CN112543408B - Closed diaphragm piezoelectric MEMS loudspeaker and preparation method thereof - Google Patents

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

A closed diaphragm piezoelectric MEMS speaker and its preparation method

technical field

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

Background technique

Micro speakers are widely used in wearable electronic products such as mobile phones, smart home appliances, headphones, computers and human-machine interfaces. With the development of wearable electronic devices, the development of micro speakers tends to be miniaturized, lightweight, low power consumption, and high sound pressure level. The rapid development of MEMS (Micro-Electro-Mechanical Systems) technology has made smaller and lower power consumption devices a reality. MEMS electrodynamic, capacitive and piezoelectric micro speakers provide an alternative to traditional speakers.

Electrodynamic MEMS micro-speakers realize electro-acoustic conversion based on the principle of electric motors. Electro-dynamic MEMS micro-speakers have become the most common type of existing speakers due to their better acoustic performance. However, the electrodynamic MEMS speaker has disadvantages such as large current and complicated packaging process due to the requirement for the magnet. Although traditional electrodynamic microspeakers have low energy consumption, large manufacturing process variations, and moderate sound quality, they have not been replaced by MEMS devices. The main reason is that the tube chip size is relatively large and still cannot generate sufficient sound pressure level. Electrostatic MEMS speakers use two separate electrodes that generate electrostatic forces to drive the diaphragm and push the air. Although the capacitive MEMS micro-speaker is the dominant speaker product in the market, and the electrostatic speaker has the advantages of extremely light diaphragm, excellent resolution, and can fully express the charm of music, the displacement of the diaphragm and the sound pressure level are affected by the gap. The limitations of the pull-in effect and the application limitations of high driving voltage. Piezoelectric MEMS micro-speaker is based on the piezoelectric effect of piezoelectric film materials to achieve sound pressure output. Compared with capacitive MEMS micro-speakers, it has the advantages of simple manufacture, high signal-to-noise ratio, fast response speed, and dust-free. So far, piezoelectric speakers have developed various piezoelectric materials, such as ZnO, AlN, PZT, PMN-PT, PZN-PT, etc. PZT piezoelectric material has become the most widely used piezoelectric material because of its high piezoelectric charge constant and electromechanical coupling coefficient. However, MEMS piezoelectric speakers suffer from relatively low sound pressure levels.

After searching for the prior art, it was found that:

Haoran Wang, Zhenfang Chen et al wrote "A high-SPL piezoelectric MEMS loud speaker based on thinceramic PZT" in Sensors and Actuators A:Physical. reported a circular closed-film piezoelectric MEMS speaker based on ceramic PZT, which can generate high sound pressure level at a small driving voltage and has a resonant frequency of 4.2 kHz, which makes the sound in the frequency range of 20-20 kHz. The pressure level is high, but the offset displacement of the closed diaphragm is not large enough, which hinders the further improvement of its sound pressure level.

Hsu-Hsiang Cheng, Weileun Fang and others wrote "Piezoelectricmicrospeaker using novel driving approach and electrode design for frequencyrange improvement" at "2020IEEE 33rd International Conference on Micro Electro Mechanical Systems (MEMS)". A dual-electrode drive mode including an edge electrode and a center electrode is introduced. Not only can the edge electrode drive the diaphragm in a piston vibration mode to maintain the sound pressure level at low frequencies, but also drive the center electrode to further increase the sound pressure level at high frequencies. sound pressure level. The improved piezoelectric MEMS speaker has a 15dB improvement over the previously designed piezoelectric MEMS speaker from 2.6kHz to 20kHz at a driving voltage of 2V _pp . Although the sound pressure level at low frequencies is increased, the sound pressure level at high frequencies is lower, sometimes only about 52dB between 10kHz and 20kHz.

Shih-Hsiung Tseng, Weileun Fang and others wrote "Sound pressure and low frequency enhancement using novel PZT MEMS microspeaker design" at the "2020 IEEE 33rd International Conference on Micro Electro Mechanical Systems (MEMS)" conference. A piezoelectric MEMS array micro-speaker is introduced, which includes four triangular plates, a connection mass and double driving electrodes. The inner and outer electrodes on the triangular plate are driven out of phase by 180°. When the driving voltage is only 2V _pp , the sound pressure level of this microspeaker with 5 arrays is 81.4dB and 84.7dB at 100Hz and 1kHz, respectively. However, the structure and fabrication process of the array piezoelectric MEMS speaker are complicated.

F.Stoppel, C.Eisermann et al. in the 2017 19th International Conference on Solid-State Sensors, Actuators and Microsystems "Novel membrane-less two-way MEMS loudspeaker loudspeaker based on piezoelectric dual-concentricactuators", demonstrated a concentric cascade based The new dual-channel piezoelectric MEMS speaker of the PZT driver achieves a sound pressure level of 95dB at frequencies above 800Hz. Although the structure is an open membrane structure, it has the problem of sound pressure level leakage.

To sum up, the currently reported piezoelectric MEMS speakers include closed-membrane piezoelectric MEMS speakers and non-closed-membrane piezoelectric MEMS speakers. The electric MEMS loudspeaker not only has a large vibration excursion and displacement of the diaphragm, but also does not produce the leakage of the sound pressure level. There are no reports so far. With the development of wearable electronic devices, piezoelectric MEMS speakers with better performance, full frequency coverage and higher sound pressure level have become an inevitable trend.

SUMMARY OF THE INVENTION

Aiming at the defects in the prior art, a closed diaphragm piezoelectric MEMS speaker and a preparation method thereof are proposed.

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

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

The second electrode, the piezoelectric layer and the first electrode are sequentially etched to obtain the patterned second electrode, the piezoelectric layer and the first electrode. and the first electrode to form a patterned vibrating film unit; the patterned vibrating film unit has six triangles of the same size, and the six triangles are arranged next to each other along the circumferential direction and share the same vertex;

The substrate is etched, and groove gaps in a radial distribution are etched on the substrate, and the size of the groove gap matches the length of the two sides of the triangle, that is, between two adjacent triangles There is a gap, and the third sides of the six triangular unetched trench gaps are used as bound edge parts, and the third sides of the six triangles are connected end to end to form a closed hexagon; the The patterned vibrating membrane unit shares a first electrode and a second electrode to obtain a device;

depositing a layer of encapsulation material on the upper surface of the device to close the sidewall and bottom of the trench gap;

The lower surface of the device is etched to form a back cavity on the back of the patterned diaphragm unit, and the outer contour of the back cavity covers the outer contour of the patterned diaphragm unit.

In the above preparation steps, before the back cavity is etched, the etched trench gap is sealed; and a thin film can be deposited to seal the gap by depositing a packaging material on the bottom substrate to provide a deposition surface. Otherwise, after the back cavity is etched, the trench gap is encapsulated, resulting in a gap that is too large, so that the deposition thickness must be larger than the gap to close the gap, not only the film is too thick, but also the film width is too narrow, which is the same as the gap width. When vibrating in this way, the effect of large vibration displacement cannot be achieved. By sealing the etched groove gap, the vibrating membrane is transformed from an unclosed structure to a closed structure to prevent the leakage of air flow and sound pressure level, so that the prepared piezoelectric MEMS speaker has a large vibration offset displacement of the unclosed membrane. At the same time, it also has the advantage that the closed membrane does not leak the sound pressure level.

The pattern of the patterned vibrating membrane is aimed at but not limited to six triangular vibrating membrane units with the same size, and is also applicable to all graphics such as triangle, trapezoid, circle, ring and square.

Preferably, the second electrode, the piezoelectric layer and the first electrode are sequentially etched to obtain the patterned second electrode, the piezoelectric layer and the first electrode. The piezoelectric layer and the first electrode form a patterned vibrating film unit; wherein, the second electrode, the piezoelectric layer and the first electrode are arranged in a regular hexagon pattern along the regular hexagon. Three mutually intersecting diagonal lines of the shaped pattern are etched to obtain a second electrode having six triangles, a piezoelectric layer having six triangles, and a first electrode having six triangles.

The etching lines are aimed at, but not limited to, three-cross etching lines, and are also applicable to all number of cross-cut etching lines, such as cross-cross etching lines and four-cross etching lines.

Preferably, the edge of the piezoelectric layer with six triangles is larger than the edge of the second electrode with six triangles, so as to isolate the second electrode from the first electrode and avoid communication between the upper and lower electrodes.

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

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

Preferably, the substrate adopts any one of SOI wafer, flexible substrate, metal substrate or non-metallic substrate.

More preferably, the non-metallic substrate can be a flexible material substrate such as PDMS (polydimethylsiloxane), PE (polyethylene), PI (polyimide).

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

Preferably, the material of the piezoelectric layer is 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 (polyparadichlorotoluene), PI (polyimide), silicone rubber, and epoxy resin.

Preferably, the cavity of the back cavity is a regular hexagonal hollow space.

A second aspect of the present invention provides a piezoelectric MEMS speaker, which is prepared by the above-mentioned method for preparing a closed diaphragm piezoelectric MEMS speaker.

Preferably, a piezoelectric MEMS speaker, comprising:

base,

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

The base, the first electrode, the piezoelectric layer and the second electrode form a vibrating membrane structure with a regular hexagon, and the regular hexagonal vibrating membrane structure is divided by three diagonal lines. Six triangles of equal size are formed, and trench gaps are arranged between adjacent triangles; an encapsulation layer is arranged on the surface of the regular hexagonal vibrating membrane structure, the sidewalls and the bottom of the trench gap, so that all the The side walls and bottom of the groove gap are closed;

The back of the vibrating membrane structure is provided with a back cavity of a hollow cavity which is recessed upward, and a layer of the encapsulation layer is spaced between the cavity of the back cavity and the groove gap; and the outer contour of the back cavity is cover the outer contour of the regular hexagonal vibrating membrane structure.

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

In the above preparation method of the present invention, by depositing a layer of encapsulation material on the upper surface and the etched sidewall and bottom of the gap before the back cavity is etched, the gap of the non-closed vibrating membrane is subtly closed to prevent airflow and sound pressure. Therefore, the prepared piezoelectric MEMS speaker has the advantages of not sealing the membrane and large vibration displacement, and at the same time, it also has the advantages of not leaking the sound pressure level of the sealing membrane; the prepared MEMS speaker completely covers the human ear can hear It can reach the frequency range of 20Hz-20000Hz, and can reach the sound pressure level enough for commercial applications, with compact structure, small size and excellent performance; it can be used in mobile phone speakers, earphones, hearing aids and other wearable electronic devices.

Description of drawings

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

FIG. 1 is a schematic flowchart of a method for preparing a piezoelectric MEMS speaker with a closed vibrating membrane according to a preferred embodiment of the present invention;

2 is a front view of a device according to a preferred embodiment of the present invention;

3 is a view of the back cavity of the device according to a preferred embodiment of the present invention;

4 is a front view of the device surface after depositing Parylene C according to a preferred embodiment of the present invention;

5 is a cross-sectional view of the device surface after depositing ParyleneC according to a preferred embodiment of the present invention;

The marks in the figure are respectively: the second electrode pad 1, the first electrode pad 2, the trench gap 3, the six triangular vibrating membranes 4, the substrate 5, the back cavity 6, and the ParyleneC7.

Detailed ways

The present invention will be described in detail below with reference to specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that, for those skilled in the art, several modifications and improvements can be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

Example 1

Referring to FIG. 1, it is a flow chart of a method for preparing a closed diaphragm piezoelectric MEMS speaker according to a preferred embodiment of the present invention, including the following steps:

S1, as shown in (a) in Figure 1, sputtering Pt with a thickness of 100 nm on the SOI wafer substrate to obtain a first electrode; sputtering a PZT material with a thickness of 1 μm on the first electrode to obtain a piezoelectric layer; Sputtering Pt with a thickness of 100 nm on the piezoelectric layer to obtain the second electrode; complete the preparation of the PZT-SOI wafer;

On the front side of the prepared PZT-SOI wafer, a photoresist of 5 μm was coated, pre-baked for 90 s, exposed for 45 s, developed for 45 s, rinsed with deionized water for 30 s, blown dry with nitrogen, post-baked for 12 min, and then etched by ion beam for a second time. After 8 minutes of layer electrodes, the patterning of the second layer electrodes was completed, and the glue was removed; the second layer electrodes with six triangular patterns were obtained. As a preferred way, ion beam is used to etch the second electrode; the specific etching process is carried out in a regular hexagonal pattern with a side length of 1 mm, and is etched along three mutually intersecting diagonal lines of the regular hexagonal pattern. , six triangular patterns with the same size are obtained; the etching gap is 50 μm. The line width for connecting the second electrode square pad 1 is 30 μm, and the length and width of the second electrode square pad are both 300 μm.

S2. As shown in (b) of Figure 1, coat photoresist 5μm on the front side, pre-bake for 90s, expose for 45s, develop for 45s, rinse with deionized water for 30s, blow dry with nitrogen, post-bake for 12min, and wet-etch PZT 90s. Then, the PZT was immersed in the prepared etching solution for etching, and the width of the PZT etching groove was 20 μm; the etching solution was stirred with a magnetic stirrer to improve the etching uniformity and speed; then the etched PZT -SOI is soaked in the prepared HNO ₃ solution for 3 minutes; finally, it is soaked in deionized water for a few minutes to clean and remove surface impurities. Blow dry with nitrogen and vacuum dried; six triangular shaped piezoelectric layers are obtained; and the edge of the six triangular shaped piezoelectric layers is 30 μm larger than the second layer electrode of the six triangular shaped shaped electrodes to isolate the second electrode and avoid The second electrode communicates with the first electrode up and down.

As a preferred way, in the above steps, the etching solution of PZT can be prepared by the following method: first, 0.6g NH ₄ F is slowly added into 1ml deionized water, and stirred continuously until it is completely dissolved; then 1ml NH ₄ F (40% ) slowly poured into 5ml HF solution, stirring constantly to make it evenly mixed to form a BHF solution; then 1ml BHF, 25ml HCl and 100ml H ₂ O were prepared to complete the etching mixture, fully stirred to make it fully mixed; then The PZT was immersed in the etching solution for etching, and the etching solution was stirred with a magnetic stirrer to improve the etching uniformity and speed.

As a preferred manner, in the above steps, the stirring speed during PZT etching is 130 r/min, and the stirring temperature during PZT etching is normal temperature.

As a preferred mode, in the above steps, the required HNO solution can be prepared by the following method _{: put 10ml HNO into 13ml H 2 O to} form a solution, and stir evenly.

S3. As shown in (c) in Figure 1, the front side is coated with photoresist of 5 μm, pre-baked for 90s, exposed for 45s, developed for 40s, rinsed with deionized water for 30s, blown dry with nitrogen, post-baked for 12min, and then etched by ion beam The first electrode is Pt8min, the etching gap is 20 μm, the patterning of the first electrode is completed, the glue is removed, and six triangular first electrodes with the same size are obtained. Wet etching PZT to form a first electrode square pad with a length and a width of 300 μm.

S4. As shown in (d) in Figure 1, the front side is coated with photoresist of 5 μm, the NMC medium is etched with 0.5 μm SiO ₂ , the NMC deep silicon is etched with 2 μm Si, the NMC medium is etched with 1.1 μm SiO ₂ , and the NMC deep silicon is etched About 15 μm Si was etched to form six trench gaps with the same size, and the length of the trench gaps matched the length of the triangle sides; Si and SiO ₂ were etched with trench widths of 5 μm; devices were obtained.

S5. As shown in (e) in Figure 1, Parylene C is deposited on the surface of the device and the gap sidewalls and bottom of the gap of the trench. The thickness of the Parylene C deposition is 0.5 μm, which closes the etched trench gap.

S6. As shown in (f) of Figure 1, the front side is coated with 5μm photoresist for protection, the back side is coated with 20μm photoresist, pre-baking for 2min, developing for 130s, rinsing with deionized water for 30s, blowing dry with nitrogen, and post-baking for 12min, NMC dielectric etch 1.5μm SiO ₂ , NMC deep silicon etch 600μm Si, then NMC deep silicon etch 1.1μm intermediate buried oxide layer SiO ₂ , the gap between the back cavity and the vibrating membrane is completed; the ratio of the radius of the back cavity The outline of the second electrode is 0.2mm larger to ensure that the back cavity can cover the entire front diaphragm.

The structure of the piezoelectric MEMS speaker obtained by the above steps is shown in FIG. 2 , FIG. 3 , FIG. 4 and FIG. 5 . In the figure, the device includes a second electrode pad 1 , a first electrode pad 2 , a gap 3 , six The triangular vibrating membrane 4, the base 5, the back cavity 6 and the Parylene C 7; it can be seen from the figure that the six triangular vibrating membranes 4 include six triangles of equal size, and the six triangles are arranged next to each other in the circumferential direction and share the same one Vertex; composed of six triangular diaphragms 4 as a whole to form a regular hexagonal diaphragm that is not closed in the middle; a layer of Parylene C 7 is deposited on the surface of the device, and Parylene C 7 covers the gap sidewall surface and gap of the trench gap It is closed on the bottom surface; on the back of the six triangular vibrating membranes 4, a back cavity 6 with an upwardly concave hollow cavity is arranged, and a layer of Parylene C 7 is separated between the cavity of the back cavity 6 and the groove gap. Convert the diaphragm from non-closed to closed.

Example 2

Referring to FIG. 1, it is a flow chart of a method for preparing a closed diaphragm piezoelectric MEMS speaker according to a preferred embodiment of the present invention, including the following steps:

S1, as shown in FIG. 1 (a), sputtering Pt with a thickness of 120 nm on the SOI wafer substrate to obtain a first electrode; sputtering a PZT material with a thickness of 2 μm on the first electrode to obtain a piezoelectric layer; Pt with a thickness of 120 nm was sputtered on the piezoelectric layer to obtain the second electrode; the preparation of the PZT-SOI wafer was completed; the front side of the prepared PZT-SOI wafer was coated with a photoresist of 5 μm, pre-baked for 90 s, and exposed to light 45s, develop for 50s, rinse with deionized water for 30s, blow dry with nitrogen, post-bake for 12min, then use ion beam to etch the upper electrode (second electrode) Pt for 8min, the patterning of the upper electrode is completed, and the glue is removed;

As a preferred way, the six etched triangular vibrating membrane units as a whole form a regular hexagonal vibrating membrane whose middle is not closed, that is, the six etched triangles share a vertex and are connected to each other; The offset is large, and the sound pressure level is prevented from leaking. The side length of the regular hexagon may be 0.5mm.

As a preferred manner, the six triangular vibrating membrane units are symmetrically arranged along the intersections of three mutually intersecting diagonal lines of the regular hexagonal vibrating membrane; the etching gap is 40 μm.

As a preferred manner, the line width connecting the square pads is 20 μm, and the length and width of the square pads are both 200 μm.

S2. As shown in (b) of Figure 1, coat photoresist 5μm on the front side, pre-bake for 90s, expose for 45s, develop for 50s, rinse with deionized water for 30s, blow dry with nitrogen, post-bake for 12min, and wet-etch PZT for 90s . Then, the PZT was immersed in the prepared etching solution for etching, and a magnetic stirrer was used to stir the etching solution to improve the etching uniformity and speed; then the etched PZT-SOI was placed in the prepared HNO ₃ Soak in the solution for 3 minutes; finally, soak in deionized water for a few minutes to clean and remove surface impurities. Dry under nitrogen and vacuum dry. The edges of the six triangular piezoelectric layers etched by PZT are 30 μm larger than the outline of the second electrode to isolate the second electrode and prevent the upper and lower electrodes from being connected. The width of the PZT etched trench is 10 μm.

As a preferred way, the etching solution of PZT in the above steps can be prepared by the following method: first, 0.6g NH ₄ F is slowly added into 1ml deionized water, and stirred continuously until it is completely dissolved; then 1ml NH ₄ F (40%) Slowly pour it into 5ml of HF solution, stir continuously to make it evenly mixed to form a BHF solution; then prepare 1ml of BHF, 25ml of HCl and 100ml of H ₂ O to complete the etching mixture, stir well to make it fully mixed; then PZT is immersed in the etching solution for etching, and a magnetic stirrer is used to stir the etching solution to improve the etching uniformity and speed;

As a preferred manner, in the above steps, the stirring speed during PZT etching is 120 r/min, and the stirring temperature during PZT etching is normal temperature.

As a preferred way, in the above steps, the required HNO ₃ solution is prepared by the following method: put 11 ml of HNO ₃ into 14 ml of H ₂ O to form a solution, and stir evenly.

S3. As shown in (c) in Figure 1, the front side is coated with photoresist of 5 μm, pre-baking 90s, exposing 50s, developing 40s, rinsing with deionized water for 30s, blowing dry with nitrogen, post-baking 12min, and then using ion beam etching The lower electrode was Pt for 8min, the patterning of the lower electrode was completed, the glue was removed, and six triangular first electrodes with the same size were obtained. After wet etching PZT, the length and width of the bottom electrode square pad are 200 μm.

As a preferred embodiment, the ion beam etching gap of the lower electrode Pt is 10 μm.

S4. As shown in (d) of Figure 1, the front side is coated with photoresist of 5 μm, the NMC medium is etched with 0.5 μm SiO ₂ , the NMC deep silicon is etched with 2 μm Si, the NMC medium is etched with 1.1 μm SiO ₂ , and the NMC deep silicon is etched 20μm Si was etched to form six triangular diaphragm trench gaps with the same size. The widths of the Si and SiO ₂ etched trenches are both 10 μm.

S5. As shown in (e) of FIG. 1, Parylene C is deposited on the surface of the device surface and the surface of the gap sidewall of the trench gap and the surface of the gap bottom. The Parylene C deposition thickness is 1 μm. The etched trench gap is closed.

S6. As shown in (f) of Figure 1, the front side is coated with 5μm photoresist for protection, the back side is coated with 20μm photoresist, pre-baking for 2min, developing for 130s, rinsing with deionized water for 30s, blowing dry with nitrogen, and post-baking for 12min, NMC dielectric etch 1.5μm SiO ₂ , NMC deep silicon etch 600μm Si, then NMC deep silicon etch 1.1μm intermediate buried oxide layer SiO ₂ , the gap between the back cavity and the vibrating membrane is completed; the ratio of the radius of the back cavity The upper electrode is 0.25mm larger to ensure that the back cavity can cover the entire front diaphragm.

In specific implementation, the etching PZT method in the above-mentioned embodiment is aimed at but not limited to wet etching, and is also applicable to all kinds of dry etching such as ion beam etching, laser cutting and other technologies that can be prepared into grooves; The Si and SiO ₂ etching method is aimed at, but not limited to, dry etching, and is also applicable to all techniques that can form trenches, such as wet etching and laser cutting.

Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various variations or modifications within the scope of the claims, which do not affect the essence of the present invention.

Claims (8)

1. a preparation method of a closed vibrating film piezoelectric MEMS loudspeaker, is characterized in that, comprises: preparing a first electrode on the substrate, preparing a piezoelectric layer on the first electrode, and preparing a second electrode on the piezoelectric layer; The second electrode, the piezoelectric layer and the first electrode are sequentially etched to obtain the patterned second electrode, the piezoelectric layer and the first electrode. and the first electrode form a patterned vibrating film unit; the patterned vibrating film unit is a triangle with six identical dimensions, and the six triangles are arranged next to each other along the circumferential direction and share the same vertex; The substrate is etched, and groove gaps in a radial distribution are etched on the substrate, and the size of the groove gap matches the length of the two sides of the triangle, that is, between two adjacent triangles There is a gap, and the third side of the six triangular unetched trench gaps is used as a bound edge part, and the third sides of the six triangles are connected end to end to form a closed hexagon; the figure The modified vibrating film unit shares a first electrode and a second electrode to obtain a device; A layer of packaging material is deposited on the upper surface of the device to close the sidewalls and bottom of the trench gap; the width of the trench gap is 3 μm-20 μm; the depth of the trench gap is 5 μm-100 μm ; etching the lower surface of the device to form a back cavity on the back of the patterned vibrating membrane unit, and the outer contour of the back cavity covers the outer contour of the patterned vibrating membrane 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 entire patterned diaphragm unit. 2. The method for preparing a closed-type vibrating film piezoelectric MEMS speaker according to claim 1, wherein the second electrode, the piezoelectric layer and the first electrode are sequentially etched, The patterned second electrode, the piezoelectric layer and the first electrode are obtained, and the patterned second electrode, the piezoelectric layer and the first electrode constitute a patterned vibrating membrane unit; wherein the second electrode, the piezoelectric layer and the The electrical layer and the first electrode are in a regular hexagonal pattern, and the second electrode with six triangles is obtained by etching along three mutually intersecting diagonal lines of the regular hexagonal pattern. The piezoelectric layer and the first electrode with six triangles. 3. The method for preparing a closed diaphragm piezoelectric MEMS speaker according to claim 2, wherein the edge of the piezoelectric layer with six triangles is larger than the edge of the second electrode with six triangles , so as to isolate the second electrode from the first electrode and avoid communication between the upper and lower electrodes. 4. the preparation method of a kind of closed vibrating film piezoelectric MEMS speaker according to any one of claim 1-3, it is characterized in that, described substrate adopts SOI wafer, flexible substrate, metal substrate or non-metallic substrate in either. 5. the preparation method of a kind of closed vibrating film piezoelectric MEMS speaker according to any one of claim 1-3, is characterized in that, has following one or more features: -The material of the first electrode and the second electrode is any one of Pt, Au, Cr or Al; - the material of the piezoelectric layer is any one of PZT piezoelectric ceramics, ZnO, AlN, PMN-PT or PVDF; -The encapsulation material is any one of Parylene C, PI, silicone rubber, and epoxy resin. 6 . The method for preparing a closed diaphragm piezoelectric MEMS speaker according to claim 1 , wherein the cavity of the back cavity is a regular hexagonal hollow space. 7 . 7 . A piezoelectric MEMS speaker, characterized in that, it is prepared by the method for preparing a closed diaphragm piezoelectric MEMS speaker according to any one of claims 1 to 6 . 8. The piezoelectric MEMS speaker according to claim 7, characterized in that, comprising: base, and a first electrode, a piezoelectric layer and a second electrode sequentially arranged above the substrate; The base, the first electrode, the piezoelectric layer and the second electrode form a vibrating membrane structure with a regular hexagon, and the regular hexagonal vibrating membrane structure is divided by three diagonal lines. Six triangles of equal size are formed, and trench gaps are arranged between adjacent triangles; an encapsulation layer is arranged on the surface of the regular hexagonal vibrating membrane structure, the sidewalls and the bottom of the trench gap, so that all the The side walls and bottom of the groove gap are closed; The back of the vibrating membrane structure is provided with a back cavity of a hollow cavity which is recessed upward, and a layer of the encapsulation layer is spaced between the cavity of the back cavity and the groove gap; and the outer contour of the back cavity is cover the outer contour of the regular hexagonal vibrating membrane structure.

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