Acoustic converter and microphone

Abstract

To suppress vibrations in thin films. [Solution] The acoustic converter 100 comprises a substrate 10 having a cavity 11, a thin film 20 arranged to cover the cavity 11 and having a deformable portion 21a that deforms under pressure, and a fixed portion 21b connected to the deformable portion 21a and fixed to the substrate 10, and a back plate 30 that faces the thin film 20 in the thickness direction of the substrate 10, is arranged on the opposite side of the substrate 10 from the thin film 20, and has a plurality of holes 31 formed in it. The back plate 30 has a main plate 32 with a plurality of holes 31 formed in it and facing the thin film 20, and a side wall portion 60 arranged to surround the outside of the plurality of holes 31 and protruding from the main plate 32 toward the thin film 20.

Description

Technical Field

[0001] The present disclosure relates to an acoustic conversion device and a microphone.

Background Art

[0002] For example, an acoustic transducer including a substrate having a cavity, a vibration electrode plate disposed above the substrate, and a fixed electrode plate facing the vibration electrode plate above the substrate is known (see, for example, Patent Document 1).

[0003] Also, an acoustic transducer including a substrate having an opening, a back plate disposed to face the opening of the substrate, and a vibration electrode film disposed to face the back plate with a gap provided between the back plate and the vibration electrode film is known (see, for example, Patent Document 2). The acoustic transducer converts the displacement of the vibration electrode film into a change in the capacitance between the vibration electrode film and the back plate. The back plate is provided with a convex portion protruding toward the vibration electrode film.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the acoustic conversion device according to the prior art, the vibration of the thin film, which is the vibration electrode plate, increases, and the thin film and the back plate may collide, resulting in damage to the thin film and the back plate.

[0006] An object of the present disclosure is to provide an acoustic conversion device capable of suppressing the vibration of a thin film.

Means for Solving the Problems

[0007] An acoustic converter according to one aspect of the present disclosure comprises a substrate having a cavity, a thin film having a deformable portion that covers the cavity and deforms in response to changes in pressure inside the cavity, and a fixed portion connected to the deformable portion and fixed to the substrate, and a back plate having a plurality of holes, which is positioned opposite the thin film in the thickness direction of the substrate and on the opposite side of the substrate from the thin film. The back plate has a main body plate having a plurality of holes and facing the thin film, and a side wall portion that is positioned to surround the outside of the plurality of holes and protrudes from the main body plate toward the thin film. [Effects of the Invention]

[0008] This disclosure provides an acoustic converter capable of suppressing vibrations of a thin film. [Brief explanation of the drawing]

[0009] [Figure 1] This is an exploded perspective view illustrating an acoustic conversion device according to the first embodiment. [Figure 2] This is a plan view illustrating an acoustic conversion device according to the first embodiment. [Figure 3] This is a plan view illustrating a diaphragm. [Figure 4] This is a cross-sectional view illustrating a section along the line IV-IV in Figure 2. [Figure 5] This is a plan view illustrating the arrangement of the side walls formed on the backplate. [Figure 6] This is a magnified plan view showing a close-up of the backplate area. [Figure 7] This is a cross-sectional view illustrating a section along the line IV-IV in Figure 2, showing the state in which the side wall and stopper are in contact with the movable membrane. [Figure 8] This is a cross-sectional view illustrating an acoustic conversion device related to a comparative example, showing the state in which the stopper and the movable membrane are in contact. [Figure 9]This is a cross-sectional view illustrating an acoustic conversion device according to the second embodiment, showing the side wall and stopper in contact with the movable membrane. [Figure 10] This is a cross-sectional view illustrating an acoustic conversion device according to the third embodiment. [Figure 11] This is a cross-sectional view illustrating an acoustic conversion device according to the third embodiment, showing the side wall and stopper in contact with the movable membrane. [Figure 12] This is a partially enlarged plan view showing an enlarged portion of the backplate of the acoustic converter according to the fourth embodiment. [Figure 13] This is a cross-sectional view illustrating a MEMS microphone according to the fifth embodiment. [Figure 14] This is a cross-sectional view illustrating a MEMS microphone according to the sixth embodiment. [Modes for carrying out the invention]

[0010] The acoustic conversion device according to the embodiment will be described below with reference to the attached drawings. In this specification and drawings, substantially identical components may be denoted by the same reference numerals to avoid redundant explanations.

[0011] [Sound conversion device 100 according to the first embodiment] Referring to FIGS. 1 to 4, the acoustic conversion device 100 according to the first embodiment will be described. FIG. 1 is an exploded perspective view illustrating the acoustic conversion device 100 according to the first embodiment. FIG. 2 is a plan view illustrating the acoustic conversion device 100 according to the first embodiment. FIG. 3 is a plan view illustrating the diaphragm 20. FIG. 4 is a cross-sectional view showing a cross-section along line IV-IV in FIG. 2. In each figure, the X-axis direction, the Y-axis direction, and the Z-axis direction, which are three orthogonal directions, are illustrated. The Z-axis direction is the thickness direction of the substrate 10. The Z-axis direction may be the vertical direction. Also, in the following description, the terms "upper" and "lower" may be used, but the arrangement of the acoustic conversion device 100 is not limited thereto. For example, when the diaphragm 20 is used as a reference, the side where the back plate 30 is arranged may be regarded as "upper", and the side where the substrate 10 is arranged may be regarded as "lower". The X-axis direction includes the direction indicated by the arrow and the opposite direction. Similarly, the Y-axis direction and the Z-axis direction include the direction indicated by the arrow and the opposite direction.

[0012] As shown in FIG. 1, the acoustic conversion device 100 includes a substrate 10, a diaphragm 20, and a back plate 30. As shown in FIG. 4, the acoustic conversion device 100 includes a fixed electrode 40 and a support member 50. The acoustic conversion device is also called an acoustic transducer. The acoustic conversion device 100 can be used in a MEMS microphone. The acoustic conversion device 100 is a capacitive element manufactured using MEMS technology. "MEMS" is an abbreviation for Micro Electro Mechanical System. The acoustic conversion device 100 may also be used in other acoustic sensors and can be used as a speaker.

[0013] [Substrate 10] The substrate 10 is formed of, for example, single crystal silicon. The substrate 10 may be formed into a rectangular parallelepiped shape by, for example, dicing. A cavity 11 penetrating in the Z-axis direction is formed in the substrate 10. The cavity 11 includes an opening. The cavity 11 has, for example, a rectangular shape when viewed in the Z-axis direction. The shape of the opening of the cavity 11 is not limited to a rectangular shape and may be other shapes. The substrate 10 has a first surface 10a and a second surface facing each other in the Z-axis direction. The first surface 10a is the surface on the diaphragm 20 side in the Z-axis direction.

[0014] [Diaphragm 20] The diaphragm 20 has conductivity and is disposed so as to cover the cavity 11. The diaphragm 20 is a polysilicon thin film having conductivity. The diaphragm 20 is an example of a thin film. The diaphragm 20 is a vibrating electrode plate. The thickness direction of the diaphragm 20 is along the Z-axis direction. The diaphragm 20 has a movable film 21 and a fixed film 22. The movable film 21 is disposed so as to cover the cavity 11 in the Z-axis direction. As shown in FIG. 3, the movable film 21 includes a main body portion 21a having a substantially rectangular shape and protruding portions 21b protruding outward from the corners of the main body portion 21a.

[0015] The main body portion 21a is disposed so as to overlap the cavity 11 when viewed in the Z-axis direction. As shown in FIG. 3, the protruding portions 21b are disposed so as to overlap the first surface 10a of the substrate 10 when viewed in the Z-axis direction. The protruding portions 21b are fixed to the first surface 10a of the substrate 10. The protruding portions 21b may be fixed to the substrate 10 via a support member 50 disposed between the protruding portions 21b and the first surface 10a of the substrate 10 in the Z-axis direction. The main body portion 21a is a portion that can vibrate in the Z-axis direction. The main body portion 21a is an example of a deformed portion of the thin film. The protruding portions 21b are examples of fixed portions of the thin film.

[0016] As shown in FIG. 4, the main body portion 21a of the movable film 21 has a first surface 21c and a second surface 21d facing each other in the thickness direction (Z-axis direction) of the movable film 21. The first surface 21c is the surface on the back plate 30 side, and the second surface 21d is the surface on the cavity 11 side.

[0017] [Fixed membrane 22] The fixed membrane 22 is positioned around the movable membrane 21 when viewed in the Z-axis direction. The fixed membrane 22 is formed to surround the movable membrane 21. When viewed in the Z-axis direction, the fixed membrane 22 is positioned to overlap the first surface 10a of the substrate 10. The fixed membrane 22 is fixed to the first surface 10a of the substrate 10 via the support member 50. Similarly, the protrusion 21b of the diaphragm 20 is fixed to the first surface 10a of the substrate 10 via the support member 50.

[0018] [Slit 23] As shown in Figures 3 and 4, slits 23 are formed between the movable membrane 21 and the fixed membrane 22 in the X-axis and Y-axis directions. The slits 23 are in areas where the diaphragm 20 is not present. The slits 23 are formed to surround the movable membrane 21. The slits 23 have a predetermined width. The slits 23 are formed to penetrate the diaphragm 20 in the Z-axis direction. The slits 23 can be formed by etching a single polysilicon film. This separates the movable membrane 21 and the fixed membrane 22.

[0019] [Backplate 30] As shown in Figure 4, the backplate 30 is positioned in the Z-axis direction on the opposite side of the diaphragm 20 from the substrate 10. The backplate 30 may have a dome shape that bulges out on the opposite side of the substrate 10.

[0020] The backplate 30 has a main plate 32 that faces the movable membrane 21 of the diaphragm 20 in the Z-axis direction. The thickness direction of the main plate 32 is aligned with the Z-axis direction. The main plate 32 is positioned away from the diaphragm 20 in the Z-axis direction. A predetermined space is formed between the diaphragm 20 and the main plate 32. The main plate 32 of the backplate 30 is positioned to cover the opening of the cavity 11 of the substrate 10 when viewed in the Z-axis direction.

[0021] The main plate 32 of the backplate 30 has a plurality of holes 31 that penetrate in the Z-axis direction. The plurality of holes 31 are arranged at predetermined intervals in the X-axis direction and the Y-axis direction. The plurality of holes 31 are acoustic holes (sound holes) for allowing sound vibrations to pass through. The main plate 32 of the backplate 30 has a first surface 30a and a second surface 30b that face each other in the Z-axis direction. The first surface 30a is the surface on the diaphragm 20 side, and the second surface 30b is the surface on the opposite side from the diaphragm 20.

[0022] The peripheral edge of the backplate 30 is positioned to overlap the first surface 10a of the substrate 10 when viewed in the Z-axis direction. The peripheral edge of the backplate 30 is formed on the outside of the main body plate 32. The peripheral edge of the backplate 30 is positioned on the outside of the diaphragm 20 in the X-axis and Y-axis directions and is fixed to the first surface 10a of the substrate 10.

[0023] As shown in Figure 2, the multiple holes 31 may be formed to form, for example, a hexagon when viewed in the Z-axis direction. The shape of the multiple holes 31 is not limited to a hexagon; it may be circular, elliptical, rectangular, or any other polygon. The shape of the multiple holes 31 is not particularly limited.

[0024] [Fixed electrode 40] As shown in Figure 4, the fixed electrode 40 is formed on the first surface 30a of the back plate 30. The fixed electrode 40 is positioned opposite the main body portion 21a of the movable membrane 21 of the diaphragm 20 in the Z-axis direction. The fixed electrode 40 is positioned inside the slit 23 in the X-axis and Y-axis directions. The fixed electrode 40 is positioned to overlap the cavity 11 of the substrate 10 when viewed in the Z-axis direction.

[0025] [Capacitance C] The diaphragm 20 and the fixed electrode 40 are positioned apart in the Z-axis direction and function as parallel plates. The main body 21a of the movable membrane 21 of the diaphragm 20 is a movable electrode and is displaced in the Z-axis direction when sound pressure acts upon it. This changes the capacitance C between the diaphragm 20 and the fixed electrode 40. The sound converter 100 can sense sound by converting the change in capacitance C into a voltage. The main body 21a of the movable membrane 21 is an example of a deformable part.

[0026] [Side wall portion 60] Figure 5 is a plan view illustrating the arrangement of the side wall portion 60 formed on the back plate 30. Figure 6 is a partially enlarged plan view showing an enlarged portion of the back plate 30. As shown in Figures 2 and 4 to 6, the back plate 30 has a side wall portion 60 that protrudes from the main plate 32 toward the movable membrane 21. As shown in Figure 2, the side wall portion 60 is formed to surround the outside of the plurality of holes 31. The side wall portion 60 is formed to have a substantially rectangular outer shape. The plurality of holes 31 are arranged inside the side wall portion 60.

[0027] As shown in Figure 5, the side wall portion 60 has a first side 61, a second side 62, a third side 63, and a fourth side 64. The first side 61 and the third side 63 face each other in the X-axis direction and extend in the Y-axis direction. The second side 62 and the fourth side 64 face each other in the Y-axis direction and extend in the X-axis direction. The first side 61, the second side 62, the third side 63, and the fourth side 64 are formed linearly when viewed in the Z-axis direction. The first side 61, the second side 62, the third side 63, and the fourth side 64 may include curved portions.

[0028] As shown in Figure 4, the cross-sectional shape of the side wall portion 60 intersecting the longitudinal direction may be rectangular. The side wall portion 60 has a bottom surface 60a facing the movable membrane 21 in the Z-axis direction. The bottom surface 60a may be a surface parallel to the XY plane. The bottom surface 60a may include a curved surface.

[0029] The side wall portion 60 is positioned inward from the slit 23 in a direction intersecting the thickness direction of the substrate 10. When viewed in the Z-axis direction, the position closest to the center of the cavity 11 is considered the inside. The multiple holes 31 are positioned inward from the side wall portion 60. The slit 23 is positioned outward from the side wall portion 60.

[0030] For example, the width of the side wall portion 60 intersecting the longitudinal direction may be wider than the width of the slit 23 intersecting the longitudinal direction.

[0031] [Stopper 34] As shown in Figures 4 and 6, the backplate 30 is positioned inward from the sidewall portion 60 in a direction intersecting the thickness direction of the substrate 10 (X-axis direction or Y-axis direction), and has a plurality of stoppers 34 that protrude toward the movable membrane 21 in the Z-axis direction. The stoppers 34 are an example of protrusions. The stoppers 34 are positioned between a plurality of holes 31 when viewed in the Z-axis direction. The stoppers 34 are formed as points when viewed in the Z-axis direction. The stoppers 34 are formed to form, for example, a circle when viewed in the Z-axis direction. The shape of the stoppers 34 is not limited to a circle; they may be rectangular or have other shapes. Also, stoppers may be formed outside the sidewall portion 60. For example, stoppers may be formed at a position overlapping the protrusion 21b when viewed in the Z-axis direction.

[0032] As shown in Figure 4, the cross-sectional shape of the stopper 34 along the Z-axis direction may be rectangular. The stopper 34 has a bottom surface 34a facing the movable membrane 21 in the Z-axis direction. The bottom surface 34a may be a surface parallel to the XY plane. The bottom surface 34a may include a curved surface.

[0033] In the Z-axis direction, the position of the bottom surface 60a of the side wall portion 60 may be the same as the position of the bottom surface 34a of the stopper 34. In the Z-axis direction, the distance from the first surface 21c of the movable membrane 21 to the bottom surface 60a of the side wall portion 60 may be the same as the distance from the first surface 21c to the bottom surface 34a of the stopper 34. Note that "same" includes "approximately the same".

[0034] [Contact between the side wall portion 60 and the movable membrane 21] Figure 7 is a cross-sectional view illustrating a cross-section along the line IV-IV in Figure 2, showing the state in which the side wall 60 and stopper 34 are in contact with the movable membrane 21. As shown in Figure 7, when the pressure inside the cavity 11 increases, the movable membrane 21 moves in a direction toward the back plate 30. When the pressure inside the cavity 11 increases, the movable membrane 21 comes into contact with the stopper 34 and the side wall 60. Specifically, the first surface 21c of the movable membrane 21 comes into contact with the bottom surface 34a of the stopper 34 and the bottom surface 60a of the side wall 60. This suppresses vibration of the movable membrane 21. Note that in Figure 7, the movable membrane 21 is shown by a dashed line in a state where no pressure is acting and it is not displaced. In the state in which the movable membrane 21 is in contact with the stopper 34 and the side wall 60, the movable membrane 21 is not in contact with the fixed electrode 40.

[0035] For example, when the first surface 21c of the movable membrane 21 and the bottom surface 60a of the side wall portion 60 are in contact, the air inside the cavity 11 does not flow into the multiple holes 31. When the movable membrane 21 and the side wall portion 60 are in contact, the cavity 11 and the multiple holes 31 are not in communication. As shown in Figure 4, when the movable membrane 21 and the side wall portion 60 are not in contact, the cavity 11 and the multiple holes 31 are in communication.

[0036] As shown in Figure 7, when the movable membrane 21 and the side wall portion 60 are in contact, the second surface 21d of the movable membrane 21 is positioned above the first surface 22a of the fixed membrane 22. In this state, the opening of the slit 23 is widened in the Z-axis direction. A gap is formed between the movable membrane 21 and the fixed membrane 22 in the Z-axis direction. In other words, when the movable membrane 21 and the side wall portion 60 are in contact, a gap is formed between the movable membrane 21 and the first surface 10a of the substrate 10.

[0037] [Sound conversion device 100B related to comparative example] Next, a comparative example of the acoustic converter 100B will be described with reference to Figure 8. Figure 8 is a cross-sectional view illustrating the acoustic converter 100B according to the comparative example. The difference between the acoustic converter 100B according to the comparative example shown in Figure 8 and the acoustic converter 100 according to the first embodiment shown in Figure 4 is that it does not have a side wall portion 60.

[0038] In the comparative acoustic converter 100B, when the pressure inside the cavity 11 increases, the movable membrane 21 moves toward the back plate 30, and the movable membrane 21 and the stopper 34 come into contact. In this state, the comparative acoustic converter 100B does not have a side wall portion 60, so the multiple holes 31 and the cavity 11 are in communication. Therefore, the air inside the cavity 11 flows into the multiple holes 31 through the gap between the movable membrane 21 and the fixed membrane 22, and the gap between the first surface 21c of the movable membrane 21 and the back plate 30.

[0039] In the comparative example acoustic converter 100B, when the pressure inside the cavity 11 increases, an airflow is generated through the multiple holes 31. Therefore, when the pressure inside the cavity 11 is high, the vibration of the movable membrane 21 increases, and there is a risk that the movable membrane 21 or the back plate 30 may be damaged. For example, the vibration of the movable membrane 21 may cause the movable membrane 21 to come into contact with the stopper 34, resulting in wear or cracking of the movable membrane 21 or the back plate 30.

[0040] In the acoustic converter 100 according to the first embodiment, as shown in Figure 7, the side wall portion 60 and the movable membrane 21 are in contact, suppressing the flow of air to the multiple holes 31. In the acoustic converter 100, the contact between the side wall portion 60 and the movable membrane 21 suppresses vibration of the movable membrane 21, thereby suppressing damage to the diaphragm 20 and the back plate 30.

[0041] [Effects of the sound conversion device 100 according to the first embodiment] The acoustic converter 100 according to the first embodiment includes a substrate 10 having a cavity 11, a diaphragm (thin film) 20 having a main body (deformable part) 21a of a movable membrane 21 that is arranged to cover the cavity 11 and deforms in response to changes in pressure inside the cavity 11, and a protruding part (fixed part) 21b connected to the main body 21a and fixed to the substrate 10, and a back plate 30 that faces the movable membrane 21 in the Z-axis direction (thickness direction of the substrate 10), is arranged on the opposite side of the substrate 10 from the movable membrane 21, and has a plurality of holes 31 formed therein. The back plate 30 has a main body plate 32 that has a plurality of holes 31 formed therein and faces the movable membrane 21, and a side wall portion 60 that is arranged to surround the outside of the plurality of holes 31 and protrudes from the main body plate 32 toward the movable membrane 21.

[0042] In this type of acoustic converter 100, when pressure is applied inside the cavity 11, the movable membrane 21 moves toward the main body plate 32 of the back plate 30 in accordance with the increase in pressure. As the pressure inside the cavity 11 rises, the movable membrane 21 comes into contact with the side wall 60. This suppresses vibration of the movable membrane 21. As a result, contact between the movable membrane 21 and the main body plate 32 of the back plate 30 is suppressed, and damage to the movable membrane 21 and the back plate 30 is suppressed.

[0043] Furthermore, in the acoustic converter 100, when pressure is applied to the movable membrane 21 in the direction from the cavity 11 toward the back plate 30, the movable membrane 21 deforms to approach the back plate 30 and comes into contact with the side wall portion 60. In the acoustic converter 100, when the movable membrane 21 is in contact with the side wall portion 60, a gap is formed between the movable membrane 21 and the substrate 10 in the Z-axis direction.

[0044] In the acoustic converter 100, when pressure is applied to the movable membrane 21 in the direction from the cavity 11 toward the back plate 30, the movable membrane 21 deforms to approach the back plate 30 and comes into contact with the side wall 60. When the movable membrane 21 is in contact with the side wall 60, the multiple holes 31 are not in communication with the cavity 11. In this state, the airflow from the cavity 11 to the multiple holes 31 is blocked. In such an acoustic converter 100, the propagation of pressure from the multiple holes 31 is suppressed, and damage to the movable membrane 21 due to vibration of the movable membrane 21 can be suppressed. In the acoustic converter 100, when the pressure inside the cavity 11 rises, the inflow of air to the side of the movable membrane 21 opposite to the cavity 11 (the first surface 21c side) is prevented, thereby suppressing vibration of the movable membrane 21 and preventing damage to the movable membrane 21.

[0045] [Acoustic converter 100C according to the second embodiment] Next, the acoustic converter 100C according to the second embodiment will be described. Figure 9 is a cross-sectional view illustrating the acoustic converter 100C according to the second embodiment, showing the state in which the side wall portion 60 and the stopper 34 are in contact with the movable membrane 21. The difference between the acoustic converter 100C according to the second embodiment shown in Figure 9 and the acoustic converter 100 according to the first embodiment shown in Figure 7 is that it does not have a fixed membrane 22. In the description of the acoustic converter 100C according to the second embodiment, the same explanation as that given for the acoustic converter 100 according to the first embodiment will be omitted.

[0046] In the acoustic converter 100C according to the second embodiment, the diaphragm 20 may include a movable membrane 21 and not include a fixed membrane 22. Even in this acoustic converter 100C according to the second embodiment, the same effects and advantages as those of the acoustic converter 100 according to the first embodiment are achieved.

[0047] Furthermore, the diaphragm 20 does not necessarily have a slit 23. Also, the movable membrane 21 of the diaphragm 20 may be larger than the opening of the cavity 11 in the Z-axis direction. The outer edge of the movable membrane 21 may be positioned to overlap with the substrate 10 when viewed in the Z-axis direction. In addition, the acoustic converter 100C according to the second embodiment does not necessarily have a support member 50.

[0048] [Acoustic converter 100D according to the third embodiment] Next, the acoustic converter 100D according to the third embodiment will be described. Figure 10 is a cross-sectional view illustrating the acoustic converter 100D according to the third embodiment. Figure 11 is a cross-sectional view illustrating the acoustic converter 100D according to the third embodiment, showing the state in which the side wall portion 60B and the stopper 34 are in contact with the movable membrane 21. The difference between the acoustic converter 100D according to the third embodiment shown in Figure 10 and the acoustic converter 100C according to the second embodiment shown in Figure 9 is that it is equipped with a side wall portion 60B instead of a side wall portion 60. Note that in the description of the acoustic converter 100D according to the third embodiment, the same explanation as that given for the acoustic converters 100 and 100C according to the above embodiments will be omitted.

[0049] The side wall portion 60B protrudes in the Z-axis direction from the stopper 34. The bottom surface 60a of the side wall portion 60B is located closer to the substrate 10 (towards the movable membrane 21) in the Z-axis direction than the bottom surface 34a of the stopper 34. The bottom surface 60a of the side wall portion 60B is an example of the tip of the side wall portion. The bottom surface 34a of the stopper 34 is an example of the tip of the protruding portion.

[0050] As shown in Figure 11, when the pressure inside the cavity 11 increases, the movable membrane 21 is displaced in a direction approaching the main body plate 32 of the back plate 30. When the pressure inside the cavity 11 increases, the movable membrane 21 comes into contact with the stopper 34 and the side wall portion 60B. Specifically, the first surface 21c of the movable membrane 21 comes into contact with the bottom surface 34a of the stopper 34 and the bottom surface 60a of the side wall portion 60B. In this state, the movable membrane 21 is bent. The first surface 21c of the movable membrane 21 is in close contact with the bottom surface 60a of the side wall portion 60B.

[0051] The sound converter 100D according to this third embodiment also provides the same effects as the sound converter 100 according to the first embodiment. The amount of protrusion of the side wall portion 60B in the Z-axis direction may differ from the amount of protrusion of the stopper 34. The position of the bottom surface 60a of the side wall portion 60B and the position of the bottom surface 34a of the stopper 34 may differ in the Z-axis direction.

[0052] [Acoustic converter 100 according to the fourth embodiment] Next, the sound converter 100 according to the fourth embodiment will be described. Figure 12 is a partially enlarged plan view showing an enlarged portion of the backplate 30 of the sound converter 100 according to the fourth embodiment. The difference between the sound converter 100 according to the fourth embodiment and the sound converter 100 according to the first embodiment described above is that a notch 69 is formed in the side wall portion 60. Note that in the description of the sound converter 100 according to the second embodiment, the same explanation as that given for the sound converter 100 according to the first embodiment will be omitted.

[0053] In the acoustic converter 100 according to the fourth embodiment, the side wall portion 60 does not have to be continuous around its entire circumference. For example, a notch 69 may be formed on the third side 63 of the side wall portion 60. The third side 63 may be divided in the longitudinal direction. The notch 69 is a portion where the side wall portion 60 is not formed. The notch 69 penetrates the side wall portion 60, for example, in the X-axis direction. The position, size, and number of the notches 69 are not particularly limited.

[0054] The acoustic converter 100 according to this fourth embodiment also provides the same effects as the acoustic converter 100 according to the first embodiment. By forming the notch 69, when the movable membrane 21 and the side wall 60 are in contact, some of the air can pass through the notch 69. This makes it possible to adjust the pressure inside the cavity 11 and adjust the pressure acting on the movable membrane 21. An opening that allows air to pass through may be formed in the side wall 60.

[0055] [MEMS microphone 101 according to the fifth embodiment] Next, a MEMS microphone 101 according to the fifth embodiment will be described. Figure 13 is a cross-sectional view illustrating a MEMS microphone 101 according to the fifth embodiment. The MEMS microphone 101 includes the acoustic converter 100 according to the above embodiment. The MEMS microphone 101 may also include acoustic converters 100C and 100D instead of acoustic converter 100. In the description of the MEMS microphone 101 according to the fifth embodiment, the same description as that of the acoustic converters 100, 100C, and 100D according to the above embodiment will be omitted.

[0056] The MEMS microphone 101 comprises an acoustic converter 100, a housing 13, a base plate 14, and a circuit section 120.

[0057] The circuit unit 120 is electrically connected to the diaphragm 20, which is a movable electrode, and the fixed electrode 40. The circuit unit 120 converts the change in capacitance C between the diaphragm 20 and the fixed electrode 40 into a voltage signal. The circuit unit 120 outputs the converted signal to the outside of the circuit unit 120.

[0058] The housing 13 has an opening and houses the acoustic converter 100. The housing 13 may be box-shaped. The housing 13 is positioned to cover the acoustic converter 100 from the back plate 30 side. The bottom plate 14 is positioned to close the opening of the housing 13. The acoustic converter 100 is positioned in the space enclosed by the housing 13 and the bottom plate 14. The thickness direction of the bottom plate 14 is along the Z-axis direction. The bottom plate 14 is positioned to close the bottom surface of the substrate 10. The bottom plate 14 is positioned on the opposite side of the substrate 10 from the diaphragm 20. The bottom plate 14 has a sound hole 15 which is a through hole.

[0059] Inside the housing 13, a first space 111 and a second space 112 are formed. The first space 111 is the space between the diaphragm 20 and the bottom plate 14. The second space 112 is the space between the diaphragm 20 and the housing 13.

[0060] Thus, the acoustic converter 100 can be applied to the MEMS microphone 101.

[0061] [MEMS microphone 101B according to the 6th embodiment] Next, the MEMS microphone 101B according to the sixth embodiment will be described. Figure 14 is a cross-sectional view illustrating the MEMS microphone 101B according to the sixth embodiment. The differences between the MEMS microphone 101B according to the sixth embodiment and the MEMS microphone 101 according to the fifth embodiment described above are the arrangement of the sound converter 100 and the arrangement of the sound holes 15B. In the description of the MEMS microphone 101B according to the sixth embodiment, the same descriptions as those for the MEMS microphone 101B and sound converters 100, 100C, and 100D according to the above embodiments will be omitted.

[0062] The MEMS microphone 101B comprises a housing 13 and a bottom plate 14. The housing 13 has a sound hole 15B formed therein. The housing 13 has a top plate 13a facing the bottom plate 14 in the Z-axis direction. The top plate 13a has a sound hole 15B formed therein that penetrates in the thickness direction of the plate.

[0063] The circuit board 10 of the sound converter 100 is attached to the top plate 13a of the housing 13. The sound hole 15B communicates with the cavity 11. The back plate 30 of the sound converter 100 is located on the opposite side of the circuit board 10 from the top plate 13a (closer to the bottom plate 14).

[0064] Inside the housing 13, a first space 111B and a second space 112B are formed. The first space 111B is the space between the diaphragm 20 and the top plate 13a of the housing 13. The second space 112B is the space between the diaphragm 20 and the bottom plate 14.

[0065] Furthermore, other embodiments may be used in which other components are combined with the configurations listed in the above embodiments, and the present invention is not limited in any way to the configurations shown herein. In this regard, modifications can be made without departing from the spirit of the present invention, and can be appropriately determined according to the application form.

[0066] [Sound conversion device 100 according to a modified example] In the modified acoustic conversion device 100, the cross-sectional shape of the bottom surface 60a of the side wall portion 60 is not limited to a plane parallel to the XY plane. The bottom surface 60a of the side wall portion 60 may include a curved surface, a convex portion, a concave portion, a stepped surface, or an inclined surface. The side wall portion 60 may be formed to be divided into multiple parts in the longitudinal direction of the side wall portion 60. For example, a convex portion formed on the bottom surface 60a may be continuous in the longitudinal direction of the side wall portion 60. For example, a concave portion formed on the bottom surface 60a may be continuous in the longitudinal direction of the side wall portion 60, or may be formed to penetrate in the width direction of the side wall portion 60. For example, an inclined surface formed on the bottom surface 60a may be formed so that its outer end in the width direction protrudes more from the main body plate 32 than its inner end. For example, a curved surface formed on the bottom surface 60a may be formed so that it gradually protrudes from the main body plate 32 from the inner end to the outer end in the width direction. The "width direction" is defined as the direction that intersects the longitudinal direction when viewed in the Z-axis direction. The "inside" is defined as the side closer to the center of the opening of the cavity 11 when viewed in the Z-axis direction, and the "outside" is defined as the side further from the center of the opening of the cavity 11. [Explanation of Symbols]

[0067] 100, 100C, 100D... Acoustic converter, 101... MEMS microphone, 10... Substrate, 11... Cavity, 13... Housing, 14... Bottom plate, 15... Sound hole (through hole), 20... Diaphragm (thin film), 21... Movable membrane, 21a... Main body (deformable part), 21b... Protruding part (fixed part), 22... Fixed membrane, 34a... Bottom surface (tip of protruding part), 30... Back plate, 31... Multiple holes, 32... Main body plate, 34... Stopper (protruding part), 40... Fixed electrode, 60... Side wall, 60a... Bottom surface (tip of side wall), 111, 111B... First space, 112, 112B... Second space, 120... Circuit section, X... X-axis direction, Y... Y-axis direction, Z... Z-axis direction (plate thickness direction).

Claims

1. A substrate having a cavity, A thin film having a deformable portion that is arranged to cover the cavity and deforms in response to changes in pressure inside the cavity, and a fixed portion that is connected to the deformable portion and fixed to the substrate, The substrate comprises a back plate that faces the thin film in the thickness direction of the substrate, is positioned on the opposite side of the substrate from the thin film, and has a plurality of holes formed on it, The aforementioned backplate is The aforementioned plurality of holes are formed in the main body plate facing the thin film, An acoustic conversion device having side wall portions arranged to surround the outside of a plurality of holes and protruding from the main body plate toward the thin film.

2. When pressure is applied to the thin film in the direction from the cavity toward the back plate, the deformed portion deforms to approach the back plate and comes into contact with the side wall portion. The acoustic conversion device according to claim 1, wherein, when the deformed portion is in contact with the side wall portion, a gap is formed between the deformed portion and the substrate in the thickness direction of the substrate.

3. When pressure is applied to the thin film in the direction from the cavity toward the back plate, the deformed portion deforms to approach the back plate and comes into contact with the side wall portion. The acoustic conversion device according to claim 1, wherein, in the state in which the deformed portion is in contact with the side wall portion, the plurality of holes are not in communication with the cavity.

4. The sound conversion device according to claim 1 or 2, wherein a notch is formed in the side wall portion, penetrating in a direction intersecting the thickness direction of the substrate.

5. The back plate has a protruding portion that protrudes toward the thin film in the thickness direction of the substrate, The acoustic conversion device according to claim 1 or 2, wherein the tip of the side wall portion is positioned closer to the thin film than the tip of the protruding portion in the thickness direction of the substrate.

6. The sound conversion device described in claim 1 or 2, A microphone comprising a circuit section that outputs the signal output from the aforementioned sound converter to the outside.

7. A housing having an opening and housing the sound conversion device, The enclosure further comprises a bottom plate that closes the opening of the enclosure, The housing or the bottom plate has through holes that penetrate in the thickness direction of the substrate and communicate with the cavity. Inside the aforementioned housing, The first space is the space between the thin film and the housing or the bottom plate in which the through hole is formed, The microphone according to claim 6, wherein a second space is formed between the thin film and the housing or bottom plate in which the through hole is not formed.

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