Piezoelectric MEMS loudspeaker and preparation method thereof
By designing reinforcement ribs under the cantilever piezoelectric diaphragm unit of the piezoelectric MEMS speaker, the twisted mode is suppressed and the resonant frequency is adjusted, and the obvious problem of formant peaks in the middle and high frequency bands of the speaker is solved, and the sound quality is flattened and quality improvement is achieved.
Patent Information
- Application Number
- CN202510229441.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-02-28
- Publication Date
- 2025-05-23
AI Technical Summary
When the piezoelectric MEMS speaker outputs the sound pressure level, formant peaks in the medium and high frequency bands often appear in the sound pressure level frequency response curve, resulting in large distortion of the sound quality output and poor uniformity.
Several reinforcement ribs are designed under each cantilever piezoelectric diaphragm unit to suppress part of the twisted mode when the diaphragm vibrates, and to adjust the resonant working frequency point of each cantilever piezoelectric diaphragm.
Significantly reduce the formant peak in the middle and high frequency bands in the sound pressure level frequency response curve, realize the planarization of the sound pressure level frequency response curve in the middle and high frequency bands, reduce distortion and improve audio quality.
Smart Images
Figure CN120034806A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of MEMS loudspeakers, and in particular to a piezoelectric MEMS loudspeaker and a preparation method thereof. Background Art
[0002] With the continuous development of micro-electromechanical system (MEMS) technology, MEMS speakers have been widely used in portable electronic devices, wearable devices, and augmented reality / virtual reality (AR / VR) devices due to their miniaturization and integration. MEMS speakers convert electrical signals into mechanical vibrations through different driving methods such as electrostatics, electromagnetics or piezoelectrics, and can realize the conversion of sound signals in a very small space. Compared with traditional speakers, MEMS speakers have the advantages of small size, light weight, low power consumption, and fast response speed. They can also be integrated with integrated circuits, thereby simplifying system design and reducing costs.
[0003] Among the many types of MEMS speakers, piezoelectric MEMS speakers have attracted much attention due to their unique advantages. They use the inverse piezoelectric effect of piezoelectric materials, that is, by applying a voltage signal to cause the piezoelectric material to produce mechanical deformation, thereby driving the diaphragm to vibrate and produce sound. With the continuous improvement of piezoelectric material deposition technology, piezoelectric MEMS speakers have attracted widespread attention due to their high integration, low power consumption, high sound pressure level output, and batch preparation. At the same time, their circuit design is relatively simple and does not require complex driving circuits, which makes them have broad application prospects in the consumer electronics market.
[0004] Although piezoelectric MEMS speakers have the above advantages, achieving high sound pressure level and wide-band response with limited design area is still an issue that needs to be considered in the design of piezoelectric MEMS speakers. A piezoelectric MEMS speaker with a multi-cantilever diaphragm uses the resonance of multiple piezoelectric diaphragms at different resonant frequencies to achieve a balance between high sound pressure level and wide-band response in a limited design area. However, when outputting the sound pressure level, due to the inherent vibration mode of each diaphragm, obvious resonance peaks often appear in the sound pressure level frequency response curve, which will lead to increased audio output distortion and unevenness, affecting the clarity and consistency of the sound quality. Summary of the invention
[0005] In order to solve the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a piezoelectric MEMS speaker and a preparation method thereof, which adopts a method of designing several reinforcing ribs under each cantilever piezoelectric diaphragm unit to adjust the resonant operating frequency point of each cantilever piezoelectric diaphragm unit and suppress some distortion modes when the diaphragm vibrates, aiming to solve the problem of obvious resonance peaks in the mid- and high-frequency bands in the sound pressure level frequency response curve of the multi-cantilever diaphragm piezoelectric MEMS speaker, resulting in large distortion and poor uniformity of sound quality output.
[0006] In order to achieve the above technical objectives, the present invention provides the following technical solutions: A piezoelectric MEMS speaker, comprising: substrate support layer; A multi-cantilever piezoelectric diaphragm array is disposed above the substrate support layer, and one side of its edge is fixedly connected to the substrate support layer; A plurality of reinforcing ribs are arranged below the multi-cantilever piezoelectric diaphragm array, formed by etching the SOI wafer substrate silicon and the SOI wafer buried oxide layer, and form an integrated structure with the multi-cantilever piezoelectric diaphragm array; A reinforcing rib is designed under the multi-cantilever piezoelectric diaphragm array to suppress some distortion modes of the multi-cantilever piezoelectric diaphragm array, and the resonant operating frequency point of each cantilever piezoelectric diaphragm is adjusted to reduce the resonance peak in the middle and high frequency bands of the sound pressure level frequency response curve when the sound pressure level is output at a high sound pressure level; wherein: The multi-cantilever piezoelectric diaphragm array includes 2n asymmetric cantilever piezoelectric diaphragm units in an n×2 configuration, and the 2n cantilever piezoelectric diaphragm units are separated by air gaps; The substrate support layer is provided with a cavity; the reinforcing rib is arranged in the cavity below the multi-cantilever piezoelectric diaphragm array; the top end of the reinforcing rib is connected to the cantilever piezoelectric diaphragm unit, and the bottom end is suspended in the cavity.
[0007] Furthermore, the single cantilever piezoelectric diaphragm unit is a multi-layer structure, including a silicon elastic layer, an insulating layer and a piezoelectric driving layer; the piezoelectric driving layer includes a lower electrode metal layer, a piezoelectric layer and an upper electrode metal layer.
[0008] Furthermore, the material of the insulating layer is SiO2 or Si3N4, the material of the piezoelectric layer is PZT or AlN, and the material of the electrode includes Pt and Au.
[0009] Furthermore, the reinforcing ribs are composed of a SOI wafer buried oxide layer and SOI wafer substrate silicon.
[0010] A method for preparing the piezoelectric MEMS speaker comprises the following steps: Step 1: Preparation of multi-cantilever piezoelectric diaphragm array 1.1 Using SOI wafer to prepare multi-cantilever piezoelectric diaphragm array; 1.2 The top silicon layer of the SOI wafer is used as the elastic layer of the cantilever piezoelectric diaphragm unit. An insulating layer, a lower electrode metal layer, a piezoelectric layer and an upper electrode metal layer are sequentially deposited on the top silicon layer of the SOI wafer from bottom to top; 1.3 patterning and etching the upper electrode metal layer and the piezoelectric layer; 1.4 Sputter or deposit metal, pattern and etch the metal to form metal pads, and lead out upper and lower electrodes; 1.5 Patterning and etching the piezoelectric layer, the lower electrode layer, the insulating layer and the silicon elastic layer on the front side to determine the size of each cantilever piezoelectric diaphragm unit and the size of the air gap between the units; Step 2: Preparation of reinforcing ribs and formation and release of the substrate support layer cavity; 2.1 Patterning and etching the SOI wafer substrate silicon multiple times to determine the size of the reinforcing ribs below each cantilever piezoelectric diaphragm unit and form a back cavity of the substrate support layer; 2.2 The buried oxide layer SiO2 of the SOI wafer is etched to complete the preparation of the reinforcing ribs. The final reinforcing ribs are prepared by using photolithography and etching processes on the buried oxide layer SiO2 of the SOI wafer and the substrate silicon of the SOI wafer; at the same time, the cavity of the substrate support layer is released to form a multi-cantilever diaphragm piezoelectric MEMS speaker with reinforcing ribs.
[0011] Compared with the prior art, the present invention has the following advantages and technical effects: The present invention discloses a piezoelectric MEMS loudspeaker and a preparation method thereof. On the basis of an existing multi-cantilever diaphragm piezoelectric MEMS loudspeaker, a plurality of reinforcing ribs are designed under the multi-cantilever piezoelectric diaphragm array to suppress a partial distortion mode of the multi-cantilever piezoelectric diaphragm array, and adjust the resonant operating frequency point of each cantilever piezoelectric diaphragm. Under the condition of high sound pressure level output, the resonance peaks in the mid-high frequency band of the sound pressure level frequency response curve can be significantly reduced, and the flattening of the mid-high frequency band sound pressure level frequency response curve is achieved, which is helpful to reduce the distortion of the multi-cantilever diaphragm piezoelectric MEMS loudspeaker and improve its audio quality. BRIEF DESCRIPTION OF THE DRAWINGS
[0012] Figure 1 A schematic diagram of the structure of a piezoelectric MEMS speaker according to an embodiment of the present invention; Figure 2 A top view of a piezoelectric MEMS speaker according to an embodiment of the present invention; Figure 3 is a cross-sectional view of a comparative piezoelectric MEMS speaker; Figure 4 is a top view of a comparative piezoelectric MEMS speaker; Figure 5 The sound pressure level spectrum diagram of the piezoelectric MEMS speakers of the embodiment and the comparative example at a driving voltage of 3 Vp-p is obtained by simulation based on finite element simulation software of the present invention; Figure 6 The present invention is a preparation flow chart of an embodiment of the present invention. DETAILED DESCRIPTION
[0013] The specific implementation modes of the present invention will be described in detail below with reference to the accompanying drawings, embodiments and comparative examples.
[0014] The purpose of the present invention is to provide a piezoelectric MEMS speaker and a preparation method thereof. By adding reinforcing ribs under the cantilever piezoelectric diaphragm array, the design of the multi-cantilever diaphragm piezoelectric MEMS speaker is optimized, aiming to reduce the sound pressure level sharp resonance peak at the mid-high frequency in the sound pressure level frequency response curve under the condition of high sound pressure level output, so as to achieve the purpose of reducing distortion and improving sound quality. Example
[0015] See also Figure 1 , Figure 2 As shown, Figure 1 (a) is a cross-sectional view, and (b) is a schematic diagram of the structure of a single cantilever diaphragm unit; a piezoelectric MEMS speaker of the present invention includes a substrate support layer 10, a multi-cantilever piezoelectric diaphragm array 20, and several reinforcing ribs 30. The substrate support layer 10 serves as a fixed beam to support the multi-cantilever piezoelectric diaphragm array 20 located above. The multi-cantilever piezoelectric diaphragm array 20 is arranged above the substrate support layer 10, and one side of its edge is fixedly connected to the substrate support layer 10. The array includes four asymmetric cantilever piezoelectric diaphragm units 20a in a 2×2 configuration, and the four cantilever piezoelectric diaphragm units are separated by an air gap 60. Several reinforcing ribs 30 are arranged below each cantilever piezoelectric diaphragm unit, and the reinforcing ribs vibrate simultaneously with the corresponding cantilever piezoelectric diaphragm unit. The cantilever piezoelectric diaphragm unit 20a includes an upper electrode 201, a piezoelectric layer 202, a lower electrode 203, an insulating layer 204, and a silicone elastic layer 205. The material of the insulating layer is SiO2, the material of the piezoelectric layer is PZT, and the materials of the electrodes include Pt and Au. In this embodiment, the multi-cantilever diaphragm piezoelectric MEMS speaker with reinforcing ribs selects SiO2 as the insulating layer 204 with a thickness of 0.1 μm, selects PZT as the piezoelectric layer material 202 with a thickness of 2 μm, and the top silicon with a thickness of 5 μm on the SOI wafer is used as the silicon elastic layer 205 of the diaphragm. Pt metal is selected as the upper and lower electrodes 201 and 203, and Au metal is selected as the pad 40. There are several reinforcing ribs 30 under the multi-cantilever piezoelectric diaphragm array 20. In this embodiment, two reinforcing ribs are designed under each cantilever piezoelectric diaphragm unit 20a. The width of each reinforcing rib is 0.1 mm, the length is the same as the width of the corresponding cantilever piezoelectric diaphragm unit fixed on the substrate support layer 10, and the height is 0.2 mm. The reinforcing ribs 30 are composed of the buried oxide layer 301 of the SOI wafer and the SOI wafer substrate silicon 302. When a voltage signal is applied to the upper and lower electrodes 201 and 203, the multi-cantilever piezoelectric diaphragm array 20 is driven to vibrate based on the inverse piezoelectric effect of the piezoelectric layer material 202, and the reinforcing ribs and the corresponding cantilever piezoelectric diaphragm units 20a vibrate simultaneously, converting the electrical signal into an acoustic signal. By designing reinforcing ribs under the multi-cantilever piezoelectric diaphragm array, some distortion modes of each cantilever piezoelectric diaphragm unit during vibration are suppressed, and the resonant operating frequency points of each cantilever piezoelectric diaphragm unit in the mid-high frequency band are adjusted.
[0016] Comparative Example Combination Figure 3 , Figure 4 As shown, the piezoelectric MEMS speaker of the comparative example only includes a substrate support layer 10 and a multi-cantilever piezoelectric diaphragm array 20, and the only difference from the piezoelectric MEMS speaker of the embodiment is that there is no design of the reinforcing rib 30. Compared with the multi-cantilever diaphragm piezoelectric MEMS speaker with reinforcing ribs in the present invention, the displacement amplitude generated by each cantilever piezoelectric diaphragm unit 20a when vibrating is larger, and except for the first-order mode, most of the vibration modes of each diaphragm are distortion modes, especially in the mid-high frequency band, the third-order and fourth-order resonance frequencies of each diaphragm are concentrated, which leads to obvious resonance peaks in the mid-high frequency band of the sound pressure level frequency response curve, which will cause large distortion of the final output audio and poor sound quality uniformity.
[0017] Combination Figure 5 As shown, the design of the piezoelectric MEMS speaker in the embodiment can significantly reduce the resonance peak in the mid-to-high frequency band after 6 kHz in the sound pressure frequency response curve while maintaining a high sound pressure level output greater than 100 dB, thereby achieving the flattening of the sound pressure level frequency response curve in the mid-to-high frequency band.
[0018] Attached Figure 6 The process flow chart of the specific implementation method of the piezoelectric MEMS speaker manufacturing method in the embodiment of the present invention is shown, which includes the following steps: Step 1: Preparation of multi-cantilever piezoelectric diaphragm array 1.1 See also Figure 6 a, using SOI wafer to prepare multi-cantilever piezoelectric diaphragm array; 1.2 See also Figure 6 b, the top silicon layer of the SOI wafer is used as the elastic layer of the cantilever piezoelectric diaphragm unit, and the insulating layer SiO2, the lower electrode metal layer Pt, the piezoelectric layer PZT and the upper electrode metal layer Pt are deposited on the top silicon layer of the SOI wafer from bottom to top; 1.3 See also Figure 6 c, patterning and etching the upper electrode metal layer Pt and the piezoelectric layer PZT; 1.4 See also Figure 6 d, sputtering metal Au, patterning and etching the metal Au to form a metal pad, and leading out the upper and lower electrodes; 1.5 See also Figure 6 e. patterning and etching the piezoelectric layer PZT, the lower electrode layer Pt, the insulating layer SiO2 and the silicon elastic layer on the front side to determine the size of each cantilever piezoelectric diaphragm unit and the size of the air gap between the diaphragm units; Step 2: Preparation of reinforcing ribs and formation and release of the substrate support layer cavity; 2.1 See Figure 6f, patterning and etching the SOI wafer substrate silicon multiple times to determine the size of the reinforcing ribs below each cantilever piezoelectric diaphragm unit and to form a back cavity of the substrate support layer; 2.2 See also Figure 6 g. Etch the buried oxide layer SiO2 of the SOI wafer to complete the preparation of the reinforcing ribs. The final reinforcing ribs are prepared by using photolithography and etching processes on the buried oxide layer SiO2 of the SOI wafer and the silicon substrate of the SOI wafer; at the same time, the release of the cavity of the substrate support layer is completed to form a multi-cantilever diaphragm piezoelectric MEMS speaker with reinforcing ribs.
[0019] The above are only preferred embodiments of the present invention and are not intended to limit the present invention in any form. Any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention are within the scope of the claims of the present invention.
Claims
1. A piezoelectric MEMS speaker, characterized in that: The piezoelectric MEMS speaker comprises: substrate support layer; A multi-cantilever piezoelectric diaphragm array is disposed above the substrate support layer, and one side of its edge is fixedly connected to the substrate support layer; A plurality of reinforcing ribs are arranged below the multi-cantilever piezoelectric diaphragm array, formed by etching the SOI wafer substrate silicon and the SOI wafer buried oxide layer, and form an integrated structure with the multi-cantilever piezoelectric diaphragm array; A reinforcing rib is designed under the multi-cantilever piezoelectric diaphragm array to suppress some distortion modes of the multi-cantilever piezoelectric diaphragm array, and the resonant operating frequency point of each cantilever piezoelectric diaphragm is adjusted to reduce the resonance peak in the middle and high frequency bands of the sound pressure level frequency response curve when the sound pressure level is output at a high sound pressure level; wherein: The multi-cantilever piezoelectric diaphragm array includes 2n asymmetric cantilever piezoelectric diaphragm units in an n×2 configuration, and the 2n cantilever piezoelectric diaphragm units are separated by air gaps; The substrate support layer is provided with a cavity; the reinforcing rib is arranged in the cavity below the multi-cantilever piezoelectric diaphragm array; the top end of the reinforcing rib is connected to the cantilever piezoelectric diaphragm unit, and the bottom end is suspended in the cavity.
2. The piezoelectric MEMS speaker according to claim 1, characterized in that: The single cantilever piezoelectric diaphragm unit is a multi-layer structure, including a silicon elastic layer, an insulating layer and a piezoelectric driving layer; The piezoelectric driving layer includes a lower electrode metal layer, a piezoelectric layer and an upper electrode metal layer.
3. The piezoelectric MEMS speaker according to claim 2, characterized in that: The material of the insulating layer is SiO2 or Si3N4, the material of the piezoelectric layer is PZT or AlN, and the material of the electrode includes Pt and Au.
4. The piezoelectric MEMS speaker according to claim 1, characterized in that: The reinforcing ribs are composed of a SOI wafer buried oxide layer and a SOI wafer substrate silicon.
5. A method for preparing the piezoelectric MEMS speaker according to claim 1, characterized in that: The preparation method comprises the following steps: Step 1: Preparation of multi-cantilever piezoelectric diaphragm array 1.1 Using SOI wafer to prepare multi-cantilever piezoelectric diaphragm array; 1.2 The top silicon layer of the SOI wafer is used as the elastic layer of the cantilever piezoelectric diaphragm unit. An insulating layer, a lower electrode metal layer, a piezoelectric layer and an upper electrode metal layer are sequentially deposited on the top silicon layer of the SOI wafer from bottom to top; 1.3 patterning and etching the upper electrode metal layer and the piezoelectric layer; 1.4 Sputter or deposit metal, pattern and etch the metal to form metal pads, and lead out upper and lower electrodes; 1.5 Patterning and etching the piezoelectric layer, the lower electrode layer, the insulating layer and the silicon elastic layer on the front side to determine the size of each cantilever piezoelectric diaphragm unit and the size of the air gap between the units; Step 2: Preparation of reinforcing ribs and formation and release of the substrate support layer cavity; 2.1 Patterning and etching the SOI wafer substrate silicon multiple times to determine the size of the reinforcing ribs below each cantilever piezoelectric diaphragm unit and form a back cavity of the substrate support layer; 2.2 The buried oxide layer SiO2 of the SOI wafer is etched to complete the preparation of the reinforcing ribs. The final reinforcing ribs are prepared by using photolithography and etching processes on the buried oxide layer SiO2 of the SOI wafer and the substrate silicon of the SOI wafer; at the same time, the cavity of the substrate support layer is released to form a multi-cantilever diaphragm piezoelectric MEMS speaker with reinforcing ribs.