Fixed end beam-cantilever beam type piezoelectric MEMS loudspeaker and preparation method and application thereof

Abstract

The invention discloses a fixed end beam-cantilever beam type piezoelectric MEMS loudspeaker and a preparation method and application thereof. The piezoelectric MEMS loudspeaker comprises a substrate, an upper electrode, a piezoelectric layer, a lower electrode and a vibrating membrane, the upper electrode, the piezoelectric layer and the lower electrode are sequentially arranged on the substrate, and the vibrating membrane and an etching gap surrounding the vibrating membrane are formed on the upper electrode, the piezoelectric layer and the lower electrode in an etching mode; the vibration displacement of the fixed end beam-cantilever beam type piezoelectric MEMS loudspeaker is very large, and is mainly attributed to the superposition of the vibration displacement of the fixed end beam and the vibration displacement of the cantilever beam.

Description

Technical Field

[0001] The present invention relates to the technical field of speakers, and in particular to a fixed-end beam-cantilever beam type piezoelectric MEMS speaker and its preparation method and application. Background Art

[0002] A speaker is a transducer that converts an electrical signal into a sound signal and is widely present in all aspects of life. The rapid development of MEMS (Micro-Electro-Mechanical Systems) technology has made piezoelectric MEMS speakers gradually tend to be miniaturized, integrated, lightweight, and low-power consumption, and has made it possible to become a potential alternative to traditional speakers.

[0003] A piezoelectric MEMS speaker realizes mechanical vibration based on the inverse piezoelectric effect of a piezoelectric material, thereby driving air vibration and generating sound pressure output, and has advantages such as miniaturization, integration, low power consumption, and high sound pressure level. Generally speaking, piezoelectric materials such as ZnO, AlN, AlScN, and PZT can all be used to prepare piezoelectric speakers. PZT piezoelectric materials have become the most widely used piezoelectric material due to their high piezoelectric constant and electromechanical coupling coefficient. However, piezoelectric MEMS speakers face the problem of relatively small vibration displacement of the vibrating membrane.

[0004] In the prior art, Haoran Wang, Zhenfang Chen et al. wrote "A high-SPL piezoelectric MEMS loud speaker based on thinceramic PZT" in Sensors and Actuators A: Physical. It reported a circular thin-film diaphragm with relatively small vibration displacement, which hindered the further improvement of its sound pressure level. Yu-Tzu Lin, Sung-Cheng Lo et al. wrote "Two-way piezoelectric MEMS microspeaker with novel structure and electrode design for bandwidth enhancement" in the proceedings of the "2021 21st International Conference on Solid-State Sensors, Actuators and Microsystems (Transducers)". It introduced a piston-type piezoelectric MEMS speaker, but its edge structure had relatively large stress, resulting in relatively small vibration displacement. Yi-Jia Wang, Mingching Wu et al. wrote "Multi-way in-phase / out-of-phase driving cantilever array for performance enhancement of PZT MEMS microspeaker" in the proceedings of the "2021 IEEE 34rd International Conference on Micro Electro Mechanical Systems (MEMS)". It introduced a cantilever diaphragm composed of four cantilevers with different sizes. Although the vibration displacement of the cantilever was larger than that of the thin-film and piston diaphragms, it was still relatively small overall.

[0005] The patent document with the application number 2025102124596 and the patent name of a center-constrained piezoelectric MEMS speaker and its preparation method and application has relatively small vibration displacement.

[0006] In summary, for the piezoelectric MEMS speakers reported currently, under the same vibration membrane area and driving voltage, compared with the thin film type and piston type structures, the vibration displacement of the cantilever beam type vibration membrane is larger. Therefore, we choose to study the cantilever beam type piezoelectric MEMS speaker. However, for the current cantilever beam type piezoelectric MEMS speakers, the sound pressure level generated by them still cannot meet the commercialization requirements. Structurally speaking, there is still a large room for improvement in their vibration displacement. For the fixed-end beam - cantilever beam type piezoelectric MEMS speaker, it has the advantage of the superposition of the vibration displacements of the fixed-end beam and the cantilever beam. For the piezoelectric MEMS speaker with a fixed-end beam - cantilever beam structure, there is no report currently. With the development trend of the miniaturization of electronic devices, piezoelectric MEMS speakers with better performance, full coverage of frequencies, and higher sound pressure levels have become an inevitable trend. Summary of the Invention

[0007] In order to solve the deficiencies of the above technical solutions, the purpose of the present invention is to provide a fixed-end beam - cantilever beam type piezoelectric MEMS speaker, its preparation method and application.

[0008] The purpose of the present invention is achieved through the following technical solutions.

[0009] A fixed-end beam - cantilever beam type piezoelectric MEMS speaker includes a substrate, an upper electrode, a piezoelectric layer, a lower electrode, and a vibration membrane. The upper electrode, the piezoelectric layer, and the lower electrode are sequentially arranged on the substrate. The vibration membrane and an etching gap surrounding the vibration membrane are etched on the upper electrode, the piezoelectric layer, and the lower electrode.

[0010] The structure of the vibration membrane includes a connection unit, a fixed-end beam unit, and at least one cantilever beam unit. The cantilever beam units are arranged at intervals and are connected through the connection unit. Each connection unit intersects with the fixed-end beam unit. Both ends of the fixed-end beam unit are connected to the upper electrode, the piezoelectric layer, and the lower electrode.

[0011] A trench gap is arranged on the upper part of the substrate. The trench gap communicates with the etching gap. A back cavity is arranged on the lower part of the substrate. The outer contour of the back cavity covers the outer contour of the vibration membrane.

[0012] In the above technical solution, the back cavity corresponds to the vibration membrane up and down.

[0013] In the above technical solution, the shape of the cantilever beam unit is one or more of semi-circular, square, and rectangular.

[0014] In the above technical solution, the number of the cantilever beam units is one, two, three, cross-shaped, or three-cross-shaped.

[0015] In the above technical solution, in step 1, the substrate is an SOI wafer, diamond, sapphire, flexible substrate, metal substrate or non-metal substrate.

[0016] In the above technical solution, in step 1, the non-metal substrate is a flexible material substrate of mica sheet, PDMS (polydimethylsiloxane), PE (polyethylene) or PI (polyimide).

[0017] In the above technical solution, in step 1, the materials of the lower electrode and the upper electrode are both one or a mixture of more than one of Pt (platinum), Ti (titanium), Au (gold), Ag (silver), Cr (chromium) and Al (aluminum).

[0018] In the above technical solution, in step 1, the material of the piezoelectric layer is one or a mixture of more than one of PZT piezoelectric ceramics, lead zirconate titanate piezoelectric ceramics, ZnO (zinc oxide), AlN (aluminum nitride), AlScN (scandium-doped aluminum nitride), PMN-PT (lead magnesium niobate-lead titanate), PVDF (polyvinylidene fluoride) and P(VDF-TrFE) poly(vinylidene fluoride-copolymer trifluoroethylene).

[0019] In the above technical solution, in step 1, the thickness of the piezoelectric layer material ≤ 50 μm.

[0020] In the above technical solution, in step 3, the width of the trench gap ≤ 100 μm; the depth of the trench gap ≤ 100 μm.

[0021] Another aspect of the present invention further includes a preparation method of a fixed-end beam-cantilever beam type piezoelectric MEMS speaker, comprising the following steps:

[0022] Step 1, sequentially prepare a lower electrode, a piezoelectric layer and an upper electrode on the substrate, and the substrate is a multi-layer structure;

[0023] Step 2, etch the upper electrode, the piezoelectric layer and the lower electrode in sequence until etching reaches the upper surface of the substrate. After etching is completed, a vibrating membrane is formed, wherein the vibrating membrane includes a patterned upper electrode, a patterned piezoelectric layer and a patterned lower electrode;

[0024] Step 3, continue to etch downward from the upper surface of the substrate until etching reaches the upper surface of one layer in the multi-layer structure of the substrate, forming the trench gap of the vibrating membrane;

[0025] Step 4, etch upward from the lower surface of the substrate until etching reaches the upper surface of one layer in the multi-layer structure of the substrate described in step 3, forming a back cavity.

[0026] In the above technical solution, in step 2, the size of the patterned piezoelectric layer is larger than the size of the patterned upper electrode to isolate the upper electrode and the lower electrode and prevent electrical connection between the upper electrode and the lower electrode.

[0027] Another aspect of the present invention further includes the application of the fixed-end beam - cantilever beam piezoelectric MEMS speaker in mobile phones, earphones, computers, hearing aids, human - machine interaction, and the Internet of Things.

[0028] The advantages and beneficial effects of the present invention are as follows:

[0029] 1. For the fixed - end beam - cantilever beam piezoelectric MEMS speaker of the present invention, the vibration membrane is arranged with the advantage of displacement superposition.

[0030] 2. The vibration displacement of the fixed - end beam - cantilever beam piezoelectric MEMS speaker of the present invention is very large, mainly due to the superposition of the vibration displacements of the fixed - end beam and the cantilever beam.

[0031] 3. The MEMS speaker of the present invention fully covers the frequency range of 20 Hz - 20000 Hz that the human ear can hear, and can reach a sound pressure level sufficient to meet commercial applications, with a compact structure and a small volume. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a top view of the speaker device according to Embodiment 1 of the present invention;

[0033] Figure 2 It is a bottom view of the speaker according to Embodiment 1 of the present invention;

[0034] Figure 3 It is a preparation schematic diagram of Embodiment 2 of the present invention.

[0035] Wherein, 1: substrate, 2: lower electrode, 3: upper electrode, 4: cantilever beam unit, 5: connection unit, 6: fixed - end beam unit, 7: etching gap, 8: back cavity. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0036] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0037] Embodiment 1

[0038] As Figure 1 - Figure 2 shown, a fixed - end beam - cantilever beam piezoelectric MEMS speaker includes a substrate 1, an upper electrode 3, a piezoelectric layer, a lower electrode 2, and a vibration membrane. The upper electrode 3, the piezoelectric layer, and the lower electrode 2 are sequentially arranged on the substrate 1, and the upper electrode 3, the piezoelectric layer, and the lower electrode 2 are sequentially etched to form the vibration membrane and an etching gap 7 surrounding the vibration membrane;

[0039] The structure of the vibrating membrane includes a connecting unit 5, a fixed-end beam unit 6, and at least one cantilever beam unit 4. The cantilever beam units 4 are arranged at intervals and are connected through the connecting unit 5. Each connecting unit 5 is arranged crosswise with the fixed-end beam unit 6. The two ends of the fixed-end beam unit 6 are respectively connected to the upper electrode 3, the piezoelectric layer, and the lower electrode 2;

[0040] A trench gap is provided on the upper part of the substrate 1. The trench gap is communicated with the etching gap 7. A back cavity 8 is provided on the lower part of the substrate 1. The back cavity 8 corresponds to the vibrating membrane up and down. The outer contour of the back cavity 8 covers the outer contour of the vibrating membrane.

[0041] Further, the shape of the cantilever beam unit 4 is rectangular. There is one cantilever beam unit 4. The substrate 1 is an SOI wafer. The materials of the upper electrode 3 and the lower electrode 2 are both Pt (platinum). The material of the piezoelectric layer is PZT piezoelectric ceramic. The SOI wafer includes an upper silicon dioxide layer, an upper silicon layer, a lower silicon dioxide layer, and a lower silicon layer from top to bottom.

[0042] Embodiment 2

[0043] This embodiment provides a method for fabricating a fixed-end beam-cantilever beam type piezoelectric MEMS speaker described in Embodiment 1, including the following steps:

[0044] As <> Figure 3 in (a), Step 1, Preparation of PZT-SOI wafer: Sputter Pt on the SOI wafer substrate 11 to obtain the lower electrode 2; Sputter a PZT material with a thickness of 2 μm on the lower electrode 2 to obtain the piezoelectric layer; Sputter Pt on the piezoelectric layer to obtain the upper electrode 3. The preparation of the PZT-SOI wafer is completed. Specifically, in this embodiment, the SOI wafer includes an upper silicon dioxide layer, an upper silicon layer, a lower silicon dioxide layer, and a lower silicon layer from top to bottom.

[0045] As <> Figure 3 in (b)-(d), Step 2, Etch the upper electrode 3, the piezoelectric layer, and the lower electrode 2 in sequence until etching reaches the upper surface of the substrate 1. After etching is completed, a vibrating membrane is formed. Among them, the vibrating membrane includes a patterned upper electrode 3, a patterned piezoelectric layer, and a patterned lower electrode 2.

[0046] Further, as <> Figure 3 in (b), Pattern the upper electrode 3: Coat photoresist on the upper surface of the upper electrode 3, pre-bake, expose, develop, rinse with deionized water, dry with nitrogen, harden the film, use ion beam etching to etch the upper electrode 3 to obtain a patterned upper electrode 3. Remove the photoresist after etching is completed. Further, etch a circuit on the upper electrode 3 and a square upper electrode pad connected to the circuit.

[0047] Further, as <> Figure 3In (c), pattern the piezoelectric layer: coat the upper surface with photoresist, pre-bake, expose, develop, rinse with deionized water, dry with nitrogen, harden the film, soak the piezoelectric layer in an etching solution to etch the piezoelectric layer by wet etching, and use a magnetic stirrer to stir the etching solution to improve the etching uniformity and speed. Then, immerse the etched PZT-SOI wafer in an HNO₃ solution, and then immerse it in deionized water for several minutes to wash away surface impurities, dry with nitrogen, and dry in vacuum to obtain a patterned piezoelectric layer, and remove the photoresist. Further, the outer edge of the etching gap 7 is aligned with the outer edge of the etching gap 7 of the upper electrode 3 to isolate the upper electrode 3 and prevent the upper electrode 3 from communicating with the lower electrode 2 vertically.

[0048] Further, the etching solution is prepared by the following method: first, slowly add 1 g of NH₄F to 1.6 ml of deionized water and continuously stir until completely dissolved; then, slowly pour 1 ml of NH₄F (40%) into 5 ml of HF solution and continuously stir and mix evenly to form a BHF solution; then, mix the BHF solution, hydrochloric acid, and water in a volume ratio of 1:25:200, stir well, and mix evenly to obtain the etching solution.

[0049] Further, the HNO₃ solution is obtained by mixing nitric acid and water in a volume ratio of 1:2 and stirring evenly.

[0050] Further, as Figure 1 In (d), pattern the lower electrode 2: coat the upper surface with photoresist, pre-bake, expose, develop, rinse with deionized water, dry with nitrogen, harden the film, etch the lower electrode 2 by ion beam etching to obtain a patterned lower electrode 2, remove the photoresist, and further, etch a square lower electrode pad connected to the circuit on the lower electrode 2.

[0051] As Figure 3 In (e), step 3, coat the upper surface with photoresist, and continue to etch the upper silicon dioxide layer, the upper silicon layer, and the lower silicon dioxide layer sequentially downward from the upper surface of the SOI wafer substrate 1 using NMC medium to form a trench gap.

[0052] As Figure 3 In (f), step 4, coat photoresist on both the upper surface and the lower surface of the substrate 1, pre-bake, develop, rinse with deionized water, dry with nitrogen, harden the film, etch the lower silicon dioxide layer upward using NMC medium to form a back cavity 8; the outer contour width of the cross-section of the back cavity 8 is greater than the outer contour of the cross-section of the vibrating membrane to ensure that the back cavity 8 can cover the entire vibrating membrane.

[0053] In specific implementation, the etching method in the above embodiments is applicable to, but not limited to, wet etching, and also applicable to various dry etching methods such as ion beam etching, and all technologies that can be used to prepare grooves such as laser cutting; the Si and SiO2 etching methods are applicable to, but not limited to, dry etching, and also applicable to wet etching, laser cutting, and all technologies that can be used to prepare grooves.

[0054] The above provides an exemplary description of the present invention. It should be noted that without departing from the core of the present invention, any simple deformation, modification, or equivalent replacement that can be made by those skilled in the art without creative efforts falls within the protection scope of the present invention.

Claims

1. A fixed-end beam - cantilever beam type piezoelectric MEMS speaker, characterized in that, It includes a substrate, an upper electrode, a piezoelectric layer, a lower electrode and a vibrating membrane. The upper electrode, the piezoelectric layer and the lower electrode are sequentially arranged on the substrate. The vibrating membrane and an etching gap surrounding the vibrating membrane are etched and formed on the upper electrode, the piezoelectric layer and the lower electrode. The structure of the vibrating membrane includes a connecting unit, a fixed-end beam unit and at least one cantilever beam unit. The cantilever beam units are arranged at intervals and communicated through the connecting unit. Each connecting unit is arranged crosswise with the fixed-end beam unit. Both ends of the fixed-end beam unit are connected to the upper electrode, the piezoelectric layer and the lower electrode. A trench gap is arranged on the upper part of the substrate. The trench gap is communicated with the etching gap. A back cavity is arranged on the lower part of the substrate. The outer contour of the back cavity covers the outer contour of the vibrating membrane.

2. The piezoelectric MEMS speaker according to claim 1, wherein The back cavity corresponds to the vibrating membrane up and down.

3. The piezoelectric MEMS speaker according to claim 1, characterized in that, The shape of the cantilever beam unit is one or more of semicircle, square and rectangle. The cantilever beam unit is one, two, three, cross-shaped or triple-cross-shaped.

4. The piezoelectric MEMS speaker according to claim 1, wherein In step 1, the substrate is an SOI wafer, diamond, sapphire, flexible substrate, metal substrate or non-metal substrate. The non-metal substrate is a flexible material substrate such as mica sheet, PDMS, PE or PI. The materials of the lower electrode and the upper electrode are both one or more mixtures of Pt, Ti, Au, Ag, Cr and Al.

5. The piezoelectric MEMS speaker according to claim 1, wherein In step 1, the material of the piezoelectric layer is one or more mixtures of PZT piezoelectric ceramics, lead zirconate titanate piezoelectric ceramics, ZnO, AlN, AlScN, PMN-PT, PVDF and P(VDF-TrFE).

6. The piezoelectric MEMS speaker according to claim 1, wherein In step 1, the thickness of the piezoelectric layer material ≤ 50 μm.

7. The piezoelectric MEMS speaker according to claim 1, wherein In step 3, the width of the trench gap ≤ 100 μm. The depth of the trench gap ≤ 100 μm.

8. The manufacturing method of the fixed-end beam - cantilever beam type piezoelectric MEMS speaker according to any one of claims 1 to 7, characterized in that, It includes the following steps: Step 1, prepare the lower electrode, the piezoelectric layer and the upper electrode on the substrate in sequence. The substrate is a multi-layer structure. Step 2, etch the upper electrode, the piezoelectric layer and the lower electrode in sequence until etching reaches the upper surface of the substrate. After etching is completed, a vibrating membrane is formed. Among them, the vibrating membrane includes a patterned upper electrode, a patterned piezoelectric layer and a patterned lower electrode. Step 3, continue to etch downward from the upper surface of the substrate until etching reaches the upper surface of one layer in the multi-layer structure of the substrate, forming the trench gap of the vibrating membrane. Step 4, etch upward from the lower surface of the substrate until etching reaches the upper surface of one layer in the multi-layer structure of the substrate described in step 3, forming a back cavity.

9. The preparation method according to claim 8, characterized in that, In step 2, the size of the patterned piezoelectric layer is larger than the size of the patterned upper electrode to isolate the upper electrode and the lower electrode and prevent communication between the upper electrode and the lower electrode.

10. Application of the fixed-end beam-cantilever beam type piezoelectric MEMS speaker as described in claim 8 or 9 in mobile phones, headphones, computers, hearing aids, human-computer interaction and the Internet of Things.

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