Piezoelectric sensor

Abstract

To provide a piezoelectric sensor capable of having the improved operation characteristic.SOLUTION: A piezoelectric sensor includes a base material 10, a plurality piezoelectric elements 2 provided on the base material 10 and each including a lower electrode 11, a piezoelectric layer 13, and an upper electrode 14 stacked in order, a protection layer 15 provided on the piezoelectric elements 2, a plurality of projection parts 16 provided on the protection layer 15 and disposed in accordance with the respective piezoelectric elements 2, and a heat insulation layer 17 provided on the projection parts 16. In each projection part 16, the area of a lower end part on the protection layer 15 side is smaller than the area of an upper end part on the heat insulation layer 17 side.SELECTED DRAWING: Figure 2

Description

[Technical field]

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

[0002] Sensors using organic piezoelectric materials such as P(VDF / TrFE) are currently in use. Organic piezoelectric materials can be applied by coating, can be produced in low-temperature processes, and can be easily made into films, so attempts are being made to apply them to flexible sensors for wearable devices and large-area sensors. Various applications are being considered for organic piezoelectric materials, such as biosensors for measuring pulse waves and myoelectric signals, tactile sensors, and pyroelectric sensors, making this a technology that is attracting attention.

[0003] Patent Document 1 proposes a pressure sensor that includes a pressure-sensitive part containing an organic piezoelectric material and a thin film transistor (TFT), and detects pressure applied to the pressure-sensitive part using the TFT. Patent Document 2 discloses a sensor device that realizes an organic piezoelectric sensor by bonding an organic piezoelectric film onto a TFT and further arranges the TFTs in an array.

[0004] Organic ferroelectric materials such as PVDF and P(VDF / TrFE) have not only piezoelectricity but also pyroelectricity. If the above organic ferroelectric materials are used in a touch sensor that is directly touched by a finger, the sensor will also detect voltage changes caused by the heat of the finger. If there is a temperature difference between the object to be measured and the sensor array, the response speed as a pressure sensor will decrease due to the effect of the temperature change before and after contact.

[0005] In Patent Document 3, a heat insulating member is placed on the sensor to suppress the influence of heat. In this configuration, pressure propagates laterally through this heat insulating member, which reduces the detection accuracy of pressure in the in-plane direction. In Patent Document 4, a deformation layer with irregularities is placed on the sensor array to suppress the influence of variations in the thickness direction of the pressure-sensitive layer. This configuration is effective in suppressing the decrease in element sensitivity due to variations in the thickness of the pressure-sensitive layer (improving the detection sensitivity threshold), but since the irregularities in the deformation layer are formed randomly, it is poor in quantitativeness, and there is a possibility that relative comparison of detection values ​​within the sensor array cannot be made correctly. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2017-219336 A [Patent Document 2] Patent Publication No. 2021-027270 [Patent Document 3] Japanese Patent Application Publication No. 2-83425 [Patent Document 4] International Publication No. 2020 / 246084 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention provides a piezoelectric sensor capable of improving operating characteristics. [Means for solving the problem]

[0008] According to a first aspect of the present invention, there is provided a piezoelectric sensor comprising a substrate, a plurality of piezoelectric elements provided on the substrate, each of the piezoelectric elements including a lower electrode, a piezoelectric layer, and an upper electrode stacked in that order, a protective layer provided on the plurality of piezoelectric elements, a plurality of protrusions provided on the protective layer and arranged corresponding to the plurality of piezoelectric elements, respectively, and a thermal insulating layer provided on the plurality of protrusions, each of the plurality of protrusions being configured such that the area of ​​its lower end on the protective layer side is smaller than the area of ​​its upper end on the thermal insulating layer side.

[0009] According to a second aspect of the present invention, there is provided the piezoelectric sensor according to the first aspect, wherein the protrusion has a semi-spherical shape.

[0010] According to a third aspect of the present invention, there is provided the piezoelectric sensor according to the second aspect, wherein the lower electrode has a rectangular shape, and a diameter of the protrusion is equal to or smaller than a length of one side of the lower electrode.

[0011] According to a fourth aspect of the present invention, there is provided the piezoelectric sensor according to the first aspect, wherein the lower electrode has a quadrangle shape and an area of ​​the lower electrode is smaller than an area of ​​the protrusion.

[0012] According to a fifth aspect of the present invention, there is provided a piezoelectric sensor according to the first aspect, further comprising a conductive adhesive layer provided between the lower electrode and the piezoelectric layer, the piezoelectric layer being provided in common to the plurality of piezoelectric elements.

[0013] According to a sixth aspect of the present invention, there is provided the piezoelectric sensor according to the first aspect, wherein the piezoelectric layer is provided on the base material so as to cover the lower electrode and is provided in common to the plurality of piezoelectric elements.

[0014] According to a seventh aspect of the present invention, there is provided the piezoelectric sensor according to the first aspect, wherein the upper electrode is provided in common to the plurality of piezoelectric elements.

[0015] According to an eighth aspect of the present invention, there is provided the piezoelectric sensor according to the first aspect, wherein the heat insulating layer and the plurality of protrusions are integrally configured.

[0016] According to a ninth aspect of the present invention, there is provided the piezoelectric sensor according to the first aspect, wherein the protrusion is adhered to the protective layer.

[0017] According to a tenth aspect of the present invention, there is provided the piezoelectric sensor according to the first aspect, wherein the piezoelectric layer is an organic piezoelectric layer.

[0018] According to an eleventh aspect of the present invention, there is provided the piezoelectric sensor according to the first aspect, wherein the substrate is flexible. Effect of the Invention

[0019] According to the present invention, it is possible to provide a piezoelectric sensor capable of improving the operating characteristics. [Brief description of the drawings]

[0020] [Figure 1] FIG. 1 is a plan view of a piezoelectric sensor according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a cross-sectional view of the piezoelectric sensor taken along the line AA′ in FIG. [Diagram 3] FIG. 3 is a partial cross-sectional view of the piezoelectric sensor according to the first comparative example. [Figure 4] FIG. 4 is a partial cross-sectional view of a piezoelectric sensor according to a second comparative example. [Diagram 5] FIG. 5 is a graph illustrating the response characteristics of the piezoelectric element according to this embodiment. [Figure 6] FIG. 6 is a graph illustrating the response characteristics of the piezoelectric element according to the first comparative example. [Figure 7] FIG. 7 is a diagram illustrating a signal distribution when the piezoelectric sensor according to this embodiment is pressed with a finger. [Figure 8] FIG. 8 is a diagram illustrating a signal distribution when the piezoelectric sensor according to the second comparative example is pressed with a finger. [Figure 9] FIG. 9 is a partial cross-sectional view of a piezoelectric sensor according to a first modified example. [Figure 10] FIG. 10 is a plan view of a piezoelectric sensor according to a second modified example. [Figure 11] FIG. 11 is a cross-sectional view of the piezoelectric sensor taken along the line AA′ in FIG. [Figure 12] FIG. 12 is a partial cross-sectional view of a piezoelectric sensor according to a third modified example. [Figure 13] FIG. 13 is a plan view of a piezoelectric sensor according to a second embodiment of the present invention. [Figure 14] FIG. 14 is a cross-sectional view of the piezoelectric sensor taken along the line AA′ in FIG. [Figure 15] FIG. 15 is a plan view of a piezoelectric sensor according to a first example of the third embodiment. [Figure 16] FIG. 16 is a cross-sectional view of the piezoelectric sensor taken along the line AA' in FIG. [Figure 17] FIG. 17 is a partial cross-sectional view of a piezoelectric sensor according to a second example of the third embodiment. [Figure 18] FIG. 18 is a partial cross-sectional view of a piezoelectric sensor according to a third example of the third embodiment. [Figure 19] FIG. 19 is a plan view of a piezoelectric sensor according to a fourth embodiment of the present invention. [Figure 20] FIG. 20 is a cross-sectional view of the piezoelectric sensor taken along the line AA′ in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Hereinafter, the embodiments will be described with reference to the drawings. However, the drawings are schematic or conceptual, and the dimensions and ratios of each drawing are not necessarily the same as those in reality. In addition, even when the same parts are shown between the drawings, the dimensional relationships and ratios of each may be different. In particular, the following embodiments are examples of devices and methods for embodying the technical idea of ​​the present invention, and the technical idea of ​​the present invention is not specified by the shape, structure, arrangement, etc. of the components. In the following description, elements having the same function and configuration are given the same reference numerals, and duplicated descriptions are omitted.

[0022] [1] First embodiment [1-1] Configuration of piezoelectric sensor 1 Fig. 1 is a plan view of a piezoelectric sensor 1 according to a first embodiment of the present invention. Fig. 2 is a cross-sectional view of the piezoelectric sensor 1 taken along line AA' in Fig. 1. The X direction in Fig. 1 is a direction along one side of the piezoelectric sensor 1, and the Y direction is a direction perpendicular to the X direction. In the plan view, parts that cannot be seen in plan view are also shown with solid lines to make it easier to understand the shape of the target object.

[0023] The piezoelectric sensor 1 includes a plurality of piezoelectric elements 2 arranged in a matrix. In Fig. 1, 36 (=6 x 6) piezoelectric elements 2 are shown as an example.

[0024] The piezoelectric sensor 1 includes a substrate 10. The substrate 10 is provided over the entire piezoelectric sensor 1. The substrate 10 has a planar shape of, for example, a rectangle. The substrate 10 is made of an insulating material, for example, a resin having flexibility and / or stretchability. The substrate 10 is made of, for example, a polyimide resin, a polyethylene terephthalate (PET) resin, an epoxy resin, a polyurethane resin, a polyolefin resin, a polystyrene resin, or a polyester resin.

[0025] A plurality of piezoelectric elements 2 are provided on a substrate 10. Each piezoelectric element 2 includes a lower electrode 11, a conductive adhesive layer 12, a piezoelectric layer 13, and an upper electrode 14.

[0026] A lower electrode 11 is provided on the substrate 10. The planar shape of the lower electrode 11 is, for example, a quadrangle (typically a square). The lower electrode 11 is made of a metal material or an organic conductive material. Examples of the metal material include silver (Ag), silver paste, molybdenum (Mo), aluminum (Al), chromium (Cr), and an alloy containing one of these. Examples of the organic conductive material include PEDOT / PSS and carbon paste. PEDOT / PSS is a composite of poly(3,4-ethylenedioxythiophene) (PEDOT) and polystyrene sulfonate (PSS). The lower electrode 11 may be made of a material that includes the above material and has flexibility and / or stretchability. For example, the lower electrode 11 may be made of a mixture of a conductive material and a resin that has flexibility and / or stretchability. Wiring (not shown) is connected to each lower electrode 11, and this wiring is drawn out to the outside of the array area in which the multiple piezoelectric elements 2 are arranged. A voltage can be applied to the lower electrode 11 using this wiring.

[0027] A conductive adhesive layer 12 is provided on the lower electrode 11. The planar shape of the conductive adhesive layer 12 is, for example, a rectangle (typically a square). The conductive adhesive layer 12 has an area that is approximately the same as or slightly smaller than that of the lower electrode 11. The conductive adhesive layer 12 is conductive and has a function of bonding layers above and below it. The conductive adhesive layer 12 is formed by dispersing a plurality of conductive particles in a binder as an adhesive. A thermosetting resin, for example, an epoxy resin, is used as the binder. For the conductive particles, for example, silver (Ag) or gold (Au) is used. The conductive adhesive layer 12 is hardened by applying heat.

[0028] A piezoelectric layer 13 is provided on the conductive adhesive layer 12. The piezoelectric layer 13 is a material that has the property of generating a potential difference when a mechanical force is applied thereto, or generating a mechanical force when a voltage is applied thereto. The piezoelectric layer 13 is provided in common to the plurality of piezoelectric elements 2. The piezoelectric layer 13 is adhered to the plurality of conductive adhesive layers 12. The piezoelectric layer 13 has an area equal to or larger than the external area occupied by the plurality of piezoelectric elements 2. The planar shape of the piezoelectric layer 13 is, for example, a rectangle. A portion of the piezoelectric layer 13 that is sandwiched between the lower electrode 11 and the upper electrode 14 functions as the piezoelectric layer of one piezoelectric element 2. The piezoelectric layer 13 is made of, for example, an organic piezoelectric material. The piezoelectric layer 13 is made of a polymer piezoelectric material such as polyvinylidene fluoride (PVDF), polyvinylidene fluoride / trifluoroethylene copolymer (P(VDF / TrFE)), vinylidene cyanide / vinyl acetate copolymer (P(VDCN / VAc)), etc. In order to give elasticity to P(VDF / TrFE), acrylic resin (PMMA: polymethyl methacrylate) may be added to P(VDF / TrFE).

[0029] An upper electrode 14 is provided on the piezoelectric layer 13. The upper electrode 14 is provided in common to the multiple piezoelectric elements 2. The upper electrode 14 has an area equal to or larger than the external area occupied by the multiple piezoelectric elements 2. The planar shape of the upper electrode 14 is, for example, a rectangle. The upper electrode 14 can be made of the conductive materials listed above for the lower electrode 11. A wiring (not shown) is connected to the upper electrode 14, and this wiring is extended to the outside of the array area in which the multiple piezoelectric elements 2 are arranged. A voltage can be applied to the upper electrode 14 using this wiring.

[0030] A protective layer 15 is provided on the upper electrode 14. The protective layer 15 has an area covering the entire upper electrode 14. The planar shape of the protective layer 15 is, for example, a rectangle. The protective layer 15 is made of an insulating material, for example, a resin having flexibility and / or stretchability. The protective layer 15 is made of, for example, a polyimide resin, a polyethylene terephthalate (PET) resin, an epoxy resin, a polyurethane resin, a polyolefin resin, a polystyrene resin, or a polyester resin. The protective layer 15 is applied to an underlying layer by coating or by using an adhesive.

[0031] A heat insulating layer 17 is provided above the protective layer 15. The heat insulating layer 17 has the function of suppressing the transfer of heat to the piezoelectric elements 2. The heat insulating layer 17 has an area equal to or larger than the external area occupied by the multiple piezoelectric elements 2. For example, the heat insulating layer 17 has approximately the same area as the substrate 10. The planar shape of the heat insulating layer 17 is, for example, rectangular. The heat insulating layer 17 is made of an insulating material, and is made of rubber or resin. The heat insulating layer 17 is made of, for example, silicone rubber.

[0032] A plurality of protrusions 16 are provided between the protective layer 15 and the insulating layer 17. The plurality of protrusions 16 are arranged corresponding to the plurality of piezoelectric elements 2, respectively. Each of the protrusions 16 has a downwardly convex shape. The protrusions 16 have, for example, a hemispherical shape. The flat surface of the hemispherical protrusions 16 is bonded to the insulating layer 17. The tip of the convex portion of the protrusions 16 contacts the protective layer 15. In other words, the area of ​​the lower end of the protrusions 16 on the lower side (protective layer 15 side) is configured to be smaller than the area of ​​the upper end of the upper side (insulating layer 17 side).

[0033] The tip of the protrusion 16 and the protective layer 15 are not bonded, for example. As another configuration example, the tip of the protrusion 16 and the protective layer 15 may be bonded using an adhesive or double-sided tape. Each protrusion 16 is made of resin, for example, UV-cured resin. The diameter of the protrusion 16 (diameter of a circle seen in a plan view) is set to be the same as or slightly smaller than the length of one side of the lower electrode 11. When the lower electrode 11 is rectangular, the diameter of the protrusion 16 is set to be the same as or slightly smaller than the length of the short side of the lower electrode 11. In a plan view, the tip of the protrusion 16 is located at the center of the lower electrode 11.

[0034] It is desirable that the gap between adjacent protrusions 16 be equal to or less than the height of protrusions 16. By setting the height or thickness of protrusions 16 in this manner, it is possible to prevent heat insulating layer 17 from contacting protective layer 15 when heat insulating layer 17 is pressed and deformed.

[0035] The base material 10 and the heat insulating layer 17 are fixed together using a frame (not shown) configured to surround the periphery of the base material 10 and the heat insulating layer 17. The frame is made of, for example, a resin. Alternatively, the base material 10 and the heat insulating layer 17 may be fixed together around the periphery of the base material 10 and the heat insulating layer 17 using an adhesive.

[0036] [1-2] Operation The operation of the piezoelectric sensor 1 configured as above will be described.

[0037] The piezoelectric sensor 1 detects a force (pressure) applied from the side of the insulating layer 17. For example, an observer presses the insulating layer 17. This pressure includes pressure caused by the observer pressing with a finger and pressure caused by the movement of a part of the body to which the piezoelectric sensor 1 is attached.

[0038] In each piezoelectric element 2, pressure applied to the heat insulating layer 17 is applied to the protective layer 15 from the tip of the protrusion 16. Pressure applied from the protrusion 16 to the protective layer 15 is applied to the piezoelectric layer 13 of the piezoelectric element 2. The state of polarization in the piezoelectric layer 13 changes in response to the stress.

[0039] In each piezoelectric element 2, a fixed voltage (for example, ground voltage (0V)) is applied to the upper electrode 14, and the lower electrode 11 outputs an output voltage. A detection circuit (not shown) is connected to the lower electrode 11 via wiring, and this detection circuit detects the output voltage of the piezoelectric element 2. Based on the output voltage detected by the detection circuit, the pressure applied to the piezoelectric element 2 can be determined.

[0040] When an observer's finger touches the insulating layer 17, the insulating layer 17 suppresses the conduction of heat. This makes it possible to suppress the conduction of heat to the piezoelectric element 2. Furthermore, the protrusions 16 can suppress the conduction of heat from the insulating layer 17 to the piezoelectric element 2. The polarization state of the piezoelectric layer 13 changes due to heat in addition to stress. This makes it possible to suppress a decrease in the response speed of the piezoelectric element 2 caused by heat.

[0041] The tip of the protrusion 16 is located at the center of the piezoelectric element 2. The pressure applied to the heat insulating layer 17 is applied via the protrusion 16, centered on the center of the piezoelectric element 2. That is, the protrusion 16 can press the center of the piezoelectric element 2. This ensures that the pressure applied to the heat insulating layer 17 is applied to each piezoelectric element 2 more reliably, thereby improving the sensitivity of each piezoelectric element 2.

[0042] The characteristics of the piezoelectric sensor 1 of this embodiment and the first and second comparative examples will be described below.

[0043] First, the configurations of the first and second comparative examples will be described.

[0044] 3 is a partial cross-sectional view of a piezoelectric sensor according to a first comparative example. The layered structure from the substrate 10 to the protective layer 15 is the same as that of the piezoelectric element 2 of this embodiment. The piezoelectric sensor of the first comparative example does not include the multiple protrusions 16 and the heat insulating layer 17.

[0045] 4 is a partial cross-sectional view of a piezoelectric sensor according to a second comparative example. The layered structure from the substrate 10 to the protective layer 15 is the same as that of the piezoelectric element 2 of this embodiment. A heat insulating layer 17 is provided on the protective layer 15. The piezoelectric sensor of the second comparative example does not include a plurality of protrusions 16.

[0046] Fig. 5 is a graph illustrating the response characteristics of the piezoelectric element 2 according to this embodiment. The horizontal axis of Fig. 5 represents time (msec), and the vertical axis represents the output voltage (arbitrary unit) of the piezoelectric element 2. In this embodiment, a voltage is applied to the piezoelectric element such that the output voltage of the piezoelectric element becomes negative when the piezoelectric layer is compressed.

[0047] The downward spike-like signal in Figure 5 is the signal generated when the observer presses the piezoelectric element 2 with his / her finger. The upward spike-like signal in Figure 5 is the signal output due to the change in pressure when the observer removes his / her finger from the piezoelectric element 2.

[0048] In this embodiment, it is possible to accurately determine the timing when the piezoelectric element 2 is pressed with a finger and the timing when the finger is released from the piezoelectric element 2. In addition, after the finger is released from the piezoelectric element 2, the output voltage instantly returns to 0 V. In other words, the deterioration of the response speed due to heat is suppressed.

[0049] 6 is a graph illustrating the response characteristics of a piezoelectric element according to Comparative Example 1. In Comparative Example 1, the heat insulating layer 17 is not provided, and an observer presses the protective layer 15 with a finger.

[0050] In the first comparative example, the response speed of the piezoelectric element is degraded due to the heat of the finger being conducted to the piezoelectric element. Specifically, when the piezoelectric element 2 is pressed with a finger, the response speed of the downward spike-like signal is degraded. In addition, the signal strength is reduced when the finger is removed from the piezoelectric element 2. In addition, the voltage change when the output voltage returns to 0V is gradual. Furthermore, when the piezoelectric element is pressed with a finger multiple times in succession, the output voltage does not return to 0V.

[0051] Thus, it can be seen that in this embodiment, the response speed of the piezoelectric element 2 can be improved.

[0052] FIG. 7 is a diagram illustrating the signal distribution when the piezoelectric sensor 1 according to this embodiment is pressed with a finger. FIG. 7 shows data on an area of ​​35 (=5×7) piezoelectric elements with an element pitch (distance between the centers of the elements) of 2 mm. R1 to R5 in FIG. 7 indicate the number of rows in the piezoelectric element array, and C1 to C7 indicate the number of columns in the piezoelectric element array. The numbers on the right side of FIG. 7 are the voltages (arbitrary units) for each area. In the experiment of FIG. 7, the piezoelectric sensor is pressed with a protrusion with a contact part having a diameter of 2 mm.

[0053] In this embodiment, the pressure applied to the heat insulating layer 17 is applied to the center of the piezoelectric element 2 via the protrusion 16. Therefore, the pressure is applied to the piezoelectric element 2 more accurately, and the pressed position of the piezoelectric sensor 1 can be detected more accurately.

[0054] 8 is a diagram illustrating the signal distribution when the piezoelectric sensor according to the second comparative example is pressed with a finger. In the second comparative example, the observer presses the heat insulating layer 17 provided directly on the protective layer 15 with the protrusion. The other conditions are the same as those in FIG. 7.

[0055] In the second comparative example, the pressure is dispersed in the in-plane direction, making it difficult to accurately determine the position where the piezoelectric sensor is pressed.

[0056] In this manner, in this embodiment, it is possible to suppress the pressure from dispersing in the in-plane direction.

[0057] [1-3] Variations Next, several modified examples of the piezoelectric sensor 1 will be described.

[0058] (First Modification) 9 is a partial cross-sectional view of the piezoelectric sensor 1 according to the first modified example. The plan view corresponding to FIG. 9 is the same as FIG.

[0059] A piezoelectric layer 13 is provided on the substrate 10 and the multiple lower electrodes 11. The piezoelectric layer 13 is provided on the substrate 10 so as to cover the multiple lower electrodes 11. The piezoelectric layer 13 is provided in common to the multiple piezoelectric elements 2. The piezoelectric layer 13 is formed by a printing process. The configuration above the piezoelectric layer 13 is the same as that in FIG. 2.

[0060] According to the first modification, it is possible to omit the conductive adhesive layer 12. In addition, the thickness of the piezoelectric sensor 1 can be reduced.

[0061] (Second Modification) Fig. 10 is a plan view of the piezoelectric sensor 1 according to the second modified example, and Fig. 11 is a cross-sectional view of the piezoelectric sensor 1 taken along the line AA' in Fig. 10.

[0062] A plurality of piezoelectric layers 13 are provided on the plurality of lower electrodes 11, respectively. The plurality of piezoelectric layers 13 are provided on the substrate 10 so as to cover the plurality of lower electrodes 11, respectively. The plurality of piezoelectric layers 13 are provided corresponding to the plurality of piezoelectric elements 2, respectively. The planar shape of each piezoelectric layer 13 is, for example, a quadrangle (typically a square). The plurality of piezoelectric layers 13 are formed by a printing process.

[0063] A plurality of upper electrodes 14 are provided respectively on the plurality of piezoelectric layers 13. The planar shape of each of the upper electrodes 14 is, for example, a quadrangle (typically a square).

[0064] A protective layer 15 is provided on the multiple upper electrodes 14. The configuration above the protective layer 15 is the same as that in FIG.

[0065] According to the second modification, it is possible to prevent the pressure applied to the piezoelectric sensor 1 from dispersing in the in-plane direction.

[0066] (Third Modification) 12 is a partial cross-sectional view of the piezoelectric sensor 1 according to the third modified example. The plan view corresponding to FIG.

[0067] The heat insulating layer 17 and the plurality of protrusions 16 are integrally formed and made of the same material. The heat insulating layer 17 and the plurality of protrusions 16 are made of resin, for example, UV curable resin.

[0068] According to the third modified example, it is possible to simplify the manufacturing process of the heat insulating layer 17 and the plurality of protrusions 16. Note that the third modified example can also be applied to the above embodiment and other modified examples.

[0069] [1-4] Effects of the first embodiment In the first embodiment, the protrusion 16 and the heat insulating layer 17 are provided on the piezoelectric element 2. Therefore, according to the first embodiment, it is possible to suppress the heat applied to the heat insulating layer 17 from being conducted to the piezoelectric element 2. This makes it possible to suppress a decrease in the response speed of the piezoelectric element 2 caused by heat.

[0070] Furthermore, a plurality of protrusions 16 are disposed on each of the piezoelectric elements 2, and the lower tips of the plurality of protrusions 16 are in contact with the vicinity of the center of each of the piezoelectric elements 2. Therefore, the pressure applied to the heat insulating layer 17 is accurately applied to the piezoelectric elements 2 via the protrusions 16. This makes it possible to prevent the pressure from being dispersed in the in-plane direction of the piezoelectric sensor 1. Also, the position where the pressure is applied can be detected more accurately. As a result, a piezoelectric sensor 1 capable of improving the operating characteristics can be realized.

[0071] In addition, since the area of ​​the tip of the protrusion 16 is small, even if misalignment occurs between the piezoelectric element 2 and the protrusion 16, the tip of the protrusion 16 can be brought into contact with the area of ​​the piezoelectric element 2. This makes it possible to increase the margin for misalignment between the piezoelectric element 2 and the protrusion 16.

[0072] [2] Second embodiment In the second embodiment, the piezoelectric element 2 is configured so that the area of ​​the lower electrode 11 is smaller than the area of ​​the protrusion 16.

[0073] Fig. 13 is a plan view of a piezoelectric sensor 1 according to a second embodiment of the present invention. Fig. 14 is a cross-sectional view of the piezoelectric sensor 1 taken along line AA' in Fig. 13. The layered structure of each piezoelectric element 2 is the same as that in Fig. 2.

[0074] A lower electrode 11 is provided on the substrate 10. The planar shape of the lower electrode 11 is, for example, a quadrangle (typically a square). The area of ​​the lower electrode 11 is set to be smaller than the area of ​​the protrusion 16. In other words, the length of one side of the lower electrode 11 is set to be smaller than the diameter of the protrusion 16. When the lower electrode 11 is rectangular, the length of the longer side of the lower electrode 11 is set to be smaller than the diameter of the protrusion 16.

[0075] In addition, assuming that the heat insulating layer 17 is pressed and the protrusions 16 are compressed and deformed, it is desirable to set the area of ​​the lower electrode 11 to be equal to or slightly larger than the contact area between the protrusions 16 and the protective layer 15. In consideration of the deformation of the protrusions 16, it is desirable that the area of ​​the lower electrode 11 be ½ or less of the area of ​​the protrusions 16.

[0076] A conductive adhesive layer 12 is provided on the lower electrode 11. The conductive adhesive layer 12 has an area that is approximately the same as or slightly smaller than that of the lower electrode 11. The other configurations are the same as those in the first embodiment.

[0077] In the second embodiment, the area of ​​the piezoelectric element 2 is smaller compared to the area of ​​the protrusion 16. When the same pressure is applied to piezoelectric elements with different areas, the piezoelectric element with the smaller area will have a larger output voltage. Therefore, in the second embodiment, the output voltage of the piezoelectric element 2 can be made larger than in the first embodiment. Also, the sensitivity of the piezoelectric element 2 can be improved.

[0078] It is possible to apply the first to third modified examples described in the first embodiment to the second embodiment.

[0079] [3] Third embodiment The third embodiment is an example relating to the shape of the protrusion 16. The protrusion 16 may be a square prism, a cylinder, a cone, or a truncated cone. Several examples according to the third embodiment will be described below.

[0080] (First Example) Fig. 15 is a plan view of the piezoelectric sensor 1 according to the first example. Fig. 16 is a cross-sectional view of the piezoelectric sensor 1 taken along line AA' in Fig. 15. The layered structure from the substrate 10 to the protective layer 15 is the same as that of the first embodiment. In this embodiment, a configuration in which a piezoelectric layer 13 is provided on a lower electrode 11 will be described as a basic example, but the present invention is also applicable to examples including a conductive adhesive layer 12 and the layered structures of the other examples described above.

[0081] A plurality of protrusions 16 are provided between the protective layer 15 and the heat insulating layer 17 so as to correspond to the plurality of piezoelectric elements 2. Each of the protrusions 16 has a rectangular column shape. The area of ​​the protrusions 16 is set to be equal to or smaller than the area of ​​the lower electrode 11.

[0082] Alternatively, the projection 16 may be cylindrical.

[0083] According to the first embodiment, the contact area between the protrusion 16 and the piezoelectric element 2 can be increased.

[0084] (Second Example) 17 is a partial cross-sectional view of the piezoelectric sensor 1 according to the second embodiment. The plan view corresponding to FIG. 17 is the same as FIG.

[0085] Each of the multiple protrusions 16 has a downwardly convex cone shape. The diameter of the protrusions 16 is set to be approximately the same as the length of one side of the lower electrode 11. As a modified example, the protrusions 16 may be polygonal pyramids (including triangular pyramids and quadrangular pyramids).

[0086] According to the second embodiment, the contact area between the protrusion 16 and the piezoelectric element 2 is small, so that the margin for misalignment between the piezoelectric element 2 and the protrusion 16 can be increased.

[0087] (Third Example) 18 is a partial cross-sectional view of the piezoelectric sensor 1 according to the third embodiment. The plan view corresponding to FIG. 18 is the same as FIG.

[0088] Each of the plurality of protrusions 16 has a downwardly convex truncated cone shape. The diameter of the protrusions 16 is set to be approximately the same as the length of one side of the lower electrode 11.

[0089] According to the third embodiment, the contact area between the protrusion 16 and the piezoelectric element 2 can be increased, while the margin for misalignment between the piezoelectric element 2 and the protrusion 16 can be increased.

[0090] Other effects of the third embodiment are the same as those of the first embodiment.

[0091] [4] Fourth embodiment In the fourth embodiment, a plurality of protrusions 16 are arranged on one piezoelectric element 2.

[0092] Fig. 19 is a plan view of a piezoelectric sensor 1 according to a fourth embodiment of the present invention, and Fig. 20 is a cross-sectional view of the piezoelectric sensor 1 taken along line AA' in Fig. 19.

[0093] The piezoelectric sensor 1 includes a plurality of piezoelectric elements 2 arranged in a matrix. In Fig. 19, nine (=3 x 3) piezoelectric elements 2 are shown as an example. The laminated structure from the substrate 10 to the protective layer 15 is the same as that of the first embodiment. In this embodiment, a configuration example in which a conductive adhesive layer 12 is provided on a lower electrode 11 will be described, but the laminated structure of the other examples described above can also be applied.

[0094] A plurality of protrusions 16 are provided between the protective layer 15 and the heat insulating layer 17. Four protrusions 16-1 to 16-4 are arranged on one piezoelectric element 2. Each of the protrusions 16-1 to 16-4 has a downwardly convex hemispherical shape. In a plan view, the four protrusions 16-1 to 16-4 are arranged on the inner side of the lower electrode 11. The other configurations are the same as those in the first embodiment.

[0095] The number of protrusions 16 arranged corresponding to one piezoelectric element 2 is not limited to four, but may be set to any number equal to or greater than two.

[0096] According to the fourth embodiment, when the area of ​​one piezoelectric element 2 is large, the thickness of the piezoelectric sensor 1 can be reduced compared to the case where one large-sized protrusion is disposed. The other effects are the same as those of the first embodiment.

[0097] The present invention is not limited to the above-mentioned embodiment, and various modifications can be made in the implementation stage without departing from the gist of the invention. In addition, the embodiments may be implemented in appropriate combination, and in that case, the combined effect can be obtained. Furthermore, the above-mentioned embodiment includes various inventions, and various inventions can be extracted by combinations selected from the multiple components disclosed. For example, if the problem can be solved and the effect can be obtained even if some components are deleted from all the components shown in the embodiment, the configuration from which the components are deleted can be extracted as an invention. [Explanation of symbols]

[0098] 1...piezoelectric sensor, 2...piezoelectric element, 10...substrate, 11...lower electrode, 12...conductive adhesive layer, 13...piezoelectric layer, 14...upper electrode, 15...protective layer, 16...protrusion, 17...thermal insulation layer.

Claims

1. A substrate; A plurality of piezoelectric elements provided on the substrate, each of which includes a lower electrode, a piezoelectric layer, and an upper electrode that are stacked in that order; a protective layer provided on the plurality of piezoelectric elements; a plurality of protrusions provided on the protective layer and arranged to correspond to the plurality of piezoelectric elements, respectively; A heat insulating layer provided on the plurality of protrusions; Equipped with Each of the plurality of protrusions is configured such that the area of ​​the lower end portion on the protective layer side is smaller than the area of ​​the upper end portion on the thermal insulation layer side. Piezoelectric sensor.

2. The protrusion has a semi-spherical shape. The piezoelectric sensor according to claim 1 .

3. the bottom electrode has a rectangular shape; The diameter of the protrusion is equal to or smaller than the length of one side of the lower electrode. The piezoelectric sensor according to claim 2 .

4. the bottom electrode has a rectangular shape; The area of ​​the lower electrode is smaller than the area of ​​the protrusion. The piezoelectric sensor according to claim 1 .

5. a conductive adhesive layer disposed between the lower electrode and the piezoelectric layer; The piezoelectric layer is provided in common to the plurality of piezoelectric elements. The piezoelectric sensor according to claim 1 .

6. The piezoelectric layer is provided on the substrate so as to cover the lower electrode, and is provided in common to the plurality of piezoelectric elements. The piezoelectric sensor according to claim 1 .

7. The upper electrode is provided in common to the plurality of piezoelectric elements. The piezoelectric sensor according to claim 1 .

8. The heat insulating layer and the plurality of protrusions are integrally formed. The piezoelectric sensor according to claim 1 .

9. The protrusion is adhered to the protective layer. The piezoelectric sensor according to claim 1 .

10. The piezoelectric layer is an organic piezoelectric layer. The piezoelectric sensor according to claim 1 .

11. The substrate is flexible. The piezoelectric sensor according to claim 1 .

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