MEMS loudspeaker sounding unit structure and preparation method thereof

Abstract

According to the MEMS loudspeaker sound production unit structure and the preparation method thereof provided by the invention, the electrostatic switch unit is connected to the piezoelectric sound production unit in a bonding manner, so that the piezoelectric sound production unit can output ultrasonic pulses with relatively high energy by utilizing relatively high conversion efficiency of the piezoelectric sound production unit; and then ultrasonic demodulation is carried out on the pulse signal through accurate on-off control of the electrostatic switch unit, and an effective part is intercepted for digital audio synthesis, so that effective modulation and control on the pulse signal are realized, and the problems of limited sound pressure level and low electro-acoustic conversion efficiency of a traditional single driving and signal processing mode are solved. And meanwhile, a new way is opened up for performance improvement and function expansion of the MEMS loudspeaker.

Description

Technical Field

[0001] The present invention relates to the field of MEMS digital sound-generating chips, and in particular to a MEMS loudspeaker sound-generating unit structure and a preparation method thereof. Background Art

[0002] MEMS (micro-electro-mechanical system) speakers are miniature speakers made using micro-manufacturing technology, which combines microelectronics technology with traditional speaker design. MEMS speakers are known for their small size, low power consumption and high integration, and are suitable for a variety of portable and high-performance audio devices. The principle is to form sound waves through the combination of pulses generated by the high-frequency vibration of the sound-emitting units arranged in an array.

[0003] The existing electrostatic digital MEMS loudspeaker has a limited sound pressure level and low electroacoustic conversion efficiency due to the positive and negative cancellation of pulse energy when a single sound-generating diaphragm vibrates. Summary of the invention

[0004] In view of the above-mentioned shortcomings of the prior art, an object of the present invention is to provide a MEMS speaker sound unit structure and a preparation method thereof, so as to solve the problems of limited sound pressure level and low electroacoustic conversion efficiency of electrostatic digital MEMS speakers in the prior art.

[0005] To achieve the above-mentioned purpose and other related purposes, the present invention provides a MEMS speaker sound unit structure, which includes, from bottom to top, a piezoelectric sound unit and an electrostatic switch unit bonded to the piezoelectric sound unit; wherein, The electrostatic switch unit includes, from bottom to top, a first substrate, a first insulating layer, a first lower electrode layer, a second insulating layer and an electrostatic diaphragm layer; and further includes: a first cavity penetrating the first substrate and the first insulating layer; a plurality of first through holes located above the first cavity and penetrating the first lower electrode layer and the second insulating layer; a second cavity located above all the first through holes and formed between the electrostatic diaphragm layer and the second insulating layer; the electrostatic diaphragm layer includes a diaphragm, a cantilever beam structure and a plurality of sound-permeable holes located between the diaphragm and the cantilever beam structure, the diaphragm is located above all the first through holes, and the diaphragm can vibrate to a surface covering all the first through holes; The piezoelectric sound unit includes, from bottom to top, a second substrate, a third insulating layer, a second lower electrode layer, a piezoelectric layer and an upper electrode layer; it also includes: a third cavity penetrating the second substrate; a groove located above the third cavity and penetrating the upper electrode layer, the piezoelectric layer and the second lower electrode layer; a fourth insulating layer formed on the surface of the upper electrode layer and on the bottom wall and side wall of the groove; and a second through hole located in the groove and penetrating the fourth insulating layer and the third insulating layer.

[0006] The present invention also provides a method for preparing a MEMS speaker sound unit structure, the method comprising: S1, providing an electrostatic switch unit and a piezoelectric sound unit; wherein, The electrostatic switch unit includes, from bottom to top, a first substrate, a first insulating layer, a first lower electrode layer, a second insulating layer and an electrostatic diaphragm layer; and further includes: a first cavity penetrating the first substrate and the first insulating layer; a plurality of first through holes located above the first cavity and penetrating the first lower electrode layer and the second insulating layer; a second cavity located above all the first through holes and formed between the electrostatic diaphragm layer and the second insulating layer; the electrostatic diaphragm layer includes a diaphragm, a cantilever beam structure and a plurality of sound-permeable holes located between the diaphragm and the cantilever beam structure, the diaphragm is located above all the first through holes, and the diaphragm can vibrate to a surface covering all the first through holes; The piezoelectric sound generating unit includes, from bottom to top, a second substrate, a third insulating layer, a second lower electrode layer, a piezoelectric layer, and an upper electrode layer; and further includes: a third cavity penetrating the second substrate; a groove located above the third cavity and penetrating the upper electrode layer, the piezoelectric layer, and the second lower electrode layer; a fourth insulating layer formed on the surface of the upper electrode layer and on the bottom wall and side wall of the groove; and a second through hole located in the groove and penetrating the fourth insulating layer and the third insulating layer; S2, bonding the first substrate of the electrostatic switch unit to the fourth insulating layer of the piezoelectric sound generating unit.

[0007] Optionally, the preparation method of the electrostatic switch unit includes: providing the first substrate; forming the first insulating layer, the first lower electrode layer and the second insulating layer in sequence on the first substrate; forming a plurality of first through holes penetrating the first lower electrode layer and the second insulating layer; forming a sacrificial layer on the second insulating layer, wherein the sacrificial layer at least fills the first through hole; Performing patterned etching on the sacrificial layer to form a groove penetrating the sacrificial layer, wherein the groove exposes the second insulating layer; forming the electrostatic diaphragm layer on the sacrificial layer, wherein the electrostatic diaphragm layer at least fills the groove; The electrostatic diaphragm layer is etched to form the cantilever beam structure, the diaphragm and the sound-transmitting hole; wherein the sound-transmitting hole penetrates the electrostatic diaphragm layer and is located between the diaphragm and the cantilever beam structure; the diaphragm is located above all the first through holes, and the diaphragm can vibrate to cover the surface of all the first through holes; Etching is performed from the lower surface of the first substrate to form the first cavity penetrating the first substrate and the first insulating layer, wherein the first cavity at least exposes all the first through holes; The sacrificial layer is removed.

[0008] Furthermore, the material of the first substrate is silicon; and the first insulating layer is formed by performing thermal oxidation treatment on the surface of the first substrate.

[0009] Furthermore, the method for forming the first lower electrode layer includes: bonding a lower electrode wafer to the upper surface of the first insulating layer, and grinding and thinning the upper surface of the lower electrode wafer to form the first lower electrode layer.

[0010] Furthermore, the second insulating layer is formed by a chemical vapor deposition process; the material of the second insulating layer is silicon nitride.

[0011] Furthermore, the method of forming the first through hole penetrating the first lower electrode layer and the second insulating layer includes: forming a photoresist layer on the second insulating layer and patterning the photoresist layer; Etching the first lower electrode layer and the second insulating layer based on the patterned photoresist layer to form the first through hole penetrating the first lower electrode layer and the second insulating layer; The patterned photoresist layer is removed.

[0012] Furthermore, before etching the sacrificial layer to form the groove penetrating the sacrificial layer, the method further includes a step of planarizing the surface of the sacrificial layer.

[0013] Furthermore, the material of the sacrificial layer is silicon dioxide; and the sacrificial layer is removed by releasing and etching gaseous hydrogen fluoride.

[0014] Optionally, the method for preparing the piezoelectric sound generating unit includes: providing the second substrate; forming the third insulating layer, the second lower electrode layer, the piezoelectric layer and the upper electrode layer in sequence on the second substrate; Etching to form the groove penetrating the upper electrode layer, the piezoelectric layer and the second lower electrode layer; forming the fourth insulating layer on the surface of the upper electrode layer and the surface of the groove; Etching the fourth insulating layer and the third insulating layer in the groove to form the second through hole penetrating the fourth insulating layer and the third insulating layer; Etching is performed from the lower surface of the second substrate to form the third cavity penetrating the second substrate; the third cavity at least exposes all the second through holes.

[0015] As described above, the MEMS speaker sound unit structure and the preparation method thereof of the present invention have the following beneficial effects: the MEMS speaker sound unit structure and the preparation method thereof of the present invention, by bonding the electrostatic switch unit to the piezoelectric sound unit, can utilize the higher conversion efficiency of the piezoelectric sound unit to output higher energy ultrasonic pulses, and then ultrasonically demodulate the pulse signal through the precise switch control of the electrostatic switch unit, and extract the effective part for digital audio synthesis, thereby realizing effective modulation and control of the pulse signal, breaking through the problems of limited sound pressure level and low electroacoustic conversion efficiency of traditional single drive and signal processing methods, and at the same time opening up a new way for performance improvement and function expansion of MEMS speakers. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram showing the cross-sectional structure of the MEMS speaker sound unit structure of the present invention when the electrostatic switch unit is turned on.

[0017] Figure 2 It is a schematic diagram showing the cross-sectional structure of the MEMS speaker sound unit structure of the present invention when the electrostatic switch unit is closed.

[0018] Figure 3 It is a schematic flow chart of a method for preparing a MEMS speaker sound unit structure of the present invention.

[0019] Figures 4 to 15 Shown are schematic cross-sectional structures presented at various steps of the method for preparing the MEMS speaker sound unit structure of the present invention.

[0020] Description of component numbers: 1 electrostatic switch unit, 10 first substrate, 11 first insulating layer, 12 first lower electrode layer, 13 second insulating layer, 14 sacrificial layer, 15 electrostatic diaphragm layer, 150 diaphragm, 16 first through hole, 17 groove, 18 cantilever beam structure, 19 sound-transmitting hole, 100 first cavity, 110 second cavity, 2 piezoelectric sound unit, 20 second substrate, 21 third insulating layer, 22 second lower electrode layer, 23 piezoelectric layer, 24 upper electrode layer, 25 fourth insulating layer, 26 groove, 27 second through hole, 28 third cavity, steps S1~S2. DETAILED DESCRIPTION

[0021] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0022] See also Figures 1 to 15 It should be noted that the illustrations provided in this embodiment are only used to illustrate the basic concept of the present invention in a schematic manner, and the illustrations only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0023] This embodiment provides a MEMS speaker sound unit structure, such as Figure 1 As shown, the sound unit structure includes, from bottom to top, a piezoelectric sound unit 2 and an electrostatic switch unit 1 bonded to the piezoelectric sound unit 2; wherein, The electrostatic switch unit 1 includes, from bottom to top, a first substrate 10, a first insulating layer 11, a first lower electrode layer 12, a second insulating layer 13 and an electrostatic diaphragm layer 15; and also includes: a first cavity 100 that penetrates the first substrate 10 and the first insulating layer 11; a plurality of first through holes 16 located above the first cavity 100 and penetrating the first lower electrode layer 12 and the second insulating layer 13; a second cavity 110 located above all the first through holes 16 and formed between the electrostatic diaphragm layer 15 and the second insulating layer 13; the electrostatic diaphragm layer 15 includes a diaphragm 150, a cantilever beam structure 18 and a plurality of sound-permeable holes 19 located between the diaphragm 150 and the cantilever beam structure 18, the diaphragm 150 is located above all the first through holes 16, and the diaphragm 150 can vibrate to cover the surface of all the first through holes 16; The piezoelectric sound unit 2 includes, from bottom to top, a second substrate 20, a third insulating layer 21, a second lower electrode layer 22, a piezoelectric layer 23 and an upper electrode layer 24; it also includes: a third cavity 28 that passes through the second substrate 20; a groove 26 located above the third cavity 28 and passing through the upper electrode layer 24, the piezoelectric layer 23 and the second lower electrode layer 22; a fourth insulating layer 25 formed on the surface of the upper electrode layer 24 and on the bottom wall and side wall of the groove; and a second through hole 27 located in the groove 26 and passing through the fourth insulating layer 25 and the third insulating layer 21.

[0024] The MEMS speaker sound unit structure of this embodiment, by bonding the electrostatic switch unit and the piezoelectric sound unit to each other, can utilize the high conversion efficiency of the piezoelectric sound unit to output ultrasonic pulses with higher energy, and then ultrasonically demodulate the pulse signal through the precise switch control of the electrostatic switch unit, and intercept the effective part for digital audio synthesis, thereby realizing effective modulation and control of the pulse signal, breaking through the problems of limited sound pressure level and low electroacoustic conversion efficiency of traditional single drive and signal processing methods, and at the same time opening up a new way to improve the performance and expand the functions of MEMS speakers.

[0025] like Figure 2 As shown, when a working voltage is applied to the first lower electrode layer 12 of the electrostatic switch unit 1 and the diaphragm 150, the diaphragm 150 will be adsorbed on the second insulating layer 13 under the action of electrostatic force and cover the surface of all the first through holes 16. At this time, the electrostatic switch unit 1 is in a closed state, and the high-frequency pulses of the piezoelectric sound unit 2 cannot radiate to the electrostatic switch unit 1.

[0026] like Figure 1 As shown, after removing the working voltage applied to the first lower electrode layer 12 of the electrostatic switch unit 1 and the diaphragm 150, the diaphragm 150 will return to the equilibrium position under the action of the cantilever beam structure 18. At this time, the electrostatic switch unit 1 is in the open state, and the high-frequency pulses of the piezoelectric sound unit 2 can be radiated outward through the first through hole 16 and the sound-permeable hole 19.

[0027] This embodiment also provides a method for preparing a MEMS speaker sound unit structure, which is used to prepare the above-mentioned MEMS speaker sound unit structure, but is not limited thereto. Other suitable preparation methods are also acceptable. As long as the method can obtain the MEMS speaker sound unit structure, it is included in the scope of this embodiment, such as Figure 3 As shown, the preparation method comprises: S1, providing an electrostatic switch unit and a piezoelectric sound unit; wherein, The electrostatic switch unit includes, from bottom to top, a first substrate, a first insulating layer, a first lower electrode layer, a second insulating layer and an electrostatic diaphragm layer; and further includes: a first cavity penetrating the first substrate and the first insulating layer; a plurality of first through holes located above the first cavity and penetrating the first lower electrode layer and the second insulating layer; a second cavity located above all the first through holes and formed between the electrostatic diaphragm layer and the second insulating layer; the electrostatic diaphragm layer includes a diaphragm, a cantilever beam structure and a plurality of sound-permeable holes located between the diaphragm and the cantilever beam structure, the diaphragm is located above all the first through holes, and the diaphragm can vibrate to a surface covering all the first through holes; The piezoelectric sound generating unit includes, from bottom to top, a second substrate, a third insulating layer, a second lower electrode layer, a piezoelectric layer and an upper electrode layer; and further includes: a third cavity penetrating the second substrate; a groove located above the third cavity and penetrating the upper electrode layer, the piezoelectric layer and the second lower electrode layer; a fourth insulating layer formed on the surface of the upper electrode layer and on the bottom wall and side wall of the groove; and a second through hole located in the groove and penetrating the fourth insulating layer and the third insulating layer; S2, bonding the first substrate of the electrostatic switch unit to the fourth insulating layer of the piezoelectric sound generating unit.

[0028] The preparation method of the MEMS speaker sound unit structure of this embodiment, by bonding the electrostatic switch unit to the piezoelectric sound unit, can make use of the high conversion efficiency of the piezoelectric sound unit to output ultrasonic pulses with higher energy, and then ultrasonically demodulate the pulse signal through the precise switch control of the electrostatic switch unit, and cut out the effective part for digital audio synthesis, thereby realizing effective modulation and control of the pulse signal, breaking through the problems of limited sound pressure level and low electroacoustic conversion efficiency of traditional single drive and signal processing methods, and at the same time opening up a new way to improve the performance and expand the functions of MEMS speakers.

[0029] The method for preparing the MEMS speaker sound unit structure of this embodiment is described in detail below with reference to the specific drawings.

[0030] like Fig. 9 and Fig.14 As shown, firstly, step S1 is performed to provide an electrostatic switch unit 1 and a piezoelectric sound generating unit 2; wherein, like Fig. 9 As shown, the electrostatic switch unit 1 includes, from bottom to top, a first substrate 10, a first insulating layer 11, a first lower electrode layer 12, a second insulating layer 13 and an electrostatic diaphragm layer 15; it also includes: a first cavity 100 that penetrates the first substrate 10 and the first insulating layer 11; a plurality of first through holes 16 located above the first cavity 100 and penetrating the first lower electrode layer 12 and the second insulating layer 13; a second cavity 110 located above all the first through holes 16 and formed between the electrostatic diaphragm layer 15 and the second insulating layer 13; the electrostatic diaphragm layer 15 includes a diaphragm 150, a cantilever beam structure 18 and a plurality of sound-permeable holes 19 located between the diaphragm 150 and the cantilever beam structure 18, the diaphragm 150 is located above all the first through holes 16, and the diaphragm 150 can vibrate to cover the surface of all the first through holes 16.

[0031] like Fig.14As shown, the piezoelectric sound unit 2 includes, from bottom to top, a second substrate 20, a third insulating layer 21, a second lower electrode layer 22, a piezoelectric layer 23 and an upper electrode layer 24; it also includes: a third cavity 28 that passes through the second substrate 20; a groove 26 that is located above the third cavity 28 and passes through the upper electrode layer 24, the piezoelectric layer 23 and the second lower electrode layer 22; a fourth insulating layer 25 formed on the surface of the upper electrode layer 24 and on the bottom wall and side wall of the groove; and a second through hole 27 that is located in the groove 26 and passes through the fourth insulating layer 25 and the third insulating layer 21.

[0032] As a specific example, Figures 4 to 9 As shown, the preparation method of the electrostatic switch unit 1 includes: S11, such as Figure 4 As shown, the first substrate 10 is provided.

[0033] S12, such as Figure 4 As shown, the first insulating layer 11 , the first lower electrode layer 12 and the second insulating layer 13 are sequentially formed on the first substrate 10 .

[0034] The material of the first substrate 10 may be, for example, silicon. As an example, the first insulating layer 11 may be formed by thermally oxidizing the surface of the first substrate 10, or by processes including but not limited to physical vapor deposition (PVD) or chemical vapor deposition (CVD). The material and formation process of the first insulating layer 11 are not overly limited herein.

[0035] Different formation methods can be selected according to the required thickness of the first lower electrode layer 12. As an example, when the required thickness of the first lower electrode layer 12 is relatively thick (e.g., greater than 6µm), the method for forming the first lower electrode layer 12 includes: bonding a lower electrode wafer to the upper surface of the first insulating layer 11, and grinding and thinning the upper surface of the lower electrode wafer to form the first lower electrode layer 12; when the required thickness of the first lower electrode layer 12 is relatively thin, the first lower electrode layer 12 can be formed by processes including but not limited to PVD or CVD. The material of the first lower electrode layer 12 includes doped polysilicon. The material and formation process of the first lower electrode layer 12 are not overly limited here.

[0036] As an example, the material of the second insulating layer 13 includes but is not limited to silicon nitride. The second insulating layer 13 may be formed by a CVD process. The material and the forming process of the second insulating layer 13 are not overly limited herein.

[0037] S13, such as Figure 5 As shown, a plurality of first through holes 16 penetrating the first lower electrode layer 12 and the second insulating layer 13 are formed.

[0038] As a preferred example, a method for forming the first through hole 16 penetrating the first lower electrode layer 12 and the second insulating layer 13 includes: First, a photoresist layer is formed on the second insulating layer 13 and patterned; wherein the photoresist layer can be formed, for example, by a spin coating process; then, the first lower electrode layer 12 and the second insulating layer 13 are etched based on the patterned photoresist layer to form the first through hole 16 penetrating the first lower electrode layer 12 and the second insulating layer 13; finally, the patterned photoresist layer is removed.

[0039] S14, such as Figure 6 As shown, a sacrificial layer 14 is formed on the second insulating layer 13 , and the sacrificial layer 14 at least fills the first through hole 16 .

[0040] S15, such as Figure 6 As shown, the sacrificial layer 14 is pattern-etched to form a groove 17 penetrating the sacrificial layer 14 , and the groove 17 exposes the second insulating layer 13 .

[0041] As a preferred example, before etching the sacrificial layer 14 to form the groove 17 penetrating the sacrificial layer 14 , the method further includes a step of planarizing the surface of the sacrificial layer 14 to improve the quality of subsequent film formation on the sacrificial layer 14 .

[0042] S16, such as Figure 7 As shown, the electrostatic diaphragm layer 15 is formed on the sacrificial layer 14 , and the electrostatic diaphragm layer 15 at least fills the groove 17 .

[0043] S17, such as Figure 7 The electrostatic diaphragm layer 15 is etched to form the cantilever beam structure 18, the diaphragm 150 and the sound-transmitting hole 19; wherein the sound-transmitting hole 19 penetrates the electrostatic diaphragm layer 15 and is located between the diaphragm 150 and the cantilever beam structure 18; the diaphragm 150 is located above all the first through holes 16, and the diaphragm 150 can vibrate to cover the surface of all the first through holes 16.

[0044] S18, such as Figure 8 As shown, etching is performed from the lower surface of the first substrate 10 to form the first cavity 10 penetrating the first substrate 10 and the first insulating layer 11 , and the first cavity 100 at least exposes all of the first through holes 16 .

[0045] S19, such as Fig. 9 As shown, the sacrificial layer 14 is removed; the material of the sacrificial layer 14 may be silicon dioxide, for example.

[0046] As an example, the sacrificial layer 14 may be removed by gaseous hydrogen fluoride release etching.

[0047] As a specific example, Figures 10 to 14 As shown, the preparation method of the piezoelectric sound unit includes: S21, such as Fig.10 As shown, the second substrate 20 is provided.

[0048] S22, such as Fig.10 As shown, the third insulating layer 21 , the second lower electrode layer 22 , the piezoelectric layer 23 and the upper electrode layer 24 are sequentially formed on the second substrate 20 .

[0049] S23, such as Fig.11 As shown, the groove 26 penetrating the upper electrode layer 24 , the piezoelectric layer 23 and the second lower electrode layer 22 is formed by etching.

[0050] S24, such as Fig.12 As shown, the fourth insulating layer 25 is formed on the surface of the upper electrode layer 24 and the surface of the groove 26 .

[0051] S25, such as Fig.13 As shown, the fourth insulating layer 25 and the third insulating layer 21 in the groove 26 are etched to form the second through hole 27 penetrating the fourth insulating layer 25 and the third insulating layer 21 .

[0052] S26, such as Fig.14 As shown, etching is performed from the lower surface of the second substrate 20 to form the third cavity 28 penetrating the second substrate 20 ; the third cavity 28 at least exposes all the second through holes 27 .

[0053] The materials and formation methods of the second substrate 20, the third insulating layer 21, the second lower electrode layer 22, the piezoelectric layer 23, the upper electrode layer 24 and the fourth insulating layer 25 can be selected according to actual needs and are not excessively restricted herein.

[0054] like Fig.15 As shown, the next step S2 is to bond the first substrate 10 of the electrostatic switch unit 1 to the fourth insulating layer 25 of the piezoelectric sound generating unit 2. Fig.15 The preparation of the MEMS speaker sound unit structure is shown.

[0055] In summary, the MEMS speaker sound unit structure and preparation method of the present invention, by bonding the electrostatic switch unit to the piezoelectric sound unit, can utilize the high conversion efficiency of the piezoelectric sound unit to output ultrasonic pulses with higher energy, and then ultrasonically demodulate the pulse signal through the precise switch control of the electrostatic switch unit, and extract the effective part for digital audio synthesis, so as to achieve effective modulation and control of the pulse signal, breaking through the problem of limited sound pressure level and low electroacoustic conversion efficiency of the traditional single drive and signal processing method, and at the same time opening up a new way for the performance improvement and function expansion of the MEMS speaker. Therefore, the present invention effectively overcomes the various shortcomings of the prior art and has a high industrial utilization value.

[0056] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A MEMS speaker sound unit structure, characterized in that: The sound unit structure includes, from bottom to top, a piezoelectric sound unit and an electrostatic switch unit bonded to the piezoelectric sound unit; wherein, The electrostatic switch unit includes, from bottom to top, a first substrate, a first insulating layer, a first lower electrode layer, a second insulating layer and an electrostatic diaphragm layer; and further includes: a first cavity penetrating the first substrate and the first insulating layer; a plurality of first through holes located above the first cavity and penetrating the first lower electrode layer and the second insulating layer; a second cavity located above all the first through holes and formed between the electrostatic diaphragm layer and the second insulating layer; the electrostatic diaphragm layer includes a diaphragm, a cantilever beam structure and a plurality of sound-permeable holes located between the diaphragm and the cantilever beam structure, the diaphragm is located above all the first through holes, and the diaphragm can vibrate to a surface covering all the first through holes; The piezoelectric sound unit includes, from bottom to top, a second substrate, a third insulating layer, a second lower electrode layer, a piezoelectric layer and an upper electrode layer; it also includes: a third cavity penetrating the second substrate; a groove located above the third cavity and penetrating the upper electrode layer, the piezoelectric layer and the second lower electrode layer; a fourth insulating layer formed on the surface of the upper electrode layer and on the bottom wall and side wall of the groove; and a second through hole located in the groove and penetrating the fourth insulating layer and the third insulating layer.

2. A method for preparing a MEMS speaker sound unit structure, characterized in that: The preparation method comprises: S1, providing an electrostatic switch unit and a piezoelectric sound unit; wherein, The electrostatic switch unit includes, from bottom to top, a first substrate, a first insulating layer, a first lower electrode layer, a second insulating layer and an electrostatic diaphragm layer; and further includes: a first cavity penetrating the first substrate and the first insulating layer; a plurality of first through holes located above the first cavity and penetrating the first lower electrode layer and the second insulating layer; a second cavity located above all the first through holes and formed between the electrostatic diaphragm layer and the second insulating layer; the electrostatic diaphragm layer includes a diaphragm, a cantilever beam structure and a plurality of sound-permeable holes located between the diaphragm and the cantilever beam structure, the diaphragm is located above all the first through holes, and the diaphragm can vibrate to a surface covering all the first through holes; The piezoelectric sound generating unit includes, from bottom to top, a second substrate, a third insulating layer, a second lower electrode layer, a piezoelectric layer, and an upper electrode layer; and further includes: a third cavity penetrating the second substrate; a groove located above the third cavity and penetrating the upper electrode layer, the piezoelectric layer, and the second lower electrode layer; a fourth insulating layer formed on the surface of the upper electrode layer and on the bottom wall and side wall of the groove; and a second through hole located in the groove and penetrating the fourth insulating layer and the third insulating layer; S2, bonding the first substrate of the electrostatic switch unit to the fourth insulating layer of the piezoelectric sound generating unit.

3. The method for preparing the MEMS speaker sound unit structure according to claim 2, characterized in that: The preparation method of the electrostatic switch unit comprises: providing the first substrate; forming the first insulating layer, the first lower electrode layer and the second insulating layer in sequence on the first substrate; forming a plurality of first through holes penetrating the first lower electrode layer and the second insulating layer; forming a sacrificial layer on the second insulating layer, wherein the sacrificial layer at least fills the first through hole; Performing patterned etching on the sacrificial layer to form a groove penetrating the sacrificial layer, wherein the groove exposes the second insulating layer; forming the electrostatic diaphragm layer on the sacrificial layer, wherein the electrostatic diaphragm layer at least fills the groove; The electrostatic diaphragm layer is etched to form the cantilever beam structure, the diaphragm and the sound-transmitting hole; wherein the sound-transmitting hole penetrates the electrostatic diaphragm layer and is located between the diaphragm and the cantilever beam structure; the diaphragm is located above all the first through holes, and the diaphragm can vibrate to cover the surface of all the first through holes; Etching is performed from the lower surface of the first substrate to form the first cavity penetrating the first substrate and the first insulating layer, wherein the first cavity at least exposes all the first through holes; The sacrificial layer is removed.

4. The method for preparing the MEMS speaker sound unit structure according to claim 3, characterized in that: The material of the first substrate is silicon; the first insulating layer is formed by performing thermal oxidation treatment on the surface of the first substrate.

5. The method for preparing the MEMS speaker sound unit structure according to claim 3, characterized in that: The method for forming the first lower electrode layer includes: bonding a lower electrode wafer to the upper surface of the first insulating layer, and grinding and thinning the upper surface of the lower electrode wafer to form the first lower electrode layer.

6. The method for preparing the MEMS speaker sound unit structure according to claim 3, characterized in that: The second insulating layer is formed by a chemical vapor deposition process; the material of the second insulating layer is silicon nitride.

7. The method for preparing the MEMS speaker sound unit structure according to claim 3, characterized in that: The method of forming the first through hole penetrating the first lower electrode layer and the second insulating layer includes: forming a photoresist layer on the second insulating layer and patterning the photoresist layer; Etching the first lower electrode layer and the second insulating layer based on the patterned photoresist layer to form the first through hole penetrating the first lower electrode layer and the second insulating layer; The patterned photoresist layer is removed.

8. The method for preparing the MEMS speaker sound unit structure according to claim 3, characterized in that: Before etching the sacrificial layer to form the groove penetrating the sacrificial layer, the method further includes a step of planarizing the surface of the sacrificial layer.

9. The method for preparing the MEMS speaker sound unit structure according to claim 3, characterized in that: The material of the sacrificial layer is silicon dioxide; the sacrificial layer is removed by etching with the release of gaseous hydrogen fluoride.

10. The method for preparing a MEMS speaker sound unit structure according to claim 2, characterized in that: The preparation method of the piezoelectric sound generating unit comprises: providing the second substrate; forming the third insulating layer, the second lower electrode layer, the piezoelectric layer and the upper electrode layer in sequence on the second substrate; Etching to form the groove penetrating the upper electrode layer, the piezoelectric layer and the second lower electrode layer; forming the fourth insulating layer on the surface of the upper electrode layer and the surface of the groove; Etching the fourth insulating layer and the third insulating layer in the groove to form the second through hole penetrating the fourth insulating layer and the third insulating layer; Etching is performed from the lower surface of the second substrate to form the third cavity penetrating the second substrate; the third cavity at least exposes all the second through holes.

Images