Sensor device

Abstract

To provide a sensor device that can suppress fluctuations in electrode voltage drop caused by temperature changes in the environment in which the sensor device is used.SOLUTION: A sensor device according to the present invention includes a functional layer and a pair of electrodes connected in series via the functional layer on a support, wherein the pair of electrodes includes a first electrode having a resistance temperature coefficient of one of a positive value and a negative value, and a second electrode having a resistance temperature coefficient of the other of a positive value and a negative value.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a sensor device. [Background technology]

[0002] 2. Description of the Related Art Sensor devices having a pair of electrodes on a substrate via a functional layer are used in electronic devices such as sensors such as pressure sensors and acceleration sensors, high frequency filter devices, and piezoelectric actuators.

[0003] As such a sensor device, for example, a piezoelectric element has been disclosed in which a first electrode layer, a piezoelectric thin film mainly composed of a piezoelectric material, and a second electrode layer are formed on a polymer thin film mainly composed of a polymer compound obtained by polymerizing a monomer (see, for example, Patent Document 1).

[0004] In the piezoelectric element of Patent Document 1, the first electrode layer and the second electrode layer are formed using, for example, tin, aluminum, nickel, platinum, gold, silver, copper, chromium, iron, magnesium, molybdenum, niobium, tantalum, titanium, zinc, zirconium, tungsten, palladium, rhodium, iridium, rubidium, titanium nitride, chromium nitride, and molybdenum disilicide. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5136973 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the piezoelectric element of Patent Document 1 has a problem in that the output varies with the environmental temperature because the electrical resistance of the first electrode layer and the second electrode layer varies with temperature changes in the environment in which it is used, causing the voltage drop in the first electrode layer and the second electrode layer to vary.

[0007] An object of one aspect of the present invention is to provide a sensor device capable of suppressing fluctuations in voltage drop of electrodes caused by temperature changes in the environment in which the sensor device is used. [Means for solving the problem]

[0008] One embodiment of the sensor device of the present invention comprises a functional layer and a pair of electrodes connected in series via the functional layer on a support, the pair of electrodes consisting of a first electrode having a resistance temperature coefficient of one of a positive value and a negative value, and a second electrode having a resistance temperature coefficient of the other of a positive value and a negative value. Effect of the Invention

[0009] One aspect of the sensor device according to the present invention can suppress fluctuations in the voltage drop of the electrodes caused by temperature changes in the environment in which the device is used. [Brief description of the drawings]

[0010] [Figure 1] 1 is a perspective view showing a configuration of a sensor device according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic cross-sectional view showing a configuration of a sensor device. [Diagram 3] FIG. 13 is a perspective view showing an example of another configuration of the sensor device. [Figure 4] FIG. 11 is a plan view showing an example of another configuration of the sensor device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, the embodiments of the present invention will be described in detail. In order to facilitate understanding of the description, the same components in each drawing are given the same reference numerals, and duplicated descriptions will be omitted. In addition, the scale of each member in the drawings may differ from the actual scale. In this specification, "~" indicating a numerical range means that the numerical values ​​before and after it are included as the lower and upper limits, unless otherwise specified.

[0012] [Sensor device] The sensor device according to this embodiment includes a support, a functional layer, and a pair of electrodes connected in series through the functional layer. The pair of electrodes includes a first electrode having a temperature coefficient of resistance (TCR) of one of a positive value and a negative value, and a second electrode having a TCR of the other of a positive value and a negative value. In this embodiment, the sensor device is a laminate including a support, a functional layer, and a pair of electrodes connected in series through the functional layer, the support is a flexible substrate, and the functional layer is a piezoelectric layer. The functional layer is not limited to a piezoelectric layer, and may be a temperature measurement layer, a strain detection layer, or the like.

[0013] Fig. 1 is a schematic cross-sectional view showing the configuration of a sensor device according to this embodiment. As shown in Fig. 1, the sensor device 1A includes a flexible substrate 10 serving as a support, a first electrode 20, a piezoelectric layer 30 serving as a functional layer, and a second electrode 40, which are laminated in this order from the flexible substrate 10 side. The sensor device 1A can be formed into any shape, such as a sheet (film).

[0014] In this specification, the thickness direction (vertical direction) of the sensor device 1A is defined as the Z-axis direction, and the lateral direction (horizontal direction) perpendicular to the thickness direction is defined as the X-axis direction. The second electrode 40 side in the Z-axis direction is defined as the +Z-axis direction, and the flexible base material 10 side is defined as the -Z-axis direction. In the following description, for convenience of explanation, the +Z-axis direction is referred to as up or upward, and the -Z-axis direction is referred to as down or downward, but this does not represent a universal up-down relationship.

[0015] (Flexible base material) The flexible substrate 10 is a substrate on which the first electrode 20 is disposed, and has flexibility so as to impart flexibility to the sensor device 1A. Any material can be used as the flexible substrate 10, and examples of the material that can be used include a plastic substrate, a silicon (Si) substrate, a metal plate, and a glass substrate.

[0016] When a plastic base material is used, it is preferable to use a flexible material that can impart flexibility to the sensor device 1A.

[0017] Examples of materials that can be used to form the plastic substrate include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polycarbonate (PC), acrylic resins, cycloolefin polymers, polyimide (PI), and the like.

[0018] The flexible substrate 10 may be transparent, translucent, or opaque. The term "transparent" refers to a transparent material having a visible light (light having a wavelength of 380 to 780 nm) transmittance to such an extent that the inside of the flexible substrate 10 can be visually recognized from the outside, and the light transmittance of the visible light is 40% or more, preferably 80% or more, and more preferably 90% or more. The light transmittance is measured using "Plastics - Determination of total light transmittance and total light reflectance" as specified in JIS K 7375:2008.

[0019] When the sensor device 1A is required to have optical transparency, it is preferable to use PET, PEN, PC, acrylic resin, cycloolefin polymer, etc. These materials are preferably used when the electrodes used in the sensor device 1A are transparent electrodes, etc. Furthermore, when the sensor device 1A is not required to have optical transparency, such as in health care products such as pulse meters and heart rate meters, and in-vehicle pressure detection sheets, the above materials, translucent or opaque plastic materials may be used.

[0020] Examples of materials that can be used to form the metal plate include aluminum, copper, stainless steel, and tantalum.

[0021] The thickness of the flexible substrate 10 is not particularly limited and can be any thickness depending on the application of the sensor device 1A, the material of the flexible substrate 10, etc., and may be, for example, 1 μm to 250 μm. The method for measuring the thickness of the flexible substrate 10 is not particularly limited and any measuring method can be used.

[0022] In this specification, the thickness of the flexible substrate 10 refers to the length in the direction perpendicular to the main surface of the flexible substrate 10. The thickness of the flexible substrate 10 may be, for example, the thickness measured at an arbitrary location on the cross section of the flexible substrate 10, or may be the average value of the measured values ​​measured at several arbitrary locations. Hereinafter, the definition of thickness is similar for other members.

[0023] (First electrode) The first electrode 20 is provided on the upper main surface (top surface) of the flexible substrate 10. The first electrode 20 may be formed as a thin film on a part of or the entire surface of the flexible substrate 10, or a plurality of first electrodes 20 may be provided in parallel in a stripe pattern. When the flexible substrate 10 is a conductive material such as a metal plate, the flexible substrate 10 can also function as an electrode, and therefore the first electrode 20 does not need to be provided.

[0024] The first electrode 20 can be made of any material having electrical conductivity. Examples of the material include metals such as Pt, Au, Ag, Cu, Mg, Al, Si, Ti, Cr, Fe, Ni, Zn, Rb, Zr, Nb, Mo, Rh, Pd, Ru, Sn, Ir, Ta, and W, zinc oxide, tin oxide, copper oxide, metal oxides such as ITO (indium tin oxide), IZO (indium zinc oxide), IZTO (indium zinc tin oxide), and IGZO (indium gallium zinc oxide), nitrides such as titanium nitride (TiN), chromium nitride (CrN), and tantalum nitride (TaN), and carbides such as silicon carbide (SiC). When light transmittance is required, the material can be an oxide conductive film made of a metal oxide such as ITO, IZO, IZTO, or IGZO. When light transmittance is not essential, a metal or the like may be used.

[0025] From the viewpoint of suppressing unevenness and grain boundaries at the interface between the first electrode 20 and the piezoelectric layer 30, the first electrode 20 may be an amorphous film. By using an amorphous film, it is possible to suppress unevenness on the surface of the first electrode 20 and the generation of grain boundaries that cause leak paths. In addition, the upper piezoelectric layer 30 can grow with good crystal orientation without being affected by the crystal orientation of the first electrode 20.

[0026] The thickness of the first electrode 20 can be appropriately designed and is preferably, for example, 3 nm to 100 nm. If the thickness of the first electrode 20 is within the above-mentioned preferable range, the function as an electrode can be exhibited and the sensor device 1A can be made thin.

[0027] The first electrode 20 has a TCR that is either a positive value or a negative value. The TCR of the first electrode 20 may have a value with a different sign from the TCR of the second electrode 40, and the TCR of one of the first electrode 20 and the second electrode 40 is a positive value, and the TCR of the other electrode is a negative value.

[0028] The TCR is one of the temperature characteristics of the first electrode 20 and the second electrode 40, and depends solely on the material that constitutes the first electrode 20 and the second electrode 40. The TCR of the first electrode 20 and the second electrode 40 can be set to exhibit metallic or semiconducting behavior depending on the type of material that constitutes the first electrode 20 and the second electrode 40, the thickness of the first electrode 20 and the second electrode 40, and, in the case where the first electrode 20 and the second electrode 40 are composite materials containing multiple materials, the content of each material, etc. When the TCR is a positive value, the first electrode 20 and the second electrode 40 exhibit metallic behavior, and when the TCR is a negative value, the first electrode 20 and the second electrode 40 exhibit semiconducting behavior.

[0029] The relationship between the TCR of the first electrode 20 and the TCR of the second electrode 40 will be described in detail later.

[0030] (Piezoelectric layer) The piezoelectric layer 30 is provided on the upper principal surface (top surface) of the first electrode 20. The piezoelectric layer 30 preferably contains an inorganic material as a main component.

[0031] The term "main component" means that the content of the inorganic material is 95 atm % or more, preferably 98 atm % or more, and more preferably 99 atm % or more.

[0032] As the inorganic material, a piezoelectric material having a perovskite crystal structure, a piezoelectric material having a wurtzite crystal structure (wurtzite crystal material), etc. can be used. In this embodiment, since the piezoelectric layer 30 is used as the functional layer, a piezoelectric material having a perovskite crystal structure, a wurtzite crystal material, etc. are used, but when the functional layer is other than the piezoelectric layer 30, metals such as Pt, Au, Ag, Cu, Mg, Al, Si, Ti, Cr, Fe, Ni, Nb, Mo, Ru, Sn, and Ta may be used depending on the type of the functional layer.

[0033] The wurtzite crystal structure has the general formula AB, where A is an electropositive element and B is an electronegative element. Wurtzite crystal materials have a hexagonal unit cell with the polarization vector parallel to the c-axis.

[0034] As the wurtzite crystal material, it is preferable to use a material that exhibits a piezoelectric characteristic of a certain value or more and can be crystallized in a low-temperature process of 200°C or less. The wurtzite crystal material contains at least Zn among Zn, Al, Ga, Cd, and Si as a positive element A represented by the general formula AB. As the wurtzite crystal material, for example, zinc oxide (ZnO), zinc sulfide (ZnS), zinc selenide (ZnSe), zinc telluride (ZnTe), etc. can be used. Among these, ZnO is preferable as the wurtzite crystal material because it is relatively easy to orient the c-axis even in a low-temperature process. These may be used alone or in combination of two or more. When two or more wurtzite crystal materials are used in combination, one or more of these components may be included as main components, and other components may be included as optional components.

[0035] The positive element A may include at least one of Al, Ga, Cd, and Si in addition to Zn. As these wurtzite crystal materials, for example, aluminum nitride (AlN), gallium nitride (GaN), cadmium selenide (CdSe), cadmium telluride (CdTe), silicon carbide (SiC), etc. can be used.

[0036] The wurtzite crystal material preferably contains ZnO, and more preferably consists essentially of ZnO. The term "substantially" means that the wurtzite crystal material may contain, in addition to ZnO, inevitable impurities that may be inevitably contained during the manufacturing process.

[0037] In addition to the above-mentioned ZnO, ZnS, ZnSe, and ZnTe, the wurtzite crystal material may contain alkaline earth metals such as Mg, Ca, and Sr, or metals such as vanadium (V), titanium (Ti), zirconium (Zr), silica (Si), and lithium (Li) in a predetermined range of proportions. These components may be contained in the form of elements or oxides.

[0038] In addition to the main component, the piezoelectric layer 30 may contain at least one of Ar, Kr, Xe, and Rn as an additive element.

[0039] The content of the additive element in the piezoelectric layer 30 is not particularly limited as long as it is within a range that allows the piezoelectric layer 30 to have a wurtzite crystal structure.

[0040] There is no particular limitation on the method for measuring the content of the additive element contained in the piezoelectric layer 30 as long as the method is capable of measurement. The content of the additive element contained in the piezoelectric layer 30 may be measured, for example, by Rutherford backscattering spectrometry (RBS) using a Pelletron 3SDH (manufactured by NEC Corporation) as a measuring device, or may be measured by secondary ion mass spectrometry using a dynamic SIMS (D-SIMS) or the like.

[0041] The thickness of the piezoelectric layer 30 is not particularly limited, and may be any thickness that provides sufficient piezoelectric characteristics, i.e., polarization characteristics proportional to pressure, reduces the occurrence of cracks in the piezoelectric layer 30, suppresses leak paths between electrodes, and stably exhibits piezoelectric characteristics. The thickness of the piezoelectric layer 30 may be, for example, 5 μm or less.

[0042] The film density of the piezoelectric layer 30 is not particularly limited and can be designed as appropriate, and may be within a range that can enhance the crystal orientation of the piezoelectric layer 30 and suppress an increase in film stress. The method for measuring the film density is not particularly limited, and for example, X-ray reflectometry (XRR) or the like can be used.

[0043] The crystal orientation of the piezoelectric layer 30 is indicated by the full width at half maximum (FWHM) obtained when the surface of the piezoelectric layer 30 is measured by the X-ray rocking curve (XRC) method. That is, the crystal orientation of the piezoelectric layer 30 is represented by the FWHM of the peak waveform of the rocking curve obtained when the diffraction from the (0002) plane of the crystal of the piezoelectric material contained as a main component in the piezoelectric layer 30 is measured by the XRC method. Since the piezoelectric material contained in the piezoelectric layer 30 has a wurtzite crystal structure such as ZnO, the FWHM indicates the degree of parallelism of the arrangement of the crystals constituting the piezoelectric material in the c-axis direction. Therefore, the FWHM of the peak waveform of the rocking curve obtained by the XRC method can be used as an index of the c-axis orientation of the piezoelectric layer 30. Therefore, it can be evaluated that the smaller the FWHM of the rocking curve, the better the crystal orientation of the piezoelectric layer 30 in the c-axis direction.

[0044] The crystal orientation of the piezoelectric layer 30 can be evaluated by the XRC method using not only the FWHM of the rocking curve obtained by measuring the diffraction from the (0002) plane of the ZnO crystals contained as a piezoelectric material in the piezoelectric layer 30, but also the peak intensity. That is, the crystal orientation of the piezoelectric layer 30 can also be evaluated by using the value obtained by dividing the integrated value of the peak intensity by the FWHM as an evaluation value. In this case, the stronger the peak intensity of the rocking curve and the smaller the FWHM, the better the c-axis orientation of ZnO can be evaluated. Therefore, the larger the evaluation value obtained by dividing the integrated value of the peak intensity by the FWHM, the better the crystal orientation of the piezoelectric layer 30 can be evaluated.

[0045] When two or more types of wurtzite crystal materials are used in combination, the piezoelectric layer 30 may be formed by laminating piezoelectric layers made of the respective wurtzite crystal materials.

[0046] (Second electrode) As shown in FIG. 1, the second electrode 40 is provided on the upper main surface (top surface) of the piezoelectric layer 30, and is arranged to face the first electrode 20. The second electrode 40 can be formed of any material having electrical conductivity, and the same material as the first electrode 20 can be used. When the sensor device 1A requires optical transparency, the second electrode 40 may be a transparent oxide conductive film such as ITO, IZO, IZTO, or IGZO. When optical transparency is not essential, the second electrode 40 may be a metal electrode of good conductor such as Au, Pt, Ag, Ti, Al, Mo, Ru, or Cu.

[0047] The second electrode 40 may be formed as a thin film on a part or the entire surface of the piezoelectric layer 30, similarly to the first electrode 20, or may be formed in any appropriate shape. For example, when a plurality of first electrodes 20 are provided in parallel to each other in a stripe pattern, a plurality of second electrodes 40 may be provided in parallel to each other in a stripe pattern in a direction perpendicular to the direction in which the stripes of the first electrodes 20 extend in a plan view.

[0048] The thickness of the second electrode 40 can be appropriately designed and is preferably, for example, 20 nm to 100 nm. If the thickness of the second electrode 40 is within the above-mentioned preferable range, the function as an electrode can be exhibited and the sensor device 1A can be made thin.

[0049] The second electrode 40 has a TCR with a different sign from that of the first electrode 20. The TCR of the second electrode 40 only needs to have a different sign from that of the first electrode 20, and when the TCR of the first electrode 20 is a positive value, the TCR of the second electrode 40 is a negative value, and when the TCR of the first electrode 20 is a negative value, the TCR of the second electrode 40 is a positive value. The sign, magnitude, etc. of the TCR of the second electrode 40 can be set in the same way as in the case of the first electrode 20, so details will be omitted.

[0050] The first electrode 20 and the second electrode 40 have TCRs with different sign values ​​to cancel out the TCR between the electrodes, and it is preferable that the ratio of the resistance of the first electrode 20 and the second electrode 40 to the temperature change satisfies the relationship of the following formula (1). |(ρ1 / t1×α1)+(ρ2 / t2×α2)|<2×min(|ρ1 / t1×α1|,|ρ2 / t2×α2|) ···(1) (In the formula, ρ1 is the electrical resistivity (unit: Ω·m) of the first electrode 20, t1 is the thickness (unit: m) of the first electrode 20, α1 is the temperature coefficient of resistance (unit: % / K) of the first electrode 20, ρ2 is the electrical resistivity (unit: Ω·m) of the second electrode 40, t2 is the thickness (unit: m) of the second electrode 40, and α2 is the temperature coefficient of resistance (unit: % / K) of the second electrode 40.)

[0051] The signs of the ratio of the resistance of the first electrode 20 to the temperature change expressed by (ρ1 / t1×α1) and the ratio of the resistance of the second electrode 40 to the temperature change expressed by (ρ2 / t2×α2) remain constant only in the signs of the TCRs of the first electrode 20 and the second electrode 40, and do not change otherwise. Therefore, if the signs of the TCRs of the first electrode 20 and the second electrode 40 are positive or negative and opposite, the sign of the ratio of the resistance of the first electrode 20 to the temperature change expressed by (ρ1 / t1×α1) and the sign of the ratio of the resistance of the second electrode 40 to the temperature change expressed by (ρ2 / t2×α2) can be maintained in the opposite state, and the ratios of the resistance of the electrodes to the temperature change are offset. In the above formula (1), by making |ρ1 / t1×α1+ρ2 / t2×α2| (2×min(|ρ1 / t1×α1|, |ρ2 / t2×α2|)) small, output fluctuations due to temperature changes in the first electrode 20 and the second electrode 40 are suppressed.

[0052] In other words, if the absolute value of the average of the sum of the ratio of the resistance of the first electrode 20 to temperature change (ρ2 / t2×α2) and the ratio of the resistance of the second electrode 40 to temperature change (ρ2 / t2×α2) is less than the minimum value of either the ratio of the resistance of the first electrode 20 to temperature change (ρ2 / t2×α2) or the ratio of the resistance of the second electrode 40 to temperature change (ρ2 / t2×α2), then output fluctuations in response to temperature changes in the first electrode 20 and the second electrode 40 are sufficiently suppressed.

[0053] There is no particular limitation on the method for manufacturing the sensor device 1A, and any appropriate manufacturing method can be used. An example of the method for manufacturing the sensor device 1A will be described.

[0054] First, the first electrode 20 is deposited (formed) on the upper surface of a flexible base material 10 that has been formed to a predetermined size.

[0055] The method for forming the first electrode 20 is not particularly limited, and may be either a dry process or a wet process. If a dry process is used as a method for forming the first electrode 20, a thin first electrode 20 can be easily formed. Examples of the dry process include sputtering and vapor deposition, and examples of the wet process include plating. Examples of the sputtering include DC (direct current) or RF (radio frequency) magnetron sputtering. By using sputtering as a method for forming the first electrode 20, a thin first electrode 20 with high density can be easily formed. Therefore, sputtering is preferable as a method for forming the first electrode 20. Examples of the first electrode 20 that can be used include an ITO film, an IZO film, a Ti film, and the like formed by DC (direct current) or RF (radio frequency) magnetron sputtering.

[0056] The first electrode 20 may be formed on the entire upper surface of the flexible substrate 10. The first electrode 20 may also be formed into any appropriate shape by processing the first electrode 20 into a pattern having a predetermined shape by etching or the like. For example, the first electrode 20 may be patterned into stripes and a plurality of first electrodes 20 may be arranged in stripes.

[0057] Next, the piezoelectric layer 30 is formed on the upper surface of the first electrode 20. For example, the piezoelectric layer 30 is formed by DC magnetron sputtering in a mixed gas atmosphere containing an inert gas such as Ar and a trace amount of oxygen, using a target containing elements constituting the piezoelectric material. The piezoelectric layer 30 is formed by sputtering the piezoelectric material on the first electrode 20.

[0058] When the piezoelectric material is a wurtzite crystal material made of ZnO, a ZnO sintered body target can be used as the target. A ZnO sintered body target is placed in a sputtering device, and a mixed gas containing an inert gas such as Ar atoms and oxygen is supplied into the sputtering device. By sputtering using the ZnO sintered body target in an atmosphere of a mixed gas containing an inert gas and oxygen, the piezoelectric layer 30 can be obtained on the first electrode 20 while suppressing the amount of inert gas that enters during the deposition of the ZnO film.

[0059] When the piezoelectric material is a wurtzite crystal material made of Mg-added ZnO containing ZnO and MgO in a predetermined mass ratio, a multi-sputtering method using a target made of a ZnO sintered compact and a target made of a MgO sintered compact, or a single-sputtering method using an alloy target containing ZnO and MgO, such as a target of a ZnO sintered compact to which MgO has been added in advance at a predetermined ratio, can be used.

[0060] When the multi-target sputtering method is used, a mixed gas containing an inert gas such as Ar atoms and oxygen is supplied into the multi-target sputtering apparatus. In an atmosphere of the mixed gas containing an inert gas and oxygen, a ZnO sintered compact target and an MgO sintered compact target are simultaneously and independently sputtered onto the first electrode 20, so that the piezoelectric layer 30 made of Mg-doped ZnO can be formed on the first electrode 20. In addition, the amount of inert gas entering during the formation of the Mg-doped ZnO film can be suppressed while the Mg-doped ZnO film is formed.

[0061] When using the single-target sputtering method, the piezoelectric layer 30 composed of a Mg-doped ZnO thin film can be formed on the first electrode 20 by sputtering using a target of ZnO sintered body to which MgO has been added in advance at a predetermined ratio in a mixed gas atmosphere containing an inert gas such as Ar atoms and oxygen. In addition, the inert gas may be contained in the Mg-doped ZnO at a desired ratio. This results in a piezoelectric layer 30 containing a desired amount of inert gas in the Mg-doped ZnO.

[0062] In the mixed gas atmosphere containing an inert gas and oxygen, the ratio of the flow rate of oxygen to the total flow rate of the inert gas and oxygen is preferably 5% to 15%. If the ratio of the flow rate of oxygen to the total flow rate of the inert gas and oxygen is within the above-mentioned preferred range, when the piezoelectric layer 30 is formed by a sputtering method using a target containing an inert gas, even if an inert gas such as Ar atoms penetrates into the crystal lattice of a wurtzite crystal material such as ZnO, the amount of the inert gas that penetrates can be suppressed. Therefore, the piezoelectric properties of the piezoelectric material can be improved.

[0063] The pressure in the mixed gas atmosphere during sputtering is preferably 0.1 Pa to 2.0 Pa. If the pressure is within the above-mentioned preferred range, when the piezoelectric layer 30 is formed by sputtering using a target containing an electropositive element constituting a wurtzite crystal material such as Zn, the amount of inert gas such as Ar atoms entering the crystal lattice of the wurtzite crystal material such as ZnO can be suppressed. Therefore, the piezoelectric properties of the piezoelectric layer 30 can be improved.

[0064] The deposition temperature of the piezoelectric layer 30 is not particularly limited and can be appropriately selected depending on the layer configuration of the sensor device 1A, etc. For example, the piezoelectric layer 30 may be deposited at 150° C. or lower.

[0065] By using a sputtering method to deposit the first electrode 20 and the piezoelectric layer 30, it is possible to form a uniform film with strong adhesion while maintaining the composition ratio of the compound target. Moreover, the first electrode 20 and the piezoelectric layer 30 can be formed to a desired thickness with high precision simply by controlling the time.

[0066] The piezoelectric layer 30 may be formed by laminating a plurality of layers.

[0067] Next, on the upper surface of the piezoelectric layer 30, a second electrode 40 having a predetermined shape is formed.

[0068] The second electrode 40 can be formed using a method similar to that for forming the first electrode 20 .

[0069] The thickness of the second electrode 40 can be designed appropriately and may be, for example, 20 nm to 100 nm.

[0070] The second electrode 40 may be formed on the entire surface of the piezoelectric layer 30, or may be formed in any appropriate shape. For example, when the first electrode 20 is formed in a striped pattern, the second electrodes 40 may be formed in a striped pattern in a direction perpendicular to the direction in which the stripes of the first electrode 20 extend in a plan view of the sensor device 1A.

[0071] By forming a second electrode 40 on the piezoelectric layer 30, the sensor device 1A is formed.

[0072] After the second electrode 40 is formed, the entire sensor device 1A may be heat-treated at a temperature (e.g., 130° C.) lower than the melting point or glass transition point of the flexible base material 10. This heat treatment can crystallize the first electrode 20 and the second electrode 40 to reduce their resistance. The heat treatment is not essential, and may not be performed after the sensor device 1A is formed in cases such as when the flexible base material 10 is made of a material that is not heat-resistant.

[0073] In this manner, the sensor device 1A according to the present embodiment includes a flexible substrate 10, a first electrode 20, a piezoelectric layer 30, and a second electrode 40, and the first electrode 20 has a TCR of one of a positive value and a negative value, and the second electrode 40 has a TCR of the other of a positive value and a negative value. This allows the sensor device 1A to offset the resistance change of the first electrode 20 caused by the temperature change and the resistance change of the second electrode 40 caused by the temperature change. Specifically, the sensor device 1A can suppress the absolute value of the average of the sum of the ratio of the resistance of the first electrode 20 to the temperature change and the ratio of the resistance of the second electrode 40 to the temperature change to be smaller than the smaller value of the ratio of the resistance of the first electrode 20 to the temperature change and the ratio of the resistance of the second electrode 40 to the temperature change. The sensor device 1A can suppress fluctuations in voltage drop in the first electrode 20 and the second electrode 40 caused by temperature changes in the environment in which it is used, by canceling out resistance changes that occur due to temperature changes in the first electrode 20 and the second electrode 40.

[0074] The sensor device 1A suppresses fluctuations in voltage drop across the first electrode 20 and the second electrode 40 due to temperature changes, allowing the piezoelectric layer 30 to stably exhibit high piezoelectric efficiency in its thickness direction and maintain excellent piezoelectric characteristics. Therefore, the sensor device 1A can maintain excellent piezoelectric characteristics.

[0075] The sensor device 1A can be arranged so that the first electrode 20 and the second electrode 40 face each other via the piezoelectric layer 30. Even if the sensor device 1A is configured so that the first electrode 20 and the second electrode 40 are arranged on the flexible substrate 10 so as to face each other in the planar direction or the height direction via the piezoelectric layer 30, the resistance change of the first electrode 20 and the second electrode 40 due to the temperature change can be cancelled out. Therefore, even if the sensor device 1A is used for various purposes, the fluctuation of the voltage drop of the first electrode 20 and the second electrode 40 caused by the temperature change of the environment in which it is used can be suppressed.

[0076] The sensor device 1A can be provided with a flexible substrate 10, a first electrode 20, a piezoelectric layer 30, and a second electrode 40, which are arranged so as to face each other, and which are laminated in this order from the flexible substrate 10 side. Even if the sensor device 1A is configured by laminating the flexible substrate 10, the first electrode 20, the piezoelectric layer 30, and the second electrode 40, the resistance changes accompanying temperature changes of the first electrode 20 and the second electrode 40 can be cancelled out, and therefore fluctuations in voltage drops of the first electrode 20 and the second electrode 40 caused by temperature changes in the environment in which the device is used can be suppressed.

[0077] The sensor device 1A can use a flexible substrate 10 as a support. Even when the first electrode 20 and the second electrode 40 are placed on a highly flexible substrate, the sensor device 1A can cancel out the resistance changes caused by temperature changes in the first electrode 20 and the second electrode 40, thereby suppressing the fluctuation in voltage drop in the first electrode 20 and the second electrode 40 caused by temperature changes in the environment in which the device is used.

[0078] The sensor device 1A can use the piezoelectric layer 30 as a functional layer. Even if the sensor device 1A uses the piezoelectric layer 30 as a functional layer, the resistance changes accompanying the temperature change of the first electrode 20 and the second electrode 40 can be cancelled out, and therefore the fluctuation of the voltage drop of the first electrode 20 and the second electrode 40 caused by the temperature change of the environment in which the sensor device 1A is used can be suppressed. Therefore, the sensor device 1A can exhibit excellent piezoelectric characteristics as a piezoelectric device.

[0079] In the sensor device 1A, the piezoelectric layer 30 can contain an inorganic material, so that the sensor device 1A can stably function as a piezoelectric device even if the piezoelectric layer 30 is made of various inorganic materials depending on the application.

[0080] The sensor device 1A can suppress fluctuations in voltage drop in the first electrode 20 and the second electrode 40 due to temperature changes in the environment in which it is used, and can maintain excellent piezoelectric characteristics, and therefore can be suitably used as a piezoelectric device. Examples of piezoelectric devices include devices that utilize the piezoelectric effect, such as force sensors for touch panels, pressure sensors, acceleration sensors, angular velocity sensors, and acoustic emission (AE) sensors, as well as speakers, transducers, high-frequency filter devices, piezoelectric actuators, optical scanners, heads for inkjet printers, and MEMS mirrors for scanners that utilize the inverse piezoelectric effect.

[0081] In this embodiment, the sensor device 1A is not limited to the above configuration, and may have other configurations as long as the first electrode 20 and the second electrode 40 are connected on the flexible substrate 10 via a functional layer and the fluctuation of the voltage drop of the first electrode 20 and the second electrode 40 caused by the temperature change of the environment in which the device is used can be suppressed. For example, as shown in FIG. 3, the sensor device 1B may be provided such that a functional layer 50A is disposed on the upper surface of the flexible substrate 10, and at least a part of the first electrode 20 and the second electrode 40 is disposed on the upper surface of the functional layer 50A, and the first electrode 20 and the second electrode 40 are horizontally opposed to each other on the upper surface of the functional layer 50A. The first electrode 20 and the second electrode 40 may be formed in a comb shape such that a part of them alternately mesh with each other on the upper surface of the functional layer 50A. The sensor device 1B shown in FIG. 3 can function as a temperature sensor, for example, by making the functional layer 50A function as a temperature measurement layer.

[0082] In this embodiment, as shown in Fig. 4, the sensor device 1C may be arranged such that the first electrode 20 and the second electrode 40 are connected to the upper surface of the flexible substrate 10 via a meandering functional layer 50B so as to face each other in the horizontal direction. The first electrode 20 and the second electrode 40 may be formed in a line shape. The sensor device 1C shown in Fig. 4 can also function as a temperature sensor by making the functional layer 50B function as a temperature measurement layer, for example.

[0083] In this embodiment, the sensor device 1A may include a single insulating layer or two or more insulating layers between the piezoelectric layer 30 and the second electrode 40. The insulating layer may be formed on the entire upper surface of the piezoelectric layer 30.

[0084] Examples of insulating materials for forming the insulating layer include metal oxides such as silicon oxide (SiOx), aluminum oxide (AlOx), tantalum oxide (TaOx), yttrium oxide (YOx), zirconium oxide (ZrOx) and hafnium oxide (HfOx), nitrides such as silicon nitride (SiNx) and silicon oxynitride (SiON), and organic insulating materials such as polypropylene (PP), polycarbonate (PC), ABS resin, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyamide (PA), polymethyl methacrylate (PMMA), polyvinyl alcohol (PVA), and polyvinylphenol (PVP). These may be used alone or in combination of two or more. EXAMPLES

[0085] The embodiments will be described in more detail below with reference to examples and comparative examples, but the embodiments are not limited to these examples and comparative examples.

[0086] <Example 1> [Fabrication of sensor device] 1. Preparation of the First Electrode On the substrate (PET, thickness: 50μm), an amorphous IZO (ZnO:In2O3=9:1) film with a composition ratio of ZnO and In2O3 adjusted to 9:1 was formed as the first electrode by DC magnetron sputtering in a mixed gas atmosphere of Ar and O2, using a sputtering target with a composition ratio of Zn and In adjusted to 9:1. The thickness of the IZO film was 100nm.

[0087] 2. Preparation of functional layer (piezoelectric layer) A ZnO thin film with a hexagonal wurtzite structure was deposited as a piezoelectric layer, which is a functional layer, on the IZO film by DC sputtering using a ZnO sputtering target in a mixed gas atmosphere of Ar and O2. The thickness of the ZnO thin film was 500 nm.

[0088] 3. Fabrication of the Second Electrode On the ZnO thin film, a Ni film was formed as a second electrode by DC magnetron sputtering in an Ar gas atmosphere using a Ni sputtering target. The thickness of the Ni film was 50 nm.

[0089] In this way, a laminate in which the first electrode, the functional layer, and the second electrode were laminated in this order on the substrate was manufactured as a sensor device. The configurations of the first electrode, the functional layer, and the second electrode are shown in Table 1.

[0090] [Evaluation of cancellation of resistance changes due to temperature changes in the first and second electrodes] From the left side of the following formula (1), "the absolute value of the average of the sum of the ratio of the resistance of the first electrode to temperature change and the ratio of the resistance of the second electrode to temperature change" was calculated, and from the right side of the following formula (1), "twice the smaller value of the ratio of the resistance of the first electrode to temperature change and the ratio of the resistance of the second electrode to temperature change" was calculated. When the right side of the following formula (1) is greater than the left side of the following formula (1), the resistance change due to the temperature change of the first electrode and the resistance change due to the temperature change of the second electrode can cancel each other out, and fluctuations in the voltage drop of the first electrode and the second electrode caused by temperature changes in the environment in which they are used can be suppressed, and the device was evaluated as being good. |ρ1 / t1×α1+ρ2 / t2×α2|<2×min(|ρ1 / t1×α1|,|ρ2 / t2×α2|) ···(1)

[0091] [Example 2] [Fabrication of sensor device] 1. Preparation of the First Electrode A Cu film was formed on a rectangular substrate (PET, thickness: 50 μm) by DC magnetron sputtering in an Ar atmosphere, and then etched to create a first electrode formed in a line shape near one end of the substrate.

[0092] 2. Preparation of functional layer (temperature sensing layer) A Ni film was formed on the substrate by DC magnetron sputtering in an Ar atmosphere, and then etched to form a serpentine line, one end of which was connected to the first electrode to create a functional layer.

[0093] 3. Fabrication of the Second Electrode A CrNi film was formed on the substrate by DC magnetron sputtering in an Ar and N2 mixed gas atmosphere, and then the film was etched to create a line-shaped second electrode facing the first electrode near the end of the substrate opposite the first electrode.

[0094] As a result, a sensor device was manufactured in which the first electrode and the second electrode were arranged on the substrate so as to face each other in the horizontal direction, and the electrodes were connected to each other via a functional layer formed in a meandering shape. The configurations of the first electrode, the functional layer, and the second electrode, and the calculation results of the left and right sides of the above formula (1) are shown in Table 1.

[0095] [Comparative Example 1] The same method as in Example 1 was used, except that the configurations of the first electrode, the functional layer, and the second electrode were changed to those shown in Table 1. Table 1 shows the configurations of the first electrode, the functional layer, and the second electrode, and the calculation results of the left and right sides of the above formula (1).

[0096] [Comparative Example 2] Example 2 was performed in the same manner as Example 2, except that the configurations of the first electrode, the functional layer, and the second electrode were changed to those shown in Table 1. Table 1 shows the configurations of the first electrode, the functional layer, and the second electrode, and the calculation results of the left and right sides of the above formula (1).

[0097] [Table 1]

[0098] From Table 1, it was confirmed that in Examples 1 and 2, the right side of the above formula (1) was larger than the left side of the above formula (1) by setting the TCR of one electrode to a positive value and the TCR of the other electrode to a negative value among the TCR of the first electrode and the TCR of the second electrode. That is, in Examples 1 and 2, the absolute value of the average of the sum of the ratio of the resistance of the first electrode to the temperature change (ρ2 / t2×α2) and the ratio of the resistance of the second electrode to the temperature change (ρ2 / t2×α2) was less than the minimum value of either the ratio of the resistance of the first electrode to the temperature change (ρ2 / t2×α2) or the ratio of the resistance of the second electrode to the temperature change (ρ2 / t2×α2).

[0099] On the other hand, it was confirmed that in Comparative Examples 1 and 2, the left and right sides of the above formula (1) became the same by setting both the TCR of the first electrode and the TCR of the second electrode to positive or negative values. That is, in Comparative Examples 1 and 2, the absolute value of the average of the sum of the ratio of the resistance of the first electrode to temperature change (ρ2 / t2×α2) and the ratio of the resistance of the second electrode to temperature change (ρ2 / t2×α2) became the same as the minimum value of either the ratio of the resistance of the first electrode to temperature change (ρ2 / t2×α2) or the ratio of the resistance of the second electrode to temperature change (ρ2 / t2×α2).

[0100] Therefore, unlike Comparative Examples 1 and 2, Examples 1 and 2 have TCRs of the first electrode and TCRs of the second electrode that have different signs, which makes it possible to cancel out the resistance change due to temperature change of the first electrode and the resistance change due to temperature change of the second electrode, thereby making it possible to suppress fluctuations in voltage drop of the electrodes of the sensor device caused by temperature changes in the environment in which the sensor device is used.

[0101] Although the embodiment has been described above, the above embodiment is presented as an example, and the present invention is not limited to the above embodiment. The above embodiment can be implemented in various other forms, and various combinations, omissions, substitutions, modifications, etc. can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0102] 1A, 1B, 1C Sensor Devices 10 Flexible substrate 20 First electrode 30 Piezoelectric layer 40 Second electrode 50A, 50B functional layer

Claims

1. A functional layer and a pair of electrodes connected in series via the functional layer are provided on a support, The sensor device comprises a pair of electrodes, a first electrode having a temperature coefficient of resistance that is one of a positive value and a negative value, and a second electrode having a temperature coefficient of resistance that is the other of a positive value and a negative value.

2. The sensor device according to claim 1 , wherein the first electrode and the second electrode are arranged to face each other.

3. the first electrode is provided on a surface of the functional layer facing the support; the second electrode is provided on a surface of the functional layer different from the support side, The sensor device according to claim 2 , wherein the support, the first electrode, the functional layer, and the second electrode are laminated in this order.

4. The sensor device according to any one of claims 1 to 3, wherein the support is a flexible substrate.

5. The sensor device according to any one of claims 1 to 4, wherein the functional layer is a piezoelectric layer.

6. The sensor device according to claim 5 , wherein the piezoelectric layer includes an inorganic material.

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