮＴ－ＦＥＴのチャネル長Ｌｃと、オン電流およびオフ電流との関係を示したグラフである。プロット点は、多数の試料による測定値の平均値を表している。横軸、縦軸はいずれも対数スケールである。図４．Ａは、フィルタ１０による収集時間を１０秒とした場合、図４．Ｂは４秒とした場合、図４．Ｃは２秒とした場合である。 Thus, a large number of CNT-FETs having seven types of channel lengths Lc of 5 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, and 100 μm were manufactured for each type. In addition, a large number of CNT-FETs were produced in which the density of the carbon nanotubes was changed into three types for each channel length Lc, with a collection time of 2 seconds, 4 seconds, and 10 seconds. FIG. 4 is a graph showing the relationship between the channel length Lc of the CNT-FET and the on-current and off-current. The plotted point represents the average value of the measured values of a large number of samples. Both the horizontal and vertical axes are logarithmic scales. FIG. A is shown in FIG. 4 when the collection time by the filter 10 is 10 seconds. When B is 4 seconds, FIG. C is the case of 2 seconds.
　図４．Ａ、４．Ｂでは、電流値はパーコレーション理論に基づいて予測される値をとっている。パーコレーション理論によると、カーボンナノチューブ薄膜１１の伝導性はその形状により依存しており、電流値は、おおよそ（Ｌｃｎｔ／Ｌｃ）m ／Ｌｃｎｔ、である。ｍは、カーボンナノチューブの規格化された被覆度によって決定される定数であり、図５に示すグラフのようにして規格化された被覆度とｍとが対応付けられる。図５の曲線は、規格化された被覆度とｍとの関係を示す理論式を示している。規格化された被覆度は、カーボンナノチューブ薄膜１１の面密度（単位面積当たりに含まれるカーボンナノチューブの本数）をρ（単位：μｍ-2）、カーボンナノチューブの長さをＬｃｎｔ（単位：μｍ）として、ρ＊（Ｌｃｎｔ）2 で表わされる。ρは単位面積当たりのカーボンナノチューブの本数であるから、ρが同一の場合には、カーボンナノチューブの長さＬｃｎｔが短い程、それらのカーボンナノチューブの接近の程度が小さくなる（離間距離が長くなる）。したがって、面積（Ｌｃｎｔ）2 当たりのカーボンナノチューブの本数を、規格化された被覆度とすることで、規格化された被覆度は、カーボンナノチューブの接近の程度、又は、交差の頻度を表すことができる。規格化された被覆度は、カーボンナノチューブの平均長さＬｃｎｔによる影響が排除された値となるので、本件発明の規格化されたカーボンナノチューブの被覆度が５～１５、７～１０の範囲は、カーボンナノチューブの長さや、チャネル長によらず、オンオフ比を大きくできる範囲である。また、ｍは、図４のグラフにおける直線の傾きである。図５のように、規格化された被覆度が１０～２５ではｍはほぼ一定の小さな値であるが、１０以下になると規格化された被覆度の減少とともに徐々にｍが増加していき、７以下になると規格化された被覆度の減少とともに急激にｍが増加する。図５のプロット点は、図４における測定されたｍが、図５の理論曲線上に位置するように表している。実際には、図４に示されているように、トランジスタのオン時の傾きとオフ時の傾きが異なるため、図５に示すように、両者を同一の傾きとする理論曲線上に、ｍを基準にプロットした場合には、同一試料であっても、規格化された被覆度は異なる値を示すことになる。 FIG. A, 4. In B, the current value is a value predicted based on the percolation theory. According to the percolation theory, the conductivity of the carbon nanotube thin film 11 depends on its shape, and the current value is approximately (Lcnt / Lc) m / Lcnt. m is a constant determined by the standardized coverage of the carbon nanotube, and the standardized coverage and m are associated with each other as shown in the graph of FIG. The curve in FIG. 5 shows a theoretical formula showing the relationship between the normalized coverage and m. The normalized coverage is defined by assuming that the surface density (number of carbon nanotubes contained per unit area) of the carbon nanotube thin film 11 is ρ (unit: μm −2 ) and the length of the carbon nanotube is Lcnt (unit: μm). , Ρ * (Lcnt) 2 . Since ρ is the number of carbon nanotubes per unit area, when ρ is the same, the shorter the length Lcnt of the carbon nanotubes, the smaller the degree of approach of the carbon nanotubes (the longer the separation distance). . Therefore, by setting the number of carbon nanotubes per area (Lcnt) 2 as a standardized coverage, the standardized coverage may indicate the degree of approach of the carbon nanotubes or the frequency of crossing. it can. Since the normalized coverage is a value in which the influence of the average length Lcnt of the carbon nanotube is excluded, the range of the normalized carbon nanotube coverage of the present invention in the range of 5 to 15 and 7 to 10 is The on / off ratio can be increased regardless of the length of the carbon nanotube and the channel length. M is the slope of the straight line in the graph of FIG. As shown in FIG. 5, when the standardized coverage is 10 to 25, m is a substantially constant small value. However, when the standardized coverage is 10 or less, m gradually increases as the standardized coverage decreases. When it becomes 7 or less, m increases abruptly as the standardized coverage decreases. The plot points in FIG. 5 are represented so that the measured m in FIG. 4 is located on the theoretical curve in FIG. Actually, as shown in FIG. 4, since the slope when the transistor is on and the slope when it is off are different, as shown in FIG. When plotted on the basis, the normalized coverage is different even for the same sample.
　図４．Ａの場合、オン電流のｍは１．０５、オフ電流のｍは１．３であり、ｍの値に大きな違いはなく、オンオフ比はおよそ１０でチャネル長Ｌｃにあまり依存していない。図４．Ｂの場合は、オン電流のｍは１．２、オフ電流のｍは２．４であり、チャネル長Ｌｃの増加とともにオンオフ比も増大しているが、オンオフ比はＬｃが１０μｍのときにおよそ１０、１００μｍのときにおよそ１０2 であり、低い値となっている。このように、オフ電流のｍの値が小さいためオンオフ比も低い結果となっているが、これはフィルタ１０による収集時間が長いためにρが高くなり、規格化された被覆度が大きな値を取る結果、図５のようにｍが小さい値をとるためである。 FIG. In the case of A, the on-current m is 1.05 and the off-current m is 1.3, and there is no significant difference in the value of m. The on-off ratio is about 10 and does not depend much on the channel length Lc. FIG. In the case of B, the on-current m is 1.2, the off-current m is 2.4, and the on-off ratio increases as the channel length Lc increases. However, the on-off ratio is approximately when Lc is 10 μm. When it is 10, 100 μm, it is about 10 2, which is a low value. As described above, since the value of m of the off current is small, the on / off ratio is also low. This is because the collection time by the filter 10 is long, so that ρ is high, and the standardized coverage is a large value. As a result, m is a small value as shown in FIG.
　一方、図４．Ｃのように、フィルタ１０による収集時間が短い場合、カーボンナノチューブの平均長さＬｃｎｔが１０μｍに対して、チャネル長Ｌｃが５～２０μｍでは、金属型のカーボンナノチューブがソース－ドレイン間を架橋してしまう確率が高く、その結果オンオフ比が１０～１０2 程度で悪くなっている。また、チャネル長Ｌｃが１００μｍ以上では、オフ電流がカーボンナノチューブの熱伝導によって生じる限界値をとっており、これ以上オフ電流を小さくすることはできない。また、チャネル長Ｌｃが３０～５０μｍでは、パーコレーション理論に基づいて予測される値をとっている。このチャネル長Ｌｃが３０～５０μｍの範囲において、ｍは１４という大きな値をとっているが、これはフィルタ１０による収集時間が短いためにカーボンナノチューブ薄膜１１の面密度が低く、規格化された被覆度が小さいためである。このようにｍが大きな値をとる結果、チャネル長Ｌｃの増加とともにオンオフ比も大きくなり、Ｌｃが３０μｍではオンオフ比がおよそ１０3 、Ｌｃが４０μｍ以上でオンオフ比は１０5 以上となっている。 On the other hand, FIG. When the collection time by the filter 10 is short as in C, when the average length Lcnt of the carbon nanotubes is 10 μm and the channel length Lc is 5 to 20 μm, the metal-type carbon nanotubes bridge between the source and the drain. As a result, the on / off ratio is about 10 to 10 2, which is worse. Further, when the channel length Lc is 100 μm or more, the off-current has a limit value generated by the heat conduction of the carbon nanotube, and the off-current cannot be further reduced. Further, when the channel length Lc is 30 to 50 μm, a value predicted based on the percolation theory is taken. When the channel length Lc is in the range of 30 to 50 μm, m takes a large value of 14. This is because the surface density of the carbon nanotube thin film 11 is low due to the short collection time by the filter 10 and the standardized coating. This is because the degree is small. As a result of the large value of m, the on / off ratio increases as the channel length Lc increases. The on / off ratio is approximately 10 3 when Lc is 30 μm, the on / off ratio is 10 5 or more when Lc is 40 μm or more.
　なお、図４．Ｃではチャネル長Ｌｃの上限が１００μｍであるが、１００μｍ以上であってもオンオフ比が１０6 以上の良好な値であることが推察される。ただし、チャネル長Ｌｃが２００μｍより大きいと、応答速度が低下したり、素子サイズが大きくなりすぎるため、２００μｍ以下とするのが望ましい。なお、上記の特性は、カーボンナノチューブの平均長さＬｃｎｔが１０μｍの時の特性である。カーボンナノチューブの平均長さＬｃｎｔとチャネル長Ｌｃとには、それらの比率が同一であれば、同一の特性が得られるような相似関係がある。したがって、カーボンナノチューブの平均長さＬｃｎｔが１０μｍよりも、さらに、短くなっても、その比率に応じて、チャネル長Ｌｃを短かくすることにより、上記の特性が得られる。このため、チャネル長Ｌｃは、製造限界まで短くしても、それに比例して、カーボンナノチューブの平均長さＬｃｎｔを短くすることで、上記のオンオフ比の大きい特性を得ることができる。 Note that FIG. In C, the upper limit of the channel length Lc is 100 μm, but it is presumed that the on / off ratio is a good value of 10 6 or more even if it is 100 μm or more. However, when the channel length Lc is larger than 200 μm, the response speed is lowered or the element size becomes too large. In addition, said characteristic is a characteristic when the average length Lcnt of a carbon nanotube is 10 micrometers. The average length Lcnt and the channel length Lc of the carbon nanotubes have a similar relationship that the same characteristics can be obtained if the ratios are the same. Therefore, even if the average length Lcnt of the carbon nanotubes is further shorter than 10 μm, the above characteristics can be obtained by shortening the channel length Lc according to the ratio. For this reason, even if the channel length Lc is shortened to the production limit, the above-described characteristics with a large on / off ratio can be obtained by shortening the average length Lcnt of the carbon nanotubes in proportion thereto.
　図４、図５から、ＣＮＴ－ＴＦＴのオンオフ比を、規格化された被覆度、チャネル長Ｌｃ、カーボンナノチューブの長さＬｃｎｔによって良好にすることが可能であることがわかる。規格化された被覆度は、フィルタ１０による収集時間での密度ρの制御、およびカーボンナノチューブ生成時の成長温度、ガス流量の制御によるカーボンナノチューブの平均長さＬｃｎｔの制御によって行うことができる。具体的には、規格化された被覆度を５～１５、カーボンナノチューブの平均長さＬｃｎｔを１０μｍとするときチャネル長Ｌｃを３０～２００μｍ、ＬｃｎｔをＬｃの１／２０～１／３倍とすることで、オンオフ比が１０3 以上のＣＮＴ－ＴＦＴを実現することができる。ＬｃｎｔをＬｃの１／２０～１／３倍とするのは、移動度の低下を防止するとともに、金属型カーボンナノチューブがソース－ドレイン間に架橋してしまう確率を低減して電流リークを防止するためである。オンオフ比および移動度をより望ましくするためには、規格化された被覆度を５～１５、カーボンナノチューブの平均長さＬｃｎｔを１０μｍとするときチャネル長Ｌｃを３０～２００μｍ、ＬｃｎｔをＬｃの１／２０～１／５倍とすることである。オンオフ比を大きく、且つ、移動度を大きく保つためには、カーボンナノチューブの平均長さＬｃｎｔを１０μｍとするときチャネル長Ｌｃを４０～１００μｍ、ＬｃｎｔをＬｃの１／１０～１／５倍とすることが望ましく、オンオフ比および移動度をより望ましくするためには、規格化された被覆度を７～１０、チャネル長Ｌｃを４０～１００μｍ、ＬｃｎｔをＬｃの１／１０～１／５倍とすることが望ましく、さらに望ましくは、規格化された被覆度を９～１０、チャネル長Ｌｃを９０～１００μｍ、ＬｃｎｔをＬｃの０．１～０．１５倍とすることである。なお、上記したように、規格化された被覆度は、カーボンナノチューブの平均長さＬｃｎｔによる影響が排除された値となるので、上記の特性は、カーボンナノチューブの長さや、チャネル長によらず、規格化された被覆度の範囲によって得ることができる。したがって、本件発明の規格化されたカーボンナノチューブの被覆度が５～１５、７～１０の範囲は、カーボンナノチューブの長さや、チャネル長によらず、オンオフ比を大きくできる範囲である。 4 and 5, it can be seen that the on / off ratio of the CNT-TFT can be improved by the normalized coverage, channel length Lc, and carbon nanotube length Lcnt. The normalized coverage can be achieved by controlling the density ρ during the collection time by the filter 10 and controlling the average length Lcnt of the carbon nanotubes by controlling the growth temperature and the gas flow rate when the carbon nanotubes are generated. Specifically, when the normalized coverage is 5 to 15, the average length Lcnt of carbon nanotubes is 10 μm, the channel length Lc is 30 to 200 μm, and Lcnt is 1/20 to 1/3 times Lc. Thus, a CNT-TFT having an on / off ratio of 10 3 or more can be realized. Setting Lcnt to 1/20 to 1/3 times Lc prevents a decrease in mobility and reduces the probability that the metal-type carbon nanotube is bridged between the source and the drain, thereby preventing current leakage. Because. In order to make the on / off ratio and the mobility more desirable, when the normalized coverage is 5 to 15, the average length Lcnt of the carbon nanotube is 10 μm, the channel length Lc is 30 to 200 μm, and Lcnt is 1 / L of Lc. 20 to 1/5 times. In order to keep the on / off ratio large and the mobility high, when the average length Lcnt of carbon nanotubes is 10 μm, the channel length Lc is 40 to 100 μm, and Lcnt is 1/10 to 1/5 times Lc. In order to make the on / off ratio and the mobility more desirable, the normalized coverage is 7 to 10, the channel length Lc is 40 to 100 μm, and Lcnt is 1/10 to 1/5 times Lc. More preferably, the standardized coverage is 9 to 10, the channel length Lc is 90 to 100 μm, and Lcnt is 0.1 to 0.15 times Lc. Note that, as described above, the normalized coverage is a value from which the influence of the average length Lcnt of the carbon nanotubes has been eliminated, and thus the above characteristics are independent of the length of the carbon nanotubes and the channel length. It can be obtained by a standard range of coverage. Accordingly, the range of the coverage of the standardized carbon nanotube of the present invention of 5 to 15 and 7 to 10 is a range in which the on / off ratio can be increased regardless of the length of the carbon nanotube and the channel length.
　図６は、実施例１のＣＮＴ－ＴＦＴのＩｄ－Ｖｇｓ特性（Ｖｄｓ＝－０．５Ｖ）を示したグラフ、図７は、Ｉｄ－Ｖｄｓ特性を示したグラフである。Ｌｃは１００μｍ、チャネル幅は１００μｍ、Ｌｃｎｔは１０μｍ、フィルタ１０による収集時間は２秒とした。図６、図７のように、実施例１のＣＮＴ－ＴＦＴは、ほぼノーマリオフなｐ型ＦＥＴの特性が得られていることがわかる。また、オンオフ比は３．４×１０6 で良好な特性を示している。また、Ｖｄｓ＝－０．５Ｖのときの相互コンダクタンスｇｍは９μＳ／ｍｍ、移動度μは８ｃｍ2 ／Ｖｓであり、移動度μも良好な特性を示している。 6 is a graph showing the Id-Vgs characteristic (Vds = −0.5 V) of the CNT-TFT of Example 1, and FIG. 7 is a graph showing the Id-Vds characteristic. Lc was 100 μm, channel width was 100 μm, Lcnt was 10 μm, and the collection time by the filter 10 was 2 seconds. As shown in FIGS. 6 and 7, it can be seen that the CNT-TFT of Example 1 has almost normally-off p-type FET characteristics. The on / off ratio is 3.4 × 10 6 , indicating good characteristics. Further, when Vds = −0.5 V, the mutual conductance gm is 9 μS / mm, the mobility μ is 8 cm 2 / Vs, and the mobility μ also shows good characteristics.
　なお、ＴＦＴの構造は実施例１に限るものではなく、絶縁膜上に接して位置するネットワーク状に連鎖したカーボンナノチューブ薄膜が、ソースとドレインとの間を架橋した構造を有していれば、任意の構造であってよい。例えば、基板上にゲートを形成し、そのゲート上及びゲートで覆われていない基板上に絶縁膜を形成し、その絶縁膜上にチャネルの長だけ離間してソース、ドレインを形成し、フィルタに収集されたカーボンナノチューブ薄膜を絶縁膜上のチャネルの上に転写した構造とすることができる。また、基板上に、フィルタに収集されたカーボンナノチューブ薄膜をチャネル領域に転写し、そのカーボンナノチューブ薄膜のチャネルの長だけ離間した端部にカーボンナノチューブを架橋するようにソース、ドレインを形成し、カーボンナノチューブ薄膜、ソース、及び、ドレインの上に、絶縁膜を形成し、その絶縁膜の上であって、チャネルの上部にゲートを形成した構造とすることができる。また、基板上に、ソース、ドレインを形成し、ソース、ドレイン間のチャネルに両者を架橋するように、フィルタに収集されたカーボンナノチューブ薄膜を転写し、カーボンナノチューブ薄膜、ソース、及び、ドレインの上に、絶縁膜を形成し、その絶縁膜の上であって、チャネルの上部にゲートを形成した構造とすることができる。　また、実施例１のＣＮＴ－ＴＦＴでは、基板としてＰＥＮを用いてフレキシブルなＴＦＴを実現しているが、Ｓｉ基板などの従来より用いられている基板を用いてもよい。 The structure of the TFT is not limited to that of the first embodiment. If the carbon nanotube thin film chained in a network located in contact with the insulating film has a structure in which the source and the drain are bridged, Any structure may be used. For example, a gate is formed on a substrate, an insulating film is formed on the gate and a substrate not covered with the gate, and a source and a drain are formed on the insulating film by a length of a channel, and the filter is formed. The collected carbon nanotube thin film can be transferred onto the channel on the insulating film. Further, the carbon nanotube thin film collected by the filter is transferred onto the channel region on the substrate, and the source and drain are formed so as to bridge the carbon nanotubes at the ends separated by the channel length of the carbon nanotube thin film. An insulating film can be formed on the nanotube thin film, the source, and the drain, and a gate can be formed on the insulating film and above the channel. In addition, the carbon nanotube thin film collected on the filter is transferred so that the source and drain are formed on the substrate, and the channel between the source and drain is bridged, and the carbon nanotube thin film, the source and the drain are formed on the substrate. In addition, an insulating film may be formed, and a gate may be formed on the insulating film and above the channel. In the CNT-TFT of Example 1, a flexible TFT is realized using PEN as a substrate, but a conventionally used substrate such as a Si substrate may be used.
　実施例１のＣＮＴ－ＴＦＴについて、カーボンナノチューブの太さ依存性について考察した。カーボンナノチューブの太さは、実施例１で示した浮遊触媒法を用いたカーボンナノチューブの製造方法において、二酸化炭素の濃度を調整することで制御した。 Regarding the CNT-TFT of Example 1, the thickness dependence of the carbon nanotube was considered. The thickness of the carbon nanotube was controlled by adjusting the concentration of carbon dioxide in the carbon nanotube production method using the floating catalyst method shown in Example 1.
　図８は、カーボンナノチューブの太さ（直径）を１．１ｎｍとした場合のＣＮＴ－ＴＦＴのＩｄｓ－Ｖｇｓ特性を示した図である。また、図９は、カーボンナノチューブの太さを１．６ｎｍとした場合のＣＮＴ－ＴＦＴのＩｄｓ－Ｖｇｓ特性を示した図である。図８のように、カーボンナノチューブの太さを１．１ｎｍとした場合には、Ｖｄｓを－０．５Ｖとしたときのオンオフ比は１０8 オーダー、Ｖｄｓを－５Ｖとしたときのオンオフ比は１０7 オーダーであり、そのオンオフ比の差は１０～１０2 程度である。一方、図９のように、カーボンナノチューブの太さを１．６ｎｍとした場合には、Ｖｄｓを－０．５Ｖとしたときのオンオフ比は１０8 オーダー、Ｖｄｓを－５Ｖとしたときのオンオフ比は１０5 オーダーであり、そのオンオフ比の差は１０2 ～１０4 程度である。ＣＮＴの特性としては、オンオフ比が高く、かつ、Ｖｄｓの変化によるオンオフ比の変動が少ないことが望ましい。したがって、カーボンナノチューブの太さは、１．１ｎｍ以下であることが望ましいことがわかる。また、作製の容易さから、カーボンナノチューブの太さは０．４ｎｍ以上とすることが望ましい。 FIG. 8 is a diagram showing the Ids-Vgs characteristics of the CNT-TFT when the thickness (diameter) of the carbon nanotube is 1.1 nm. FIG. 9 is a diagram showing Ids-Vgs characteristics of the CNT-TFT when the thickness of the carbon nanotube is 1.6 nm. As shown in FIG. 8, when the thickness of the carbon nanotube is 1.1 nm, the on / off ratio when Vds is −0.5V is on the order of 10 8 , and the on / off ratio when Vds is −5V is 10 7 is of the order, the difference between the on-off ratio is 10 to 10 2 about. On the other hand, as shown in FIG. 9, when the thickness of the carbon nanotube is 1.6 nm, the on / off ratio when Vds is −0.5V is on the order of 10 8 , and the on / off ratio when Vds is −5V. Is on the order of 10 5 , and the difference in on / off ratio is about 10 2 to 10 4 . As characteristics of the CNT, it is desirable that the on / off ratio is high and the fluctuation of the on / off ratio due to the change in Vds is small. Therefore, it can be seen that the thickness of the carbon nanotube is desirably 1.1 nm or less. Moreover, it is desirable that the thickness of the carbon nanotube is 0.4 nm or more from the viewpoint of ease of production.
　実施例１で示した浮遊触媒法を用いたカーボンナノチューブの製造方法において、二酸化炭素の濃度を変化させたときに得られるカーボンナノチューブの波長吸収特性を測定した。結果を図１１に示す。、この波長吸収特性の吸収ピークの波長から、カーボンナノチューブの直径を測定することができる。ＣＯ2 ガスの流量が０、１、２、３、４ｃｍ3 ／ｍｉｎ、ＣＯガスに対する流量比（ＣＯ2 ／ＣＯ）が、０、２．５×１０-3、７．５×１０-3、１．０×１０-2  の時に、得られるカーボンナノチューブの直径は、それぞれ、１．１、１．２、１．３、１．６、１．９ｎｍであることが分かる。ＣＯガスに対するＣＯ2 ガス流量比が多くなるほど、カーボンナノチューブの直径は大きくなることが分かる。ソースドレイン間電圧の広い範囲において、オンオフ比を大きくできるためのカーボンナノチューブの直径を１．２ｎｍ以下にするためには、ＣＯガスに対するＣＯ2 ガス流量比は、２．５×１０-3以下とすることが望ましい。 In the method for producing carbon nanotubes using the floating catalyst method shown in Example 1, the wavelength absorption characteristics of the carbon nanotubes obtained when the carbon dioxide concentration was changed were measured. The results are shown in FIG. The diameter of the carbon nanotube can be measured from the wavelength of the absorption peak of this wavelength absorption characteristic. The flow rate of CO 2 gas is 0, 1, 2, 3 , 4 cm 3 / min, and the flow rate ratio to CO gas (CO 2 / CO) is 0, 2.5 × 10 −3 , 7.5 × 10 −3 , It can be seen that the diameters of the carbon nanotubes obtained at 1.0 × 10 −2 are 1.1, 1.2, 1.3, 1.6, and 1.9 nm, respectively. It can be seen that the diameter of the carbon nanotubes increases as the CO 2 gas flow rate ratio relative to the CO gas increases. In order to make the carbon nanotube diameter 1.2 nm or less in order to increase the on / off ratio in a wide range of the source-drain voltage, the CO 2 gas flow rate ratio to the CO gas is 2.5 × 10 −3 or less. It is desirable to do.
　また、実施例１で示した浮遊触媒法を用いたカーボンナノチューブの製造方法において、形成時の温度を変化させたときに得られるカーボンナノチューブの波長吸収特性を測定した。結果を図１２に示す。この波長吸収特性の吸収ピークの波長から、カーボンナノチューブの直径を測定することができる。形成温度が８００、８２５、８５０、９００℃との場合には、得られるカーボンナノチューブの直径は、それぞれ、１．０、１．１、１．２、１．３ｎｍであることが分かる。形成温度が高くなる程、カーボンナノチューブの直径は大きくなることが理解される。このように、形成温度の制御により、直径１．１ｎｍ以下においても、カーボンナノチューブの直径の制御が可能である。 Further, in the method for producing carbon nanotubes using the floating catalyst method shown in Example 1, the wavelength absorption characteristics of the carbon nanotubes obtained when the temperature during formation was changed were measured. The results are shown in FIG. From the wavelength of the absorption peak of this wavelength absorption characteristic, the diameter of the carbon nanotube can be measured. When the forming temperatures are 800, 825, 850, and 900 ° C., it can be seen that the diameters of the obtained carbon nanotubes are 1.0, 1.1, 1.2, and 1.3 nm, respectively. It is understood that the higher the formation temperature, the larger the diameter of the carbon nanotube. Thus, by controlling the formation temperature, the diameter of the carbon nanotube can be controlled even when the diameter is 1.1 nm or less.
　ＣＮＴ－ＴＦＴを用いた集積回路を作製するには、ＣＮＴ－ＴＦＴのしきい値電圧を制御することが重要となる。発明者らは、次の手段により実施例１のＣＮＴ－ＴＦＴのしきい値電圧の制御が可能であることを示した。それは、Ｆ4 ＴＣＮＱ（2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane）を含む溶液をスピンコートすることにより、ＣＮＴ－ＴＦＴのチャネルであるカーボンナノチューブをＦ4 ＴＣＮＱで被覆し、そのスピンコートする溶液のＦ4 ＴＣＮＱの濃度を制御することである。Ｆ4 ＴＣＮＱは、カーボンナノチューブに対してｐ型ドーパントとして作用する。 In order to manufacture an integrated circuit using a CNT-TFT, it is important to control the threshold voltage of the CNT-TFT. The inventors have shown that the threshold voltage of the CNT-TFT of Example 1 can be controlled by the following means. It spin-coats a solution containing F 4 TCNQ (2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane), so that the carbon nanotubes that are channels of the CNT-TFT are formed with F 4 TCNQ. Coating and spin coating the solution to control the concentration of F 4 TCNQ. F 4 TCNQ acts as a p-type dopant for carbon nanotubes.
　図１０は、実施例１に示したＣＮＴ－ＴＦＴにおいて、カーボンナノチューブにＦ4 ＴＣＮＱを被膜した場合のＩｄｓ－Ｖｇｓ特性（Ｖｄｓ＝－５Ｖ）を示したグラフである。溶媒にはトルエンを用い、Ｆ4 ＴＣＮＱの濃度は、０．０１、０．０２、０．０４、０．０８ｍＭｏｌ／ｌ（ミリモル／リットル）とした。また、図１０にはＦ4 ＴＣＮＱの溶液をスピンコートしない場合も示している。図１０のように、Ｆ4 ＴＣＮＱの濃度を高くしていくと、しきい値電圧が高くなっていくことがわかる。また、Ｆ4 ＴＣＮＱの濃度が０．０１～０．０４ｍＭｏｌ／ｌの場合には、ＣＮＴ－ＴＦＴは速やかにオンオフ動作できるのに対し、Ｆ4 ＴＣＮＱの濃度が０．０８ｍＭｏｌ／ｌの場合には、ＣＮＴ－ＴＦＴは速やかなオンオフ動作ができていないことがわかる。このことから、Ｆ4 ＴＣＮＱの濃度は０．０１ｍＭｏｌ／ｌ以上、０．０４ｍＭｏｌ／ｌ以下の範囲で制御することが望ましいと考えられる。 FIG. 10 is a graph showing Ids-Vgs characteristics (Vds = −5 V) when carbon nanotubes are coated with F 4 TCNQ in the CNT-TFT shown in Example 1. Toluene was used as the solvent, and the concentrations of F 4 TCNQ were 0.01, 0.02, 0.04, and 0.08 mMol / l (mmol / liter). FIG. 10 also shows the case where the F 4 TCNQ solution is not spin-coated. As shown in FIG. 10, the threshold voltage increases as the concentration of F 4 TCNQ is increased. In addition, when the concentration of F 4 TCNQ is 0.01 to 0.04 mMol / l, the CNT-TFT can be quickly turned on and off, whereas when the concentration of F 4 TCNQ is 0.08 mMol / l. It can be seen that the CNT-TFT is not capable of prompt on / off operation. From this, it is considered that the concentration of F 4 TCNQ is desirably controlled in the range of 0.01 mMol / l or more and 0.04 mMol / l or less.
　以上のように、実施例１のＣＮＴ－ＴＦＴのしきい値電圧の制御は、Ｆ4 ＴＣＮＱ溶液のスピンコートによりカーボンナノチューブをＦ4 ＴＣＮＱによって被膜する際に、その溶液のＦ4 ＴＣＮＱ濃度を制御することによって行うことができる。 As described above, the threshold voltage of the CNT-TFT of Example 1 is controlled by controlling the F 4 TCNQ concentration of the carbon nanotube when the carbon nanotube is coated with F 4 TCNQ by spin coating of the F 4 TCNQ solution. Can be done.
　本発明は、ディスプレイや電子ペーパーなどで使用されるＴＦＴとして利用することができる。 The present invention can be used as a TFT used in a display or electronic paper.
　１０：フィルタ
　１１：カーボンナノチューブ薄膜
　２０：基板
　２１：樹脂フィルム基板
　２２：ゲート電極
　２３：絶縁膜
　２４：ソース電極
　２５：ドレイン電極 10: Filter 11: Carbon nanotube thin film 20: Substrate 21: Resin film substrate 22: Gate electrode 23: Insulating film 24: Source electrode 25: Drain electrode

Claims (17)

  1. 　絶縁膜上に接して位置するネットワーク状に連鎖したカーボンナノチューブ薄膜が、ソースとドレインとの間を架橋した構造を有し、
    　前記ソースと前記ドレイン間のチャネル長Ｌｃを越える長さのカーボンナノチューブが実質上存在せず、カーボンナノチューブの平均長さＬｃｎｔがチャネル長Ｌｃの１／２０～１／３倍の範囲であり、
    　規格化されたカーボンナノチューブの被覆度を、カーボンナノチューブ薄膜の面密度をρとして、ρ＊（Ｌｃｎｔ）2 で定義するとき、規格化されたカーボンナノチューブの被覆度が５～１５である、
    　ことを特徴とする電界効果トランジスタ。     A carbon nanotube thin film chained in a network located in contact with the insulating film has a structure in which the source and the drain are bridged,
    There is substantially no carbon nanotube having a length exceeding the channel length Lc between the source and the drain, and the average length Lcnt of the carbon nanotube is in a range of 1/20 to 1/3 times the channel length Lc.
    When the standardized carbon nanotube coverage is defined as ρ * (Lcnt) 2 where ρ is the surface density of the carbon nanotube thin film, the standardized carbon nanotube coverage is 5 to 15.
    A field effect transistor.
  2. 　前記チャネル長Ｌｃは、１０～２００μｍであることを特徴とする請求項１に記載の電界効果トランジスタ。 2. The field effect transistor according to claim 1, wherein the channel length Lc is 10 to 200 μm.
  3. 　前記チャネル長Ｌｃが３０～２００μｍであることを特徴とする請求項１に記載の電界効果トランジスタ。 2. The field effect transistor according to claim 1, wherein the channel length Lc is 30 to 200 μm.
  4. 　前記チャネル長Ｌｃが４０～１００μｍであることを特徴とする請求項１に記載の電界効果トランジスタ。 2. The field effect transistor according to claim 1, wherein the channel length Lc is 40 to 100 μm.
  5. 　前記カーボンナノチューブの平均長さＬｃｎｔが前記チャネル長Ｌｃの１／１０～１／５倍の範囲であり、規格化されたカーボンナノチューブの前記被覆度が７～１０であることを特徴とする請求項１ないし請求項４のいずれか１項に記載の電界効果トランジスタ。 The average length Lcnt of the carbon nanotubes is in a range of 1/10 to 1/5 times the channel length Lc, and the coverage of the standardized carbon nanotubes is 7 to 10. The field effect transistor according to any one of claims 1 to 4.
  6. 　前記カーボンナノチューブは、Ｆ4 ＴＣＮＱで被覆されていることを特徴とする請求項１ないし請求項５のいずれか１項に記載の電界効果トランジスタ。 The field effect transistor according to claim 1, wherein the carbon nanotube is coated with F 4 TCNQ.
  7. 　前記カーボンナノチューブは、前記Ｆ4 ＴＣＮＱの濃度が０．０１～０．０４ｍＭｏｌ／ｌの溶液を用いて被覆されたことを特徴とする請求項６に記載の電界効果トランジスタ。 The field effect transistor according to claim 6, wherein the carbon nanotubes are coated with a solution having the F 4 TCNQ concentration of 0.01 to 0.04 mMol / l.
  8. 　前記カーボンナノチューブの平均太さは、直径１．１ｎｍ以下であることを特徴とする請求項１ないし請求項７のいずれか１項に記載の電界効果トランジスタ。 The field effect transistor according to any one of claims 1 to 7, wherein an average thickness of the carbon nanotube is 1.1 nm or less in diameter.
  9. 　フレキシブルなプラスチック基板上に素子構造が形成されていることを特徴とする請求項１ないし請求項８のいずれか１項に記載の電界効果トランジスタ。 9. The field effect transistor according to claim 1, wherein an element structure is formed on a flexible plastic substrate.
  10. 　絶縁膜上に接して位置するネットワーク状に連鎖したカーボンナノチューブ薄膜が、ソースとドレインとの間のチャネルを架橋した構造を有する電界効果トランジスタの製造方法において、
    　基板上に、ソース、ドレイン、ソースとドレイン間のチャネルを接続するカーボンナノチューブ薄膜、ゲート、ゲートとカーボンナノチューブ薄膜とを絶縁分離する絶縁膜とから成る素子構造を形成し、
    　浮遊触媒法によりカーボンナノチューブを生成し、生成されたカーボンナノチューブをフィルタに収集して薄膜を生成し、
    　前記フィルタに収集されたカーボンナノチューブ薄膜を、前記チャネルの上に転写する
    　ことを特徴とする電界効果トランジスタの製造方法。     In the method of manufacturing a field effect transistor having a structure in which a thin film of carbon nanotubes chained in a network located in contact with an insulating film bridges a channel between a source and a drain,
    On the substrate, an element structure comprising a source, a drain, a carbon nanotube thin film for connecting a channel between the source and the drain, a gate, and an insulating film for insulating and separating the gate and the carbon nanotube thin film is formed.
    Carbon nanotubes are produced by the floating catalyst method, and the produced carbon nanotubes are collected in a filter to produce a thin film.
    The carbon nanotube thin film collected on the filter is transferred onto the channel.
  11. 　前記ソースと前記ドレイン間のチャネル長Ｌｃを越える長さのカーボンナノチューブが実質上存在せず、カーボンナノチューブの平均長さＬｃｎｔがチャネル長Ｌｃの１／２０～１／３倍の範囲であり、規格化されたカーボンナノチューブの被覆度を、カーボンナノチューブ薄膜の面密度をρとして、ρ＊（Ｌｃｎｔ）2 で定義するとき、規格化されたカーボンナノチューブの被覆度が５～１５とすることを特徴とする請求項１０に記載の電界効果トランジスタの製造方法。 There is substantially no carbon nanotube having a length exceeding the channel length Lc between the source and the drain, and the average length Lcnt of the carbon nanotube is in a range of 1/20 to 1/3 times the channel length Lc. When the coverage of the carbon nanotubes is defined as ρ * (Lcnt) 2 where ρ is the surface density of the carbon nanotube thin film, the normalized coverage of the carbon nanotubes is 5 to 15. The method of manufacturing a field effect transistor according to claim 10.
  12. 　カーボンナノチューブ薄膜の面密度を、前記フィルタでの収集時間により制御することを特徴とする請求項１０または請求項１１に記載の電界効果トランジスタの製造方法。 12. The method of manufacturing a field effect transistor according to claim 10, wherein the surface density of the carbon nanotube thin film is controlled by the collection time in the filter.
  13. 　前記カーボンナノチューブの平均直径は、カーボンナノチューブの形成時の温度を制御することにより行うことを特徴とする請求項１０ないし請求項１２のいずれか１項に記載の電界効果トランジスタの製造方法。 13. The method of manufacturing a field effect transistor according to claim 10, wherein the average diameter of the carbon nanotubes is controlled by controlling a temperature at the time of forming the carbon nanotubes.
  14. 　前記カーボンナノチューブの平均直径は、カーボンナノチューブの形成時に追加する二酸化炭素ガスの原料ガスに対する比率を制御することにより行うことを特徴とする請求項１０ないし請求項１３のいずれか１項に記載の電界効果トランジスタの製造方法。 The electric field according to any one of claims 10 to 13, wherein the average diameter of the carbon nanotube is controlled by controlling a ratio of carbon dioxide gas added to the raw material gas when the carbon nanotube is formed. Effect transistor manufacturing method.
  15. 　前記カーボンナノチューブの平均直径を１．１ｎｍ以下とすることを特徴とする請求項１０ないし請求項１４のいずれか１項に記載の電界効果トランジスタの製造方法。 15. The method of manufacturing a field effect transistor according to claim 10, wherein an average diameter of the carbon nanotube is 1.1 nm or less.
  16. 　前記カーボンナノチューブの形成時の温度は、８２５℃以下であることを特徴とする請求項１０ないし請求項１５のいずれか１項に記載の電界効果トランジスタの製造方法。 The method for manufacturing a field effect transistor according to any one of claims 10 to 15, wherein a temperature at the time of forming the carbon nanotube is 825 ° C or lower.
  17. 　前記カーボンナノチューブに、Ｆ4 ＴＣＮＱの濃度が０．０１～０．０４ｍＭｏｌ／ｌの溶液を用いて、被覆することを特徴とする請求項１０ないし請求項１６のいずれか１項に記載の電界効果トランジスタの製造方法。 The field effect according to any one of claims 10 to 16, wherein the carbon nanotube is coated with a solution having an F 4 TCNQ concentration of 0.01 to 0.04 mMol / l. A method for manufacturing a transistor.
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