Piezoelectric device

Abstract

To provide a piezoelectric device that can suppress curvature that inhibits vibration of a cantilevered beam-shaped portion.SOLUTION: A beam-shaped portion 32 has a concave-convex structure 36, and the concave-convex structure 36 has a plurality of first concave-convex portions 37 and a plurality of second concave-convex portions 38. The first concave-convex portion 37 is formed with a first concave shape 371 on one surface 32c of the beam-shaped portion 32 and a first convex shape 372 on the other surface 32d of the beam-shaped portion 32, at a portion overlapping the first concave shape 371 on the other side of the directional axis direction Da with the first concave shape 371. Meanwhile, the second concave-convex portion 38 is formed with a second convex shape 381 on one surface 32c of the beam-shaped portion 32 and a second concave shape 382 on the other surface 32d of the beam-shaped portion 32, at a portion overlapping the second convex shape 381 on the other side of the directional axis direction Da with the second convex shape 381. The first and second concave shapes 371 and 382 and the first and second convex shapes 372 and 381 each extend linearly in the second direction D2.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present disclosure relates to piezoelectric devices that function as microphones or speakers. [Background technology]

[0002] In a cantilever-structured piezoelectric MEMS microphone, the beam-shaped part, which is supported in a cantilevered shape and formed into a plate-like shape with a piezoelectric layer, vibrates when exposed to sound waves or ultrasonic waves. The vibration of the beam-shaped part is then converted into an electrical signal. MEMS is an abbreviation for Micro Electro Mechanical Systems.

[0003] In such a cantilever-structured piezoelectric MEMS microphone, the beam portion formed in a plate shape may bend due to stress distribution in the thickness direction. The bending of the beam portion occurs not only in a cross section along the beam extension direction extending from the fixed end to the free end of the beam portion and along the thickness direction, but also in a cross section perpendicular to the beam extension direction. In particular, the bending of the beam portion that appears in the cross section inhibits the vibration of the beam portion, resulting in a decrease in the sensitivity of the microphone.

[0004] In response to this, Patent Document 1 proposes a method of dividing the beam portion of a piezoelectric MEMS microphone into layers in the thickness direction, thereby adjusting the stress distribution in the beam portion. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] U.S. Patent Application Publication No. 2022 / 0199893 Summary of the Invention [Problem to be solved by the invention]

[0006] Even if the stress distribution in the beam-like portion is adjusted by the method proposed in Patent Document 1, it is difficult to suppress the curvature of the beam-like portion due to the in-plane variation in stress distribution in the deposition of each layer of the beam-like portion and the variation in stress distribution between lots. As a result of detailed investigations by the inventors, the above findings were discovered.

[0007] In view of the above, the present disclosure aims to provide a piezoelectric device that can suppress the curvature of the cantilevered beam portion that appears in the cross section while not hindering the vibration of the cantilevered beam portion. [Means for solving the problem]

[0008] In order to achieve the above object, a piezoelectric device according to one aspect of the present disclosure comprises: A piezoelectric device that functions as a microphone or speaker, a beam-like portion (32) including a piezoelectric layer (35, 351, 352) made of a piezoelectric material, formed in a plate shape perpendicular to the axial direction (Da) of the directivity axis (Lc), having a fixed end (32a) provided on one side in a first direction (D1) perpendicular to the axial direction, a free end (32b) provided on the other side in the first direction, one face (32c) formed on one side in the axial direction, and another face (32d) formed on the other side in the axial direction, the free end being configured in a cantilever shape so as to be displaceable back and forth in the axial direction relative to the fixed end; a support part (2) to which the fixed end part is fixed and which supports the fixed end part, The beam-shaped portion has a concave-convex structure portion (36, 361, 362, 363) constituted by at least one of a first concave-convex portion (37) and a second concave-convex portion (38), The first uneven portion is formed with a first concave shape (371) that extends linearly in a second direction (D2) perpendicular to the axial direction and the first direction and is provided on one surface, and a first convex shape (372) that is provided on the other surface at a position that overlaps the first concave shape on the other side of the axial direction and extends linearly in the second direction, The second uneven portion has a second convex shape (381) that extends linearly in the second direction and is provided on one surface, and a second concave shape (382) that extends linearly in the second direction and is provided on the other surface at a location that overlaps the second convex shape on the other side of the axial direction.

[0009] In this way, by providing the concave-convex structure on the beam-shaped portion, the bending rigidity of the beam-shaped portion against the curvature of the beam-shaped portion that appears in the cross section perpendicular to the second direction is not increased, but the bending rigidity of the beam-shaped portion against the curvature of the beam-shaped portion that appears in the cross section perpendicular to the first direction is increased. Therefore, while not impeding the vibration of the beam-shaped portion, the curvature of the beam-shaped portion that appears in the cross section perpendicular to the first direction can be suppressed compared to, for example, when the concave-convex structure is not provided and the entire beam-shaped portion is flat. Note that the cross section perpendicular to the first direction corresponds to the transverse cross section.

[0010] In addition, in each section of the application documents, each element may be assigned a reference number in parentheses. In this case, the reference number merely indicates an example of the correspondence between the element and the specific configuration described in the embodiment described below. Therefore, the present disclosure is not limited in any way by the description of the reference number. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a plan view schematically showing a piezoelectric device according to a first embodiment. [Figure 2] FIG. 2 is a perspective view showing one vibration plate and its periphery in the piezoelectric device in the first embodiment, specifically showing a schematic view of part II in FIG. 1. [Figure 3] FIG. 3 is a cross-sectional view schematically showing the cross section taken along line III-III in FIG. 2. [Figure 4] 3A and 3B are diagrams illustrating, in a simplified manner, the outline shapes of portions of the cross-sectional shapes of the beam-like portion appearing in the III-III cross section of FIG. 2 that are different between the conventional structure and the structure of the first embodiment, in which (a) shows the conventional cross-sectional shape and (b) shows the cross-sectional shape in the first embodiment. [Figure 5]3A and 3B are diagrams showing schematic shapes of parts of the cross-sectional shapes of the beam-shaped parts appearing in the VV cross section of FIG. 2 that are different between the conventional structure and the structure of the first embodiment, in which (a) shows the conventional cross-sectional shape and (b) shows the cross-sectional shape in the first embodiment. [Figure 6] 3 is a perspective view similar to FIG. 2, in which a plurality of concave-convex structures on a beam-like portion of a diaphragm are shown by dashed lines in a simplified illustration. [Figure 7] 7 is a cross-sectional view schematically showing a cross section taken along line VII-VII in FIG. 6 in the first embodiment, and is also a cross-sectional view schematically showing an enlarged VIIa portion in FIG. [Figure 8] 8 is a cross-sectional view schematically showing the VIII-VIII cross section of FIG. 6 in the first embodiment, and is also a cross-sectional view schematically showing an enlarged VIIIa portion of FIG. 3. FIG. [Figure 9] 9 is a cross-sectional view schematically showing the cross section taken along line IX-IX in FIG. 6 in the first embodiment, and is also a cross-sectional view schematically showing an enlarged portion IXa in FIG. [Figure 10] This is a perspective view of one vibration plate and its surroundings in the piezoelectric device of the second embodiment, in which the multiple uneven structures of the beam-shaped portion of the vibration plate are shown by dashed lines in a simplified illustration, and corresponds to Figure 6. [Figure 11] This is a perspective view of one vibration plate and its surroundings in the piezoelectric device of the third embodiment, in which the uneven structure of the beam-shaped portion of the vibration plate is shown by dashed lines in a simplified illustration, and corresponds to Figure 6. [Figure 12] This is a perspective view of one vibration plate and its surroundings in the piezoelectric device of the fourth embodiment, in which the uneven structure of the beam-shaped portion of the vibration plate is shown by dashed lines in a simplified illustration, and corresponds to Figure 6. [Figure 13] 13 is a cross-sectional view schematically showing the XIII-XIII cross section of FIG. 12 in the fourth embodiment, and is also a cross-sectional view schematically showing an enlarged portion corresponding to the XIIIa portion of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, each embodiment will be described with reference to the drawings. In the following embodiments, the same or equivalent parts are denoted by the same reference numerals in the drawings.

[0013] (First embodiment) 1 to 3 is an electroacoustic transducer configured as a piezoelectric MEMS microphone. Therefore, the piezoelectric device 1 of this embodiment is configured to convert sound vibrations or ultrasonic vibrations propagated from an external space Sz into an electric signal. MEMS stands for Micro Electro Mechanical System.

[0014] In this embodiment, each component of the piezoelectric device 1 may be described based on the directional axis Lc of the piezoelectric device 1. The directional axis Lc is an imaginary line that serves as a reference for the directivity of the piezoelectric device 1 that receives sound waves or ultrasonic waves, and may also be referred to as the "center directional axis." The directional axis Lc typically corresponds to an imaginary line that indicates the center of the axis of a three-dimensional shape, such as a substantially conical or spindle-shaped shape, that represents the range of directivity (for example, the range in which a predetermined gain can be obtained). Specifically, for example, the directional axis Lc is the central axis of the sound pressure half-value angle.

[0015] 2 and 3, the orientation axis direction Da, which is the axial direction of the orientation axis Lc, the first direction D1, and the second direction D2 are each indicated by a double-headed arrow. The orientation axis direction Da is parallel to the orientation axis Lc. The first direction D1 is perpendicular to the orientation axis direction Da, and the second direction D2 is perpendicular to the orientation axis direction Da and the first direction D1.

[0016] As shown in FIGS. 1 to 3, a piezoelectric device 1 of this embodiment includes a base substrate 2, a diaphragm 3, an oxide film 4, and a signal wiring 5.

[0017] The base substrate 2 functions as a support for supporting the diaphragm 3, and is formed in a cylindrical or annular shape surrounding the directional axis Lc. In this embodiment, the base substrate 2 has a rectangular cylindrical or annular shape with the directional axis Lc as its central axis. The base substrate 2 has a square outer shape in plan view. The base substrate 2 is made of a ceramic substrate such as alumina, a silicon-based semiconductor substrate, or the like. Note that a plan view refers to a view in the direction along the directional axis Da.

[0018] The base substrate 2 has an outer wall surface 21 that is parallel to the directional axis Lc and exposed outward in the radial direction of the directional axis Lc, and an inner wall surface 22 that is parallel to the directional axis Lc and surrounds the directional axis Lc. A cavity 23, which is a space surrounded by the inner wall surface 22, is formed in the shape of a quadrangular prism that is square in plan view.

[0019] The base substrate 2 also has one end face 24, which is an end face formed on one side in the directional axis direction Da, and another end face 25, which is an end face formed on the other side in the directional axis direction Da. The one end face 24 and the other end face 25 are formed as flat planes with the directional axis direction Da as their normal direction. The one end face 24 is bonded to the diaphragm 3 via an insulating oxide film 4. The oxide film 4 is laminated between the base substrate 2 and the fixing portion 31 of the diaphragm 3 in the directional axis direction Da. For example, the oxide film 4 is made from a material such as TEOS. TEOS is an abbreviation for tetra ethoxy silane.

[0020] The diaphragm 3 is formed in a thin plate shape having a thickness in the directional axis direction Da. In other words, the diaphragm 3 is formed in a plate shape perpendicular to the directional axis direction Da, that is, a plate shape extending in the first direction D1 and the second direction D2. Focusing on the role of each part of the diaphragm 3, the diaphragm 3 has a fixed part 31 and a beam-like part 32.

[0021] The fixed portion 31 of the diaphragm 3 is bonded to one end surface 24 of the base substrate 2 via the oxide film 4, and is thereby fixed to the base substrate 2. Therefore, the base substrate 2 is disposed on the other side of the fixed portion 31 and the beam portion 32 of the diaphragm 3 in the directional axis direction Da.

[0022] The beam-like portions 32 of the diaphragm 3 are formed to extend from the fixed portion 31 toward the directional axis Lc along the first direction D1. As described above, the diaphragm 3 is formed in a plate shape perpendicular to the directional axis direction Da, and therefore the beam-like portions 32 are also formed in a plate shape perpendicular to the directional axis direction Da.

[0023] The beam-like portion 32 is formed to overlap one side of the cavity 23 in the directional axis direction Da. In other words, the beam-like portion 32 constitutes the part of the diaphragm 3 that is on the directional axis Lc side relative to the inner wall surface 22 of the base substrate 2. Therefore, the beam-like portion 32 faces the cavity 23 from one side in the directional axis direction Da. The beam-like portion 32 is configured to flexibly vibrate in a manner such that the antinode of vibration moves along the directional axis Lc. That is, the beam-like portion 32 has a fixed end 32a and a free end 32b.

[0024] The fixed end 32a is an end of the beam-shaped portion 32 provided on one side in the first direction D1. The fixed end 32a is a portion that constitutes a vibration node of the beam-shaped portion 32, and is provided at a position that overlaps with the inner wall surface 22 of the base substrate 2 in a plan view. On the other hand, the free end 32b is an end of the beam-shaped portion 32 provided on the other side in the first direction D1. The free end 32b is a portion that constitutes a vibration loop of the beam-shaped portion 32, and is provided at a position close to the directional axis Lc.

[0025] Fixed end 32a is fixed to base substrate 2 via fixed portion 31 of diaphragm 3 and oxide film 4, and base substrate 2 supports fixed end 32a. In other words, base substrate 2 supports beam portion 32 at fixed end 32a. Therefore, beam portion 32 of diaphragm 3 is configured as a cantilever beam in which free end 32b can move back and forth in direction of directional axis Da relative to fixed end 32a. In other words, beam portion 32 is provided so as to be vibrable in such a manner that fixed end 32a is fixedly supported by base substrate 2 while free end 32b moves back and forth along direction of directional axis Lc.

[0026] Furthermore, the beam-like portion 32 of the diaphragm 3 has one surface 32c formed on one side in the directional axis direction Da and another surface 32d formed on the other side in the directional axis direction Da. The one surface 32c and the other surface 32d of the beam-like portion 32 are formed so as to extend in a first direction D1 and a second direction D2, respectively, with the directional axis direction Da as the normal direction.

[0027] In this embodiment, corresponding to the square external shape of the base substrate 2 in a plan view, the beam-like portions 32 of the diaphragm 3 have a substantially right-angled isosceles triangle shape in a plan view with the fixed end 32a as the base and the free end 32b as the apex. Therefore, the beam-like portions 32 are formed so that their width in the second direction D2 increases from the free end 32b toward the fixed end 32a. In other words, the beam-like portions 32 are formed so that their width increases in the second direction D2 toward one side in the first direction D1.

[0028] 1, the piezoelectric device 1 of this embodiment has a total of four diaphragms 3 having the above-described configuration. The four diaphragms 3 are arranged side by side at equal intervals (specifically, 90° intervals) in the circumferential direction around the directional axis Lc, with the free end portions 32b facing the directional axis Lc in a plan view. That is, for all four diaphragms 3, the other side in the first direction D1 is the directional axis Lc side.

[0029] The beam portions 32 of the multiple diaphragms 3 are each divided by slits 33 so as to be spaced apart in the circumferential direction of the directional axis Lc. Therefore, the slits 33 penetrate between the beam portions 32 in the directional axis direction Da and are formed in a substantially X-shape in plan view, which corresponds to the diagonal of the square shape of the cavity 23. Note that the multiple diaphragms 3 of the piezoelectric device 1 of this embodiment all have the same configuration, and therefore, in this embodiment, the diaphragm 3 will be described by focusing on one of the multiple diaphragms 3.

[0030] 2 and 3, the diaphragm 3 has a multi-layer structure, and focusing on the multi-layer structure of the diaphragm 3, the diaphragm 3 has a first electrode layer 341, a second electrode layer 342, a third electrode layer 343, a first piezoelectric layer 351, and a second piezoelectric layer 352. For example, the first and second piezoelectric layers 351, 352 and the first and second electrode layers 341, 342 extend to both the fixed portion 31 and the beam-like portion 32 of the diaphragm 3, and the third electrode layer 343 extends to the beam-like portion 32.

[0031] In the description of this embodiment, when the first electrode layer 341, the second electrode layer 342, and the third electrode layer 343 are referred to collectively without distinction, they may be referred to as electrode layers 34. When the first piezoelectric layer 351 and the second piezoelectric layer 352 are referred to collectively without distinction, they may be referred to as piezoelectric layers 35.

[0032] The electrode layer 34 is made of a conductive material such as a molybdenum film, an amorphous molybdenum film, or a polycrystalline silicon film. The piezoelectric layer 35 is made of a piezoelectric material. Examples of the piezoelectric material that makes up the piezoelectric layer 35 include AlN (i.e., aluminum nitride), ScAlN (i.e., scandium aluminum nitride), ZnO (i.e., zinc oxide), PZT, KLN, KNN, and BaTiO3 (i.e., barium titanate). PZT stands for zinc zirconate titanate, and KLN stands for K3Li2Nb5O 15 and KNN means (K,Na)NbO3.

[0033] Furthermore, the multiple electrode layers 34 and the multiple piezoelectric layers 35 are stacked in the axial direction Da in the order of the first electrode layer 341, the first piezoelectric layer 351, the second electrode layer 342, the second piezoelectric layer 352, and the third electrode layer 343, starting from the other side of the axial direction Da. In other words, the multiple electrode layers 34 and the multiple piezoelectric layers 35 are stacked alternately in the axial direction Da, so that each of the multiple piezoelectric layers 35 is sandwiched between a pair of electrode layers 34. In other words, the multiple electrode layers 34 constitute different layers of the beam portion 32 of the diaphragm 3, separated from each other by the piezoelectric layers 35.

[0034] The first electrode layer 341 is laminated and bonded to one side of the oxide film 4 in the axial direction Da, and forms the other surface 32d of the beam-shaped portion 32. In contrast, the third electrode layer 343 forms the one surface 32c of the beam-shaped portion 32. Since the first piezoelectric layer 351 has a portion that is not covered by the first electrode layer 341, the first piezoelectric layer 351 is bonded to a portion of the oxide film 4 without the first electrode layer 341 therebetween, and forms part of the other surface 32d of the beam-shaped portion 32. Since the second piezoelectric layer 352 has a portion that is not covered by the third electrode layer 343, the second piezoelectric layer 352 forms part of the one surface 32c of the beam-shaped portion 32.

[0035] The first electrode layer 341 has a first sensor electrode 341a and a first floating electrode 341b. Similarly, the second electrode layer 342 has a second sensor electrode 342a and a second floating electrode 342b, and the third electrode layer 343 has a third sensor electrode 343a and a third floating electrode 343b. The first to third sensor electrodes 341a, 342a, and 343a are electrodes for outputting electrical signals corresponding to the bending vibration of the beam-like portion 32, and are therefore electrically connected to signal wiring 5, which is wiring leading to the outside of the piezoelectric device 1. In contrast, the first to third floating electrodes 341b, 342b, and 343b are each provided away from the wiring and are electrically insulated.

[0036] The first to third sensor electrodes 341a, 342a, and 343a are arranged on the base side of the cantilever structure of the beam-like portion 32 of the diaphragm 3, and the first to third floating electrodes 341b, 342b, and 343b are arranged on the tip side of the cantilever structure. Specifically, in the first electrode layer 341, the first floating electrode 341b is arranged on the other side of the first sensor electrode 341a in the first direction D1, and in the second electrode layer 342, the second floating electrode 342b is arranged on the other side of the second sensor electrode 342a in the first direction D1. And, in the third electrode layer 343, the third floating electrode 343b is arranged on the other side of the third sensor electrode 343a in the first direction D1.

[0037] Furthermore, since there is a small gap between the first sensor electrode 341a and the first floating electrode 341b, the first floating electrode 341b is spaced apart from the first sensor electrode 341a. Similarly, there is a small gap between the second sensor electrode 342a and the second floating electrode 342b, so the second floating electrode 342b is spaced apart from the second sensor electrode 342a. And there is a small gap between the third sensor electrode 343a and the third floating electrode 343b, so the third floating electrode 343b is spaced apart from the third sensor electrode 343a. This blocks conduction between the first to third sensor electrodes 341a, 342a, 343a and the first to third floating electrodes 341b, 342b, 343b, respectively.

[0038] The distance between the first sensor electrode 341a and the first floating electrode 341b, the distance between the second sensor electrode 342a and the second floating electrode 342b, and the distance between the third sensor electrode 343a and the third floating electrode 343b each extend linearly along the second direction D2. These distances, i.e., the electrode spacing, are formed, for example, by removing a portion of each electrode layer 34 by etching or the like. The first piezoelectric layer 351 extends into the electrode spacing between the first sensor electrode 341a and the first floating electrode 341b, and the second piezoelectric layer 352 extends into the electrode spacing between the second sensor electrode 342a and the second floating electrode 342b.

[0039] The first to third sensor electrodes 341a, 342a, 343a are formed so that all of the sensor electrodes 341a, 342a, 343a overlap in a plan view. The electrode spacings provided on the first to third electrode layers 341, 342, 343 may be aligned with each other in the first direction D1, but in this embodiment, they are offset from each other in the first direction D1.

[0040] The operation of the piezoelectric device 1 of this embodiment configured as described above will now be described. The piezoelectric device 1 of this embodiment has a function of converting strain caused by flexural deformation when the free end 32b of the beam-like portion 32 moves in the directional axis direction Da into voltage between a pair of electrode layers 34 provided on both sides of the piezoelectric layer 35. That is, for example, flexural vibration of the beam-like portion 32 caused by receiving sound waves or ultrasonic waves is extracted as an inter-electrode voltage between the first sensor electrode 341a and the second sensor electrode 342a, and an inter-electrode voltage between the second sensor electrode 342a and the third sensor electrode 343a. These inter-electrode voltages are processed by a signal processing circuit, such as an amplifier circuit (not shown), to generate an output signal corresponding to the sound waves or ultrasonic waves received by the piezoelectric device 1.

[0041] Here, let us consider a case where the beam-like portion 32 of the diaphragm 3 warps, causing a curvature that appears in a cross section perpendicular to the first direction D1 (for example, the VV cross section in FIG. 2). When such a curvature that appears in the cross section, i.e., a cross-sectional curvature, occurs in the beam-like portion 32, the vibration of the cantilevered beam-like portion 32 that reciprocates the free end portion 32b in the directional axis direction Da is inhibited, and as a result, the sensitivity of the piezoelectric device 1 that functions as a microphone decreases.

[0042] Therefore, the inventors conceived of changing a part of the beam-like portion 32 from the conventional flat plate shape shown in Figures 4(a) and 5(a) to a corrugated structure SW shown in Figures 4(b) and 5(b). The corrugated structure SW is formed in a corrugated shape as shown in Figure 4(b) in a cross section perpendicular to the second direction D2 (for example, cross section III-III in Figure 2), and is linearly extended along the second direction D2 as shown in Figure 5(b). In other words, the corrugated structure SW is linearly extended along the second direction D2 while maintaining the corrugated cross section shown in Figure 4(b).

[0043] When such a corrugated structure SW is provided on the beam-like portion 32, the second moment of area of ​​the beam-like portion 32 with respect to the neutral axis Ln of bending deformation of the beam-like portion 32 becomes larger in a cross section perpendicular to the second direction D2 as shown in (a) and (b) of Figure 4, compared to when the entire beam-like portion 32 is flat. On the other hand, in a transverse cross section perpendicular to the first direction D1, the second moment of area is the same whether the corrugated structure SW is provided on the beam-like portion 32 or when the entire beam-like portion 32 is flat, as shown in (a) and (b) of Figure 5.

[0044] From these facts, it was considered that the wave structure SW has the effect of countering and suppressing the above-mentioned cross-sectional curvature of the beam-like portion 32 without inhibiting the vibration of the beam-like portion 32 that reciprocates the free end portion 32b in the directional axis direction Da. In this embodiment, the beam-like portion 32 of the diaphragm 3 is configured taking into consideration the effect of the wave structure SW.

[0045] 6 to 9, the beam-like portion 32 of the diaphragm 3 has a first concave-convex structure portion 361, a second concave-convex structure portion 362, and a third concave-convex structure portion 363, which correspond to the above-mentioned wave structure SW. The first to third concave-convex structure portions 361, 362, and 363 each have a shape that extends linearly in the second direction D2, and extend from one edge of the beam-like portion 32 in the second direction D2 to the other edge. The first to third concave-convex structure portions 361, 362, and 363 are arranged in parallel to one another at intervals from one side in the first direction D1 in the order of the first concave-convex structure portion 361, the second concave-convex structure portion 362, and the third concave-convex structure portion 363.

[0046] In the description of this embodiment, when the first concave-convex structure portion 361, the second concave-convex structure portion 362, and the third concave-convex structure portion 363 are collectively referred to without distinction, they may be referred to as the concave-convex structure portion 36. In addition, in Fig. 6, the illustration of the concave-convex structure portion 36 is simplified, and each of the multiple concave-convex structure portions 36 is represented by a dashed line. The method of representing the concave-convex structure portion 36 by a dashed line is also adopted in later-described figures corresponding to Fig. 6.

[0047] 6 and 7, the first concave-convex structure 361 is disposed so that its position in the first direction D1 overlaps with all of the sensor electrodes 341a, 342a, and 343a of the beam-shaped portion 32. In other words, the first concave-convex structure 361 is disposed within a first sensor electrode range W1, a second sensor electrode range W2, and a third sensor electrode range W3 of the beam-shaped portion 32 in FIG. 3. The first sensor electrode range W1 is the range occupied by the first sensor electrode 341a in the first direction D1, the second sensor electrode range W2 is the range occupied by the second sensor electrode 342a in the first direction D1, and the third sensor electrode range W3 is the range occupied by the third sensor electrode 343a in the first direction D1. In other words, the first concave-convex structure 361 is disposed within an overlapping range where the sensor electrode ranges W1, W2, and W3 of the sensor electrodes 341a, 342a, and 343a all overlap in the beam-shaped portion 32. In this embodiment, the overlapping range coincides with the third sensor electrode range W3 as shown in FIG.

[0048] 6 and 8, the second uneven structure 362 is disposed between the third sensor electrode 343a and the third floating electrode 343b of the beam-shaped portion 32. Furthermore, as shown in Fig. 6 and 9, the third uneven structure 363 is disposed so that its position in the first direction D1 overlaps with all of the floating electrodes 341b, 342b, 343b of the beam-shaped portion 32.

[0049] 7 to 9, each of the plurality of concave-convex structures 36 has a plurality of first concave-convex portions 37 and a plurality of second concave-convex portions 38. Each of the plurality of first concave-convex portions 37 has a first concave shape 371 provided on one surface 32c of the beam-shaped portion 32 and a first convex shape 372 provided on the other surface 32d of the beam-shaped portion 32 at a portion that overlaps with the first concave shape 371 on the other side in the directional axis direction Da. The first concave shape 371 and the first convex shape 372 each extend linearly in the second direction D2.

[0050] On the other hand, the second uneven portions 38 have a shape obtained by inverting the first uneven portions 37 in the directional axis direction Da. That is, each of the multiple second uneven portions 38 has a second convex shape 381 provided on one surface 32c of the beam-shaped portion 32 and a second concave shape 382 provided on the other surface 32d of the beam-shaped portion 32 at a position that overlaps with the second convex shape 381 on the other side in the directional axis direction Da. The second convex shape 381 and the second concave shape 382 each extend linearly in the second direction D2.

[0051] Furthermore, in each of the multiple concave-convex structures 36, the first concave-convex portions 37 and the second concave-convex portions 38 are alternately arranged in the first direction D1, and the first concave-convex portions 37 and the second concave-convex portions 38 adjacent to each other in the first direction D1 are continuously connected. That is, in a cross section perpendicular to the second direction D2, each of the multiple concave-convex structures 36 forms a wave-shaped configuration in which the first concave-convex portions 37 and the second concave-convex portions 38 are alternately connected continuously. The wave-shaped cross-sectional shape of such a concave-convex structure 36 is formed by, for example, etching or the like.

[0052] Each of the plurality of concave-convex structure portions 36 is formed to have a uniform thickness tw in a cross section perpendicular to the second direction D2. Here, the uniformity of the thickness tw of the concave-convex structure portion 36 does not necessarily mean that the thickness tw is strictly constant, and the thickness tw is interpreted as being uniform if the variation in the thickness tw is approximately the same as the presence or absence of the electrode layer 34. Furthermore, the thickness tw of the concave-convex structure portion 36 does not mean the dimension in the direction along the directional axis direction Da, but means the thickness in the direction following the waveform shape of the concave-convex structure portion 36.

[0053] For example, in this embodiment, the plurality of piezoelectric layers 35 occupy most of the beam-like portion 32 of the diaphragm 3. The plurality of piezoelectric layers 35 are formed so that the total thickness of the plurality of piezoelectric layers 35 is uniform in a cross section perpendicular to the second direction D2.

[0054] 7, in each of the plurality of concave-convex structures 36, the recess amount H1 of the first recessed shape 371 from one surface 32c of the beam-shaped portion 32 and the recess amount H2 of the second recessed shape 382 from the other surface 32d are each less than half the plate thickness tb of the beam-shaped portion 32 in the axial direction Da. Therefore, neither the first recessed shape 371 nor the second recessed shape 382 reaches the neutral axis Ln of the bending deformation of the beam-shaped portion 32.

[0055] The piezoelectric device 1 of this embodiment described above can achieve the following effects. As shown in FIGS. 6 to 9 , according to this embodiment, the beam-like portion 32 of the diaphragm 3 has a plurality of concave-convex structures 36, and each of the plurality of concave-convex structures 36 has a plurality of first concave-convex portions 37 and a plurality of second concave-convex portions 38. The first concave-convex portions 37 are formed with a first concave shape 371 on one surface 32c of the beam-like portion 32 and a first convex shape 372 on the other surface 32d of the beam-like portion 32 at a position that overlaps with the first concave shape 371 on the other side of the directional axis direction Da. The first concave shape 371 and the first convex shape 372 each extend linearly in the second direction D2. On the other hand, the second uneven portion 38 is formed with a second convex shape 381 provided on one surface 32c of the beam-shaped portion 32, and a second concave shape 382 provided on the other surface 32d of the beam-shaped portion 32 at a portion that overlaps with the second convex shape 381 on the other side in the directional axis direction Da. The second convex shape 381 and the second concave shape 382 each extend linearly in the second direction D2.

[0056] By providing the concave-convex structure 36 on the beam-like portion 32 in this way, the bending rigidity of the beam-like portion 32 against the curvature of the beam-like portion 32 that appears in a cross section perpendicular to the first direction D1 is higher than when, for example, the beam-like portion 32 is flat as a whole without the concave-convex structure 36. On the other hand, since the first and second concave shapes 371, 382 and the first and second convex shapes 372, 381 each extend linearly in the second direction D2, the bending rigidity of the beam-like portion 32 against the curvature of the beam-like portion 32 that appears in a cross section perpendicular to the second direction D2 is not increased.

[0057] Therefore, while not hindering the vibration of the beam-like portion 32 of the diaphragm 3, the curvature of the beam-like portion 32 appearing in a cross section perpendicular to the first direction D1 can be suppressed compared to, for example, when there is no uneven structure portion 36 and the entire beam-like portion 32 is flat.

[0058] (1) Furthermore, according to this embodiment, the recess amount H1 of the first recessed shape 371 from the one surface 32c of the beam-shaped portion 32 and the recess amount H2 of the second recessed shape 382 from the other surface 32d are each less than half the plate thickness tb of the beam-shaped portion 32 in the axial direction Da. Therefore, neither the first recessed shape 371 nor the second recessed shape 382 reaches the neutral axis Ln of the bending deformation of the beam-shaped portion 32. In other words, the neutral axis Ln does not intersect with either the first or second recessed shape 371, 382, ​​and therefore passes through the concave-convex structure portion 36 without partially departing from the concave-convex structure portion 36.

[0059] Here, in vibrations accompanied by bending deformation of the beam-like portion 32, tensile strain occurs on one side of the neutral axis Ln of the beam-like portion 32, and simultaneously compressive strain occurs on the other side. However, in the above configuration, both tensile strain and compressive strain occur simultaneously over the entire area of ​​the concave-convex structure portion 36 in a plan view. Therefore, it is possible to suppress a decrease in sensitivity of the piezoelectric device 1 caused by the provision of the concave-convex structure portion 36.

[0060] (2) Furthermore, according to this embodiment, the first concave-convex structure 361 is disposed within an overlapping range of the beam-shaped portion 32, where the sensor electrode ranges W1, W2, and W3 of the sensor electrodes 341a, 342a, and 343a all overlap. Here, cross-sectional curvature of the beam-shaped portion 32 occurring at the locations of the entire beam-shaped portion 32 where the first to third sensor electrodes 341a, 342a, and 343a are disposed is most likely to lead to a decrease in the sensitivity of the piezoelectric device 1. Therefore, by disposing the first concave-convex structure 361 within the overlapping range, it is possible to effectively suppress the cross-sectional curvature that is likely to lead to a decrease in the sensitivity of the piezoelectric device 1.

[0061] (3) Furthermore, according to this embodiment, the second concave-convex structure 362 is disposed between the third sensor electrode 343a and the third floating electrode 343b in the beam-shaped portion 32. Therefore, the second concave-convex structure 362 can be disposed near the third sensor electrode 343a while avoiding design restrictions imposed by the third sensor electrode 343a and the third floating electrode 343b, and it is possible to suppress cross-sectional curvature of the beam-shaped portion 32 that may occur at the location where the third sensor electrode 343a is disposed.

[0062] (4) Furthermore, according to this embodiment, each of the plurality of concave-convex structure portions 36 is formed to have a uniform thickness tw in a cross section perpendicular to the second direction D2. Therefore, it is possible to suppress variations in the bending rigidity of the beam-like portion 32 against bending deformation that appear in a cross section perpendicular to the second direction D2 within the concave-convex structure portion 36.

[0063] (Second embodiment) Next, a second embodiment will be described. In this embodiment, differences from the first embodiment will be mainly described. Furthermore, parts that are the same as or equivalent to the first embodiment will be omitted or simplified. This also applies to the following embodiments.

[0064] 10, in this embodiment, the beam-like portion 32 of the diaphragm 3 has two concave-convex structure portions 36. Therefore, the beam-like portion 32 of this embodiment has a first concave-convex structure portion 361 and a second concave-convex structure portion 362, but does not have a third concave-convex structure portion 363 (see FIG. 6), unlike the first embodiment.

[0065] 10, the second concave-convex structure portion 362 of this embodiment is not disposed between the third sensor electrode 343a and the third floating electrode 343b, as in the first embodiment. As shown in FIG. 3 and FIG. 10, the second concave-convex structure portion 362 of this embodiment is disposed in the first sensor electrode range W1, the second sensor electrode range W2, and the third sensor electrode range W3 of the beam-shaped portion 32, which overlap each other, similar to the first concave-convex structure portion 361.

[0066] Specifically, all of the concave-convex structure portions 36 of the beam-shaped portion 32 are arranged only within the first sensor electrode range W1, the second sensor electrode range W2, and the third sensor electrode range W3, which overlap each other, of the beam-shaped portion 32. In other words, all of the concave-convex structure portions 36 of the beam-shaped portion 32 are arranged only within the overlapping range in which the sensor electrode ranges W1, W2, and W3 of the sensor electrodes 341a, 342a, and 343a all overlap. Note that, since the second concave-convex structure portion 362 is arranged within the overlapping range, its cross-section perpendicular to the second direction D2 has the same cross-sectional configuration as the first concave-convex structure portion 361 shown in FIG. 7.

[0067] (1) According to this embodiment, the first sensor electrode range W1, the second sensor electrode range W2, and the third sensor electrode range W3 overlap with each other as shown in Fig. 3. As shown in Fig. 3 and Fig. 10, all of the concave-convex structure portions 36 of the beam-shaped portion 32 are arranged only within the first sensor electrode range W1, the second sensor electrode range W2, and the third sensor electrode range W3 of the beam-shaped portion 32.

[0068] Therefore, by providing the concave-convex structure 36 at the locations of the sensor electrodes 341a, 342a, and 343a where cross-sectional curvature of the beam-shaped portion 32 is most likely to lead to a decrease in sensitivity, it is possible to effectively suppress the decrease in sensitivity due to that cross-sectional curvature. On the other hand, since the concave-convex structure 36 is not provided in a location where the effect of suppressing a decrease in sensitivity due to cross-sectional curvature is relatively weak, it is possible to alleviate any restrictions that may arise due to the provision of the concave-convex structure 36. As a result, it is easier to ensure the reliability of the piezoelectric device 1, for example.

[0069] Furthermore, the first to third sensor electrode ranges W1, W2, and W3 in which all of the concave-convex structure portions 36 are arranged are biased toward one side of the beam-shaped portion 32 in the first direction D1, and the beam-shaped portion 32 is formed so that it widens in the second direction D2 toward one side of the first direction D1. The wider the width of the beam-shaped portion 32 in the second direction D2, the more likely it is that the beam-shaped portion 32 will be significantly curved in cross section. Therefore, the concave-convex structure portions 36 are concentrated in locations where the curvature in cross section is likely to be significant, which also makes it possible to effectively suppress a decrease in sensitivity due to the curvature in cross section.

[0070] Except for the points described above, this embodiment is the same as the first embodiment. In this embodiment, the same effects as those of the first embodiment can be obtained from the configuration common to the first embodiment.

[0071] (Third embodiment) Next, a third embodiment will be described, focusing on the differences from the first embodiment.

[0072] 11, in this embodiment, the beam-like portion 32 of the diaphragm 3 has the second concave-convex structure portion 362 among the first to third concave-convex structure portions 361, 362, 363 in FIG. 6, but does not have the first concave-convex structure portion 361 or the third concave-convex structure portion 363. Therefore, in the following description of this embodiment, the second concave-convex structure portion 362 will be simply referred to as the concave-convex structure portion 362.

[0073] According to this embodiment, the concave-convex structure 362 of the beam-shaped portion 32 is disposed only between the third sensor electrode 343a and the third floating electrode 343b of the beam-shaped portion 32. In other words, the concave-convex structure 362 is disposed at a position away from both the third sensor electrode 343a and the third floating electrode 343b.

[0074] Therefore, when designing the concave-convex structure 362, there is no need to be concerned about design restrictions imposed by the third sensor electrode 343a and the third floating electrode 343b, which increases the degree of freedom in designing the diaphragm 3. Furthermore, since the concave-convex structure 362 is disposed near the third sensor electrode 343a, it is possible to obtain the effect of suppressing cross-sectional curvature of the beam-like portion 32 that may occur at the location where the third sensor electrode 343a is disposed.

[0075] Except for the points described above, this embodiment is the same as the first embodiment. In this embodiment, the same effects as those of the first embodiment can be obtained from the configuration common to the first embodiment.

[0076] (Fourth embodiment) Next, a fourth embodiment will be described, focusing on the differences from the third embodiment.

[0077] 12 and 13, the concave-convex structure portion 362 of this embodiment is disposed between the first sensor electrode 341a and the first floating electrode 341b, not between the third sensor electrode 343a and the third floating electrode 343b, in the beam-shaped portion 32. That is, the concave-convex structure portion 362 of this embodiment is disposed only between the first sensor electrode 341a and the first floating electrode 341b in the beam-shaped portion 32. Note that in FIGS. 12 and 13, a dash-dotted line La is drawn to clearly show the arrangement of the concave-convex structure portion 362, and the dash-dotted line La represents the center position between the first sensor electrode 341a and the first floating electrode 341b in the first direction D1.

[0078] Moreover, the concave-convex structure portion 362 of this embodiment does not have the second concave-convex portion 38 (see FIG. 8 ), and is composed of the first concave-convex portion 37. To be more specific, in this embodiment, the concave-convex structure portion 362 is composed of one first concave-convex portion 37.

[0079] (1) Since the concave-convex structure 362 is configured as described above, it is possible to form the concave-convex structure 362 by over-etching the etching that separates the first sensor electrode 341a and the first floating electrode 341b during the manufacture of the piezoelectric device 1. Therefore, it is possible to form the concave-convex structure 362 while suppressing an increase in the number of manufacturing steps that would otherwise be required to form the concave-convex structure 362.

[0080] Except for the points described above, this embodiment is the same as the third embodiment. In this embodiment, the same effects as those of the third embodiment can be obtained from the configuration common to the third embodiment.

[0081] (Other embodiments) (1) In each of the above-described embodiments, the piezoelectric device 1 functions as a microphone that converts sound waves or ultrasonic waves into electrical signals, but this is just one example. Conversely, the piezoelectric device 1 may function as a speaker that converts electrical signals into sound waves or ultrasonic waves.

[0082] (2) In each of the above-described embodiments, the diaphragm 3 has three electrode layers 34 and two piezoelectric layers 35, as shown in Fig. 3, but this is just an example. Four or more electrode layers 34 may be provided, and three or more piezoelectric layers 35 may be provided.

[0083] (3) In the first embodiment described above, as shown in Figures 7 to 9, the concave-convex structure 36 has a plurality of first concave-convex portions 37 and a plurality of second concave-convex portions 38, but this is just one example. For example, the concave-convex structure 36 may have one each of the first concave-convex portion 37 and the second concave-convex portion 38. Alternatively, the concave-convex structure 36 may have only one of the first concave-convex portion 37 and the second concave-convex portion 38, and not the other.

[0084] (4) In the first embodiment described above, the corrugated shape of the concave-convex structure 36 that appears in a cross section perpendicular to the second direction D2 is smoothly curved, as shown in Figures 7 to 9. However, this is just one example. For example, the corrugated shape of the concave-convex structure 36 that appears in a cross section perpendicular to the second direction D2 may be corrugated while bending the first and second convex shapes 372, 381 to sharpen them.

[0085] (5) In each of the above-described embodiments, the separation portion between the first sensor electrode 341a and the first floating electrode 341b, the separation portion between the second sensor electrode 342a and the second floating electrode 342b, and the separation portion between the third sensor electrode 343a and the third floating electrode 343b are offset from one another in the first direction D1, as shown in Fig. 3. However, this is just one example, and the positions of these separation portions in the first direction D1 may be aligned with one another.

[0086] (6) In each of the above-described embodiments, the beam-like portions 32 of the diaphragm 3 have a triangular shape in plan view, as shown in Figures 1 and 2, but this is not limited thereto. For example, the shape of the beam-like portions 32 in plan view may be rectangular, trapezoidal, or various other shapes.

[0087] (7) In each of the above-described embodiments, the piezoelectric device 1 has four diaphragms 3. However, this is merely an example. For example, the piezoelectric device 1 may have one, two, or three diaphragms 3, or may have five or more diaphragms 3.

[0088] (8) Various shapes are conceivable for the base substrate 2. For example, the base substrate 2 may have a shape such as a cylinder, an elliptical cylinder, a triangular cylinder, a pentagonal cylinder, a hexagonal cylinder, or an octagonal cylinder surrounding the directional axis Lc. Alternatively, the base substrate 2 may have a shape such as a circular ring, an elliptical ring, a triangular ring, a pentagonal ring, a hexagonal ring, or an octagonal ring surrounding the directional axis Lc.

[0089] (9) In each of the above-described embodiments, the diaphragm 3 is fixed to one end surface 24 of the base substrate 2, but the present disclosure is not limited to such an embodiment. For example, it is not impossible in principle to configure the diaphragm 3 such that the outer edge of the diaphragm 3, which is provided at one end in the first direction D1 and forms the fixed end portion 32a, is fixed by a groove or adhesive layer provided on the inner wall surface 22 of the base substrate 2. In other words, the fixed portion 31 of the diaphragm 3, which does not flexurally vibrate, can be omitted. In this case, the entire diaphragm 3 forms the beam-like portion 32 that flexurally vibrates.

[0090] (10) In each of the above-described embodiments, the oxide film 4 may be omitted. Alternatively, a film for improving the bonding state between the base substrate 2 and the diaphragm 3 may be provided in place of the oxide film 4. There are also no particular limitations on the materials constituting each part. Furthermore, the terms "film" and "layer" are interchangeable.

[0091] (11) In the above description, multiple components that were formed seamlessly and integrally with each other may be formed by bonding separate members together. Similarly, multiple components that were formed by bonding separate members together may be formed seamlessly and integrally with each other. Furthermore, in the above description, multiple components that were formed from the same material may be formed from different materials. Similarly, multiple components that were formed from different materials may be formed from the same material.

[0092] (12) Note that the present disclosure is not limited to the above-described embodiments and can be implemented in various modified forms. Furthermore, it goes without saying that, in each of the above-described embodiments, elements constituting the embodiments are not necessarily essential unless they are specifically stated as essential or are clearly considered essential in principle.

[0093] Furthermore, in each of the above embodiments, when numerical values ​​such as the number, values, amounts, and ranges of components of the embodiments are mentioned, they are not limited to the specific numbers, except when it is particularly clearly stated that they are essential or when they are clearly limited to a specific number in principle, etc. Furthermore, in each of the above embodiments, when the material, shape, positional relationship, etc. of components are mentioned, they are not limited to the material, shape, positional relationship, etc., except when it is particularly clearly stated or when they are clearly limited to a specific material, shape, positional relationship, etc. in principle, etc.

[0094] (Aspects of the present disclosure) The present disclosure described above can be understood from the following viewpoints, for example. [First viewpoint] A piezoelectric device that functions as a microphone or speaker, a beam-like portion (32) including a piezoelectric layer (35, 351, 352) made of a piezoelectric material, formed in a plate shape perpendicular to an axial direction (Da) of a directivity axis (Lc), and having a fixed end (32a) provided on one side in a first direction (D1) perpendicular to the axial direction, a free end (32b) provided on the other side in the first direction, one face (32c) formed on one side in the axial direction, and another face (32d) formed on the other side in the axial direction, the free end being configured in a cantilever shape so as to be displaceable back and forth in the axial direction relative to the fixed end; a support portion (2) to which the fixed end portion is fixed and which supports the fixed end portion, the beam-shaped portion has a concave-convex structure portion (36, 361, 362, 363) constituted by at least one of a first concave-convex portion (37) and a second concave-convex portion (38); The first uneven portion is formed with a first concave shape (371) that extends linearly in a second direction (D2) perpendicular to the axial direction and the first direction and is provided on the one surface, and a first convex shape (372) that is provided on the other surface at a portion that overlaps the other side of the first concave shape in the axial direction and extends linearly in the second direction, A piezoelectric device in which the second uneven portion is formed with a second convex shape (381) extending linearly in the second direction and provided on the one surface, and a second concave shape (382) extending linearly in the second direction and provided on the other surface in a portion that overlaps the other side of the axial direction with the second convex shape. [Second viewpoint] A piezoelectric device as described in a first aspect, wherein the recess amount (H1) of the first recessed shape from the one surface and the recess amount (H2) of the second recessed shape from the other surface are each less than half the plate thickness (tb) of the beam-shaped portion in the axial direction. [Third Perspective] The beam-shaped portion has a plurality of sensor electrodes (341a, 342a, 343a) electrically connected to wiring (5) leading to the outside and stacked on different layers of the piezoelectric layer, A piezoelectric device described in the first or second aspect, wherein the uneven structure portion is arranged within an overlapping range of the beam-shaped portion in which the ranges (W1, W2, W3) of each sensor electrode occupied in the first direction all overlap. [Fourth viewpoint] the beam-shaped portion is formed to widen in the second direction toward the one side in the first direction, The beam-shaped portion includes an electrode layer (34, 341, 342, 343) made of a conductive material and laminated on the piezoelectric layer, the electrode layer includes sensor electrodes (341a, 342a, 343a) electrically connected to wiring (5) leading to the outside, and floating electrodes (341b, 342b, 343b) spaced apart from the wiring and disposed on the other side of the sensor electrodes in the first direction; A piezoelectric device described in the first or second aspect, wherein the uneven structure portion is arranged only within the range (W1, W2, W3) of the beam-shaped portion that the sensor electrode occupies in the first direction. [Fifth viewpoint] the beam-shaped portion is formed to widen in the second direction toward the one side in the first direction, The beam-shaped portion includes an electrode layer (34, 341, 342, 343) made of a conductive material and laminated on the piezoelectric layer, the electrode layer includes sensor electrodes (341a, 342a, 343a) electrically connected to wiring (5) leading to the outside, and floating electrodes (341b, 342b, 343b) spaced apart from the wiring and disposed on the other side of the sensor electrodes in the first direction; The piezoelectric device according to the first or second aspect, wherein the concave-convex structure is disposed on the beam-shaped portion between the sensor electrode and the floating electrode. [Sixth viewpoint] Two or more piezoelectric layers are provided, The beam-shaped portion includes three or more electrode layers (34) made of a conductive material, The piezoelectric device according to the first or second aspect, wherein the electrode layers and the piezoelectric layers are alternately stacked in the axial direction. [Seventh viewpoint] the support portion is disposed on the other side in the axial direction with respect to the beam portion, the beam-shaped portion includes an electrode layer (341) made of a conductive material, laminated on the piezoelectric layer, and forming the other surface; the electrode layer has a sensor electrode (341a) electrically connected to a wiring (5) leading to the outside, and a floating electrode (341b) spaced apart from the wiring and disposed on the other side of the sensor electrode in the first direction; A piezoelectric device as described in the first or second aspect, wherein the uneven structure portion (362) has the first uneven portion without the second uneven portion, and is arranged between the sensor electrode and the floating electrode in the beam-shaped portion. [Eighth viewpoint] The piezoelectric device according to any one of the first to seventh aspects, wherein the concave-convex structure portion is formed to have a uniform thickness (tw) in a cross section perpendicular to the second direction. [Ninth viewpoint] The piezoelectric device according to any one of the first to eighth aspects, wherein the piezoelectric material is any one of AlN, ScAlN, ZnO, PZT, KLN, KNN, and BaTiO3. [Explanation of symbols]

[0095] 1. Piezoelectric devices 2 Base board (support part) 32 Beam-like part 32a Fixed end 32b Free end 32c one side 32d other side 36 Uneven structure 37 First uneven part 38 Second uneven part

Claims

1. A piezoelectric device that functions as a microphone or speaker, a beam-like portion (32) including a piezoelectric layer (35, 351, 352) made of a piezoelectric material, formed in a plate shape perpendicular to an axial direction (Da) of a directivity axis (Lc), having a fixed end (32a) provided on one side in a first direction (D1) perpendicular to the axial direction, a free end (32b) provided on the other side in the first direction, one face (32c) formed on one side in the axial direction, and another face (32d) formed on the other side in the axial direction, the free end being configured in a cantilever shape so as to be displaceable back and forth in the axial direction relative to the fixed end; a support part (2) to which the fixed end part is fixed and which supports the fixed end part, The beam-shaped portion has a concave-convex structure portion (36, 361, 362, 363) constituted by at least one of a first concave-convex portion (37) and a second concave-convex portion (38), The first uneven portion has a first concave shape (371) provided on the one surface and extending linearly in a second direction (D2) perpendicular to the axial direction and the first direction, and a first convex shape (372) provided on the other surface at a portion overlapping the other side of the first concave shape in the axial direction and extending linearly in the second direction, A piezoelectric device in which the second uneven portion is formed with a second convex shape (381) extending linearly in the second direction and provided on the one surface, and a second concave shape (382) extending linearly in the second direction and provided on the other surface in a portion that overlaps the other side of the second convex shape in the axial direction.

2. 2. The piezoelectric device of claim 1, wherein the recess amount (H1) of the first recessed shape from the one surface and the recess amount (H2) of the second recessed shape from the other surface are each less than half the plate thickness (tb) of the beam-shaped portion in the axial direction.

3. The beam-shaped portion has a plurality of sensor electrodes (341a, 342a, 343a) electrically connected to wiring (5) leading to the outside and stacked in different layers on the piezoelectric layer, The piezoelectric device of claim 1 or 2, wherein the uneven structure portion is arranged within an overlapping range of the beam-shaped portion in which the ranges (W1, W2, W3) of each sensor electrode occupied by the sensor electrode in the first direction all overlap.

4. the beam-shaped portion is formed to widen in the second direction toward the one side in the first direction, The beam-shaped portion includes an electrode layer (34, 341, 342, 343) made of a conductive material and laminated on the piezoelectric layer, the electrode layer has sensor electrodes (341 a, 342 a, 343 a) electrically connected to wiring (5) leading to the outside, and floating electrodes (341 b, 342 b, 343 b) spaced apart from the wiring and arranged on the other side of the sensor electrodes in the first direction, The piezoelectric device according to claim 1 , wherein the concave-convex structure is disposed only within a range (W1, W2, W3) of the beam-shaped portion that is occupied by the sensor electrode in the first direction.

5. the beam-shaped portion is formed to widen in the second direction toward the one side in the first direction, The beam-shaped portion includes an electrode layer (34, 341, 342, 343) made of a conductive material and laminated on the piezoelectric layer, the electrode layer has sensor electrodes (341 a, 342 a, 343 a) electrically connected to wiring (5) leading to the outside, and floating electrodes (341 b, 342 b, 343 b) spaced apart from the wiring and arranged on the other side of the sensor electrodes in the first direction, The piezoelectric device according to claim 1 , wherein the concave-convex structure is disposed on the beam-shaped portion between the sensor electrode and the floating electrode.

6. Two or more piezoelectric layers are provided, The beam-shaped portion includes three or more electrode layers (34) made of a conductive material, The piezoelectric device according to claim 1 , wherein the electrode layers and the piezoelectric layers are alternately stacked in the axial direction.

7. the support portion is disposed on the other side in the axial direction with respect to the beam portion, The beam-shaped portion includes an electrode layer (341) made of a conductive material, laminated on the piezoelectric layer, and forming the other surface, the electrode layer has a sensor electrode (341a) electrically connected to a wiring (5) leading to the outside, and a floating electrode (341b) spaced apart from the wiring and disposed on the other side of the sensor electrode in the first direction; The piezoelectric device of claim 1 or 2, wherein the uneven structure portion (362) has the first uneven portion without the second uneven portion, and is arranged between the sensor electrode and the floating electrode in the beam-shaped portion.

8. The piezoelectric device according to claim 1 , wherein the concave-convex structure portion is formed to have a uniform thickness (tw) in a cross section perpendicular to the second direction.

9. The piezoelectric material is AlN, ScAlN, ZnO, PZT, KLN, KNN, or BaTiO 3 3. The piezoelectric device according to claim 1, wherein the piezoelectric element is any one of the following:

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