WO2018168151A1 - 焦電センサ - Google Patents
焦電センサ Download PDFInfo
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- WO2018168151A1 WO2018168151A1 PCT/JP2017/046480 JP2017046480W WO2018168151A1 WO 2018168151 A1 WO2018168151 A1 WO 2018168151A1 JP 2017046480 W JP2017046480 W JP 2017046480W WO 2018168151 A1 WO2018168151 A1 WO 2018168151A1
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- Prior art keywords
- substrate
- pyroelectric sensor
- film
- pyroelectric
- optical filter
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- 239000000758 substrate Substances 0.000 claims abstract description 100
- 230000003287 optical effect Effects 0.000 claims abstract description 42
- 229910010272 inorganic material Inorganic materials 0.000 claims abstract description 13
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- 230000000052 comparative effect Effects 0.000 description 7
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- 239000006096 absorbing agent Substances 0.000 description 2
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- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 1
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- JRPBQTZRNDNNOP-UHFFFAOYSA-N barium titanate Chemical compound [Ba+2].[Ba+2].[O-][Ti]([O-])([O-])[O-] JRPBQTZRNDNNOP-UHFFFAOYSA-N 0.000 description 1
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- NKZSPGSOXYXWQA-UHFFFAOYSA-N dioxido(oxo)titanium;lead(2+) Chemical compound [Pb+2].[O-][Ti]([O-])=O NKZSPGSOXYXWQA-UHFFFAOYSA-N 0.000 description 1
- HTXDPTMKBJXEOW-UHFFFAOYSA-N dioxoiridium Chemical compound O=[Ir]=O HTXDPTMKBJXEOW-UHFFFAOYSA-N 0.000 description 1
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- UKDIAJWKFXFVFG-UHFFFAOYSA-N potassium;oxido(dioxo)niobium Chemical compound [K+].[O-][Nb](=O)=O UKDIAJWKFXFVFG-UHFFFAOYSA-N 0.000 description 1
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Images
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J5/00—Radiation pyrometry, e.g. infrared or optical thermometry
- G01J5/10—Radiation pyrometry, e.g. infrared or optical thermometry using electric radiation detectors
- G01J5/34—Radiation pyrometry, e.g. infrared or optical thermometry using electric radiation detectors using capacitors, e.g. pyroelectric capacitors
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J1/00—Photometry, e.g. photographic exposure meter
- G01J1/02—Details
- G01J1/04—Optical or mechanical part supplementary adjustable parts
- G01J1/0407—Optical elements not provided otherwise, e.g. manifolds, windows, holograms, gratings
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J5/00—Radiation pyrometry, e.g. infrared or optical thermometry
- G01J5/02—Constructional details
- G01J5/04—Casings
- G01J5/046—Materials; Selection of thermal materials
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J5/00—Radiation pyrometry, e.g. infrared or optical thermometry
- G01J5/02—Constructional details
- G01J5/08—Optical arrangements
- G01J5/0801—Means for wavelength selection or discrimination
- G01J5/0802—Optical filters
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N30/00—Piezoelectric or electrostrictive devices
- H10N30/80—Constructional details
- H10N30/85—Piezoelectric or electrostrictive active materials
- H10N30/853—Ceramic compositions
- H10N30/8548—Lead-based oxides
- H10N30/8554—Lead-zirconium titanate [PZT] based
Definitions
- the present invention relates to a pyroelectric sensor provided with a pyroelectric element that is used as an infrared sensor.
- the infrared sensor is a sensor that detects thermal radiation (infrared rays) from an object to be measured.
- a silicon (Si) substrate 102 and an infrared sensing unit 103 provided on a first surface 102a of the Si substrate 102 are provided as an infrared sensor 101.
- a cavity 105 for thermal insulation is formed on the first surface 102a of the Si substrate 102 where the infrared sensing unit 103 is located, and only infrared rays are formed on the second surface 102b of the Si substrate 102.
- transmits predetermined is disclosed.
- the infrared sensing unit 103 is provided with an infrared absorption film 103a.
- Japanese Patent Application Laid-Open No. 2006-317232 discloses that the detailed configuration of the infrared sensing unit 103 is not disclosed and can be formed using a thermopile, a thermistor, a pyroelectric element, or the like.
- Japanese Patent Laid-Open No. 2006-317232 does not fully disclose the configuration of the infrared sensing unit, and does not mention the thickness of the infrared sensing unit. However, since the infrared sensing part is disposed on the cavity, a bulk-like element having a certain degree of rigidity is used.
- a bulk element is used for an infrared sensing unit in a conventional infrared sensor.
- an element there is a pyroelectric element using pyroelectric ceramics which is a kind of piezoelectric ceramic, and a pyroelectric sensor including the pyroelectric element is well known as an infrared sensor.
- the pyroelectric element detects infrared rays by using a pyroelectric effect in which polarization (surface charge) is generated due to a temperature change.
- the pyroelectric ceramics provided in the conventional pyroelectric sensor have a thickness of approximately 1 mm or more because a bulk material is used.
- the pyroelectric sensor has an infrared filter (optical filter) having a function of transmitting only infrared rays of a specific wavelength of a measurement object to be detected and cutting other wavelengths. Installed. Since such an optical filter is generally formed by forming multiple layers on a glass plate, it has a thickness of 0.5 mm or more including the thickness of the glass plate. Therefore, the thickness (device height) of the conventional pyroelectric sensor is 1.5 mm or more.
- an object of the present invention is to provide a pyroelectric sensor that can be sufficiently thinned.
- the pyroelectric sensor of the present invention comprises a Si substrate, A laminated portion in which a heat absorption layer made of an inorganic material, a lower electrode, a piezoelectric film, and an upper electrode are laminated in this order on one surface of the Si substrate, An optical filter that selectively transmits infrared rays, provided at a position opposite to the laminated portion on the other surface of the Si substrate; It is a pyroelectric sensor that senses infrared rays that are incident on the laminated portion through the Si substrate from the optical filter side.
- the piezoelectric film means a thin film piezoelectric body having a thickness of 10 ⁇ m or less.
- the lower electrode is made of a metal
- the inorganic material constituting the heat absorption layer is an oxide of the metal constituting the lower electrode.
- the inorganic material constituting the heat absorption layer is preferably a noble metal oxide.
- the piezoelectric film is preferably a sputtered film.
- the thickness of the Si substrate through which infrared rays incident on the laminated portion are transmitted is 250 ⁇ m or less.
- the Si substrate may include a thick portion thicker than the thickness of the region at the peripheral portion of the region where the laminated portion is provided.
- the Si substrate may have a hollow portion.
- the area of the Si substrate is preferably larger than the area of the laminated portion, the hollow portion is overlapped with the laminated portion, and the laminated portion is positioned inside the region of the hollow portion.
- the piezoelectric film is preferably a (100) oriented film of a perovskite oxide.
- the pyroelectric sensor of the present invention includes a Si substrate, a laminated portion in which a heat absorption layer made of an inorganic material, a lower electrode, a piezoelectric film, and an upper electrode are laminated in this order on one surface of the Si substrate, And an optical filter that selectively transmits infrared rays provided at a position opposite to the laminated portion on the other surface of the Si substrate, and senses infrared rays incident on the laminated portion through the Si substrate from the optical filter side. . Since the laminated portion including the piezoelectric film on one surface of the Si substrate is provided and the optical filter is provided on the other surface, the thickness can be reduced. Since the heat absorption layer is provided between the Si substrate and the lower electrode, infrared rays can be detected with high sensitivity.
- FIG. 6 is a schematic cross-sectional view showing a substrate used in Example 2.
- FIG. It is sectional drawing of the conventional infrared sensor.
- FIG. 1 is a schematic cross-sectional view of a pyroelectric sensor 1 according to the first embodiment of the present invention.
- the thickness of each layer and the ratio thereof are drawn as appropriate, and do not necessarily reflect the actual thickness and ratio (the same applies in the following drawings).
- a Si substrate 10, a heat absorption layer 18 made of an inorganic material, a lower electrode 22, a (100) -oriented piezoelectric film 23 and an upper electrode 24 are provided on one surface 10 a of the Si substrate 10.
- the optical filter 30 includes a stacked unit 20 that is stacked in this order, and an optical filter 30 that is provided at a position facing the stacked unit 20 on the other surface 10b of the Si substrate 10 and selectively transmits infrared rays. Infrared IR incident on the laminated portion 20 from the side through the Si substrate 10 is sensed.
- the lower electrode 22, the piezoelectric film 23 and the upper electrode 24 constitute a sensing unit 25.
- the sensing unit 25 coincides with the stacked unit 20 in plan view.
- infrared rays enter the sensing unit 25 the temperature rises, and surface charges are generated in the piezoelectric film 23, which is a pyroelectric body, due to the pyroelectric effect.
- This surface charge is taken out via a lead wire (not shown) connected to the lower electrode 22 and the upper electrode 24, and infrared rays can be detected by measuring it as an output signal using an appropriate electric circuit.
- “lower” and “upper” do not mean top and bottom.
- one electrode disposed on the Si substrate 10 side is simply referred to as a lower electrode, and the other electrode is referred to as an upper electrode.
- the main component of the lower electrode 22 is not particularly limited, and materials that can generally be used as an electrode can be appropriately used. However, it is preferable to use a metal. In particular, noble metals such as Pt, Ir, and Ru are preferable.
- the main component of the upper electrode 24 is not particularly limited, and includes electrode materials generally used in semiconductor processes such as Al, Ti, Ta, Cr, and Cu, and combinations thereof.
- the thickness of the lower electrode 22 and the upper electrode 24 is not particularly limited. However, if the thickness is too thin, the resistance value becomes high and the function as an electrode is deteriorated, and if it is thick, there is a problem that adhesion and heat capacity are increased. For this reason, the thicknesses of the electrodes 22 and 24 are preferably 50 nm or more and 300 nm or less.
- the piezoelectric film 23 is preferably made of one or more perovskite oxides represented by the following general formula (P).
- General formula ABO 3 (P) (In the general formula P, A: an element at the A site, at least one element selected from the group consisting of Pb, Ba, La, Sr, Bi, Li, Na, Ca, Cd, Mg, and K; B: Element of B site, from the group consisting of Ti, Zr, V, Nb, Ta, Cr, Mo, W, Mn, Sc, Co, Cu, In, Sn, Ga, Zn, Cd, Fe and Ni
- the standard is the case where the number of moles of the A-site element is 1.0 and the number of moles of the B-site element is 1.0, but the number of moles of the A-site element and the B-site element is within a range where a perovskite structure can be taken. May deviate from 1.0.
- Perovskite oxides represented by the above general formula include lead titanate, lead zirconate titanate (PZT), lead zirconate, lead lanthanum titanate, lead lanthanum zirconate titanate, lead zirconium titanate niobate , Lead-containing compounds such as lead zirconium niobate titanate titanate, lead zinc niobate titanate titanate, and mixed crystals thereof; barium titanate, strontium barium titanate, bismuth sodium titanate, bismuth potassium titanate, niobic acid Non-lead-containing compounds such as sodium, potassium niobate, lithium niobate, bismuth ferrite, and mixed crystal systems thereof can be mentioned.
- the piezoelectric film 23 more preferably contains one or more perovskite oxides represented by the following general formula PX.
- A is an A site element, at least one element including Pb, and M is at least one element selected from the group consisting of V, Nb, Ta, and Sb.
- 0 ⁇ x ⁇ b, 0 ⁇ y ⁇ b, 0 ⁇ b ⁇ x ⁇ y, and a: b: c 1: 1: 3 is standard, but these molar ratios are within a range that can take a perovskite structure. Within the reference molar ratio.
- the perovskite oxide (PX) is an intrinsic PZT or a part of the B site of PZT substituted with M. It is known that PZT to which various donor ions having a valence higher than that of the substituted ion are added has improved characteristics such as piezoelectric performance as compared with intrinsic PZT.
- M is preferably one or more donor ions having a valence higher than that of tetravalent Zr or Ti. Examples of such donor ions include V 5+ , Nb 5+ , Ta 5+ , Sb 5 +, Mo 6+ , and W 6+ .
- Bxy is not particularly limited as long as it has a perovskite structure.
- M is Nb
- the Nb / (Zr + Ti + Nb) molar ratio is preferably 0.05 or more and 0.25 or less, and more preferably 0.06 or more and 0.20 or less.
- the piezoelectric film in the pyroelectric element of the present invention may be any material other than a piezoelectric material made of a perovskite oxide as long as it can be formed into a thin film.
- the piezoelectric film 23 is preferably a columnar structure film made of a large number of columnar crystals extending in a non-parallel direction with respect to the substrate surface. This is because high piezoelectric performance can be obtained. With a film structure composed of a large number of columnar crystals extending non-parallel to the substrate surface, an alignment film having a uniform crystal orientation can be obtained. A (100) oriented film having a perovskite structure can be obtained by forming a PZT-based piezoelectric film by vapor phase growth or sol-gel at a substrate temperature of 500 ° C. or higher. If an alignment film can be obtained by film formation, polarization treatment is unnecessary, which is preferable.
- the growth direction of the columnar crystals may be non-parallel to the substrate surface, and may be substantially vertical or oblique.
- the average column diameter of many columnar crystals forming the piezoelectric film is not particularly limited, and is preferably 30 nm or more and 1 ⁇ m or less.
- (100) Oriented film means a film having a perovskite structure preferentially oriented in the (100) plane.
- the preferential orientation refers to a state in which the orientation direction of the crystal is not disordered and a specific crystal plane is oriented in a substantially constant direction.
- “preferentially oriented in the (100) plane” means diffraction of the (100) plane, the (110) plane, and the (111) plane that occurs when the piezoelectric film is measured by the X-ray diffraction wide angle method. It means that the intensity ratio (100) / ((100) + (110) + (111)) is larger than 0.5.
- the film thickness of the piezoelectric film 23 is not particularly limited as long as it is 10 ⁇ m or less, and is usually 1 ⁇ m or more, for example, 1 to 5 ⁇ m. Since a piezoelectric film having a thickness of 10 ⁇ m or less is used, the size can be reduced particularly in the thickness direction compared to a conventional pyroelectric sensor using a bulk piezoelectric material, and the overall height of the pyroelectric sensor can be reduced. It becomes possible.
- the thickness of the Si substrate 10 is preferably thinner. This is because the thinner the thickness, the smaller the heat capacity and the faster the response. Specifically, it is preferably 600 ⁇ m or less, more preferably 400 ⁇ m or less, and particularly preferably 250 ⁇ m or less. On the other hand, in the case of using a flat substrate as in this embodiment, the thickness is preferably 100 ⁇ m or more and 200 ⁇ m or more in order to suppress warping due to stress generated during the formation of the piezoelectric film. More preferred.
- the Si substrate 10 may include a stress adjustment layer and the like.
- the Si substrate 10 needs to transmit infrared rays. Therefore, as the Si substrate 10, it is preferable to use a wafer with a small amount of doped impurities, that is, a wafer having a high resistivity. Specifically, it preferably has a volume resistivity of 10 ⁇ cm or more, more preferably 100 ⁇ cm or more.
- At least the other surface 10b of the Si substrate 10 is mirror-polished and the surface roughness Ra is 1 nm or less in order to form a highly accurate optical filter 30.
- the heat absorption layer 18 absorbs infrared rays (heat) and efficiently transfers heat to the sensing unit 25. By providing this heat absorption layer 18, sensing sensitivity can be improved.
- the heat absorption layer 18 is not provided and the lower electrode 22 is a metal electrode such as Ir or Pt, the infrared IR is reflected by the metal electrode, and heat cannot be efficiently transmitted to the sensing unit 25. May not be fully demonstrated.
- the heat absorption layer 18 is made of an inorganic black material.
- a black absorber layer made of an organic material containing a pigment is well known, but the organic material has low heat resistance.
- the heat absorption layer is made of an inorganic material having high heat resistance. Due to the configuration of the pyroelectric sensor 1, it is necessary to form the heat absorption layer 18 on the substrate before the piezoelectric film 23, and the film forming process of the piezoelectric film 23 is a subsequent process. A heat absorption layer made of an organic material or the like having low heat resistance cannot be processed at a high temperature in the film formation process of the piezoelectric film 23.
- the heat absorption layer 18 it is preferable to use a metal whose oxide is black among the metals applicable to the lower electrode 22 described above.
- a noble metal oxide is preferable because it has high adhesion to Si as a substrate material and heat resistance.
- PtOx, IrOx, RuO and the like are preferable.
- the heat absorption layer 18 and the lower electrode 22 are formed seamlessly.
- the heat absorbing layer 18 and the lower electrode 22 can be formed seamlessly by forming the metal constituting the lower electrode 22 and the metal oxide metal constituting the heat absorbing layer 18 to be the same and continuously forming the film.
- the lower electrode 22 is made of Ir
- an IrOx film is formed by reactive sputtering using Ir as a target while flowing a mixed gas of O 2 and Ar as a film forming gas in vapor phase film formation such as sputtering.
- O 2 and Ar a mixed gas of O 2 and Ar
- Ir-only film can be formed following the IrOx film.
- Ir film can be formed seamlessly.
- the boundary between the IrOx film and the Ir film is not clear, and there is a region where the O content gradually decreases.
- the thickness of the heat absorption layer 18 is preferably 1 nm or more in order to efficiently absorb infrared rays. Further, in order to maintain good adhesion and not to increase the heat capacity too much, it is preferable to set the thickness to 100 nm or less.
- the optical filter 30 is an infrared filter that cuts out infrared rays that are not detected as a noise source as much as possible and transmits infrared wavelengths that are detection targets.
- an inorganic material multilayer filter or an organic material coating filter may be used.
- the surface roughness Ra of the film formation surface of the optical filter is preferably 1 nm or less. Therefore, it is preferable to use a Si wafer that has been back-polished.
- the transmission wavelength of the optical filter 30 can be selected depending on the target detection target.
- a bandpass filter that transmits only a wavelength of about 9 to 10 ⁇ m corresponding to infrared rays emitted from the human body.
- a known long-pass filter that transmits a wavelength of more than 5 ⁇ m (cuts a wavelength of 5 ⁇ m or less) from the viewpoint of cost or the like may be used.
- a Si wafer (for example, a thickness of 250 ⁇ m) polished on both sides is used as the Si substrate 10.
- the Si wafer may or may not be provided with a thermal oxide film.
- the heat absorption layer 18 and the lower electrode 22 are sequentially formed on the Si substrate 10 by sputtering.
- an IrOx film is seamlessly formed as the heat absorption layer 18 and an Ir film is seamlessly formed as the lower electrode 22.
- an IrOx film is formed to about 10 nm by reactive sputtering, and O 2 in the film forming gas is changed without turning off the sputtering plasma. Sputtering is continued with Ar alone, and an Ir film is formed to about 150 nm.
- an adhesion layer such as Ti of several nm or less may be formed on the Si substrate before the IrOx film is formed. However, the reason why the adhesion layer is set to several nm or less is that if it is too thick, the function of IrOx as the heat absorption layer is lowered.
- a piezoelectric film 23 is formed on the lower electrode 22.
- the substrate is heated to a temperature at which PZT is crystallized (500 to 650 ° C.), and a PZT film is formed as the piezoelectric film 23.
- a temperature at which PZT is crystallized 500 to 650 ° C.
- the substrate temperature is set to a high temperature of 500 ° C. or higher, if a heat absorption layer made of an organic material is provided, the substrate is damaged by heat and does not exhibit the function as the heat absorption layer.
- the heat absorption layer uses an inorganic material having high heat resistance, the heat absorption layer functions effectively as a heat absorption layer even after such a high temperature treatment.
- the obtained piezoelectric film 23 is partially etched and patterned, and then the upper electrode 24 is formed on the piezoelectric film 23.
- the optical filter 30 is formed on the other surface 10 b of the Si substrate 10.
- the optical filter 30 can be formed by vapor deposition, for example.
- an organic material absorber may be applied to the other surface 10b of the Si substrate 10 to form an optical filter.
- the pyroelectric sensor 1 of the first embodiment can be manufactured.
- the pyroelectric sensor 1 having this configuration includes a piezoelectric film having a thickness of 10 ⁇ m or less instead of the conventional bulk piezoelectric body in the sensing unit 25, the sensing unit 25 on one surface of one substrate, and the optical surface on the other surface. Since the filter 30 is provided, the thickness of the entire sensor can be reduced, and a low-profile pyroelectric sensor that can suppress the thickness of the entire sensor to 1 mm or less can be realized.
- FIG. 2 is a schematic cross-sectional view of the pyroelectric sensor 2 of the second embodiment.
- the same components as those in the pyroelectric sensor 1 shown in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted (the same applies to the following drawings).
- the pyroelectric sensor 2 of the present embodiment includes a Si substrate 11 having a diaphragm structure instead of the flat plate Si substrate 10 in the first embodiment.
- the stacked unit 20 (sensing unit 25) is provided on one surface 12a of the diaphragm 12, and the optical filter 30 is provided on the other surface 12b of the diaphragm 12.
- the Si substrate 11 having a diaphragm structure provided with a diaphragm support portion formed of a thick portion thicker than the diaphragm 12 is used at the peripheral portion of the diaphragm 12 provided with the laminated portion 20.
- the thickness of the Si portion through which the infrared IR incident on the sensing unit 25 passes can be reduced.
- the thickness of the Si substrate through which the infrared IR incident on the sensing unit 25 passes is preferably 250 ⁇ m or less.
- the entire Si substrate is thin, handling properties are reduced. According to this configuration, it is possible to improve the response by reducing the thickness of the portion where the sensing unit 25 is provided, and it is possible to realize a good handling property by providing the thick part at the periphery. it can.
- the thickness of the diaphragm 12 is preferably 200 ⁇ m or less, more preferably 100 ⁇ m or less, and even more preferably 50 ⁇ m or less.
- the pyroelectric sensor 2 of the second embodiment can further improve the response in addition to the effects obtained by the pyroelectric sensor 1 of the first embodiment.
- FIG. 3 is a schematic plan view and a schematic cross-sectional view taken along the line BB of the pyroelectric sensor 3 according to the third embodiment.
- the pyroelectric sensor 3 of the third embodiment includes a Si substrate 14 having a hollow portion 14a instead of the Si substrate 10 of the pyroelectric sensor 1 of the first embodiment.
- the laminated portion 20 is provided not on the entire surface of the Si substrate 14 but on the hollow portion 14a. As shown in the schematic plan view of FIG. 3, the area of the Si substrate 14 in plan view is larger than the area of the laminated part 20 (sensing part 25), and the laminated part 20 is provided so as to overlap the hollow part 14a.
- the laminated portion 20 is provided in a region smaller than the hollow portion 14a inside the hollow portion 14a.
- the hollow portion 14a is preferably vacuumed or depressurized, more preferably vacuum. This is because the closer to the vacuum, the less affected by air and the more noise can be suppressed.
- the Si substrate 14 has the hollow part 14 a, the infrared IR incident on the optical filter 30 passes through the hollow part 14 a and reaches the heat absorption layer 18. Since the actual part of the Si substrate 14 through which the infrared IR incident on the optical filter 30 passes is only a thin layer on the front and back surfaces constituting the hollow part 14a, sensing with fast response is possible.
- the response can be further improved.
- handling property is higher than the pyroelectric sensor 2 of 2nd Embodiment provided with the board
- substrate 14 provided with the hollow part 14a can be produced as follows, for example. Two SOI (Silicon on Insulator) wafers are prepared, and one SOI wafer is deeply dug by RIE (Reactive Ion Etching) to form a recess. Another SOI wafer is attached so as to cover the concave portion of the SOI wafer. Thereafter, the cavity SOI wafer (substrate provided with a hollow portion) can be manufactured by polishing and / or etching the surface.
- RIE Reactive Ion Etching
- FIG. 4 is a plan view and a cross-sectional view taken along the line CC of an example of an image sensor including pyroelectric sensors arranged in an array.
- the image sensor 5 includes a heat absorption layer 18 on one surface of a Si substrate 14 having a hollow portion 14 a, and a lower electrode 22, a piezoelectric film 23, and an upper electrode 24 are laminated on the heat absorption layer 18.
- a plurality of sensing units 25 are arranged vertically and horizontally.
- the lower electrode 22 is a uniform common electrode common to the plurality of sensing units 25.
- the piezoelectric film 23 and the upper electrode 24 are patterned and separated for each sensing unit 25.
- the image sensor 5 includes an optical filter 30 on the entire other surface of the Si substrate 14.
- the image sensor 5 includes a plurality of pyroelectric sensors similar to those of the third embodiment, and has the same thickness. Therefore, the image sensor 5 can be configured as a very low-profile device.
- Example 1 A 250 ⁇ m thick double-side polished Si wafer was used as the Si substrate.
- the thing of specification with 100 ohmcm or more with little volume of doping and large volume resistance was used as Si substrate in order to permeate
- the Si wafer may or may not be provided with a thermal oxide film.
- an iridium oxide film (IrOx film) was formed on the Si substrate by sputtering, and the substrate was heated to 300 ° C. to form a light absorption layer with an Ar + 30% O 2 gas composition of about 10 nm.
- oxygen in the film forming gas was set to 0%, and sputtering was performed only with Ar to form about 150 nm of Ir metal as the lower electrode.
- Ir was formed from IrOx seamlessly with good adhesion.
- the film forming gas is a mixed gas of 97.5% Ar + 2.5% O 2 and has a composition of Pb 1.3 (Zr 0.52 Ti 0.48 ) 0.88 Nb 0.12 ) O 3 as a target material. A thing was used.
- Nb-PZT film A part of the obtained piezoelectric film (hereinafter referred to as Nb-PZT film) is patterned by wet etching, and Ir is formed as an upper electrode on the Nb-PZT film. did.
- this invention equips the other surface of Si substrate with an optical filter, it evaluated in the state which does not provide an optical filter here.
- the presence or absence of the optical filter does not directly affect the response speed of the response and the sensitivity to infrared light of a specific wavelength, and therefore does not affect the evaluation of the effect of the present invention.
- this example does not include an optical filter on the back surface of the Si substrate.
- a general optical filter approximately 7 ⁇ m thick
- the thickness of the optical filter is reduced.
- an ultra-thin pyroelectric sensor having a total thickness of about 270 ⁇ m can be manufactured. If it is this thickness, even if a package is included, 1 mm thickness or less can be achieved without a problem.
- the optical filter is provided on a quartz glass having a thickness of 0.5 mm as in the prior art, the total thickness as a pyroelectric sensor is 0.85 mm or more, and exceeds 1.0 mm when the package is included. Thickness becomes difficult to apply to electronic devices with height restrictions.
- Comparative Example 1 In the pyroelectric sensor of Example 1 described above, a pyroelectric sensor having a configuration without a heat absorption layer was produced as Comparative Example 1. The manufacturing process other than the formation of the heat absorption layer was the same as in Example 1.
- Example 1 evaluated as an infrared sensor.
- the sensor was installed in a room at room temperature of 25 ° C., and the pyroelectric current and responsiveness when a 70 ° C. heat source was installed at a distance of 100 mm were examined.
- a pyroelectric current of 35 nA was observed about 10 seconds after the heat source was installed.
- a pyroelectric current of 3 nA was observed about 10 seconds after the heat source was installed. That is, it was confirmed that the sensitivity was greatly different depending on the presence or absence of the heat absorption layer, and that high sensitivity was obtained by providing the heat absorption layer.
- Example 2 instead of the plate-like Si substrate in Example 1, a cavity wafer having a hollow portion whose inside was in a reduced pressure state was used as the substrate. As shown in FIG. 5, a substrate 14 having a hollow portion 14a inside the Si wafer, an upper layer 14b and a lower layer 14c surrounding the hollow portion 14a having a thickness of 20 ⁇ m and a wafer thickness of 500 ⁇ m was used.
- the pyroelectric sensor of Example 2 was produced by the same production process as Example 1 except for the substrate. In the patterning of the piezoelectric film, the sensing portion 25 is formed in a region narrower than the hollow portion 14a in the region of the hollow portion 14a as shown in FIG.
- the pyroelectric sensor of Example 2 was produced as described above.
- an optical filter is not provided, but when an optical filter (approximately 7 ⁇ m thick) is directly deposited on the back surface of the substrate, a sensor having a total thickness of about 510 ⁇ m or less can be manufactured.
- Example 3 Using a cavity wafer similar to that in Example 2 as a substrate, a pyroelectric sensor was manufactured by the same manufacturing process as in Example 1. However, the piezoelectric film was not patterned, and the sensing unit was provided on the entire surface of the substrate.
- Example 2 and Example 3 pyroelectric current and responsiveness were evaluated in the same manner as in Example 1 and Comparative Example 1 above.
- a pyroelectric current of 35 nA was observed about 1 second after the installation of the heat source, and a very good response was obtained.
- the pyroelectric sensor of Example 3 was slightly worse in responsiveness than the pyroelectric sensor of Example 2 because the peak value of the pyroelectric current was about 1.5 seconds later.
- the thickness of the substrate through which infrared rays incident on the sensing unit pass is thinner than that in Example 1, it is considered that the heat capacity is reduced and the responsiveness is improved. Further, when the sensing unit is provided on the entire surface, it is considered that the response is relatively low because it is more easily affected by the heat of the substrate than when the sensing unit is provided only on the hollow part.
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Abstract
Description
特開2006-317232号公報には、図6に示すように、赤外線センサ101として、シリコン(Si)基板102と、Si基板102の第1の表面102a上に備えられた赤外線センシング部103とを備え、赤外線センシング部103が位置するSi基板102の第1の表面102aには熱絶縁のための空洞部105が形成されており、Si基板102の第2の表面102b上には、赤外線のみを所定透過させる光学フィルタFを備えた構成が開示されている。また、感度を向上させるために赤外線センシング部103に赤外線吸収膜103aを備えている。特開2006-317232号公報において、赤外線センシング部103の詳細な構成は開示されておらず、サーモパイル、サーミスタ、焦電素子などを用いて形成できる、と記載されている。
Si基板の一面に、その一面側から無機材料からなる熱吸収層、下部電極、圧電体膜および上部電極がこの順に積層されてなる積層部と、
Si基板の他面の、積層部に対向する位置に備えられた、赤外線を選択的に透過させる光学フィルタとを有し、
光学フィルタ側からSi基板を経て積層部に入射される赤外線を感知する焦電センサである。
このとき、平面視において、Si基板の面積が積層部の面積よりも大きく、中空部が積層部と重畳し、かつ積層部が中空部の領域の内側に位置する構成であることが好ましい。
図1は、本発明の第1の実施形態の焦電センサ1の断面模式図である。なお、視認容易のため、各層の膜厚やそれらの比率は、適宜変更して描いており、必ずしも実際の膜厚や比率を反映したものではない(以下の図面において同様とする。)。
焦電センサ1において下部電極22、圧電体膜23および上部電極24がセンシング部25を構成する。なお、センシング部25は平面視において積層部20と一致する。センシング部25に赤外線が入射すると温度が上昇し、焦電効果により焦電体である圧電体膜23に表面電荷が発生する。この表面電荷を下部電極22および上部電極24に接続された図示しないリード線を介して取り出し、適切な電気回路を用いて出力信号として計測することで赤外線の検知が可能となる。ここで、「下部」および「上部」は天地を意味するものではない。圧電体膜を挟んで設けられる一対の電極に関し、Si基板10側に配置される一方の電極を下部電極、他方の電極を上部電極と称しているに過ぎない。
下部電極22の主成分としては、特に制限はなく、一般に電極として利用できる材料を適宜用いることができるが、金属を用いることが好ましい。特には、Pt、Ir、Ru等の貴金属が好ましい。
圧電体膜23は、下記一般式(P)で表される1種又は複数種のペロブスカイト型酸化物からなるものであることが好ましい。
一般式ABO3 (P)
(一般式P中、A:Aサイトの元素であり、Pb,Ba,La,Sr,Bi,Li,Na,Ca,Cd,Mg,及びKからなる群より選ばれた少なくとも1種の元素、B:Bサイトの元素であり、Ti,Zr,V,Nb,Ta,Cr,Mo,W,Mn,Sc,Co,Cu,In,Sn,Ga,Zn,Cd,FeおよびNiからなる群より選ばれた少なくとも1種の元素、
O:酸素原子、
Aサイト元素のモル数が1.0であり、かつBサイト元素のモル数が1.0である場合が標準であるが、Aサイト元素とBサイト元素のモル数はペロブスカイト構造を取り得る範囲内で1.0からずれてもよい。)
(一般式PX中、AはAサイトの元素であり、Pbを含む少なくとも1種の元素、Mが、V、Nb、Ta、およびSbからなる群より選ばれた少なくとも1種の元素である。
0<x<b、0<y<b、0≦b-x-yであり、a:b:c=1:1:3が標準であるが、これらのモル比はペロブスカイト構造を取り得る範囲内で基準モル比からずれてもよい。)
明の焦電素子における圧電体膜には、薄膜形成することができる圧電体材料であればペロブスカイト型酸化物からなる圧電体材料のみならず、いかなる材料を採用してもよい。
Si基板10の厚みは薄い方が好ましい。厚みが薄い方ほど熱容量が小さく、レスポンスが速いためである。具体的には600μm以下が好ましく、より好ましくは400μm以下であり、特に好ましくは250μm以下である。一方で、本実施形態のような平板状の基板を用いる場合には、圧電体膜形成時に生じる応力による反りを抑制するために、厚みが100μm以上であることが好ましく、200μm以上であることがより好ましい。なお、Si基板10は、応力調整層などを含んでいても構わない。
熱吸収層18は、赤外線(熱)を吸収し、センシング部25に熱を効率的に伝える。この熱吸収層18を備えることにより、センシング感度を向上させることができる。熱吸収層18を備えておらず、下部電極22がIrやPtなど金属電極である場合、赤外線IRが金属電極で反射して、熱を効率的にセンシング部25に伝えることができず、性能が十分に発揮できない場合がある。
焦電センサ1の構成上、圧電体膜23より先に熱吸収層18を基板上に成膜しておく必要があり、圧電体膜23の成膜工程が後工程となる。有機材料などからなる耐熱性が低い熱吸収層では、圧電体膜23の成膜工程において高い温度での処理ができない。本発明では熱吸収層に耐熱性の高い無機材料を用いているので、500℃以上の温度に曝されるような圧電体膜の成膜工程を実施することも可能であり、製造の自由度が高い。
光学フィルタ30は、ノイズ源となる検出対象外の赤外線を極力カットし、検出対象である赤外線波長を透過する赤外線フィルタである。光学フィルタとしては、無機材料の多層膜フィルタを用いてもよいし、有機材料の塗布型フィルタを用いてもよい。性能の良好なフィルタを形成するために、光学フィルタの成膜面の表面粗さRaは1nm以下であることが好ましい。そのため、裏面研磨してあるSiウエハを用いることが好ましい。
上記第1の実施形態の焦電センサ1の製造方法の一例を説明する。
両面研磨されたSiウエハ(例えば、厚み250μm)をSi基板10として用いる。Siウエハは熱酸化膜が形成されていても、されていなくても構わない。
まず、Si基板10上に熱吸収層18および下部電極22をスパッタ法によって順次成膜する。例えば、熱吸収層18としてIrOx膜、下部電極22としてIr膜をシームレスに成膜する。例えば、Irをターゲットとして用い、成膜ガスとしてAr+30%O2ガスをフローさせ、反応性スパッタによりIrOx膜を約10nm形成し、スパッタのプラズマをOFFにしないまま、成膜ガス中のO2を0%とし、Arのみとしてスパッタを継続して、Ir膜を約150nm形成する。なお、IrOxとSi基板の密着性を向上させるために、数nm以下のTiなどの密着層をIrOxの成膜前にSi基板上に形成しても良い。但し、密着層を数nm以下とするのは、厚すぎると熱吸収層としてのIrOxの機能が低下するためである。
本構成の焦電センサ1は、センシング部25に従来のバルク圧電体に代えて厚み10μm以下の圧電体膜を備えており、1枚の基板の一面にセンシング部25を備え、他面に光学フィルタ30を備えているので、全体としての厚みを薄くすることができ、センサ全体としての厚みを1mm以下に抑えた低背化の焦電センサを実現できる。
図2は、第2の実施形態の焦電センサ2の断面模式図である。図1に示した焦電センサ1と同じ構成要素には同一の符号を付し、詳細な説明を省略する(以下の図において同様とする。)。
本実施形態の焦電センサ2は、第1の実施形態における平板状のSi基板10に代えて、ダイアフラム構造を有するSi基板11を備えている。積層部20(センシング部25)はダイアフラム12の一面12aに設けられており、光学フィルタ30はダイアフラム12の他面12bに設けられている。すなわち、積層部20が設けられたダイアフラム12の周縁部に、ダイアフラム12の厚みよりも厚い肉厚部からなるダイアフラム支持部を備えたダイアフラム構造のSi基板11を用いている。
図3は、第3の実施形態の焦電センサ3の平面模式図およびB-B線断面模式図である。
てRIE(Reactive Ion Etching)にて深掘りし、凹部を形成する。そのSOIウエハの
凹部を覆うように、もう1枚のSOIウエハを貼り付ける。その後、表面を研磨および/またはエッチングすることによりキャビティSOIウエハ(中空部を備えた基板)を作製することができる。
上記のような焦電センサをアレイ状に配列形成して、イメージセンサとして用いることができる。図4は、アレイ状に配列された焦電センサを備えたイメージセンサの一例の概略構成を示す平面図およびC-C線断面図である。
250μm厚の両面研磨されたSiウエハをSi基板として用いた。なお、Si基板として、赤外線を透過させるためにドープ量が少なく、体積抵抗の大きい100Ωcm以上の仕様ものを用いた。
なお、従来のように、光学フィルタを0.5mm厚の石英ガラス上に形成して備えた場合、焦電センサとしてのトータルの厚みは0.85mm以上となり、パッケージを含めると1.0mmを超える厚みになり、高さ制限のある電子デバイスには適用しにくいものとなる。
上記実施例1の焦電センサにおいて、熱吸収層を備えない構成の焦電センサを比較例1として作製した。熱吸収層を形成しない以外の作製工程は実施例1と同様とした。
室温25℃の室内にセンサを設置し、70℃の熱源を100mmの距離に設置した場合の焦電電流および応答性を調べた。
実施例1における板状のSi基板に代えて、内部が減圧状態とされた中空部を備えたキャビディウエハを基板として用いた。基板14として、図5に示すように、Siウエハの内部に中空部14aを有し、中空部14aを囲む上層14bおよび下層14cの厚みがそれぞれ20μm、ウエハの厚みが500μmのものを用いた。
基板以外は実施例1と同様の作製工程により実施例2の焦電センサを作製した。なお、圧電体膜のパターニングの際には、図3に示したように中空部14aの領域内において中空部14aよりも狭い領域にセンシング部25が形成されるようにした。
実施例2と同様のキャビティウエハを基板として用い、実施例1と同様の作製工程により焦電センサを作製した。但し、圧電体膜のパターニングを行わず、基板の全面にセンシング部を備えた構成とした。
実施例2の焦電センサは、熱源設置の約1秒後には35nAの焦電電流が観察され、非常の良好な応答性が得られた。なお、実施例3の焦電センサは実施例2の焦電センサと比較すると、焦電電流のピーク値が約1.5秒後となり応答性が少し悪かった。
5 イメージセンサ
10 Si基板
10a Si基板の一面
10b Si基板の他面
11 Si基板
12 ダイアフラム
12a ダイアフラムの一面
12b ダイアフラムの他面
14 Si基板
14a 中空部
18 熱吸収層
20 積層部
22 下部電極
23 圧電体膜
24 上部電極
25 センシング部
30 光学フィルタ
101 赤外線センサ
102 Si基板
102a 第1の表面
102b 第2の表面
103 赤外線センシング部
103a 赤外線吸収膜
105 空洞部
Claims (9)
- Si基板と、
該Si基板の一面に、該一面側から無機材料からなる熱吸収層、下部電極、圧電体膜および上部電極がこの順に積層されてなる積層部と、
前記Si基板の他面の、前記積層部に対向する位置に備えられた、赤外線を選択的に透過させる光学フィルタとを有し、
該光学フィルタ側から前記Si基板を経て前記積層部に入射される赤外線を感知する焦電センサ。 - 前記下部電極が金属からなり、
前記無機材料が前記金属の酸化物である請求項1記載の焦電センサ。 - 前記無機材料が貴金属の酸化物である請求項1または2記載の焦電センサ。
- 前記圧電体膜がスパッタ膜である請求項1から3いずれか1項記載の焦電センサ。
- 前記積層部に入射される赤外線が透過する前記Si基板の厚みが250μm以下である請求項1から4いずれか1項に記載の焦電センサ。
- 前記Si基板が、前記積層部が設けられている領域の周縁部に、前記領域の厚みよりも厚い肉厚部を備えている請求項1から5いずれか1項に記載の焦電センサ。
- 前記Si基板が中空部を備えている請求項1から5いずれか1項記載の焦電センサ。
- 平面視において、前記Si基板の面積が前記積層部の面積よりも大きく、前記中空部が前記積層部と重畳し、かつ前記積層部が前記中空部の領域の内側に位置する請求項7記載の焦電センサ。
- 前記圧電体膜がペロブスカイト型酸化物の(100)配向膜である請求項1から8いずれか1項記載の焦電センサ。
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