Laminated piezoelectric body and manufacturing method therefor

Abstract

A laminated piezoelectric body according to the present invention comprises: a polymer piezoelectric film; and a transparent conductive layer that is disposed on at least one surface of the polymer piezoelectric film and contains an indium-tin composite oxide as a main component. The ratio of the content of tin atoms to the total amount of indium and tin atoms in the transparent conductive layer is 1-6 mass%, the hole mobility of the transparent conductive layer is 10 cm2 / (V⋅s) to 20 cm2 / (V⋅s), and the carrier density is 1.0 × 1021 cm−3 to 3.0 × 1021 cm−3.

Description

Multilayer piezoelectric element and its manufacturing method

[0001] The present invention relates to a laminated piezoelectric element and a method for manufacturing the same.

[0002] In recent years, piezoelectric films applicable to display applications have been reported (see, for example, Non-Patent Document 1). Furthermore, development of piezoelectric films with transparent conductive layers is also underway. An indium-tin oxide (ITO) film is used as the transparent conductive layer (see, for example, Patent Document 1).

[0003] Generally, ITO films are formed by sputtering and then heat-treated at a high temperature of approximately 150°C to enhance their crystallinity, thereby achieving both high transparency and conductivity. However, when piezoelectric films are exposed to such high temperatures, they tend to become discolored, lose transparency, deform, and their piezoelectric properties are also likely to deteriorate. Therefore, it is desirable to be able to use amorphous ITO films that do not require high-temperature heat treatment.

[0004] Furthermore, ITO films used in elements such as image electrodes of TFTs (Thin Film Transistors) require circuit patterning, and therefore are also required to have good etching properties. Amorphous ITO films are known to have better etching properties than crystalline ITO films. For example, a process has been reported in which an amorphous ITO film with low resistivity and excellent wet etching properties is formed by adding a certain amount of water or hydrogen during film formation (see, for example, Non-Patent Document 1). Thus, it is desirable to be able to use amorphous ITO films from the perspective of having good etching properties.

[0005] Japanese Patent Application Laid-Open No. 2017-216451

[0006] S. Ishibashi et al, J. Vac. Sci. Technol. A8, 1403, 1990

[0007] As described above, it is desirable to be able to apply an amorphous transparent conductive layer to a piezoelectric film in order to eliminate the need for high-temperature heat treatment and obtain good etching properties. However, amorphous transparent conductive layers have the problem of being less transparent and conductive than crystalline transparent conductive layers. Furthermore, amorphous transparent conductive layers have the problem of exhibiting large changes in volume resistivity (hereinafter sometimes referred to as "resistivity") when stored for a certain period of time in a high-temperature, high-humidity environment, resulting in poor stability in a high-temperature, high-humidity environment.

[0008] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a laminated piezoelectric element that has excellent transparency, conductivity, and stability in high-temperature and high-humidity environments even when it has an amorphous transparent conductive layer, and a method for manufacturing the same.

[0009] [1] A laminated piezoelectric body comprising a polymeric piezoelectric film and a transparent conductive layer mainly composed of indium-tin composite oxide, the transparent conductive layer being disposed on at least one surface of the polymeric piezoelectric film, the content of tin atoms relative to the total amount of indium and tin atoms in the transparent conductive layer being 1% by mass or more and 6% by mass or less, and the hole mobility of the transparent conductive layer being 10 cm ２ / (V・s) or more 20cm ２ / (V s) or less, and the carrier density is 1.0 × 10 ２１ cm －３ Above 3.0 x 10 ２１ cm －３[2] The laminated piezoelectric element according to [1], wherein the transparent conductive layer has an inter-terminal resistance of 10 kΩ or more at an inter-terminal distance of 5 mm after immersion in a 5 mass % aqueous oxalic acid solution for 30 minutes. [3] The laminated piezoelectric element according to [1] or [2], wherein the polymeric piezoelectric film contains a vinylidene fluoride resin as a main component. [4] The laminated piezoelectric element according to any of [1] to [3], wherein the transparent conductive layer has a thickness of 20 nm or more and 40 nm or less. [5] The laminated piezoelectric element according to any of [1] to [4], further comprising at least one of a hard coat layer and an optical adjustment layer disposed between the polymeric piezoelectric film and the transparent conductive layer. [6] A method for manufacturing a laminated piezoelectric body according to any one of [1] to [5], comprising the steps of preparing a polymeric piezoelectric film and forming the transparent conductive layer on at least one surface of the polymeric piezoelectric film by a sputtering method, wherein the sputtering is performed under conditions of a pressure of 0.30 Pa or more and 0.90 Pa or less, and a temperature of the polymeric piezoelectric film of 0° C. or more and 80° C. or less. [7] A method for manufacturing a laminated piezoelectric body according to [6], wherein the sputtering is performed in an introduction gas containing argon gas and oxygen gas, and the content of oxygen gas in the introduction gas is 0.7 mol % or more and less than 1.8 mol %, and the content of water in the introduction gas is 0.05 mol % or less.

[0010] According to the present invention, it is possible to provide a laminated piezoelectric element that has excellent transparency, conductivity, and stability in high-temperature and high-humidity environments even when it has an amorphous transparent conductive layer, and a method for producing the same.

[0011] FIG. 1 is a schematic cross-sectional view showing an example of a laminated piezoelectric element according to the present embodiment.

[0012] The present inventors have found that by adjusting the content of tin atoms relative to the total amount of indium atoms (In) and tin atoms (Sn) in a transparent conductive layer containing an indium-tin composite oxide as a main component (hereinafter also referred to as the "Sn content"), the Hall mobility, and the carrier density, each within a predetermined range, it is possible to increase the transparency, while reducing the resistivity and the rate of change in resistivity under high-temperature, high-humidity environments, even in an amorphous transparent conductive layer.

[0013] Furthermore, it was found that a transparent conductive layer having a Sn content, Hall mobility, and carrier density within a predetermined range can be adjusted by adjusting the film formation conditions (Sn content of the target, pressure in the sputtering chamber, and oxygen gas and water contents in the introduced gas) when the layer is formed by a sputtering method. In particular, it was found that the Hall mobility and carrier density can be adjusted to the above ranges by lowering the pressure in the chamber, the water content in the introduced gas, and the Sn content of the target to a predetermined level or lower and adjusting the oxygen gas content in the introduced gas to an appropriate range.

[0014] A laminated piezoelectric element according to an embodiment of the present invention and a method for manufacturing the same will be specifically described below.

[0015] 1. Laminated Piezoelectric Body A laminated piezoelectric body according to one embodiment of the present invention includes a polymeric piezoelectric film and a transparent conductive layer disposed on at least one surface of the polymeric piezoelectric film. The laminated piezoelectric body may further include other layers as necessary. For example, from the viewpoint of further enhancing transparency, the laminated piezoelectric body may further include at least one of a hard coat layer and an optical adjustment layer.

[0016] FIG. 1 is a schematic cross-sectional view showing an example of a laminated piezoelectric element 10 according to an embodiment of the present invention.

[0017] As shown in FIG. 1, the laminated piezoelectric element 10 includes a polymeric piezoelectric film 11, a hard coat layer 12, an optical adjustment layer 13, and a transparent conductive layer 14.

[0018] 1-1. Polymer Piezoelectric Film 11 The polymer piezoelectric film is a film containing a polymer piezoelectric material. Examples of polymer piezoelectric materials include fluorine-based resins, polyvinylidene cyanide (PVDCN), vinylidene cyanide vinyl acetate copolymer (P(VDCN / VAc)), polyvinyl chloride, odd-numbered nylon, polylactic acid, and poly-γ-benzyl-L-glutamate. Among these, fluorine-based resins are preferred from the viewpoint of high piezoelectricity and heat resistance.

[0019] That is, the polymeric piezoelectric film preferably contains a fluororesin as a main component. "Containing a fluororesin as a main component" means that the content of the fluororesin in the polymeric piezoelectric film is 50% by mass or more, preferably 60% by mass or more.

[0020] Among fluororesins, vinylidene fluoride resins are preferred because they can provide a higher piezoelectric effect. Vinylidene fluoride resins are polymers containing structural units derived from vinylidene fluoride.

[0021] The content of the vinylidene fluoride-derived structural units in the polymer is preferably 50% by mass or more, more preferably 70% by mass or more, based on the total amount of the structural units in the polymer. The higher the content of the vinylidene fluoride-derived structural units, the more likely it is that a higher piezoelectric effect will be obtained. The upper limit of the content is not particularly limited and may be 100% by mass or 90% by mass or less.

[0022] The polymer may further contain a structural unit derived from a monomer copolymerizable with vinylidene fluoride, provided that the effects of the present invention are not impaired. Examples of the monomer copolymerizable with vinylidene fluoride include fluorine-containing monomers such as trifluoroethylene, tetrafluoroethylene, hexafluoropropylene, trifluorochloroethylene, and vinyl fluoride. Two or more of these monomers may be contained.

[0023] Among these, a homopolymer of vinylidene fluoride is preferred from the viewpoint of obtaining a higher piezoelectric effect.

[0024] When the polymer piezoelectric film contains a fluorine-based resin, the piezoelectric constant d ３３ The piezoelectric constant d of the polymeric piezoelectric film is preferably 7 pC / N or more and 40 pC / N or less. ３３ When the piezoelectric constant d of the polymeric piezoelectric film is 7 pC / N or more, the amount of electric charge generated by the piezoelectric effect is larger, and therefore the pressure sensitivity can be further improved. ３３When the piezoelectric constant d of the polymeric piezoelectric film is 40 pC / N or less, it is possible to make it less likely that the appearance of the film will be deteriorated due to the decrease in the flatness of the surface of the polymeric piezoelectric film caused by the polarization treatment. ３３ is more preferably 10 pC / N or more and 40 pC / N or less, further preferably 13 pC / N or more and 35 pC / N or less, and particularly preferably 15 pC / N or more and 30 pC / N or less.

[0025] Piezoelectric constant d of polymer piezoelectric film ３３ is the direct quasi-static method (d ３３ The piezoelectric constant d of the piezoelectric ceramic measured by the Meter method and the Berlincoat method ３３ The piezoelectric constant can be measured in accordance with the test method ISO 19622:2018. Specifically, using a piezoelectric constant measuring device (e.g., Piezometer System PM300 manufactured by PIEZOTEST), a sample is clipped with a holding force of 1.0 N, and an alternating force of 0.15 N and a frequency of 110 Hz is applied, and the generated charge is read. The absolute value of the measured value is then used to calculate the piezoelectric constant. The intersection of the diagonal lines of the piezoelectric film is taken as the center point, and the piezoelectric constant d ３３ Measure.

[0026] Piezoelectric constant d of polymer piezoelectric film ３３ can be adjusted mainly by the type of resin contained in the polymeric piezoelectric film and the manufacturing conditions (conditions for polarization and stretching). For example, among fluorine-based resins, the more structural units derived from vinylidene fluoride a resin contains, the lower the piezoelectric constant d ３３ In addition, by strengthening the polarization process or stretching process, the piezoelectric constant d ３３ tends to become large.

[0027] The thickness of the polymer piezoelectric film is preferably, for example, 25 μm or more and 120 μm or less. When the thickness of the piezoelectric film is 25 μm or more, the amount of charge generated by the piezoelectric effect becomes larger, and higher piezoelectricity is likely to be obtained. The thickness of the polymer piezoelectric film is more preferably 30 μm or more, and even more preferably 35 μm or more. When the thickness of the polymer piezoelectric film is 120 μm or less, the transparency of the polymer piezoelectric film is less likely to be impaired, and 100 μm or less is more preferable, and 80 μm or less is even more preferable. From the same viewpoint, the thickness of the polymer piezoelectric film is more preferably 35 μm or more and 80 μm or less.

[0028] The thickness of the polymeric piezoelectric film can be measured by the following method. A digital linear gauge (DG525H, manufactured by Ono Sokki Co., Ltd.) and a gauge stand (SH-022, manufactured by Ono Sokki Co., Ltd.) were used. Specifically, the intersection of the diagonal lines of the piezoelectric film is set as the center point, and the thickness of the area including the center point is measured.

[0029] 1-2. Hard Coat Layer 12 The hard coat layer can suppress an increase in haze by making the surface of the polymer piezoelectric film less susceptible to scratches during the production of the laminated piezoelectric element. The hard coat layer is preferably disposed between the polymer piezoelectric film and the transparent conductive layer (see FIG. 1). Only one hard coat layer may be included, or two or more hard coat layers may be included. When two or more hard coat layers are included, one of the two or more hard coat layers may be disposed on one side of the polymer piezoelectric film, and the other may be disposed on the other side.

[0030] The hard coat layer preferably contains a cured product of a curable composition containing a polymerizable compound.

[0031] (Polymerizable Compound) The polymerizable compound may be any one of a monomer, an oligomer, or a polymer. The polymerizable compound may be a thermosetting compound or an ionizing radiation compound, but is preferably an ionizing radiation compound. The ionizing radiation may usually be ultraviolet (UV) or an electron beam (EB).

[0032] The ionizing radiation-curable compound is a compound having an ionizing radiation-curable functional group. Examples of the ionizing radiation-curable functional group include ethylenically unsaturated bond groups such as (meth)acryloyl groups, vinyl groups, and allyl groups, and ring-opening polymerizable groups such as epoxy groups and oxetanyl groups. Among these, compounds having an ethylenically unsaturated bond group are preferred, compounds having two or more ethylenically unsaturated bond groups are more preferred, and polyfunctional (meth)acrylate compounds are even more preferred. The term "(meth)acrylate" refers to either or both of acrylate and methacrylate.

[0033] Among the polyfunctional (meth)acrylate compounds, examples of bifunctional (meth)acrylate monomers include ethylene glycol di(meth)acrylate, bisphenol A tetraethoxydiacrylate, bisphenol A tetrapropoxydiacrylate, 1,6-hexanediol diacrylate, etc. Examples of trifunctional or higher functional (meth)acrylate monomers include trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, dipentaerythritol tetra(meth)acrylate, isocyanuric acid-modified tri(meth)acrylate, etc. Furthermore, the above-mentioned (meth)acrylate monomers may be partially modified in the molecular skeleton, and those modified with ethylene oxide, propylene oxide, caprolactone, isocyanuric acid, alkyl, cyclic alkyl, aromatic, bisphenol, etc. can also be used.

[0034] Examples of polyfunctional (meth)acrylate oligomers include acrylate polymers such as urethane (meth)acrylate, epoxy (meth)acrylate, polyester (meth)acrylate, polyether (meth)acrylate, etc. Urethane (meth)acrylate can be obtained, for example, by reacting a polyhydric alcohol and an organic diisocyanate with a hydroxy (meth)acrylate.

[0035] (Polymerization Initiator) When the ionizing radiation-curable compound is an ultraviolet-curable compound, the curable composition preferably contains a photopolymerization initiator. Examples of the photopolymerization initiator include one or more selected from acetophenone, benzophenone, α-hydroxyalkylphenone, Michler's ketone, benzoin, benzyl methyl ketal, benzoyl benzoate, α-acyloxime ester, thioxanthones, etc.

[0036] (Other Components) The curable composition may further contain other components in addition to those described above, as necessary. For example, from the viewpoint of suppressing blocking during the production of the laminated piezoelectric body or adjusting the refractive index, the curable composition may further contain particles. The particles may be inorganic particles or organic particles.

[0037] Examples of inorganic particles include particles of silica (silicon oxide), titanium oxide, zirconium oxide, aluminum oxide, zinc oxide, tin oxide, etc., diamond powder, sapphire particles, boron carbide particles, silicon carbide particles, antimony pentoxide particles, etc. Examples of organic particles include resin particles of acrylic resin, acrylic-styrene copolymer, silicone resin, etc. Among these, inorganic particles are preferred, and silica particles are more preferred, as they are less likely to impair the transparency of the hard coat layer. The surfaces of the inorganic particles may be treated with a surface modifier such as a silane coupling agent.

[0038] The thickness of the hard coat layer is not particularly limited, but is preferably from 0.3 μm to 3.0 μm, more preferably from 0.5 μm to 2.0 μm, and even more preferably from 0.5 μm to 1.5 μm.

[0039] The refractive index of the hard coat layer is not particularly limited, but is preferably lower than the refractive index of the optical adjustment layer 13. For example, the refractive index of the hard coat layer can be 1.40 or more and less than 1.60, preferably 1.45 or more and less than 1.60, more preferably 1.47 or more and 1.57 or less, and even more preferably 1.49 or more and 1.55 or less. In this specification, the refractive index means the refractive index at a wavelength of 589 nm measured using an Abbe refractometer in accordance with JIS K 7142:2014.

[0040] The thickness of the hard coat layer can be measured by observing the cross section of the laminated piezoelectric body using an electron microscope. Specifically, the laminated piezoelectric body is embedded in epoxy resin, and the resulting epoxy resin block is cut so that the cross section of the laminated piezoelectric body is exposed. Next, the exposed cross section of the laminated piezoelectric body is observed using a scanning electron microscope (e.g., SU3800, manufactured by Hitachi High-Tech Corporation) under conditions of an acceleration voltage of 3.0 kV and a magnification of 50,000 times, and the thickness of the hard coat layer is measured. Measurements are performed at two locations, and the arithmetic average value is taken as the "thickness." The thickness of each of the following layers can also be measured in a similar manner.

[0041] 1-3. Optical Adjustment Layer 13 By appropriately adjusting the refractive index and thickness of the optical adjustment layer, the yellowish tint of the laminated piezoelectric body can be further reduced. The optical adjustment layer 13 is preferably disposed between the polymer piezoelectric film 11 and the transparent conductive layer 14, and in FIG. 1 it is disposed between the hard coat layer 12 and the transparent conductive layer 14. Only one optical adjustment layer 13 may be included, or two or more optical adjustment layers may be included. When two or more optical adjustment layers are included, one of the two or more optical adjustment layers may be disposed on one side of the polymer piezoelectric film, and the other may be disposed on the other side.

[0042] The refractive index of the optical adjustment layer is preferably higher than that of the hard coat layer and lower than that of the transparent conductive layer, thereby enabling the transmittance of the laminated piezoelectric body to be further increased and the yellowish tint to be further reduced.

[0043] For example, the refractive index of the optical adjustment layer can be 1.60 or more and less than 1.80, preferably 1.63 or more and less than 1.78, and more preferably 1.65 or more and less than 1.75. The refractive index of the optical adjustment layer is more preferably 0.05 or more higher than the refractive index of the first hard coat layer.

[0044] The material of the optical adjustment layer may be any material that satisfies such a refractive index. For example, the refractive index may be adjusted by adding metal oxide particles to the curable composition exemplified as the material of the hard coat layer. The metal oxide particles are preferably a refractive index material having a refractive index of 1.50 or more. Examples of such metal oxide particles include aluminum oxide, titanium oxide, zirconium oxide, zinc oxide, and tin oxide, and among these, titanium oxide and zirconium oxide are preferred.

[0045] The thickness of the optical adjustment layer is not particularly limited, but may be 0.05 μm or more and 0.50 μm or less, or 0.08 μm or more and 0.18 μm or less. When the thickness of the optical adjustment layer is within the above range, the transmittance of the laminated piezoelectric body can be further increased and the color can be further reduced.

[0046] 1-4. Transparent conductive layer 14 The transparent conductive layer is disposed on at least one surface of the polymer piezoelectric film. In FIG. 1, the transparent conductive layer is disposed on the surface of the optical adjustment layer 13. Only one transparent conductive layer may be included, or two or more transparent conductive layers may be included. When two or more transparent conductive layers are included, one of the two or more transparent conductive layers may be disposed on the other surface side of the polymer piezoelectric film, and the other one may be disposed on one surface side. The transparent conductive layer contains indium-tin composite oxide (ITO) as a main component.

[0047] "Containing indium-tin composite oxide as a main component" means that the content of indium-tin composite oxide in the transparent conductive layer is 60% by mass or more, and preferably 90% by mass or more.

[0048] The Sn content in the transparent conductive layer is preferably 1% by mass or more and 6% by mass or less. When the Sn content is 6% by mass or less, the yellowness of the transparent conductive layer can be reduced, while the Hall mobility can be increased and the resistivity can be reduced. In other words, by controlling the upper limit of the Sn content, excess Sn that is not incorporated into the crystal lattice of indium oxide can be reduced. This can further reduce the yellowness and resistivity of the first transparent conductive layer. When the Sn content is 1% by mass or more, the carrier density can be further increased and the resistivity can be further reduced. From the same perspective, the Sn content of the first transparent conductive layer is preferably 2% by mass or more and 5% by mass or less, and more preferably 2% by mass or more and 4% by mass or less.

[0049] The Sn content can be measured by fluorescent X-ray analysis in accordance with JIS K 0119:2008.

[0050] The transparent conductive layer may further contain components other than the indium-tin composite oxide as long as the effects of the present invention are not impaired.

[0051] In the laminated piezoelectric element of the present invention, all components other than the transparent conductive layer are insulating materials, so the carrier density, Hall mobility, and resistivity measured in the transparent conductive layer are physical property values ​​attributable to the transparent conductive layer. Therefore, the physical property values ​​of the transparent conductive layer formed in the laminated piezoelectric element are described as the physical property values ​​of the transparent conductive layer. The resistivity of the transparent conductive layer is inversely proportional to the product of the Hall mobility and the carrier density. Therefore, it is preferable that the product of the Hall mobility and the carrier density of the transparent conductive layer be appropriately high.

[0052] Specifically, the hole mobility of the transparent conductive layer is 10 cm ２ / (V・s) or more 20cm ２ The hole mobility of the transparent conductive layer is 10 cm ２ When the hole mobility of the transparent conductive layer is 20 cm / (V·s) or more, the resistivity of the transparent conductive layer can be reduced. ２ / (V·s) or less, the environmental resistance of the transparent conductive layer can be improved (the rate of change in resistivity in a high-humidity and high-temperature environment can be reduced). From the same viewpoint, the hole mobility of the transparent conductive layer is 10 cm２ / (V・s) or more 18cm ２ / (V·s) or less, and ２ / (V・s) or more 17cm ２ / (V·s) or less is more preferable, and 11 cm ２ / (V・s) or more 17cm ２ / (V·s) or less is more preferable, ２ / (V・s) or more 15cm ２ It is particularly preferable that the value is / (V·s) or less.

[0053] The carrier density of the transparent conductive layer is 1.0×10 ２１ cm －３ Above 3.0 x 10 ２１ cm －３ The carrier density of the transparent conductive layer is 1.0×10 or less. ２１ cm －３ When the carrier density of the transparent conductive layer is 3.0×10 or more, the resistivity of the transparent conductive layer can be reduced. ２１ cm －３ From the same viewpoint, the carrier density of the transparent conductive layer is 1.1×10 or less, and thus the environmental resistance can be improved (the rate of change in resistivity in a high-humidity and high-heat environment can be reduced). ２１ cm －３ 2.8 x 10 ２１ cm －３ Preferably, it is 1.2 × 10 or less. ２１ cm －３ 2.8 x 10 ２１ cm －３ More preferably, it is 1.2 × 10 or less. ２１ cm －３ 2.6 x 10 ２１ cm －３ More preferably, it is 1.3 × 10 or less. ２１ cm －３ The above is 2.4 x 10 ２１ cm －３ It is particularly preferred that:

[0054] The resistivity of the transparent conductive layer is not particularly limited, but is preferably 4.5×10 －４ The resistivity of the transparent conductive layer is preferably 4.5×10 Ω cm or less. －４From the same viewpoint, the resistivity of the transparent conductive layer is 4.0×10 －４ More preferably, it is 3.6×10 Ω cm or less. －４ The lower limit of the resistivity of the transparent conductive layer is not particularly limited, but from the viewpoint of transparency, it is preferably 1.0×10 －５ It can be made Ω·cm or more.

[0055] The Hall mobility, carrier density, and resistivity of the transparent conductive layer can be measured by Hall effect measurement based on the Van der Pauw method. That is, using a Hall effect measurement system (for example, Resitest 8200 manufactured by Toyo Technica Co., Ltd.), an applied magnetic field of 10 kGauss, an applied current of 2×10 －４ A. Measurement temperature: At room temperature (295 K), the carrier density, Hall mobility, and resistivity of the transparent conductive layer can be measured based on the Van der Pauw method.

[0056] The hole mobility, carrier density, and resistivity of the transparent conductive layer can be adjusted by the film formation conditions during sputtering (Sn content of the target, pressure in the chamber, oxygen gas and water content of the introduced gas, etc.) described below. By lowering the Sn content, lowering the pressure in the chamber, lowering the water content in the introduced gas, and setting the oxygen gas content within a predetermined range, the hole mobility and carrier density of the transparent conductive layer tend to be increased, and the resistivity tend to be decreased.

[0057] The transparent conductive layer is preferably an amorphous transparent conductive layer containing ITO as a main component, because, as described above, an amorphous transparent conductive layer not only does not require high-temperature heat treatment for crystallization after being formed on a polymer piezoelectric film, but also has excellent wet etching properties.

[0058] The term "amorphous transparent conductive layer" does not necessarily mean a completely amorphous layer, but may also contain a small amount of crystalline components. Whether a transparent conductive layer is amorphous can be confirmed by determining whether the resistance after immersion in a 5% by mass aqueous solution of oxalic acid for a predetermined period of time is greater than or equal to a predetermined value. Specifically, a laminate (e.g., a laminated piezoelectric element according to the present embodiment) having a transparent conductive layer formed on a substrate is immersed in a 5% by mass aqueous solution of oxalic acid for 30 minutes, followed by rinsing with water and drying. A probe with a pin electrode having a tip diameter of 2 mm or less and arranged with a terminal distance of 5 mm is placed on the surface on which the transparent conductive layer is formed, and the resistance is measured with a resistivity meter (e.g., Loresta GP MCP-T610, ASP Probe, manufactured by Nitto Seiko Analytech Co., Ltd.). The amorphous transparent conductive layer is etched and disappears in the 5% by mass aqueous solution of oxalic acid, resulting in increased terminal resistance. In this specification, a transparent conductive layer is considered to be amorphous if the inter-terminal resistance measured at a terminal distance of 5 mm after immersion in a 5 mass % aqueous oxalic acid solution under the above conditions, washing with water, and drying exceeds 10 kΩ.

[0059] The inter-terminal resistance after immersing the transparent conductive layer in a 5% by mass aqueous solution of oxalic acid for 30 minutes is more preferably 1 MΩ or more. The higher the inter-terminal resistance after immersion, the less the transparent conductive layer is wet-etched, and the more likely it is that the inter-terminal resistance will be too high when the conductive layer is completely removed by etching, resulting in an OVER LOAD indication indicating that the resistance is outside the measurable range of the resistance measuring device.

[0060] The refractive index of the transparent conductive layer is not particularly limited, but is preferably higher than the refractive index of the optical adjustment layer. The refractive index of the transparent conductive layer can be, for example, 1.80 or more and 2.20 or less.

[0061] The thickness of the transparent conductive layer is not particularly limited, but is preferably 20 nm or more and 40 nm or less. When the thickness of the transparent conductive layer is 20 nm or more, not only can the resistivity be lowered, but also the rate of change in resistivity under high temperature and high humidity environments can be reduced. When the thickness of the transparent conductive layer is 40 nm or less, transparency is less likely to be impaired, making it suitable for use in, for example, touch panels. From the same viewpoint, the thickness of the transparent conductive layer is more preferably 22 nm or more and 37 nm or less, and more preferably 24 nm or more and 35 nm or less.

[0062] 1-5. Physical Properties of the Laminated Piezoelectric Body (Total Light Transmittance) From the viewpoint of application to, for example, touch panels, the laminated piezoelectric body preferably has high transparency. Specifically, the total light transmittance of the laminated piezoelectric body is preferably 80% or more, and more preferably 85% or more. The total light transmittance of the laminated piezoelectric body can be measured using a haze meter (for example, NDH7000SP II, manufactured by Nippon Denshoku Industries Co., Ltd.) based on the method described in JIS K 7361-1:1997.

[0063] (Piezoelectric constant) Piezoelectric constant d of the laminated piezoelectric body ３３ The piezoelectric constant d of the laminated piezoelectric material is preferably 7 pC / N or more and 40 pC / N or less. ３３ When the piezoelectric constant d of the laminated piezoelectric material is 7 pC / N or more, higher pressure sensitivity is likely to be obtained. ３３ From the same viewpoint, when the piezoelectric constant d of the laminated piezoelectric body is 40 pC / N or less, the above-mentioned appearance defects can be further reduced. ３３ The piezoelectric constant d of the laminated piezoelectric body is more preferably 10 pC / N or more and 40 pC / N or less, further preferably 13 pC / N or more and 35 pC / N or less, and particularly preferably 15 pC / N or more and 30 pC / N or less. ３３ can be measured in the same manner as above.

[0064] Piezoelectric constant d of the laminated piezoelectric material ３３ is, for example, the piezoelectric constant d ３３ The piezoelectric constant d of the piezoelectric film can be adjusted by ３３ When the piezoelectric constant d３３ It is also likely to be expensive.

[0065] (Applications) The laminated piezoelectric body can be used for various applications, among which the laminated piezoelectric body can be preferably used for piezoelectric panels including capacitive touch panels, resistive touch panels, pressure sensors, actuators for haptic devices, piezoelectric vibration power generators, flat speakers, etc.

[0066] 1 can be manufactured through, for example, 1) a step of preparing a polymer piezoelectric film 11, 2) a step of forming a hard coat layer 12 and an optical adjustment layer 13 on the polymer piezoelectric film 11, and 3) a step of forming a transparent conductive layer 14 on the optical adjustment layer 13. Note that if the laminated piezoelectric body 10 does not include the hard coat layer 12 or the optical adjustment layer 13, step 2) may be omitted.

[0067] 1) Step of Preparing Polymer Piezoelectric Film 11 The polymer piezoelectric film may be a commercially available product or may be manufactured. For example, a polymer piezoelectric film containing a fluorine-based resin as a main component can be manufactured through a step of manufacturing a fluorine-based resin film (film-forming step), a step of stretching the fluorine-based resin film (stretching step), and a step of polarizing the fluorine-based resin film (polarization step).

[0068] (Film Forming Process) The fluororesin film can be produced by any method such as melt extrusion, hot pressing, solution casting, etc. Among these, the fluororesin film is preferably produced by melt extrusion, from the viewpoint of easily obtaining a polymer piezoelectric film having a predetermined thickness or more.

[0069] (Stretching step) In the stretching step, the produced fluororesin film is stretched. The fluororesin film has a structure in which α-type crystals (main chain has a helical structure) and β-type crystals (main chain has a planar zigzag structure) are mixed. β-type crystals have a large polarization structure. By stretching the fluororesin film, a transition from α-type crystals to β-type crystals occurs, and the proportion of β-type crystals can be increased. Therefore, the stretching step is preferably performed as necessary to increase the proportion of β-type crystals in the fluororesin. The stretching direction may be either the TD direction or the MD direction, and the MD direction is more preferable.

[0070] The stretching method is not particularly limited, and can be a known stretching method such as a tenter method or a drum method.

[0071] The stretching ratio can be, for example, 3.0 times or more and 6.0 times or less. When the stretching ratio is 3.0 times or more, it is easy to adjust the thickness and polarity of the film to a more appropriate range. When the stretching ratio is 3.0 times or more, the rearrangement of the β-type crystals becomes more sufficient, and not only is it easy to exhibit higher piezoelectricity, but transparency can also be further improved. When the stretching ratio is 6.0 times or less, breakage due to stretching can be further suppressed.

[0072] (Polarization Step) In the polarization step, a DC voltage is applied to the fluororesin film to impart piezoelectricity to the fluororesin film. By applying a DC voltage to the fluororesin film in which the proportion of polar β crystals has been increased in the stretching step, a piezoelectric film with high piezoelectricity can be obtained. The DC voltage to be applied may be adjusted depending on the thickness of the stretched film, and may be, for example, 1 kV or more and 50 kV or less.

[0073] 2) Step of forming hard coat layer 12 and optical adjustment layer 13 A hard coat layer and an optical adjustment layer are formed in this order on the polymer piezoelectric film. From the viewpoint of forming these layers while making the surface of the polymer piezoelectric film more flat, it is preferable to form the hard coat layer and the optical adjustment layer in this order on one side of the polymer piezoelectric film while a carrier film is attached to the other side of the polymer piezoelectric film.

[0074] The carrier film can be attached to one side of the polymer piezoelectric film via an adhesive layer. The type of carrier film is not particularly limited, and it can be, for example, a resin film. Among resin films, resin films with a high Young's modulus are preferred from the viewpoint of further improving the flatness of the surface of the polymer piezoelectric film, and films made of polyester such as polyethylene terephthalate (PET) or polyolefin such as polypropylene (PP) are preferred. The thickness of the carrier film is preferably, for example, 35 μm or more and 200 μm or less, more preferably 50 μm or more and 175 μm or less, and even more preferably 70 μm or more and 150 μm or less.

[0075] Examples of adhesives for the adhesive layer include acrylic adhesives, rubber adhesives, and silicone adhesives, but from the viewpoint of adhesiveness and releasability, acrylic adhesives are preferred.

[0076] Next, the above-described curable composition for the hard coat layer is applied to the other surface of the polymeric piezoelectric film having the carrier film attached to the other surface, and then dried and cured to form a hard coat layer.

[0077] The curable composition may further contain a dilution solvent. The dilution solvent preferably has a polarity similar to that of the particles. Examples of the dilution solvent include organic solvents such as alcohol-based solvents, ketone-based solvents, ester-based solvents, carbonate-based solvents, and aromatic solvents.

[0078] The method for applying the curable composition is not particularly limited, and may be any of spin coating, gravure coating, die coating, bar coating, dip coating, and the like.

[0079] The curable composition can be dried by heating the applied curable composition. The heating temperature is preferably a temperature at which the solvent can be removed or higher and a temperature at or lower than the heat distortion temperature of the polymeric piezoelectric film, and in the case of a fluorine-based resin, the heating temperature can be, for example, 60°C or higher and 100°C or lower. The heat distortion temperature can be measured, for example, in accordance with JIS K 7191-2:2015.

[0080] The curable composition may be cured by heat or by ionizing radiation. Curing by ionizing radiation can be carried out by irradiation with ultraviolet rays or electron beams. Alternatively, curing by heat and curing by ionizing radiation may be used in combination.

[0081] Similarly, a coating liquid containing the curable composition for the optical adjustment layer is applied onto the obtained hard coat layer, and then dried and cured to form the optical adjustment layer.

[0082] 3) Step of forming transparent conductive layer 14 The above-described transparent conductive layer is formed on the obtained optical adjustment layer by sputtering.

[0083] As the sputtering method, various sputtering methods can be used, such as a standard magnetron sputtering method using a DC power supply, an RF sputtering method, an RF+DC sputtering method, a pulse sputtering method, and a dual magnetron sputtering method.

[0084] The target used for sputtering is a metal target (In—Sn target) or an oxide target (In ２ O ３ -SnO ２ The target may have a composition such that the Sn content of the resulting transparent conductive layer falls within the above range, and the Sn content in the target is more than 1 mass % and not more than 6 mass %, preferably 2 mass % or more and 5 mass % or less, and more preferably 2 mass % or more and 4 mass % or less. In other words, the Sn content in the target is approximately equal to the Sn content in the transparent conductive layer.

[0085] Sputtering using such a target can be carried out by introducing Ar gas, an inert gas, into the chamber of a sputtering apparatus evacuated to a high vacuum. When a metal target of a solid solution of indium and tin is used as the target, an oxidizing agent such as oxygen gas is introduced together with Ar gas to perform reactive sputtering film formation. Note that even when an indium-tin composite oxide is used as the target, oxygen gas or the like may be introduced in addition to Ar gas.

[0086] The pressure in the chamber during sputtering is preferably 0.30 Pa or more and 0.90 Pa or less. When the pressure in the chamber during sputtering is 0.90 Pa or less, the rate of change in resistivity of the resulting transparent conductive layer in a high-humidity environment can be further reduced. When the pressure in the chamber during sputtering is 0.30 Pa or more, a denser transparent conductive layer can be formed, thereby further reducing the Hall mobility and increasing adhesion. The increase in resistivity in a high-temperature, high-humidity environment can be reduced. From the same viewpoint, the pressure in the chamber during sputtering is more preferably 0.30 Pa or more and 0.70 Pa or less, and even more preferably 0.30 Pa or more and 0.60 Pa or less.

[0087] In order to further reduce the resistivity of the transparent conductive layer, it is preferable that the water content in the chamber during sputtering is small. Specifically, the water content in the gas introduced during sputtering is preferably 0.05 mol% or less, and more preferably 0.02 mol% or less. If the water content in the introduced gas is 0.05 mol% or less, the resistivity of the obtained transparent conductive layer can be further reduced. From the same viewpoint, it is more preferable that the water content in the introduced gas is 0.02 mol% or less.

[0088] In order to keep the moisture content of the gas introduced during sputtering within the above range, it is preferable to lower the pressure in the chamber of the sputtering apparatus before sputtering to create an atmosphere from which moisture in the apparatus and impurities such as organic gases generated from the substrate have been removed. The pressure in the chamber for removing moisture and impurities in the chamber is preferably 2.0 × 10 －４ Pa or less, more preferably 1.5 × 10 －４ Pa or less, more preferably 1.0 × 10 －４ Pa or less, particularly preferably 5.0 × 10 －５ Pa or less.

[0089] The content of oxygen gas in the gas introduced during sputtering is preferably 0.7 mol% or more and less than 1.8 mol%. When the content of oxygen gas in the gas introduced is within the above range, oxygen vacancies are more likely to be formed in the resulting transparent conductive layer, and electrons are more likely to be released, thereby making it possible to further reduce the resistivity. That is, when the content of oxygen gas is 0.7 mol% or more, Sn ４＋ is Sn ２＋ The decrease in hole mobility around tin due to the above phenomenon can be further suppressed. On the other hand, when the oxygen gas content is 1.8 mol% or less, the change in the coordination form of tin suppresses an increase in hepta- and octa-coordinated tin, which cannot be released by donors, and the decrease in hole mobility can be further suppressed. From the same viewpoint, the oxygen gas content in the introduced gas is more preferably 0.7 mol% or more and 1.6 mol% or less, and even more preferably 0.7 mol% or more and 1.4 mol% or less.

[0090] The temperature (substrate temperature) of the polymer piezoelectric film during sputtering is preferably lower than 100°C. By lowering the substrate temperature to below 100°C, thermal degradation of the polymer piezoelectric film can be further suppressed. From the viewpoint of further suppressing thermal damage to the polymer piezoelectric film, the substrate temperature is more preferably 80°C or lower, even more preferably 60°C or lower, and particularly preferably 40°C or lower. There are no particular restrictions on the lower limit of the temperature of the polymer piezoelectric film, but from the viewpoint of improving film formability, it is preferably, for example, 0°C or higher, and more preferably 10°C or higher.

[0091] In this specification, the temperature of the piezoelectric polymer film during sputtering (substrate temperature) refers to the set temperature of the substrate of the piezoelectric polymer film during sputtering. For example, when continuous sputtering is performed using a roll sputtering device, the temperature of the piezoelectric polymer film refers to the temperature of the can roll on which sputtering is performed. Furthermore, when sputtering is performed using a sheet-type (batch type) method, the temperature of the piezoelectric polymer film refers to the temperature of the holder on which the piezoelectric polymer film is placed.

[0092] Among these, it is preferable to set the Sn content of the target within the above range, the pressure in the chamber to 0.30 Pa or more and 0.90 Pa or less, and the temperature of the polymer piezoelectric film to 0°C or more and 80°C or less, and it is even more preferable to set the contents of water and oxygen gas in the introduced gas within the above ranges.

[0093] In this manner, an amorphous transparent conductive layer having the above-mentioned hole mobility and carrier density can be formed on the polymeric piezoelectric film.

[0094] 4) Other Steps The method for manufacturing a laminated piezoelectric body may further include steps other than those described above. For example, after step 3), a step of peeling off the carrier film together with the adhesive layer from the other surface of the polymeric piezoelectric film may be further carried out.

[0095] The present invention will be further described below with reference to examples and comparative examples, but the technical scope of the present invention is not limited thereto.

[0096] [Example 1] (Preparation of polymer piezoelectric film) A 160 μm thick film made of vinylidene fluoride resin (vinylidene fluoride homopolymer, manufactured by Kureha Corporation) was stretched in the MD direction to a stretching ratio of 4.2. Next, the stretched film was passed between a ground electrode and a needle-shaped electrode while a DC voltage of 13.0 kV was applied between the electrodes, thereby performing a polarization treatment, to obtain a polymer piezoelectric film with a thickness of 40 μm.

[0097] Piezoelectric constant d of polymer piezoelectric film ３３ is calculated by the direct quasi-static method (d ３３ The piezoelectric constant d of the piezoelectric ceramic measured by the Meter method and the Berlincoat method ３３ The measurement was performed in accordance with the test method ISO 19622:2018. Specifically, using a piezoelectric constant measurement device (for example, Piezometer System PM300 manufactured by PIEZOTEST), the sample was clipped with a holding force of 1.0 N, and an alternating force of 0.15 N and a frequency of 110 Hz was applied, and the generated charge was read. The absolute value of the measured value was then used to calculate the piezoelectric constant d ３３ The piezoelectric constant d is calculated by taking the intersection of the diagonal lines of the piezoelectric film as the center point and calculating the piezoelectric constant d ３３As a result, the piezoelectric constant d ３３ was 17 pC / N.

[0098] (Formation of Hard Coat Layer) Next, a carrier film (polyethylene terephthalate) having a thickness of 125 μm was bonded to the other surface (Y surface) of the obtained polymeric piezoelectric film using a laminator at room temperature (25° C.), and then the film was wound into a roll. An ultraviolet-curable composition containing an acrylic compound and amorphous silica was applied to one surface (X surface) of the polymeric piezoelectric film to which the carrier film was bonded, dried at 60° C., and then irradiated with ultraviolet light to form a hard coat layer having a thickness of 750 μm (refractive index of 1.50 at a wavelength of 589 nm).

[0099] (Formation of Optical Adjustment Layer) Next, an ultraviolet-curable composition containing zirconium oxide particles was applied onto the obtained hard coat layer, dried at 60°C, and then irradiated with ultraviolet light to form an optical adjustment layer (refractive index of 1.70 at a wavelength of 589 nm) having a thickness of 102 nm.

[0100] (Formation of Transparent Conductive Layer) A metal target of a solid solution of indium and tin with an Sn content of 3 mass % was set in a magnetron sputtering device, and the polymeric piezoelectric film on which the above-mentioned layers were formed was set as a substrate. Then, while winding up the polymeric piezoelectric film on which the above-mentioned layers were formed, dehydration and degassing were performed until the pressure in the chamber reached 7×10. －５ The pressure was then evacuated to Pa.

[0101] Next, the substrate temperature was set to room temperature (25°C), and a mixed gas composed of 99.2 mol% argon gas and 0.8 mol% oxygen gas was introduced into the chamber, while the chamber was evacuated so that the pressure inside the chamber became 0.4 Pa. A transparent conductive layer having a thickness of 30 nm and consisting essentially of indium tin composite oxide was formed on the optical adjustment layer by a reactive sputtering method, thereby obtaining a laminated piezoelectric body.

[0102] (Amorphous nature of transparent conductive layer) The laminated piezoelectric body having the transparent conductive layer was cut into a rectangle, immersed in a 5% by mass aqueous solution of oxalic acid for 30 minutes, washed with water, and dried. A probe (ASP probe, manufactured by Nitto Seiko Analytech Co., Ltd.) having pin electrodes (pin tip diameter φ0.37 mm) with a terminal distance of 5 mm was placed on the side on which the transparent conductive layer was formed, and measurement was performed using a resistivity meter (Loresta GP MCP-T610, manufactured by Nitto Seiko Analytech Co., Ltd.). It was found that the transparent conductive layer was etched and the resistance value was 10 kΩ or more. This confirmed that the transparent conductive layer was amorphous.

[0103] Example 2 A laminated piezoelectric body was fabricated in the same manner as in Example 1, except that the composition of the gas introduced in the reactive sputtering was changed to 98.8 mol % of argon gas and 1.2 mol % of oxygen gas. The transparent conductive layer of the laminated piezoelectric body was confirmed to be amorphous in the same manner as in Example 1.

[0104] Example 3 A laminated piezoelectric body was produced in the same manner as in Example 1, except that the pressure inside the reactive sputtering chamber was changed to 0.55 Pa. The transparent conductive layer of the laminated piezoelectric body was confirmed to be amorphous in the same manner as in Example 1.

[0105] Example 4 A laminated piezoelectric body was produced in the same manner as in Example 1, except that the thickness of the transparent conductive layer was changed to 25 nm. The transparent conductive layer of the laminated piezoelectric body was confirmed to be amorphous in the same manner as in Example 1.

[0106] Example 5 A laminated piezoelectric body was produced in the same manner as in Example 1, except that the thickness of the transparent conductive layer was changed to 35 nm. The transparent conductive layer of the laminated piezoelectric body was confirmed to be amorphous in the same manner as in Example 1.

[0107] Comparative Example 1 A laminated piezoelectric body was fabricated in the same manner as in Example 1, except that the composition of the gas introduced in the reactive sputtering was changed to 99.6 mol % of argon gas and 0.4 mol % of oxygen gas. The transparent conductive layer of the laminated piezoelectric body was confirmed to be amorphous in the same manner as in Example 1.

[0108] Comparative Example 2 A laminated piezoelectric body was fabricated in the same manner as in Example 1, except that the composition of the gas introduced in the reactive sputtering was changed to 98.2 mol % of argon gas and 1.8 mol % of oxygen gas. The transparent conductive layer of the laminated piezoelectric body was confirmed to be amorphous in the same manner as in Example 1.

[0109] Comparative Example 3 A laminated piezoelectric body was fabricated in the same manner as in Example 1, except that the composition of the gas introduced in the reactive sputtering was changed to 99.0 mol % of argon gas, 0.8 mol % of oxygen gas, and 0.2 mol % of water. The transparent conductive layer of the laminated piezoelectric body was confirmed to be amorphous in the same manner as in Example 1.

[0110] Comparative Example 4 A laminated piezoelectric body was produced in the same manner as in Example 1, except that the metal target was changed to a solid solution of indium and tin with an Sn content of 10 mass %. The transparent conductive layer of the laminated piezoelectric body was confirmed to be amorphous in the same manner as in Example 1.

[0111] Comparative Example 5 A laminated piezoelectric body was produced in the same manner as in Example 1, except that the pressure inside the reactive sputtering chamber was changed to 1.0 Pa. The transparent conductive layer of the laminated piezoelectric body was confirmed to be amorphous in the same manner as in Example 1.

[0112] [Evaluation] (Thickness of Transparent Conductive Layer) The thickness of the transparent conductive layer was determined by observing the cross section of the laminated piezoelectric body using an electron microscope. Specifically, the obtained laminated piezoelectric body was embedded in epoxy resin to form an epoxy resin block. This epoxy resin block was cut so that the cross section of the laminated piezoelectric body was exposed. The exposed cross section of the laminated piezoelectric body was then observed using a scanning electron microscope (SU3800, manufactured by Hitachi High-Tech Corporation) at an acceleration voltage of 3.0 kV and a magnification of 50,000 times, and the thickness of the transparent conductive layer was measured.

[0113] (Total Light Transmittance) The total light transmittance of the laminated piezoelectric body was measured using a haze meter (for example, NDH7000SP II manufactured by Nippon Denshoku Industries Co., Ltd.) based on the method described in JIS K 7361-1:1997.

[0114] (Carrier Density, Hall Mobility, and Resistivity) The carrier density, Hall mobility, and resistivity of the transparent conductive layer were measured using a Hall effect measurement system (manufactured by Toyo Technica Co., Ltd., Resitest 8200) under the following conditions: applied magnetic field: 10 kGauss, applied current: 2×10 －４ A. Measurement temperature: Measurement was carried out at room temperature (295 K) based on the Van der Pauw method.

[0115] (Rate of change in resistivity) The obtained laminated piezoelectric body was kept for 250 hours in a thermostatic chamber (Econas LH34-14M, manufactured by Nagano Science Co., Ltd.) controlled to an atmosphere of 85°C and 85% RH. The surface resistivity (unit: Ω / sq.) of the transparent conductive layer of the laminated piezoelectric body was measured before being placed in the atmosphere (0 hour) and after being kept in the atmosphere for 250 hours. The surface resistivity was measured using a resistivity meter (Loresta GP MCP-T700, manufactured by Nitto Seiko Analytech Co., Ltd.) in accordance with JIS K7194:1994. The measurement was carried out three times in total, and the average value of the three measurements was used as the representative value. The surface resistivity (ρ Ｓ０ ) after being kept in the above atmosphere for 250 hours relative to the surface resistivity (ρ Ｓ２５０ ) ratio ρ Ｓ２５０ / ρ Ｓ０ The surface resistivity ρ Ｓ is the volume resistivity ρ Ｖ is divided by the transparent conductive layer t, and since the thickness of the transparent conductive layer does not change due to the above-mentioned holding, the surface resistivity ratio can be taken as the volume resistivity (resistivity) ratio. Here, the surface resistivity ratio is taken as the resistivity ratio.

[0116] Table 1 shows the film formation conditions and evaluation results for the laminated piezoelectric bodies of Examples 1 to 5 and Comparative Examples 1 to 5.

[0117]

[0118] As shown in Table 1, the laminated piezoelectric elements of Comparative Examples 1 to 3, in which the oxygen gas content and water content in the gas introduced during sputtering were outside the predetermined ranges, had a Hall mobility of 10 cm ２ In addition, in the laminated piezoelectric body of Comparative Example 4, in which the Sn content of the target was high, the Hall mobility was 10 cm２ It can be seen that the laminated piezoelectric element of Comparative Example 5, in which the pressure inside the chamber was high, had a relatively low resistivity but a large rate of change in resistivity under a high-temperature, high-humidity environment.

[0119] In contrast, the laminated piezoelectric elements of Examples 1 to 5, in which the Sn content, the composition of the atmosphere during sputtering, and the total pressure were set within predetermined ranges, had a Hall mobility of 10 cm ２ / (V・s) or more 20cm ２ / (V s) or less, and the carrier density is 1.0 × 10 ２１ cm －３ Above 3.0 x 10 ２１ cm －３ It can be seen that the resistivity is low and the rate of change in resistivity is also low while having high transparency.

[0120] These findings indicate that the Hall mobility and carrier density can be adjusted to appropriate ranges by adjusting the Sn content, the composition of the gas introduced during sputtering, and the pressure in the chamber within predetermined ranges, and that a laminated piezoelectric element having such a transparent conductive layer has high transparency, low resistivity, and a low rate of change in resistivity.

[0121] This application claims priority from Japanese Patent Application No. 2024-039963, filed March 14, 2024. The contents of the specification and drawings of that application are incorporated herein by reference in their entirety.

[0122] According to the present invention, it is possible to provide a laminated piezoelectric material that has excellent transparency, conductivity, and stability under high-temperature and high-humidity environments even when it has an amorphous transparent conductive layer, and therefore the laminated piezoelectric material can be suitably used as a piezoelectric sensor for a touch panel.

[0123] REFERENCE SIGNS LIST 10 laminated piezoelectric body 11 polymer piezoelectric film 12 hard coat layer 13 optical adjustment layer 14 transparent conductive layer

Claims

1. A laminated piezoelectric element comprising: a polymeric piezoelectric film; and a transparent conductive layer, disposed on at least one surface of the polymeric piezoelectric film, containing an indium-tin composite oxide as a main component, wherein the content of tin atoms in the transparent conductive layer relative to the total amount of indium and tin atoms is 1% by mass or more and 6% by mass or less, and the hole mobility of the transparent conductive layer is 10 cm ２ / (V・s) or more 20cm ２ / (V s) or less, and the carrier density is 1.0 × 10 ２１ cm －３ Above 3.0 x 10 ２１ cm －３ The laminated piezoelectric element is as follows:

2. The laminated piezoelectric element according to claim 1, wherein the transparent conductive layer has an inter-terminal resistance of 10 kΩ or more at an inter-terminal distance of 5 mm after immersion in a 5 mass % aqueous oxalic acid solution for 30 minutes.

3. The laminated piezoelectric element according to claim 1 or 2, wherein the polymeric piezoelectric film contains a vinylidene fluoride resin as a main component.

4. The laminated piezoelectric element according to any one of claims 1 to 3, wherein the transparent conductive layer has a thickness of 20 nm or more and 40 nm or less.

5. The laminated piezoelectric element according to any one of claims 1 to 4, further comprising at least one of a hard coat layer and an optical adjustment layer disposed between the polymer piezoelectric film and the transparent conductive layer.

6. A method for manufacturing a laminated piezoelectric element according to any one of claims 1 to 5, comprising the steps of: preparing a polymeric piezoelectric film; and forming the transparent conductive layer on at least one surface of the polymeric piezoelectric film by a sputtering method, wherein the sputtering is carried out under a pressure of 0.30 Pa or more and 0.90 Pa or less, and at a temperature of the polymeric piezoelectric film of 0°C or more and 80°C or less.

7. The method for manufacturing a laminated piezoelectric element according to claim 6, wherein the sputtering is carried out in an introduced gas containing argon gas and oxygen gas, and the content of oxygen gas in the introduced gas is 0.7 mol % or more but less than 1.8 mol %, and the content of water is 0.05 mol % or less.

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