CN112543408B

CN112543408B - Closed diaphragm piezoelectric MEMS loudspeaker and preparation method thereof

Info

Publication number: CN112543408B
Application number: CN202011529954.3A
Authority: CN
Inventors: 刘景全; 王淇
Original assignee: Shanghai Jiaotong University
Current assignee: Shanghai Jiaotong University
Priority date: 2020-12-22
Filing date: 2020-12-22
Publication date: 2022-04-26
Anticipated expiration: 2040-12-22
Also published as: CN112543408A

Abstract

The invention provides a closed type vibrating membrane piezoelectric MEMS loudspeaker and a preparation method thereof, wherein the preparation method comprises the following steps: sequentially preparing a first electrode, a piezoelectric layer and a second electrode on a substrate; sequentially etching the second electrode, the piezoelectric layer and the first electrode to obtain a patterned second electrode, a patterned piezoelectric layer and a patterned first electrode to form a patterned vibrating membrane unit; the patterned vibration film unit is provided with six triangles with the same size; etching the substrate to form six groove gaps with the same size on the patterned vibration film unit to obtain a device; depositing a layer of packaging material on the upper surface of the device to seal the gap of the groove; and etching the lower surface of the device, forming a back cavity on the back of the patterned vibration film unit, and covering the outer contour of the patterned vibration film unit with the outer contour of the back cavity. The invention has the advantages of the piezoelectric MEMS loudspeaker with the enclosed membrane and the unclosed membrane, not only has larger vibration excursion displacement of the vibration membrane, but also can not generate sound pressure level leakage.

Description

Closed diaphragm piezoelectric MEMS loudspeaker and preparation method thereof

Technical Field

The invention relates to the field of MEMS micro-speakers, in particular to a closed diaphragm piezoelectric MEMS speaker and a preparation method thereof.

Background

Micro-speakers are widely used in wearable electronics, such as mobile phones, smart appliances, headsets, computers, and human-computer interfaces. With the development demand of wearable electronic devices, the development of micro speakers tends to be miniaturized, light-weighted, low-power, and high-sound-pressure level. The rapid development of MEMS (Micro-Electro-Mechanical Systems) technology has enabled smaller and lower power devices, with MEMS electrodynamic, capacitive and piezoelectric microspeakers providing alternatives to traditional loudspeakers.

Electrodynamic MEMS micro-speakers, which are the most common type of existing speakers due to their better acoustic performance, perform electro-acoustic conversion according to the motor principle. However, the electrodynamic MEMS speaker has disadvantages of large current, complicated packaging process, and the like due to the requirement for the magnet. The traditional electric micro-speaker is not replaced by MEMS device, though it has low energy consumption, large variation of manufacturing process and moderate sound quality. The main reason is that die size is relatively large and still not capable of generating sufficient sound pressure levels. The electrostatic MEMS speaker drives a diaphragm and pushes air using two independent electrodes that generate electrostatic force. Although the capacitive MEMS micro-speaker is the leading speaker product occupying the market, and because the electrostatic speaker has the advantages of extremely light diaphragm mass and excellent resolving power, it can fully express the musical spirit, but its diaphragm displacement and sound pressure level are limited by the gap, and there are more application limitations of the pull-in effect and high driving voltage. The piezoelectric MEMS micro-speaker realizes sound pressure output based on the piezoelectric effect of the piezoelectric film material, and has the advantages of simple manufacture, high signal-to-noise ratio, high response speed, dust prevention and the like compared with a capacitive MEMS micro-speaker. To date, piezoelectric speakers have been developed with various piezoelectric materials, such as ZnO, AlN, PZT, PMN-PT, PZN-PT, etc. PZT piezoelectric materials are the most widely used piezoelectric materials because of their high piezoelectric charge constants and electromechanical coupling coefficients. However, MEMS piezoelectric speakers face the problem of relatively low sound pressure levels.

Through the search discovery for the prior art:

haoran Wang, Zhenfang Chen et al in Sensors and actors A Physical write "A high-SPL piezoelectric MEMS loud speaker based on piezoelectric PZT". A circular closed-film piezoelectric MEMS speaker based on ceramic PZT is reported, which can generate a high sound pressure level at a small driving voltage and a resonance frequency of 4.2kHz, so that the sound pressure level is high in a frequency range of 20-20kHz, but the offset displacement of the closed-type diaphragm is not large enough to prevent further increase of the sound pressure level thereof.

Hsu-Hsiang Cheng, Weiileun Fang et al, at "2020 IEEE 33rd International Conference on Micro Electro Mechanical Systems (MEMS)" Conference, write "Piezoelectric microspaker using novel driving approach and electrode design for frequency range improvement". A dual-electrode drive mode is described comprising an edge electrode and a center electrode, whereby not only can the diaphragm be driven by the edge electrode in a piston vibration mode to maintain the sound pressure level at low frequencies, but also the center electrode can be drivenThe sound pressure level at high frequencies is further increased. Improved piezoelectric MEMS loudspeaker at 2V_ppFrom 2.6kHz to 20kHz, 15dB higher than previously designed piezoelectric MEMS speakers. Although the sound pressure level at low frequencies is increased, it is lower at high frequencies, between 10kHz and 20kHz and sometimes only around 52 dB.

Shih-Hsiung Tseng, Weieun Fang et al, at "2020 IEEE 33rd International Conference on Micro Electro Mechanical Systems (MEMS)" Conference, "Sound pressure and Low frequency enhancement using PZT MEMS microspeaker design". A piezoelectric MEMS array microspeaker is disclosed, which comprises four triangular plates, a connecting mass block and dual driving electrodes, wherein the inner and outer electrodes on the triangular plates are driven 180 DEG out of phase. At a driving voltage of only 2V_ppThe sound pressure levels of this micro-speaker with 5 arrays at 100Hz, 1kHz were 81.4dB and 84.7dB, respectively. However, the structure and the manufacturing process of the array type piezoelectric MEMS speaker are complicated.

Stoppel, c.eisermann et al, written in 201719 th International Conference on Solid-State Sensors, actors and Microsystems, "Novel membrane-less two-way MEMS loud speaker based on concentric cascade PZT drivers, show a Novel two-channel piezoelectric MEMS speaker that achieves a 95dB sound pressure level at frequencies above 800Hz, although the structure is an unclosed membrane structure, it has a problem of sound pressure level leakage.

In summary, the piezoelectric MEMS speakers reported at present include a closed-film type piezoelectric MEMS speaker and an unclosed-film type piezoelectric MEMS speaker, and for a piezoelectric MEMS speaker having advantages of both a closed-film type diaphragm and an unclosed-film type diaphragm, not only a large diaphragm vibration offset displacement is obtained, but also no sound pressure level leakage is generated. At present, no report is found. With the development of wearable electronic devices, better performance, full coverage frequency, piezoelectric MEMS speakers with higher sound pressure level are becoming a necessary trend.

Disclosure of Invention

Aiming at the defects in the prior art, a closed type vibrating membrane piezoelectric MEMS loudspeaker and a preparation method thereof are provided.

The first aspect of the present invention provides a method for manufacturing a closed diaphragm piezoelectric MEMS speaker, comprising:

preparing a first electrode on a substrate, preparing a piezoelectric layer on the first electrode, and preparing a second electrode on the piezoelectric layer;

etching the second electrode, the piezoelectric layer and the first electrode in sequence to obtain a patterned second electrode, a patterned piezoelectric layer and a patterned first electrode, wherein the patterned second electrode, the patterned piezoelectric layer and the patterned first electrode form a patterned vibrating membrane unit; the patterned vibration film unit is provided with six triangles with the same size, and the six triangles are arranged closely along the circumferential direction and share the same vertex;

etching the substrate to form groove gaps distributed in a radial shape, wherein the size of each groove gap is matched with the two side lengths of each triangle, namely, a gap is formed between every two adjacent triangles, the third sides of the gaps of the grooves which are not etched in the six triangles are used as binding edge parts, and the third sides of the six triangles are connected end to form a closed hexagon; the patterned vibration film unit shares a first electrode and a second electrode to obtain a device;

depositing a layer of packaging material on the upper surface of the device to seal the side wall and the bottom of the gap of the groove;

and etching the lower surface of the device, forming a back cavity on the back surface of the patterned vibration film unit, wherein the outer contour of the back cavity covers the outer contour of the patterned vibration film unit.

In the preparation step, before etching the back cavity, the etched groove gap is sealed; the deposition of the encapsulation material through the bottom substrate provides a deposition surface to deposit a thin film to close the gap. Otherwise, after the back cavity is etched, the gap of the groove is encapsulated, so that the gap is too large, the deposition thickness is larger than the gap to close the gap, and the film is too thick, too narrow and the same as the gap. Thus, the effect of large vibration displacement cannot be achieved during vibration. The etched groove gap is sealed, so that the vibrating membrane is converted into a sealed structure from non-sealed, leakage of airflow and sound pressure level is prevented, and the prepared piezoelectric MEMS loudspeaker has the advantages of large vibration offset displacement of the non-sealed membrane and no leakage of the sound pressure level of the sealed membrane.

The pattern of the patterned diaphragm is not limited to six triangular diaphragm units with the same size, and is also applicable to all patterns such as triangles, ladders, circles, rings, squares and the like.

Preferably, the second electrode, the piezoelectric layer and the first electrode are sequentially etched to obtain a patterned second electrode, a patterned piezoelectric layer and a patterned first electrode, and the patterned second electrode, the patterned piezoelectric layer and the patterned first electrode form a patterned vibrating membrane unit; and etching the second electrode, the piezoelectric layer and the first electrode in a regular hexagonal pattern along three mutually crossed diagonals of the regular hexagonal pattern to obtain the second electrode with six triangles, the piezoelectric layer with six triangles and the first electrode with six triangles.

The etching lines are not limited to three crossed etching lines, and are also applicable to all numbers of crossed etching lines such as crossed etching lines, four crossed etching lines and the like.

Preferably, the edge of the piezoelectric layer with six triangles is larger than the edge of the second electrode with six triangles, so that the second electrode is isolated from the first electrode, and communication between the upper layer electrode and the lower layer electrode is avoided.

Preferably, the size of the back cavity is larger than the size of the patterned second electrode to ensure that the back cavity covers the entire patterned diaphragm unit.

Preferably, the width of the trench gap is between 3 μm and 20 μm; the depth of the groove gap is 5-100 μm.

Preferably, the substrate is any one of an SOI wafer, a flexible substrate, a metal substrate or a non-metal substrate.

More preferably, the non-metal substrate can be selected from flexible material substrates such as PDMS (polydimethylsiloxane), PE (polyethylene), PI (polyimide), and the like.

Preferably, the first electrode and the second electrode are made of any one of Pt (platinum), Au (gold), Cr (chromium) or Al (aluminum);

preferably, the material of the piezoelectric layer is any one of PZT piezoelectric ceramics (lead zirconate titanate piezoelectric ceramics), ZnO (zinc oxide), AlN (aluminum nitride), PMN-PT (lead magnesium niobate-lead titanate), or PVDF (polyvinylidene fluoride).

Preferably, the material of the encapsulation layer is any one of Parylene C (poly-p-xylylene), PI (polyimide), silicone rubber, and epoxy resin.

Preferably, the cavity of the back cavity is a hollow space in a regular hexagon shape.

The invention provides a piezoelectric MEMS loudspeaker, which is prepared by the preparation method of the closed type vibrating membrane piezoelectric MEMS loudspeaker.

Preferably, the piezoelectric MEMS speaker comprises:

a substrate, a first electrode and a second electrode,

the first electrode, the piezoelectric layer and the second electrode are sequentially arranged above the substrate;

the substrate, the first electrode, the piezoelectric layer and the second electrode form a regular-hexagon vibration film structure, the regular-hexagon vibration film structure is divided into six triangles with equal size by three diagonal lines in a crossed manner, and a groove gap is formed between every two adjacent triangles; packaging layers are arranged on the surface of the regular hexagonal vibration film structure and the side wall and the bottom of the groove gap, so that the side wall and the bottom of the groove gap are sealed;

the back surface of the vibrating membrane structure is provided with a back cavity of an upwardly concave hollow cavity, and a layer of packaging layer is arranged between the cavity of the back cavity and the gap of the groove; and the outer contour of the back cavity covers the outer contour of the regular hexagonal diaphragm structure.

Compared with the prior art, the invention has at least one of the following beneficial effects:

according to the preparation method, the upper surface, the etched gap side wall and the etched gap bottom are deposited with a layer of packaging material before the back cavity is etched, so that the gap of the unsealed type vibrating membrane is skillfully sealed, the leakage of airflow and sound pressure level is prevented, and the prepared piezoelectric MEMS loudspeaker has the advantages of large vibration offset displacement of the unsealed type vibrating membrane and the advantage of no sound pressure level leakage of the sealed membrane; the prepared MEMS loudspeaker completely covers the frequency range of 20Hz-20000Hz which can be heard by human ears, can reach the sound pressure level which can sufficiently meet commercial application, and has compact structure, smaller volume and excellent performance; the wearable electronic device can be used for mobile phone speakers, earphones, hearing aids and the like.

Drawings

Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments with reference to the following drawings:

fig. 1 is a schematic flow chart of a method for manufacturing a piezoelectric MEMS speaker with a closed diaphragm according to a preferred embodiment of the present invention;

FIG. 2 is a front view of a device in accordance with a preferred embodiment of the present invention;

FIG. 3 is a backside cavity view of a device in accordance with a preferred embodiment of the present invention;

FIG. 4 is a front view of a device having a surface deposited with Parylene C in accordance with a preferred embodiment of the present invention;

FIG. 5 is a cross-sectional view of a device having a surface deposited with parylene C in accordance with a preferred embodiment of the present invention;

the scores in the figure are indicated as: a second electrode pad 1, a first electrode pad 2, a trench gap 3, six triangular diaphragms 4, a substrate 5, a back cavity 6, parylene c 7.

Detailed Description

The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that variations and modifications can be made by persons skilled in the art without departing from the spirit of the invention. All falling within the scope of the present invention.

Example 1

Referring to fig. 1, a flow chart of a method for manufacturing a closed diaphragm piezoelectric MEMS speaker according to a preferred embodiment of the present invention includes the following steps:

s1, as shown in fig. 1 (a), sputtering Pt with a thickness of 100nm on the SOI wafer substrate to obtain a first electrode; sputtering a PZT material with the thickness of 1 mu m on the first electrode to obtain a piezoelectric layer; sputtering Pt with the thickness of 100nm on the piezoelectric layer to obtain a second electrode; completing the preparation of the PZT-SOI wafer;

coating photoresist 5 microns on the front surface of the prepared PZT-SOI wafer, pre-baking for 90s, exposing for 45s, developing for 45s, flushing with deionized water for 30s, drying with nitrogen, post-baking for 12min, then etching the second layer electrode for 8min by adopting ion beams, finishing patterning the second layer electrode, and removing the photoresist; six second-layer electrodes in a triangular pattern are obtained. As a preferred mode, etching the second electrode by adopting ion beams; the specific etching process is carried out in a regular hexagon graph with the side length of 1mm, and six triangular graphs with the same size are obtained by etching along three mutually crossed diagonals of the regular hexagon graph; the etching gap was 50 μm. The line width for connecting the second electrode square bonding pad 1 is 30 μm, and the length and width of the second electrode square bonding pad are both 300 μm.

S2, as shown in (b) of FIG. 1, coating photoresist 5 μm on the front surface, pre-baking for 90S, exposing for 45S, developing for 45S, rinsing with deionized water for 30S, drying with nitrogen gas, post-baking for 12min, and wet etching PZT for 90S. Then immersing PZT into prepared etching liquid for etching, wherein the width of a PZT etching groove is 20 mu m; stirring the etching solution by using a magnetic stirrer to improve the etching uniformity and speed; then putting the etched PZT-SOI into the configured HNO₃Soaking in the solution for 3 min; finally, the mixture is put into deionized water to be soaked for a few minutes so as to clean and remove surface impurities. Drying by nitrogen and vacuum drying; obtaining six piezoelectric layers with triangular patterns; the edges of the piezoelectric layers with six triangular patterns are 30 μm larger than the edges of the second layer electrodes with six triangular patterns to isolate the second electrodes and prevent the second electrodes from being connected with the first electrodes up and downThe method is simple.

In a preferred embodiment, in the above step, the PZT etching solution can be prepared by the following steps: first 0.6g NH₄F, slowly adding the mixture into 1ml of deionized water, and continuously stirring until the mixture is completely dissolved; then 1ml of NH₄Slowly pouring F (40%) into 5ml of HF solution, and continuously stirring to uniformly mix the solution to form BHF solution; then 1ml BHF, 25ml HCl and 100ml H₂O, preparing etching mixed liquid, and fully stirring to fully and uniformly mix the etching mixed liquid; and then immersing PZT into the etching solution for etching, and stirring the etching solution by using a magnetic stirrer to improve the etching uniformity and speed.

In a preferred embodiment, in the above step, the stirring speed during PZT etching is 130r/min, and the stirring temperature during PZT etching is normal temperature.

Preferably, in the above step, HNO is required₃The solution can be prepared by mixing 10ml of HNO₃Put into 13ml of H₂And O forms a solution and is stirred uniformly.

S3, as shown in (c) of FIG. 1, coating photoresist on the front surface for 5 microns, pre-baking for 90 seconds, exposing for 45 seconds, developing for 40 seconds, flushing with deionized water for 30 seconds, drying with nitrogen gas, post-baking for 12 minutes, then etching the first electrode Pt for 8 minutes by adopting an ion beam, wherein the etching gap is 20 microns, and after patterning of the first electrode is finished, removing photoresist to obtain six triangular first electrodes with the same size. And wet etching the PZT to form the first electrode square bonding pad, wherein the length and the width of the first electrode square bonding pad are both 300 mu m.

S4, as shown in (d) of FIG. 1, the front surface is coated with 5 μm photoresist, and NMC medium is etched with 0.5 μm SiO₂NMC deep silicon etching 2 μm Si, NMC dielectric etching 1.1 μm SiO₂Six groove gaps with the same size are formed by NMC deep silicon etching of about 15 mu m Si, and the length of each groove gap is matched with the side length of a triangle; si, SiO₂The width of each etched groove is 5 mu m; and obtaining the device.

S5, as shown in (e) in FIG. 1, carrying out Parylene C deposition on the surface of the device and the gap side wall and the gap bottom of the trench gap, wherein the thickness of the Parylene C deposition is 0.5 μm, and the etched trench gap is closed.

S6, as shown in (f) of FIG. 1,coating 5 mu m photoresist on the front surface for protection, coating 20 mu m photoresist on the back surface, prebaking for 2min, developing for 130s, flushing with deionized water for 30s, blowing dry with nitrogen, postbaking for 12min, etching with NMC medium to obtain 1.5 mu m SiO₂NMC deep silicon etch 600 μm Si, then NMC deep silicon etch 1.1 μm intermediate buried oxide SiO₂The gap between the back cavity and the vibrating membrane is prepared; the radius of the back cavity is 0.2mm larger than the outline of the second electrode to ensure that the back cavity can cover the whole front diaphragm.

The structure of the piezoelectric MEMS speaker obtained by the above steps is shown in fig. 2, 3, 4, and 5, and the device in the drawing includes a second electrode pad 1, a first electrode pad 2, a gap 3, six triangular diaphragms 4, a substrate 5, a back cavity 6, and a Parylene C7; as can be seen in the figure, the six triangular diaphragms 4 comprise six triangles of equal size, and the six triangles are arranged next to each other in the circumferential direction and share the same vertex; the six triangular vibration membranes 4 integrally form a regular hexagonal vibration membrane with unclosed middle; depositing a layer of Parylene C7 on the surface of the device, wherein the Parylene C7 covers the surface of the side wall of the gap of the groove and the surface of the bottom of the gap to seal the gap; the back cavity 6 of the hollow cavity which is concave upwards is arranged on the back of the six triangular vibration membranes 4, and a layer of Parylene C7 is arranged between the cavity of the back cavity 6 and the gap of the groove, so that the vibration membranes are converted from non-closed to closed.

Example 2

s1, as shown in fig. 1 (a), sputtering Pt with a thickness of 120nm on the SOI wafer substrate to obtain a first electrode; sputtering PZT material with the thickness of 2 mu m on the first electrode to obtain a piezoelectric layer; sputtering Pt with the thickness of 120nm on the piezoelectric layer to obtain a second electrode; completing the preparation of the PZT-SOI wafer; coating photoresist 5 mu m on the front surface of the prepared PZT-SOI wafer, pre-baking for 90s, exposing for 45s, developing for 50s, flushing with deionized water for 30s, drying with nitrogen, post-baking for 12min, etching an upper electrode (a second electrode) Pt for 8min by adopting an ion beam, finishing patterning the upper electrode, and removing the photoresist;

as a preferred mode, the etched six triangular diaphragm units integrally form a regular hexagonal diaphragm with unclosed middle, namely, the etched six triangles share one vertex and are communicated with each other; so that only the vibration excursion is large and the sound pressure level leakage is prevented. The sides of the regular hexagon may be 0.5 mm.

As a preferable mode, six triangular diaphragm units are symmetrically arranged by intersecting points along 3 mutually intersecting diagonals of the regular hexagonal diaphragm; the etching gap was 40 μm.

Preferably, the line width of the square bonding pad is 20 μm, and the length and width of the square bonding pad are both 200 μm.

S2, as shown in (b) of FIG. 1, coating photoresist 5 μm on the front surface, pre-baking for 90S, exposing for 45S, developing for 50S, rinsing with deionized water for 30S, drying with nitrogen gas, post-baking for 12min, and wet etching PZT 90S. Then immersing PZT into prepared etching liquid for etching, and stirring the etching liquid by using a magnetic stirrer to improve the etching uniformity and speed; then putting the etched PZT-SOI into the configured HNO₃Soaking in the solution for 3 min; finally, the mixture is put into deionized water to be soaked for a few minutes so as to clean and remove surface impurities. Drying by nitrogen and vacuum drying. The edges of six triangular piezoelectric layers etched by the PZT and having the same size are 30 mu m larger than the outline of the second electrode so as to isolate the second electrode and avoid the communication of the upper and lower electrodes. The PZT etching groove width was 10 μm.

As a preferable mode, the PZT etching solution in the above step can be prepared by the following method: first 0.6g NH₄F, slowly adding the mixture into 1ml of deionized water, and continuously stirring until the mixture is completely dissolved; then 1ml of NH₄Slowly pouring F (40%) into 5ml of HF solution, and continuously stirring to uniformly mix the solution to form BHF solution; then 1ml BHF, 25ml HCl and 100ml H₂O, preparing etching mixed liquid, and fully stirring to fully and uniformly mix the etching mixed liquid; then immersing PZT into the etching liquid for etching, and stirring the etching liquid by using a magnetic stirrer to improve the etching uniformity and speed;

in a preferable mode, in the above step, the stirring speed during PZT etching is 120r/min, and the stirring temperature during PZT etching is normal temperature.

Preferably, in the above step, HNO is required₃The solution is prepared by the following method: adding 11ml of HNO₃Put into 14ml of H₂And O forms a solution and is stirred uniformly.

S3, as shown in (c) of FIG. 1, coating photoresist on the front surface for 5 microns, pre-baking for 90S, exposing for 50S, developing for 40S, flushing with deionized water for 30S, drying with nitrogen, post-baking for 12min, then etching the lower electrode Pt for 8min by adopting ion beams, finishing patterning the lower electrode, and removing photoresist to obtain six triangular first electrodes with the same size. The length and width of the square bonding pad of the lower electrode which is leaked after the PZT is etched by a wet method are both 200 mu m.

In a preferred embodiment, the lower electrode Pt is ion-beam etched with a gap of 10 μm.

S4, as shown in (d) of FIG. 1, the front surface is coated with 5 μm photoresist, and NMC medium is etched with 0.5 μm SiO₂NMC deep silicon etching 2 μm Si, NMC dielectric etching 1.1 μm SiO₂NMC deep silicon etches 20 μm Si to form six triangular diaphragm trench gaps of the same size. Si, SiO₂The width of each etched groove is 10 mu m.

S5, as shown in fig. 1 (e), Parylene C deposition is performed on the surface of the device and the surfaces of the gap sidewall and the gap bottom of the trench gap. Parylene C was deposited to a thickness of 1 μm. The etched trench gaps are closed.

S6, as shown in (f) of FIG. 1, coating 5 μm photoresist on the front surface for protection, coating 20 μm photoresist on the back surface, prebaking for 2min, developing for 130S, rinsing with deionized water for 30S, blowing dry with nitrogen, prebaking for 12min, and etching with NMC medium to obtain 1.5 μm SiO₂NMC deep silicon etch 600 μm Si, then NMC deep silicon etch 1.1 μm intermediate buried oxide SiO₂The gap between the back cavity and the vibrating membrane is prepared; the radius of the back cavity is 0.25mm larger than that of the upper electrode, so that the back cavity can cover the whole front vibrating membrane.

In specific implementation, the PZT etching method in the above embodiment is not limited to wet etching, but is also applicable to all technologies capable of forming a trench, such as ion beam etching and various dry etching, laser cutting, and the like; si and SiO₂The etching method aims atBut not limited to dry etching, and is also applicable to all technologies capable of preparing grooves, such as wet etching, laser cutting and the like.

The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes or modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention.

Claims

1. A method for preparing a closed diaphragm piezoelectric MEMS loudspeaker is characterized by comprising the following steps:

etching the second electrode, the piezoelectric layer and the first electrode in sequence to obtain a patterned second electrode, a patterned piezoelectric layer and a patterned first electrode, wherein the patterned second electrode, the patterned piezoelectric layer and the patterned first electrode form a patterned vibrating membrane unit; the patterned vibration film unit is a triangle with six same sizes, and the six triangles are arranged closely along the circumferential direction and share the same vertex;

depositing a layer of packaging material on the upper surface of the device to seal the side wall and the bottom of the gap of the groove; the width of the groove gap is 3-20 μm; the depth of the groove gap is 5-100 μm;

etching the lower surface of the device, forming a back cavity on the back surface of the patterned vibration film unit, wherein the outer contour of the back cavity covers the outer contour of the patterned vibration film unit;

the size of the back cavity is larger than that of the patterned second electrode so as to ensure that the back cavity can cover the whole patterned diaphragm unit.

2. The method for manufacturing the closed type diaphragm piezoelectric MEMS speaker according to claim 1, wherein the second electrode, the piezoelectric layer, and the first electrode are sequentially etched to obtain a patterned second electrode, a patterned piezoelectric layer, and a patterned first electrode, and the patterned second electrode, the patterned piezoelectric layer, and the patterned first electrode form a patterned diaphragm unit; and etching the second electrode, the piezoelectric layer and the first electrode in a regular hexagonal pattern along three mutually crossed diagonals of the regular hexagonal pattern to obtain the second electrode with six triangles, the piezoelectric layer with six triangles and the first electrode with six triangles.

3. The method according to claim 2, wherein the edges of the piezoelectric layer having six triangles are larger than the edges of the second electrode having six triangles, so that the second electrode is isolated from the first electrode and communication between the upper and lower electrodes is avoided.

4. A method of manufacturing a closed diaphragm piezoelectric MEMS speaker as claimed in any one of claims 1 to 3, wherein the substrate is any one of an SOI wafer, a flexible substrate, a metal substrate or a non-metal substrate.

5. A method of manufacturing a closed diaphragm piezoelectric MEMS speaker as claimed in any one of claims 1 to 3, wherein one or more of the following features are provided:

-the first electrode, the second electrode material is any one of Pt, Au, Cr or Al;

-the material of the piezoelectric layer is any one of PZT piezoelectric ceramic, ZnO, AlN, PMN-PT or PVDF;

-the encapsulating material is any one of Parylene C, PI, silicone rubber, epoxy resin.

6. The method for manufacturing a closed diaphragm piezoelectric MEMS speaker according to any one of claims 1 to 3, wherein the cavity of the back cavity is a hollow space in the shape of a regular hexagon.

7. A piezoelectric MEMS speaker, characterized by being produced by the method for producing a closed-type diaphragm piezoelectric MEMS speaker according to any one of claims 1 to 6.

8. The piezoelectric MEMS speaker of claim 7, comprising:

a substrate, a first electrode and a second electrode,