Piezoelectric element

Abstract

A piezo-electric element 10 is provided with: a piezo-electric element part 12 including a piezo-electric film 14 and electrodes 16 which nip the piezo-electric film 14 in a thickness direction Z; a support part 18 which supports a peripheral edge section E1 of the piezo-electric element part 12; and a stretching film 22. The stretching film 22 is provided in an oscillation region E2 located inward of the peripheral edge section E1 of the piezo-electric element part 12. Furthermore, the stretching film 22 is more stretchable than the piezo-electric element part 12.

Description

[Technical field]

[0001] FIELD OF THE DISCLOSURE An embodiment of the present invention relates to a piezoelectric element. [Background technology]

[0002] A piezoelectric element is known that extracts the distortion of a piezoelectric film sandwiched between electrode films as a voltage change. A configuration has also been disclosed in which slits are formed in the piezoelectric film in order to suppress residual stress in the piezoelectric film whose periphery is fixed to a support substrate or the like.

[0003] However, in the conventional technology, the signal-to-noise ratio may decrease. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5707323 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention has been made in view of the above, and has an object to provide a piezoelectric element capable of suppressing a decrease in the S / N ratio. [Means for solving the problem]

[0006] The piezoelectric element of the embodiment includes a piezoelectric element portion, a support portion, and a stretchable film. The piezoelectric element portion includes a piezoelectric film and electrodes that sandwich the piezoelectric film in a thickness direction. The support portion supports a peripheral portion of the piezoelectric element portion. The stretchable film is provided in a vibration region inside the peripheral portion of the piezoelectric element portion and has higher stretchability than the piezoelectric element portion. The elastic film is provided on at least one end surface in the thickness direction of the vibration region of the piezoelectric element portion. The elastic film does not cover at least one end surface in the thickness direction of the peripheral portion. Effect of the Invention

[0007] According to the present invention, it is possible to suppress the decrease in the S / N ratio. [Brief description of the drawings]

[0008] [Figure 1A] FIG. 1A is a top view of a piezoelectric element. [Figure 1B] FIG. 1B is a cross-sectional view of the piezoelectric element. [Figure 1C] FIG. 1C is a schematic diagram showing an example of a piezoelectric element. [Figure 1D] FIG. 1D is a schematic diagram showing an example of a piezoelectric element. [Figure 1E] FIG. 1E is a schematic diagram showing an example of a piezoelectric element. [Figure 1F] FIG. 1F is a schematic diagram showing an example of a piezoelectric element. [Figure 1G] FIG. 1G is a schematic diagram showing an example of a piezoelectric element. [Figure 1H] FIG. 1H is a top view of the piezoelectric element. [Figure 1I] FIG. 1I is a cross-sectional view of a piezoelectric element. [Figure 1J] FIG. 1J 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 reception sensitivity of the piezoelectric element portion. [Figure 2A] FIG. 2A is a top view of a piezoelectric element. [Figure 2B] FIG. 2B is a cross-sectional view of the piezoelectric element. [Figure 2C] FIG. 2C is a top view of the piezoelectric element. [Figure 3A] FIG. 3A is a top view of the piezoelectric element. [Figure 3B] FIG. 3B is a cross-sectional view of the piezoelectric element. [Figure 4] FIG. 4 is a top view of the piezoelectric element. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The present embodiment will be described in detail below with reference to the accompanying drawings. In the following embodiment and modified examples, parts having the same configurations and functions are given the same reference numerals, and detailed description thereof may be omitted.

[0010] (First embodiment) Fig. 1A is an example of a top view of a piezoelectric element 10 according to the present embodiment. Fig. 1B is a cross-sectional view taken along line AA' of the piezoelectric element 10 shown in Fig. 1A.

[0011] The piezoelectric element 10 includes a piezoelectric element portion 12 , a support portion 18 , and a stretchable film 22 .

[0012] The piezoelectric element portion 12 has a piezoelectric film 14 and electrodes 16 that sandwich the piezoelectric film 14 in the thickness direction (direction of arrow Z).

[0013] 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 disposed so as to sandwich the piezoelectric film 14 in the thickness direction of the piezoelectric film 14 (the direction of the arrow Z).

[0014] In the following description, the thickness direction of the piezoelectric film 14 may be referred to as the thickness direction Z. That is, the thickness direction Z is a direction that coincides with the thickness direction of the piezoelectric film 14. In addition, directions perpendicular to the thickness direction Z are referred to as the X direction and the Y direction. In addition, a two-dimensional plane (XY plane) perpendicular to the thickness direction Z is referred to as the intersecting direction of the thickness direction Z.

[0015] The piezoelectric element portion 12 may be a laminate in which a plurality of piezoelectric films 14 are laminated in the thickness direction Z. In this case, as shown in Fig. 1B, each of the piezoelectric films 14 constituting the laminate may be sandwiched between electrodes 16 in the thickness direction Z. In other words, the piezoelectric element portion 12 may have a bimorph structure.

[0016] 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 holes 19 in a plate-shaped support substrate, penetrating the support substrate in the thickness direction Z. An end face of the support portion 18 in the thickness direction Z is disposed in contact with the peripheral portion E1 of the piezoelectric element portion 12, whereby the support portion 18 supports the peripheral portion E1 of the piezoelectric element portion 12.

[0017] As the peripheral portion E1 is supported by the support portion 18, a vibration region E2 inside the peripheral portion E1 in the piezoelectric element portion 12 becomes a vibrating region. The vibration region E2 inside the peripheral portion E1 is a 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 a region that overlaps with the holes 19 in a planar view of the piezoelectric element portion 12 viewed from a direction along the thickness direction Z. Therefore, the vibration region E2 can vibrate without being hindered by the support portion 18 in the piezoelectric element portion 12.

[0018] On the other hand, the peripheral portion E1 of the piezoelectric element portion 12 is an area that is fixed so as not to vibrate by the support portion 18. In the following, a plan view of the piezoelectric element 10 viewed from a direction along the thickness direction Z of the piezoelectric element portion 12 will be simply referred to as a plan view.

[0019] In this embodiment, a case where the vibration region E2 of the piezoelectric element portion 12 is circular in a planar view will be described as an example. That is, in this embodiment, a case where the support portion 18 is a circular frame-shaped member having holes 19 that are circular in a planar view will be described as an example. For this reason, in this embodiment, a case where the peripheral portion E1 of the piezoelectric element portion 12 is a circular frame-shaped region in a planar view will be described as an example. For this reason, in this embodiment, a case where the vibration region E2 of the piezoelectric element portion 12 is a circular region in a planar view will be described as an example.

[0020] In this embodiment, the piezoelectric element portion 12 is provided with a slit 20 .

[0021] 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.

[0022] As shown in FIG. 1A, for example, the slit 20 is formed along a straight line that passes through the center C of a circle of a vibration area E2 that is circular in plan view and connects two points on the circumference.

[0023] The slits 20 may be through-holes formed in at least the vibration region E2 of the piezoelectric element portion 12, and the position, shape, formation area, and number of the slits 20 are not limited.

[0024] The extension direction of the slits 20 is not limited. For example, the slits 20 may extend in a direction from the peripheral edge E1 of the piezoelectric element portion 12 toward the vibration region E2. It is preferable that the slits 20 extend 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.

[0025] For example, as shown in FIG. 1A, the slit 20 may be composed of a plurality of first slits 20A and a through hole 20B.

[0026] The first slits 20A are slits 20 extending from first points P1 arranged at equal intervals along the circumferential direction of the peripheral portion E1 (see arrow R) of the boundary between the peripheral portion E1 and the vibration region E2 of the piezoelectric element portion 12 toward the center C. The circumferential direction of the peripheral portion E1 is the direction along the extension direction of the peripheral portion E1 in a plan view (see arrow R). The center C is the center of the intersecting direction (XY direction) intersecting the thickness direction Z in the vibration region E2 of the piezoelectric element portion 12. The distance between the first points P1 adjacent to each other in the circumferential direction may be equal or different. However, it is preferable that the distance between the first points P1 is equal.

[0027] In this embodiment, a case will be described as an example in which the width L of the first slit 20A is constant along the extension direction (see the direction of the arrow W) of the first slit 20A. The width L of the first slit 20A indicates the distance in the direction perpendicular to the extension direction (direction of the arrow W) in a plan view in the first slit 20A. In other words, the width L of the first slit 20A is the length of the gap between the side surfaces of the vibration region E2 divided by the first slit 20A that are adjacent to each other via the first slit 20A. Hereinafter, the extension direction of the first slit 20A may be referred to as the extension direction W.

[0028] The through hole 20B is provided in the center C of the vibration region E2 of the piezoelectric element portion 12, and is continuous with each of the multiple first slits 20A that extend from the peripheral edge portion E1 toward the center C.

[0029] Next, the stretchable film 22 will be described.

[0030] The stretchable film 22 is a film having stretchability. That the stretchable film 22 has stretchability means that the stretchability of the stretchable film 22 is higher than that of the piezoelectric element section 12. In other words, that the stretchable film 22 has stretchability means that it has a lower Young's modulus than the piezoelectric element section 12 or is more easily bent than the piezoelectric element section 12.

[0031] The stretchable film 22 is provided in a vibration region E2 inside the peripheral portion E1 of the piezoelectric element portion 12. The stretchable film 22 may constitute a part of the vibration region E2 of the piezoelectric element portion 12. In addition, the stretchable film 22 may be provided on the vibration region E2 of the piezoelectric element portion 12.

[0032] 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 on at least one end face in the thickness direction Z of the piezoelectric element portion 12.

[0033] 1B shows, as an example, a configuration in which the stretch film 22 is provided on an end surface of the vibration region E2 of the piezoelectric element portion 12 opposite to the support portion 18. However, the stretch film 22 may be disposed on the end surface of the vibration region E2 of the piezoelectric element portion 12 on the support portion 18 side (i.e., inside the hole 19).

[0034] 1C is a schematic diagram showing an example of a piezoelectric element 10A. The piezoelectric element 10A is an example of the piezoelectric element 10. As shown in FIG. 1C, the piezoelectric element 10A may have a stretchable film 22 disposed on an end face of the vibration region E2 of the piezoelectric element portion 12 on the support portion 18 side (i.e., inside the hole 19). The configuration of the piezoelectric element 10A is the same as that of the piezoelectric element 10, except that the position of the stretchable film 22 is different. Note that the stretchable film 22 may be provided on both end faces in the thickness direction Z of the vibration region E2 of the piezoelectric element portion 12.

[0035] As described above, the stretchable film 22 may constitute a part of the vibration region E2 of the piezoelectric element portion 12.

[0036] 1D is a schematic diagram showing an example of a piezoelectric element 10A1. FIG. 1E is a schematic diagram showing an example of a piezoelectric element 10A2. The piezoelectric elements 10A1 and 10A2 are examples of the piezoelectric element 10.

[0037] 1D and 1E, the stretchable film 22 may constitute a part of the vibration region E2 of the piezoelectric element portion 12. In this case, the stretchable film 22 may be arranged in contact with the side surface of the piezoelectric film 14 in the intersecting direction (XY direction) intersecting with the thickness direction Z of the piezoelectric film 14. In other words, the stretchable film 22 may be provided so as to fill at least a part of the slit 20 provided in the vibration region E2.

[0038] Fig. 1F is a schematic diagram showing an example of a piezoelectric element 10A3. Fig. 1G is a schematic diagram showing an example of a piezoelectric element 10A4. The piezoelectric elements 10A3 and 10A4 are examples of the piezoelectric element 10.

[0039] 1F and 1G, a part of the stretchable film 22 may enter the slit 20 provided in the vibration region E2 so as to fill at least a part of the slit 20. In other words, the stretchable film 22 may be provided in the vibration region E2 inside the peripheral portion E1 on one end face in the thickness direction Z of the piezoelectric element part 12, and may constitute a part of the vibration region E2 of the piezoelectric element part 12.

[0040] 1A and 1B, the description will be continued. In the present embodiment, a case where the stretchable film 22 is provided on the end face of the vibration region E2 of the piezoelectric element portion 12 opposite to the support portion 18 and does not enter the slit 20 will be described as an example.

[0041] The stretchable film 22 may be disposed at a position overlapping the vibration region E2 of the piezoelectric element portion 12 in a plan view. However, the stretchable film 22 is preferably disposed so as to fill or cover a region having a higher elastic modulus in the vibration region E2 of the piezoelectric element portion 12.

[0042] For example, there are cases where the thickness of the piezoelectric film 14 in a portion of the vibration region E2 is thinner than that in the other portions, or where the material constituting the piezoelectric film 14 in a portion of the vibration region E2 has a higher elastic modulus than that in the other portions, etc. In such cases, the vibration region E2 includes a region having a higher elastic modulus than the other portions within the vibration region E2.

[0043] For example, it is assumed 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 stretch film 22 may be disposed in a region that covers at least a part of the center C of the vibration region E2 of the piezoelectric element portion 12.

[0044] When the stretch film 22 is disposed so as to fill at least a part of the slit 20 provided in the vibration region E2, the region of the slit 20 filled with the stretch film 22 becomes a region with a high elastic modulus. Therefore, in this case, the stretch film 22 may be further disposed so as to further cover the region of the slit 20 filled with the stretch film 22.

[0045] In addition, when the vibration region E2 of the piezoelectric element part 12 has slits 20 that are not filled with the stretch film 22, the region of the piezoelectric element part 12 where the slits 20 are provided corresponds to a region with a higher elastic modulus. Therefore, in this case, it is preferable that the stretch film 22 is disposed at the following position in the vibration region E2.

[0046] In detail, the stretchable film 22 is disposed so as to cover at least a part of the opening of the slit 20 in the vibration region E2 of the piezoelectric element portion 12.

[0047] FIG. 1A shows, as an example, a case in which the stretchable film 22 is disposed so as to cover a part of the opening of the slit 20 in the vibration area E2.

[0048] By disposing the stretch film 22 so as to cover a part of the opening of the slit 20 in the vibration region E2, the region of the slit 20 that is not covered by the stretch film 22 functions as an escape hole for the air in the hole 19. Therefore, in this case, cracking of the piezoelectric element portion 12 can be suppressed.

[0049] In addition, from the viewpoint of effectively suppressing the deterioration of sensitivity characteristics due to a decrease in acoustic resistance and suppressing the deterioration of the S / N ratio, it is preferable that the stretchable film 22 is arranged so as to cover all of the openings of the slits 20 in the vibration area E2.

[0050] The stretchable film 22 may be disposed in the vibration region E2 of the piezoelectric element portion 12, but it is preferable that at least one end face in the thickness direction Z of the peripheral portion E1 is not covered.

[0051] Moreover, it is preferable that the stretchable film 22 is disposed so as to continuously cover the through hole 20B provided in the center C of the vibration region E2 and a part of each of the plurality of first slits 20A continuing to the through hole 20B. By covering a part of the opening of the slit 20 with the stretchable film 22, the piezoelectric element parts 12 separated by the slits 20 can be integrated. In this case, it is preferable that the opening region D of the first slit 20A that is not covered by the stretchable film 22 is the end part on the peripheral part E1 side of the first slit 20A.

[0052] By positioning the stretchable membrane 22 so as to cover the through hole 20B provided at the center C of the vibration region E2, the vibration of the vibration region E2 due to acoustic pressure or the vibration of the vibration region E2 due to an AC voltage applied to the electrode 16 can be made greater than when the stretchable membrane 22 is positioned so as to cover a portion other than the center C.

[0053] The thickness of the stretchable film 22 may be any thickness that does not inhibit 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, etc.

[0054] The material of the stretchable film 22 is not limited as long as it has a higher stretchability than the piezoelectric element portion 12. For example, the stretchable film 22 may be made of an organic film or a metal film.

[0055] When the stretch film 22 is made of an organic film, it is preferable to use polyurethane, for example, for the stretch film 22 .

[0056] 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 from an organic film, it is possible to suppress the residual stress of the stretchable film 22 from affecting the resonance frequency of the vibration region E2 of the piezoelectric element portion 12.

[0057] When the stretch film 22 is made of a metal film, it is preferable that the stretch film 22 be made of a material that is commonly used in the manufacturing process of semiconductor devices, and in particular, it is preferable that the material be Al, Ti, Au, Ag, Cu, Ni, Mo, Pt, or an alloy containing these.

[0058] By forming the stretch film 22 from a metal film, the width L of the slit 20 can be made larger than when the stretch film 22 is formed from an organic film. In addition, since the metal film has a high affinity with the manufacturing process of the piezoelectric element section 12 (for example, a MEMS (Micro Electro Mechanical Systems) process), the degree of freedom in process design is increased. In addition, when the stretch film 22 is formed from a metal film, deterioration over time due to hydrolysis and the like is suppressed compared to when the stretch film 22 is formed from an organic film, and the film is also excellent in heat resistance and light resistance. Therefore, in this case, the reliability of the piezoelectric element section 12 can be improved. In order to achieve the desired stretchability, at least one of the thickness and shape of the stretch film 22 may be further adjusted.

[0059] From the viewpoint of preventing the stretchable film 22 from peeling off from the piezoelectric element section 12, it is preferable that the contact surface S of the piezoelectric element section 12 with the stretchable film 22 has irregularities. The surface roughness of the uneven contact surface S may be appropriately adjusted according to the constituent material of the stretchable film 22 so as to prevent the stretchable film 22 from peeling off from the piezoelectric element section 12. The irregularities of the contact surface S may be formed by providing the contact surface S with a plurality of holes, recesses, or holes.

[0060] Next, the function of the piezoelectric element 10 will be described.

[0061] In the piezoelectric element section 12, the vibration region E2 of the piezoelectric element section 12 vibrates. The vibration region E2 of the piezoelectric element section 12 vibrates due to acoustic pressure, for example, in the audible sound or ultrasonic range. The vibration region E2 of the piezoelectric element section 12 also vibrates due to an 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. Note that the acoustic pressure is not limited to acoustic pressure due to the audible sound and ultrasonic range. Similarly, the frequency of the AC voltage applied to the electrode 16 is not limited to a frequency in the audible sound and ultrasonic range.

[0062] When the vibration region E2 of the piezoelectric element portion 12 is distorted by acoustic pressure or the like, polarization occurs inside due to the transverse piezoelectric effect, and an electrical signal is extracted via the electrode 16.

[0063] In this embodiment, a stretchable film 22 is provided in the vibration region E2 of the piezoelectric element part 12. By providing the stretchable film 22, it is possible to suppress curvature of the vibration region E2 of the piezoelectric element part 12. Therefore, the residual stress of the stretchable film 22 is suppressed. Therefore, it is possible to suppress a decrease in the S / N ratio of the piezoelectric element 10. Furthermore, when the slit 20 is provided in the stretchable film 22, it is possible to suppress a decrease in the acoustic resistance caused by an increase in the gap between the regions facing each other through the slit 20 in the vibration region E2. Therefore, even when the slit 20 is provided in the vibration region E2, it is possible to suppress a decrease in the S / N ratio of the piezoelectric element 10 by providing the stretchable film 22.

[0064] As described above, the piezoelectric element 10 of this embodiment includes the piezoelectric element portion 12 having the piezoelectric film 14 and the electrodes 16 sandwiching the piezoelectric film 14 in the thickness direction Z, the support portion 18 supporting the peripheral portion E1 of the piezoelectric element portion 12, and the stretchable film 22. The stretchable film 22 is provided in the vibration region E2 inside the peripheral portion E1 of the piezoelectric element portion 12. The stretchable film 22 has higher stretchability than the piezoelectric element portion 12.

[0065] Here, in the past, the resonant frequency of the piezoelectric film with the peripheral edge fixed may change due to residual stress, leading to a decrease in the signal-to-noise ratio and a decrease in sensitivity characteristics. Also, in a conventional piezoelectric element in which a slit is provided in the piezoelectric film to form a cantilever structure, the bending of the piezoelectric film or electrode film may increase the effective gap between the beams, resulting in a decrease in acoustic resistance. For this reason, the conventional piezoelectric element may lead to a decrease in the signal-to-noise ratio. Also, in the conventional piezoelectric element, the sensitivity characteristics may lead to a decrease.

[0066] On the other hand, in the piezoelectric element 10 of this embodiment, a stretchable film 22 having higher stretchability than the piezoelectric element portion 12 is provided in a vibration region E2 inside a peripheral portion E1 of the piezoelectric element portion 12 supported by a support portion 18.

[0067] Therefore, in the piezoelectric element 10 of the present embodiment, the residual stress in the piezoelectric element portion 12 can be reduced, and a decrease in the S / N ratio can be suppressed.

[0068] Therefore, the piezoelectric element 10 of the present embodiment can suppress the decrease in the S / N ratio.

[0069] In addition to the above effects, the piezoelectric element 10 of the present embodiment can also suppress deterioration in sensitivity characteristics.

[0070] Furthermore, in the piezoelectric element 10 of the present embodiment, even if the slit 20 is provided in the vibration region E2, the bending of the vibration region E2 is suppressed by providing the stretchable film 22. This suppresses an increase in the gap (i.e., width L) between regions facing each other across the slit 20 in the vibration region E2. Furthermore, even if the vibration region E2 is bent, by arranging the stretchable film 22 so as to cover at least a portion of the slit 20, a decrease in acoustic resistance can be suppressed.

[0071] Therefore, the piezoelectric element 10 of the present embodiment can suppress the decrease in acoustic resistance, suppress the decrease in the S / N ratio, and suppress the decrease in sensitivity characteristics.

[0072] In addition, the stretchable film 22 has higher stretchability than the piezoelectric element portion 12. This makes it possible to suppress adverse effects on the resonance frequency caused by residual stress in the stretchable film 22. In addition, damage to the stretchable film 22 due to vibration of the vibration region E2 in the piezoelectric element portion 12 is also suppressed.

[0073] In addition, by providing an elastic film 22 in the vibration area E2 of the piezoelectric element 10 of this embodiment, it is possible to easily suppress a decrease in the signal-to-noise ratio and a decrease in the sensitivity characteristics, and therefore it is also possible to easily suppress a decrease in yield during the manufacture of the piezoelectric element portion 12.

[0074] Furthermore, since the piezoelectric element 10 of the present embodiment includes the elastic film 22, it is possible to improve the sensitivity to AC voltage or acoustic pressure, particularly in the low frequency range.

[0075] The opening shape and opening dimensions of the through hole 20B can be adjusted as desired.

[0076] Fig. 1H is an example of a top view of the piezoelectric element 10A5. Fig. 1I is a cross-sectional view of the piezoelectric element 10A5 taken along line AA' in Fig. 1H. The piezoelectric element 10A5 is an example of the piezoelectric element 10.

[0077] As shown in Figures 1H and 1I, the through hole 20B of the piezoelectric element 10A5 has a larger opening shape than the through hole 20B of the piezoelectric element 10 shown in Figures 1A and 1B. Specifically, in the example shown in Figures 1H and 1I, the through hole 20B has a circular opening shape with an opening diameter of LO.

[0078] The opening diameter LO of the through hole 20B can be adjusted arbitrarily.

[0079] In one example, the opening diameter LO can be adjusted according to 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 ratio of the opening diameter LO to the size of the vibration region E2 (i.e., the diameter LD of the vibration region E2 here) and the reception sensitivity of the piezoelectric element portion 12.

[0080] 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 reception sensitivity of the piezoelectric element portion 12. It can be seen from FIG. 1J that the reception sensitivity is almost constant when the ratio LO / LD is in the range of 0.01 to 0.1, and that the reception sensitivity significantly decreases when the ratio LO / LD is out of the range of 0.01 to 0.1. Therefore, if the designer sets the opening diameter LO so that the ratio LO / LD is in the range of 0.01 to 0.1, a piezoelectric element 10A5 with high sensitivity characteristics can be obtained.

[0081] In addition, although a circular opening shape is illustrated in Fig. 1H, the same effect can be obtained by replacing LO with the diameter of the circumscribed circle in a polygonal shape. Furthermore, although the stretch film 22 is not embedded inside the through hole 20B in Fig. 1I, it may enter the through hole 20B.

[0082] The method of 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 does not have to be within the range of 0.01 to 0.1. In addition, the opening shape of the through hole 20B is not limited to a circular shape.

[0083] (Second embodiment) In the above embodiment, the case where the width L of the first slit 20A is constant along the extension direction (direction of the arrow W) of the first slit 20A has been described as an example. In the present embodiment, a case where the width L of the first slit 20A is different from that in the above embodiment will be described.

[0084] Fig. 2A is an example of a top view of a piezoelectric element 10B according to the present embodiment, and Fig. 2B is a cross-sectional view taken along line AA' of the piezoelectric element 10B shown in Fig. 2A.

[0085] The piezoelectric element 10B has the same configuration as the piezoelectric element 10 of the first embodiment, except that the width L of the slits 20 is different from that of the first embodiment.

[0086] 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 piezoelectric element portion 13B includes the slit 21 instead of the slit 20.

[0087] The slit 21 is composed of a plurality of first slits 21A and a through hole 20B. The through hole 20B is the same as in the above embodiment. The first slit 21A is the same as the first slit 20A in the above embodiment except that the width L is different.

[0088] In the present embodiment, the stretchable film 22 is disposed so as to continuously cover a portion of each of the plurality of first slits 21A and the through-hole 20B.

[0089] In this embodiment, the slit width L1 of the covered area 21A1 covered by the stretch film 22 in the first slit 21A is larger than the slit width L2 of the uncovered area 21A2 not covered by the stretch film 22.

[0090] By making the slit width L1 of the covered area 21A1 in the slit 21 larger than the slit width L2 of the uncovered area 21A2, the stress applied to the stretch film 22 can be reduced.

[0091] It is preferable that the width L of the first slit 21A increases stepwise or continuously as it approaches the center C from the boundary between the vibration region E2 and the peripheral edge portion E1.

[0092] 2C is a 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. A slit 23 is provided in the piezoelectric element portion 13C. The piezoelectric element portion 13C is similar to the piezoelectric element portion 13B (see FIGS. 2A and 2B) except that the piezoelectric element portion 13C includes the slit 23 instead of the slit 21.

[0093] The slit 23 is composed of a plurality of first slits 23A and a through hole 20B. The through hole 20B is the same as in the above embodiment. The first slit 23A is the same as the first slit 20A in the above embodiment except that the width L is different.

[0094] As shown in FIG. 2C, the width L of the first slit 23A may be configured to increase as it approaches the center C.

[0095] 2A and 2B, as described above, in the piezoelectric element 10B of the present embodiment, the slit width L1 of the covered area 21A1 covered by the stretch film 22 in the first slit 21A is larger than the slit width L2 of the uncovered area 21A2 not covered by the stretch film 22.

[0096] By making the slit width L1 of the covered area 21A1 in the first slit 21A larger than the slit width L2 of the uncovered area 21A2, the piezoelectric elements 10B and 10C of the present embodiment can reduce the stress applied to the stretch film 22 in addition to achieving the effects described above.

[0097] (Variation 1) The shape of the stretch film 22 is not limited to a planar shape along a direction (direction along the XY plane) intersecting the thickness direction Z. For example, at least a part of the stretch film 22 may be bellows-shaped.

[0098] Fig. 3A is an example of a top view of a piezoelectric element 10D according to this modified example, and Fig. 3B is a cross-sectional view of the piezoelectric element 10D shown in Fig. 3A taken along the line AA'.

[0099] The piezoelectric element 10D includes a piezoelectric element portion 13D, a support portion 18, and a stretchable film 25. The piezoelectric element 10D includes a stretchable film 25 instead of the stretchable film 22 of the piezoelectric element 10C (see FIG. 2C) of the second embodiment. The stretchable film 25 is similar to the stretchable film 22 except that the shape of the stretchable film 25 is different from that of the stretchable film 22.

[0100] At least a portion of the stretch film 25 is formed in a bellows shape that is stretchable in intersecting directions (XY directions) that intersect with the thickness direction Z.

[0101] For example, the stretchable film 25 is made up of a bellows region 25A and a flat region 25B. The bellows region 25A is a bellows-shaped region consisting of repeated mountain folds and valley folds so that the film can stretch in the intersecting directions (XY directions). The flat region 25B is a two-dimensional flat region along the intersecting directions (XY directions). The region of the stretchable film 25 that overlaps with the opening of the slit 23 in a planar view is the bellows region 25A, and the contact region with the vibration region E2 of the piezoelectric element portion 13D is the flat region 25B.

[0102] In this manner, by configuring the stretch film 25 to include the bellows region 25A, the stretchability of the stretch film 25 can be easily improved.

[0103] Furthermore, even if there is a possibility that the desired elasticity may not be obtained by using a metal film or the like for the elastic film 25, the desired elasticity can be obtained by adjusting the shape of the elastic film 25 to an accordion-like shape.

[0104] Furthermore, by arranging the bellows region 25A in a region in the vibration region E2 where the openings of the slits 23 overlap in a plan view, it is possible to effectively improve the sensitivity characteristics of the piezoelectric element portion 13D.

[0105] The stretch film 25 is not limited to a bellows shape as long as it has a shape that can improve the stretchability of the stretch film 25. In other words, the shape of at least a part of the region of the stretch film 25 is a shape that can stretch in intersecting directions (XY directions) that intersect with the thickness direction Z.

[0106] (Variation 2) In the above embodiment and modified example, the vibration region E2 is circular in plan view. In the above embodiment and modified example, the support portion 18 has holes 19 that are circular in plan view, and is a circular frame-shaped member. Therefore, in the above embodiment and modified example, the peripheral portion E1 is a circular frame-shaped region in plan view, and the vibration region E2 is a circular region in plan view.

[0107] However, the shapes of the support portion 18, the holes 19 in the support portion 18, the peripheral portion E1, and the vibration region E2 are not limited to a circular shape.

[0108] For example, the vibration area E2 may be rectangular or polygonal in plan view. Fig. 4 is a top view showing an example of the piezoelectric element 10E.

[0109] 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 its shape.

[0110] As shown in FIG. 4, the piezoelectric element 10E may be configured to include 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 frame member that is rectangular in plan view, a vibration region E2 that is rectangular in plan view, and a stretch film 22 that is rectangular in plan view.

[0111] The scope of application of the piezoelectric element 10, the piezoelectric element 10B, the piezoelectric element 10C, the piezoelectric element 10D, and the piezoelectric element 10E described in the above embodiment and modification is not limited. For example, the piezoelectric element 10, the piezoelectric element 10B, the piezoelectric element 10C, the piezoelectric element 10D, and the piezoelectric element 10E described in the above embodiment and modification can be suitably applied to a microelectromechanical system (MEMS) including a piezoelectric element.

[0112] Although the embodiments and modifications of the present invention have been described above, these embodiments and modifications are presented as examples and are not intended to limit the scope of the invention. These novel embodiments and modifications can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the gist of the invention. These embodiments and modifications are included in the scope and gist of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0113] 10, 10A, 10A1, 10A2, 10B, 10C, 10D, 10E Piezoelectric elements 12, 13B, 13C, 13D Piezoelectric element part 14 Piezoelectric film 16 electrodes 18 Support part 20, 21, 23 Slit 20A, 21A, 23A First slit 20B through hole 22 Stretch membrane E1 Periphery E2 vibration area

Claims

1. a piezoelectric element portion having a piezoelectric film and electrodes sandwiching the piezoelectric film in a thickness direction; a support portion for 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 higher stretchability than the piezoelectric element portion; Equipped with The stretchable film is The piezoelectric element portion is provided on at least one end surface in the thickness direction of the vibration region of the piezoelectric element portion, At least one end surface of the peripheral portion in the thickness direction is uncoated. Piezoelectric element.

2. A piezoelectric element portion having a piezoelectric film and electrodes sandwiching the piezoelectric film in a thickness direction; a support portion for 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 higher stretchability than the piezoelectric element portion; a slit provided in the vibration region of the piezoelectric element portion and penetrating the vibration region in the thickness direction; Equipped with The stretchable film is The vibration region is arranged to cover at least a part of the opening of the slit in the vibration region and to integrate the vibration region separated by the slit, The slit has a covered area where the opening is covered by the stretch film and a non-covered area where the opening is not covered by the stretch film. Piezoelectric element.

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

4. The slit is The piezoelectric element according to claim 3 , wherein a slit width in the covered region is greater than a slit width in the uncovered region.

5. The slit widths of the covered and uncovered regions of the slit are The closer to the center from the peripheral portion, the larger The piezoelectric element according to claim 3 or 4.

6. The stretchable film is an organic film or a metal film. The piezoelectric element according to any one of claims 1 to 5.

7. The stretchable film is At least a portion of the region is bellows-shaped and expandable in a direction intersecting the thickness direction. The piezoelectric element according to any one of claims 1 to 6.

8. The contact surface of the piezoelectric element with the stretchable film has projections and recesses. The piezoelectric element according to any one of claims 1 to 7.

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