Electroacoustic converter

Abstract

The electroacoustic converter will be made thinner. [Solution] The electroacoustic converter 1 comprises a metal backplate 10, a frame 30 disposed on the backplate 10, a MEMS device 20 located inside the frame 30 and disposed on the backplate 10, a membrane 50 disposed on the frame 30 and the MEMS device 20, and a metal cover member 70 disposed on the membrane 50.

Description

Technical Field

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

Background Art

[0002] MEMS devices fabricated by microfabrication techniques in Micro Electro Mechanical Systems (MEMS) have been developed. Since MEMS devices are manufactured by semiconductor processes, they have few variations and many features such as small size, thinness, light weight, low power consumption, and good frequency characteristics. MEMS devices have a fixed part and a movable part, and by driving the movable part, they can be used in electroacoustic transducers such as earphones and microphones (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The present disclosure aims to reduce the thickness of an electroacoustic transducer.

Means for Solving the Problems

[0005] An electroacoustic transducer according to an embodiment of the present disclosure includes a metal backplate, a frame disposed on the backplate, a MEMS device disposed on the backplate inside the frame, a membrane disposed on the frame and on the MEMS device, and a metal lid member disposed on the membrane.

Effects of the Invention

[0006] According to this disclosure, the electroacoustic converter can be made thinner. [Brief explanation of the drawing]

[0007] [Figure 1] This is a top perspective view illustrating a MEMS device according to the first embodiment. [Figure 2] This is a bottom perspective view illustrating a MEMS device according to the first embodiment. [Figure 3] This is a top view illustrating a MEMS device according to the first embodiment. [Figure 4] This is a bottom view illustrating a MEMS device according to the first embodiment. [Figure 5] This is a cross-sectional view illustrating a MEMS device according to the first embodiment. [Figure 6] This is a diagram (part 1) illustrating the reduction of stress in the MEMS device 20. [Figure 7] This figure shows the effect of the structure shown in Figure 6. [Figure 8] This is a diagram (part 2) illustrating the reduction of stress in the MEMS device 20. [Figure 9] This is Figure (Part 3) illustrating the reduction of stress in the MEMS device 20. [Figure 10] This is Figure (Part 4) illustrating the reduction of stress in the MEMS device 20. [Figure 11] This is the simulation result of the resonant frequency in the MEMS device 20. [Figure 12] This is a top perspective view illustrating an electroacoustic converter according to the first embodiment. [Figure 13] This is a bottom perspective view illustrating an electroacoustic converter according to the first embodiment. [Figure 14] This is a cross-sectional view illustrating an electroacoustic converter according to the first embodiment. [Figure 15] This is a partial bottom view illustrating an electroacoustic converter according to the first embodiment. [Figure 16]It is a bottom-side perspective view with the back plate and the mesh removed from FIG. 13. [Figure 17] It is an upper-side exploded perspective view illustrating the electroacoustic transducer according to the first embodiment. [Figure 18] It is a bottom-side exploded perspective view illustrating the electroacoustic transducer according to the first embodiment. [Figure 19] It is a top view illustrating the lid member of the electroacoustic transducer according to the first embodiment. [Figure 20] It is a diagram (part 1) for explaining the manufacturing method of the electroacoustic transducer according to the first embodiment. [Figure 21] It is a diagram (part 2) for explaining the manufacturing method of the electroacoustic transducer according to the first embodiment. [Figure 22] It is a top view for explaining the adhesion between the frame and the lid member. [Figure 23] It is a bottom view for explaining the adhesion between the frame and the back plate. [Figure 24] It is a partial cross-sectional view illustrating the electroacoustic transducer according to the first embodiment.

Mode for Carrying Out the Invention

[0008] Hereinafter, embodiments for carrying out the invention will be described with reference to the drawings. In each drawing, the same reference numerals are given to the same components, and redundant explanations may be omitted.

[0009] 〈First Embodiment〉 (MEMS Device) FIG. 1 is an upper-side perspective view illustrating the MEMS device according to the first embodiment. FIG. 2 is a bottom-side perspective view illustrating the MEMS device according to the first embodiment. FIG. 3 is a top view illustrating the MEMS device according to the first embodiment. FIG. 4 is a bottom view illustrating the MEMS device according to the first embodiment. FIG. 5 is a cross-sectional view illustrating the MEMS device according to the first embodiment, showing a cross-section along the line A-A in FIG. 1.

[0010] In addition, for reference, each drawing may show a Cartesian coordinate system with X, Y, and Z axes. In the X, Y, and Z directions, the side in which the arrow points may be referred to as the "+ side," and the opposite side as the "- side." Furthermore, the Z+ side of each component may be referred to as the top surface, and the Z- side as the bottom surface. However, these do not restrict the orientation of the MEMS device, etc., when using the embodiment, and the orientation of the MEMS device, etc., according to the embodiment is arbitrary. Also, viewing an object from the Z+ side to the Z- side, or viewing an object from the Z- side to the Z+ side, may be referred to as a plan view.

[0011] Referring to Figures 1 to 5, the MEMS device 20 has a fixed part 21, a movable part 22, a plurality of torsion beams 23, a plurality of drive beams 24, and a plurality of drive sources 25. The number of torsion beams 23, drive beams 24, and drive sources 25 are equal. In Figures 2 and 4, for convenience, the drive sources 25 are shown as a dot pattern. A similar representation may be used in subsequent figures.

[0012] The fixing portion 21 is formed in a frame shape in plan view. The fixing portion 21 has an outer edge and an inner edge in plan view. The inner edge and outer edge may or may not be similar in shape. For example, the inner edge may be polygonal and the outer edge may be circular or elliptical. In the examples in Figures 1 to 5, the inner edge of the fixing portion 21 is square, and the outer edge is square or rectangular. When the outer edge is square or rectangular, it is preferable because it can be easily processed by blade dicing, thus reducing processing costs.

[0013] The length of one side of the outer edge of the fixing part 21 can be, for example, about 3 mm to 10 mm. The width of the fixing part 21 (distance from the inner edge to the outer edge) can be, for example, about 0.3 mm to 1.0 mm. The thickness of the fixing part 21 can be, for example, about 100 μm to 500 μm.

[0014] Furthermore, in this application, with respect to polygons such as quadrilaterals, cases where the corners of the polygon are rounded or chamfered, or where protrusions or grooves are provided in parts of the polygon, are also included as polygons.

[0015] The movable part 22 is positioned inside the fixed part 21 in a plan view and is supported so as to be movable relative to the fixed part 21. In a plan view, it is preferable that the center O of the movable part 22 coincides with the center of the inner edge of the fixed part 21. In a plan view, it is preferable that the movable part 22 is point-symmetric with respect to the center O of the movable part 22. The thickness of the movable part 22 is the same as the thickness of the fixed part 21. The upper surface of the movable part 22 is coplane with the upper surface of the fixed part 21. The lower surface of the movable part 22 is coplane with the lower surface of the fixed part 21.

[0016] The structure may be such that the upper and lower surfaces of the movable part 22 are not on the same plane as the upper and lower surfaces of the fixed part 21. For example, the drive beam 24 can be bent by intentionally changing the film formation conditions or polarization conditions of the drive source 25, thereby shifting the height of the movable part 22 towards the upper side relative to the fixed part 21. The distance between the upper surface of the fixed part 21 and the upper surface of the movable part 22 can be, for example, about 20 to 100 μm. Also, the distance between the lower surface of the fixed part 21 and the lower surface of the movable part 22 can be, for example, about 20 to 100 μm.

[0017] In this application, "coplanar" refers to a case where the difference in height between the two is 20 μm or less.

[0018] In plan view, the movable part 22 has the same number of extensions as the twisted beam 23, extending radially from the center. Each extension includes an upper surface, a lower surface, one end surface, and two sides connected to the end surface. In the examples in Figures 1 to 5, the movable part 22 has a cross shape in plan view, with four extensions extending radially from the center.

[0019] When the movable part 22 is cross-shaped, the surfaces other than the top and bottom surfaces are referred to as end faces (two pairs of faces facing each other in the longitudinal direction) and side faces (all other faces). In other words, when the movable part 22 is cross-shaped, it has four end faces of the same area and eight side faces of the same area. The eight side faces include four pairs of adjacent side faces. Note that rounded corners, chamfers, etc., located between the end faces and side faces, and between side faces, are not included in the end faces and side faces.

[0020] The torsion beams 23 and drive beams 24 connect the fixed portion 21 and the movable portion 22 at a position closer to the lower surface than the upper surface of each. Multiple torsion beams 23 support the movable portion 22 from the outside. The torsion beams 23 are elastically deformable. The torsion beams 23 are thinner than the movable portion 22. The thickness of the torsion beams 23 can be, for example, about 5 μm to 60 μm. The torsion beams 23 are connected to the lower end of the side surface of the movable portion 22. In the example shown in Figures 1 to 5, four torsion beams 23 are provided. Preferably, each torsion beam 23 is arranged point-symmetrically with respect to the center O of the movable portion 22 in a plan view.

[0021] The upper surface of the twisted beam 23 is lower than the upper surfaces of the fixed part 21 and the movable part 22. The lower surface of the twisted beam 23 is on the same plane as the lower surfaces of the fixed part 21 and the movable part 22. In a plan view, each twisted beam 23 includes, for example, an L-shaped region. Including an L-shaped region in the twisted beam 23 allows the length of the twisted beam 23 to be increased. This makes the twisted beam 23 more prone to twisting, thus increasing the displacement of the movable part 22. As a result, when the MEMS device 20 is used in an electroacoustic converter, high sound pressure can be obtained.

[0022] When the movable part 22 is cross-shaped in plan view, the length of the torsion beam 23 can be increased compared to when the movable part 22 is a square with sides of the same length as the longitudinal length of the cross. This allows for a larger displacement of the movable part 22. As a result, high sound pressure can be obtained when the MEMS device 20 is used in an electroacoustic converter. Furthermore, when the movable part 22 is cross-shaped in plan view, it can be made lighter compared to when the movable part 22 is a square with sides of the same length as the longitudinal length of the cross, thus allowing for a higher resonant frequency.

[0023] Multiple drive beams 24 are provided, one for each torsion beam 23. In the examples shown in Figures 1 to 5, since there are four torsion beams 23, there are also four drive beams 24. One end of each drive beam 24 is connected to a torsion beam 23, and the other end is connected to the inner edge of the fixed part 21. More specifically, each drive beam 24 is connected to the lower end of the inner surface of the fixed part 21. Each drive beam 24 is connected to only one of the four sides that make up the inner edge of the fixed part 21 in a plan view. Note that the number of torsion beams 23 and drive beams 24 may be other than four.

[0024] The drive beam 24 is elastically deformable. The thickness of the drive beam 24 is the same as the thickness of the torsion beam 23. The upper surface of the drive beam 24 is lower than the upper surfaces of the fixed part 21 and the movable part 22. The lower surface of the drive beam 24 is coplane with the lower surfaces of the fixed part 21 and the movable part 22. Also, the upper surface of the drive beam 24 is coplane with the upper surface of the torsion beam 23. The lower surface of the drive beam 24 is coplane with the lower surface of the torsion beam 23. Preferably, each drive beam 24 is arranged point-symmetrically with respect to the center O of the movable part 22 in a plan view.

[0025] The drive source 25 is positioned on the underside of each drive beam 24. From the viewpoint of increasing the driving force, it is preferable that the drive source 25 be positioned over substantially the entire underside of each drive beam 24. The drive source 25 has, for example, a piezoelectric film made up of a piezoelectric material that converts applied electrical energy into mechanical energy. The drive source 25 vibrates in response to the input of an AC signal.

[0026] The drive source 25 can be configured to include, for example, a lower electrode positioned on the lower surface of the drive beam 24, a piezoelectric film laminated on the lower electrode, and an upper electrode laminated on the piezoelectric film. The upper and lower electrodes can be made of, for example, gold (Au) or platinum (Pt). The upper and lower electrodes may have a structure in which multiple films are laminated.

[0027] A piezoelectric film can be made from, for example, a piezoelectric material such as PZT (lead zirconate titanate). The piezoelectric film may also be made from PNZT (lead niobate zirconate titanate), PLZT (lead lanthanum zirconate titanate), PLT (lead lanthanum titanate), PMN (lead niobate magnesium oxide), PMNN (lead niobate manganese oxide), BaTiO3 (barium titanate), etc.

[0028] The drive source 25 is not limited to a three-layer structure consisting of a lower electrode, a piezoelectric film, and an upper electrode. For example, the drive source 25 may have two or more piezoelectric films and an intermediate electrode. In this case, the piezoelectric film and intermediate electrode are alternately stacked on the lower electrode in the required number of layers, and finally, the piezoelectric film and upper electrode are sequentially stacked on the uppermost intermediate electrode. The intermediate electrode can be made of the same material as the upper electrode and the lower electrode.

[0029] When the drive source 25 has a piezoelectric film and an intermediate electrode, the intermediate electrode is connected to ground, and a drive signal is supplied to the lower electrode and the upper electrode. When a drive signal is supplied to the lower electrode and the upper electrode, the drive source 25 is displaced according to the voltage of the drive signal. Alternatively, the drive signal can be supplied to the intermediate electrode, and the lower electrode and the upper electrode can be connected to ground, and the drive source can be driven in the same way. By using n layers of piezoelectric film, the drive voltage of the drive source 25 can be reduced to 1 / n of that when there is one layer of piezoelectric film.

[0030] The MEMS device 20 can be fabricated by a semiconductor process using, for example, an SOI (Silicon On Insulator) substrate. However, the MEMS device 20 is not limited to this and may be composed of a Si (silicon) substrate, sapphire substrate, alumina substrate, spinel substrate, quartz substrate, crystal substrate, glass substrate, or ceramic substrate, etc. Among these, SOI substrates and Si substrates are preferred from the viewpoint of facilitating microfabrication.

[0031] An SOI substrate is a substrate in which a buried oxide (BOX) layer made of silicon oxide is provided on a support layer made of single-crystal silicon (Si), and an active layer made of single-crystal silicon is provided on top of the buried oxide layer. When a MEMS device 20 is fabricated from an SOI substrate, the fixed part 21 and the movable part 22 can be formed from, for example, the support layer, the buried layer, and the active layer. The twisted beam 23 and the drive beam 24 can be formed from, for example, the active layer. Because the active layer is thin, the twisted beam 23 and the drive beam 24 formed from the active layer are elastic.

[0032] As shown in Figure 3, in plan view, each drive beam 24 has a region in which the width in the direction parallel to the first side 24a, which is connected to the inner edge of the fixed part 21, gradually widens toward the first side 24a. In the example in Figure 3, in plan view, each drive beam 24 has its widest width in the direction parallel to the first side 24a at the position of the first side 24a.

[0033] Furthermore, in the example shown in Figure 3, in a plan view, each drive beam 24 has its narrowest width in the direction parallel to the first side 24a at the position of the second side 24b where it is connected to the torsion beam 23. Note that in the example shown in Figure 3, the first side 24a and the second side 24b are parallel.

[0034] Furthermore, as shown in Figure 3, in plan view, each drive beam 24 may include a trapezoidal first region 241 and a trapezoidal second region 242 having a smaller area than the first region 241. The first region 241 is located on the side closer to the first side 24a, and the second region 242 is located on the side further from the first side 24a than the first region 241. Also, in each of the trapezoids constituting the first region 241 and the second region 242, when the side closer to the first side 24a is considered the lower base and the side further from the first side 24a is considered the upper base, the length of the lower base of the trapezoid constituting the second region 242 is equal to or less than the length of the upper base of the trapezoid constituting the first region 241. In plan view, the first side 24a, the upper base of the trapezoid constituting the first region 241, and the upper base of the trapezoid constituting the second region 242 may be parallel.

[0035] In the example shown in Figure 3, in plan view, one leg of the trapezoid constituting the first region 241 and one leg of the trapezoid constituting the second region 242 are perpendicular to the first side 24a. Also, in plan view, the other leg of the trapezoid constituting the first region 241 and the other leg of the trapezoid constituting the second region 242 have different directions of inclination with respect to the first side 24a.

[0036] In other words, the other leg of the trapezoid constituting the first region 241 is inclined such that the first side 24a moves closer to the first side 24a as it moves away from the corner of the fixing part 21. Similarly, the other leg of the trapezoid constituting the second region 242 is inclined such that the first side 24a moves away from the first side 24a as it moves away from the corner of the fixing part 21.

[0037] In the example shown in Figure 3, in a plan view, the upper base of the trapezoid constituting the second region 242 is connected to the twist beam 23, but one leg or the other leg of the trapezoid constituting the second region 242 may also be connected to the twist beam 23.

[0038] Furthermore, in plan view, there may be a third region 243, such as a rectangle, between the first side 24a and the first region 241, and a fourth region 244, such as a trapezoid, between the first region 241 and the second region 242. Note that even without the third region 243, the lower base of the trapezoid constituting the first region 241 may coincide with the first side 24a. Also, even without the fourth region 244, the upper base of the trapezoid constituting the first region 241 may coincide with the lower base of the trapezoid constituting the second region 242.

[0039] Thus, in the MEMS device 20, in a plan view, each drive beam 24 has a region in which the width in the direction parallel to the first side 24a connected to the inner edge of the fixed part 21 gradually widens toward the first side 24a. With this structure, the portion of the drive beam 24 that connects to the inner edge of the fixed part 21 can be made wider, so that the movable part 22 can be moved with high torque and large displacement. As a result, when the MEMS device 20 is used in an electroacoustic converter, high sound pressure can be obtained. Specifically, for example, as described above, by making each drive beam 24 a shape that includes a trapezoidal first region 241 and a second region 242, the movable part 22 can be moved with high torque and large displacement.

[0040] Furthermore, in the MEMS device 20, each drive beam 24 has the same shape and is arranged point-symmetrically with respect to the center of the movable part 22 in a plan view. This makes it less likely for the movable part 22 to tilt when it is moved, thus reducing the risk of unwanted resonance.

[0041] (Stress reduction in MEMS device 20) Figure 6 is a diagram (part 1) illustrating the reduction of stress in the MEMS device 20. The upper part of Figure 6 is a top-side perspective view of the MEMS device 20, and the lower part is an enlarged view of the area inside the dashed line E1 in the upper part.

[0042] In the example shown in Figure 6, the movable part 22, in plan view, comprises extensions 22a, 22b, 22c, and 22d radiating from the center, and has a point-symmetric cross shape with respect to the center of the movable part 22. As shown in Figure 6, it is preferable that each torsion beam 23 is connected to both adjacent sides included in different extensions that constitute the movable part 22. In the example shown in Figure 6, in plan view, each torsion beam 23 is connected to the entirety of one adjacent side and a portion of the other. Also, in plan view, the corner of the portion E2 of each torsion beam 23 that is connected to the other adjacent side is rounded.

[0043] In this way, each twisted beam 23 is connected to both adjacent sides, resulting in a structure where the L-shaped tip of each twisted beam 23 is offset by L1 relative to one of the adjacent sides of the movable part 22. If the length of the side of the movable part 22 is 400 μm, then, for example, L1 can be approximately 50 to 300 μm.

[0044] Figure 7 shows the effect of the structure shown in Figure 6. In Figure 7, "no offset" represents the case where each torsional beam 23 is connected to only one of the adjacent sides of the movable part 22, and L1 shown in Figure 6 is zero. "with offset" represents the case of the structure shown in Figure 6. Also in Figure 7, the "Results" column is a contour plot showing the simulation results of the stress generated when the movable part 22 is moved. The arrows in the "Results" column indicate the location of the maximum stress and the value of the maximum stress. However, the figure shown in "Results" is inverted vertically compared to the figure shown in "Structure". That is, the figure shown in "Results" shows the stress near the boundary between the torsional beam 23 and the movable part 22.

[0045] As shown in Figure 7, when the movable part 22 is moved, a large stress is generated near the boundary between the torsional beam 23 and the movable part 22. However, by providing an offset at the connection point between each torsional beam 23 and the movable part 22, the starting point when the torsional beam 23 bends is shifted from the side surface of the movable part 22, which is the boundary between the torsional beam 23 and the movable part 22, thereby reducing the maximum stress. As a result, the risk of the torsional beam 23 breaking can be reduced.

[0046] Figure 8 is a diagram (part 2) illustrating the reduction of stress in the MEMS device 20. The upper part of Figure 8 is a top-side perspective view of the MEMS device 20, and the lower part is an enlarged view of the area inside the dashed line E3 in the upper part.

[0047] As shown in Figure 8, the MEMS device 20 has protrusions 26 that project from each side of the inner surface 21a of the fixed portion 21 toward the movable portion 22 in a plan view. The protrusions 26 are the same thickness as the fixed portion 21. In a plan view, the protrusions 26 are, for example, approximately right triangles.

[0048] Furthermore, each drive beam 24 is connected to the inner surface 21a of the fixed portion 21 and to the side surface 26a of the protrusion 26 which is continuous with the inner surface 21a. In a plan view, the corners of the portion E4 connected to the side surface 26a of the protrusion 26 in each drive beam 24 are rounded.

[0049] In this way, each drive beam 24 is connected to the inner surface 21a of the fixed portion 21 and the side surface 26a of the protrusion 26 which is continuous with the inner surface 21a. As a result, one end of the connection portion between each drive beam 24 and the fixed portion 21 is offset by L2 relative to the inner surface 21a of the fixed portion 21. If the length of the side surface 26a of the protrusion 26 is 200 μm, for example, L2 can be set to about 50 to 150 μm. By providing such an offset, the starting point when the drive beam 24 bends is shifted from the inner surface 21a of the fixed portion 21, which is the boundary between the drive beam 24 and the fixed portion 21. This reduces the maximum stress generated at one end of the connection portion between the drive beam 24 and the fixed portion 21. As a result, the risk of the drive beam 24 breaking can be reduced.

[0050] Figure 9 is the third diagram illustrating the reduction of stress in the MEMS device 20. The upper part of Figure 9 is a top-side perspective view of the MEMS device 20, and the lower part is an enlarged view of the area inside the dashed line E5 in the upper part.

[0051] As shown in Figure 9, the MEMS device 20 has recesses 27 that, in plan view, extend from each side of the inner surface 21a of the fixed portion 21 toward the outer surface. Each drive beam 24 is connected to the inner surface 21a of the fixed portion 21 and to the inner surface 27a of the recess 27 which is continuous with the inner surface 21a. In plan view, the corners of the portion E6 of each drive beam 24 that is connected to the inner surface 27a of the recess 27 are rounded.

[0052] In this way, each drive beam 24 is connected to the inner surface 21a of the fixed part 21 and the inner surface 27a of the recess 27 which is continuous with the inner surface 21a. As a result, the other end of the connection portion between each drive beam 24 and the fixed part 21 is offset by L3 relative to the inner surface 21a of the fixed part 21. If the length of the inner surface 27a of the recess 27 is 400 μm, for example, L3 can be set to about 50 to 300 μm. By providing such an offset, the starting point when the drive beam 24 bends is shifted from the inner surface 21a of the fixed part 21, which is the boundary between the drive beam 24 and the fixed part 21. This reduces the maximum stress generated on the other end of the connection portion between the drive beam 24 and the fixed part 21. As a result, the risk of the drive beam 24 breaking can be reduced.

[0053] Figure 10 is the fourth diagram illustrating the reduction of stress in the MEMS device 20. The upper part of Figure 10 is a perspective view of the bottom surface of the MEMS device 20, and the lower part is an enlarged view of the area inside the dashed line E7 in the upper part.

[0054] As shown in Figure 10, in the MEMS device 20, the corner E8 of the drive source 25 is rounded in a plan view. This reduces the risk of damage to the drive source 25 due to electric field concentration.

[0055] (Size of the movable part 22 in the MEMS device 20) Figure 11 shows the simulation results of the resonant frequency in the MEMS device 20. In Figure 11, "large movable part" refers to the case where the shape of the movable part 22 is relatively large, and "small movable part" refers to the case where the shape of the movable part 22 is relatively small. As shown in Figure 11, the resonant frequency can be adjusted by changing the size of the movable part 22. Specifically, the resonant frequency can be increased by miniaturizing the movable part 22. Considering the Harman curve, the resonant frequency of the movable part 22 is preferably between 1 kHz and 3 kHz, and more preferably around 2 kHz. The Harman curve is a frequency characteristic of sound pressure level and is used as an indicator when adjusting the characteristics of headphones, etc.

[0056] (Electroacoustic converter) Figure 12 is a top perspective view illustrating an electroacoustic converter according to the first embodiment. Figure 13 is a bottom perspective view illustrating an electroacoustic converter according to the first embodiment. Figure 14 is a cross-sectional view illustrating an electroacoustic converter according to the first embodiment, showing a cross-section along line BB in Figure 12. Figure 15 is a partial bottom view illustrating an electroacoustic converter according to the first embodiment, showing the backplate 10, frame 30, and part of the substrate 40, etc. Figure 16 is a bottom perspective view from Figure 13 with the backplate and mesh removed. Figure 17 is an exploded top perspective view illustrating an electroacoustic converter according to the first embodiment. Figure 18 is an exploded bottom perspective view illustrating an electroacoustic converter according to the first embodiment.

[0057] Referring to Figures 12 to 18, the electroacoustic converter 1 includes a backplate 10, a MEMS device 20, a frame 30, a substrate 40, a membrane 50, a diaphragm 60, a cover member 70, and a mesh 90. The electroacoustic converter 1 is an earphone or a stationary speaker.

[0058] The backplate 10 is a base component of the electroacoustic converter 1. The backplate 10 is preferably made of metal. Stainless steel (SUS) or aluminum can be used as the metal constituting the backplate 10. An insulating film may be coated on the surface of the backplate 10.

[0059] The backplate 10 has a frame-shaped upper surface 10a and a lower surface 10b. The backplate 10 also has a cavity portion 10x that opens towards the frame 30. The cavity portion 10x is a bottomed recess that is recessed from the upper surface 10a to the lower surface 10b of the backplate 10. When a drive voltage is applied to the MEMS device 20, the movable part 22 is displaced toward the backplate 10. At this time, if the backplate 10 does not have a cavity portion 10x and the upper surface of the backplate 10 is flat, there is a risk that the movable part 22 will come into contact with the backplate 10. By providing the cavity portion 10x on the backplate 10, this concern is eliminated.

[0060] The depth from the top surface 10a of the backplate 10 to the bottom surface of the cavity portion 10x is determined considering the maximum displacement of the movable part 22, but can be, for example, about 0.1 mm to 0.3 mm. If the backplate 10 is made of metal, the strength can be maintained even if the bottom surface of the cavity portion 10x is made thinner. Therefore, it is possible to make the entire backplate 10 thinner. The thickness of the thickest part of the backplate 10 can be, for example, about 0.2 mm to 0.4 mm. The thickness of the bottom surface of the cavity portion 10x can be, for example, about 0.1 mm.

[0061] The cavity portion 10x can be formed, for example, by creating a recess in the center of a single plate-shaped metal sheet through processing. The processing method may be either physical processing such as counterboring or chemical processing such as etching. The backplate 10 may also be formed by joining a frame-shaped metal sheet to the outer periphery of a plate-shaped metal sheet.

[0062] Although a structure in which through holes are provided in the backplate 10 instead of the cavity portion 10x is also conceivable, the rigidity of the entire electroacoustic converter 1 cannot be ensured, so the structure in which the cavity portion 10x is provided in the backplate 10 is more advantageous.

[0063] Furthermore, by providing a cavity 10x in the backplate 10, a back volume can be formed for the electroacoustic converter 1. This reduces the sharpness at the resonant frequency.

[0064] Furthermore, it is preferable that the back plate 10 is provided with a through hole 10y. The through hole 10y can be provided, for example, in the center of the cavity portion 10x in a plan view. The through hole 10y serves as a passage for air to enter and exit the inside of the back plate 10. In other words, by providing a through hole 10y, air can enter and exit through the through hole 10y, thereby reducing air resistance when the movable part 22 of the MEMS device 20 moves. As a result, the movable part 22 becomes easier to move, and the amount of displacement of the movable part 22 can be increased.

[0065] Furthermore, the back plate 10 is provided with a through hole 10z. The through hole 10z can be provided, for example, on the outside of the cavity portion 10x in a plan view, and at a distance from the cavity portion 10x. If the outer edge of the cavity portion 10x is rectangular in a plan view, the through hole 10z can be provided, for example, on the outside near the midpoint of one side of the rectangle that constitutes the outer edge of the cavity portion 10x.

[0066] In the backplate 10, a portion of the area surrounding the through-hole 10z in a plan view protrudes on the opposite side from the cavity portion 10x. The through-hole 10z is, for example, rectangular in a plan view. When a virtual line is drawn to divide the through-hole 10z in the longitudinal direction in a plan view, for example, the virtual line passes through the center of the cavity portion 10x.

[0067] The MEMS device 20 is positioned on the backplate 10 with the drive source 25 facing the backplate 10. In the MEMS device 20, for example, the lower surface of the fixed portion 21 can be joined to the upper surface 10a of the backplate 10 via an adhesive layer. The adhesive layer can be formed from, for example, a thermosetting adhesive. Examples of thermosetting adhesives include epoxy adhesives. The adhesive layer may also be formed from double-sided tape or an ultraviolet-curing adhesive. The movable portion 22, torsion beam 23, drive beam 24, and drive source 25 of the MEMS device 20 are positioned on the cavity portion 10x, separated from the backplate 10.

[0068] The frame 30 is positioned on the backplate 10 and outside the MEMS device 20. The frame 30 can be formed from resin. Examples of resins include polycarbonate (PC), acrylonitrile butadiene styrene (ABS), and liquid crystal polymer (LCP). The frame 30 can be molded, for example, by heating and pressurizing the resin material using a mold.

[0069] The frame 30 has a frame-shaped upper surface 30a, a lower surface 30b, and a protruding surface 30c located higher than the upper surface 30a. The upper surface 30a is, for example, substantially rectangular in shape when viewed from above. The upper surface 30a, the lower surface 30b, and the protruding surface 30c are, for example, parallel. The protruding surface 30c is, for example, composed of arc-shaped edges and straight edges when viewed from above.

[0070] The MEMS device 20 is positioned inside the frame formed by the upper surface 30a in a plan view. The frame 30 does not come into contact with the MEMS device 20. The distance from the upper surface 30a to the lower surface 30b of the frame 30 can be, for example, about 0.1 mm to 0.5 mm. The distance from the upper surface 30a to the protruding surface 30c of the frame 30 can be, for example, about 0.1 mm to 0.2 mm.

[0071] The frame 30 has a cavity portion 30x that opens towards the back plate 10. The cavity portion 30x is a bottomed recess that is recessed from the lower surface 30b of the frame 30 towards the projection surface 30c. The cavity portion 30x can be positioned, for example, so as to overlap with the projection surface 30c in a plan view. The cavity portion 30x is, for example, elongated in a plan view, with a substantially rectangular area in the center of the longitudinal direction where the width in the short direction is substantially constant, and substantially trapezoidal areas on both sides of the substantially rectangular area where the width in the short direction narrows as it approaches both ends in the longitudinal direction. The depth from the lower surface 30b of the frame 30 to the bottom surface of the cavity portion 30x can be, for example, about 0.2 mm to 0.3 mm.

[0072] The substrate 40 is positioned to the side of the MEMS device 20 and is electrically connected to the MEMS device 20. The substrate 40 is positioned so as not to overlap with the MEMS device 20 in a plan view. Specifically, the substrate 40 is fixed within the cavity portion 30x of the frame 30. It is preferable that the substrate 40 does not protrude from the lower surface 30b of the frame 30. The shape of the substrate 40 can be substantially similar to the cavity portion 30x in a plan view. That is, the substrate 40 can be, for example, elongated in a plan view, with a substantially rectangular region in the center of the longitudinal direction having a substantially constant width in the short direction, and substantially trapezoidal regions on both sides of the substantially rectangular region, where the width in the short direction narrows as it approaches both ends in the longitudinal direction. Note that the substrate 40 may also be rectangular in a plan view. When the substrate 40 is rectangular in a plan view, it is preferable from the viewpoint of material utilization for the substrate 40.

[0073] The substrate 40 can be an organic substrate such as a glass epoxy substrate. A substrate other than an organic substrate may also be used for the substrate 40. The substrate 40 has a wiring layer formed from, for example, gold or copper. The wiring layer may be provided on the upper surface 10a and / or the lower surface 10b of the substrate 40, or it may be provided inside the substrate 40. That is, the substrate 40 may be a multilayer wiring substrate. The wiring layer may include pads, through-holes, dummy wiring, etc.

[0074] On the upper surface 40a of the substrate 40, there is a pair of internal connection pads 41a and 41b, which serve as the signal path for supplying signals to all the drive sources 25. Also on the upper surface 40a of the substrate 40, there is a pair of external connection pads 42a and 42b for supplying signals to the electroacoustic converter 1 from outside the electroacoustic converter 1. The substrate 40 is fixed in the cavity 30x with the internal connection pads 41a and 41b and the external connection pads 42a and 42b facing the backplate 10.

[0075] The internal connection pads 41a and 41b can be positioned, for example, in the center of the upper surface 40a of the substrate 40. The external connection pads 42a and 42b can be positioned, for example, on the upper surface 40a of the substrate 40, facing each other in a plan view, with the internal connection pads 41a and 41b in between. The internal connection pad 41a and the external connection pad 42a are electrically connected. Similarly, the internal connection pad 41b and the external connection pad 42b are electrically connected.

[0076] Furthermore, the upper surface 40a of the circuit board 40 is marked with a positive terminal mark 43a and a negative terminal mark 43b to indicate the polarity of the external connection pads 42a and 42b. The positive terminal mark 43a indicates that the external connection pad 42a is a '+' terminal, and the negative terminal mark 43b indicates that the external connection pad 42b is a '-' terminal.

[0077] The positive electrode mark 43a and the negative electrode mark 43b can be formed from the same metal material as, for example, the external connection pads 42a and 42b. The thickness of the positive electrode mark 43a and the negative electrode mark 43b can be the same as, for example, the thickness of the external connection pads 42a and 42b. The positive electrode mark 43a and the negative electrode mark 43b may be electrically unconnected (floating).

[0078] A pair of conductive pads 28a and 28b are arranged on the backplate 10 side of the MEMS device 20, and the conductive pads 28a and 28b are electrically connected to the internal connection pads 41a and 41b of the substrate 40 via metal wires 101a and 101b. In detail, the internal connection pad 41a of the substrate 40 is electrically connected via metal wire 101a to the conductive pad 28a located on the lower surface of the fixing portion 21 of the MEMS device 20. The internal connection pad 41b of the substrate 40 is electrically connected via metal wire 101b to the conductive pad 28b located on the lower surface of the fixing portion 21 of the MEMS device 20. For example, gold wire or copper wire can be used as the metal wires 101a and 101b.

[0079] Viewed from the backplate 10 side, the internal connection pads 41a and 41b, the conductive pads 28a and 28b, and the metal wires 101a and 101b are located within the through-hole 10z. This prevents the internal connection pads 41a and 41b, the conductive pads 28a and 28b, and the metal wires 101a and 101b from making electrical contact with the backplate 10. Viewed from the backplate 10 side, the external connection pads 42a and 42b face each other, for example, across the through-hole 10z, and are exposed from the backplate 10. This facilitates connection between the external connection pads 42a and 42b and the outside.

[0080] The through-hole 10z is provided with a resin portion 110 that covers the internal connection pads 41a and 41b, the conductive pads 28a and 28b, and the metal wires 101a and 101b. By providing the resin portion 110, the metal wires 101a and 101b can be protected. Furthermore, by providing the resin portion 110, sound leakage from the area surrounded by the backplate 10 and the frame 30 through the through-hole 10z can be suppressed. The resin portion 110 can be made of, for example, an ultraviolet-curable resin such as an epoxy resin.

[0081] The membrane 50 is a flexible film-like member. The membrane 50 is placed on the frame 30 and on the MEMS device 20, and a portion of it is bonded to the MEMS device 20. The membrane 50 is, for example, rectangular in plan view. However, it is not limited to this. The membrane 50 may have other shapes in plan view, such as circular, elliptical, triangular, or polygons with pentagons or more.

[0082] The membrane 50 has a frame portion 51, a central portion 52 located inside the inner edge of the frame portion 51, and a connecting portion 53 that connects the inner edge of the frame portion 51 and the outer edge of the central portion 52. In the membrane 50, the upper surface of the frame portion 51 and the upper surface of the central portion 52 are located on the same plane, for example, and the lower surface of the frame portion 51 and the lower surface of the central portion 52 are located on the same plane. The connecting portion 53 protrudes in the direction of the lid member 70 from the upper surfaces of the frame portion 51 and the central portion 52, and in a cross-sectional view cut perpendicular to the upper surface of the central portion 52, the upper and lower surfaces of the connecting portion 53 are curved in the same direction.

[0083] The upper and lower surfaces of the frame portion 51 may not be on the same plane as the upper and lower surfaces of the central portion 52. For example, the height of the central portion 52 can be offset from that of the frame portion 51 by intentionally changing the molding conditions of the membrane 50. The distance between the upper surface of the frame portion 51 and the upper surface of the central portion 52 can be, for example, 20 to 100 μm. The distance between the lower surface of the frame portion 51 and the lower surface of the central portion 52 can be, for example, 20 to 100 μm.

[0084] The connecting portion 53 has a plurality of slits 54 arranged at predetermined intervals in a direction substantially perpendicular to the annular extension direction. With this structure, when the membrane 50 vibrates, the displacement of the central portion 52 due to the displacement of the movable portion 22 is less likely to be suppressed by the tension from the frame portion 51 fixed to the fixed portion 21.

[0085] The thickness of the membrane 50 can be, for example, about 5 to 50 μm. The membrane 50 can be made of, for example, an elastomer or a resin. Examples of elastomers include TPEE (polyester elastomer) and TPU (polyurethane elastomer). Examples of resins include PET (polyethylene terephthalate), PI (polyimide), and PEEK (polyether ether ketone). The membrane 50 may also be formed from a thin metal.

[0086] The frame portion 51, the central portion 52, and the connecting portion 53 are preferably an integrated structure from the viewpoint of simplifying the structure and ease of processing, but they may also be a structure in which different members are joined together. When the frame portion 51, the central portion 52, and the connecting portion 53 are an integrated structure, for example, the membrane 50 can be molded by heating and pressurizing a resin film using a mold.

[0087] In the membrane 50, the lower surface of the frame portion 51 can be joined to the upper surface 30a of the frame 30, for example, via an adhesive layer. The lower surface of the central portion 52 can also be joined to the upper surface of the movable portion 22 of the MEMS device 20, for example, via an adhesive layer. The adhesive layer can be formed from, for example, a thermosetting adhesive. Examples of thermosetting adhesives include epoxy adhesives. The adhesive layer may also be formed from double-sided tape or an ultraviolet-curing adhesive.

[0088] In a plan view, the central portion 52 of the membrane 50 is located inside the fixing portion 21 of the MEMS device 20 and overlaps with the cavity portion 10x of the backplate 10. A portion of the connecting portion 53 of the membrane 50 may also be located inside the fixing portion 21 of the MEMS device 20 and overlapping with the cavity portion 10x of the backplate 10.

[0089] The central portion 52 of the membrane 50 vibrates in response to the vibration of the movable portion 22 of the MEMS device 20. This generates sound waves with frequencies within the audible range, corresponding to the vibration of the movable portion 22 of the MEMS device 20.

[0090] In the examples shown in Figures 12 to 18, the diaphragm 60 is fixed to the upper surface of the central portion 52 of the membrane 50. While the membrane 50 itself requires a soft physical property, it is preferable to provide a hard region in order to increase sound pressure. By placing the diaphragm 60 on the central portion 52 of the membrane 50, the central portion 52 becomes a hard region, thereby increasing sound pressure.

[0091] For example, a resin such as PEN (polyethylene naphthalate) can be used as the material for the diaphragm 60. Alternatively, a metal such as aluminum or carbon may be used as the material for the diaphragm 60. The diaphragm 60 can be fixed to the upper surface of the central portion 52 of the membrane 50, for example, via an adhesive or double-sided tape. The thickness of the diaphragm 60 can be, for example, about 25 to 100 μm. The diaphragm 60 may also be placed on the lower surface of the central portion 52 of the membrane 50.

[0092] The cover member 70 is placed on the membrane 50 as needed. By providing the cover member 70, the membrane 50 is protected and the overall rigidity of the electroacoustic converter 1 can be increased. In addition, when attaching the electroacoustic converter 1 to other components, the cover member 70 can be used as a mounting reference.

[0093] The lid member 70 has a cavity portion 70x that opens towards the membrane 50. The cavity portion 70x is a bottomed recess that extends from the bottom to the top of the lid member 70. The outer peripheral region of the lid member 70 located outside the cavity portion 70x is a frame-shaped thick plate portion, and the cavity portion 70x is a thin plate portion located inside the thick plate portion.

[0094] The lower surface of the thick plate portion of the lid member 70 can be joined to the upper surface of the frame portion 51 of the membrane 50, for example, via an adhesive layer. The outer periphery of the lower surface of the thick plate portion of the lid member 70 may be joined to the upper surface 30a of the frame 30 via an adhesive layer. The adhesive layer can be formed from, for example, a thermosetting adhesive. Examples of thermosetting adhesives include epoxy adhesives. The adhesive layer may also be formed from double-sided tape or an ultraviolet-curing adhesive. The cavity portion 70x of the lid member 70 is provided with one or more openings 70y, through which sound waves are output.

[0095] The electroacoustic converter 1 can maintain rigidity despite its thin profile by having a lid member 70. While a resin such as PC (polycarbonate) may be used as the material for the lid member 70, it is preferable that the lid member 70 be made of metal. Stainless steel or aluminum can be used as the metal constituting the lid member 70.

[0096] When the lid member 70 is made of metal, the strength can be maintained even if the bottom portion of the cavity 70x is made thinner. Therefore, the overall thickness of the lid member 70 can be reduced. The thickness of the thickest part of the lid member 70 can be, for example, about 0.2 mm to 0.4 mm. The thickness of the bottom portion of the cavity 70x can be, for example, about 0.1 mm.

[0097] The cavity portion 70x can be formed, for example, by creating a recess in the center of a single plate-shaped metal sheet through processing. The processing method may be either physical processing such as counterboring or chemical processing such as etching. The lid member 70 may also be formed by joining a frame-shaped metal sheet to the outer periphery of the plate-shaped metal sheet.

[0098] The mesh 90 is positioned on the lower surface 10b side of the backplate 10 as needed. The mesh 90 has numerous small openings. A resin such as polyester can be used as the material for the mesh 90. The mesh 90 can be joined to the lower surface 10b of the backplate 10 via an adhesive layer 80 having an opening in the center, so as to close the through hole 10y of the backplate 10. The adhesive layer 80 is, for example, double-sided tape.

[0099] By providing mesh 90 and adjusting the aperture ratio of mesh 90, the Q value of the resonant frequency of the electroacoustic converter 1 can be lowered, thereby achieving a frequency response that is close to flat. In addition, by providing mesh 90, it is possible to maintain the exchange of air through the through-hole 10y while reducing the risk of foreign matter such as dust and water entering the inside of the electroacoustic converter 1.

[0100] Figure 19 is a top view illustrating a lid member of an electroacoustic converter according to the first embodiment. As described above, the lid member 70 can be used as a mounting reference when attaching the electroacoustic converter 1 to other members. Examples of other members include housings for earphones, etc. When using the lid member 70 as a mounting reference, it is preferable, for example, that the upper surface 70a of the lid member 70 be a flat surface, as shown in Figure 19. Furthermore, in order to increase the adhesive strength with other members, it is preferable that the area of ​​the adhesive region within the upper surface 70a be large.

[0101] For example, in each opening 70y, a portion of the edge defining the opening 70y is inscribed within the same virtual circle C1. For example, the area indicated by the dot pattern located outside the virtual circle C1 can be used as the bonding area. It is preferable that the diameter of the virtual circle C1 is larger than the diameter of the diaphragm 60.

[0102] From the viewpoint of increasing adhesive strength, the area of ​​the adhesive region is preferably 80% or more of the total area of ​​the upper surface 70a of the lid member 70, and more preferably 90% or more. For example, in a plan view, the total area of ​​the upper surface 70a of the lid member 70 is 69.3 mm². 2Assuming the diameter of the virtual circle C1 is 5 mm, the area of ​​the bonding region is 63.3 mm². 2 In this case, the area of ​​the adhesive region is approximately 91% of the total area of ​​the upper surface 70a of the lid member 70, thus providing sufficient adhesive strength.

[0103] Thus, in the electroacoustic converter 1, the substrate 40, which is electrically connected to the MEMS device 20, is positioned to the side of the MEMS device 20. This makes it possible to make the electroacoustic converter 1 thinner. In addition, it is advantageous for cost reduction as the substrate 40 can be made smaller.

[0104] Furthermore, in the electroacoustic converter 1, the MEMS device 20 is positioned on a back plate 10 located inside the frame 30. This makes it possible to make the electroacoustic converter 1 thinner.

[0105] Furthermore, in the electroacoustic converter 1, when a metal backplate 10 and a metal lid member 70 are used, the MEMS device 20 is sandwiched between these high-strength members from above and below. This makes it possible to increase the strength of the electroacoustic converter 1.

[0106] Furthermore, since the metal backplate 10 and the metal lid member 70 are high-strength materials, it is possible to make the materials themselves thinner compared to, for example, using a relatively low-strength material such as resin for the backplate 10 and / or lid member 70. This also makes it possible to make the entire electroacoustic converter 1 thinner.

[0107] It is preferable that the back plate 10 and the lid member 70 are made of the same metal of the same thickness. Since the back plate 10 and the lid member 70 can be manufactured by processing the same metal plate, manufacturing costs can be reduced. Furthermore, when the back plate 10 and the lid member 70 are made of metal, using stainless steel will result in higher strength than using aluminum, thus enabling even thinner designs.

[0108] Figures 20 and 21 illustrate a method for manufacturing an electroacoustic converter according to the first embodiment. For convenience, adhesive layers 200 to 250 are shown as a dot pattern.

[0109] First, a lid member 70 having a cavity portion 70x and an opening 70y is prepared, as shown in the upper left of Figure 20. Next, an adhesive layer 200 is arranged in a ring on the lower surface surrounding the outer circumference of the cavity portion 70x of the lid member 70, as shown in the upper center of Figure 20. The adhesive layer 200 may be arranged so as not to reach the outer edge of the lower surface of the lid member 70. The adhesive layer 200 is, for example, double-sided tape. The adhesive layer 200 may be formed from a thermosetting adhesive such as an epoxy adhesive. Next, a membrane 50 including a frame portion 51, a central portion 52, and a connecting portion 53 is prepared, and the upper surface of the frame portion 51 of the membrane 50 is joined to the lower surface of the thick plate portion of the lid member 70 via the adhesive layer 200, as shown in the upper right of Figure 20. Before joining with the lid member 70, the diaphragm 60 is pre-positioned on the central portion 52 of the membrane 50 by adhesive or the like.

[0110] Next, as shown in the leftmost part of the middle section of Figure 20, a frame 30 having a cavity portion 30x that opens to the lower surface 30b is prepared. Next, as shown in the center of the middle section of Figure 20, an adhesive layer 210 is placed on the bottom surface of the cavity portion 30x. The adhesive layer 210 can be formed from a thermosetting adhesive such as an epoxy adhesive. As shown in the rightmost part of the middle section of Figure 20, a substrate 40 with wiring formed on it is joined to the bottom surface of the cavity portion 30x of the frame 30 via the adhesive layer 210, with the wiring facing upwards. When a thermosetting adhesive is used as the adhesive layer 210, the substrate 40 is joined to the frame 30 by heating and curing the adhesive.

[0111] Next, as shown in the lower left of Figure 20, a back plate 10 having a cavity portion 10x and through holes 10y and 10z is prepared. Next, as shown in the lower center of Figure 20, an adhesive layer 220 is placed on the upper surface 10a of the back plate 10 so as to surround the cavity portion 10x. The adhesive layer 220 can be formed from a thermosetting adhesive such as an epoxy adhesive. Next, as shown in the lower right of Figure 20, a MEMS device 20 is prepared, and with the movable part 22 facing upwards, the MEMS device 20 is joined to the upper surface 10a of the back plate 10 via the adhesive layer 220. When a thermosetting adhesive is used as the adhesive layer 220, the MEMS device 20 is joined to the back plate 10 by heating and curing the adhesive.

[0112] Next, as shown in the upper left of Figure 21, an adhesive layer 230 is arranged in a ring shape on the upper surface 10a of the backplate 10, surrounding the MEMS device 20 and the through-hole 10z. The adhesive layer 230 can be formed from a thermosetting adhesive, such as an epoxy adhesive. As shown in the upper center of Figure 21, the frame 30 to which the substrate 40 shown in the middle right of Figure 20 is attached is joined to the upper surface 10a of the backplate 10 via the adhesive layer 230, with the substrate 40 facing the backplate 10. Next, as shown in the upper right of Figure 21, a mesh 90 is fixed to the lower surface 10b of the backplate 10 via the adhesive layer 80 so as to block the through-hole 10y of the backplate 10. If a thermosetting adhesive is used as the adhesive layer 230, the frame 30 is joined to the backplate 10 by heating and curing the adhesive. The mesh 90 may be fixed to the lower surface 10b of the backplate 10 in advance.

[0113] Next, as shown in the leftmost part of the middle section of Figure 21, the internal connection pad 41a of the substrate 40 exposed in the through-hole 10z is electrically connected to the conductive pad 28a of the MEMS device 20 exposed in the through-hole 10z via the metal wire 101a. Similarly, the internal connection pad 41b of the substrate 40 exposed in the through-hole 10z is electrically connected to the conductive pad 28b of the MEMS device 20 exposed in the through-hole 10z via the metal wire 101b. The state after connection is shown in Figure 15. The metal wires 101a and 101b can be joined to the object by, for example, a wire bonding method using a wire bonder. Since a wire bonder is a device commonly used in semiconductor devices, objects can be joined to each other without special capital investment.

[0114] Next, as shown in the center of the middle section of Figure 21, a resin portion 110 is provided within the through-hole 10z to cover the internal connection pads 41a and 41b, the conductive pads 28a and 28b, and the metal wires 101a and 101b. The resin portion 110 can be provided, for example, using a dispenser. It is preferable to use an ultraviolet-curable resin such as an epoxy resin as the material for the resin portion 110.

[0115] If a thermosetting resin is used as the material for the resin part 110, thermal shrinkage during curing may put stress on the joints between the metal wires 101a and 101b and the internal connection pads 41a and 41b and the conductive pads 28a and 28b. By using an ultraviolet-curable resin as the material for the resin part 110, the stress on the above-mentioned joints due to thermal shrinkage is reduced, thereby improving the reliability of the joints. In addition, since ultraviolet-curable resins have a shorter curing time compared to thermosetting resins, it is possible to shorten the cycle time by reducing the number of steps.

[0116] Next, as shown on the left end of the middle section of Figure 21, the structure shown in the center of the middle section of Figure 21 is inverted vertically. Next, as shown on the left side of the lower section of Figure 21, an adhesive layer 240 is arranged in a ring on the upper surface 30a of the frame 30 so as to surround the MEMS device 20. An adhesive layer 250 is also placed on the upper surface of the movable part 22 of the MEMS device 20. The adhesive layers 240 and 250 can be formed from a thermosetting adhesive such as an epoxy adhesive. Next, as shown on the right side of the lower section of Figure 21, the assembly of the membrane 50 and the lid member 70 shown on the right end of the upper section of Figure 20 is joined to the upper surface 30a of the frame 30 via the adhesive layer 240. The central part 52 of the membrane 50 is also joined to the upper surface of the movable part 22 of the MEMS device 20 via the adhesive layer 250. When thermosetting adhesives are used as adhesive layers 240 and 250, the lid member 70 is bonded to the frame 30 and the membrane 50 to the MEMS device 20 by heating and curing the adhesive. This completes the electroacoustic converter 1.

[0117] Figure 22 is a top view illustrating the bonding of the frame and the lid member. The lower part of Figure 22 is an enlarged view of the dashed line area in the upper part. As shown in the lower part of Figure 21, the lid member 70 is joined to the upper surface 30a of the frame 30 via the adhesive layer 240. After the adhesive layer 240 has hardened, the application of the adhesive constituting the adhesive layer 240 may be checked from the top by visual inspection.

[0118] In the electroacoustic converter 1, it is preferable that the outer dimensions of the frame 30 be larger than the outer dimensions of the lid member 70. This makes it possible to provide an annular region on the upper surface 30a of the frame 30 that does not overlap with the lid member 70 in a plan view. That is, when viewed from the lid member 70 side, the outer periphery of the upper surface 30a of the frame 30 is exposed from the lid member 70. The adhesive layer 240 is placed between the lid member 70 and the frame 30, and it is preferable that a part of the adhesive layer 240 protrudes in an annular shape from between the lid member 70 and the frame 30 to the outer periphery of the upper surface 30a of the frame 30 that is exposed from the lid member 70. By adjusting the amount of adhesive applied so that the adhesive constituting the adhesive layer 240 protrudes into this annular region, visual inspection can be made easier. As a result, an appropriate amount of adhesive can be obtained, and variations in the adhesive strength between the frame 30 and the lid member 70 can be reduced.

[0119] In addition, although the lower part of Figure 22 shows a magnified view of only a portion of the outer circumference of the frame 30 and the lid member 70, it is preferable to adjust the amount of adhesive applied to the adhesive constituting the adhesive layer 240 so that it spills over the entire annular region described above.

[0120] Figure 23 is a bottom view illustrating the bonding between the frame and the backplate. The lower part of Figure 23 is an enlarged view of the dashed line area in the upper part. As shown in the upper part of Figure 21, the backplate 10 is bonded to the lower surface 30b of the frame 30 via the adhesive layer 230. After the adhesive layer 230 has cured, the application of the adhesive constituting the adhesive layer 230 may be checked from the top by visual inspection.

[0121] In the electroacoustic converter 1, it is preferable to make the outer dimensions of the frame 30 larger than the outer dimensions of the back plate 10. This makes it possible to provide an annular region on the lower surface 30b of the frame 30 that does not overlap with the back plate 10 when viewed from below. That is, when viewed from the back plate 10 side, the outer periphery of the lower surface 30b of the frame 30 is exposed from the back plate 10. The adhesive layer 230 is placed between the back plate 10 and the frame 30, and it is preferable that a part of the adhesive layer 230 protrudes in an annular shape from between the back plate 10 and the frame 30 to the outer periphery of the lower surface 30b of the frame 30 that is exposed from the back plate 10. By adjusting the amount of adhesive applied so that the adhesive constituting the adhesive layer 230 protrudes into this annular region, visual inspection can be made easier. As a result, an appropriate amount of adhesive can be obtained, and variations in the adhesive strength between the frame 30 and the back plate 10 can be reduced.

[0122] Although the lower part of Figure 23 shows a magnified view of only a portion of the outer periphery of the backplate 10 and frame 30, it is preferable to adjust the amount of adhesive applied to the adhesive layer 230 so that it spills over the entire annular region described above.

[0123] Figure 24 is a partial cross-sectional view illustrating an electroacoustic converter according to the first embodiment, showing a portion of the longitudinal cross-section passing through the center of the membrane 50. In the electroacoustic converter 1, it is preferable that the outer dimensions of the frame 30 and the outer dimensions of the lid member 70 be larger than the outer dimensions of the membrane 50. In the example of Figure 24, the outer dimensions of the lid member 70 are larger than the outer dimensions of the membrane 50, and the outer dimensions of the frame 30 are even larger than the outer dimensions of the lid member 70.

[0124] Due to this dimensional relationship, a region R can be created where the outer periphery of the frame 30 and the outer periphery of the lid member 70 directly face each other without the membrane 50 in between. By placing the adhesive layer 240 in region R, the frame 30 and the lid member 70 can be directly joined by the adhesive layer 240, thereby improving the strength of the electroacoustic converter 1. Note that the adhesive layer 240 only needs to be placed in at least a part of region R. For example, the adhesive layer 200 may be placed in a part of region R. In this case, the same effect is achieved.

[0125] Furthermore, in Figure 24, the distance L4 between the lower end on the outer circumference of the cavity portion 70x constituting the lid member 70 and the upper end on the inner circumference of the frame portion 51 constituting the membrane 50 is preferably as short as possible across the entire outer circumference of the connecting portion 53 in a plan view. The distance L4 can be, for example, 0.1 mm or more and 0.2 mm or less. The distance L4 may also be zero. By making the distance L4 as short as possible, the risk of unwanted resonance occurring on the outer circumference of the connecting portion 53 can be reduced. This makes it possible to obtain the vibration that should be obtained in the central portion 52 of the membrane 50.

[0126] Although preferred embodiments have been described in detail above, the present invention is not limited to the embodiments described above, and various modifications and substitutions can be made to the embodiments described above without departing from the scope of the claims. Furthermore, the content described in one embodiment is applicable to other embodiments as well. [Explanation of symbols]

[0127] 1 Electroacoustic converter, 10 Backplate, 10a Top surface, 10b Bottom surface, 10x Cavity section, 10y, 10z Through holes, 20 MEMS device, 21 Fixing section, 21a Inner surface, 22 Movable section, 23 Torsion beam, 24 Drive beam, 24a First side, 24b Second side, 241 First region, 242 Second region, 243 Third region, 244 Fourth region, 25 Drive source, 26 Protrusion, 26a Side surface, 27 Recess, 27a Inner surface, 28a, 28b Conductive pads, 30 Frame, 30a Top surface, 30b Bottom surface, 30c Protruding surface, 30x Cavity section, 40 Substrate, 40a Top surface, 41a, 41b Internal connection pads, 42a, 42b External connection pad, 43a positive electrode mark, 43b negative electrode mark, 50 membrane, 51 frame, 52 central part, 53 connection part, 54 slit, 60 diaphragm, 70 lid member, 70a top surface, 70x cavity part, 70y opening, 80 adhesive layer, 90 mesh, 101a, 101b metal wire, 110 resin part, 200, 210, 230, 240, 250 adhesive layer

Claims

1. A metal backplate, A frame placed on the back plate, A MEMS device is positioned on the backplate located inside the frame, A membrane disposed on the frame and the MEMS device, An electroacoustic converter comprising a metal lid member disposed on the membrane.

2. The electroacoustic converter according to claim 1, wherein the back plate and the lid member are formed of the same metal.

3. The electroacoustic converter according to claim 2, wherein the metal is stainless steel or aluminum.

4. The electroacoustic converter according to any one of claims 1 to 3, wherein the back plate and the lid member have the same thickness.

5. The MEMS device comprises a frame-shaped fixed part, a movable part positioned inside the fixed part in a plan view, a torsion beam and a drive beam connecting the fixed part and the movable part at a position closer to the lower surface than the upper surface of each, and a drive source positioned on the lower surface of the drive beam. The back plate has a first cavity portion that opens towards the frame side, The electroacoustic converter according to any one of claims 1 to 3, wherein the movable part, the torsion beam, the drive beam, and the drive source are arranged on the first cavity part at a distance from the back plate.

6. The frame has a second cavity portion that opens towards the back plate side, The substrate is positioned to the side of the MEMS device and fixed within the second cavity, The electroacoustic converter according to any one of claims 1 to 3, wherein the substrate is electrically connected to the MEMS device.

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