Piezoelectric element

Abstract

To provide a piezoelectric element which surely performs an electric connection to an electrode layer.SOLUTION: A piezoelectric element includes: a piezoelectric layer; electrode layers formed on both surfaces of the piezoelectric layer; and a protection layer that is laminated on a surface opposite to a surface on a polymer composite piezoelectric body of the electrode layer. The protection layer includes a pore part penetrated from the front surface to the electrode layer, and includes: a filling member that is formed from the inside of the pore part to a part of the front surface of the protection layer, electrically connected to the electrode layer, and made of a conductive material; a conductive member that covers at least a part of the filling member, and is electrically connected to the filling member; and a fixing member that fixes the conductive member.SELECTED DRAWING: Figure 3

Description

[Technical field]

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

[0002] As displays such as liquid crystal displays and organic electroluminescence displays become thinner, speakers used in these thin displays are also required to be lighter and thinner. Furthermore, flexible displays are also required to be flexible so that they can be integrated into the flexible display without losing their lightness and flexibility. As a lightweight, thin, and flexible speaker, it has been considered to use a sheet-shaped piezoelectric element (electroacoustic conversion film) that has the property of expanding and contracting in response to an applied voltage.

[0003] As such a flexible sheet-like piezoelectric element, a piezoelectric element having an electrode layer and a protective layer on both sides of a piezoelectric layer has been proposed.

[0004] For example, Patent Document 1 describes an electroacoustic conversion film having a dielectric layer, thin-film electrodes formed on both sides of the dielectric layer (piezoelectric layer), and protective layers formed on the surfaces of both thin-film electrodes, and at least one of the protective layers has a thin portion that is thinner than the surrounding portions.

[0005] In such an electroacoustic converter film, in order to apply a voltage to the electrode layer to vibrate the electroacoustic converter film, the thickness of the electrode layer needs to be very thin. For example, a vapor deposition film with a thickness of 1 μm or less is suitable for the electrode layer.

[0006] On the other hand, in order to mount the electroacoustic converter film as a speaker or the like, it is necessary to extend the electrode layer and connect wiring thereto. However, it is difficult to pull out a thin electrode layer such as a vapor-deposited film outside the surface of the electroacoustic converter film. Also, if a thin electrode such as a vapor-deposited film is exposed to the outside for connection to wiring and stored in this state, the electrode may oxidize depending on the storage environment, resulting in a decrease in conductivity.

[0007] In response to this, it has been proposed to provide a hole in the protective layer, insert a conductive material into the hole, and connect a lead wire to the conductive material.

[0008] For example, Patent Document 1 describes a configuration in which a recess is provided in a protective layer, a conductive material is inserted into the recess, and a lead-out wiring for electrically connecting the electrode layer to an external device is connected to the conductive material. This ensures a reliable electrical connection between the electrode layer and the lead-out wiring, and also describes that since the electrode layer is entirely covered with the protective layer, deterioration of the electrode layer due to oxidation or the like can be prevented. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] JP 2016-015354 A Summary of the Invention [Problem to be solved by the invention]

[0010] However, according to the study by the present inventors, when a coating solution of a liquid conductive material is applied to the holes provided in the protective layer, the coating thickness may vary depending on the viscosity of the coating solution, making it difficult to ensure conductivity. In addition, since the protective layer is thin, for example, about 4 μm, the depth of the holes provided in the protective layer is about 4 μm, and considering warping of the electroacoustic conversion film, it is difficult to reliably apply the coating solution on the holes. Therefore, there is a risk that electrical connection to the electrode layer cannot be reliably established. In addition, because the silver paste used as the conductive material is expensive, there is a desire to reduce its amount, and it is difficult to increase the amount of conductive material used and ensure that the conductive material is present in the hole.

[0011] An object of the present invention is to solve such problems in the prior art and to provide a piezoelectric element that can be reliably electrically connected to an electrode layer. [Means for solving the problem]

[0012] In order to solve the above-mentioned problems, the present invention has the following configuration. [1] A piezoelectric element having a piezoelectric layer, electrode layers formed on both sides of the piezoelectric layer, and a protective layer laminated on a surface of the electrode layer opposite to the surface of the piezoelectric layer, the protective layer has a hole penetrating from the surface to the electrode layer, a filler member made of a conductive material, the filler member being formed on a part of the surface of the protective layer from within the hole and electrically connected to the electrode layer; a conductive member covering at least a portion of the filling member and electrically connected to the filling member; A piezoelectric element having a fixing member that fixes the conductive member. [2] The piezoelectric element according to [1], wherein the conductive member is a conductive sheet. [3] The piezoelectric element according to [1], wherein the conductive member has a conductor connected to the filling member and a conductive wire or a conductive sheet connected to the conductor. [4] The piezoelectric element according to any one of [1] to [3], wherein the fixing member fixes the conductive member to the protective layer. [5] The piezoelectric element according to any one of [1] to [4], wherein the protective layer has a convex portion formed on the periphery of the hole. [6] The piezoelectric element according to any one of [1] to [5], wherein the hole has a circular equivalent diameter that changes stepwise in the depth direction, and the circular equivalent diameter on the electrode layer side is smaller than the circular equivalent diameter on the conductive member side. [7] The piezoelectric element according to any one of [1] to [6], wherein the amount of carbon in the surface of the electrode layer within the hole is less in the central portion in the surface direction than in the other regions. [8] The piezoelectric element according to any one of [1] to [7], wherein the amount of carbon on the surface of the electrode layer within the hole is greater in the central portion in the surface direction than in the other regions. [9] The piezoelectric element according to any one of [1] to [8], wherein the opening shape of the hole is circular.

[10] The protective layer has a plurality of holes, The piezoelectric element according to any one of [1] to [9], comprising a plurality of filling members formed in the respective holes.

[11] The piezoelectric element according to

[10] , wherein the multiple filling members are connected to each other on the surface of the protective layer.

[12] A surrounding member that surrounds the hole is provided on the surface of the protective layer, The piezoelectric element according to any one of [1] to

[11] , wherein the filling member is formed at least inside the enclosing member.

[13] The piezoelectric element according to any one of [1] to

[12] , wherein the protective layer has a recess formed around the hole.

[14] The piezoelectric element according to any one of [1] to

[13] , wherein the protective layer has a thickness of 3 μm to 100 μm.

[15] The piezoelectric element according to any one of [1] to

[14] , wherein the electrode layer has a thickness of 0.05 μm to 10 μm.

[16] A gap is provided between the electrode layer and the piezoelectric layer at the position of the hole, The piezoelectric element according to any one of [1] to

[15] , wherein the difference between the average height of the interface between the piezoelectric layer and the electrode layer at positions where no holes are formed and the average height of the interface between the piezoelectric layer and the electrode layer at positions where the holes are formed is 25 μm or less.

[17] The conductive member has an elongated shape, The conductive member has a folded portion folded back in the longitudinal direction, The piezoelectric element according to any one of [1] to

[16] , wherein the fixing member fixes the conductive member and the protective layer in an area opposite to the connection position between the conductive member and the filling member, across the folded portion.

[18] The conductive member has an elongated shape, The conductive member is connected to the filling member at one end side in the longitudinal direction, The piezoelectric element according to any one of [1] to

[17] , wherein the fixing member is disposed at a position in the longitudinal direction of the conductive member farther from one end than a connection position between the conductive member and the filling member.

[19] A piezoelectric element according to

[18] , further comprising a second fixing member for fixing at least a portion of a peripheral portion of a region between one end of the conductive member and the fixing member to the protective layer.

[20] The piezoelectric element according to any one of [1] to

[19] , wherein the piezoelectric layer is made of a polymer composite piezoelectric material containing piezoelectric particles in a matrix containing a polymer material. Effect of the Invention

[0013] According to the present invention, there is provided a piezoelectric element that can ensure reliable electrical connection to the electrode layer. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a cross-sectional view illustrating a schematic example of a piezoelectric element of the present invention. [Diagram 2] FIG. 2 is a plan view of the piezoelectric element of FIG. [Diagram 3] 2 is an enlarged cross-sectional view showing a part of the piezoelectric layer of FIG. 1. [Figure 4] FIG. 4 is a partially enlarged cross-sectional view of another example of the piezoelectric element of the present invention. [Diagram 5] FIG. 4 is a partially enlarged cross-sectional view of another example of the piezoelectric element of the present invention. [Figure 6] FIG. 4 is a partially enlarged cross-sectional view of another example of the piezoelectric element of the present invention. [Figure 7] FIG. 4 is a partially enlarged cross-sectional view of another example of the piezoelectric element of the present invention. [Figure 8] FIG. 4 is a partially enlarged cross-sectional view of another example of the piezoelectric element of the present invention. [Figure 9] FIG. 4 is a partially enlarged cross-sectional view of another example of the piezoelectric element of the present invention. [Figure 10] FIG. 2 is a conceptual diagram for explaining the average height of an interface. [Figure 11]FIG. 4 is a partially enlarged cross-sectional view of another example of the piezoelectric element of the present invention. [Figure 12] FIG. 4 is a partially enlarged plan view of another example of the piezoelectric element of the present invention. [Figure 13] FIG. 4 is a partially enlarged plan view of another example of the piezoelectric element of the present invention. [Figure 14] 1A to 1C are conceptual diagrams for explaining an example of a method for producing a piezoelectric element. [Figure 15] 1A to 1C are conceptual diagrams for explaining an example of a method for producing a piezoelectric element. [Figure 16] 1A to 1C are conceptual diagrams for explaining an example of a method for producing a piezoelectric element. [Figure 17] 1A to 1C are conceptual diagrams for explaining an example of a method for producing a piezoelectric element. [Figure 18] 1A to 1C are conceptual diagrams for explaining an example of a method for producing a piezoelectric element. [Figure 19] 1A to 1C are conceptual diagrams for explaining an example of a method for producing a piezoelectric element. [Figure 20] FIG. 4 is a partially enlarged cross-sectional view of another example of the piezoelectric element of the present invention. [Figure 21] FIG. 4 is a partially enlarged cross-sectional view of another example of the piezoelectric element of the present invention. [Figure 22] FIG. 1 is a schematic diagram of an example of an article including a piezoelectric element of the present invention. [Diagram 23] FIG. 4 is a partially enlarged cross-sectional view of another example of the piezoelectric element of the present invention. [Figure 24] FIG. 4 is a partially enlarged cross-sectional view of another example of the piezoelectric element of the present invention. [Diagram 25] FIG. 25 is a top view of FIG. 24. [Figure 26] FIG. 4 is a partially enlarged cross-sectional view of another example of the piezoelectric element of the present invention. [Figure 27] FIG. 4 is a partially enlarged cross-sectional view of another example of the piezoelectric element of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the piezoelectric element of the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings.

[0016] The following description of the components may be based on representative embodiments of the present invention, but the present invention is not limited to such embodiments. In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits.

[0017] [Piezoelectric element] The piezoelectric element of the present invention is A piezoelectric element having a piezoelectric layer, electrode layers formed on both sides of the piezoelectric layer, and a protective layer laminated on a surface of the electrode layer opposite to the surface on which the piezoelectric layer is disposed, the protective layer has a hole penetrating from the surface to the electrode layer, a filler member made of a conductive material, the filler member being formed on a part of the surface of the protective layer from within the hole and electrically connected to the electrode layer; a conductive member covering at least a portion of the filling member and electrically connected to the filling member; and a fixing member for fixing the conductive member.

[0018] In the piezoelectric element of the present invention, the conductive member may be a conductive sheet such as copper foil. Alternatively, the conductive member may be a combination of a plurality of conductive members. For example, a configuration having a conductor and a conductive wire or conductive sheet connected to the conductor is exemplified.

[0019] In the piezoelectric element of the present invention, the fixing member fixes the conductive member to a predetermined location. The fixing member may fix the conductive member to a protective layer, or may fix the conductive member to another location of the piezoelectric element. Alternatively, the fixing member may fix the conductive member to another member. For example, as shown in FIG. 22, when the piezoelectric element 10 is fixed to the vibration plate 100, the fixing member 74 may fix the conductive member 72 to the vibration plate 100.

[0020] Fig. 1 conceptually shows a cross-sectional view of an example of a piezoelectric element of the present invention. Fig. 2 shows a plan view of the piezoelectric element of Fig. 1 seen from above. Fig. 3 shows an enlarged cross-sectional view of a portion of the piezoelectric element of Fig. 1.

[0021] The piezoelectric element 10 shown in Figures 1 to 3 has a piezoelectric layer 20 which is a sheet-like material having piezoelectric properties, a lower electrode 24 laminated on one side of the piezoelectric layer 20, a lower protective layer 28 laminated on the lower electrode 24, an upper electrode 26 laminated on the other side of the piezoelectric layer 20, an upper protective layer 30 laminated on the upper electrode 26, a filling member 70, a conductive member 72, and a fixing member 74.

[0022] 1 includes piezoelectric particles 36 in a matrix 34 containing a polymer material. The lower electrode 24 and the upper electrode 26 are electrode layers in the present invention. The lower protective layer 28 and the upper protective layer 30 are protective layers in the present invention. As will be described later, the piezoelectric element 10 (piezoelectric layer 20) is preferably polarized in the thickness direction.

[0023] Here, the piezoelectric element of the present invention has a hole in the protective layer, a filling member formed in the hole, a conductive member connected to the filling member, and a fixing member for fixing the conductive member. This will be described with reference to Fig. 3. Note that Fig. 3 is an enlarged view of a portion of the upper protective layer 30 side, but the lower protective layer 28 side also has a similar configuration. In the following description, the upper protective layer 30 and upper electrode 26 side will be used as an example.

[0024] 3, the upper protective layer 30 has a hole 31 penetrating from the surface to the upper electrode 26. That is, the hole 31 is formed penetrating the upper protective layer 30 from the surface opposite the upper electrode 26 to the interface on the upper electrode 26 side. As shown in FIGS. 1 and 2, the hole 31 is formed near the end of the upper protective layer 30 in the surface direction.

[0025] 3, as a preferred embodiment, a protrusion 32 is formed on the periphery of the hole 31. The protrusion 32 is formed in a substantially annular shape on the periphery of the hole 31 so as to surround the hole 31.

[0026] The filling member 70 is made of a conductive material, and is formed to fill the hole 31 and cover a part of the surface of the upper protective layer 30. Hereinafter, the portion of the filling member 70 protruding from the hole 31 is also referred to as a protruding portion 71. The filling member 70 contacts the upper electrode 26 in the hole 31 and is electrically connected to the upper electrode 26. In the example shown in FIG. 3, the upper protective layer 30 has a convex portion 32, but the protruding portion 71 of the filling member 70 is formed from the hole 31 to the outside of the convex portion 32.

[0027] The conductive member 72 is disposed so as to cover at least a portion of the filling member 70, and is electrically connected to the filling member 70. In the illustrated example, the conductive member 72 is disposed so as to cover the entire surface of the filling member 70 when viewed from a direction perpendicular to the surface of the upper protective layer 30. 1 and 2, the conductive member 72 is an elongated conductive sheet, and one end of the conductive member 72 in the longitudinal direction is connected to the filling member 70. The conductive member 72 is disposed such that the other end of the conductive member 72 in the longitudinal direction extends to the outside of the upper protective layer 30 in the planar direction.

[0028] The fixing member 74 fixes the conductive member 72 and the upper protective layer 30 at a position of the conductive member 72 that does not cover the filling member 70. In the example shown in FIG. 3, the fixing member 74 is disposed at a position farther from the end of the conductive member 72 on the filling member 70 side than the connection position of the conductive member 72 and the filling member 70 in the longitudinal direction of the conductive member 72. Also, the fixing member 74 is disposed between the connection position of the conductive member 72 and the filling member 70 and the end side of the upper protective layer 30 in the longitudinal direction of the conductive member 72. Also, in the illustrated example, the fixing member 74 is disposed between the upper protective layer 30 and the conductive member 72, and bonds the upper protective layer 30 and the conductive member 72.

[0029] As described above, in the piezoelectric element 10, the conductive member 72 is electrically connected to the filling member 70, and the filling member 70 is electrically connected to the upper electrode 26, so that the conductive member 72 can be used as a lead-out wiring, and wiring can be connected to the conductive member 72.

[0030] Here, as described above, when a coating solution of a liquid conductive material is applied to the holes provided in the protective layer, the coating thickness may vary depending on the viscosity of the coating solution, making it difficult to ensure conductivity. In addition, since the protective layer is thin, for example, about 4 μm, the depth of the holes provided in the protective layer is about 4 μm, and considering warping of the electroacoustic conversion film, it is difficult to reliably apply the coating solution on the holes. In addition, since the silver paste used as the conductive material is expensive, there is a demand to reduce the amount used, and it is difficult to increase the amount of the conductive material used to ensure that the conductive material is present in the holes.

[0031] In contrast, the piezoelectric element of the present invention has a hole in the protective layer, a filling member formed in the hole, a conductive member covering the filling member, and a fixing member fixing the conductive member and the protective layer. In a piezoelectric element having such a configuration, the filling member is formed by applying a coating liquid of a conductive material to the hole provided in the protective layer, covering the coating liquid with the conductive member, and then drying and curing the coating liquid. When the conductive member is applied to cover the coating liquid, the fixing member fixes the conductive member and the protective layer, so that the position of the conductive member can be prevented from shifting when the coating liquid is not cured. In addition, by covering the coating liquid with the conductive member, the coating liquid can be prevented from moving from above the hole, and the filling member can be reliably present in the hole. Therefore, the piezoelectric element of the present invention can reliably perform electrical connection between the conductive member 72 and the filling member 70, and electrical connection between the filling member 70 and the upper electrode 26. Furthermore, since the filling material can be reliably present in the holes, there is no need to increase the amount of conductive material used.

[0032] Here, there is no limitation on the shape of the opening surface of the hole 31, and various shapes such as a circle, an ellipse, a rectangle, a polygon, an irregular shape, etc. From the viewpoint of ease of formation, etc., a circle is preferable. The size of the opening surface of the hole 31 is not particularly limited as long as it can ensure electrical connection with the filling member 70 and allow the piezoelectric element to operate properly. The equivalent circle diameter of the opening surface of the hole 31 is preferably 0.5 mm to 20 mm, more preferably 1.5 mm to 5 mm, and even more preferably 2 mm to 3 mm.

[0033] Furthermore, the height of the portion of the filling member 70 protruding from the hole 31 (height from the surface of the upper protective layer 30, hereinafter also referred to as "height of the filling member") is not particularly limited as long as it ensures electrical connection with the conductive member 72. The height of the filling member is preferably 2 μm to 200 μm, more preferably 10 μm to 100 μm, and further preferably 20 μm to 50 μm.

[0034] Furthermore, the size (size in the planar direction) of the protruding portion 71 of the filling member 70 is not particularly limited as long as it can ensure electrical connection with the conductive member 72. The circle equivalent diameter of the protruding portion 71 is preferably 1 mm to 40 mm, more preferably 2 mm to 30 mm, and further preferably 2 mm to 20 mm.

[0035] 3, the upper protective layer 30 has a configuration having a protrusion 32 on the periphery of the hole 31, but is not limited thereto, and may have a configuration not having the protrusion 32. By having the protrusion 32, the depth of the hole 31 can be made deeper than the thickness of the upper protective layer 30, making it easier for the conductive material coating liquid to accumulate, and ensuring the contact area between the filling member 70 and the upper electrode 26, and between the filling member 70 and the conductive member 72.

[0036] The height of the protrusions 32 is preferably 0.2 μm to 100 μm, more preferably 0.5 μm to 50 μm, and further preferably 0.7 μm to 10 μm.

[0037] Here, in the example shown in FIG. 3, a configuration is provided with one hole 31 and one filling member 70, but this is not limited thereto, and a plurality of holes 31 and filling members 70 may be provided.

[0038] For example, in the example shown in FIG. 4, there are two holes 31, and two filling members 70 are disposed in each of the two holes 31. The two holes 31 are arranged adjacent to each other in the longitudinal direction of the conductive member 72. The two filling members 70 are filled in the holes 31 in the same manner as the above-mentioned filling members, and are formed so as to cover up to a part of the surface of the upper protective layer 30. The conductive member 72 is disposed so as to cover the two filling members 70 disposed in the two holes 31. In addition, the two filling members 70 are connected by their protruding portions 71 on the surface of the upper protective layer 30.

[0039] 5 has five holes 31 arranged in a cross shape, and a filling member 70 is arranged in each of the five holes 31. The filling members 70 are integrated with each other by connecting their protruding portions 71 on the surface of the upper protective layer 30. The protruding portions 71 of the filling members 70 are formed to entirely cover the inner region surrounded by the five holes 31 on the surface of the upper protective layer 30.

[0040] When the piezoelectric element has a configuration including a plurality of filling members 70, it is sufficient that at least one filling member 70 has a protruding portion 71, but it is preferable that all filling members 70 have a protruding portion 71.

[0041] The piezoelectric element of the present invention may have a configuration in which a surrounding member is provided on the surface of the protective layer to surround the periphery of the hole, and the filling member is formed inside the surrounding member. 6, the surface of the upper protective layer 30 has an enclosing member 76 surrounding the hole 31 on the outer periphery side of the hole 31 and the protrusion 32. A protruding portion 71 of the filling member 70 is present in the area surrounded by the enclosing member 76. In addition, the upper surface of the enclosing member 76 (the surface opposite to the upper protective layer 30 side) is covered with a conductive member 72.

[0042] The surrounding member 76 is, for example, a circular ring-shaped member, and has a height (thickness) greater than the protrusion 32. In order to configure the filling member 70 formed inside the surrounding member 76 and the conductive member 72 to be in contact with each other, it is preferable that the height of the surrounding member 76 is equal to or less than the height of the filling member 70.

[0043] By providing the surrounding member 76, it is possible to prevent the coating liquid of the conductive material from moving out of the hole 31 when the coating liquid is applied, and it is possible to ensure that the filling member 70 is present at the position of the hole 31.

[0044] The shape of the opening of the surrounding member 76 is not limited to a circular shape, but may be various shapes such as an elliptical shape, a rectangular shape, a polygonal shape, or an irregular shape. Furthermore, when the upper protective layer 30 has multiple holes 31, it may have multiple surrounding members 76 arranged at the positions of the holes 31, or it may be configured to have one surrounding member 76 large enough to surround the multiple holes 31.

[0045] The size (diameter) and height of the surrounding member 76 may be appropriately set according to the size of the hole 31, the height of the protrusion 32, the size and height of the protruding portion 71 of the filling member 70, and the like. The enclosing member 76 has a circle equivalent diameter of preferably 3 mm to 60 mm, more preferably 5 mm to 50 mm, and further preferably 5 mm to 40 mm. The height of the surrounding member 76 is preferably 0.01 mm to 1 mm, more preferably 0.1 mm to 0.5 mm, and even more preferably 0.1 mm to 0.3 mm.

[0046] The surrounding member 76 is preferably bonded to the upper protective layer 30 with an adhesive or the like, and is also preferably bonded to the conductive member 72 with an adhesive or the like.

[0047] The piezoelectric element of the present invention may have a recess formed around the hole in the protective layer. 7, the surface of the upper protective layer 30 has a recess 33 around the hole 31 on the outer periphery side of the hole 31 and the protrusion 32. A protruding portion 71 of the filling member 70 exists within the recess 33. By having the recess 33, when a coating liquid of a conductive material is applied, the coating liquid can be kept at the position of the hole 31, and the filling member 70 can be reliably present at the position of the hole 31.

[0048] When the upper protective layer 30 has the protrusions 32, the recesses 33 are formed on the outer periphery side of the protrusions 32. When the upper protective layer 30 has the surrounding member 76, the recesses 33 are formed inside the surrounding member 76.

[0049] The depth of the recess 33 from the surface of the upper protective layer 30 is preferably 0.1 μm to 3 μm, more preferably 0.5 μm to 2 μm, and further preferably 1 μm to 2 μm.

[0050] Here, it is preferable that the hole has a circular equivalent diameter that changes stepwise in the depth direction, and the circular equivalent diameter on the electrode layer side is smaller than the circular equivalent diameter on the conductive member side. 8, the size of the hole 31 changes halfway in the depth direction, and the equivalent circle diameter D2 in the region on the upper electrode 26 side is smaller than the equivalent circle diameter D1 in the region on the front surface side (conductive member side). Note that the conductive member is not shown in FIG.

[0051] As will be described in detail later, the holes formed in the protective layer are formed by laser processing. Heat is generated during the laser processing, and the protective layer, piezoelectric layer, etc. near the holes become hot, so the electrode layer at the position of the holes is heated and its strength is likely to decrease. In particular, the electrode layer is likely to be damaged at the boundary between the holes and the protective layer.

[0052] In response to this, by reducing the size of the holes in the region on the electrode layer side, the electrode layer can be prevented from being heated and the strength of the electrode layer can be prevented from decreasing, and by increasing the size of the holes in the region on the surface side, the coating liquid of the conductive material can be appropriately retained within the holes when the coating liquid is applied.

[0053] In addition, when a hole is formed in the protective layer by laser processing, the electrode layer and the piezoelectric layer expand due to heat, but since the electrode layer and the piezoelectric layer have different thermal expansion coefficients and thermal conductivities, a void may be formed between the electrode layer and the piezoelectric layer in the hole due to expansion due to heating and contraction due to cooling. In particular, since heat is likely to be trapped in the center of the hole, a void is likely to be formed in the center.

[0054] For example, as shown in FIG. 9, the piezoelectric layer 20 is deformed to form a void 80. In FIG. 9, the filling member 70 and the conductive member 72 are omitted.

[0055] If such a gap 80 is present, the relative dielectric constant between the electrode layers changes, and there is a risk of the performance of the piezoelectric element being degraded. On the other hand, the difference d between the average height of the interface between the piezoelectric layer and the electrode layer at positions where no holes are formed and the average height of the interface between the piezoelectric layer and the electrode layer at positions where the holes are formed is preferably 25 μm or less, more preferably 0 μm to 20 μm, and even more preferably 0 μm to 15 μm. Also, this difference d is preferably 50% or less of the average thickness of the piezoelectric layer, more preferably 0% to 40%, and even more preferably 0% to 30%.

[0056] The method for measuring this difference d will be described with reference to FIG. The piezoelectric layer, including the positions of the holes, is cut to the desired size and embedded in epoxy resin or the like and hardened. Next, the piezoelectric layer in the resin is cut using a focused ion beam (FIB) or the like to expose the cross section of the piezoelectric layer. This cross section is observed using an optical microscope or the like, and the boundary line (interface) between the piezoelectric layer and the electrode layer, which is about 40 mm long, is converted into a curve formula using image conversion software. The interface between the piezoelectric layer and the electrode layer has roughness as shown in Figure 10.

[0057] In this cross section, the arithmetic mean roughness Ra, etc. of the boundary line in the part other than the hole is calculated by image analysis for about 10 cut surfaces, and the average value is calculated to calculate the average height d0 of the interface of the piezoelectric layer in the part other than the hole. Similarly, the average height d1 of the interface of the piezoelectric layer is calculated from the image analysis of the boundary line in the hole portion. The difference between the calculated average height d0 and the average height d1 is calculated to obtain the difference d in average height. Specifically, the average height is determined for the portion other than the hole using the average height (Rc) of the roughness curve element as specified in JIS B 0601-2001. At that time, the average height d0 of the interface on the left and right sides of the hole is calculated for the cross-sectional curve. Similarly, the average height d1 of the interface of the piezoelectric layer is calculated from image analysis of the boundary line in the hole portion. The larger deviation between d1 and d0 on the left and right is set to d.

[0058] In addition, when holes are formed in the protective layer by laser processing, the protective layer may not be completely removed, and a residue of the protective layer may remain on the surface of the electrode layer. The residue of the protective layer may be unevenly distributed on the surface of the electrode layer depending on the conditions of the laser processing, etc. For example, the center of the hole is likely to have less residual protective layer than the peripheral area because heat is likely to be trapped there during laser processing. On the other hand, depending on the laser processing conditions, it is possible to have more residual protective layer in the center of the hole and less in the peripheral area.

[0059] A configuration in which the residue of the protective layer is less in the center of the hole than in the peripheral area ensures electrical connection between the filling member and the electrode layer in the center and suppresses a decrease in strength of the electrode layer in the peripheral area. On the other hand, in a configuration in which the residual protective layer in the center of the hole is greater than in the peripheral areas, heat can be prevented from building up in the center during laser processing, thereby preventing the occurrence of the above-mentioned void and suppressing changes in the dielectric constant.

[0060] In addition, since the protective layer is made of a resin film such as polyethylene terephthalate (PET), the residue of the protective layer contains carbon. Therefore, when measuring the amount of the residue of the protective layer on the surface of the electrode layer, it is sufficient to measure the amount of carbon on the surface of the electrode layer. The amount of carbon on the surface of the electrode layer can be determined by peeling the conductive member from the piezoelectric element, etching the surface of the filling member while performing elemental analysis using XPS (X-ray photoelectron spectroscopy) to observe the presence or absence of carbon.

[0061] That is, a configuration in which the protective layer residue is less in the center of the hole than in the peripheral area is a configuration in which the carbon amount on the surface of the electrode layer in the hole is less in the center in the planar direction than in the area other than the center, and a configuration in which the protective layer residue is more in the center of the hole than in the peripheral area is a configuration in which the carbon amount on the surface of the electrode layer in the hole is more in the center in the planar direction than in the area other than the center.

[0062] The central part of the hole is a region with an area of ​​1 / 16 of the area of ​​the hole, centered on the center of gravity of the hole in the surface direction. The peripheral part is the region other than the central part. The amount of residue of the protective layer is the average value of measurements at 10 points in this range.

[0063] Here, the piezoelectric element of the present invention may be configured such that the conductive member has an elongated shape, the conductive member has a folded portion that is folded back in the longitudinal direction, and the fixing member fixes the conductive member and the protective layer in an area opposite to the connection position between the conductive member and the filling member, sandwiching the folded portion. This configuration will be described with reference to FIG.

[0064] FIG. 11 is an enlarged cross-sectional view showing a part of another example of the piezoelectric element of the present invention. In FIG. 11, except for the shape of the conductive member 72, the piezoelectric element has the same configuration as that shown in FIG. 3, and therefore the following description will mainly focus on the differences.

[0065] In FIG. 11, conductive member 72 is folded back in the longitudinal direction, and one area on either side of folded portion 73 is region 72a and the other area is region 72b. One side of region 72a is connected to filling member 70, and one side of region 72b is connected to fixing member 74. That is, the region 72b of the conductive member 72 fixed to the upper protective layer 30 by the fixing member 74 is the region opposite the region 72a connected to the filling member 70, with the folded portion 73 sandwiched therebetween. 11, the conductive member 72 is disposed on the filling member 70 with a region 72a being shorter than a region 72b, and the shorter region 72a facing the filling member 70. Furthermore, the region 72b of the conductive member 72 is fixed to the upper protective layer 30 by a fixing member 74 at a position not overlapping with the region 72a.

[0066] In this manner, the conductive member 72 is folded and one region 72a is connected to the filling member 70 via the folded portion 73, while the other region 72b is fixed to the upper protective layer 30 by the fixing member 74. When a coating liquid of a conductive material is applied to the hole provided in the protective layer and the conductive member 72 is placed over the coating liquid, a force is applied to the region 72a toward the coating liquid, thereby ensuring close contact between the conductive member 72 and the coating liquid and obtaining a reliable electrical connection between the conductive member 72 and the filling member 70. Furthermore, even if a force such as a tensile force is applied to the region 72b of the conductive member 72, the force is less likely to be transmitted to the region 72a, so that a reliable electrical connection can be obtained between the conductive member 72 and the filling member 70.

[0067] When there are a plurality of holes and filling members, the position of folded portion 73 may be adjusted and disposed so that region 72a of conductive member 72 covers a plurality of filling members 70, as shown in FIG.

[0068] The conductive member may also have a second fixing member that fixes the edge portion of the conductive member near the position where the filling member is connected to the protective layer.

[0069] 5, the conductive member 72 has an elongated shape. The conductive member 72 is connected to the filling member 70 at one end in the longitudinal direction, and the fixing member 74 is disposed at a position farther from the end on the filling member 70 side in the longitudinal direction of the conductive member 72 than the connection position between the conductive member 72 and the filling member 70. In addition, the conductive member 72 has three sides fixed to the upper protective layer 30 by second fixing members 82 at the respective sides of the region between the end on the filling member 70 side and the fixing member 74. The second fixing member 82 is preferably provided at a position that does not overlap with the filling member 70 (protruding portion 71) in the planar direction.

[0070] In this manner, by providing the second fixing member that fixes the edge portion of the conductive member near the connection position with the filling member to the protective layer, peeling between the conductive member and the filling member can be suppressed.

[0071] In Figures 3, 5, etc., the fixing member 74 is a so-called adhesive layer / sticky layer disposed between the conductive member 72 and the upper protective layer 30, but is not limited to this and may be a so-called adhesive sheet that is fixed to the upper protective layer 30 from above the conductive member 72, as shown in Figure 13.

[0072] Similarly, in FIG. 5, the second fixing member 82 is a so-called adhesive sheet that is fixed to the upper protective layer 30 from above the conductive member 72, but this is not limited to this, and as shown in FIG. 13, the second fixing member 82 may be a so-called adhesive layer / sticky layer that is disposed between the conductive member 72 and the upper protective layer 30.

[0073] In the piezoelectric element of the present invention, the filling member 70 may have a recess at the connection position between the filling member 70 and the conductive member 72, and the conductive member 72 may be formed so as to curve along the recess.

[0074] 20, a recess is formed on the surface of the filling member 70 on the conductive member 72 side. Moreover, the conductive member 72 is curved along the recess formed in the filling member 70 and is in contact with and connected to the filling member 70.

[0075] 21 is an example of a configuration in which conductive member 72 has a folded portion 73. In the example shown in Fig. 21, a recess is formed on the surface of filling member 70 on the conductive member 72 side. Furthermore, region 72a of conductive member 72 curves along the recess formed in filling member 70 and comes into contact with and is connected to filling member 70.

[0076] In this way, at the connection position between the filling member 70 and the conductive member 72, the filling member 70 has a recess, and the conductive member 72 is curved along the recess, thereby increasing the contact area between the filling member 70 and the conductive member 72 and ensuring reliable electrical connection between the filling member 70 and the conductive member 72.

[0077] 20 and 21, the recesses formed in the filling member 70 are configured to be formed at positions corresponding to the holes 31 in the protective layer, but the present invention is not limited to this. For example, in a configuration in which a plurality of holes 31 are formed in the protective layer and the filling members 70 formed in the respective holes 31 are connected to each other, recesses may be formed at the positions where the filling members 70 are connected to each other.

[0078] The recess in the filling member 70 can be formed in the manufacturing method of the piezoelectric element described later by applying a conductive material to become the filling member 70 to the hole 31, placing the conductive member 72 on the conductive material 84, and then pressing the conductive material 84 against the conductive member 72. Alternatively, a curved portion corresponding to the recess can be provided in advance in the conductive member 72, and the conductive member 72 is placed so that the curved portion of the conductive member 72 is on top of the conductive material 84, thereby transferring the recess to the conductive material 84, thereby forming the recess in the filling member 70.

[0079] Here, in the example shown in FIG. 3 etc., an example has been described in which the conductive member is a conductive sheet, but as described above, the conductive member may be a combination of multiple conductive members.

[0080] 23 shows an example having a conductor 92 and a conductive wire 86 as conductive members. The conductor 92 and the conductive wire 86 are connected by solder 87. The conductor 92 is only connected onto the filling member 70, and is not fixed to the upper protective layer 30 or the like. The conductive wire 86 is fixed to the upper protective layer 30 by a fixing member 74.

[0081] 24 and 25 show an example having a conductor 92 and a printed wiring sheet 98 as the conductive member. As shown in Fig. 25, the printed wiring sheet 98 has wiring 96 printed on an insulating substrate 94 such as a plastic sheet. The wiring 96 of the printed wiring sheet 98 is connected to the conductor 92. The conductor 92 is merely connected onto the filling member 70 and is not fixed to the upper protective layer 30 etc. The printed wiring sheet 98 is fixed to the upper protective layer 30 by a fixing member 74.

[0082] In this manner, the conductive member may be a combination of a plurality of conductive members. In this case, at least one of the members constituting the conductive member may be fixed to a predetermined location by the fixing member 74.

[0083] Moreover, a conductive member such as a conductive wire may be further connected to the conductive member 72 made of a conductive sheet. The conductive member such as the conductive wire may be connected to any position of the conductive member 72.

[0084] 26, a conductive wire 86 is fixed by solder 87 to the surface side of a position where a conductive member 72 made of a conductive sheet is connected to a filling member 70. The conductive wire 86 is fixed to the upper protective layer 30 by an adhesive member 88 at a midpoint in the extension direction.

[0085] In the configuration shown in FIG. 26, it can be said that the conductive member 72, the solder 87, and the conductive wire 86 are the conductive member of the present invention, and the adhesive member 88 is the fixing member of the present invention.

[0086] 27, a conductive post 90 is provided on the surface side of a conductive member 72 made of a conductive sheet at a position where the conductive member 72 is connected to the filling member 70, and a conductive wire 86 having a socket 89 at its tip that fits into the post 90 is connected to the conductive wire 86. The conductive wire 86 is fixed to the upper protective layer 30 by an adhesive member 88 at a midpoint in the extension direction.

[0087] In the configuration shown in FIG. 27, the conductive member 72, the support 90, the socket 89, and the conductive wire 86 can be considered as the conductive member of the present invention, and the adhesive member 88 can be considered as the fixing member of the present invention.

[0088] 2, the conductive member 72 electrically connected to the upper electrode 26 via the filling member 70 on the upper protective layer 30 side and the conductive member 72 electrically connected to the lower electrode 24 via the filling member 70 on the lower protective layer 28 side are preferably arranged so as not to overlap in the planar position. This makes it possible to prevent the conductive member 72 on the upper electrode side 26 and the conductive member 72 on the lower electrode 24 side from coming into contact with each other and causing a short circuit.

[0089] Such piezoelectric elements 10 are used, for example, in various acoustic devices (acoustic equipment) such as speakers, microphones, and pickups used in musical instruments such as guitars, to generate (reproduce) sound by vibrating in response to an electrical signal, or to convert sound vibrations into an electrical signal. In addition, the piezoelectric element can also be used as a pressure sensor, a power generation element, and the like.

[0090] Furthermore, for example, when the piezoelectric element 10 is used in a speaker, it may be used to generate sound by the vibration of the film-like piezoelectric element 10 itself. Alternatively, the piezoelectric element 10 may be attached to a diaphragm and used as an exciter that generates sound by vibrating the diaphragm with the vibration of the piezoelectric element 10. Each component of the piezoelectric element of the present invention will now be described.

[0091] [Piezoelectric Layer] The piezoelectric layer 20 may be a layer made of a known piezoelectric material. In the present invention, the piezoelectric layer 20 is preferably a polymer composite piezoelectric material containing piezoelectric particles 36 in a matrix 34 containing a polymer material.

[0092] The material of the matrix 34 (which also serves as a matrix and binder) of the polymer composite piezoelectric body that constitutes the piezoelectric layer 20 is preferably a polymer material that has viscoelasticity at room temperature. The piezoelectric element 10 of the present invention is suitable for use in flexible speakers, such as speakers for flexible displays. Here, the polymer composite piezoelectric material (piezoelectric layer 20) used in a flexible speaker preferably satisfies the following requirements. Therefore, it is preferable to use a polymer material that has viscoelasticity at room temperature as a material that satisfies the following requirements. In this specification, "room temperature" refers to a temperature range of about 0 to 50°C.

[0093] (i) Flexibility For example, when a portable piezoelectric material is held loosely bent like a newspaper or magazine, it is constantly subjected to relatively slow, large bending deformation from the outside at a frequency of a few Hz or less. If the polymer composite piezoelectric material is hard, a large bending stress will be generated, which may cause cracks to form at the interface between the matrix and the piezoelectric particles, eventually leading to destruction. Therefore, polymer composite piezoelectric material is required to have an appropriate level of softness. Furthermore, if the strain energy can be diffused to the outside as heat, the stress can be alleviated. Therefore, the loss tangent of the polymer composite piezoelectric material is required to be appropriately large. (ii) Sound quality Speakers vibrate piezoelectric particles at frequencies in the audio band between 20Hz and 20kHz, and the vibration energy causes the entire polymer composite piezoelectric material (piezoelectric element) to vibrate as a unit, reproducing sound. Therefore, polymer composite piezoelectric materials are required to have an appropriate hardness to increase the efficiency of vibration energy transmission. Furthermore, if the frequency characteristics of a speaker are smooth, the amount of change in sound quality when the minimum resonance frequency changes with changes in curvature will also be small. Therefore, the loss tangent of polymer composite piezoelectric materials is required to be appropriately large.

[0094] In summary, the polymer composite piezoelectric material is required to be hard against vibrations of 20 Hz to 20 kHz, and soft against vibrations of a few Hz or less. In addition, the loss tangent of the polymer composite piezoelectric material is required to be appropriately large against vibrations of all frequencies below 20 kHz.

[0095] Generally, polymer solids have a viscoelastic relaxation mechanism, and large-scale molecular motion is observed as a decrease (relaxation) in the storage modulus (Young's modulus) or a maximum (absorption) in the loss modulus with an increase in temperature or decrease in frequency. Among these, relaxation caused by the micro-Brownian motion of molecular chains in the amorphous region is called primary dispersion, and a very large relaxation phenomenon is observed. The temperature at which this primary dispersion occurs is the glass transition point (Tg), and the viscoelastic relaxation mechanism is most prominent. In the polymer composite piezoelectric body (piezoelectric layer 20), by using a polymer material whose glass transition point is at room temperature, in other words, a polymer material that has viscoelasticity at room temperature, for the matrix, a polymer composite piezoelectric body that behaves hard to vibrations of 20 Hz to 20 kHz and soft to slow vibrations of a few Hz or less is realized. In particular, in order to favorably express this behavior, it is preferable to use a polymer material whose glass transition temperature at a frequency of 1 Hz is at room temperature, i.e., 0 to 50°C, for the matrix of the polymer composite piezoelectric body.

[0096] As the polymeric material having viscoelasticity at room temperature, various known materials can be used as long as they have dielectric properties. Preferably, the polymeric material has a maximum loss tangent of 0.5 or more at a frequency of 1 Hz in a dynamic viscoelasticity test at room temperature, i.e., 0°C to 50°C. This alleviates stress concentration at the interface between the matrix and the piezoelectric particles in the maximum bending moment portion when the polymer composite piezoelectric body is slowly bent by an external force, thereby providing good flexibility.

[0097] The polymeric material preferably has a storage modulus (E') at a frequency of 1 Hz, as measured by dynamic viscoelasticity measurement, of 100 MPa or more at 0°C and 10 MPa or less at 50°C. This reduces the bending moment that occurs when the polymer composite piezoelectric body is slowly bent by an external force, and at the same time, allows the polymer composite piezoelectric body to behave rigidly against acoustic vibrations of 20 Hz to 20 kHz.

[0098] It is more preferable that the polymer material has a relative dielectric constant of 10 or more at 25° C. This allows a higher electric field to be applied to the piezoelectric particles in the matrix when a voltage is applied to the polymer composite piezoelectric material, and thus a larger deformation amount can be expected. On the other hand, however, in consideration of ensuring good moisture resistance, it is also preferable that the polymer material has a relative dielectric constant of 10 or less at 25°C.

[0099] Examples of polymeric materials that satisfy these conditions include cyanoethylated polyvinyl alcohol (cyanoethylated PVA), polyvinyl acetate, polyvinylidene chloride-co-acrylonitrile, polystyrene-vinyl polyisoprene block copolymer, polyvinyl methyl ketone, and polybutyl methacrylate. Commercially available products such as Hybra 5127 (manufactured by Kuraray Co., Ltd.) can also be suitably used as these polymeric materials. Among them, it is preferable to use a material having a cyanoethyl group as the polymeric material, and it is particularly preferable to use cyanoethylated PVA. These polymer materials may be used alone or in combination (mixture) of two or more kinds.

[0100] The matrix 34 using such a polymer material may use a plurality of polymer materials in combination, if necessary. That is, in addition to the polymer material having viscoelasticity at room temperature, other dielectric polymer materials may be added to the matrix 34 as necessary for the purpose of adjusting the dielectric properties and mechanical properties.

[0101] Examples of the dielectric polymer material that can be added include fluorine-based polymers such as polyvinylidene fluoride, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, polyvinylidene fluoride-trifluoroethylene copolymer, and polyvinylidene fluoride-tetrafluoroethylene copolymer, vinylidene cyanide-vinyl acetate copolymer, cyanoethyl cellulose, cyanoethyl hydroxysaccharose, cyanoethyl hydroxycellulose, cyanoethyl hydroxypullulan, cyanoethyl methacrylate, cyanoethyl acrylate, Examples of the polymer include polymers having a cyano group or a cyanoethyl group, such as cyanoethyl hydroxyethyl cellulose, cyanoethyl amylose, cyanoethyl hydroxypropyl cellulose, cyanoethyl dihydroxypropyl cellulose, cyanoethyl hydroxypropyl amylose, cyanoethyl polyacrylamide, cyanoethyl polyacrylate, cyanoethyl pullulan, cyanoethyl polyhydroxymethylene, cyanoethyl glycidol pullulan, cyanoethyl saccharose, and cyanoethyl sorbitol, as well as synthetic rubbers, such as nitrile rubber and chloroprene rubber. Among these, polymeric materials having a cyanoethyl group are preferably used. Furthermore, in the matrix 34 of the piezoelectric layer 20, the dielectric polymer material added in addition to the polymer material having viscoelasticity at room temperature, such as cyanoethylated PVA, is not limited to one type, and multiple types may be added.

[0102] In addition to the dielectric polymer material, thermoplastic resins such as polyvinyl chloride resin, polyethylene, polystyrene, methacrylic resin, polybutene, and isobutylene, as well as thermosetting resins such as phenolic resin, urea resin, melamine resin, alkyd resin, and mica may be added to the matrix 34 in order to adjust the glass transition point. Furthermore, for the purpose of improving adhesion, a tackifier such as rosin ester, rosin, terpene, terpene phenol, or petroleum resin may be added.

[0103] When materials other than viscoelastic polymeric materials such as cyanoethylated PVA are added to the matrix 34 of the piezoelectric layer 20, there is no particular limitation on the amount of the materials added, but it is preferable that the amount of the materials added be 30 mass % or less in terms of the proportion of the matrix 34. This allows the characteristics of the added polymer material to be expressed without impairing the viscoelastic relaxation mechanism in the matrix 34, thereby achieving favorable results in terms of increasing the dielectric constant, improving heat resistance, and improving adhesion between the piezoelectric particles 36 and the electrode layer, etc.

[0104] The piezoelectric layer 20 is a polymer composite piezoelectric material that contains piezoelectric particles 36 in such a matrix 34 . The piezoelectric particles 36 are made of ceramic particles having a perovskite or wurtzite crystal structure. Examples of ceramic particles that make up the piezoelectric particles 36 include lead zirconate titanate (PZT), lead lanthanum zirconate titanate (PLZT), barium titanate (BaTiO3), zinc oxide (ZnO), and a solid solution of barium titanate and bismuth ferrite (BiFe3) (BFBT). These piezoelectric particles 36 may be used alone or in combination (mixture) of two or more kinds.

[0105] There is no restriction on the particle size of the piezoelectric particles 36, and it may be appropriately selected depending on the size and application of the polymer composite piezoelectric material (piezoelectric element 10). The particle size of the piezoelectric particles 36 is preferably 1 to 10 μm. By setting the particle size of the piezoelectric particles 36 within this range, favorable results can be obtained in that the polymer composite piezoelectric (piezoelectric element 10) can achieve both high piezoelectric properties and flexibility.

[0106] In FIG. 1, the piezoelectric particles 36 in the piezoelectric layer 20 are dispersed uniformly and regularly in the matrix 34, but the present invention is not limited to this. That is, the piezoelectric particles 36 in the piezoelectric layer 20 may be randomly dispersed in the matrix 34, although preferably they are uniformly dispersed.

[0107] In the piezoelectric layer 20 (polymer composite piezoelectric), there is no limitation on the quantitative ratio of the matrix 34 to the piezoelectric particles 36 in the piezoelectric layer 20, and it may be set appropriately depending on the size and thickness in the planar direction of the piezoelectric layer 20, the application of the polymer composite piezoelectric, and the properties required of the polymer composite piezoelectric. The volume fraction of the piezoelectric particles 36 in the piezoelectric layer 20 is preferably 30 to 80%, more preferably 50% or more, and therefore is further preferably 50 to 80%. By setting the ratio of the amounts of the matrix 34 and the piezoelectric particles 36 within the above range, favorable results can be obtained in terms of being able to simultaneously achieve high piezoelectric properties and flexibility.

[0108] There is no limit to the thickness of the piezoelectric layer 20, and it may be set appropriately depending on the application of the polymer composite piezoelectric material and the properties required of the polymer composite piezoelectric material, etc. A thicker piezoelectric layer 20 is more advantageous in terms of rigidity, such as the stiffness of the sheet-like material, but the voltage (potential difference) required to expand and contract the piezoelectric layer 20 by the same amount becomes larger. The thickness of the piezoelectric layer 20 is preferably 10 to 300 μm, more preferably 20 to 200 μm, and further preferably 30 to 150 μm. By setting the thickness of the piezoelectric layer 20 within the above range, it is possible to obtain favorable results in terms of ensuring both rigidity and appropriate flexibility.

[0109] [Electrode layer and protective layer] 1, the piezoelectric element 10 in the illustrated example has a configuration in which a lower electrode 24 is provided on one surface of a piezoelectric layer 20, a lower protective layer 28 is provided on the surface thereof, and an upper electrode 26 is provided on the other surface of the piezoelectric layer 20, and an upper protective layer 30 is provided on the surface thereof. Here, the upper electrode 26 and the lower electrode 24 form an electrode pair.

[0110] That is, the piezoelectric element 10 has a configuration in which both sides of the piezoelectric layer 20 are sandwiched between an electrode pair, that is, an upper electrode 26 and a lower electrode 24 , and this laminate is sandwiched between a lower protective layer 28 and an upper protective layer 30 . In this manner, in the piezoelectric element 10, the area sandwiched between the upper electrode 26 and the lower electrode 24 expands and contracts in response to the applied voltage.

[0111] The lower protective layer 28 and the upper protective layer 30 cover the upper electrode 26 and the lower electrode 24, and also serve to impart appropriate rigidity and mechanical strength to the piezoelectric layer 20. That is, in the piezoelectric element 10, the piezoelectric layer 20 made of the matrix 34 and the piezoelectric particles 36 exhibits very good flexibility with respect to slow bending deformation, but depending on the application, the rigidity and mechanical strength may be insufficient. To compensate for this, the lower protective layer 28 and the upper protective layer 30 are provided in the piezoelectric element 10.

[0112] There are no limitations on the lower protective layer 28 and the upper protective layer 30, and various sheet-like materials can be used. Suitable examples include various resin films. Among these, resin films made of polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), polycarbonate (PC), polyphenylene sulfite (PPS), polymethyl methacrylate (PMMA), polyetherimide (PEI), polyimide (PI), polyethylene naphthalate (PEN), triacetyl cellulose (TAC), and cyclic olefin resins are preferably used because of their excellent mechanical properties and heat resistance.

[0113] There is also no limitation on the thickness of the lower protective layer 28 and the upper protective layer 30. In addition, the thicknesses of the lower protective layer 28 and the upper protective layer 30 are basically the same, but may be different. Here, if the rigidity of the lower protective layer 28 and the upper protective layer 30 is too high, not only will the expansion and contraction of the piezoelectric layer 20 be restricted, but the flexibility will also be impaired. Therefore, except for cases where mechanical strength or good handleability as a sheet-like material is required, it is more advantageous for the lower protective layer 28 and the upper protective layer 30 to be as thin as possible.

[0114] The thickness of the lower protective layer 28 and the upper protective layer 30 is preferably 3 μm to 100 μm, more preferably 3 μm to 50 μm, further preferably 3 μm to 30 μm, and particularly preferably 4 μm to 10 μm. Here, in the piezoelectric element 10, if the thickness of the lower protective layer 28 and the upper protective layer 30 is not more than twice the thickness of the piezoelectric layer 20, favorable results can be obtained in terms of ensuring both rigidity and appropriate flexibility. For example, when the piezoelectric layer 20 is 50 μm thick and the lower protective layer 28 and the upper protective layer 30 are made of PET, the thickness of the lower protective layer 28 and the upper protective layer 30 is preferably 100 μm or less, more preferably 50 μm or less, and even more preferably 25 μm or less.

[0115] In the piezoelectric element 10, a lower electrode 24 is formed between the piezoelectric layer 20 and the lower protective layer 28, and an upper electrode 26 is formed between the piezoelectric layer 20 and the upper protective layer 30. A bottom electrode 24 and a top electrode 26 are provided for applying a driving voltage to the piezoelectric layer 20 .

[0116] In the present invention, there is no limitation on the material for forming the lower electrode 24 and the upper electrode 26, and various conductors can be used. Specific examples include carbon, palladium, iron, tin, aluminum, nickel, platinum, gold, silver, copper, titanium, chromium, molybdenum, and the like, alloys thereof, laminates and composites of these metals and alloys, and indium tin oxide. Among these, copper, aluminum, gold, silver, platinum, and indium tin oxide are preferred examples for the lower electrode 24 and the upper electrode 26.

[0117] There is also no limitation on the method for forming the lower electrode 24 and the upper electrode 26, and various known methods can be used, such as gas phase deposition methods (vacuum film formation methods) such as vacuum deposition and sputtering, film formation by plating, and methods of adhering foils formed from the above-mentioned materials.

[0118] Among these, thin films of copper, aluminum, or the like formed by vacuum deposition are particularly suitable for use as the lower electrode 24 and the upper electrode 26, because they can ensure the flexibility of the piezoelectric element 10. Among these, thin films of copper formed by vacuum deposition are particularly suitable for use. There is no limitation on the thickness of the lower electrode 24 and the upper electrode 26. Furthermore, the thickness of the lower electrode 24 and the upper electrode 26 is basically the same, but may be different.

[0119] Here, similarly to the lower protective layer 28 and the upper protective layer 30 described above, if the rigidity of the lower electrode 24 and the upper electrode 26 is too high, not only will it restrict the expansion and contraction of the piezoelectric layer 20, but it will also impair flexibility. Therefore, it is more advantageous for the lower electrode 24 and the upper electrode 26 to be as thin as possible, provided that the electrical resistance is not too high. In other words, the lower electrode 24 and the upper electrode 26 are preferably thin-film electrodes.

[0120] The thickness of the lower electrode 24 and the upper electrode 26 is thinner than the protective layer, and is preferably 0.05 μm to 10 μm, more preferably 0.05 μm to 5 μm, further preferably 0.08 μm to 3 μm, and particularly preferably 0.1 μm to 2 μm.

[0121] Here, in the piezoelectric element 10, it is preferable that the product of the thickness and Young's modulus of the lower electrode 24 and the upper electrode 26 is less than the product of the thickness and Young's modulus of the lower protective layer 28 and the upper protective layer 30, since this does not significantly impair flexibility. For example, in the case of a combination in which the lower protective layer 28 and the upper protective layer 30 are made of PET (Young's modulus: approximately 6.2 GPa) and the lower electrode 24 and the upper electrode 26 are made of copper (Young's modulus: approximately 130 GPa), if the thickness of the lower protective layer 28 and the upper protective layer 30 is 25 μm, the thickness of the lower electrode 24 and the upper electrode 26 is preferably 1.2 μm or less, more preferably 0.3 μm or less, and of these, preferably 0.1 μm or less.

[0122] The piezoelectric element 10 preferably has a maximum loss tangent (Tan δ) at a frequency of 1 Hz as measured by dynamic viscoelasticity measurement at room temperature, and more preferably has a maximum value of 0.1 or more at room temperature. As a result, even if the piezoelectric element 10 is subjected to a relatively slow, large bending deformation of a few Hz or less from the outside, the strain energy can be effectively diffused to the outside as heat, thereby preventing cracks from occurring at the interface between the matrix and the piezoelectric particles.

[0123] The piezoelectric element 10 preferably has a storage modulus (E') at a frequency of 1 Hz, as measured by dynamic viscoelasticity measurement, of 10 GPa to 30 GPa at 0° C. and 1 GPa to 10 GPa at 50° C. The same conditions apply to the piezoelectric layer 20. This allows the piezoelectric element 10 to have a large frequency dispersion in the storage elastic modulus (E'). That is, the piezoelectric element 10 behaves hard against vibrations of 20 Hz to 20 kHz, and softly against vibrations of a few Hz or less.

[0124] In addition, the product of the thickness and the storage modulus at a frequency of 1 Hz according to dynamic viscoelasticity measurement of the piezoelectric element 10 is 1.0×10 5 ~2.0×10 6 (1.0E+05~2.0E+06)N / m, 1.0×10 at 50℃ 5 ~1.0×10 6 The preferable range is (1.0E+05 to 1.0E+06) N / m. The same conditions apply to the piezoelectric layer 20. This allows the piezoelectric element 10 to have appropriate rigidity and mechanical strength without impairing its flexibility and acoustic characteristics.

[0125] Furthermore, the piezoelectric element 10 preferably has a loss tangent of 0.05 or more at 25° C. and a frequency of 1 kHz in a master curve obtained from dynamic viscoelasticity measurement. This condition also applies to the piezoelectric layer 20. This makes it possible to smooth the frequency characteristics of a speaker using the piezoelectric element 10, and to reduce changes in sound quality when the minimum resonance frequency f0 changes in accordance with changes in the curvature of the speaker.

[0126] In the present invention, the storage modulus (Young's modulus) and loss tangent of the piezoelectric element 10, the piezoelectric layer 20, etc. may be measured by a known method. As an example, the measurement may be performed using a dynamic viscoelasticity measuring device DMS6100 manufactured by SII NanoTechnology Corporation. Examples of measurement conditions include a measurement frequency of 0.1 Hz to 20 Hz (0.1 Hz, 0.2 Hz, 0.5 Hz, 1 Hz, 2 Hz, 5 Hz, 10 Hz and 20 Hz), a measurement temperature of -50 to 150°C, a heating rate of 2°C / min (in a nitrogen atmosphere), a sample size of 40 mm x 10 mm (including the clamping area), and a chuck distance of 20 mm.

[0127] [Filling member] The filling member 70 is made by hardening a liquid conductive material. The conductive material used for the filling member 70 may be silver paste, metal nanoparticle ink (Ag, Au), or the like.

[0128] The viscosity of the conductive material is preferably 10 mPa·s (millipascal seconds) to 20 Pa·s (pascal seconds), more preferably 0.1 Pa·s to 15 Pa·s, and even more preferably 0.5 Pa·s to 10 Pa·s.

[0129] The resistivity of the filling member 70 after hardening is preferably 1×10^-6 (Ω·cm) to 1×10^-3 (Ω·cm), more preferably 1×10^-6 (Ω·cm) to 8×10^-4 (Ω·cm), and even more preferably 1×10^-6 (Ω·cm) to 1×10^-4 (Ω·cm).

[0130] [Conductive member] (Conductive sheet) The conductive sheet used as the conductive member 72 is a sheet-like object made of a metal material having electrical conductivity, such as copper foil. Suitable examples of the material of the conductive sheet include copper, aluminum, gold, and silver. The shape of the conductive sheet is not particularly limited, but as described above, a long shape is preferable. The size of the conductive sheet is not particularly limited, so long as it is large enough to cover the filling member 70.

[0131] (conductor) As described above, the conductive member 72 may be configured to include a conductor and a conductive wire or a conductive sheet connected to the conductor. Suitable examples of the conductive material include copper, aluminum, gold, silver, and brass. There are also no particular limitations on the shape and size of the conductor, so long as it can be connected to the filling member 70 and can be connected to a conductive sheet or conductive wire.

[0132] (Conductive Wire) It is a wire made of conductive material such as copper, aluminum, gold and silver. There is no particular limitation on the diameter and length of the conductive wire, so long as it can be connected to a conductor and can provide a reliable electrical connection.

[0133] [Fixing member and second fixing member] As the fixing member and the second fixing member, various adhesive materials, adhesive materials, double-sided tapes, and adhesive tapes can be used as long as they are capable of fixing the conductive member and the protective layer. As mentioned above, the fixing member and the second fixing member may be a so-called adhesive layer provided between the conductive member and the protective layer, or may be a so-called pressure-sensitive adhesive sheet that fixes the conductive member to the protective layer from above.

[0134] An example of a method for manufacturing the piezoelectric element 10 will now be described with reference to FIGS.

[0135] 14, a sheet-like material 10a is prepared in which a lower electrode 24 is formed on a lower protective layer 28. This sheet-like material 10a may be produced by forming a copper thin film or the like as the lower electrode 24 on the surface of the lower protective layer 28 by vacuum deposition, sputtering, plating, or the like. When the lower protective layer 28 is very thin and difficult to handle, a lower protective layer 28 with a separator (temporary support) may be used as necessary. The separator may be made of PET or the like having a thickness of 25 μm to 100 μm. The separator may be removed after the upper electrode 26 and the upper protective layer 30 are thermocompression bonded together and before any member is laminated on the lower protective layer 28.

[0136] On the other hand, a polymeric material that will be the matrix material is dissolved in an organic solvent, and piezoelectric particles 36 such as PZT particles are further added and stirred to prepare a coating material that is dispersed. As the organic solvent other than the above substances, various organic solvents can be used without any limitation.

[0137] After preparing the sheet-like material 10a and preparing the paint, the paint is cast (applied) onto the sheet-like material 10a, and the organic solvent is evaporated and dried. As a result, as shown in Fig. 15, a laminate 10b is produced in which a lower electrode 24 is provided on a lower protective layer 28 and a piezoelectric layer 20 is formed on the lower electrode 24. Note that the lower electrode 24 refers to the electrode on the substrate side when applying the piezoelectric layer 20, and does not indicate the vertical positional relationship in the laminate.

[0138] There is no limitation on the method for casting the coating material, and all known methods (coating devices) such as a slide coater and a doctor knife can be used.

[0139] As described above, in the piezoelectric element 10, a dielectric polymer material may be added to the matrix 34 in addition to the viscoelastic material such as cyanoethylated PVA. When adding these polymeric materials to the matrix 34, the polymeric materials to be added may be dissolved in the above-mentioned coating material.

[0140] After fabricating the laminate 10b having the lower electrode 24 on the lower protective layer 28 and the piezoelectric layer 20 on the lower electrode 24, the piezoelectric layer 20 is preferably subjected to a polarization treatment (poling).

[0141] There is no limitation on the method for polarization of the piezoelectric layer 20, and any known method can be used. Before the polarization process, the surface of the piezoelectric layer 20 may be smoothed by a calendar process using a heated roller or the like. By performing the calendar process, the thermocompression bonding process described below can be carried out smoothly.

[0142] While the piezoelectric layer 20 of the laminate 10b is polarized in this manner, a sheet-like material 10c is prepared in which an upper electrode 26 is formed on an upper protective layer 30. The sheet-like material 10c may be produced by forming a copper thin film or the like as the upper electrode 26 on the surface of the upper protective layer 30 by vacuum deposition, sputtering, plating, or the like. Next, as shown in FIG. 16, with the upper electrode 26 facing the piezoelectric layer 20, the sheet-like material 10c is laminated on the laminate 10b whose piezoelectric layer 20 has been subjected to the polarization process. Furthermore, the laminate of the laminate 10b and the sheet-like material 10c is thermocompressed by a heat press device or a pair of heat rollers so as to sandwich the upper protective layer 30 and the lower protective layer 28 therebetween.

[0143] Through the above steps, a laminate is produced in which the electrode layers and the protective layers are laminated on both sides of the piezoelectric layer 20. The produced laminate may be cut into desired shapes according to various applications. Such a laminate may be manufactured using a cut sheet-like material, or may be produced by roll-to-roll (hereinafter, also referred to as RtoR).

[0144] Next, a hole is provided in the protective layer of this laminate, a filler is formed in the hole, and a conductive member is placed on the filler. Specifically, first, a hole 31 is formed in the upper protective layer 30 as shown in FIG. The hole 31 may be formed by a method such as laser processing (carbon dioxide laser, etc.) or by a method in which a cut is made in the protective layer in the depth direction by press processing (for example, when the protective layer is 10 μm thick and the electrode layer is 2 μm thick, a circular cut is made in the protective layer in the thickness direction to a depth of 8 to 9.5 μm and then the circular cut is peeled off) and then the protective layer is peeled off. Furthermore, during processing, the protrusions 32 may be formed by forcibly deforming the protective layer by applying heat or an external force in the outward direction to the periphery of the hole. Furthermore, after or before processing the hole 31, a recess 33 may be formed around the hole 31 by laser processing or the like.

[0145] Here, when forming the hole 31 by laser processing, a laser is scanned to form a hole of a desired opening shape. In this case, if the opening shape of the hole is circular, the laser can be scanned in a spiral manner from the center to the outside or from the outside to the center, so that heat generated by the laser processing is less likely to be trapped, and a decrease in the strength of the electrode layer can be suppressed.

[0146] When multiple holes are provided, assuming that the total area of ​​the holes is the same, the provision of multiple holes is preferable because it makes it less likely for heat generated during laser processing to accumulate compared to the case where there is only one hole, thereby preventing a decrease in the strength of the electrode layer.

[0147] In addition, the interval between the scanning lines of the laser during the laser processing may be different between the center side and the outside of the hole. By making the interval between the scanning lines of the laser different between the center side and the outside of the hole, as described above, it is possible to adjust the amount of the protective layer residue in the center and the amount of the protective layer residue in the peripheral portion. In addition, by adjusting the spacing of the laser scanning lines so that they are different on the center side and the outside of the hole, the size of the gap that occurs between the electrode layer and the piezoelectric layer as described above can be reduced.

[0148] Also, during laser processing, large-diameter holes may be formed partway through the thickness of the protective layer, and then small-diameter holes may be formed in the remaining thickness up to the electrode layer, resulting in a configuration in which the equivalent circle diameter changes stepwise as shown in Fig. 8 above, with the equivalent circle diameter on the electrode layer side being smaller than the equivalent circle diameter on the conductive member side.

[0149] After the holes 31 are formed in the protective layer, a liquid conductive material 84 is applied to the holes 31 as shown in Fig. 18. The conductive material 84 is applied so that it overflows from the holes 31. The conductive material 84 can be applied by silk screen printing, dripping with a dispenser, applying with a brush, or the like.

[0150] After the conductive material 84 is applied to the hole 31, the conductive member 72 is placed on the conductive material 84 as shown in Fig. 19. That is, the conductive member 72 is placed so as to cover the conductive material 84 before the conductive material 84 hardens.

[0151] 19, a fixing member 74 is adhered to the surface of the conductive member 72 on the upper protective layer 30 side, and the conductive member 72 is placed on the conductive material 84 and fixed to the upper protective layer 30. This makes it possible to prevent the conductive member 72 from shifting in position when the conductive material 84 is in an uncured state. Furthermore, by covering the conductive material 84 with the conductive member 72, it is possible to prevent the conductive material 84 from moving from above the hole 31, and it is possible to ensure that the filling member 70 is present in the hole 31.

[0152] After placing the conductive member 72 on the conductive material 84 , the conductive material 84 is cured to form the filler member 70 . The conductive material 84 may be cured by a method appropriate for the conductive material 84. For example, the conductive material 84 may be cured by heating and drying.

[0153] Through the above steps, the piezoelectric element of the present invention is produced.

[0154] When a voltage is applied to the lower electrode 24 and the upper electrode 26 of such a piezoelectric element 10, the piezoelectric particles 36 expand and contract in the polarization direction in response to the applied voltage. As a result, the piezoelectric element 10 (piezoelectric layer 20) contracts in the thickness direction. At the same time, due to the Poisson's ratio, the piezoelectric element 10 also expands and contracts in the in-plane direction. This expansion and contraction is approximately 0.01 to 0.1%. As described above, the in-plane direction expands and contracts isotropically in all directions. As described above, the thickness of the piezoelectric layer 20 is preferably about 10 to 300 μm. Therefore, the expansion and contraction in the thickness direction is very small, about 0.3 μm at most. In contrast, the piezoelectric element 10, i.e., the piezoelectric layer 20, has a size in the planar direction that is much larger than its thickness. Therefore, for example, if the length of the piezoelectric element 10 is 20 cm, the piezoelectric element 10 will expand and contract by a maximum of about 0.2 mm when a voltage is applied. Furthermore, when pressure is applied to the piezoelectric element 10, the piezoelectric particles 36 act to generate electricity. By utilizing this property, the piezoelectric element 10 can be used for various purposes such as a speaker, a microphone, and a pressure sensor, as described above.

[0155] Here, a typical piezoelectric element made of a polymer material such as PVDF has in-plane anisotropy in its piezoelectric properties, and there is anisotropy in the amount of expansion and contraction in the planar direction when a voltage is applied. In contrast, a piezoelectric layer made of a polymer composite piezoelectric material containing piezoelectric particles in a matrix containing a polymer material has no in-plane anisotropy in its piezoelectric properties and expands and contracts isotropically in all in-plane directions. The piezoelectric element 10, which expands and contracts isotropically in two dimensions, can vibrate with greater force and produce a louder, more beautiful sound than a laminate of general piezoelectric elements such as PVDF, which only expands and contracts significantly in one direction.

[0156] In the example shown in FIG. 1, a configuration including one piezoelectric element 10 is used, but the present invention is not limited to this. A configuration may be used in which a plurality of piezoelectric elements 10 of the present invention are laminated. Also, the piezoelectric element 10 of the present invention may be formed into an elongated shape and folded back in the longitudinal direction one or more times, preferably multiple times, to form a configuration in which a plurality of piezoelectric elements 10 are laminated.

[0157] Although the piezoelectric element of the present invention has been described in detail above, the present invention is not limited to the above-mentioned examples, and various improvements and modifications may of course be made without departing from the gist of the present invention. [Industrial Applicability]

[0158] The present invention can be suitably used for various applications, such as audio equipment such as speakers and microphones, and pressure sensors. [Explanation of symbols]

[0159] 10 Piezoelectric element 10a, 10c Sheet-like object 10b Laminate 20 Piezoelectric layer 24 Lower electrode 26 Upper electrode 28 Lower protective layer 30 Upper protective layer 31 Hole 32 Convex 33 Recess 34 Matrix 36 Piezoelectric particles 70 Filling material 71 Protruding part 72 Conductive materials 72a, 72b area 73 Folded part 74 Fixing member 76 Enclosure material 80 Void 82 Second fixing member 84 Conductive materials 86 Conductive Wire 87 Solder 88 Adhesive Materials 90 pillars 92 Conductors 94 Substrate 96 Wiring 98 Printed Wiring Sheet 100 diaphragm

Claims

1. A piezoelectric element including a piezoelectric layer, electrode layers formed on both sides of the piezoelectric layer, and a protective layer laminated on a surface of the electrode layer opposite to the surface of the piezoelectric layer, the protective layer has a hole penetrating from a surface to the electrode layer, a filler member made of a conductive material, the filler member being formed on a part of a surface of the protective layer from within the hole and electrically connected to the electrode layer; a conductive member covering at least a portion of the filling member and electrically connected to the filling member; A fixing member that fixes the conductive member, The piezoelectric element has a protrusion formed on the edge of the hole of the protective layer.

2. The piezoelectric element according to claim 1 , wherein the conductive member is a conductive sheet.

3. The piezoelectric element according to claim 1 , wherein the conductive member has a conductor connected to the filling member, and a conductive wire or a conductive sheet connected to the conductor.

4. The piezoelectric element according to any one of claims 1 to 3, wherein the hole has a circular equivalent diameter that changes stepwise in the depth direction, and the circular equivalent diameter on the electrode layer side is smaller than the circular equivalent diameter on the conductive member side.

5. 5. The piezoelectric element according to claim 1, wherein the amount of carbon in the surface of the electrode layer within the hole is less in a central portion in a surface direction than in the area other than the central portion.

6. 5. The piezoelectric element according to claim 1, wherein the amount of carbon in the surface of the electrode layer within the hole is greater in a central portion in a surface direction than in the area other than the central portion.

7. 7. The piezoelectric element according to claim 1, wherein the opening shape of the hole is circular.

8. the protective layer has a plurality of the holes, 8. The piezoelectric element according to claim 1, further comprising a plurality of the filling members formed in the plurality of holes, respectively.

9. The piezoelectric element according to claim 8 , wherein the plurality of filling members are connected to each other on the surface of the protective layer.

10. a surrounding member that surrounds the hole on a surface of the protective layer; The piezoelectric element according to any one of claims 1 to 9, wherein the filling member is formed at least inside the surrounding member.

11. 11. The piezoelectric element according to claim 1, wherein the protective layer has a recess formed around the hole.

12. 12. The piezoelectric element according to claim 1, wherein the protective layer has a thickness of 3 μm to 100 μm.

13. The piezoelectric element according to any one of claims 1 to 12, wherein the electrode layer has a thickness of 0.05 µm to 10 µm.

14. a gap is provided between the electrode layer and the piezoelectric layer at the position of the hole, A piezoelectric element according to any one of claims 1 to 13, wherein the difference between the average height of the interface between the piezoelectric layer and the electrode layer at a position where the hole is not formed and the average height of the interface between the piezoelectric layer and the electrode layer at the position of the hole is 25 μm or less.

15. The conductive member has an elongated shape, The conductive member has a folded portion folded in a longitudinal direction, The piezoelectric element according to any one of claims 1 to 14, wherein the fixing member fixes the conductive member and the protective layer in an area opposite to the connection position between the conductive member and the filling member, across the folded portion.

16. The conductive member has an elongated shape, the conductive member is connected to the filling member at one end side in a longitudinal direction, A piezoelectric element according to any one of claims 1 to 15, wherein the fixing member is positioned in a position farther from the one end in the longitudinal direction of the conductive member than the connection position between the conductive member and the filling member.

17. The piezoelectric element according to claim 16 , further comprising a second fixing member that fixes at least a portion of a peripheral portion of the conductive member in a region between the one end and the fixing member to the protective layer.

18. 18. The piezoelectric element according to claim 1, wherein the piezoelectric layer is made of a polymer composite piezoelectric material containing piezoelectric particles in a matrix containing a polymer material.

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