Piezoelectric elements

Abstract

The present disclosure relates to a piezoelectric element. The piezoelectric element comprises a piezoelectric element portion having a piezoelectric film and electrodes sandwiching the piezoelectric film in the thickness direction; a support portion supporting the peripheral edge of the piezoelectric element portion; and a stretchable film. The stretchable film is disposed within a vibration region within the peripheral edge of the piezoelectric element portion. Furthermore, the stretchability of the stretchable film is higher than that of the piezoelectric element portion.

Description

[0001] The present application is an application entering the Chinese national phase of international application PCT / JP2020 / 028931 (international filing date: July 28, 2020), which is incorporated herein by reference. Technical Field

[0002] Embodiments of the present invention relate to a piezoelectric element. Background Art

[0003] Piezoelectric elements are known that extract the deformation of a piezoelectric film sandwiched between electrode films as a voltage change. Furthermore, a structure is disclosed in which slits are formed in the piezoelectric film to suppress residual stress in the piezoelectric film whose periphery is fixed by a support substrate or the like.

[0004] However, in the conventional technology, the SN ratio may be reduced (for example, refer to JP Patent No. 5707323). Summary of the Invention

[0005] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a piezoelectric element capable of suppressing a decrease in the SN ratio.

[0006] A piezoelectric element according to an embodiment includes a piezoelectric element portion, a support portion, and a stretchable film. The piezoelectric element portion includes a piezoelectric film and electrodes sandwiching the piezoelectric film in the thickness direction. The support portion supports the peripheral edge of the piezoelectric element portion. The stretchable film is provided in a vibration region within the peripheral edge of the piezoelectric element portion and has a higher stretchability than the piezoelectric element portion. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1A is a top view of the piezoelectric element.

[0008] Figure 1B is a cross-sectional view of a piezoelectric element.

[0009] Figure 1C Schematic diagram showing an example of a piezoelectric element.

[0010] Figure 1D Schematic diagram showing an example of a piezoelectric element.

[0011] Figure 1E Schematic diagram showing an example of a piezoelectric element.

[0012] Figure 1F Schematic diagram showing an example of a piezoelectric element.

[0013] Figure 1G Schematic diagram showing an example of a piezoelectric element.

[0014] Figure 1H is a top view of the piezoelectric element.

[0015] Figure 1I is a cross-sectional view of a piezoelectric element.

[0016] Figure 1J This is a graph showing the relationship between the ratio of the opening diameter of the through hole to the diameter of the vibration region and the receiving sensitivity of the piezoelectric element portion.

[0017] Figure 2A is a top view of the piezoelectric element.

[0018] Figure 2B is a cross-sectional view of a piezoelectric element.

[0019] Figure 2C is a top view of the piezoelectric element.

[0020] Figure 3A is a top view of the piezoelectric element.

[0021] Figure 3B is a cross-sectional view of a piezoelectric element.

[0022] Figure 4 is a top view of the piezoelectric element. DETAILED DESCRIPTION

[0023] Hereinafter, the details of this embodiment will be described with reference to the accompanying drawings. In the following embodiments and modifications, the same reference numerals are given to parts representing the same structure and function, and detailed description thereof may be omitted.

[0024] (First embodiment)

[0025] Figure 1A This is an example of a plan view of the piezoelectric element 10 according to the present embodiment. Figure 1B yes Figure 1A The piezoelectric element 10 is shown in a cross-sectional view taken along line AA′.

[0026] The piezoelectric element 10 includes a piezoelectric element portion 12 , a support portion 18 , and a stretchable film 22 .

[0027] The piezoelectric element portion 12 includes a piezoelectric film 14 and electrodes 16 that sandwich the piezoelectric film 14 in the thickness direction (arrow Z direction).

[0028] The piezoelectric film 14 is a film that exhibits an electromechanical conversion effect. The piezoelectric film 14 is made of a known piezoelectric material. The electrodes 16 are arranged so as to sandwich the piezoelectric film 14 in the thickness direction (arrow Z direction) of the piezoelectric film 14 .

[0029] In the following description, the thickness direction of the piezoelectric film 14 is sometimes referred to as the thickness direction Z. That is, the thickness direction Z is the direction that coincides with the thickness direction of the piezoelectric film 14. Furthermore, directions orthogonal to the thickness direction Z are referred to as the X direction and the Y direction. Furthermore, a two-dimensional plane orthogonal to the thickness direction Z (XY plane) is referred to as a direction intersecting the thickness direction Z.

[0030] The piezoelectric element portion 12 may be a laminated body in which a plurality of piezoelectric films 14 are laminated in the thickness direction Z. In this case, Figure 1B As shown, the piezoelectric films 14 constituting the stacked body may be structured so as to be sandwiched between the electrodes 16 in the thickness direction Z. That is, the piezoelectric element portion 12 may also have a bimorph structure.

[0031] The support portion 18 supports the peripheral portion E1 of the piezoelectric element portion 12. The support portion 18 is produced, for example, by forming a hole 19 in a plate-shaped support substrate that penetrates the support substrate in the thickness direction Z. The end surface of the support portion 18 in the thickness direction Z is arranged to contact the peripheral portion E1 of the piezoelectric element portion 12, thereby supporting the peripheral portion E1 of the piezoelectric element portion 12.

[0032] The peripheral portion E1 is supported by the support portion 18, thereby allowing the vibration region E2 inside the peripheral portion E1 of the piezoelectric element portion 12 to vibrate. The vibration region E2 inside the peripheral portion E1 refers to the region inside the peripheral portion E1 in a two-dimensional plane along a direction intersecting the thickness direction Z of the piezoelectric element portion 12. In other words, the vibration region E2 is the region that overlaps with the hole 19 when the piezoelectric element portion 12 is viewed from above along the thickness direction Z. Therefore, the vibration region E2 can vibrate without being hindered by the support portion 18 of the piezoelectric element portion 12.

[0033] On the other hand, the peripheral edge E1 of the piezoelectric element portion 12 is fixed non-vibrationally by the support portion 18. In the following description, a plan view of the piezoelectric element 10 viewed along the thickness direction Z of the piezoelectric element portion 12 is simply referred to as a plan view.

[0034] In this embodiment, a case where the vibration region E2 of the piezoelectric element portion 12 is circular in a plan view is described as an example. That is, in this embodiment, a case where the support portion 18 is a circular frame-shaped member having a circular hole 19 in a plan view is described as an example. Therefore, in this embodiment, a case where the peripheral portion E1 of the piezoelectric element portion 12 is a circular frame-shaped region in a plan view is described as an example. Therefore, in this embodiment, a case where the vibration region E2 of the piezoelectric element portion 12 is a circular region in a plan view is described as an example.

[0035] In the present embodiment, the piezoelectric element portion 12 is provided with the slit 20 .

[0036] The slit 20 is provided in the vibration region E2 of the piezoelectric element portion 12. The slit 20 penetrates the vibration region E2 of the piezoelectric element portion 12 in the thickness direction Z.

[0037] like Figure 1A As shown, for example, the slit 20 is formed along a straight line that passes through the center C of the circular vibration region E2 in a plan view and connects two points on the circumference.

[0038] The slits 20 only need to be through-holes formed in at least the vibration region E2 of the piezoelectric element portion 12 , and the position, shape, formation range, and number of the slits 20 are not limited.

[0039] The extending direction of the slit 20 is not limited. For example, the slit 20 may extend in the direction from the peripheral edge E1 toward the vibration region E2 of the piezoelectric element portion 12. Furthermore, the slit 20 preferably extends from the boundary with the peripheral edge E1 in the vibration region E2 of the piezoelectric element portion 12 toward the center C of the vibration region E2.

[0040] For example, Figure 1A As shown, the slit 20 may be formed by a plurality of first slits 20A and through holes 20B.

[0041] The first slit 20A is a slit 20 extending from first points P1 arranged at equal intervals along the circumferential direction of the peripheral portion E1 (see arrow R) toward the center C at the boundary between the peripheral portion E1 and the vibration area E2 of the piezoelectric element portion 12. The circumferential direction of the peripheral portion E1 refers to the direction along the extension direction of the peripheral portion E1 when viewed from above (see arrow R). The center C refers to the center of the intersecting direction (XY direction) that intersects the thickness direction Z in the vibration area E2 of the piezoelectric element portion 12. In addition, the distances between adjacent first points P1 in the circumferential direction can be equally spaced or different. Among them, the distances between the first points P1 are preferably equally spaced.

[0042] In this embodiment, the case where the width L of the first slit 20A is constant along the extension direction of the first slit 20A (see the direction indicated by arrow W) is described as an example. The width L of the first slit 20A represents the distance of the first slit 20A in a direction perpendicular to the extension direction (direction indicated by arrow W) when viewed from above. In other words, the width L of the first slit 20A refers to the length of the gap between adjacent side surfaces of the vibration region E2 separated by the first slit 20A. Hereinafter, the extension direction of the first slit 20A will sometimes be referred to as the extension direction W.

[0043] The through hole 20B is provided at the center C of the vibration region E2 of the piezoelectric element portion 12 and is continuous with each of the plurality of first slits 20A extending from the peripheral portion E1 toward the center C.

[0044] Next, the stretch film 22 will be described.

[0045] The stretchable film 22 is a stretchable film. The stretchability of the stretchable film 22 means that the stretchability of the stretchable film 22 is higher than that of the piezoelectric element 12. In other words, the stretchability of the stretchable film 22 means that the Young's modulus of the stretchable film 22 is lower than that of the piezoelectric element 12, or that the stretchable film 22 is more easily deformed than the piezoelectric element 12.

[0046] The stretchable film 22 is provided in the vibration region E2 inside the peripheral portion E1 of the piezoelectric element 12. The stretchable film 22 may constitute a portion of the vibration region E2 of the piezoelectric element 12. Alternatively, the stretchable film 22 may be provided on the vibration region E2 of the piezoelectric element 12.

[0047] When the stretchable film 22 is provided on the vibration region E2 of the piezoelectric element portion 12 , the stretchable film 22 only needs to be provided in the vibration region E2 inside the peripheral portion E1 in at least one end surface in the thickness direction Z of the piezoelectric element portion 12 .

[0048] exist Figure 1B In the embodiment shown, as an example, the stretchable film 22 is provided on the end surface opposite to the support portion 18 in the vibration region E2 of the piezoelectric element portion 12. However, the stretchable film 22 may also be provided on the end surface on the support portion 18 side in the vibration region E2 of the piezoelectric element portion 12 (i.e., within the hole 19).

[0049] Figure 1C 1 is a schematic diagram showing an example of a piezoelectric element 10A. The piezoelectric element 10A is an example of the piezoelectric element 10. Figure 1C As shown, the piezoelectric element 10A may also have the stretchable film 22 disposed on the end surface (i.e., within the hole 19) on the support portion 18 side within the vibration region E2 of the piezoelectric element portion 12. Aside from the position of the stretchable film 22, the structure of the piezoelectric element 10A is identical to that of the piezoelectric element 10. Alternatively, the stretchable film 22 may be disposed on both end surfaces in the thickness direction Z within the vibration region E2 of the piezoelectric element portion 12.

[0050] Furthermore, as described above, the stretchable film 22 may constitute a part of the vibration region E2 of the piezoelectric element portion 12 .

[0051] Figure 1D Schematic diagram showing an example of the piezoelectric element 10A1. Figure 1ESchematic diagram showing an example of a piezoelectric element 10A2 . The piezoelectric element 10A1 and the piezoelectric element 10A2 are examples of the piezoelectric element 10 .

[0052] like Figure 1D and Figure 1E As shown, the stretchable film 22 may also constitute a portion of the vibration region E2 of the piezoelectric element portion 12. In this case, the stretchable film 22 may be arranged so as to contact the side surface of the piezoelectric film 14 in a direction (XY direction) intersecting the thickness direction Z of the piezoelectric film 14. In other words, the stretchable film 22 may be arranged so as to fill at least a portion of the slit 20 provided in the vibration region E2.

[0053] Figure 1F It is a schematic diagram showing an example of the piezoelectric element 10A3. Figure 1G Schematic diagram showing an example of a piezoelectric element 10A4 . The piezoelectric element 10A3 and the piezoelectric element 10A4 are examples of the piezoelectric element 10 .

[0054] like Figure 1F and Figure 1G As shown, a portion of the stretch film 22 may enter the slit 20 so as to cover at least a portion of the slit 20 provided in the vibration region E2. In other words, the stretch film 22 may be provided in the vibration region E2 inside the peripheral portion E1 of one end surface of the piezoelectric element portion 12 in the thickness direction Z, and the stretch film 22 may constitute a portion of the vibration region E2 of the piezoelectric element portion 12.

[0055] return Figure 1A and Figure 1B In this embodiment, a case where the stretchable film 22 is provided on the end surface opposite to the support portion 18 in the vibration region E2 of the piezoelectric element portion 12 and does not enter the slit 20 is described as an example.

[0056] The stretch film 22 may be arranged at a position overlapping the vibration region E2 of the piezoelectric element 12 in a plan view. The stretch film 22 is preferably arranged to bury or cover a region having a higher elastic modulus in the vibration region E2 of the piezoelectric element 12 .

[0057] For example, the thickness of the piezoelectric film 14 in a portion of the vibration region E2 may be thinner than in other regions, or the piezoelectric film 14 in a portion of the vibration region E2 may be made of a material having a higher elastic modulus than in other regions. In such cases, the vibration region E2 includes a region having a higher elastic modulus than other regions within the vibration region E2.

[0058] For example, assume that the elastic modulus of the center C portion of the vibration region E2 of the piezoelectric element portion 12 is higher than the elastic modulus of the region other than the center C. In this case, the stretchable film 22 only needs to be arranged in a region that covers at least a portion of the center C in the vibration region E2 of the piezoelectric element portion 12.

[0059] Furthermore, when the stretch film 22 is arranged so as to cover at least a portion of the slit 20 provided in the vibration region E2, the region of the slit 20 covered by the stretch film 22 has a high elastic modulus. Therefore, in this case, the stretch film 22 may be arranged so as to also cover the region of the slit 20 already covered by the stretch film 22.

[0060] Furthermore, if the vibration region E2 of the piezoelectric element portion 12 includes a slit 20 that is not buried by the stretch film 22, the region of the piezoelectric element portion 12 where the slit 20 is located corresponds to a region with a higher elastic modulus. Therefore, in this case, the stretch film 22 is preferably disposed at the following position within the vibration region E2.

[0061] Specifically, the stretchable film 22 is arranged to cover at least a portion of the opening of the slit 20 in the vibration region E2 of the piezoelectric element portion 12 .

[0062] exist Figure 1A , a case where the stretchable film 22 is arranged to cover a portion of the opening of the slit 20 in the vibration region E2 is shown as an example.

[0063] The stretch film 22 is arranged to partially cover the opening of the slit 20 in the vibration region E2, so that the region of the slit 20 not covered by the stretch film 22 functions as a vent for the air in the pore 19. Therefore, in this case, cracking of the piezoelectric element 12 can be suppressed.

[0064] Furthermore, from the viewpoint of effectively suppressing a decrease in sensitivity due to a decrease in acoustic resistance and suppressing a decrease in the S / N ratio, the stretchable film 22 is preferably arranged to cover the entire opening of the slit 20 in the vibration region E2 .

[0065] The stretchable film 22 only needs to be arranged in the vibration region E2 of the piezoelectric element portion 12 , but preferably does not cover at least one end surface in the thickness direction Z of the peripheral portion E1 .

[0066] Furthermore, the stretchable film 22 is preferably arranged to continuously cover a portion of each of the through-hole 20B provided at the center C of the vibration region E2 and the plurality of first slits 20A continuous with the through-hole 20B. Covering a portion of the opening of the slit 20 by the stretchable film 22 allows the piezoelectric element portions 12 separated by the slits 20 to be integrated. In this case, the opening region D of the first slit 20A not covered by the stretchable film 22 is preferably the end portion of the first slit 20A on the side of the peripheral edge E1.

[0067] By arranging the stretchable film 22 so as to cover the through hole 20B provided in the center C of the vibration region E2, the vibration of the vibration region E2 based on the sound pressure or the vibration of the vibration region E2 based on the AC voltage applied to the electrode 16 can be increased compared to the case where the stretchable film 22 is arranged to cover the through hole 20B except for the center C.

[0068] The thickness of the stretchable film 22 may be any thickness that does not hinder the vibration of the vibration region E2 of the piezoelectric element portion 12 , and may be appropriately adjusted depending on the constituent material of the stretchable film 22 .

[0069] The material constituting the stretchable film 22 is not limited as long as it is a material having higher stretchability than the piezoelectric element portion 12. For example, the stretchable film 22 may be formed of an organic film or a metal film.

[0070] When the stretch film 22 is formed of an organic film, it is preferable that polyurethane be used for the stretch film 22 , for example.

[0071] The Young's modulus of the organic film is much smaller than that of the piezoelectric element portion 12. Therefore, by forming the stretchable film 22 with an organic film, the influence of the residual stress of the stretchable film 22 on the resonance frequency of the vibration region E2 of the piezoelectric element portion 12 can be suppressed.

[0072] When the stretch film 22 is formed of a metal film, the stretch film 22 is preferably made of a material commonly used in the manufacturing process of semiconductor devices, and preferably Al, Ti, Au, Ag, Cu, Ni, Mo, Pt, or an alloy thereof.

[0073] By constructing the stretchable membrane 22 using a metal film, the width L of the slit 20 can be increased compared to when the stretchable membrane 22 is constructed using an organic film. Furthermore, the metal film has a high affinity with the manufacturing process (e.g., MEMS (Micro Electro Mechanical Systems) process) used for the piezoelectric element 12, thereby increasing the degree of freedom in process design. Furthermore, when the stretchable membrane 22 is constructed using a metal film, compared to when constructed using an organic film, aging degradation due to hydrolysis and other factors is suppressed, and heat and light resistance are also superior. Therefore, in this case, the reliability of the piezoelectric element 12 can be improved. Furthermore, to achieve the desired stretchability, at least one of the thickness and shape of the stretchable membrane 22 can be further adjusted.

[0074] Furthermore, from the perspective of suppressing separation of the stretchable film 22 from the piezoelectric element portion 12, the contact surface S of the piezoelectric element portion 12 with the stretchable film 22 preferably has irregularities. The surface roughness of the irregularities of the contact surface S can be appropriately adjusted based on the constituent material of the stretchable film 22, etc., to suppress separation from the piezoelectric element portion 12. Furthermore, the irregularities of the contact surface S can be formed by providing a hole, a recess, or a plurality of holes in the contact surface S.

[0075] Next, the operation of the piezoelectric element 10 will be described.

[0076] In the piezoelectric element portion 12, the vibration region E2 of the piezoelectric element portion 12 vibrates. The vibration region E2 of the piezoelectric element portion 12 vibrates, for example, in response to sound pressure in the audible sound or ultrasonic range. Furthermore, the vibration region E2 of the piezoelectric element portion 12 vibrates in response to the AC voltage applied to the electrode 16. The frequency of the AC voltage is, for example, a frequency in the audible sound or ultrasonic range. Furthermore, the sound pressure is not limited to that generated in the audible sound or ultrasonic range. Similarly, the frequency of the AC voltage applied to the electrode 16 is not limited to that in the audible sound or ultrasonic range.

[0077] When the vibration region E2 of the piezoelectric element portion 12 is deformed by sound pressure or the like, polarization is induced inside due to the transverse piezoelectric effect, and an electrical signal is extracted through the electrode 16 .

[0078] In this embodiment, a stretchable membrane 22 is provided in the vibration region E2 of the piezoelectric element 12. The provision of the stretchable membrane 22 suppresses bending in the vibration region E2 of the piezoelectric element 12. Consequently, residual stress in the stretchable membrane 22 is suppressed. This suppresses a decrease in the SN ratio of the piezoelectric element 10. Furthermore, when the stretchable membrane 22 is provided with slits 20, a decrease in acoustic impedance caused by an increase in the gap between opposing regions across the slits 20 in the vibration region E2 can be suppressed. Therefore, even when the slits 20 are provided in the vibration region E2, the provision of the stretchable membrane 22 suppresses a decrease in the SN ratio of the piezoelectric element 10.

[0079] As described above, the piezoelectric element 10 of this embodiment includes a piezoelectric element portion 12 having a piezoelectric film 14 and electrodes 16 that sandwich the piezoelectric film 14 in the thickness direction Z; a support portion 18 that supports the peripheral edge portion E1 of the piezoelectric element portion 12; and a stretchable film 22. The stretchable film 22 is provided in the vibration region E2 inside the peripheral edge portion E1 of the piezoelectric element portion 12. Furthermore, the stretchability of the stretchable film 22 is higher than that of the piezoelectric element portion 12.

[0080] In the past, piezoelectric films with fixed peripheral edges sometimes experienced a change in resonant frequency due to residual stress, resulting in a decrease in the SN ratio or sensitivity. Furthermore, in existing piezoelectric elements with slits in the piezoelectric film and a cantilever structure, the gap between the arms can be increased due to the bending of the piezoelectric film or electrode film, resulting in a decrease in acoustic impedance. Consequently, this can lead to a decrease in the SN ratio in existing piezoelectric elements. Furthermore, this can lead to a decrease in sensitivity in existing piezoelectric elements.

[0081] On the other hand, the piezoelectric element 10 of this embodiment includes a stretchable film 22 having a higher stretchability than the piezoelectric element portion 12 in the vibration region E2 inside the peripheral portion E1 supported by the support portion 18 of the piezoelectric element portion 12 .

[0082] Therefore, the piezoelectric element 10 of the present embodiment can reduce the residual stress in the piezoelectric element portion 12 and suppress a decrease in the SN ratio.

[0083] Therefore, the piezoelectric element 10 of this embodiment can suppress a decrease in the SN ratio.

[0084] Furthermore, in addition to the above-mentioned effects, the piezoelectric element 10 of this embodiment can suppress a decrease in sensitivity characteristics.

[0085] Furthermore, the piezoelectric element 10 of this embodiment suppresses bending of the vibration region E2 by providing the stretchable membrane 22, even when the vibration region E2 is provided with the slit 20. Consequently, the increase in the gap (i.e., width L) between regions of the vibration region E2 that face each other across the slit 20 is suppressed. Furthermore, even if the vibration region E2 is curved, the stretchable membrane 22 is arranged to cover at least a portion of the slit 20, thereby suppressing a decrease in acoustic resistance.

[0086] Therefore, the piezoelectric element 10 of the present embodiment can suppress a decrease in acoustic resistance, suppress a decrease in the SN ratio, and suppress a decrease in sensitivity characteristics.

[0087] Furthermore, the stretchability of the stretchable film 22 is higher than that of the piezoelectric element portion 12. Therefore, it is possible to suppress the adverse effects of residual stress in the stretchable film 22 on the resonance frequency. Furthermore, damage to the stretchable film 22 can be suppressed by the vibration of the vibration region E2 in the piezoelectric element portion 12.

[0088] Furthermore, in the piezoelectric element 10 of this embodiment, by providing the stretchable film 22 in the vibration region E2 , it is possible to easily suppress a decrease in the SN ratio and sensitivity characteristics, thereby easily suppressing a decrease in the yield during the manufacture of the piezoelectric element portion 12 .

[0089] Furthermore, since the piezoelectric element 10 of this embodiment includes the stretchable film 22 , it is possible to improve sensitivity to AC voltage or sound pressure, particularly in a low-frequency region.

[0090] In addition, the opening shape and opening size of the through hole 20B can be adjusted arbitrarily.

[0091] Figure 1H This is an example of a top view of the piezoelectric element 10A5. Figure 1I yes Figure 1H The piezoelectric element 10A5 is an example of the piezoelectric element 10 , and is taken along line AA′.

[0092] like Figure 1H and Figure 1I As shown, the through hole 20B of the piezoelectric element 10A5 has a Figure 1A and Figure 1B The through hole 20B of the piezoelectric element 10 shown in FIG. Figure 1H and Figure 1I In the illustrated example, the through hole 20B has a circular opening shape with an opening diameter of L0.

[0093] The opening diameter LO of the through hole 20B can be adjusted arbitrarily.

[0094] In one example, the opening diameter LO can be adjusted based on the size and sensitivity characteristics of the vibration region E2. More specifically, the designer can determine the opening diameter LO based on the relationship between the size of the vibration region E2 (in this case, the ratio of the opening diameter LO to the diameter LD of the vibration region E2) and the receiving sensitivity of the piezoelectric element portion 12.

[0095] Figure 1J : is a graph showing the relationship between the ratio LO / LD of the opening diameter LO of the through hole 20B to the diameter LD of the vibration region E2 and the receiving sensitivity of the piezoelectric element portion 12. Figure 1J It can be seen that the receiving sensitivity is nearly constant within the LO / LD ratio range of 0.01 to 0.1, but deteriorates when the LO / LD ratio deviates from this range. Therefore, if the designer sets the opening diameter LO so that the LO / LD ratio falls within the range of 0.01 to 0.1, a piezoelectric element 10A5 with high sensitivity characteristics can be obtained.

[0096] In addition, Figure 1H Although a circular opening shape is shown as an example, in a polygonal shape, even if LO is replaced by the diameter of the circumscribed circle, the same effect can be obtained. Figure 1I Although the stretch film 22 is not embedded in the through hole 20B, it may enter the through hole 20B.

[0097] The method for determining the opening diameter LO of the through-hole 20B is not limited to this. The ratio LO / LD of the opening diameter LO of the through-hole 20B to the diameter LD of the vibration region E2 may not fall within the range of 0.01 to 0.1. Furthermore, the opening shape of the through-hole 20B is not limited to a circular shape.

[0098] (Second embodiment)

[0099] In the above embodiment, the case where the width L of the first slit 20A is constant along the extending direction (arrow W direction) of the first slit 20A is described as an example. In this embodiment, the case where the width L of the first slit 20A is different from that in the above embodiment is described.

[0100] Figure 2A This is an example of a plan view of the piezoelectric element 10B according to the present embodiment. Figure 2B yes Figure 2A A cross-sectional view taken along line AA' of the piezoelectric element 10B is shown.

[0101] The piezoelectric element 10B has the same structure as the piezoelectric element 10 of the first embodiment except that the width L of the slit 20 is different from that of the first embodiment.

[0102] The piezoelectric element 10B includes a piezoelectric element portion 13B, a support portion 18, and a stretchable film 22. The piezoelectric element portion 13B includes a piezoelectric film 14 and an electrode 16. A slit 21 is provided in the piezoelectric element portion 13B. The piezoelectric element portion 13B is similar to the piezoelectric element portion 12 of the above embodiment, except that the slit 21 is provided instead of the slit 20.

[0103] The slits 21 are composed of a plurality of first slits 21A and through-holes 20B. The through-holes 20B are the same as those in the above embodiment. The first slits 21A are the same as the first slits 20A in the above embodiment except for the difference in width L.

[0104] In the present embodiment, the stretch film 22 is arranged so as to continuously cover a portion of each of the plurality of first slits 21A and the through-hole 20B.

[0105] Here, in this embodiment, the slit width L1 of the covered region 21A1 of the first slit 21A covered by the stretch film 22 is larger than the slit width L2 of the uncovered region 21A2 not covered by the stretch film 22 .

[0106] By making the slit width L1 of the covered region 21A1 larger than the slit width L2 of the non-covered region 21A2 in the slit 21 , it is possible to reduce the stress applied to the stretch film 22 .

[0107] Furthermore, it is preferable that the width L of the first slit 21A increases gradually or continuously as it approaches the center C from the boundary between the vibration region E2 and the peripheral portion E1 .

[0108] Figure 2C Schematic diagram showing an example of a piezoelectric element 10C. The piezoelectric element 10C includes a piezoelectric element portion 13C, a support portion 18, and a stretchable film 22. The piezoelectric element portion 13C includes a piezoelectric film 14 and an electrode 16. The piezoelectric element portion 13C includes a slit 23 instead of the slit 21. The piezoelectric element portion 13C is similar to the piezoelectric element portion 13B (see FIG. 1 ). Figure 2A 、 Figure 2B )same.

[0109] The slits 23 are composed of a plurality of first slits 23A and through-holes 20B. The through-holes 20B are the same as those in the above embodiment. The first slits 23A are the same as the first slits 20A in the above embodiment except for the difference in width L.

[0110] like Figure 2C As shown, the width L of the first slit 23A may be increased as it approaches the center C.

[0111] return Figure 2A and Figure 2BAs described above, in the piezoelectric element 10B of this embodiment, the slit width L1 of the covered region 21A1 of the first slit 21A covered by the stretch film 22 is larger than the slit width L2 of the uncovered region 21A2 not covered by the stretch film 22 .

[0112] By making the slit width L1 of the covering region 21A1 in the first slit 21A larger than the slit width L2 of the non-covering region 21A2 , the piezoelectric elements 10B and 10C of this embodiment can achieve, in addition to the above-described effects, a reduction in stress applied to the stretchable film 22 .

[0113] (Variation 1)

[0114] The shape of the stretch film 22 is not limited to a planar shape along a direction intersecting the thickness direction Z (a direction along the XY plane). For example, at least a portion of the stretch film 22 may have a bellows shape.

[0115] Figure 3A This is an example of a plan view of a piezoelectric element 10D according to this modification. Figure 3B yes Figure 3A A cross-sectional view taken along line AA' of the piezoelectric element 10D is shown.

[0116] The piezoelectric element 10D includes a piezoelectric element portion 13D, a support portion 18, and a stretchable film 25. The piezoelectric element 10D replaces the piezoelectric element 10C of the second embodiment (see Figure 2C ) is provided with a stretch film 25 instead of the stretch film 22. The stretch film 25 is the same as the stretch film 22 except that the shape is different from that of the stretch film 22.

[0117] At least a portion of the stretch film 25 is formed in a bellows shape that is stretchable in a direction intersecting the thickness direction Z (XY direction).

[0118] For example, the stretchable membrane 25 consists of a bellows region 25A and a flat region 25B. The bellows region 25A is a region formed in a bellows shape with repeated peaks and troughs, allowing expansion and contraction in the intersecting directions (XY directions). The flat region 25B is a two-dimensional planar region along the intersecting directions (XY directions). The bellows region 25A is the region of the stretchable membrane 25 that overlaps the opening of the slit 23 when viewed from above, while the flat region 25B is the region in contact with the vibration area E2 of the piezoelectric element 13D.

[0119] As described above, by configuring the stretch film 25 to include the accordion-shaped accordion region 25A, it is possible to easily improve the stretchability of the stretch film 25 .

[0120] Furthermore, by using a metal film or the like for the stretch film 25 , even when the intended stretchability may not be obtained, the intended stretchability can be obtained by adjusting the shape of the stretch film 25 to a bellows shape.

[0121] Furthermore, by arranging the bellows region 25A in the region of the vibration region E2 that overlaps with the opening of the slit 23 in a plan view, it is possible to effectively improve the sensitivity characteristics of the piezoelectric element portion 13D.

[0122] The stretch film 25 may have any shape that improves its stretchability and is not limited to a bellows shape. Specifically, at least a portion of the stretch film 25 may have a shape that is stretchable in a direction intersecting the thickness direction Z (the XY direction).

[0123] (Variation 2)

[0124] In the above-described embodiment and modified examples, the case where the vibration region E2 is circular in a plan view is described as an example. Furthermore, in the above-described embodiment and modified examples, the case where the support portion 18 is a circular frame-shaped member having a circular hole 19 in a plan view is described as an example. Therefore, in the above-described embodiment and modified examples, the case where the peripheral portion E1 is a circular frame-shaped region in a plan view and the vibration region E2 is a circular region in a plan view is described as an example.

[0125] However, the shapes of the support portion 18 , the hole 19 of the support portion 18 , the peripheral edge portion E1 , and the vibration region E2 are not limited to circular shapes.

[0126] For example, the vibration region E2 may be rectangular or polygonal in a plan view. Figure 4 It is a plan view showing an example of a piezoelectric element 10E.

[0127] The piezoelectric element 10E includes a piezoelectric element portion 12, a support portion 18, and a stretchable film 22. The stretchable film 22 is provided with a slit 20. The piezoelectric element 10E is similar to the piezoelectric element 10 of the above embodiment except for the difference in shape.

[0128] like Figure 4 As shown, the piezoelectric element 10E may also have the following structure, comprising: a piezoelectric element portion 12 that is rectangular in plan view; a rectangular peripheral portion E1 supported by a support portion 18 that is a rectangular frame member in plan view; a vibration region E2 that is rectangular in plan view; and a stretchable membrane 22 that is rectangular in plan view.

[0129] The piezoelectric elements 10, 10B, 10C, 10D, and 10E described in the above embodiments and modifications are not limited in their scope of application. For example, the piezoelectric elements 10, 10B, 10C, 10D, and 10E described in the above embodiments and modifications are preferably applicable to microelectromechanical systems (MEMS) including piezoelectric elements.

[0130] According to the present invention, it is possible to suppress a decrease in the SN ratio.

[0131] While the embodiments and modifications of the present invention have been described above, these embodiments and modifications are provided as examples and are not intended to limit the scope of the invention. These new embodiments and modifications can be implemented in various other ways, and various omissions, substitutions, and changes can be made without departing from the gist of the invention. These embodiments and modifications are intended to be within the scope or gist of the invention and are within the scope of the invention described in the claims and their equivalents.

[0132] -Explanation of symbols-

[0133] 10, 10A, 10A1, 10A2, 10B, 10C, 10D, 10E piezoelectric elements

[0134] 12, 13B, 13C, 13D Piezoelectric element

[0135] 14 Piezoelectric film

[0136] 16 electrodes

[0137] 18 Support

[0138] Slits 20, 21, and 23

[0139] 20A, 21A, 23A First slit

[0140] 20B through hole

[0141] 22 Stretch Film

[0142] E1 peripheral part

[0143] E2 vibration area.

Claims

1. A piezoelectric element comprising: a piezoelectric element portion including a piezoelectric film and electrodes sandwiching the piezoelectric film in a thickness direction; a support portion that supports a peripheral portion of the piezoelectric element portion; and a stretchable film provided in a vibration region inside the peripheral portion of the piezoelectric element portion and having a higher stretchability than the piezoelectric element portion; The stretchable film is provided on at least one end surface in the thickness direction of the vibration region of the piezoelectric element portion. The stretch film does not cover at least one end surface of the peripheral portion in the thickness direction.

2. A piezoelectric element comprising: a piezoelectric element portion including a piezoelectric film and electrodes sandwiching the piezoelectric film in a thickness direction; a support portion supporting a peripheral portion of the piezoelectric element portion; a stretchable film provided in a vibration region inside the peripheral portion of the piezoelectric element portion and having a higher stretchability than the piezoelectric element portion; as well as a slit provided in the vibration region of the piezoelectric element portion and penetrating the vibration region in the thickness direction; The stretch film is configured to cover at least a portion of the opening of the slit in the vibration region and to integrate the vibration regions separated by the slit. The slit includes a covered area where the opening is covered by the stretch film and an uncovered area where the opening is not covered by the stretch film.

3. The piezoelectric element according to claim 2, wherein The slit extends in a direction from the peripheral edge portion toward the center of the vibration region.

4. The piezoelectric element according to claim 3, wherein In the slit, the slit width of the covering area is larger than the slit width of the non-covering area.

5. The piezoelectric element according to claim 3 or 4, wherein The slit widths of the covered region and the non-covered region of the slit increase as the slit approaches the center from the peripheral portion.

6. The piezoelectric element according to any one of claims 1 to 4, wherein The stretch film is an organic film or a metal film.

7. The piezoelectric element according to any one of claims 1 to 4, wherein At least a portion of the stretch film has a bellows shape that is stretchable in a direction intersecting the thickness direction.

8. The piezoelectric element according to any one of claims 1 to 4, wherein A surface of the piezoelectric element portion that contacts the stretchable film has projections and depressions.

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