MEMS Speaker Sound Generation Unit Structure and Its Preparation Method

Abstract

The present invention provides a MEMS speaker sound generating unit structure and a preparation method thereof. By bonding an electrostatic switch unit to a piezoelectric sound generating unit, it can utilize the higher conversion efficiency of the piezoelectric sound generating unit to output ultrasonic pulses with higher energy. Then, through the precise switching control of the electrostatic switch unit, ultrasonic demodulation is performed on the pulse signal, and the effective part is intercepted for digital audio synthesis, realizing effective modulation and control of the pulse signal, breaking through the problems of limited sound pressure level and low electro-acoustic conversion efficiency in the traditional single drive and signal processing methods. At the same time, it opens up a new way for the performance improvement and function expansion of MEMS speakers.

Description

Technical Field

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

[0002] A MEMS (Micro - Electro - Mechanical System) speaker is a micro - speaker made by using micro - manufacturing technology, which combines micro - electronics technology and traditional speaker design. MEMS speakers are famous for their small size, low power consumption and high integration, and are suitable for various portable and high - performance audio devices. Its principle is to form sound waves through a pulse combination generated by high - frequency vibration of an array - arranged sound - generating unit.

[0003] In the existing electrostatic digital MEMS speakers, due to the positive - negative cancellation of the pulse energy during the vibration of a single sound - generating diaphragm, the sound pressure level is limited and the electro - acoustic conversion efficiency is low. Summary of the Invention

[0004] In view of the above - mentioned disadvantages of the prior art, the purpose of the present invention is to provide a structure of a sound - generating unit of a MEMS speaker and a preparation method thereof, which are used to solve the problems of limited sound pressure level and low electro - acoustic 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 structure of a sound - generating unit of a MEMS speaker. The sound - generating unit structure sequentially includes, from bottom to top: a piezoelectric sound - generating unit and an electrostatic switch unit bonded to the piezoelectric sound - generating unit; wherein,

[0006] The electrostatic switch unit sequentially 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 through the first substrate and the first insulating layer; a plurality of first through - holes located above the first cavity and penetrating through 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 - transmitting 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 cover the surfaces of all the first through - holes.

[0007] The piezoelectric sound generating unit sequentially 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 further includes: a third cavity penetrating the second substrate; a trench 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 the bottom wall and side walls of the trench; and a second via hole located in the trench and penetrating the fourth insulating layer and the third insulating layer.

[0008] The present invention also provides a method for manufacturing a sound generating unit structure of a MEMS speaker, and the manufacturing method includes:

[0009] S1, providing an electrostatic switch unit and a piezoelectric sound generating unit; wherein,

[0010] The electrostatic switch unit sequentially 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; it further includes: a first cavity penetrating the first substrate and the first insulating layer; a plurality of first via 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 via 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 transmission holes located between the diaphragm and the cantilever beam structure, the diaphragm is located above all the first via holes, and the diaphragm can vibrate to cover the surfaces of all the first via holes;

[0011] The piezoelectric sound generating unit sequentially 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 further includes: a third cavity penetrating the second substrate; a trench 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 the bottom wall and side walls of the trench; and a second via hole located in the trench and penetrating the fourth insulating layer and the third insulating layer;

[0012] S2, bonding and connecting the first substrate of the electrostatic switch unit to the fourth insulating layer of the piezoelectric sound generating unit.

[0013] Optionally, the manufacturing method of the electrostatic switch unit includes:

[0014] Providing the first substrate;

[0015] Sequentially forming the first insulating layer, the first lower electrode layer, and the second insulating layer on the first substrate;

[0016] Forming a plurality of the first via holes penetrating the first lower electrode layer and the second insulating layer;

[0017] A sacrificial layer is formed on the second insulating layer, and the sacrificial layer at least fills the first through hole;

[0018] The sacrificial layer is etched and patterned to form a groove penetrating the sacrificial layer, and the groove exposes the second insulating layer;

[0019] The electrostatic diaphragm layer is formed on the sacrificial layer, and the electrostatic diaphragm layer at least fills the groove;

[0020] The electrostatic diaphragm layer is etched to form the cantilever beam structure, the diaphragm and the sound transmission holes; wherein, the sound transmission holes penetrate the electrostatic diaphragm layer and are 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 surfaces of all the first through holes;

[0021] 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, and the first cavity at least exposes all the first through holes;

[0022] Remove the sacrificial layer.

[0023] Further, the material of the first substrate is silicon; the first insulating layer is formed by thermally oxidizing the surface of the first substrate.

[0024] Further, the method for forming the first lower electrode layer includes: bonding a lower electrode wafer on 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.

[0025] Further, the second insulating layer is formed by chemical vapor deposition; the material of the second insulating layer is silicon nitride.

[0026] Further, the method for forming the first through hole penetrating the first lower electrode layer and the second insulating layer includes:

[0027] Forming a photoresist layer on the second insulating layer and patterning it;

[0028] 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;

[0029] Remove the patterned photoresist layer.

[0030] Further, before etching the sacrificial layer to form the groove penetrating the sacrificial layer, a step of planarizing the surface of the sacrificial layer is further included.

[0031] Further, the material of the sacrificial layer is silicon dioxide; the sacrificial layer is removed by etching with gaseous hydrogen fluoride.

[0032] Optionally, the method for preparing the piezoelectric sound generating unit includes:

[0033] Providing the second substrate;

[0034] Successively forming the third insulating layer, the second lower electrode layer, the piezoelectric layer, and the upper electrode layer on the second substrate;

[0035] Etching to form the trench penetrating through the upper electrode layer, the piezoelectric layer, and the second lower electrode layer;

[0036] Forming the fourth insulating layer on the surface of the upper electrode layer and the surface of the trench;

[0037] Etching the fourth insulating layer and the third insulating layer in the trench to form the second through hole penetrating through the fourth insulating layer and the third insulating layer;

[0038] Etching from the lower surface of the second substrate to form the third cavity penetrating through the second substrate; the third cavity exposes at least all the second through holes.

[0039] As described above, the MEMS speaker sound generating unit structure and its preparation method of the present invention have the following beneficial effects: the MEMS speaker sound generating unit structure and its preparation method of the present invention bond and connect the electrostatic switch unit to the piezoelectric sound generating unit, enabling it to output ultrasonic pulses with higher energy by utilizing the higher conversion efficiency of the piezoelectric sound generating unit, and then performing ultrasonic demodulation on the pulse signal through the precise switch control of the electrostatic switch unit, intercepting the effective part for digital audio synthesis, realizing the effective modulation and control of the pulse signal, breaking through the problems of limited sound pressure level and low electro-acoustic conversion efficiency of the traditional single driving and signal processing methods, and at the same time opening up a new way for the performance improvement and function expansion of MEMS speakers. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It shows a cross-sectional structural schematic diagram of the MEMS speaker sound generating unit structure of the present invention when the electrostatic switch unit is open.

[0041] Figure 2 It shows a cross-sectional structural schematic diagram of the MEMS speaker sound generating unit structure of the present invention when the electrostatic switch unit is closed.

[0042] Figure 3 It shows a schematic flow chart of the preparation method of the MEMS speaker sound generating unit structure of the present invention.

[0043] Figures 4 to 15 It shows a cross-sectional structure diagram presented by each step of the preparation method of the MEMS speaker sound generating unit structure of the present invention.

[0044] Element number description: 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 transmission hole, 100 first cavity, 110 second cavity, 2 piezoelectric sound generating 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 to S2. Specific embodiments

[0045] The following uses specific specific examples to illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific implementation manners. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0046] Please refer to Figures 1 to 15 . It should be noted that the illustrations provided in this embodiment only illustrate the basic concept of the present invention in a schematic manner. Therefore, only the components related to the present invention are shown in the illustrations, rather than being drawn according to the number, shape, and size of the components in actual implementation. The type, quantity, and ratio of each component in actual implementation can be an arbitrary change, and the component layout type may also be more complex.

[0047] This embodiment provides a MEMS speaker sound generating unit structure, as Figure 1 shown, the sound generating unit structure sequentially includes from bottom to top: a piezoelectric sound generating unit 2 and an electrostatic switch unit 1 bonded to the piezoelectric sound generating unit 2; wherein,

[0048] The electrostatic switch unit 1 sequentially 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 further includes: a first cavity 100 penetrating through 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 through 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 transmission 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 surfaces of all the first through-holes 16;

[0049] The piezoelectric sound generating unit 2 sequentially 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; and further includes: a third cavity 28 penetrating through the second substrate 20; a groove 26 located above the third cavity 28 and penetrating 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 the bottom wall and side walls of the groove; and a second through-hole 27 located in the groove 26 and penetrating through the fourth insulating layer 25 and the third insulating layer 21.

[0050] The MEMS speaker sound generating unit structure of this embodiment, by bonding the electrostatic switch unit and the piezoelectric sound generating unit to each other, can utilize the higher conversion efficiency of the piezoelectric sound generating unit to output ultrasonic pulses with higher energy, and then perform ultrasonic demodulation on the pulse signal through the precise switch control of the electrostatic switch unit, intercept the effective part for digital audio synthesis, realize the effective modulation and control of the pulse signal, break through the problems of limited sound pressure level and low electro-acoustic conversion efficiency of the traditional single drive and signal processing methods, and at the same time open up a new way for the performance improvement and function expansion of MEMS speakers.

[0051] As Figure 2 shown, when a working voltage is applied to the first lower electrode layer 12 and the diaphragm 150 of the electrostatic switch unit 1, the diaphragm 150 will be adsorbed on the second insulating layer 13 under the action of electrostatic force and cover the surfaces 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 generating unit 2 cannot radiate to the electrostatic switch unit 1.

[0052] As Figure 1As shown, after removing the operating voltage applied to the first lower electrode layer 12 of the electrostatic switch unit 1 and the diaphragm 150, the diaphragm 150 returns 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 generating unit 2 can be radiated outward through the first through hole 16 and the sound transmission hole 19.

[0053] This embodiment also provides a method for manufacturing a MEMS speaker sound generating unit structure for manufacturing the above MEMS speaker sound generating unit structure, but it is not limited thereto. Other suitable manufacturing methods can also be used, as long as the method can obtain the MEMS speaker sound generating unit structure, it is included in the scope of this embodiment, such as Figure 3 As shown, the manufacturing method includes:

[0054] S1, providing an electrostatic switch unit and a piezoelectric sound generating unit; wherein,

[0055] The electrostatic switch unit sequentially 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; it also 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 transmission holes 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 surfaces of all the first through holes;

[0056] The piezoelectric sound generating unit sequentially 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 the bottom wall and side walls of the groove; and a second through hole located in the groove and penetrating the fourth insulating layer and the third insulating layer;

[0057] S2, bonding and connecting the first substrate of the electrostatic switch unit to the fourth insulating layer of the piezoelectric sound generating unit.

[0058] The preparation method of the MEMS speaker sound generating unit structure in this embodiment is to bond the electrostatic switch unit to the piezoelectric sound generating unit, so that it can output ultrasonic pulses with higher energy by utilizing the higher conversion efficiency of the piezoelectric sound generating unit, and then perform ultrasonic demodulation on the pulse signal through the precise switching control of the electrostatic switch unit, intercept the effective part for digital audio synthesis, realize the effective modulation and control of the pulse signal, break through the problems of limited sound pressure level and low electro-acoustic conversion efficiency of the traditional single drive and signal processing methods, and at the same time open up a new way for the performance improvement and function expansion of MEMS speakers.

[0059] The following will describe in detail the preparation method of the MEMS speaker sound generating unit structure in this embodiment with reference to specific drawings.

[0060] As shown in Figure 9 and Figure 14 first, step S1 is carried out to provide an electrostatic switch unit 1 and a piezoelectric sound generating unit 2; among them,

[0061] As shown in Figure 9 the electrostatic switch unit 1 sequentially 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 penetrating through 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 through 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 transmission 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 surfaces of all the first through holes 16.

[0062] As shown in Figure 14 the piezoelectric sound generating unit 2 sequentially 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 penetrating through the second substrate 20; a groove 26 located above the third cavity 28 and penetrating 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 the bottom wall and side walls of the groove; and a second through hole 27 located in the groove 26 and penetrating through the fourth insulating layer 25 and the third insulating layer 21.

[0063] As a specific example, as shown in Figures 4 to 9As shown, the manufacturing method of the electrostatic switch unit 1 includes:

[0064] S11, as Figure 4 shown, provide the first substrate 10.

[0065] S12, as Figure 4 shown, sequentially form the first insulating layer 11, the first lower electrode layer 12 and the second insulating layer 13 on the first substrate 10.

[0066] Among them, the material of the first substrate 10 can be silicon, for example; as an example, the first insulating layer 11 can be formed by thermal oxidation of the surface of the first substrate 10, or the first insulating layer 11 can be formed by processes including but not limited to physical vapor deposition (PVD, Physical Vapor Deposition) or chemical vapor deposition (CVD, Chemical Vapor Deposition). Regarding the material and formation process of the first insulating layer 11, no excessive limitation is made here.

[0067] According to the required thickness of the first lower electrode layer 12, different formation methods can be selected. As an example, when the required thickness of the first lower electrode layer 12 is relatively thick (such as greater than 6 µm), the method for forming the first lower electrode layer 12 includes: bonding a lower electrode wafer on 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. Regarding the material and formation process of the first lower electrode layer 12, no excessive limitation is made here.

[0068] As an example, the material of the second insulating layer 13 includes but is not limited to silicon nitride; the second insulating layer 13 can be formed by CVD process. Regarding the material and formation process of the second insulating layer 13, no excessive limitation is made here.

[0069] S13, as Figure 5 shown, form a plurality of first through holes 16 penetrating through the first lower electrode layer 12 and the second insulating layer 13.

[0070] As a preferred example, the method for forming the first through holes 16 penetrating through the first lower electrode layer 12 and the second insulating layer 13 includes:

[0071] First, a photoresist layer is formed on the second insulating layer 13 and patterned; wherein, the photoresist layer can be formed by, for example, a spin coating process; then, based on the patterned photoresist layer, the first lower electrode layer 12 and the second insulating layer 13 are etched to form the first through hole 16 that penetrates the first lower electrode layer 12 and the second insulating layer 13; finally, the patterned photoresist layer is removed.

[0072] S14, as Figure 6 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.

[0073] S15, as Figure 6 shown, the sacrificial layer 14 is pattern-etched to form a groove 17 that penetrates the sacrificial layer 14, and the groove 17 exposes the second insulating layer 13.

[0074] As a preferred example, before etching the sacrificial layer 14 to form the groove 17 that penetrates the sacrificial layer 14, it further includes a step of planarizing the surface of the sacrificial layer 14 to improve the film-forming quality on the sacrificial layer 14 subsequently.

[0075] S16, as Figure 7 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.

[0076] S17, as Figure 7 shown. The electrostatic diaphragm layer 15 is etched to form the cantilever beam structure 18, the diaphragm 150, and the sound transmission holes 19; wherein, the sound transmission holes 19 penetrate the electrostatic diaphragm layer 15 and are 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 surfaces of all the first through holes 16.

[0077] S18, as Figure 8 shown, etching is performed from the lower surface of the first substrate 10 to form the first cavity 100 that penetrates the first substrate 10 and the first insulating layer 11, and the first cavity 100 at least exposes all the first through holes 16.

[0078] S19, as Figure 9 shown, the sacrificial layer 14 is removed; the material of the sacrificial layer 14 can be, for example, silicon dioxide.

[0079] As an example, the sacrificial layer 14 can be removed by release etching with gaseous hydrogen fluoride.

[0080] As a specific example, asFigures 10 to 14 As shown, the preparation method of the piezoelectric sound generating unit includes:

[0081] S21, as Figure 10 shown, provide the second substrate 20.

[0082] S22, as Figure 10 shown, sequentially form the third insulating layer 21, the second lower electrode layer 22, the piezoelectric layer 23, and the upper electrode layer 24 on the second substrate 20.

[0083] S23, as Figure 11 shown, etch to form the trench 26 penetrating through the upper electrode layer 24, the piezoelectric layer 23, and the second lower electrode layer 22.

[0084] S24, as Figure 12 shown, form the fourth insulating layer 25 on the surface of the upper electrode layer 24 and the surface of the trench 26.

[0085] S25, as Figure 13 shown, etch the fourth insulating layer 25 and the third insulating layer 21 in the trench 26 to form the second through hole 27 penetrating through the fourth insulating layer 25 and the third insulating layer 21.

[0086] S26, as Figure 14 shown, etch from the lower surface of the second substrate 20 to form the third cavity 28 penetrating through the second substrate 20; the third cavity 28 at least exposes all the second through holes 27.

[0087] Regarding 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, they can be selected according to actual needs and are not overly restricted here.

[0088] As Figure 15 shown, then perform step S2 to bond and connect the first substrate 10 of the electrostatic switch unit 1 and the fourth insulating layer 25 of the piezoelectric sound generating unit 2. Thus, the preparation of the MEMS speaker sound generating unit structure as Figure 15 shown is completed.

[0089] In summary, for the MEMS speaker sound generating unit structure and its manufacturing method of the present invention, by bonding the electrostatic switch unit to the piezoelectric sound generating unit, it can output ultrasonic pulses with higher energy using the higher conversion efficiency of the piezoelectric sound generating unit, and then perform ultrasonic demodulation on the pulse signal through the precise switching control of the electrostatic switch unit to intercept the effective part for digital audio synthesis, realizing the effective modulation and control of the pulse signal, breaking through the problems of limited sound pressure level and low electro-acoustic conversion efficiency in the traditional single drive and signal processing methods, and at the same time opening up a new way for the performance improvement and function expansion of MEMS speakers. Therefore, the present invention effectively overcomes various disadvantages in the prior art and has high industrial utilization value.

[0090] The above embodiments are only illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes completed by those with ordinary knowledge in the technical field without departing from the spirit and technical idea disclosed by the present invention should 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.

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