Bending sensor, bending detection device, and method for manufacturing bending sensor

Abstract

To provide a bend sensor with which it is possible to detect a bend stably, a bend detection device, and a method for manufacturing the bend sensor.SOLUTION: The bend sensor is used to detect a bend, and comprises: a flexible substrate which is deformable by bending; a thin-film transistor layer which is located on the substrate and includes a thin-film transistor; a pixel electrode which is located on the thin-film transistor layer; a piezoelectric layer which is located on the pixel electrode and includes a piezoelectric substance; a counter electrode which is located on the piezoelectric layer and faces the pixel electrode via the piezoelectric layer; and an insulating layer which is located between the pixel electrode and the piezoelectric layer and is joined to the pixel electrode and the piezoelectric layer.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a bending sensor, a bending detection device, and a method for manufacturing a bending sensor. [Background technology]

[0002] Known technologies relating to bending sensors include those described in Patent Documents 1 and 2. For example, Patent Document 2 discloses a bending sensor provided in an organic EL display device. The bending sensor described in Patent Document 2 has a configuration in which a piezoelectric layer is sandwiched between two electrode layers. This bending sensor outputs a signal indicating a change in voltage generated between the two electrode layers in response to bending. Based on this signal, it is possible to determine the state of bending applied to the bending sensor. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 4-233442 [Patent Document 2] Japanese Patent Application Publication No. 2017-207886 Summary of the Invention [Problem to be solved by the invention]

[0004] However, piezoelectric layers typically undergo orientation processes such as poling (applying an AC voltage with gradually increasing amplitude) after fabrication, and are therefore incorporated into bending sensors after fabrication and poling. Therefore, the connection between the piezoelectric layer and the underlying electrode layer becomes an issue. In a configuration where the piezoelectric layer is simply sandwiched between two electrode layers without being bonded, the position of the electrode layer relative to the piezoelectric layer is likely to be unstable, resulting in insufficient contact between the piezoelectric layer and the electrode layer. In this case, the signal output from the bending sensor is likely to be unstable, making it difficult to stably detect the bending applied to the bending sensor.

[0005] The present invention provides a bending sensor, a bending detection device, and a method for manufacturing a bending sensor that can stably detect bending. [Means for solving the problem]

[0006] A bending sensor according to one aspect of the present invention is a bending sensor for detecting bending, and includes: a flexible substrate that can be deformed by bending; a thin-film transistor layer disposed on the substrate and including a thin-film transistor; a pixel electrode disposed on the thin-film transistor layer; a piezoelectric layer disposed on the pixel electrode and including a piezoelectric; a counter electrode disposed on the piezoelectric layer and facing the pixel electrode via the piezoelectric layer; and an insulating layer disposed between the pixel electrode and the piezoelectric layer and bonded to the pixel electrode and the piezoelectric layer.

[0007] In the bending sensor described above, an insulating layer is disposed between the pixel electrode and the piezoelectric layer, and the insulating layer is bonded to the pixel electrode and the piezoelectric layer. In this case, the position of the pixel electrode relative to the piezoelectric layer is more stable than when the piezoelectric layer is in direct contact with the pixel electrode. Here, the insulating layer functions as a capacitor connecting the pixel electrode and the piezoelectric layer. Therefore, a voltage generated in the piezoelectric layer in response to bending is applied to the pixel electrode via the insulating layer and detected as a signal indicating the bending state. Therefore, in the bending sensor described above, a signal indicating the bending state can be extracted while the position of the pixel electrode relative to the piezoelectric layer is stabilized. In this case, the signal output from the bending sensor can be stabilized, making it possible to stably detect bending based on the signal. Furthermore, the presence of the insulating layer between the pixel electrode and the piezoelectric layer increases the mechanical strength of the bending sensor while ensuring electrical insulation between the pixel electrode and other electrodes.

[0008] The insulating layer may be a single adhesive layer. In this case, the thickness of the insulating layer can be made thinner than when the insulating layer is a laminate. The thinner the insulating layer, the greater the capacitance of the capacitor using the insulating layer as a dielectric, making it possible to suppress an increase in the attenuation rate of the signal output from the bending sensor. As a result, bending can be detected more stably.

[0009] The insulating layer may be a laminate in which a first adhesive layer, a base material, and a second adhesive layer are laminated in this order. When a base material is interposed in the insulating layer in this way, the variation in the overall thickness of the insulating layer can be reduced compared to when the insulating layer is composed of only an adhesive layer.

[0010] The substrate may be made of a polyester resin. In this case, the flexibility of the substrate can be improved, allowing the substrate to deform in response to bending. As a result, damage to the substrate caused by bending the bending sensor can be suppressed.

[0011] The adhesive layer constituting the insulating layer may be made of an acrylic resin, a polyurethane resin, or a polyester resin. The improved flexibility of the adhesive layer allows the adhesive layer to deform in response to bending. As a result, damage to the adhesive layer caused by bending the bending sensor can be suppressed.

[0012] The thickness of the insulating layer between the pixel electrode and the piezoelectric layer may be equal to or less than the thickness of the piezoelectric layer. In this case, the capacitance of the capacitor, which uses the insulating layer as a dielectric, can be prevented from decreasing, thereby preventing an increase in the attenuation rate of the signal output from the bending sensor. As a result, bending can be detected more stably.

[0013] The capacitance of the insulating layer between the pixel electrode and the piezoelectric layer may be greater than the capacitance of the piezoelectric layer between the counter electrode and the insulating layer. Increasing the absolute value of the capacitance of the insulating layer in this way can reduce the effect of capacitance variation on the absolute value. Suppressing the variation in capacitance of the insulating layer can suppress variation in the attenuation rate of the signal output from the bending sensor. As a result, bending can be detected more stably.

[0014] The bending sensor may further include an electrically insulating cover sheet disposed on the counter electrode. In this case, the electrically insulating cover sheet can ensure electrical insulation between the counter electrode and other electrodes. Furthermore, by disposing the cover sheet on the counter electrode, it is possible to prevent scratches and the like from occurring on the counter electrode.

[0015] The bending sensor may further include an electrically insulating sealant arranged to surround the side surfaces of the laminate of the counter electrode, the piezoelectric layer, and the insulating layer. In this case, the electrically insulating cover sheet and sealant ensure electrical insulation between the electrodes constituting the bending sensor and other electrodes. Furthermore, by protecting the laminate with the cover sheet and sealant, the occurrence of scratches on the laminate can be suppressed.

[0016] The cover sheet may be provided so as to cover from the surface of the counter electrode to the side surface of the laminate of the counter electrode, the piezoelectric layer, and the insulating layer. In this case, the laminate can be protected with a simple structure in which the laminate is covered only with the cover sheet without using a sealing material.

[0017] A bending detection device according to another aspect of the present invention includes any one of the bending sensors described above and a detection unit that detects a bending applied to the bending sensor, the thin film transistor outputs a signal indicative of a change in electrical characteristics between the pixel electrode and the counter electrode that occurs in response to bending, and the detection unit detects the signal as information indicative of the bending state. Because this bending detection device includes any one of the bending sensors described above, it is possible to stably detect bending, as described above.

[0018] A manufacturing method of a bending sensor according to yet another aspect of the present invention is a manufacturing method of a bending sensor for detecting bending, comprising the steps of forming a thin film transistor layer including a thin film transistor on a flexible substrate that can be deformed by bending, forming a pixel electrode on the thin film transistor layer, forming a piezoelectric layer including a piezoelectric on the pixel electrode, and forming a counter electrode on the piezoelectric layer so as to face the pixel electrode via the piezoelectric layer, and in the step of forming the piezoelectric layer on the pixel electrode, the piezoelectric layer is joined to the pixel electrode via an insulating layer.

[0019] In the bending sensor manufacturing method described above, the piezoelectric layer is bonded to the pixel electrode and the surface of the thin-film transistor layer between the pixel electrodes via an insulating layer. In this case, the position of the pixel electrode relative to the piezoelectric layer is more stable than when the piezoelectric layer is simply in contact with the pixel electrode. Here, the insulating layer functions as a capacitor connecting the pixel electrode and the piezoelectric layer. Therefore, a voltage generated in the piezoelectric layer in response to bending is applied to the pixel electrode via the insulating layer and detected as a signal indicating the bending state. Therefore, according to the bending sensor manufacturing method described above, it is possible to extract a signal indicating the bending state while stabilizing the position of the pixel electrode relative to the piezoelectric layer. In this case, the signal output from the bending sensor can be stabilized, enabling stable bending detection based on the signal. Furthermore, the presence of an insulating layer between the pixel electrode and the piezoelectric layer enhances the mechanical strength of the bending sensor while ensuring electrical insulation between the pixel electrode and other electrodes.

[0020] In the process of forming the piezoelectric layer on the pixel electrode, a sheet-like adhesive may be prepared as an insulating layer, and after bonding the insulating layer to the piezoelectric layer, the piezoelectric layer may be bonded to the pixel electrode via the insulating layer. In this case, after bonding the insulating layer to the piezoelectric layer, the insulating layer and the piezoelectric layer can be cut to the required shape, so there is no need to prepare an insulating layer that precisely matches the shape of the piezoelectric layer in advance. This makes it possible to easily manufacture a bending sensor.

[0021] The method for manufacturing the bending sensor may further include a step of forming an electrically insulating cover sheet on the counter electrode. In this case, the electrically insulating cover sheet can ensure electrical insulation between the counter electrode and other electrodes. Furthermore, by disposing the cover sheet on the counter electrode, it is possible to prevent scratches and the like from occurring on the counter electrode. [Effects of the Invention]

[0022] According to the present invention, it is possible to stably detect bending. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 1 is a plan view showing an example of a bending sensor included in a bending detection device according to an embodiment. [Figure 2] FIG. 2 is a cross-sectional view of the bending sensor taken along line II-II in FIG. [Figure 3] Fig. 3(a) is a cross-sectional view showing the bending sensor of Fig. 2 bent into a convex shape, and Fig. 3(b) is a cross-sectional view showing the bending sensor of Fig. 2 bent into a concave shape. [Figure 4] Fig. 4(a) is a circuit diagram showing the connection relationship between the piezoelectric layer and the insulating layer in the bending sensor of Fig. 2. Fig. 4(b) is an equivalent circuit diagram of the circuit shown in Fig. 4(a). [Figure 5] FIG. 5 is a cross-sectional view showing an example of the configuration of a group of thin film transistors for one pixel included in the thin film transistor layer of FIG. [Figure 6] FIG. 6 is a plan view showing the configuration of the thin film transistor group of FIG. [Figure 7] FIG. 7 is a circuit diagram of a thin film transistor array configured by the thin film transistor group of FIG. [Figure 8] FIG. 8 is a cross-sectional view showing another example of the configuration of a group of thin film transistors for one pixel included in the thin film transistor layer of FIG. [Figure 9] FIG. 9 is a plan view showing the configuration of the thin film transistor group of FIG. [Figure 10]FIG. 10 is a circuit diagram of a thin film transistor array configured by the thin film transistor group of FIG. [Figure 11] FIG. 11 is a diagram illustrating an example of a bending detection device according to an embodiment. [Figure 12] FIG. 12 is a diagram illustrating an example of the configuration of a detection unit included in a bending detection device according to an embodiment. [Figure 13] FIG. 13 is a diagram illustrating another example of the configuration of the detection unit included in the bending detection device according to an embodiment. [Figure 14] 14(a), 14(b), and 14(c) are cross-sectional views showing an example of a manufacturing process for the bending sensor of FIG. [Figure 15] 15(a) and 15(b) are cross-sectional views showing a manufacturing step subsequent to the manufacturing step of FIG. [Figure 16] 16(a) and 16(b) are cross-sectional views showing another example of the manufacturing process of the bending sensor of FIG. [Figure 17] FIG. 17 is a cross-sectional view showing a bending sensor according to the first modification. [Figure 18] FIG. 18 is a cross-sectional view showing a bending sensor according to the second modification. [Figure 19] FIG. 19 is a cross-sectional view showing a bending sensor according to the third modification. DETAILED DESCRIPTION OF THE INVENTION

[0024] A bending sensor, a bending detection device, and a method for manufacturing a bending sensor according to embodiments of the present invention will be described in detail below with reference to the drawings. In the following description, the same or equivalent elements will be designated by the same reference numerals, and duplicated descriptions will be omitted as appropriate. The dimensions and dimensional ratios in the drawings do not necessarily correspond to the actual dimensions and dimensional ratios.

[0025] FIG. 1 is a plan view showing a bending sensor 10 according to this embodiment. FIG. 2 is a cross-sectional view of the bending sensor 10 taken along line II-II in FIG. 1. The bending sensor 10 detects bending applied to the bending sensor 10. The bending sensor 10, together with a detection unit 5 described below, constitutes a bending detection device 1 (see FIG. 11). The bending sensor 10 is a sensor array in which a plurality of sensors 11 are arranged in a matrix (two-dimensionally). The plurality of sensors 11 that constitute the bending sensor 10 are arranged one for each pixel.

[0026] In this specification, the term "pixel" refers to a detection point corresponding to the intersection of scanning wiring 61 and signal wiring 62 (see FIG. 7), which will be described later. In this embodiment, a case will be described in which a plurality of pixels are arranged in N rows and M columns (M and N are integers of 2 or more) in the plan view of FIG. 1. The plurality of pixels can be divided into a plurality of pixel regions RP arranged in N rows and M columns. FIG. 1 shows the boundary line BL between adjacent pixels (i.e., the boundary line of each pixel region RP). However, the boundary line BL is a virtual line indicating the boundary between each pixel, and is not a line indicating the boundary of an actually existing component.

[0027] As shown in FIG. 2, the bending sensor 10 includes an insulating substrate 15 (substrate), a thin-film transistor layer 20, a plurality of pixel electrodes 25, an insulating layer 30, a piezoelectric layer 35, and a counter electrode 40. The insulating substrate 15 is a substrate made of an insulating material. The insulating substrate 15 has flexibility that allows it to deform in response to bending applied to the bending sensor 10. The insulating substrate 15 is, for example, a film made of an organic insulating material. Examples of materials for the insulating substrate 15 include polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), polyimide (PI), polyamide (PA), polyamideimide (PAI), polyetherimide (PEI), and polyethersulfone (PES).

[0028] As shown in FIG. 2, a thin-film transistor layer 20, a plurality of pixel electrodes 25, an insulating layer 30, a piezoelectric layer 35, and a counter electrode 40 are stacked in this order on the surface 15a of the insulating substrate 15. Hereinafter, the X-direction will be taken as the direction along the surface 15a of the insulating substrate 15, the Y-direction will be taken as the direction along the surface 15a and perpendicular to the X-direction, and the Z-direction will be taken as the direction perpendicular to the surface 15a (i.e., the thickness direction of the insulating substrate 15). In this embodiment, the view from the Z-direction will be referred to as a "planar view," and the insulating substrate 15 side in the Z-direction will be referred to as the "bottom," and the counter electrode 40 side, which is the opposite side, will be referred to as the "top." When describing the height of a certain configuration, the height of the back surface 15b of the insulating substrate 15 will be used as a reference.

[0029] The thin-film transistor layer 20 is disposed on the surface 15a of the insulating substrate 15. While FIG. 2 refers to the thin-film transistor layer 20 for simplicity, the thin-film transistor layer 20 actually comprises multiple layers (see FIGS. 5 and 8). The thin-film transistor layer 20 includes multiple thin-film transistor groups 24 (see FIG. 7) arranged in a matrix. The thin-film transistor group 24 is a collection of multiple thin-film transistors (TFTs: Thin Film Transistors). The thin-film transistors may be, for example, organic thin-film transistors (organic semiconductors) or oxide thin-film transistors (oxide semiconductors). The multiple thin-film transistor groups 24 are disposed, for example, one for each pixel. Therefore, the multiple thin-film transistor groups 24 are arranged in N rows and M columns corresponding to the multiple pixels. For example, the multiple thin-film transistor groups 24 are arranged along the X and Y directions. The multiple thin-film transistor groups 24 arranged in a matrix may also be referred to as a thin-film transistor array.

[0030] A plurality of pixel electrodes 25 are arranged on the surface 20a of the thin film transistor layer 20. Each pixel electrode 25 is, for example, a rectangular electrode in a planar view. The material of each pixel electrode 25 may be, for example, a metal such as molybdenum (Mo), aluminum (Al), or silver (Ag), an alloy containing these metals, or a mixture containing metal particles (e.g., a sintered body). Typically, one pixel electrode 25 is arranged for each pixel. Like each thin film transistor group 24, the pixel electrodes 25 are arranged in N rows and M columns corresponding to each pixel. For example, the pixel electrodes 25 are arranged along the X and Y directions and are arranged so as to overlap with each thin film transistor group 24 in a planar view. The pixel electrodes 25 are arranged so as to be spaced apart from each other in the X and Y directions. The state in which the pixel electrodes 25 are spaced apart from each other means that the pixel electrodes 25 are physically spaced apart from each other so as to ensure electrical insulation between the pixel electrodes 25.

[0031] The piezoelectric layer 35 is disposed on the surfaces 25a of the pixel electrodes 25 via the insulating layer 30. The back surface 35b of the piezoelectric layer 35 is spaced apart from the surfaces 25a of the pixel electrodes 25. The piezoelectric layer 35 is a layer made of a piezoelectric material. Examples of materials for the piezoelectric layer 35 include polyvinylidene difluoride (PVDF), poly(vinylidene difluoride-trifluoroethylene) copolymer (P(VDF-TrFE)), and polylactic acid. When stress is applied due to bending of the bending sensor 10, the piezoelectric layer 35 generates a voltage corresponding to the stress due to the piezoelectric effect, in which polarization occurs in the piezoelectric material.

[0032] The counter electrode 40 is disposed on the surface 30a of the piezoelectric layer 35. The back surface 40b of the counter electrode 40 is bonded to the surface 30a of the piezoelectric layer 35. The surface 40a of the counter electrode 40 faces away from the piezoelectric layer 35. The counter electrode 40 faces the pixel electrodes 25 in the Z direction via the piezoelectric layer 35 and the insulating layer 30. The counter electrode 40 is a common electrode arranged to overlap all of the pixel electrodes 25 in a planar view. The counter electrode 40 has, for example, a rectangular shape that encompasses all of the pixel electrodes 25 in a planar view. The counter electrode 40 may be made of a metal such as molybdenum (Mo), aluminum (Al), or silver (Ag), an alloy containing these metals, or a mixture containing metal particles (e.g., a sintered body). The counter electrode 40 is electrically connected to a counter electrode wiring 65 (see FIG. 14(c)), which will be described later. The counter electrode wiring 65 is an electrode wiring arranged on the surface 20a of the thin film transistor layer 20 together with the plurality of pixel electrodes 25. An arbitrary constant voltage Vc is applied to the counter electrode 40 via the counter electrode wiring 65. A ground (GND) potential may be applied to the counter electrode 40.

[0033] The insulating layer 30 is disposed between the piezoelectric layer 35 and the thin-film transistor layer 20. Specifically, the insulating layer 30 is disposed on the surface 20a of the thin-film transistor layer 20 so as to cover all of the pixel electrodes 25. Therefore, the pixel electrodes 25 are spaced apart in the X and Y directions via the insulating layer 30. The insulating layer 30 ensures electrical insulation between the pixel electrodes 25. In other words, the insulating layer 30 electrically insulates the pixel electrodes 25 from one another and from other electrodes. The back surface 30b of the insulating layer 30 is bonded to the surface 20a of the thin-film transistor layer 20 and the surface 25a of each pixel electrode 25. The back surface 30b may also be bonded to the side surface 25c of each pixel electrode 25. The front surface 30a of the insulating layer 30 is bonded to the back surface 35b of the piezoelectric layer 35.

[0034] The insulating layer 30 is, for example, a single-layer adhesive layer having electrical insulation properties. Therefore, in addition to its electrical insulation function, the insulating layer 30 also functions to bond the piezoelectric layer 35 and the plurality of pixel electrodes 25. Therefore, the surface 30a of the insulating layer 30 is bonded to the back surface 35b of the piezoelectric layer 35. The back surface 30b of the insulating layer 30 is bonded to the surface 20a of the thin-film transistor layer 20 and the surface 25a of each pixel electrode 25. The back surface 30b may also be bonded to the side surface 25c of each pixel electrode 25. In this embodiment, the state in which the insulating layer 30 is bonded to a certain structure refers to a state in which the relative position between the insulating layer 30 and the certain structure is fixed (maintained). As long as the relative position between the insulating layer 30 and the certain structure is fixed, the method of bonding the insulating layer 30 to the certain structure is not limited to adhesion, and other methods may also be used. Therefore, the term "bonding" as used herein includes adhesion of the insulating layer 30 to a certain structure, fusion bonding of the insulating layer 30 to a certain structure, room temperature bonding of the insulating layer 30 to a certain structure, and the like.

[0035] The insulating layer 30 is, for example, an electrically insulating adhesive. The insulating layer 30 may also be a pressure-sensitive adhesive. The insulating layer 30 may be, for example, a liquid adhesive that has been applied and cured, or a sheet-like adhesive such as a hot-melt adhesive or double-sided tape. Examples of materials for the insulating layer 30 include acrylic resins, urethane resins, polyester resins, and synthetic resins thereof. These materials are deformable in response to bending. An insulating layer 30 made of such a flexible material is suitable for use in a bending sensor 10 that is subjected to bending. The adhesive that constitutes the insulating layer 30 has high adhesive strength to prevent peeling of the insulating layer 30 from the piezoelectric layer 35 and each pixel electrode 25 when bending is applied to the bending sensor 10.

[0036] The thickness T30 of the insulating layer 30 between the pixel electrode 25 and the piezoelectric layer 35 is desirably equal to or less than the thickness T35 of the piezoelectric layer 35, for example. The thickness T30 of the insulating layer 30 is the distance in the Z direction from the surface 25a of the pixel electrode 25 to the back surface 35b of the piezoelectric layer 35. The thickness T35 of the piezoelectric layer 35 is the distance in the Z direction from the surface 35a to the back surface 35b of the piezoelectric layer 35. The thickness T30 of the insulating layer 30 may be equal to or greater than the thickness T25 of the pixel electrode 25. The thickness T25 of the pixel electrode 25 is the distance in the Z direction from the surface 25a to the back surface 25b of the pixel electrode 25.

[0037] The insulating layer 30 functions as a capacitor connecting the pixel electrode 25 and the piezoelectric layer 35. The capacitance Ci of a capacitor using the insulating layer 30 as a dielectric increases as the thickness T30 of the insulating layer 30 decreases, and decreases as the thickness T30 of the insulating layer 30 increases. By setting the thickness T30 of the insulating layer 30 to be thin, the capacitance Ci can be increased. The thickness T30 of the insulating layer 30 is set, for example, so that the capacitance Ci is larger than the capacitance Cp of a capacitor using the piezoelectric layer 35 as a dielectric. For example, the thickness T30 of the insulating layer 30 may be set to 60 μm or less. On the other hand, by setting the thickness T30 of the insulating layer 30 to be thick, the mechanical strength of the insulating layer 30 can be ensured. For example, the thickness T30 of the insulating layer 30 may be set to be 1 μm or more.

[0038] As shown in Fig. 2, the piezoelectric layer 35 is positioned at a position different from the neutral plane NP so that stress is applied when the bending sensor 10 is bent. The neutral plane NP is a plane to which no tensile or compressive stress is applied when the bending sensor 10 is bent. In the cross section shown in Fig. 2, the neutral plane NP can be shown as an imaginary plane along the XY plane. The neutral plane NP is located in any of the layers constituting the bending sensor 10 (i.e., the insulating substrate 15, the thin-film transistor layer 20, the pixel electrode 25, the insulating layer 30, the piezoelectric layer 35, and the counter electrode 40).

[0039] The position of the neutral plane NP in the Z direction can be expressed by the height λ from the rear surface 15b of the insulating substrate 15. The height λ of the neutral plane NP depends on the Young's modulus and thickness of each layer that makes up the bending sensor 10. When the bending sensor 10 is composed of N layers (N is a natural number), with the lowest layer being the first layer, the Young's modulus of the ith layer (i is a natural number equal to or less than N) is Ei, the thickness of the ith layer is Ti, and the height of the center of the ith layer from the lowest layer is Yi, the height λ of the neutral plane NP is generally expressed by the following formula (1):

number

[0040] As described above, the height λ of the neutral plane NP varies depending on the Young's modulus and thickness of each layer of the bending sensor 10, and can be adjusted by adjusting the Young's modulus and thickness of each layer. The height λ of the neutral plane NP is, for example, located lower than the rear surface 30b of the piezoelectric layer 35. In the example shown in FIG. 2, the height λ of the neutral plane NP is located at the height of the rear surface 25b of the pixel electrode 25 (i.e., the height of the front surface 20a of the thin-film transistor layer 20). Therefore, the piezoelectric layer 35 is located higher than the height λ of the neutral plane NP. (However, if the Young's modulus and film thickness of each layer are different, the height λ of the neutral plane NP is not necessarily the height of the rear surface 25b of the pixel electrode 25, and may be higher or lower than the rear surface 25b. For example, the height λ of the neutral plane NP may be the internal height of one of the layers.)

[0041] FIG. 3A is a cross-sectional view showing the bending sensor 10 bent in a convex shape. In FIG. 3A, bending the bending sensor 10 in the X-direction causes the bending sensor 10 to bend convexly upward in the XZ cross section. In this embodiment, when the piezoelectric layer 35 is located above the neutral plane NP, bending the bending sensor 10 convexly as shown in FIG. 3A applies a tensile stress ST1 in the X-direction to the piezoelectric layer 35. If the distance from the neutral plane NP to the center of the piezoelectric layer 35 in the Z-direction is d, i.e., the height of the center of the piezoelectric layer 35 is λ+d, and the radius of curvature of the center of the piezoelectric layer 35 is R, ignoring shear deformation, the tensile stress ST1 applied to the piezoelectric layer 35 is expressed as d / R. Therefore, the tensile stress ST1 is inversely proportional to the radius of curvature R (i.e., proportional to the curvature).

[0042] The tensile stress ST1 generates an electric flux density in the thickness direction of the piezoelectric layer 35. As a result, a voltage Vp is generated between the front surface 35a and the rear surface 35b of the piezoelectric layer 35. The voltage Vp is the potential of the rear surface 35b relative to the front surface 35a. The voltage Vp can be expressed as charge q / capacitance Cp. The voltage Vp is proportional to the tensile stress ST1. If the voltage of the counter electrode 40 is Vc, since the counter electrode 40 is connected to the front surface 35a of the piezoelectric layer 35, the voltage of the front surface 35a is Vc. Meanwhile, the voltage of the rear surface 35b of the piezoelectric layer 35 is Vc+Vp, which is the sum of the voltage Vc of the counter electrode 40 and the voltage Vp of the piezoelectric layer 35. The voltage Vc+Vp of the rear surface 35b is applied to the pixel electrode 25 via a capacitor using the insulating layer 30 as a dielectric.

[0043] FIG. 3B is a cross-sectional view showing the bending sensor 10 bent concavely. In FIG. 3B, bending the bending sensor 10 in the X-direction causes the bending sensor 10 to bend concavely upward in the XZ cross section. In this embodiment, when the piezoelectric layer 35 is located above the neutral plane NP, bending the bending sensor 10 concavely as shown in FIG. 3B causes a compressive stress ST2 in the X-direction to be applied to the piezoelectric layer 35. If the distance from the neutral plane NP to the center of the piezoelectric layer 35 in the Z-direction is d, i.e., the height of the center of the piezoelectric layer 35 is λ+d, and the radius of curvature of the center of the piezoelectric layer 35 is R, ignoring shear deformation, the compressive stress ST2 applied to the piezoelectric layer 35 can be expressed as d / R. Therefore, the compressive stress ST2 is inversely proportional to the radius of curvature R (i.e., proportional to the curvature). Similarly to the tensile stress ST1 described above, the compressive stress ST2 applies a voltage Vc+Vp to the pixel electrode 25. However, the voltage Vc+Vp generated by the compressive stress ST2 is in the opposite direction to the voltage Vc+Vp generated by the tensile stress ST1.

[0044] The voltage Vc+Vp generated by the bending as described above is applied to the pixel electrode 25 via a capacitor using the insulating layer 30 as a dielectric. FIG. 4(a) is a circuit diagram showing the connection between the piezoelectric layer 35 and the insulating layer 30. FIG. 4(b) is an equivalent circuit diagram of the circuit shown in FIG. 4(a). As shown in FIG. 4(a), the capacitance Cp of the capacitor using the piezoelectric layer 35 between the front surface 35a and the back surface 35b as a dielectric is connected in series with the capacitance Ci of the capacitor using the insulating layer 30 between the back surface 35b and the front surface 25a as a dielectric. If the combined capacitance of the capacitances Cp and Ci is Cpi, the circuit shown in FIG. 4(a) can be expressed as the equivalent circuit shown in FIG. 4(b). The combined capacitance Cpi can be expressed as CpCi / (Cp+Ci).

[0045] When the capacitances Cp and Ci are connected in series, the composite capacitance Cpi is smaller than when only the capacitance Cp is present. However, because the leakage current of the capacitor formed by the piezoelectric layer 35 and the insulating layer 30 is small, the voltage applied to the pixel electrode 25 via the piezoelectric layer 35 and the insulating layer 30 is maintained at a constant value (Vc + Vp) for the short period of time required to detect bending, such as the few seconds required. In other words, even if the capacitance Ci is present, the voltage Vc + Vp is input to the pixel electrode 25, and the sensing operation of the bending sensor 10 is not hindered. However, after several minutes, the voltage Vp gradually decays and approaches zero due to the leakage current of the capacitor. This decay of the voltage Vp can occur even when the capacitance Ci is not present, but the decay rate of the voltage Vp (i.e., the signal corresponding to the voltage Vp) depends on the magnitude of the composite capacitance Cpi. Specifically, the signal decay rate increases as the composite capacitance Cpi decreases, and decreases as the composite capacitance Cpi increases.

[0046] Therefore, in this embodiment, in order to suppress the signal decay rate, the insulating layer 30 is thinned to increase the capacitance Ci in order to increase the composite capacitance Cpi. Furthermore, to suppress variations in the signal decay rate, the capacitance Ci is made larger than the capacitance Cp. By increasing the absolute value of the capacitance Ci in this way, the influence of variations in the capacitance Ci on the absolute value can be reduced, thereby suppressing variations in the signal decay rate. If the signal decay rates are uniform, correction can be made to compensate for the amount of signal decay, thereby enabling stable signal detection. The voltage Vc+Vp applied to the pixel electrode 25 in this manner is applied to the thin-film transistor group 24 of the thin-film transistor layer 20.

[0047] FIG. 5 is a cross-sectional view showing an example of the configuration of the thin-film transistor group 24 for one pixel included in the thin-film transistor layer 20 (portion A in FIG. 2). FIG. 6 is a plan view showing the configuration of the thin-film transistor group 24 of FIG. 5. As shown in FIGS. 5 and 6, the thin-film transistor layer 20 has the thin-film transistor group 24, a gate insulating film 50, and an interlayer insulating film 51. The thin-film transistor group 24 includes, for example, a pixel thin-film transistor 21 and a selection thin-film transistor 22. That is, the thin-film transistor group 24 includes two thin-film transistors 21 and 22 per pixel. The thin-film transistor 21 includes a gate electrode G1, a source electrode S1, a semiconductor layer SC1, and a drain electrode D1. The thin-film transistor 22 includes a gate electrode G2, a source electrode S2, a semiconductor layer SC2, and a drain electrode D2.

[0048] 5, gate electrode G1 and gate electrode G2 are disposed on the surface 15a of the insulating substrate 15 and are spaced apart from each other in the X direction. A gate insulating film 50 is disposed on the surface 15a of the insulating substrate 15 so as to cover the gate electrode G1 and gate electrode G2. The gate insulating film 50 electrically insulates the gate electrode G1 from the gate electrode G2 and the gate electrodes G1 and G2 from other electrodes. A source electrode S1, a drain electrode D1, a semiconductor layer SC1, a source electrode S2, a drain electrode D2, and a semiconductor layer SC2 are disposed on the gate insulating film 50. The source electrode S1, the drain electrode D1, and the semiconductor layer SC1 are disposed on the gate electrode G1 with the gate insulating film 50 interposed therebetween. The source electrode S2, the drain electrode D2, and the semiconductor layer SC2 are disposed on the gate electrode G2 with the gate insulating film 50 interposed therebetween.

[0049] The interlayer insulating film 51 is disposed on the gate insulating film 50 so as to cover the source electrode S1, the drain electrode D1, the semiconductor layer SC1, the source electrode S2, the drain electrode D2, and the semiconductor layer SC2. The pixel electrode 25 is disposed on the interlayer insulating film 51. The interlayer insulating film 51 electrically insulates the pixel electrode 25 from an electrode group including the source electrode S1, the drain electrode D1, the source electrode S2, and the drain electrode D2. The gate electrode G1 is electrically connected to the pixel electrode 25 through a via wiring 53 formed in the gate insulating film 50 and a via wiring 54 formed in the interlayer insulating film 51. The gate insulating film 50 has an opening at the position of the via wiring 53. The interlayer insulating film 51 has an opening at the position of the via wiring 54. The source electrode S1 is electrically connected to the drain electrode D2 through a connection wiring 55.

[0050] As shown in FIG. 6, the bending sensor 10 is provided with a drain wiring 60, a scanning wiring 61, and a signal wiring 62. The drain wiring 60 is a wiring connected to the drain electrode D1 and extending along the Y direction. The drain electrode D1 is electrically connected to a power source via the drain wiring 60. The scanning wiring 61 is a wiring connected to the gate electrode G2 and extending along the X direction. The signal wiring 62 is a wiring connected to the source electrode S2 and extending along the Y direction. The signal wiring 62 is arranged spaced apart from the drain wiring 60 in the X direction. In a plan view, the drain wiring 60 and the signal wiring 62 intersect (for example, perpendicular to) the scanning wiring 61.

[0051] FIG. 7 is a diagram showing the circuit configuration of a thin-film transistor array composed of a plurality of thin-film transistor groups 24. As shown in FIG. 7, the plurality of thin-film transistor groups 24 are arranged in a matrix of N rows and M columns. A plurality (e.g., N lines) of signal wirings 62 are arranged at intervals in the X direction. Each signal wiring 62 connects the source electrodes S2 of a plurality of thin-film transistor groups 24 arranged in a row in the Y direction. Each signal wiring 62 intersects (e.g., perpendicular to) each of the signal wirings 62, and a plurality (e.g., M lines) of scanning wirings 61 are arranged at intervals in the Y direction. Each scanning wiring 61 connects the gate electrodes G2 of a plurality of thin-film transistor groups 24 arranged in a row in the X direction.

[0052] When a tensile stress ST1 or a compressive stress ST2 is applied to the piezoelectric layer 35 by bending the bending sensor 10, the voltage Vc+Vp applied to the pixel electrode 25 is input to the thin-film transistor 21 connected to the pixel electrode 25. For simplicity's sake, focusing on one thin-film transistor group 24, the voltage Vc+Vp of the pixel electrode 25 is input to the gate electrode G1 of the thin-film transistor 21. Based on the voltage of the power supply connected to the drain wiring 60, the thin-film transistor 21 outputs a signal corresponding to the voltage Vc+Vp input to the gate electrode G1 from the drain electrode D1 to the source electrode S1. The signal output to the source electrode S1 is input to the drain electrode D2 of the thin-film transistor 22.

[0053] The thin-film transistor 22 controls whether or not a signal input to the drain electrode D2 is output to the signal wiring 62. A gate voltage that switches the thin-film transistor 22 on / off is applied from the scanning wiring 61 to the gate electrode G2 of the thin-film transistor 22. The thin-film transistor 22 functions as a switch that switches on / off between the drain electrode D2 and the source electrode S2 based on the gate voltage applied to the gate electrode G2. When a gate voltage (off voltage) that turns the thin-film transistor 22 off is applied from the scanning wiring 61 to the gate electrode G2, the signal input to the drain electrode D2 is not output to the signal wiring 62. On the other hand, when a gate voltage (on voltage) that turns the thin-film transistor 22 on is applied from the scanning wiring 61 to the gate electrode G2, the signal input to the drain electrode D2 is output from the source electrode S2 to the signal wiring 62.

[0054] The signal output to the signal wiring 62 is detected for each pixel by the detection unit 5 (see FIG. 11 ), which will be described later. The voltage indicated by the signal is proportional to the magnitude of the bending, and therefore the magnitude of the bending can be determined from the signal. The magnitude of the bending can provide bending information such as the presence or absence of bending, the amount of bending, and the direction of bending (i.e., whether the bending is upwardly convex or downwardly concave). In this embodiment, the signal provides the sum of the magnitude of bending in the X direction and the magnitude of bending in the Y direction. Bending in the X direction refers to bending when stress is applied in the X direction. More specifically, bending in the X direction refers to bending in a direction in which the bending sensor 10 is convex or concave in the Z direction in the XZ cross section. Bending in the Y direction refers to bending when stress is applied in the Y direction. More specifically, bending in the Y direction refers to bending in a direction in which the bending sensor 10 is convex or concave in the Z direction in the YZ cross section.

[0055] Fig. 8 is a cross-sectional view showing another example of the configuration of the thin film transistor group 24. Fig. 9 is a plan view showing the configuration of the thin film transistor group 24A of Fig. 8. As shown in Figs. 8 and 9, the thin film transistor layer 20A has a thin film transistor group 24A instead of the thin film transistor group 24. The thin film transistor group 24A includes a reset thin film transistor 23 in addition to a pixel thin film transistor 21 and a selection thin film transistor 22. The reset thin film transistor 23 includes a gate electrode G3, a source electrode S3, a semiconductor layer SC3, and a drain electrode D3.

[0056] 8, the gate electrode G3 is disposed on the surface 15a of the insulating substrate 15, and is spaced apart from the gate electrodes G1 and G2 in the X direction. The gate electrode G3, together with the gate electrodes G1 and G2, is covered by a gate insulating film 50 on the surface 15a of the insulating substrate 15. The source electrode S3, the semiconductor layer SC3, and the drain electrode D3 are disposed on the gate insulating film 50. The source electrode S3, the drain electrode D3, and the semiconductor layer SC3 are disposed on the gate electrode G3 with the gate insulating film 50 interposed therebetween. The source electrode S3, the drain electrode D3, and the semiconductor layer SC3 are covered by an interlayer insulating film 51.

[0057] The drain electrode D3 is connected to via wirings 53 and 54. The drain electrode D3 is electrically connected to the gate electrode G1 of the thin-film transistor 21 and the pixel electrode 25 through the via wirings 53 and 54. As shown in FIG. 9 , the thin-film transistor 23 is provided with a common wiring 63 and a reset wiring 64. The common wiring 63 is connected to the source electrode S3 and extends along the Y direction. The common wiring 63 is disposed on the opposite side of the drain wiring 60 from the signal wiring 62 in the X direction and spaced apart from the drain wiring 60. The common wiring 63 is set to the same potential as the counter electrode 40. The reset wiring 64 is connected to the gate electrode G3 and extends along the X direction. The reset wiring 64 is disposed, for example, parallel to the scanning wiring 61. The reset wiring 64 and the scanning wiring 61 intersect (for example, perpendicular to) the drain wiring 60, the signal wiring 62, and the common wiring 63 in a plan view. A gate voltage that switches the thin-film transistor 23 on / off is applied to the reset wiring 64.

[0058] FIG. 10 is a diagram showing the circuit configuration of a thin-film transistor array composed of a plurality of thin-film transistor groups 24A. The thin-film transistor 23 resets the voltage of the piezoelectric layer 35 to zero by shorting the pixel electrode 25 to the common wiring 63 (i.e., setting the pixel electrode 25 to the same potential as the counter electrode 40) before bending detection by the bending sensor 10. This enables the circuit shown in FIG. 10 to perform more precise detection than the circuit shown in FIG. 7. Note that the circuits shown in FIGS. 7 and 10 are merely examples of circuit configurations of thin-film transistor arrays, and other circuits may be used. In the circuits shown in FIGS. 7 and 10, the voltage of the piezoelectric layer 35 is applied to the gate electrode G1 of the thin-film transistor 21 in the thin-film transistor array integrated with the bending sensor 10 and the current is amplified, which has the advantage of reducing noise in the output signal.

[0059] [Bending detection device] Next, a bending detection device 1 equipped with the bending sensor 10 described above will be described. As shown in FIG. 11 , the bending detection device 1 includes the bending sensor 10 and a detection unit 5 for detecting signals from the bending sensor 10. The detection unit 5 distinguishes and detects each signal output from each thin film transistor group 24 to obtain bending information for each pixel based on the signals. The bending sensor 10 may include a cable 100. The cable 100 may include a power supply line connected to the drain wiring 60, a drive line connected to the scanning wiring 61, a signal line connected to the signal wiring 62, a reset line connected to the reset wiring 64, and a counter voltage line connected to the counter electrode 40 and the common wiring 63. In addition, a control circuit 80 (see FIG. 12 described later) included in the detection unit 5 may include a display unit and an external output terminal.

[0060] FIG. 12 is a diagram showing the configuration of the detection unit 5. As shown in FIG. 12, the detection unit 5 has a signal detection circuit 75, a control circuit 80, and a drive circuit 85. In the example shown in FIG. 12, M signal wirings 62 are divided into M2 blocks B (areas surrounded by dashed lines in FIG. 12) with M1 wirings in between. In other words, M1 signal wirings 62 are provided in one block B. M1 and M2 are each an integer of 2 or greater that satisfies the relationship M=M1×M2.

[0061] The signal detection circuit 75 is electrically connected to the M signal wirings 62 and detects signals output from the M signal wirings 62. The signal detection circuit 75 is configured to sequentially read out each signal row by row in order to distinguish and detect each signal output from each signal wiring 62. The signal detection circuit 75 includes, for example, M2 switching circuits 81, M2 counters 82, M2 load resistors 76, M2 amplifiers 77, one switching circuit 78, and one AD converter 79. The M2 switching circuits 81, the M2 load resistors 76, and the M2 amplifiers 77 are each divided into M2 blocks B. That is, each block B includes M1 signal wirings 62, as well as one switching circuit 81, one load resistor 76, and one amplifier 77.

[0062] M2 counters 82 are provided for each block B. That is, one counter 82 is provided for each block B. In each block B, the counter 82 is electrically connected to the switching circuit 81 and the control circuit 80. The counter 82 receives a control signal S82 from the control circuit 80 and outputs a control signal S81 to the switching circuit 81 for controlling switching of the connection destination of the switching circuit 81. When a counter 82 is used for each block B in this way, one digital wire is connected from the control circuit 80 to each counter 82 for each block B. In this case, there is no need to connect a large number of digital wires from the control circuit 80 to each counter 82, which is particularly effective when the number of digital outputs of the control circuit 80 is small.

[0063] The switching circuit 81 is, for example, an analog multiplexer including M1 input terminals and one output terminal. An analog multiplexer can perform high-speed switching without losing analog signal information. However, when it is difficult to use an analog multiplexer, such as when the signal voltage range is wide, a relay may be used instead of the analog multiplexer. The M1 input terminals of the switching circuit 81 are electrically connected to the M1 signal wirings 62 in the block B. The switching circuit 81 switches the connection destination of the output terminal to one of the M1 input terminals in response to a control signal S81 from the counter 82. In other words, the switching circuit 81 selects one of the M1 signal wirings 62 as the connection destination of the output terminal.

[0064] The amplifier 77 is, for example, a voltage detection amplifier. The amplifier 77 is, for example, a voltage follower circuit. The output terminal of the switching circuit 81 is connected to the positive input terminal of the amplifier 77. The negative input terminal of the amplifier 77 is connected to the output terminal of the amplifier 77. The amplifier 77 current-amplifies a signal input from the signal wiring 62 via the switching circuit 81. The load resistor 76 is disposed between the switching circuit 81 and the amplifier 77. One terminal of the load resistor 76 is connected to a connection line that connects the output terminal of the switching circuit 81 and one input terminal of the amplifier 77, and the other terminal of the load resistor 76 is connected to ground (GND).

[0065] The switching circuit 78 is, for example, an analog multiplexer including M2 input terminals and one output terminal. The M2 input terminals are connected to the output terminals of the amplifiers 77 of the M2 blocks B, respectively. The switching circuit 78 switches the connection destination of the output terminal to one of the M2 input terminals in response to a control signal S78 from the control circuit 80. In other words, the switching circuit 78 selects one of the M2 blocks B as the connection destination of the output terminal. The AD converter 79 is electrically connected to the output terminal of the switching circuit 78. Therefore, the AD converter 79 is electrically connected to one of the signal wirings 62 selected by the switching circuit 81 and the switching circuit 78. The AD converter 79 converts a signal output from one of the signal wirings 62 into a digital value and outputs the digital value to the control circuit 80.

[0066] The drive circuit 85 is electrically connected to the N scanning wirings 61. The drive circuit 85 receives a control signal S85 from the control circuit 80 and outputs a drive signal S61 to the scanning wirings 61, thereby applying an ON voltage to one of the N scanning wirings 61 and applying an OFF voltage to all the other scanning wirings 61. The control circuit 80 is electrically connected to the signal detection circuit 75 and the drive circuit 85, and controls the signal detection circuit 75 and the drive circuit 85. The control circuit 80 is configured by, for example, a computer (for example, a microcomputer) including a processor such as a CPU and a storage device such as a memory.

[0067] The control circuit 80 outputs a control signal S82 to the signal detection circuit 75, which switches the connection destination of the switching circuit 81 to one of the signal lines 62. The control circuit 80 also outputs a control signal S78 to the switching circuit 78, which switches the connection destination of the switching circuit 78 to one of the blocks B. Then, the control circuit 80 outputs a control signal S85 to the drive circuit 85, which applies an on-voltage to one of the scanning lines 61 and an off-voltage to all the other scanning lines 61.

[0068] As a result, an on-voltage is applied only to the scanning wiring 61 of one row, and signals are output to the signal wiring 62 connected to each of the M thin film transistor groups 24 arranged in that row. The signal output from the thin film transistor 21 of one pixel is then input to the AD converter 79 via the switching circuit 81, the switching circuit 78, etc., and read out to the control circuit 80. In this way, bending information for one pixel is obtained. Next, with the on-voltage applied only to the scanning wiring 61 of one row, the control circuit 80 switches the connection destination of the switching circuit 81 and the connection destination of the switching circuit 78 so that signals are sequentially read out from each signal wiring 62 of one row. In this way, bending information for one row is obtained.

[0069] Next, the control circuit 80 outputs a control signal S85 to the drive circuit 85, causing it to apply an ON voltage to the scan lines 61 in the next row and an OFF voltage to all other scan lines 61. In this state, the control circuit 80 sequentially reads out signals from each signal line 62 by switching the connection destination of the switching circuit 81 and the connection destination of the switching circuit 78, as described above. This allows bending information for the next row to be obtained. The control circuit 80 repeats the above operation, sequentially switching the scan lines 61 to which the ON voltage is applied, and sequentially reads out signals from each row. This allows bending information to be sequentially obtained for each row. When the signals for all rows have been read out, bending information for all pixels, i.e., bending information for each pixel for one screen, is obtained. Furthermore, by repeating the above operation, bending information for each pixel for multiple screens, i.e., time-dependent bending information for all pixels, is obtained.

[0070] FIG. 13 is a diagram showing another example of the detection unit 5. In the detection unit 5A shown in FIG. 13, the signal detection circuit 75A does not include a switching circuit 81. In this case, the M signal wirings 62 are not divided into blocks B, so M load resistors 76 and M amplifiers 77 are required corresponding to the M signal wirings 62. The switching circuit 78 may be, for example, an analog switch. Even with this configuration, signals can be sequentially read out row by row, as in the detection unit 5 shown in FIG. 12, thereby obtaining bending information for each pixel. While a configuration using the same number of AD converters 79 as the number of signal wirings 62 without using the switching circuit 78 is also possible, a configuration using the switching circuit 78 requires fewer AD converters 79 than the number of signal wirings 62. Furthermore, as shown in FIGS. 7 and 10, by arranging multiple thin-film transistor groups in a matrix, where each intersection of each scanning wiring 61 and each signal wiring 62 is defined as one pixel, it is possible to obtain multi-point information at high speed while reducing the number of wirings.

[0071] [Manufacturing method of bending sensor] Next, a method for manufacturing the bending sensor 10 will be described. FIGS. 14(a) to 14(c), 15(a), and 15(b) are cross-sectional views showing an example of the manufacturing process for the bending sensor 10. First, as shown in FIG. 14(a), an insulating substrate 15 is prepared. As described above, an organic insulating film such as polyethylene terephthalate (PET) can be used as the insulating substrate 15. The organic insulating film can be formed by attaching it to a glass plate or by applying it to a glass plate and baking it. The glass plate may be peeled off at any time during the manufacturing process for the bending sensor 10.

[0072] Next, as shown in FIG. 14(b), a thin-film transistor layer 20 is formed on the surface 15a of the insulating substrate 15. The thin-film transistor layer 20 is composed of a combination of a silicon semiconductor, an organic semiconductor, or an oxide semiconductor, an organic insulating film or an inorganic insulating film, and a metal electrode or an oxide electrode. The thin-film transistor layer 20 preferably includes an organic insulating film to make it less likely to break even when bent. For example, chemical vapor deposition (CVD), coating and baking, and sputtering can be used to form a silicon semiconductor film. For organic semiconductor film, coating and baking, vapor deposition, and printing can be used. For oxide semiconductor film, CVD, coating and baking, and sputtering can be used, and photolithography and etching can be used for patterning.

[0073] Acrylic resins or epoxy resins can be used as organic insulating films. Coating and baking can be used to form organic insulating films. If the organic insulating film material is photosensitive, it can be patterned simply by exposure and development. Silicon dioxide (SiO2), silicon nitride (SiN), silicon oxynitride (SiON), etc. can be used as inorganic insulating films. CVD, sputtering, and vapor deposition can be used to form inorganic insulating films, and photolithography and etching can be used to pattern them. Metal electrodes can be made of metals such as molybdenum (Mo), aluminum (Al), or silver (Ag), or alloys containing these. Sputtering and vapor deposition can be used to form metal electrodes. Indium tin oxide (ITO) can be used as oxide electrodes. Sputtering can be used to form oxide electrodes, and photolithography and etching can be used to pattern them.

[0074] Next, as shown in FIG. 14(c), multiple pixel electrodes 25 are formed on the surface 20a of the thin-film transistor layer 20. Each pixel electrode 25 can be made of a metal such as molybdenum (Mo), aluminum (Al), or silver (Ag), or an alloy containing these metals, or a mixture containing metal particles. Chemical vapor deposition (CVD), sputtering, and vapor deposition can be used to form each pixel electrode 25, and photolithography and etching can be used to pattern each pixel electrode 25. Alternatively, each pixel electrode 25 can be formed by printing and baking an ink containing metal particles or a metal compound. In the process shown in FIG. 14(c), counter electrode wiring 65 is also formed on the surface 20a along with each pixel electrode 25. Specifically, the counter electrode wiring 65 is formed on the surface 20a at a position spaced apart from the multiple pixel electrodes 25.

[0075] Next, as shown in FIG. 15( a), the piezoelectric layer 35 is bonded to the pixel electrode 25 and the thin-film transistor layer 20 via the insulating layer 30. "Bonding via the insulating layer 30" means that the piezoelectric layer 35 is bonded to the insulating layer 30, and the insulating layer 30 is bonded to the pixel electrode 25 and the thin-film transistor layer 20 between the pixel electrodes 25. The piezoelectric layer 35 can be made of polyvinylidene difluoride (PVDF), poly(vinylidene difluoride-trifluoroethylene) copolymer (P(VDF-TrFE)), or the like. The piezoelectric layer 35 is obtained by applying the material for the piezoelectric layer 35 to a glass plate, baking it, and then peeling the material from the glass plate. The piezoelectric layer 35 is then polarized by a poling process (i.e., a process in which the front and back of the piezoelectric layer 35 are sandwiched between electrodes, and positive and negative voltages are applied alternately to the piezoelectric layer 35 while gradually increasing the amplitude).

[0076] In FIG. 15, the insulating layer 30 is a single-layer adhesive layer. Examples of the single-layer adhesive layer include a liquid adhesive, a hot-melt adhesive, and a sheet-like adhesive such as double-sided tape. In the process shown in FIG. 15(a), the insulating layer 30 is bonded to one of the pixel electrodes 25 and the thin-film transistor layer 20 and the piezoelectric layer 35, and then the insulating layer 30 bonded to the one layer is bonded to the other layer. At this time, the counter electrode wiring 65 on the thin-film transistor layer 20 is exposed to the outside without being covered by the insulating layer 30. In this embodiment, a sheet-like adhesive is used as the insulating layer 30. In this case, for example, the front surface 30a of the insulating layer 30 is bonded to the back surface 35b of the piezoelectric layer 35 and pressure is applied, and then the back surface 30b of the insulating layer 30 bonded to the piezoelectric layer 35 is bonded to the front surface 25a of the pixel electrode 25 and the front surface 20a of the thin-film transistor layer 20 and pressure is applied. Conversely, the back surface 30b of the insulating layer 30 may be attached to the surface 25a of the pixel electrode 25 and the surface 20a of the thin-film transistor layer 20 and then pressurized, and then the surface 30a of the insulating layer 30 attached to the pixel electrode 25 and the thin-film transistor layer 20 may be attached to the back surface 35b of the piezoelectric layer 35 and then pressurized.

[0077] The method of bonding the piezoelectric layer 35 to the pixel electrode 25 and the thin film transistor layer 20 via the insulating layer 30 is not limited to the above method. For example, when a liquid adhesive is used as the insulating layer 30, the material for the insulating layer 30 may be applied to the back surface 35b of the piezoelectric layer 35 and baked at a low temperature, and then the material for the insulating layer 30 applied to the piezoelectric layer 35 may be attached to the front surface 25a of the pixel electrode 25 and the front surface 20a of the thin film transistor layer 20 and baked at a high temperature. Conversely, the material for the insulating layer 30 may be applied to the front surface 25a of the pixel electrode 25 and the front surface 20a of the thin film transistor layer 20 and baked at a low temperature, and then the material for the insulating layer 30 applied to the pixel electrode 25 and the thin film transistor layer 20 may be attached to the back surface 35b of the piezoelectric layer 35 and baked at a high temperature.

[0078] Next, as shown in FIG. 15(b), a counter electrode 40 is formed on the surface 35a of the piezoelectric layer 35. The counter electrode 40 can be made of a metal such as molybdenum (Mo), aluminum (Al), or silver (Ag), or an alloy containing these metals, or a mixture containing metal particles. Mask sputtering and mask evaporation can be used to form and pattern the counter electrode 40. Alternatively, the counter electrode 40 can be formed by printing and baking an ink containing metal particles or a metal compound. In the process shown in FIG. 15(b), the counter electrode 40 is formed so as to be connected to the counter electrode wiring 65 on the thin-film transistor layer 20. Specifically, the counter electrode 40 is formed so as to extend from the surface 35a of the piezoelectric layer 35 to the surface 20a of the thin-film transistor layer 20 and to cover the counter electrode wiring 65 on the surface 20a.

[0079] As a result, the counter electrode 40 has an electrode portion P1 covering the surface 35a of the piezoelectric layer 35, an electrode portion P2 covering the side surface SB1 of the laminate B1 of the insulating layer 30 and the piezoelectric layer 35, and an electrode portion P3 covering the counter electrode wiring 65 on the surface 20a of the thin-film transistor layer 20. The electrode portion P3 is formed to cover the counter electrode wiring 65 from above and is in contact with the counter electrode wiring 65 and the surface 20a of the thin-film transistor layer 20. The electrode portion P3 is electrically connected to the counter electrode wiring 65 and can supply a voltage to the counter electrode 40. In other words, power can be supplied to the counter electrode 40 via the counter electrode wiring 65. The counter electrode wiring 65 is also electrically connected to the thin-film transistor group 24 included in the thin-film transistor layer 20 and can supply a voltage to the common wiring 63 of the thin-film transistor group 24. Note that the counter electrode wiring 65 does not necessarily have to be formed, and power may be supplied directly to the counter electrode 40 and the thin-film transistor group 24.

[0080] 16(a) and 16(b) are cross-sectional views showing another example of the manufacturing process of the bending sensor 10. In this example, the process shown in FIG. 14(a) and the process shown in FIG. 14(b) are performed in order, followed by the process shown in FIG. 16(a) and the process shown in FIG. 16(b). In the process shown in FIG. 16(a), similar to FIG. 14(c), each pixel electrode 25 is formed on the surface 20a of the thin-film transistor layer 20. At this time, for example, as shown in FIG. 16(a), it is not necessary to form the counter electrode wiring 65 on the surface 20a of the thin-film transistor layer 20. Then, in the process shown in FIG. 16(b), the counter electrode 40 is formed in advance on the surface 35a of the piezoelectric layer 35 before bonding the piezoelectric layer 35 to the thin-film transistor layer 20 via the insulating layer 30. In other words, a laminate B2 of the piezoelectric layer 35 and the counter electrode 40 is formed in advance. Then, using a method similar to the process shown in Figure 15(a), an insulating layer 30 is bonded to one of the layers of the pixel electrode 25, the thin film transistor layer 20, and the laminate B2, and then the insulating layer 30 bonded to the one layer is bonded to the other layer.

[0081] For example, the back surface 30b of the insulating layer 30 may be bonded to the back surface 35b of the piezoelectric layer 35 of the laminate B2 after bonding the back surface 30a of the insulating layer 30 to the back surface 35b of the piezoelectric layer 35 of the laminate B2. Alternatively, the back surface 30a of the insulating layer 30 may be bonded to the back surface 35b of the laminate B2 after bonding the back surface 30b of the insulating layer 30 to the back surface 25a of the pixel electrode 25 and the front surface 20a of the thin film transistor layer 20. In the process shown in FIGS. 16(a) and 16(b), if the counter electrode wiring 65 is not formed on the thin film transistor layer 20, power may be supplied directly to the counter electrode 40 and the thin film transistor group 24. In the process shown in FIGS. 16(a) and 16(b), if the counter electrode wiring 65 is formed on the thin film transistor layer 20, a separate process of connecting the counter electrode 40 and the counter electrode wiring 65 may be performed. When the steps shown in Figures 16(a) and 16(b) are performed, the laminate B2 of the piezoelectric layer 35 and the counter electrode 40 can be produced in advance in a separate step, which makes it easier to manufacture the bending sensor 10.

[0082] [Action and effect] The effects of the above-described embodiment will now be described. In this embodiment, the insulating layer 30 is disposed between the pixel electrodes 25 and the piezoelectric layer 35, and the insulating layer 30 is bonded to the pixel electrodes 25 (and the surface 20a of the thin-film transistor layer 20 between the pixel electrodes 25) and the piezoelectric layer 35. Therefore, the position of the pixel electrode 25 relative to the piezoelectric layer 35 is more stable than when the piezoelectric layer 35 is only in contact with the pixel electrodes 25. As described above, the insulating layer 30 functions as a capacitor connecting the pixel electrodes 25 and the piezoelectric layer 35. Therefore, a voltage generated in the piezoelectric layer 35 in response to bending is applied to the pixel electrodes 25 via the insulating layer 30 and detected as a signal indicating the bending state. Therefore, in the bending sensor 10, it is possible to extract a signal indicating the bending state while the position of the pixel electrode 25 relative to the piezoelectric layer 35 is stabilized (i.e., while the insulating layer 30 firmly holds the piezoelectric layer 35 and the pixel electrodes 25 (and the surface 20a of the thin-film transistor layer 20 between the pixel electrodes 25)). In this case, the signal output from the bending sensor 10 can be stabilized, making it possible to stably detect bending based on the signal. Furthermore, the presence of the insulating layer 30 between the pixel electrode 25 and the piezoelectric layer 35 increases the mechanical strength of the bending sensor 10 while ensuring electrical insulation between the pixel electrode 25 and other electrodes.

[0083] In this embodiment, the insulating layer 30 is a single-layer adhesive layer. In this case, the thickness of the insulating layer 30 can be made thinner than when the insulating layer 30 is a laminate. The thinner the insulating layer 30 is, the larger the capacitance Ci of the capacitor using the insulating layer 30 as a dielectric, making it possible to suppress an increase in the attenuation rate of the signal output from the bending sensor 10. As a result, bending can be detected more stably.

[0084] In this embodiment, the insulating layer 30 is made of an acrylic resin, a polyurethane resin, a polyester resin, or a synthetic resin thereof. In this case, the flexibility of the insulating layer 30 can be improved, and the insulating layer 30 can be deformed in response to bending. As a result, damage to the insulating layer 30 caused by bending the bending sensor 10 can be suppressed.

[0085] In this embodiment, it is desirable that the thickness T30 of the insulating layer 30 between the pixel electrode 25 and the piezoelectric layer 35 is equal to or less than the thickness T35 of the piezoelectric layer 35. In this case, it is possible to suppress a decrease in the capacitance Ci of the capacitor that uses the insulating layer 30 as a dielectric, and therefore it is possible to suppress an increase in the attenuation rate of the signal output from the bending sensor 10. As a result, bending can be detected more stably.

[0086] In this embodiment, the capacitance Ci of the insulating layer 30 between the pixel electrode 25 and the piezoelectric layer 35 is larger than the capacitance Cp of the piezoelectric layer 35 between the counter electrode 40 and the insulating layer 30. Increasing the value of the capacitance Ci of the insulating layer 30 in this way reduces the effect of variations in the capacitance Ci on this value. Suppressing variations in the capacitance Ci of the insulating layer 30 makes it possible to suppress variations in the attenuation rate of the signal output from the bending sensor 10. As a result, bending can be detected more stably.

[0087] In this embodiment, when forming the piezoelectric layer 35 on the pixel electrode 25, an insulating layer 30 made of a sheet-like adhesive may be attached to the piezoelectric layer 35, and then the piezoelectric layer 35 may be attached to the pixel electrode 25 via the insulating layer 30. In this case, after the insulating layer 30 is attached to the piezoelectric layer 35, the insulating layer 30 can be cut to match the shape of the piezoelectric layer 35, so there is no need to prepare an insulating layer 30 that matches the shape of the piezoelectric layer 35 in advance. This makes it possible to easily manufacture the bending sensor 10.

[0088] The bending sensor 10, bending detection device 1, and manufacturing method of the bending sensor 10 according to the present invention are not limited to the above-described embodiments, and various modifications are possible without departing from the gist of the present invention.

[0089] [Variation 1] FIG. 17 is a cross-sectional view showing a bending sensor 10A according to Modification 1. The bending sensor 10A includes an insulating layer 30A instead of the insulating layer 30. Unlike the single-layer insulating layer 30, the insulating layer 30A is a laminate in which an adhesive layer 301 (first adhesive layer), a base material 302, and an adhesive layer 303 (second adhesive layer) are laminated in this order. The base material 302 is, for example, an electrically insulating film having a uniform thickness. To ensure the flexibility of the base material 302, for example, a polyester-based resin is used as the material for the base material 302. The adhesive layers 301 and 303 are disposed on both sides of the base material 302. Each of the adhesive layers 301 and 303 is, for example, an electrically insulating adhesive. The insulating layer 30A may be, for example, a sheet-like adhesive such as double-sided tape. To ensure the flexibility of the adhesive layers 301 and 303, for example, an acrylic-based resin, a urethane-based resin, a polyester-based resin, or the like is used as the material for the adhesive layers 301 and 303.

[0090] The adhesive layer 301 is disposed on the back surface 302b of the substrate 302 and is bonded to the back surface 302b. Furthermore, the adhesive layer 301 is bonded to the front surface 20a of the thin film transistor layer 20 and the front surface 25a of the pixel electrodes 25 on the front surface 20a. The adhesive layer 303 is disposed on the front surface 302a of the substrate 302 and is bonded to the front surface 302a. Furthermore, the adhesive layer 303 is bonded to the back surface 35b of the piezoelectric layer 35. Each of the adhesive layers 301 and 303 has a high adhesive strength so that peeling of the insulating layer 30A from the substrate 302, the piezoelectric layer 35, the pixel electrodes 25, and the thin film transistor layer 20 does not occur when bending is applied to the bending sensor 10A.

[0091] The thickness T301 of the adhesive layer 301 and the thickness T303 of the adhesive layer 303 are, for example, the same thickness. The thickness T302 of the base material 302 is, for example, thinner than the thicknesses T301 and T303. The thickness T301 is the distance in the Z direction from the front surface 20a to the back surface 302b. The thickness T302 is the distance in the Z direction from the back surface 302b to the front surface 302a. The thickness T303 is the distance in the Z direction from the front surface 302a to the back surface 35b. The thickness T302 of the base material 302 may be, for example, not less than 1 μm and not more than 30 μm. The thicknesses T301 and T303 of the adhesive layers 301 and 303 may each be not less than 1 μm and not more than 30 μm.

[0092] The thickness T30A of the insulating layer 30A between the pixel electrode 25 and the piezoelectric layer 35 is, for example, less than the thickness T35 of the piezoelectric layer 35. The thickness T30A is the distance in the Z direction from the front surface 25a of the pixel electrode 25 to the back surface 35b of the piezoelectric layer 35. The capacitance Ci of a capacitor using the insulating layer 30A as a dielectric is greater than, for example, the capacitance Cp of a capacitor using the piezoelectric layer 35 as a dielectric. Even with the bending sensor 10A having this configuration, the piezoelectric layer 35 is bonded to each pixel electrode 25 via the insulating layer 30A, thereby achieving the same effects as the bending sensor 10 according to the above-described embodiment. Furthermore, when the base material 302 is interposed between the insulating layer 30A, as in the bending sensor 10A, the variation in the overall thickness of the insulating layer 30A can be reduced compared to when the insulating layer is composed of only an adhesive layer.

[0093] [Variation 2] 18 is a cross-sectional view showing a bending sensor 10B according to Modification 2. In addition to the configuration of the bending sensor 10 according to the above-described embodiment, the bending sensor 10B further includes a cover sheet 45 and a sealing material 46. The cover sheet 45 is, for example, an electrically insulating sheet-like member. The cover sheet 45 is, for example, a rubber sheet. An adhesive is provided on a back surface 45a of the cover sheet 45.

[0094] The cover sheet 45 is disposed on the counter electrode 40 and covers the surface 40a of the counter electrode 40 from above. The back surface 45a of the cover sheet 45 is bonded to the surface 40a of the counter electrode 40 via an adhesive. In a plan view, the cover sheet 45 has a rectangular shape that is slightly larger than the counter electrode 40. As a result, in the cross section shown in FIG. 18, the cover sheet 45 protrudes outward in the X direction beyond the counter electrode 40. The cover sheet 45 electrically insulates the counter electrode 40 from other electrodes and prevents scratches and the like from occurring on the surface 40a of the counter electrode 40. The thickness T45 of the cover sheet 45 is, for example, thicker than the counter electrode 40.

[0095] The sealant 46 is provided to surround the side surface SB3 of the laminate B3, which includes each pixel electrode 25, the insulating layer 30, the piezoelectric layer 35, and the counter electrode 40. The sealant 46 is provided to fill the space surrounded by the side surface SB3 of the laminate B3, the surface 20a of the thin-film transistor layer 20, and the back surface 45a of the cover sheet 45. The sealant 46 is bonded to the side surface SB3, the surface 20a, and the back surface 45a. The sealant 46 is made of, for example, an electrically insulating resin material. Examples of the material for the sealant 46 include thermosetting resin and UV-curable resin. Examples of the resin that makes up the sealant 46 include acrylic resin, epoxy resin, and silicone resin. The sealant 46 ensures electrical insulation between the laminate B3 and the surface 20a of the thin-film transistor layer 20 and prevents scratches and other damage to the laminate B3 and the surface 20a of the thin-film transistor layer 20.

[0096] When manufacturing the bending sensor 10B, after the step shown in FIG. 15(b), the back surface 45a of the cover sheet 45 is attached to the front surface 40a of the counter electrode 40 with an adhesive. Then, a liquid material constituting the sealing material 46 is applied to the space surrounded by the side surface SB3 of the laminate B3, the front surface 20a of the thin-film transistor layer 20, and the back surface 45a of the cover sheet 45. Then, if the sealing material 46 is a thermosetting resin, the sealing material 46 is hardened by applying heat to the sealing material 46. If the sealing material 46 is a UV-curable resin, the sealing material 46 is hardened by irradiating it with UV light. This completes the bending sensor 10B.

[0097] The bending sensor 10B having the above configuration also achieves the same effects as the bending sensor 10 according to the above-described embodiment. Furthermore, in the bending sensor 10B, the electrically insulating cover sheet 45 and sealing material 46 ensure electrical insulation between the electrodes constituting the bending sensor 10B and other electrodes. Furthermore, by protecting the surface 20a of the laminate B3 and the thin-film transistor layer 20 with the cover sheet 45 and sealing material 46, it is possible to prevent scratches and the like from occurring on the laminate B3 and the thin-film transistor layer 20. Furthermore, because the rubber sheet has a small Young's modulus, the influence of the rubber sheet on the height λ of the neutral plane NP is extremely small, and the influence on the operation of the bending sensor 10B is therefore small.

[0098] [Variation 3] FIG. 19 is a cross-sectional view showing a bending sensor 10C according to Modification 3. The bending sensor 10C further includes a cover sheet 45A in addition to the configuration of the bending sensor 10 according to the above-described embodiment. The cover sheet 45A is an electrically insulating sheet-like member (e.g., a rubber sheet) similar to the cover sheet 45 according to Modification 2. The cover sheet 45A has a thickness T45A that is thinner than the thickness T45 (see FIG. 18) of the cover sheet 45 according to Modification 2. Therefore, the cover sheet 45A has higher flexibility than the cover sheet 45. Specifically, the cover sheet 45A has a Young's modulus that enables it to deform to follow the shape of the object covered by the cover sheet 45A. An adhesive is provided on the back surface 45a of the cover sheet 45.

[0099] The cover sheet 45A is disposed on the counter electrode 40 and covers the surface 40a of the counter electrode 40 from above. The cover sheet 45A deforms to conform to the shape of the laminate B3, which is made up of the pixel electrodes 25, the insulating layer 30, the piezoelectric layer 35, and the counter electrode 40. Specifically, the cover sheet 45A is provided so as to cover from the surface 40a of the counter electrode 40 of the laminate B3 to the surface 20a of the thin-film transistor layer 20 outside the laminate B3. As a result, the cover sheet 45A has a sheet portion P11 that covers the surface 40a of the counter electrode 40, a sheet portion P12 that covers the side surface SB3 of the laminate B3, and a sheet portion P13 that covers the surface 20a of the thin-film transistor layer 20. The back surfaces 45a of the sheet portions P11, P12, and P13 are bonded to the surface 40a of the counter electrode 40, the side surface SB3 of the laminate B3, and the surface 20a of the thin-film transistor layer 20, respectively. 15(b), the cover sheet 45A is deformed to fit the shape of the laminate B3, and the back surfaces 45a of the sheet portions P11, P12, and P13 of the cover sheet 45A are attached to the front surface 40a, the side surface SB3, and the front surface 20a with an adhesive, thereby obtaining the bending sensor 10C.

[0100] The bending sensor 10C having the above configuration achieves the same effects as the bending sensor 10 according to the above-described embodiment. Furthermore, in the bending sensor 10C, the electrically insulating cover sheet 45A ensures electrical insulation between the electrodes constituting the bending sensor 10C and other electrodes. Furthermore, by protecting the laminate B3 with the cover sheet 45A, the occurrence of scratches on the laminate B3 can be suppressed. Furthermore, compared to the bending sensor 10B according to Modification 2, the laminate B3 and the surface 20a of the thin-film transistor layer 20 can be protected with a simple configuration in which only the cover sheet 45A covers the laminate B3 and the surface 20a of the thin-film transistor layer 20. Furthermore, because the rubber sheet has a small Young's modulus, the influence of the rubber sheet on the height λ of the neutral plane NP is extremely small, and the influence on the operation of the bending sensor 10C is therefore minimal. [Example]

[0101] Hereinafter, bending sensors according to the present invention will be described in accordance with Examples 1 to 7. However, the present invention is not limited to Examples 1 to 7.

[0102] Example 1 The bending sensor 10 shown in FIG. 1 was fabricated using the manufacturing processes shown in FIGS. 14(a), 14(b), 16(a), and 16(b). First, a PI film on a glass substrate was prepared as the insulating substrate 15 (see FIG. 14(a)). A thin-film transistor layer 20A was fabricated on the insulating substrate 15 (see FIG. 14(b)). The circuit of the thin-film transistor array included in the thin-film transistor layer 20A is the circuit shown in FIG. 10. The gate electrodes G1, G2, and G3 constituting the thin-film transistor group 24A are mainly composed of molybdenum (Mo). The gate insulating film 50 is mainly composed of an organic insulator. The semiconductor layers SC1, SC2, and SC3 are mainly composed of InGaZnO. The source electrodes S1, S2, and S3 are mainly composed of molybdenum (Mo). The drain electrodes D1, D2, and D3 are mainly composed of molybdenum (Mo). The main component of the interlayer insulating film 51 is an organic insulator.

[0103] Next, a molybdenum (Mo)-based alloy was formed on the thin-film transistor layer 20A as the pixel electrode 25, followed by lithography and etching (see FIG. 16(a)). At this time, a counter electrode wiring 65 was also formed on the thin-film transistor layer 20A. Next, using double-sided acrylic resin tape as the insulating layer 30, a separately prepared piezoelectric layer 35 with a counter electrode 40 was attached to the thin-film transistor layer 20A on which the pixel electrode 25 was formed, via the insulating layer 30, and pressure was applied (see FIG. 16(b)). In this way, the piezoelectric layer 35 and the pixel electrode 25 were bonded via the insulating layer 30. The counter electrode 40 was mainly composed of molybdenum (Mo). A PVDF film was used for the piezoelectric layer 35. Next, the counter electrode 40 and the counter electrode wiring 65 were connected using Ag paste, and the glass substrate was then peeled off to produce the bending sensor 10.

[0104] The insulating substrate 15 is 20 μm thick, the thin-film transistor layer 20A is 4 μm thick, the pixel electrode 25 is 0.1 μm thick, the insulating layer 30 is 50 μm thick, the piezoelectric layer 35 is 20 μm thick, and the counter electrode 40 is 0.1 μm thick. The Young's modulus of the insulating substrate 15 is 3 GPa, the Young's modulus of the thin-film transistor layer 20A is 5 GPa, the Young's modulus of the pixel electrode 25 is 300 GPa, the Young's modulus of the insulating layer 30 is 100 MPa, the Young's modulus of the piezoelectric layer 35 is 3 GPa, and the Young's modulus of the counter electrode 40 is 300 GPa. In this case, the neutral plane NP is located inside the insulating layer 30, and the piezoelectric layer 35 is located above the neutral plane NP. The pixel pitch is 5 mm, and the number of pixels is 8 × 8. The pixel electrode 25 is a square with a side length of 3.6 mm.

[0105] 13 was used to detect the signal output from the bending sensor 10, and it was possible to detect the bending applied to the bending sensor 10. The piezoelectric layer 35 was bent upward in a direction that was convex with a curvature of 0.5 mm. -1 ~20m -1 When a bending (convex bending) of 0.5m is applied to the bending sensor 10, the portion of the signal output from the bending sensor 10 corresponding to the voltage Vp is proportional to the curvature of the bending, and the proportionality coefficient is about 0.15Vm. -1 ~20m -1 A bend (convex bend) of 1000 mW was applied to the bending sensor 10. At this time, the portion of the signal output from the bending sensor 10 corresponding to the voltage Vp was proportional to the curvature of the bend, with a proportionality coefficient of approximately -0.15 Vm. The data points obtained by detecting the signal were distributed between a proportionality coefficient of 0.1 and 0.2 in the case of a convex bend, and between a proportionality coefficient of -0.1 and -0.2 in the case of a concave bend.

[0106] Example 2 The bending sensor 10 shown in FIG. 1 was fabricated using the manufacturing processes shown in FIGS. 14(a), 14(b), 16(a), and 16(b). First, a PI film on a glass substrate was prepared as the insulating substrate 15 (see FIG. 14(a)). A thin-film transistor layer 20A was fabricated on the insulating substrate 15 (see FIG. 14(b)). The circuit of the thin-film transistor array included in the thin-film transistor layer 20A is the circuit shown in FIG. 10. The gate electrodes G1, G2, and G3 constituting the thin-film transistor group 24A are mainly composed of molybdenum (Mo). The gate insulating film 50 is mainly composed of an organic insulator. The semiconductor layers SC1, SC2, and SC3 are mainly composed of InGaZnO. The source electrodes S1, S2, and S3 are mainly composed of molybdenum (Mo). The drain electrodes D1, D2, and D3 are mainly composed of molybdenum (Mo). The main component of the interlayer insulating film 51 is an organic insulator.

[0107] Next, a molybdenum (Mo)-based alloy was deposited on the thin-film transistor layer 20A as the pixel electrode 25, followed by lithography and etching (see FIG. 16(a)). At this time, a counter electrode wiring 65 was also formed on the thin-film transistor layer 20A. Next, a liquid adhesive made of urethane resin was used as the insulating layer 30. This liquid adhesive was applied to the thin-film transistor layer 20A on which the pixel electrode 25 was formed and then baked at a low temperature. A separately prepared piezoelectric layer 35 with a counter electrode 40 was then pressed onto the thin-film transistor layer 20A on which the liquid adhesive had been applied, followed by baking at a high temperature (see FIG. 16(b)). In this way, the piezoelectric layer 35 and the pixel electrode 25 were bonded via the insulating layer 30. The counter electrode 40 was primarily composed of molybdenum (Mo). A PVDF film was used for the piezoelectric layer 35. The counter electrode 40 and the counter electrode wiring 65 were then connected using Ag paste, and the glass substrate was then peeled off to produce the bending sensor 10.

[0108] The insulating substrate 15 is 20 μm thick, the thin-film transistor layer 20A is 4 μm thick, the pixel electrode 25 is 0.1 μm thick, the insulating layer 30 is 10 μm thick, the piezoelectric layer 35 is 20 μm thick, and the counter electrode 40 is 0.1 μm thick. The Young's modulus of the insulating substrate 15 is 3 GPa, the Young's modulus of the thin-film transistor layer 20A is 5 GPa, the Young's modulus of the pixel electrode 25 is 300 GPa, the Young's modulus of the insulating layer 30 is 100 MPa, the Young's modulus of the piezoelectric layer 35 is 3 GPa, and the Young's modulus of the counter electrode 40 is 300 GPa. In this case, the neutral plane NP is located inside the insulating layer 30, and the piezoelectric layer 35 is located above the neutral plane NP. The pixel pitch is 5 mm, and the number of pixels is 8 × 8. The pixel electrode 25 is a square with a side length of 3.6 mm.

[0109] 13 was used to detect the signal output from the bending sensor 10, and it was possible to detect the bending applied to the bending sensor 10. The piezoelectric layer 35 was bent upward in a direction that was convex with a curvature of 0.5 mm. -1 ~20m -1 When a bending (convex bending) of 0.5 mm is applied to the bending sensor 10, the portion of the signal output from the bending sensor 10 corresponding to the voltage Vp is proportional to the curvature of the bending, and the proportionality coefficient is about 0.06 Vm. -1 ~20m -1 A bend (concave bend) of 1000 mW was applied to the bending sensor 10. At this time, the portion of the signal output from the bending sensor 10 corresponding to the voltage Vp was proportional to the curvature of the bend, and the proportionality coefficient was approximately -0.06 Vm. All data obtained by detecting the signal was within ±20% of the proportionality coefficient.

[0110] Example 3 The bending sensor 10 shown in FIG. 1 was fabricated by the manufacturing steps shown in FIGS. 14(a), 14(b), 16(a), and 16(b). First, a PI film on a glass substrate was prepared as the insulating substrate 15 (see FIG. 14(a)), and a thin-film transistor layer 20A was fabricated on the insulating substrate 15 (see FIG. 14(b)). The circuit of the thin-film transistor array included in the thin-film transistor layer 20A is the circuit shown in FIG. 10. The gate electrodes G1, G2, and G3 constituting the thin-film transistor group 24A are mainly composed of aluminum (Al). The gate insulating film 50 is mainly composed of an organic insulator. The semiconductor layers SC1, SC2, and SC3 are mainly composed of InGaZnO. The source electrodes S1, S2, and S3 are mainly composed of aluminum (Al). The drain electrodes D1, D2, and D3 are mainly composed of aluminum (Al). The interlayer insulating film 51 is mainly composed of an organic insulator.

[0111] Next, an aluminum (Al) alloy was formed on the thin-film transistor layer 20A as the pixel electrode 25, and lithography and etching were performed (see FIG. 16(a)). Next, a sheet-like hot-melt adhesive made of polyester resin was used as the insulating layer 30, and a separately prepared piezoelectric layer 35 with a counter electrode 40 was pressed and baked via the hot-melt adhesive onto the thin-film transistor layer 20A on which the pixel electrode 25 was formed (see FIG. 16(b)). In this way, the piezoelectric layer 35 and the pixel electrode 25 were bonded via the insulating layer 30. The main component of the counter electrode 40 was aluminum (Al). A PVDF film was used as the piezoelectric layer 35. The glass substrate was then peeled off to produce the bending sensor 10.

[0112] The insulating substrate 15 is 20 μm thick, the thin-film transistor layer 20A is 4 μm thick, the pixel electrode 25 is 0.1 μm thick, the insulating layer 30 is 30 μm thick, the piezoelectric layer 35 is 30 μm thick, and the counter electrode 40 is 0.1 μm thick. The Young's modulus of the insulating substrate 15 is 3 GPa, the Young's modulus of the thin-film transistor layer 20A is 5 GPa, the Young's modulus of the pixel electrode 25 is 70 GPa, the Young's modulus of the insulating layer 30 is 40 MPa, the Young's modulus of the piezoelectric layer 35 is 3 GPa, and the Young's modulus of the counter electrode 40 is 70 GPa. In this case, the neutral plane NP is located inside the insulating layer 30, and the piezoelectric layer 35 is located above the neutral plane NP. The pixel pitch is 5 mm, and the number of pixels is 8 × 8. The pixel electrode 25 is a square with a side length of 3.6 mm.

[0113] 13 was used to detect the signal output from the bending sensor 10, and it was possible to detect the bending applied to the bending sensor 10. The piezoelectric layer 35 was bent upward in a direction that was convex with a curvature of 0.5 mm. -1 ~20m -1 When a bending (convex bending) of 0.5 mm is applied to the bending sensor 10, the portion of the signal output from the bending sensor 10 corresponding to the voltage Vp is proportional to the curvature of the bending, and the proportionality coefficient is about 0.06 Vm. -1 ~20m -1 A bend (concave bend) of 1000 mW was applied to the bending sensor 10. At this time, the portion of the signal output from the bending sensor 10 corresponding to the voltage Vp was proportional to the curvature of the bend, and the proportionality coefficient was approximately -0.06 Vm. All data obtained by detecting the signal was within ±20% of the proportionality coefficient.

[0114] Example 4 The bending sensor 10 shown in FIG. 1 was fabricated by the manufacturing steps shown in FIGS. 14(a) to 14(c), 15(a), and 15(b). First, a PEN film was prepared as the insulating substrate 15, which was attached to a glass substrate via a film that can be adhered at room temperature and peeled off at high temperatures (see FIG. 14(a)). A thin-film transistor layer 20 was fabricated on the insulating substrate 15 (see FIG. 14(b)). The circuit of the thin-film transistor array included in the thin-film transistor layer 20 is the circuit shown in FIG. 7. The gate electrodes G1 and G2 constituting the thin-film transistor group 24 are mainly composed of aluminum (Al). The gate insulating film 50 is mainly composed of an organic insulator. The semiconductor layers SC1 and SC2 are mainly composed of InGaZnO. The source electrodes S1 and S2 are mainly composed of aluminum (Al). The drain electrodes D1 and D2 are mainly composed of aluminum (Al). The interlayer insulating film 51 is mainly composed of an organic insulator.

[0115] Next, an aluminum (Al) alloy was formed on the thin-film transistor layer 20 as the pixel electrode 25, and lithography and etching were performed (see FIG. 14(c)). Next, a single-layer double-sided tape made of acrylic resin was used as the insulating layer 30, and a separately prepared piezoelectric layer 35 was attached to the thin-film transistor layer 20 on which the pixel electrode 25 was formed, via the double-sided tape, and pressure was applied (see FIG. 15(a)). In this way, the piezoelectric layer 35 and the pixel electrode 25 were bonded via the insulating layer 30. The main component of the counter electrode 40 was aluminum (Al). A PVDF film was used as the piezoelectric layer 35. Next, the counter electrode 40 was formed on the piezoelectric layer 35 by screen printing Ag paste (see FIG. 15(b)). The glass substrate was then peeled off to produce the bending sensor 10.

[0116] The insulating substrate 15 is 100 μm thick, the thin-film transistor layer 20 is 4 μm thick, the pixel electrode 25 is 0.1 μm thick, the insulating layer 30 is 30 μm thick, the piezoelectric layer 35 is 30 μm thick, and the counter electrode 40 is 10 μm thick. The Young's modulus of the insulating substrate 15 is 10 GPa, the Young's modulus of the thin-film transistor layer 20 is 5 GPa, the Young's modulus of the pixel electrode 25 is 70 GPa, the Young's modulus of the insulating layer 30 is 100 MPa, the Young's modulus of the piezoelectric layer 35 is 3 GPa, and the Young's modulus of the counter electrode 40 is 10 GPa. In this case, the neutral plane NP is located inside the insulating substrate 15, and the piezoelectric layer 35 is located above the neutral plane NP. The pixel pitch is 5 mm, and the number of pixels is 8 × 8. The pixel electrode 25 is a square with a side length of 3.6 mm.

[0117] 12 was used to detect the signal output from the bending sensor 10, and it was possible to detect the bending applied to the bending sensor 10. The piezoelectric layer 35 was bent upward in a direction that was convex with a curvature of 0.5 mm. -1 ~10m -1 When a bending (convex bending) of 0.5m is applied to the bending sensor 10, the portion of the signal output from the bending sensor 10 corresponding to the voltage Vp is proportional to the curvature of the bending, and the proportionality coefficient is about 0.3Vm. -1 ~10m -1 A bend (concave bend) of 1000 mW was applied to the bending sensor 10. At this time, the portion of the signal output from the bending sensor 10 corresponding to the voltage Vp was proportional to the curvature of the bend, and the proportionality coefficient was approximately -0.3 Vm. All data obtained by detecting the signal was within ±20% of the proportionality coefficient.

[0118] Example 5 The bending sensor 10A shown in FIG. 17 was fabricated using the manufacturing processes shown in FIGS. 14(a), 14(b), 16(a), and 16(b). First, a PI film on a glass substrate was prepared as the insulating substrate 15 (see FIG. 14(a)), and a thin-film transistor layer 20A was fabricated on the insulating substrate 15 (see FIG. 14(b)). The circuit of the thin-film transistor array included in the thin-film transistor layer 20A is the circuit shown in FIG. 10. The gate electrodes G1, G2, and G3 constituting the thin-film transistor group 24A are mainly composed of aluminum (Al). The gate insulating film 50 is mainly composed of an organic insulator. The semiconductor layers SC1, SC2, and SC3 are mainly composed of InGaZnO. The source electrodes S1, S2, and S3 are mainly composed of aluminum (Al). The drain electrodes D1, D2, and D3 are mainly composed of aluminum (Al). The interlayer insulating film 51 is mainly composed of an organic insulator.

[0119] Next, an aluminum (Al)-based alloy was formed on the thin-film transistor layer 20A as the pixel electrode 25, and lithography and etching were performed (see FIG. 16(a)). At this time, a counter electrode wiring 65 was also formed on the thin-film transistor layer 20A. Next, using a laminated double-sided tape as the insulating layer 30A, a separately prepared piezoelectric layer 35 with a counter electrode 40 was attached via the insulating layer 30A to the thin-film transistor layer 20A on which the pixel electrode 25 was formed, and pressure was applied (see FIG. 16(b)). In this way, the piezoelectric layer 35 and the pixel electrode 25 were bonded via the insulating layer 30A. The adhesive layers 301 and 303 of the insulating layer 30A were mainly composed of acrylic resin, and the base material 302 was mainly composed of polyethylene terephthalate (PET). The counter electrode 40 was mainly composed of aluminum (Al). A PVDF film was used as the piezoelectric layer 35. Next, the counter electrode 40 and the counter electrode wiring 65 were connected with Ag paste, and then the glass substrate was peeled off to produce the bending sensor 10A.

[0120] The insulating substrate 15 has a thickness of 20 μm, the thin-film transistor layer 20A has a thickness of 4 μm, the pixel electrode 25 has a thickness of 0.1 μm, the insulating layer 30A has a thickness of 10 μm (specifically, the base material 302 has a thickness of 2 μm, and the adhesive layers 301 and 303 have a thickness of 4 μm each), the piezoelectric layer 35 has a thickness of 20 μm, and the counter electrode 40 has a thickness of 0.1 μm. The Young's modulus of the insulating substrate 15 is 3 GPa, the Young's modulus of the thin-film transistor layer 20A is 5 GPa, the Young's modulus of the pixel electrode 25 is 70 GPa, the Young's modulus of the adhesive layers 301 and 303 of the insulating layer 30A is 100 MPa each, the Young's modulus of the base material 302 of the insulating layer 30A is 6 GPa, the Young's modulus of the piezoelectric layer 35 is 3 GPa, and the Young's modulus of the counter electrode 40 is 70 GPa. In this case, the neutral plane NP is located inside the insulating layer 30A, and the piezoelectric layer 35 is located above the neutral plane NP. The pixel pitch is 5 mm, and the number of pixels is 8 x 8. The pixel electrode 25 has a square shape with sides of 3.6 mm.

[0121] 13 was used to detect the signal output from the bending sensor 10A, and it was possible to detect the bending applied to the bending sensor 10A. -1 ~20m -1 When a bending (convex bending) of 0.5 m is applied to the bending sensor 10A, the portion of the signal output from the bending sensor 10A corresponding to the voltage Vp is proportional to the curvature of the bending, and the proportionality coefficient is about 0.07 Vm. -1 ~20m -1 A bending (concave bending) of 100 m / s was applied to bending sensor 10A. At this time, the portion of the signal output from bending sensor 10A corresponding to voltage Vp was proportional to the curvature of the bending, and the proportionality coefficient was approximately -0.07 Vm. All data obtained by detecting the signal was within ±20% of the proportionality coefficient.

[0122] Example 6 A cover sheet 45 and a sealant 46 were attached to the bending sensor 10 produced in Example 1 to produce the bending sensor 10B shown in FIG. 18. Specifically, an adhesive-backed rubber plate was used as the cover sheet 45, and the cover sheet 45 was attached to the counter electrode 40. Then, a sealant 46 made of acrylic resin was applied to the periphery of the side surface SB3 of the laminate B3 of the insulating layer 30, the piezoelectric layer 35, and the counter electrode 40, and UV-cured. In this way, the bending sensor 10B shown in FIG. 18 was produced. The detection unit 5A shown in FIG. 13 was used to detect the signal output from the bending sensor 10B, and it was possible to detect the bending applied to the bending sensor 10B. The bending detection results by the bending sensor 10B were equivalent to those when the cover sheet 45 was not provided (i.e., the bending sensor 10 produced in Example 1).

[0123] Example 7 A cover sheet 45A was attached to the bending sensor 10 produced in Example 4 to produce the bending sensor 10C shown in FIG. 19. Specifically, an adhesive-backed rubber plate was used as the cover sheet 45A, and the cover sheet 45A was attached to the laminate B3 while being deformed to follow the shape of the laminate B3. In this way, the bending sensor 10C shown in FIG. 19 was produced. The detection unit 5A shown in FIG. 13 was used to detect the signal output from the bending sensor 10C, and it was possible to detect the bending applied to the bending sensor 10C. The bending detection results by the bending sensor 10C were equivalent to those when the cover sheet 45A was not provided (i.e., the bending sensor 10 produced in Example 4).

[0124] The bending sensor, bending detection device, and bending sensor manufacturing method according to the present invention are not limited to the above-described embodiment and each modified example, and can be modified as appropriate. In the above-described embodiment and each modified example, a change in voltage between the counter electrode and the pixel electrode is detected as a "change in electrical characteristics." However, a change in current between the counter electrode and the pixel electrode may be detected as a "change in electrical characteristics." Alternatively, a change in resistance value between the counter electrode and the pixel electrode may be detected as a "change in electrical characteristics." In the above-described embodiment and each modified example, the "insulating layer" is an adhesive. However, the "insulating layer" may be formed of a material other than an adhesive as long as it can be bonded to the piezoelectric layer and the pixel electrode. [Explanation of symbols]

[0125] 1...Bending detection device 5,5A…Detection section 10, 10A, 10B, 10C...Bending sensor 15...Insulating substrate (substrate) 20, 20A...Thin film transistor layer 21, 22, 23...Thin film transistors 25...Pixel electrode 30, 30A...insulating layer 35...Piezoelectric layer 40...Counter electrode 45, 45A...Cover sheet 46...Sealing material 301...adhesive layer (first adhesive layer) 302...Base material 303...adhesive layer (second adhesive layer) B3...Laminate Ci, Cp...Capacitance

Claims

1. A bending sensor for detecting bending, comprising: a substrate having flexibility that can be deformed by bending; a thin film transistor layer disposed on the substrate and including thin film transistors; a pixel electrode disposed on the thin film transistor layer; a piezoelectric layer disposed on the pixel electrode and including a piezoelectric material; a counter electrode disposed on the piezoelectric layer and facing the pixel electrode with the piezoelectric layer interposed therebetween; an insulating layer disposed between the pixel electrode and the piezoelectric layer and bonded to the pixel electrode and the piezoelectric layer, the thin film transistor has a gate electrode; The pixel electrode is electrically connected to the gate electrode of the thin film transistor.

2. The bending sensor according to claim 1 , wherein the insulating layer is a single adhesive layer.

3. The bending sensor according to claim 1 , wherein the insulating layer is a laminate in which a first adhesive layer, a base material, and a second adhesive layer are laminated in this order.

4. The bending sensor according to claim 3 , wherein the substrate is made of a polyester resin.

5. The adhesive layer constituting the insulating layer is composed of at least one resin selected from the group consisting of acrylic resins, polyurethane resins, and polyester resins. The bending sensor according to any one of claims 2 to 4.

6. 6. The bending sensor according to claim 1, wherein the thickness of the insulating layer between the pixel electrode and the piezoelectric layer is equal to or less than the thickness of the piezoelectric layer.

7. The bending sensor according to any one of claims 1 to 6, wherein the capacitance of the insulating layer between the pixel electrode and the piezoelectric layer is greater than the capacitance of the piezoelectric layer between the opposing electrode and the insulating layer.

8. The bending sensor according to any one of claims 1 to 7, further comprising an electrically insulating cover sheet disposed on the counter electrode.

9. The bending sensor according to claim 8 , further comprising an electrically insulating sealing material arranged to surround a side surface of the stack of the counter electrode, the piezoelectric layer, and the insulating layer.

10. The bending sensor according to claim 8 , wherein the cover sheet is provided so as to cover from a surface of the counter electrode to a side surface of a laminate of the counter electrode, the piezoelectric layer, and the insulating layer.

11. A bending sensor according to any one of claims 1 to 10; a detection unit that detects the bending applied to the bending sensor, the thin film transistor outputs a signal indicating a change in an electrical characteristic between the pixel electrode and the counter electrode that occurs in response to the bending; The detection unit detects the signal as information indicating the state of the bending.

12. A method for manufacturing a bending sensor for detecting bending, comprising: forming a thin film transistor layer including a thin film transistor on the substrate having flexibility that can be deformed by bending; forming a pixel electrode on the thin film transistor layer; forming a piezoelectric layer containing a piezoelectric material on the pixel electrode; forming a counter electrode on the piezoelectric layer so as to face the pixel electrode with the piezoelectric layer interposed therebetween; In the step of forming the pixel electrode on the thin film transistor layer, the pixel electrode is formed so as to be electrically connected to a gate electrode of the thin film transistor; In the step of forming the piezoelectric layer on the pixel electrode, the piezoelectric layer is bonded to the pixel electrode via an insulating layer.

13. 13. The method for manufacturing a bending sensor according to claim 12, wherein in the step of forming the piezoelectric layer on the pixel electrode, a sheet-like adhesive is prepared as the insulating layer, the insulating layer is bonded to the piezoelectric layer, and then the piezoelectric layer is bonded to the pixel electrode via the insulating layer.

14. The method for manufacturing a bending sensor according to claim 12 or 13, further comprising the step of forming an electrically insulating cover sheet on the counter electrode.

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