Electroacoustic converter

Abstract

To provide an electroacoustic transducer capable of achieving both good roll-off frequency characteristics and good sensitivity characteristics.SOLUTION: A piezoelectric element (3) includes: a through hole penetrating in the thickness direction (35); and a vibrating part (34) extending in a cantilever state in an extension direction from a fixed edge (34a) toward the through hole. A stretchable membrane (4) has a diaphragm covering portion (41) that covers at least a free edge (34b) on the tip side in the extension direction of the vibrating portion; and a through hole covering part (42) that covers the through hole. The through hole covering part has a peripheral portion (44) provided at a joint with an inner edge surface (35a), which is a wall surface constituting an inner edge of the through hole, and a thin-walled portion (45) whose dimension in the thickness direction is smaller than that of the periphery portion.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an electroacoustic transducer.

Background Art

[0002] The piezoelectric element described in Patent Document 1 includes a piezoelectric element portion, a support portion that supports the peripheral edge of the piezoelectric element portion, and an elastic film that is more stretchable than the piezoelectric element portion. The elastic film is provided in a vibration region inside the peripheral edge of the piezoelectric element portion. A slit penetrating the vibration region in the thickness direction is provided in the vibration region of the piezoelectric element portion. The elastic film covers at least a part of the opening of the slit in the vibration region and is arranged so as to integrate the vibration regions separated by the slit.

[0003] By the way, in this type of piezoelectric element in which a slit is provided in the piezoelectric film to form a cantilever beam structure, due to the curvature of the piezoelectric film, the substantial gap between the beams may increase, and the acoustic resistance may decrease. In this regard, according to the configuration described in Patent Document 1, by providing the elastic film, the curvature of the vibration region is suppressed, and the increase in the gap is suppressed. Further, even if the vibration region is curved, by arranging the elastic film so as to cover at least a part of the slit, it is possible to suppress the decrease in the acoustic resistance. Therefore, according to such a configuration, it is possible to suppress the decrease in the S / N ratio and the sensitivity characteristics. Further, the elastic film is more stretchable than the piezoelectric element portion. Therefore, it is possible to suppress the adverse effect on the resonance frequency due to the residual stress of the elastic film. Further, it is also possible to suppress the breakage of the elastic film due to the vibration of the vibration region.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In this type of configuration, it is known that increasing the slit opening area worsens the roll-off frequency characteristics. In this regard, the configuration described in Patent Document 1 attempts to suppress the deterioration of the roll-off frequency characteristics by reducing the slit opening area by providing an expandable membrane that covers at least a part of the slit. On the other hand, providing such an expandable membrane suppresses deformation in the vibration region, which raises concerns about a decrease in sensitivity. The present invention has been made in view of the circumstances illustrated above. That is, the present invention provides a configuration that makes it possible to achieve both good roll-off frequency characteristics and good sensitivity characteristics. [Means for solving the problem]

[0006] The electroacoustic transducer (1) described in claim 1 is A piezoelectric element portion (3) is formed in the shape of a plate having a thickness direction along the directional axis (CA) and comprises a piezoelectric film (31) made of a piezoelectric material, A support portion (2) is provided to fixally support the fixed end portion (34a), which is the outer edge of the piezoelectric element portion in an in-plane direction perpendicular to the directional axis, A stretchable film (4) is laminated with the piezoelectric element portion in the thickness direction of the plate and bonded to the piezoelectric element portion, Equipped with, The piezoelectric element portion is The through hole (35) that penetrates in the thickness direction of the plate, A vibrating section (34) extending in a cantilevered shape in the direction of extension from the fixed end toward the through hole, as the in-plane direction, Equipped with, The expandable membrane has a diaphragm covering portion (41) that covers at least the free end (34b) on the leading edge side in the extending direction of the vibrating portion, and a through-hole covering portion (42) that covers the through-hole. The through-hole covering portion includes a peripheral portion (44) provided at the joint with the inner edge surface (35a), which is a wall surface constituting the inner edge of the through-hole, and a thin-walled portion (45) formed to be smaller in dimensions in the plate thickness direction than the peripheral portion. and a thickened portion (46) whose dimensions in the thickness direction are larger than those of the thinned portion. To possess.

[0007] In addition, each element in the application documents may be denoted by a reference numeral in parentheses. In this case, the reference numeral is merely an example of the correspondence between the element and the specific configuration described in the embodiments below. Therefore, the present invention is not limited in any way by the notation of the reference numeral. [Brief explanation of the drawing]

[0008] [Figure 1] This is a side cross-sectional view showing a schematic configuration of an electroacoustic transducer according to the first embodiment of the present invention. [Figure 2] Figure 1 is a plan view showing a schematic configuration of the piezoelectric element and the stretchable membrane in the electroacoustic converter according to the first embodiment. [Figure 3] Figure 1 is a schematic diagram showing the dimensional relationships of each part of the stretchable membrane in the electroacoustic converter according to the first embodiment. [Figure 4] This is a side cross-sectional view showing a schematic configuration of an electroacoustic converter according to a second embodiment of the present invention. [Figure 5] Figure 4 is a plan view showing the schematic configuration of the piezoelectric element and the stretchable membrane in the electroacoustic converter according to the second embodiment shown. [Figure 6] Figure 4 is a schematic diagram showing the dimensional relationships of each part of the stretchable membrane in the electroacoustic converter according to the second embodiment. [Figure 7] Figures 1 and 4 are plan views showing a modified example of the in-plane shape of the through-hole in the piezoelectric element section. [Figure 8] This is a plan view showing another modified example of the in-plane shape of the through-hole in the piezoelectric element shown in Figures 1 and 4. [Figure 9] This is a plan view showing yet another modified example of the in-plane shape of the through-hole in the piezoelectric element shown in Figures 1 and 4. [Figure 10] This is a plan view showing yet another modified example of the in-plane shape of the through-hole in the piezoelectric element shown in Figures 1 and 4. [Figure 11] This is a plan view showing yet another modified example of the in-plane shape of the through-hole in the piezoelectric element shown in Figures 1 and 4. [Figure 12] It is a plan view showing still another modified example of the in-plane shape of the through hole in the piezoelectric element portion shown in FIGS. 1 and 4. [Figure 13] It is a plan view showing still another modified example of the in-plane shape of the through hole in the piezoelectric element portion shown in FIGS. 1 and 4. [Figure 14] It is a plan view showing still another modified example of the in-plane shape of the through hole in the piezoelectric element portion shown in FIGS. 1 and 4. [Figure 15] It is a plan view showing still another modified example of the in-plane shape of the through hole in the piezoelectric element portion shown in FIGS. 1 and 4. [Figure 16] It is a plan view showing still another modified example of the in-plane shape of the through hole in the piezoelectric element portion shown in FIGS. 1 and 4. [Figure 17] It is a plan view showing still another modified example of the in-plane shape of the through hole in the piezoelectric element portion shown in FIGS. 1 and 4. [Figure 18] It is a plan view showing still another modified example of the in-plane shape of the through hole in the piezoelectric element portion shown in FIGS. 1 and 4. [Figure 19] It is a plan view showing a modified example of the fixing structure of the expansion and contraction film in the electroacoustic transducer shown in FIGS. 1 and 4. [Figure 20] It is a plan view showing a modified example of the shape of the slit and the expansion and contraction film in the electroacoustic transducer shown in FIGS. 1 and 4. [Figure 21] It is a plan view showing a modified example of the in-plane shape of the thin portion forming hole and the thin portion shown in FIGS. 1 and 4. [Figure 22] It is a plan view showing another modified example of the in-plane shape of the thin portion forming hole and the thin portion shown in FIGS. 1 and 4. [Figure 23] It is a plan view showing still another modified example of the in-plane shape of the thin portion forming hole and the thin portion shown in FIGS. 1 and 4. [Figure 24] It is a plan view showing still another modified example of the in-plane shape of the thin portion forming hole and the thin portion shown in FIGS. 1 and 4. [Figure 25]Figures 1 and 4 are plan views showing yet another modified example of the hole forming the thin-walled portion and the in-plane shape of the thin-walled portion. [Figure 26] Figures 1 and 4 are plan views showing yet another modified example of the hole forming the thin-walled portion and the in-plane shape of the thin-walled portion. [Figure 27] Figures 1 and 4 are plan views showing yet another modified example of the hole forming the thin-walled portion and the in-plane shape of the thin-walled portion. [Figure 28] Figures 1 and 4 are plan views showing yet another modified example of the hole forming the thin-walled portion and the in-plane shape of the thin-walled portion. [Figure 29] Figures 1 and 4 are plan views showing yet another modified example of the hole forming the thin-walled portion and the in-plane shape of the thin-walled portion. [Figure 30] Figures 1 and 4 are plan views showing yet another modified example of the hole forming the thin-walled portion and the in-plane shape of the thin-walled portion. [Figure 31] This is a plan view showing the schematic configuration of the piezoelectric element and expandable membrane in relation to other modified examples. [Figure 32] This is a plan view showing one modified example of the in-plane shape of an expandable membrane having a thickened section, as shown in Figure 4. [Figure 33] This is a plan view showing another modified example of the in-plane shape of the stretchable membrane having a thickened section, as shown in Figure 4. [Figure 34] This is a side cross-sectional view showing a modified example of how the thickened portion is formed, as shown in Figure 4. [Figure 35] Figure 4 shows a cross-sectional view illustrating another modified example of the formation of the thickened portion. [Modes for carrying out the invention]

[0009] (Embodiment) Hereinafter, embodiments of the present invention will be described based on the drawings. Note that various modifications applicable to a single embodiment may be impeded in the middle of a series of descriptions relating to that embodiment if they are inserted into the description. Therefore, modifications will not be inserted in the middle of a series of descriptions relating to that embodiment, but will be described collectively afterward. Furthermore, the descriptions in each drawing, and the corresponding descriptions of the device configurations, functions, or operations described below, are simplified for the purpose of concisely explaining the content of the present invention and do not limit the content of the present invention in any way. Therefore, it goes without saying that the exemplary configurations shown in each drawing do not necessarily correspond to the specific configurations actually manufactured and sold. In other words, unless explicitly limited by the applicant in the application history, the present invention should not be interpreted restrictively by the descriptions in each drawing, or the corresponding descriptions of the device configurations, functions, or operations described below.

[0010] (First Embodiment) The electroacoustic transducer 1 according to the first embodiment will be described with reference to Figures 1 and 2. Note that Figure 1 corresponds to the II cross-sectional view in Figure 2. For the sake of explanation, as shown in the figure, a right-handed XYZ Cartesian coordinate system is set up so that the Z axis is parallel to the directional axis CA. The directional axis CA is a virtual straight line that serves as the reference for directivity in the electroacoustic transducer 1 that transmits or receives sound waves or ultrasonic waves, and may also be called the "directional center axis". Typically, the directional axis CA corresponds to a virtual straight line that indicates the axis center of a three-dimensional shape, such as a roughly conical or spindle shape, when the range of directivity, for example, the range in which a predetermined gain or predetermined sound level can be obtained, is represented by a three-dimensional shape. Specifically, for example, the directional axis CA is the central axis of the sound pressure half-angle.

[0011] The direction along the directional axis CA, that is, the direction parallel to the directional axis CA, will be referred to as the "axial direction" below. Therefore, the axial direction is the direction parallel to the Z-axis in the figure. Furthermore, the direction intersecting the axial direction, typically any direction perpendicular to the axial direction, will be referred to as the "in-plane direction." The "in-plane direction" is the direction parallel to the XY plane in the figure. The position and shape in the in-plane direction may be referred to as the "in-plane position" or "in-plane shape" below. The "in-plane shape" corresponds to the shape obtained by mapping the shape of a certain component onto the XY plane. The "in-plane direction" may also be referred to as the "radial direction" in some cases. The "radial direction" is the direction perpendicular to the directional axis CA and moving away from the directional axis CA. That is, the "radial direction" is the direction parallel to the direction in which a half-line extends when a half-line is drawn in the virtual plane starting from the intersection point of the virtual plane perpendicular to the directional axis CA and the directional axis CA. In other words, the "radial direction" is the radial direction of a circle drawn within the virtual plane, centered at the intersection of the virtual plane and the directional axis CA. Of the radial directions, the direction toward the directional axis CA will be referred to as the "centripetal direction," and the direction away from the directional axis CA will be referred to as the "centrifugal direction." The "in-plane direction" may also be referred to as the "circumferential direction" in some cases. The "circumferential direction" is the circumferential direction of the circle described above.

[0012] The electroacoustic transducer 1 has the configuration of a so-called piezoelectric MEMS microphone. MEMS is an abbreviation for Micro Electro Mechanical System. In other words, the electroacoustic transducer 1 is configured to generate an electrical signal corresponding to the received intensity of sound waves or ultrasonic waves propagating from the external space on the positive Z-axis side in the figure. Specifically, as shown in Figure 1, the electroacoustic transducer 1 comprises a support part 2, a piezoelectric element part 3, and a stretchable membrane 4. The parts constituting the electroacoustic transducer 1 will be described in order below. For the sake of simplicity, the positive Z-axis side in the figure may be referred to as "top" and the negative Z-axis side as "bottom". Correspondingly, viewing the electroacoustic transducer 1 and its components from above in the opposite direction to the Z-axis in Figure 1 may be referred to as a "plan view". Furthermore, in a multilayer structure stacked in the axial direction, the layer furthest towards the positive Z-axis side, i.e., the external space side, may be referred to as the "outermost layer", and the layer furthest towards the negative Z-axis side may be referred to as the "bottommost layer". Furthermore, the surface facing the positive Z-axis direction is sometimes referred to as the "top surface," and the surface facing the negative Z-axis direction is sometimes referred to as the "bottom surface." However, such descriptions are merely for convenience in briefly explaining the configuration, operation, and effects of the electroacoustic transducer 1, and do not mean that the direction of the directional axis CA in the electroacoustic transducer 1 is parallel to the direction of gravity.

[0013] The support portion 2 is formed in a cylindrical or annular shape surrounding the directional axis CA. In this embodiment, the support portion 2 has a rectangular cylindrical or rectangular annular shape with the directional axis CA as the central axis of symmetry. That is, the support portion 2 has a structure in which four flat plate-shaped wall materials, each having a constant thickness in the radial direction and a constant height in the axial direction, and arranged parallel to the directional axis CA, are seamlessly and integrally joined together. Furthermore, the in-plane shape of the support portion 2 is formed to be square. Specifically, the cavity portion 23, which is the space surrounded by the inner wall surface 22 facing the directional axis CA in the support portion 2, is formed in a rectangular prism shape with a square in-plane shape. This cavity portion 23 is covered by the piezoelectric element portion 3, by joining its upper end surface 24, which is the end surface on the positive Z-axis side in the figure, to the piezoelectric element portion 3. The support portion 2 can be formed from, for example, ceramics such as alumina or a silicon-based semiconductor substrate.

[0014] The piezoelectric element portion 3 is formed in a plate shape having a thickness direction along the directional axis CA, i.e., the axial direction. That is, the pair of main surfaces of the piezoelectric element portion 3, the upper surface 30a and the lower surface 30b, are formed in a planar shape perpendicular to the directional axis CA. A "main surface" is a surface of a plate-shaped portion or member that is perpendicular to the thickness direction. The piezoelectric element portion 3 is fixedly supported by the support portion 2 by joining the upper end surface 24 of the support portion 2 at the radial outer edge of the lower surface 30b. In this embodiment, the piezoelectric element portion 3 is formed in a square in-plane shape corresponding to the in-plane shape of the support portion 2. The piezoelectric element portion 3 comprises a piezoelectric film 31 formed of a piezoelectric material and an electrode film 32 formed of a conductive material. In this embodiment, the piezoelectric film 31 is formed in a thin film form of a piezoelectric material such as scandium aluminum nitride. Furthermore, the piezoelectric element portion 3 has a multilayer structure in which a plurality of piezoelectric films 31 are stacked in the axial direction with an electrode film 32 in between. The electrode film 32, which is made of a thin metal film such as copper foil, is provided on both sides of the piezoelectric film 31.

[0015] The piezoelectric element section 3 has a fixed section 33 and a vibrating section 34. The fixed section 33 is the radial outer edge of the piezoelectric element section 3 and is fixed to the support section 2 by being joined to the upper end surface 24 of the support section 2. The vibrating section 34 is provided radially inward, i.e., on the centripetal side, of the fixed section 33. The vibrating section 34 has a fixed end 34a and a free end 34b and is formed in a cantilever beam shape extending in the extension direction from the fixed end 34a to the free end 34b. The fixed end 34a is provided on the radial outer edge of the vibrating section 34, i.e., the piezoelectric element section 3, and is fixedly supported by the support section 2.

[0016] In this embodiment, the piezoelectric element section 3 has multiple vibrating sections 34 arranged circumferentially around the directional axis CA, each extending in a centripetal direction toward the directional axis CA. Specifically, a through hole 35 is formed at the center of the piezoelectric element section 3 in the in-plane direction, penetrating the piezoelectric element section 3 in the thickness direction. The through hole 35 has a circular in-plane shape centered on the directional axis CA. That is, the through hole 35 has an inner edge surface 35a, which is an inner circumferential surface with a cylindrical inner surface shape. The inner edge surface 35a is a wall surface that constitutes the inner edge of the through hole 35. Each of the multiple vibrating sections 34, which constitute the vibration region of the piezoelectric element section 3, extends from a fixed section 33, i.e., a fixed end 34a, toward the through hole 35, and is provided to vibrate in such a manner that its free end 34b moves along the directional axis CA. Each of the multiple vibrating sections 34 is formed with the same in-plane shape and is arranged at equal intervals in the circumferential direction. More specifically, the piezoelectric element section 3 comprises a pair of vibrating sections 34 extending parallel to the X-axis and facing each other across the through-hole 35, and a pair of vibrating sections 34 extending parallel to the Y-axis and facing each other across the through-hole 35. In Figure 2, the upper vibrating section 34 is formed such that the negative Y-axis direction is the extension direction and the X-axis direction is the width direction. In the same figure, the lower vibrating section 34 is formed such that the positive Y-axis direction is the extension direction and the X-axis direction is the width direction. In the same figure, the right vibrating section 34 is formed such that the negative X-axis direction is the extension direction and the Y-axis direction is the width direction. In the same figure, the left vibrating section 34 is formed such that the positive X-axis direction is the extension direction and the Y-axis direction is the width direction.

[0017] Slits 36 are provided at both ends of the vibrating part 34 in the width direction. The slits 36 are formed to penetrate the piezoelectric element part 3 in the thickness direction. That is, the vibrating part 34 is provided between a pair of slits 36. In this embodiment, the slits 36 are formed with a constant width. The direction that defines the "width" of the slits 36 is the direction perpendicular to the direction in which the slits 36 extend and the plate thickness direction, and specifically, in the figure, it is the direction perpendicular to the Z axis and intersects the X axis and Y axis at a 45-degree angle. Corresponding to the provision of four vibrating parts 34, four slits 36 are provided in the piezoelectric element part 3, each extending from a corner of the square shape of the piezoelectric element part 3 toward the directional axis CA. The slits 36 are provided to communicate with the through holes 35. That is, the slits 36 extend radially from the through holes 35.

[0018] The expandable membrane 4 is bonded to the piezoelectric element portion 3 in a state where it is laminated with the piezoelectric element portion 3 in the thickness direction of the plate. The expandable membrane 4 is provided so as to cover the through hole 35 and a portion of the vibrating portion 34 and slit 36 ​​(i.e., the portion on the free end 34b side) from the upper surface 30a side of the piezoelectric element portion 3. In other words, the expandable membrane 4 is formed as a film on the upper surface 30a. In this embodiment, the expandable membrane 4 has an outer shape larger than the through hole 35 and has a square in-plane shape with diagonals parallel to the X and Y axes. The expandable membrane 4 has higher expandability than the piezoelectric element portion 3. Specifically, the expandable membrane 4 is formed from a synthetic resin material (e.g., a photosensitive resin material) such that its Young's modulus is 1 / 10 or less of that of the vibrating portion 34.

[0019] The expandable membrane 4 has a diaphragm covering portion 41 and a through-hole covering portion 42. The diaphragm covering portion 41 is provided to cover at least the free end portion 34b on the leading edge side in the extending direction of the vibrating portion 34, and the portion communicating with the through-hole 35 in the slit 36. The diaphragm covering portion 41 is formed to have a substantially constant thickness in the axial direction. The through-hole covering portion 42 is provided to cover the through-hole 35. That is, the through-hole covering portion 42 is positioned in a location corresponding to the through-hole 35 in the in-plane direction. Furthermore, the through-hole covering portion 42 is provided to close the through-hole 35. More specifically, the through-hole covering portion 42 is housed within the through-hole 35 so as to be in close contact with the inner edge surface 35a of the through-hole 35 without any gaps over its entire circumferential direction. In this embodiment, the through-hole covering portion 42 is provided over the entire thickness direction of the through-hole 35. In other words, the through-hole covering portion 42 is formed in the axial direction from the outermost surface of the diaphragm covering portion 41, i.e., the upper end in Figure 1, to the lower surface 30b of the piezoelectric element portion 3.

[0020] The through-hole covering portion 42 has a thin-walled portion forming hole 43, a peripheral portion 44, and a thin-walled portion 45. The thin-walled portion forming hole 43, which is not a through-hole, is formed to open in the positive Z-axis direction in the figure. In this embodiment, the thin-walled portion forming hole 43 has a round hole shape provided along the axial direction. The thin-walled portion forming hole 43 is provided so as to constitute the inner circumferential surface in the radial direction of the cylindrical peripheral portion 44 provided at the joint with the inner edge surface 35a of the through-hole 35. That is, the peripheral portion 44 is formed in a cylindrical shape. The peripheral portion 44 is provided in the axial direction from the upper end of the diaphragm covering portion 41 in Figure 1 to the lower surface 30b of the piezoelectric element portion 3. In other words, the peripheral portion 44 is formed to have a larger dimension in the plate thickness direction than the vibrating portion 34. The thin-walled portion 45 is provided radially inward from the peripheral portion 44. The thin-walled portion 45 is formed with dimensions in the thickness direction smaller than those of the peripheral portion 44. The thin-walled portion 45 is the thinnest part of the expandable membrane 4, and its dimensions in the thickness direction are smaller than those of the vibrating portion 34, i.e., the piezoelectric element portion 3. The thin-walled portion 45 is provided at one end of the through-hole covering portion 42 in the thickness direction, specifically at the bottom of the thin-walled portion forming hole 43.

[0021] Figure 3 shows the dimensional relationship between the piezoelectric element 3 and the expandable membrane 4. In Figure 3, the vertical axis Z indicates the position in the plate thickness direction parallel to the Z axis in each figure, and the origin (i.e., Z=0) is the position of the back surface Pa of the beam. The back surface Pa of the beam is the main surface of the vibrating part 34 of the cantilever beam structure, i.e., the bottom surface, i.e., the main surface on the side of the cavity 23. Specifically, the back surface Pa of the beam is the lower surface 30b in Figure 1, or the bottom surface of the lowest layer in the multilayer structure of the vibrating part 34, i.e., the main surface facing the cavity 23. The lowest layer in the multilayer structure of the vibrating part 34 is, for example, the electrode film 32 bonded to the bottom surface of the piezoelectric film 31 located closest to the cavity 23, or the coating layer covering it. The beam surface Pb of the beam is the main surface of the vibrating part 34 on the opposite side of the back surface Pa of the beam. Specifically, the beam surface Pb is the upper surface 30a in Figure 1, or the main surface of the outermost layer in the multilayer structure of the vibrating part 34. In the multilayer structure, the outermost layer is, for example, an electrode film 32 formed on the top surface of the piezoelectric film 31 located closest to the diaphragm covering portion 41, i.e., the external space side, or a coating layer covering it.

[0022] The membrane surface Pc is the top surface of the diaphragm covering portion 41 in the expandable membrane 4, i.e., the surface facing the external space. The hole surface Pd is the surface in the expandable membrane 4 at the in-plane position corresponding to the through hole 35, i.e., the top surface. In Figure 3, assuming a state in which the expandable membrane 4 is formed on the beam surface Pb with a constant film thickness without providing the thin-walled portion forming hole 43, the membrane surface Pc and hole surface Pd are shown by dashed lines for multiple different film formation conditions, i.e., film thickness conditions. When the thin-walled portion forming hole 43 is formed, the hole surface Pd is the bottom surface of the thin-walled portion forming hole 43, i.e., the top surface of the thin-walled portion 45. T1 is the thickness of the thin-walled portion 45, i.e., the dimension in the plate thickness direction. T2 is the thickness of the vibrating portion 34, i.e., the piezoelectric element portion 3. S1 is the position of the beam surface Pb on the vertical axis Z. H1 is the position of the membrane surface Pc on the vertical axis Z. H2 is the position of the hole surface Pd on the vertical axis Z.

[0023] Even if the stretchable film 4 is to be formed on the beam surface Pb with a constant film thickness without providing the thin part formation holes 43, due to the influence of forming the through holes 35 in the piezoelectric element part 3, as shown by the two-dot chain line in FIG. 3, shallow depressions or recesses may occur at the in-plane positions corresponding to the through holes 35. In this regard, the thin part formation holes 43 in the present embodiment are different from such depressions or recesses that occur spontaneously. Specifically, for example, when the stretchable film 4 is formed by the spin coating method, when the rotation speed is increased, the height of H1 decreases, and correspondingly, the height of H2 also decreases. However, unless the hole formation process for forming the thin part formation holes 43 is performed, H2 will not be lower than S1. On the contrary, by performing the hole formation process for forming the thin part formation holes 43, as shown in FIG. 3, it is possible to set H2 lower than S1. Thus, in the present embodiment, the stretchable film 4, that is, the through hole covering part 42, is formed such that H2 < S1. Note that as the above hole formation process, for example, exposure patterning using a photosensitive resin material, ablation processing by irradiation with an excimer laser, or the like can be used.

[0024] (Effect) Hereinafter, the operation outline of the configuration of the present embodiment will be described while referring to each drawing together with the effects achieved by the same configuration.

[0025] In the electroacoustic transducer 1 according to the present embodiment, the vibrating part 34 provided between the pair of slits 36 flexurally vibrates in such a manner that the free end 34b moves up and down in FIG. 1 along the direction axis CA. And the electroacoustic transducer 1 has a conversion function between the strain caused by such flexure and the voltage between the pair of electrode films 32 provided on both surfaces of the piezoelectric film 31. Therefore, for example, the flexural vibration of the vibrating part 34 due to the reception of sound waves or ultrasonic waves is taken out as the inter-electrode voltage. In this way, the electroacoustic transducer 1 generates an electrical signal corresponding to the reception intensity of the sound waves or ultrasonic waves propagating from the external space on the positive Z-axis side in the figure.

[0026] In this configuration, the piezoelectric element section 3 is provided with multiple cantilever-shaped vibrating sections 34 by forming through holes 35 and slits 36. In this configuration, if the vibrating section 34 warps due to curvature of the piezoelectric film 31 caused by residual stress, the opening width, i.e., the gap, created by the through holes 35 and slits 36 increases, reducing acoustic resistance and degrading the characteristics in the low-frequency band. Furthermore, a larger opening area worsens the roll-off frequency characteristics. In this embodiment, however, a portion of the through holes 35 and slits 36, which are provided around the free end 34b at the tip of the cantilever-shaped vibrating section 34, are covered by the expandable membrane 4. This effectively suppresses the occurrence of warping in the vibrating section 34 and reduces the opening area. As a result, the decrease in acoustic resistance and the deterioration of the roll-off frequency characteristics are effectively suppressed.

[0027] On the other hand, providing the expandable membrane 4 suppresses the bending deformation in the vibrating section 34, which raises concerns about a decrease in sensitivity. In this regard, as mentioned above, there are limits to how thin the expandable membrane 4 can be made by adjusting the film formation conditions. Therefore, in this embodiment, the expandable membrane 4 is formed such that its Young's modulus is 1 / 10 or less of that of the vibrating section 34. In addition, a thin-walled portion 45 is provided in the through-hole covering portion 42 that covers the through-hole 35 of the expandable membrane 4. This allows the vibrating section 34 to bend and deform well even with the expandable membrane 4 in place. Thus, according to this embodiment, it is possible to achieve both good roll-off frequency characteristics and good sensitivity characteristics.

[0028] (Second embodiment) The second embodiment will be described below with reference to Figures 4 to 6. In the description of the second embodiment below, we will primarily describe the parts that differ from the first embodiment described above. Furthermore, parts that are identical or equivalent to each other in the first and second embodiments are denoted by the same reference numerals. Therefore, in the description of the second embodiment below, with respect to components having the same reference numerals as in the first embodiment, the description in the first embodiment above may be appropriately applied unless there is a technical inconsistency or additional explanation is required.

[0029] In this embodiment, the through-hole covering portion 42 further has a thick portion 46 formed with a dimension in the plate thickness direction larger than that of the thin portion 45. The thick portion 46 corresponds to a portion where a part of the thin portion 45, which was formed with a uniform thickness in the first embodiment, is thickened in the in-plane direction. Specifically, the thick portion 46 protrudes from the thin portion 45 along the direction axis CA upward in FIG. 4, that is, in the positive direction of the Z axis. More specifically, as shown in FIGS. 4 and 5, the thick portion 46 is formed in a cylindrical shape with the direction axis CA as the central axis. Further, as shown in FIG. 6, the expansion and contraction film 4, that is, the through-hole covering portion 42, is formed such that H2 < H3 < H1. H3 is the position of the top surface of the thick portion 46. If the protruding height of the thick portion 46 from the thin portion 45 is T3, then H3 = T1 + T3. Thus, by thickening a part of the thin portion 45, in addition to improving the sensitivity by providing the thin portion 45, it is possible to improve the reliability.

[0030] (Modification example) The present invention is not limited to the above embodiment. Therefore, the above embodiment can be appropriately modified. Hereinafter, typical modification examples will be described. In the description of the following modification examples, the differences from the above embodiment will be mainly described. Also, in the above embodiment and the modification examples, the same reference numerals are assigned to parts that are identical or equivalent to each other. Therefore, in the description of the following modification examples, for components having the same reference numerals as those in the above embodiment, the description in the above embodiment can be appropriately incorporated, unless there is a technical contradiction or special additional explanation.

[0031] The present invention is not limited to the specific device configuration described in the above embodiment. That is, as described above, the description of the above embodiment is simplified for the purpose of briefly explaining the content of the present invention. For this reason, components that are usually provided in a product actually manufactured and sold, such as a casing, a bonding material (that is, an adhesive, etc.), terminals, wiring, etc., are appropriately omitted in the above embodiment and the corresponding drawings.

[0032] The support portion 2 may have a cylindrical, elliptical, triangular, pentagonal, hexagonal, or octagonal shape surrounding the directional axis CA. Alternatively, the support portion 2 may have an annular, elliptical, triangular, pentagonal, hexagonal, or octagonal shape surrounding the directional axis CA. Similarly, the piezoelectric element portion 3 may have a circular, elliptical, triangular, pentagonal, hexagonal, or octagonal shape.

[0033] In the above embodiment, the piezoelectric element portion 3 is fixed to the upper end surface 24 of the support portion 2, but the present invention is not limited to this configuration. That is, for example, the outer edge of the piezoelectric element portion 3 in the in-plane or radial direction may be fixed by a groove or adhesive layer provided on the inner wall surface 22 of the support portion 2. In this case, the fixed portion 33 and the fixed end portion 34a coincide.

[0034] There are no particular limitations on the number of vibrating parts 34 provided in the piezoelectric element section 3. That is, for example, the piezoelectric element section 3 may have a pair of square-shaped vibrating parts 34 facing each other, similar to the configuration described in International Publication No. 2007 / 060768. Alternatively, for example, the piezoelectric element section 3 may have three or five or more vibrating parts 34.

[0035] There are no particular limitations on the in-plane shape of the through-hole 35. That is, for example, as shown in Figures 7 and 8, the through-hole 35 can be formed in a square shape. There are also no particular limitations on the orientation of the through-hole 35. That is, for example, a square through-hole 35 may be provided so that each side is parallel to the X-axis or Y-axis, as shown in Figure 7, or it may be provided so that each side is inclined at a predetermined angle (typically 45 degrees) with respect to the X-axis or Y-axis, as shown in Figure 8. Also, as shown in Figures 9 and 10, the through-hole 35 may have a cross or X-shape. Here, as shown in Figure 10, if the through-hole 35 is formed in an X-shape with four square-shaped protrusions 350 that project centrifugally along the slit 36, and the width direction of the protrusions 350 is parallel to the width direction of the slit 36, then the protrusions 350 can be considered as a part of the slit 36, i.e., a widened portion. Furthermore, the protrusion 350 in Figures 9 and 10 can be formed in a trapezoidal shape, as shown in Figure 11.

[0036] As shown in Figures 12 and 13, the through-hole 35 can be formed in an elliptical cross shape. An "elliptical cross shape" is a shape in which two ellipses are superimposed in a cross shape. Specifically, an "elliptical cross shape" is a shape in which two ellipses with the same in-plane shape and a common center point are superimposed so that the major axes of one ellipse intersect (typically orthogonal) with those of the other. Here, in the example of Figure 13, as in the example of Figure 10, it is possible to consider this as a configuration in which the width of the communication point between the slit 36 ​​and the through-hole 35 is widened. By forming the through-hole 35 in an elliptical cross shape and rounding the ends, the intersection of the through-hole 35 and the expansion membrane 4 can be avoided from being orthogonal, thereby increasing reliability.

[0037] The relationship between the in-plane shape of the through-hole 35 and the through-hole covering portion 42 of the expandable membrane 4 that covers (i.e., closes) it, and the sensitivity will be considered below. If the spring constant of the expandable membrane 4 is k1 and the spring constant of the vibrating portion 34 is k2, then in order to reduce the overall resonant frequency, it is necessary to reduce k1 and k2. Here, in order to reduce the spring constant, it is necessary to increase the length, reduce the second moment of area, reduce Young's modulus, or reduce the stress. Therefore, in the above embodiment, a synthetic resin material with a low Young's modulus was used as the expandable membrane 4. In addition, a thin-walled portion 45 was provided in the through-hole covering portion 42 to form a step. On the other hand, regarding the in-plane shape, from the viewpoint of increasing the length and reducing the second moment of area, it is preferable to have a circular shape, or a shape that can be considered equivalent thereto, as in the above embodiment. A shape that can be considered equivalent to a circle is, for example, a polygon, i.e., an N-sided polygon, as shown in Figures 14 to 16. Preferably, N is an integer of 5 or more, more preferably a regular N-sided polygon, and even more preferably N is 6, 8, 12, etc. Figure 14 shows an example of a regular hexagon, and Figures 15 and 16 show examples of regular octagons. As the value of N increases (for example, N=16 or 24), it approaches a circle, and thus almost the same effect as a circle can be obtained. Also, as shown in Figures 15 and 16, there are no particular restrictions on the orientation of N-gons or regular N-gons. It is also possible to round the corners of an N-gon. Furthermore, star polygons as shown in Figure 17, the shape shown in Figure 18 with rounded corners, gear shapes, and sinusoidal shapes along the circumference can also be adopted.

[0038] Figure 19 shows another example of the expandable membrane 4 and its fixing structure. In Figure 19, the expandable membrane 4 is shown as a dashed line, or dotted line, to make it easier to see the structure for supporting and fixing the expandable membrane 4 in the vibrating section 34. As shown in Figure 19, in this modified example, the expandable membrane 4 is formed in a substantially cylindrical shape with an outer diameter smaller than the outer diameter of the through hole 35. That is, the diaphragm covering portion 41 that covers the free end 34b and a part of the slit 36 ​​in the vibrating section 34, as shown in Figures 2 and 5, is substantially absent in this modified example. On the other hand, in a plan view, a gap G is provided between the inner edge of the through hole 35 and the outer edge of the expandable membrane 4, penetrating the piezoelectric element portion 3 in the thickness direction. That is, the gap G corresponds to the outer edge of the through hole 35 in the radial direction. The vibrating section 34 is equipped with gripping claws 351 for fixing the expandable membrane 4. The gripping claws 351 protrude from the free end 34b toward the through hole 35.

[0039] In this modified example, the structure in which the expandable membrane 4 provided in the through-hole 35 is gripped by a plurality of gripping claws 351 projecting from the free end 34b toward the through-hole 35 effectively suppresses the warping of the vibrating part 34. Furthermore, by providing a gap G that penetrates the piezoelectric element part 3 in the plate thickness direction, and by not covering the end of the slit 36, i.e., the connection part with the through-hole 35, with the expandable membrane 4, it is possible to effectively suppress the decrease in sensitivity caused by the presence of the expandable membrane 4. Therefore, according to this modified example, it is possible to achieve both good roll-off frequency characteristics and good sensitivity characteristics.

[0040] The in-plane shape of the slit 36 ​​is not limited to a linear shape of constant width, as shown in Figure 2, etc. Therefore, for example, the slit 36 ​​may be formed in a tapered shape in which the width increases continuously, i.e. linearly, as it approaches the directional axis CA. Alternatively, the slit 36 ​​may be formed in a stepped shape in which the width increases intermittently, i.e. stepwise, as it approaches the directional axis CA. Alternatively, the slit 36 ​​may be formed in a shape that combines a tapered shape and a stepped shape. Figure 20 shows an example in which the slit 36 ​​is formed in a stepped shape in which the width changes in two stages. In the example shown in Figure 20, a wide portion 361 is formed at the end of the slit 36, i.e., the connection portion with the through hole 35. The outer edge 362, which is the centrifugal edge of the wide portion 361, is provided as a stepped portion perpendicular to the direction in which the slit 36 ​​extends, in a plan view. In this case, the through-hole 35 with a square in-plane shape and the four wide portions 361 extending radially from the through-hole 35 correspond to the X-shaped through-hole 35 shown in Figure 10.

[0041] The expandable membrane 4 is provided to close only a portion of the slit 36 ​​in its extending direction, rather than the entire slit 36. That is, the expandable membrane 4 is provided so as not to close the portion of the slit 36 ​​other than the wide portion 361 (i.e., the narrow portion) and the outer edge 362 of the wide portion 361. Specifically, a gap G is formed between the outer edge 362 and the outer edge 401 of the expandable membrane 4. In this modified example, the expandable membrane 4 is formed in an X-shape in plan view, corresponding to the X-shape formed by the through hole 35 and the wide portion 361 in plan view. That is, in plan view, the expandable membrane 4 has a shape that extends centrifugally from the through hole 35 along the slit 36, i.e., the wide portion 361. Therefore, it is possible to consider the expandable membrane 4 as having four notches 402 arranged in the circumferential direction surrounding the directional axis CA. The notches 402 are provided between a pair of circumferentially adjacent diaphragm covering portions 41 so as to form a V-shape. This configuration also makes it possible to achieve both good roll-off frequency characteristics and good sensitivity characteristics.

[0042] The wide portion 361 may be formed in a shape in which its width changes continuously or intermittently as it approaches the directional axis CA. The continuous change may be linear, or curved, for example, an arc, an elliptical arc, or a hyperbola. The same applies to the narrow portion of the slit 36. Furthermore, the outer edge 362 of the wide portion 361 may be formed in a curved shape in a plan view, or in a linear shape inclined with respect to the extension direction of the narrow portion. There are no other particular limitations on the in-plane shape of the slit 36.

[0043] The expandable membrane 4 may penetrate into the slit 36 ​​in the axial direction, i.e., the thickness direction of the piezoelectric element portion 3, or it may be provided so as to cover the slit 36 ​​from the outside without penetrating. Furthermore, the expandable membrane 4 is not limited to being provided on the upper surface 30a side of the piezoelectric element portion 3. That is, in the above embodiment, the expandable membrane 4 is formed by overlapping it on the surface of the beam (i.e., the vibrating portion 34), but the present invention is not limited to this embodiment. Therefore, as long as adhesion is ensured, it is not necessarily required to be on the surface of the beam. Accordingly, for example, the expandable membrane 4 may be formed from the lower surface 30b side of the piezoelectric element portion 3. If the adhesion is low, it will break due to the force of the beam contracting or being pulled up and down, so if the adhesion is low, it becomes necessary to cover the surface. When covering, covering the surface of the beam with the expandable membrane 4 leads to the beam becoming stiffer, making it difficult to deform and causing a decrease in sensitivity, so it is not desirable to carelessly increase the amount of covering.

[0044] There are no particular limitations on the in-plane shape of the stretchable membrane 4. That is, for example, the outer shape of the stretchable membrane 4 may be a square shape as shown in Figures 2 and 5, a circle shape as shown in Figure 19, or a cross or X shape as shown in Figure 20, or it may be an elliptical cross shape, an N-sided polygon shape, or a star-shaped polygon shape. Also, the in-plane shape of the thin-walled portion forming hole 43 or the thin-walled portion 45 may be a quadrilateral (e.g., a square) shape as shown in Figures 21 and 22, an N-sided polygon (e.g., a regular N-sided polygon) shape as shown in Figures 23 to 26, a cross or X shape as shown in Figures 27 and 28, or an elliptical cross shape as shown in Figures 29 and 30.

[0045] Figure 31 shows an example configuration in which the inner wall surface 22 is cylindrical, three fan-shaped vibrating parts 34 are arranged circumferentially, a triangular through-hole 35 is formed, and three slits 36 are provided so as to intersect each side of the triangular through-hole 35. In the example configuration shown in Figure 31, the expandable membrane 4 is formed in a substantially triangular shape. Specifically, the thin-walled part forming hole 43 is formed in a triangular shape, and the peripheral part 44 is formed in a triangular tube shape. Even in this example configuration, the effects of polygonization can be well achieved. In Figure 31, notches 402 are provided at each of the three corners of the substantially triangular shape of the expandable membrane 4. The expandable membrane 4 is locked in the through-hole 35 by diaphragm covering parts 41 that protrude outward on both sides of these notches 402. However, the present invention is not limited to this configuration. That is, the notches 402 are not essential. Also, the gap G may not be provided.

[0046] There are no particular limitations on the in-plane shape or number of thickened sections 46, and they can be set as appropriate according to the design. Specifically, for example, as shown in Figure 32, multiple thickened sections 46 may be provided. Also, as shown in Figure 33, the thickened sections 46 may be formed continuously with the peripheral sections 44. That is, the thickened sections 46 may be provided so as to connect opposing peripheral sections 44 in the in-plane direction. In this case, multiple such thickened sections 46 may be provided. Figure 33 shows an example in which a cross shape or an X shape is formed by two intersecting thickened sections 46.

[0047] Furthermore, as shown in Figure 34, the thickened portion 46 can be provided at stress concentration points 403 in the through-hole covering portion 42. With this configuration, reliability can be improved by thickening the stress concentration points 403. Stress concentration points 403 include, for example, joints and connections, locations where defects such as cracks occur, point-symmetrical parts (i.e., the central position, etc.), edge parts, etc. For this reason, as shown in the examples in Figures 5, 32, and 33, it is preferable that the thickened portion 46 be provided at least at the central position of the thinned portion 45. Also, as shown in Figure 35, reliability can be further improved by providing a transition portion 461 in the rising portion of the thickened portion 46 from the thinned portion 45, in which the thickness, i.e., the protruding height, changes continuously or intermittently. Furthermore, as shown in Figures 1, 4, 31, 32, and 33, by providing a transition portion 461 as a thickened portion 46 at the boundary between the cylindrical peripheral portion 44 and the thin plate-like thin-walled portion 45, the occurrence of stress concentration at such boundary locations can be effectively suppressed.

[0048] In the above description, multiple components that were formed as a single, seamless unit may be formed by bonding together separate components. Similarly, multiple components that were formed by bonding together separate components may be formed as a single, seamless unit. 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.

[0049] It goes without saying that the elements constituting the above embodiments are not necessarily essential unless explicitly stated to be particularly essential or considered to be fundamentally essential. Furthermore, when numerical values ​​such as the number of components, numerical values, quantities, or ranges are mentioned, the present invention is not limited to those specific numbers unless explicitly stated to be particularly essential or considered to be fundamentally limited to those specific numbers. Similarly, when the shape, direction, positional relationship, etc., of components are mentioned, the present invention is not limited to those shapes, directions, positional relationships, etc., unless explicitly stated to be particularly essential or considered to be fundamentally limited to those specific shapes, directions, positional relationships, etc.

[0050] The variations are not limited to the examples given above. That is, for example, multiple embodiments may be applied in combination. In other words, a part of one embodiment may be combined with a part of another embodiment. There are no particular limitations on the number or manner in which multiple embodiments are combined. Furthermore, any one of the multiple embodiments and any one of the multiple variations may be combined with each other, as long as it does not conflict with the technical standards. Similarly, one of the multiple variations and another may be combined with each other, as long as it does not conflict with the technical standards.

[0051] (Disclosure details) As is evident from the above description of embodiments and modifications, this specification discloses at least the following aspects: [Perspective 1] Electroacoustic transducer (1), A piezoelectric element portion (3) is formed in the shape of a plate having a thickness direction along the directional axis (CA) and comprises a piezoelectric film (31) made of a piezoelectric material, A support portion (2) is provided to fixally support the fixed end portion (34a), which is the outer edge of the piezoelectric element portion in an in-plane direction perpendicular to the directional axis, A stretchable film (4) is laminated with the piezoelectric element portion in the thickness direction of the plate and bonded to the piezoelectric element portion, Equipped with, The piezoelectric element portion is The through hole (35) that penetrates in the thickness direction of the plate, A vibrating section (34) extends in a cantilevered shape in the direction extending from the fixed end toward the through hole, as the in-plane direction, Equipped with, The expandable membrane has a diaphragm covering portion (41) that covers at least the free end (34b) on the leading edge side in the extending direction of the vibrating portion, and a through-hole covering portion (42) that covers the through-hole. The through-hole covering portion has a peripheral portion (44) provided at the joint with the inner edge surface (35a), which is a wall surface constituting the inner edge of the through-hole, and a thin-walled portion (45) formed to be smaller in dimensions in the plate thickness direction than the peripheral portion. Electroacoustic converter. [Perspective 2] The through hole, the expandable membrane, or the thin-walled portion is formed to have a circular or polygonal shape in the in-plane direction. The electroacoustic transducer described in Perspective 1. [Perspective 3] The through-hole covering portion further includes a thickened portion (46) whose dimensions in the thickness direction are larger than those of the thinned portion. An electroacoustic transducer as described in perspective 1 or 2. [Perspective 4] The aforementioned thickened portion is provided at the stress concentration point in the through-hole covering portion. The electroacoustic converter described in perspective 3. [Perspective 5] The stretchable membrane is formed such that the Young's modulus is 1 / 10 or less of that of the vibrating part. An electroacoustic converter described in one of the following points 1-4. [Perspective 6] The stretchable membrane is formed from a photosensitive resin material. An electroacoustic converter described in one of the following points 1 to 5. [perspective 7] The through-hole covering portion is provided over the entire length of the through-hole in the thickness direction of the plate, An electroacoustic converter described in any one of the viewpoints 1 to 6. [Perspective 8] The thin-walled portion is provided at one end of the through-hole covering portion in the thickness direction, An electroacoustic transducer described in any one of the viewpoints 1 to 7. [Perspective 9] The thin-walled portion is provided at the bottom of the thin-walled portion forming hole (43) formed in the expansion membrane so as to open toward the other side in the thickness direction of the plate. The electroacoustic converter described in perspective 8. [Perspective 10] The peripheral portion is formed to have a larger dimension in the plate thickness direction than the vibrating portion. An electroacoustic converter described in any one of the viewpoints 1 to 9. [Perspective 11] The thin-walled portion is formed to have dimensions in the thickness direction smaller than those of the vibrating portion. An electroacoustic converter described in any one of the viewpoints 1 to 10. [Perspective 12] The piezoelectric element portion comprises a pair of vibrating portions facing each other across the through-hole, An electroacoustic converter described in any one of the viewpoints 1 to 11. [Explanation of symbols]

[0052] 1. Electroacoustic transducer 3. Piezoelectric element section 34 Vibration section 34a Fixed end 34b Free end 35 Through hole 35a Inner edge surface 4 Stretch membrane 42 Through-hole covering 45 Thin-walled section

Claims

1. Electroacoustic converter (1), A piezoelectric element portion (3) is formed in the shape of a plate having a thickness direction along the directional axis (CA), and comprises a piezoelectric film (31) made of a piezoelectric material, A support portion (2) is provided to fixally support the fixed end portion (34a), which is the outer edge of the piezoelectric element portion in an in-plane direction perpendicular to the directional axis, A stretchable film (4) is laminated with the piezoelectric element portion in the thickness direction of the plate and bonded to the piezoelectric element portion, Equipped with, The piezoelectric element portion is The through hole (35) that penetrates in the thickness direction of the plate, A vibrating section (34) extending in a cantilevered shape in the direction of extension from the fixed end toward the through hole, as the in-plane direction, Equipped with, The expandable membrane has a diaphragm covering portion (41) that covers at least the free end (34b) on the leading edge side in the extending direction of the vibrating portion, and a through-hole covering portion (42) that covers the through-hole. The through-hole covering portion has a peripheral portion (44) provided at the joint with the inner edge surface (35a), which is a wall surface constituting the inner edge of the through-hole, a thin portion (45) formed to be smaller in the thickness direction than the peripheral portion, and a thick portion (46) formed to be larger in the thickness direction than the thin portion. Electroacoustic converter.

2. The through hole, the expandable membrane, or the thin-walled portion is formed to have a circular or polygonal shape in the in-plane direction. The electroacoustic converter according to claim 1.

3. The aforementioned thickened portion is provided at the stress concentration point in the through-hole covering portion. The electroacoustic converter according to claim 1.

4. The stretchable membrane is formed such that the Young's modulus is 1 / 10 or less of that of the vibrating part. The electroacoustic converter according to claim 1.

5. The stretchable membrane is formed from a photosensitive resin material. The electroacoustic converter according to claim 1.

6. The through-hole covering portion is provided over the entire length of the through-hole in the thickness direction of the plate, The electroacoustic converter according to claim 1.

7. The thin-walled portion is provided at one end of the through-hole covering portion in the thickness direction, The electroacoustic converter according to claim 1.

8. The thin-walled portion is provided at the bottom of the thin-walled portion forming hole (43) formed in the expansion membrane so as to open toward the other side in the plate thickness direction. The electroacoustic transducer according to claim 7.

9. The peripheral portion is formed to have a larger dimension in the plate thickness direction than the vibrating portion. The electroacoustic converter according to claim 1.

10. The thin-walled portion is formed to have dimensions in the thickness direction smaller than those of the vibrating portion. The electroacoustic converter according to claim 1.

11. The piezoelectric element portion comprises a pair of vibrating portions facing each other across the through-hole, The electroacoustic converter according to claim 1.

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