Center-clamped piezoelectric MEMS loudspeaker
Through the central solid-branch structure and flexible air isolation layer design, the problem of insufficient displacement outside the diaphragm surface of the piezoelectric MEMS speaker is solved, and the speaker's high-sound pressure level output and low-frequency performance improvement under miniaturization conditions is achieved.
Patent Information
- Application Number
- CN202510492137.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-18
- Publication Date
- 2025-07-25
AI Technical Summary
In the case of miniaturization, the existing piezoelectric MEMS speakers have a smaller displacement outside the diaphragm surface, resulting in a lower output sound pressure level, especially in the low frequency range.
The central solid-branch structure design is adopted, combining flexible air isolation layer and arc-shaped gap filling, which increases the displacement outside the diaphragm surface and reduces air leakage, improves acoustic resistance, and optimizes the diaphragm layout to improve the sound pressure level output.
The sound pressure level output of the speaker is significantly improved at the same size, enhance low-frequency performance, reduce air leakage and acoustic short circuit problems, and improve the out-of-plane displacement uniformity of the diaphragm.
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Figure CN120378810A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the field of acoustic MEMS devices, and in particular, relates to a piezoelectric MEMS speaker and a manufacturing method thereof. Background Art
[0002] Wearable devices such as TWS in-ear headphones, AR / VR devices, and hearing aids have a strong demand for lightweight and miniaturized speakers. Although traditional moving coil speakers assembled based on coils and magnets have the characteristics of simple structure and excellent mid-low frequency performance, due to the size limitations of inherent structures such as permanent magnets and coils, there are many problems with their miniaturized products, such as reduced audio bandwidth and degraded sound quality.
[0003] MEMS speakers prepared based on MEMS technology have gradually been applied to the audio market due to their high processing accuracy, small feature size, and advantages such as small volume, low power consumption, and easy integration. The driving methods of MEMS speakers include electrostatic MEMS speakers, electrothermal MEMS speakers, piezoelectric MEMS speakers, and electromagnetic MEMS speakers. Among them, electrostatic MEMS speakers can be compatible with CMOS processes, but have the disadvantages of complex manufacturing processes and high driving voltages; electrothermal MEMS speakers have a simple structure and few manufacturing process steps, however, problems such as large volume, high power consumption, and heating effects limit their further application; electromagnetic MEMS speakers have the advantages of high output sound pressure level and low driving voltage, but like coil speakers, they are difficult to miniaturize in structure and have complex manufacturing processes; piezoelectric MEMS speakers utilize the inverse piezoelectric effect of piezoelectric thin films to achieve sound pressure output, and have performance advantages such as high driving force, fast response speed, large frequency response bandwidth, and low power consumption, while also having the advantages of simple manufacturing processes and small occupied area. Piezoelectric MEMS speakers generally perform well in the mid-high frequency range, but have poor acoustic output performance in the low frequency range. One of the core indicators of MEMS speakers is the output sound pressure level (SPL). Since the output sound pressure of a speaker is proportional to the square of the frequency and the first power of the diaphragm displacement, the SPL is usually small at low frequencies (20 Hz to 1 kHz). One of the reasons is that the structure of miniaturized products is limited by size, and it is often difficult for the diaphragm to achieve a large out-of-plane displacement. Therefore, how to achieve a large out-of-plane displacement of the diaphragm under the same size structure is an urgent problem to be solved for piezoelectric MEMS speakers.
[0004] In 2018, F. Stoppel et al. from the Fraunhofer Institute for Silicon Technology in Germany proposed a piezoelectric MEMS speaker based on a PZT sputtered thin film. The diaphragm of this device is square. Different from traditional closed diaphragms, the diaphragm of this device is divided into four isosceles triangular actuators by two narrow slits at the diagonal. The narrow slits are fabricated by etching through the PZT thin film, the bottom electrode, and the device layer. The existence of this structure relieves the physical coupling of the square diaphragm at the diagonal, increases the out-of-plane displacement of the overall diaphragm, and thus improves the SPL of the device. In the structure of this MEMS speaker, the fixed support of the diaphragm is located at the periphery of the device, and the free end of the diaphragm extends to the center of the device. Therefore, the area of the free end is relatively small, and there is a certain limit to the improvement of the SPL of the device. Summary of the Invention
[0005] Aiming at the problems of the small out-of-plane displacement of the diaphragm and the low SPL of the device of the MEMES speaker, the present invention provides a center-clamped piezoelectric MEMS speaker. Its diaphragm is fixed and supported in the center position, further increasing the out-of-plane displacement of the diaphragm and improving the SPL.
[0006] Advantages:
[0007] 1. The present invention creatively adjusts the clamping position of the diaphragm from the peripheral support area to the center. Under the same shape and area, the diaphragm has a larger proportion of the diaphragm area far from the fixed end to obtain a larger out-of-plane displacement, so as to achieve the purpose of improving the SPL.
[0008] 2. A flexible air isolation layer is deposited on the base, increasing the acoustic resistance of the MEMS speaker and effectively improving the sound pressure level output of the center-clamped MEMS speaker, solving the problem of acoustic short circuit caused by air leakage during the out-of-plane displacement of the separated diaphragm structure.
[0009] 3. Arc-shaped gaps are formed by multi-segment etching along the radial direction of the diaphragm, and the gap areas are filled with flexible materials such as parylene-C or PDMS. Thereby, the mass load of the diaphragm can be reduced, the stiffness of the diaphragm can be reasonably reduced, and the uniformity of the overall out-of-plane displacement can be improved, thereby further improving the sound pressure level of the speaker output at low frequencies.
[0010] 4. The sector-shaped diaphragm is supported and fixed by a fixed column located at the center, and each part of the sector-shaped diaphragm unit is electrically connected through the top electrode in the central connection area. Compared with other sector-shaped diaphragm arrangement methods, the diaphragm arrangement carried out in the above manner has the highest concentration and device plane utilization rate. Description of the Drawings
[0011] Figure 1 It is a schematic diagram of a centrally supported piezoelectric MEMS speaker provided by the first embodiment of the present invention;
[0012] Figure 2 It is a cross-sectional view of a centrally supported piezoelectric MEMS speaker provided by the first embodiment of the present invention;
[0013] Figure 3 is Figure 1 the top view of;
[0014] Figure 4 It is a schematic diagram of the manufacturing process of a centrally supported piezoelectric MEMS speaker provided by the first embodiment of the present invention;
[0015] Figure 5 It is a schematic diagram of a centrally supported piezoelectric MEMS speaker provided by the second embodiment of the present invention;
[0016] Figure 6 It is a cross-sectional view of a centrally supported piezoelectric MEMS speaker provided by the second embodiment of the present invention;
[0017] Figure 7 is Figure 5 the top view of;
[0018] Figure 8 It is a schematic diagram of a piezoelectric centrally supported MEMS speaker provided by the third embodiment of the present invention;
[0019] Figure 9 It is a schematic diagram of the base of a piezoelectric centrally supported MEMS speaker provided by the third embodiment of the present invention. Detailed implementation manners
[0020] To better illustrate the purpose and advantages of the present invention, the following further describes the content of the invention in conjunction with the drawings and examples.
[0021] It should be noted that all directional indicators (such as up, down, left, right, front, back, inside, outside, top, bottom...) in the embodiments of the present invention are only used to explain the relative positional relationship between components in a certain specific posture (as shown in the drawings). If this specific posture changes, then the directional indicators will also change accordingly.
[0022] Example 1, as Figure 1 , 2, as shown in FIGS. 3 and 4, a center-clamped piezoelectric MEMS speaker includes a substrate 110, a diaphragm 120, an acoustic isolation layer 130, fixing posts 140, and rib plates 150. The middle of the substrate 110 has a circular through-hole, on the inner wall of the through-hole is provided with the acoustic isolation layer 130, at the center position of the through-hole is vertically provided with the fixing posts 140, one end of the rib plate 150 is connected to the fixing posts 140, and the other end is connected to the substrate 110. There are 4 rib plates 150 evenly distributed along the circumferential direction. The rib plates 150 and the fixing posts 140 divide the through-hole of the substrate 110 into four fan-shaped holes. The diaphragm 120 is fan-shaped and adapted to the fan-shaped holes. One end of the diaphragm 120 is connected to the upper end of the fixing posts 140. As Figure 2 shown, the fan-shaped hole is the vibration space of the diaphragm 120.
[0023] Compared with a piezoelectric MEMS speaker based on PZT sputtered thin film proposed by F. Stoppel et al. of the Fraunhofer Institute for Silicon Technology in Germany in 2018, in this embodiment, the diaphragm is fan-shaped, the end with a smaller diaphragm area is fixed, and the end with a larger diaphragm area is the free end. During vibration, the diaphragm area on the side where the arc of the free end of the fan-shaped diaphragm is located will achieve the largest out-of-plane displacement due to being far from the restraint, and a higher proportion of the diaphragm area can achieve a larger out-of-plane displacement when the diaphragm vibrates.
[0024] As Figure 3 shown, Figure 3 is Figure 1 the top view of, there are certain gaps between the diaphragm 120 and the acoustic isolation layer 130, and between the rib plates 150. Based on the design principle that the gap between the diaphragm and the support structure should be as small as possible to prevent air leakage problems, the width of the gap is generally set to about five microns.
[0025] The width of the rib plate 150 is 100 microns to 300 microns and can be adjusted according to the rationality of the actual design size and the results of the processing technology.
[0026] As Figure 2 shown, the distributed acoustic isolation layer increases the height of the base 110 of the free end of the diaphragm 120, reduces the gap between the edge of the diaphragm and the base 110 during vibration, reduces acoustic loss, increases the acoustic resistance of the speaker, and thus obtains a higher sound pressure level output.
[0027] As Figure 4 shown, the manufacturing method of the center-clamped piezoelectric MEMS speaker in Embodiment 1 includes the following steps:
[0028] Step S101, referring to Figure 4(a)-(b), the provided SOI wafer includes at least a device layer 105, a buried oxide layer 106, and a silicon body layer 107. First, a bottom electrode layer 102 is deposited on the device silicon layer 105 of the SOI wafer;
[0029] Step S102, refer to Figure 4 (c), deposit a piezoelectric layer 101 on the bottom electrode layer 102;
[0030] Step S103, refer to Figure 4 (d), deposit and pattern a top electrode layer 103 on the piezoelectric layer 101. Among them, the top electrode region on the fan-shaped diaphragm is connected to the top metal electrode of the central connection region, and the top electrode of the central connection region is connected to the top metal of the support layer and the metal pin at the top of the outer ring support structure through patterning;
[0031] Step S104, refer to Figure 4 (e), etch the piezoelectric layer 101 to complete the patterning of the piezoelectric layer. At the same time as this step is carried out, the bottom electrode of the device and the scribing lane region of the wafer are etched through the wet PZT etching process;
[0032] Step S105, refer to Figure 4 (f), according to the dividing gap and the position where the scribing lane is located, complete the etching of the bottom electrode layer 102 and the bulk silicon layer 101 in two steps to complete the patterning of the bottom electrode layer and the bulk silicon layer 100. During the etching process, the etching width of the regions where the above two parts are etched should be slightly smaller than the etching width of the piezoelectric layer 101;
[0033] Step S106, refer to Figure 4 (g), deposit a top layer flexible material layer 104 and etch the top layer flexible material layer to complete the patterning.
[0034] Step S107, refer to Figure 4 (h), etch the SOI bulk silicon layer 107 from the back, stop etching when reaching the silicon oxide layer, and form the vibration cavity, that is, the region where the diaphragm vibrates;
[0035] Step S108, refer to Figure 4 (i), etch the SOI buried oxide layer 106, and separate single devices after scribing to complete the preparation of the center-clamped piezoelectric MEMS speaker.
[0036] As Figure 4 (h) shows, the diaphragm 120 is composed of four layers of structures, which are, from bottom to top, a 105 structural silicon layer, a 102 bottom electrode layer, a 101 piezoelectric layer, and a 103 top electrode layer.
[0037] Optionally, refer to Figure 4, during the manufacturing process of the center-clamped piezoelectric MEMS speaker, after the deposition step of the top flexible material layer 104 is completed, the etching process for the top flexible material layer can be adjusted after step S107, that is, after the step of etching the SOI bulk silicon layer from the back, and the flexible thin film on the front of the piezoelectric actuator is removed through the plasma surface treatment process. This adjustment of the manufacturing process can improve the yield during the device manufacturing process.
[0038] Embodiment 2, as Figures 5 - 7 shown, a center-clamped piezoelectric MEMS speaker has two differences from Embodiment 1. One is that there are a total of three rib plates 150 evenly distributed along the circumferential direction. The rib plates 150 and the fixing columns 140 divide the through holes in the substrate 110 into three fan-shaped holes. In contrast, fewer air gap regions are beneficial to reducing air leakage, thereby avoiding the occurrence of acoustic short-circuit phenomena. The other is that each sector-shaped diaphragm 120 is formed with arc-shaped gaps by multi-segment etching along the radial direction. Within a reasonable design range, the width of each part of the arc-shaped gap is generally 10 to 20 micrometers. The arc-shaped long hole 160 region is filled with the flexible material parylene-C or PDMS, which can reduce the mass load of the diaphragm, reasonably reduce the stiffness of the diaphragm, and improve the uniformity of the overall out-of-plane displacement, thereby further increasing the sound pressure level output by the speaker at low frequencies.
[0039] In terms of the manufacturing method, the manufacturing method of the embodiments of the present invention is basically the same as that of Embodiment 1 described above, except that in step S106, the internal gap of the diaphragm is filled while the flexible thin film is deposited.
[0040] Embodiment 3, as Figure 8 、 9 shown, different from Embodiment 1, the provided center-clamped piezoelectric MEMS speaker has only one rib plate 150. The rib plate 150, the fixing column 140, and the base 110 form a fan-shaped vibration cavity. The diaphragm 120 is adapted to the shape of the vibration cavity. The diaphragm 120 is close to a circular ring shape, and the inner ring region of the diaphragm is connected to the central support structure 140. There is no isolation gap region inside the diaphragm, avoiding the acoustic short-circuit problem and the decrease in sound pressure level caused by asynchronous vibration during the vibration of the annular diaphragm array.
[0041] Under the same diaphragm shape and area, the diaphragm with a central fixed support structure has a larger proportion of the diaphragm area far from the fixed end. During vibration, this will cause a larger area of the diaphragm to generate a larger out-of-plane displacement. At the same time, to alleviate the problem of acoustic short circuit caused by possible air leakage during the out-of-plane displacement of the separated diaphragm structure, a flexible air isolation layer is deposited on the base, increasing the acoustic resistance of the MEMS speaker, thereby effectively improving the sound pressure level output of the centrally supported MEMS speaker. In addition, by optimizing the design of the central connection structure area, the diaphragm distribution method, the top electrode distribution, and using different air isolation layer materials, the effect of further increasing the acoustic resistance and the output sound pressure level can be achieved.
[0042] Optionally, during the manufacturing process of the piezoelectric MEMS speaker manufactured in the embodiment of the present invention, the top electrode on the diaphragm surface is connected to the Pad on the peripheral substrate through a connection substrate that isolates each part of the diaphragm.
[0043] The above specific description further details the purpose, technical solution, and beneficial effects of the invention. It should be understood that the above is only a specific embodiment of the present invention and is not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.
Claims
1. A center-clamped piezoelectric MEMS speaker, characterized in that, The circular fixed support area of the speaker diaphragm is located at the center of the structural area. A plurality of discrete symmetric sector diaphragm structures extending from the inside out are designed around the central circular fixed support area. The circular fixed support area is connected to the peripheral support area where the base (110) is located through rib plates (150). The rib plates (150) also serve as the air isolation support structure and the electrode connection area of the sector diaphragm.
2. A center-clamped piezoelectric MEMS speaker, characterized in that: The structure includes a base (110), a diaphragm (120), a fixing column (140), and rib plates (150). The base (110) has a circular through-hole in the middle, and a fixing column (140) is vertically arranged at the center position of the through-hole. One end of the rib plate (150) is connected to the fixing column (140), and the other end is connected to the base (110). There are one or more rib plates (150), and one or more rib plates (150) are evenly distributed in the through-hole of the base (110) along the circumferential direction. One or more rib plates (150) and the fixing column (140) divide the through-hole of the base (110) into one or more sector holes. The number and shape of the diaphragm (120) are the same as those of the sector holes. One end of the diaphragm (120) is fixedly connected to the upper end of the fixing column (140), and there is an air gap structure with a certain width between the edge of the diaphragm (120) and the rib plates (150) and the base (110). That is, the connecting fixing column is the displacement support area of the diaphragm (120).
3. The center-clamped piezoelectric MEMS speaker according to claim 1, characterized in that, The diaphragm (120), the fixing column (140), the rib plates (150), and the base (110) are part of a sector structure in the plane direction. Among them, the area where each sector diaphragm is located serves as the sector cantilever actuator part of the speaker, and each sector structure actuator is in the same plane. All the sector diaphragms are within the concentric circle range centered on the center point of the fixing column (140) in this plane.
4. The center-clamped piezoelectric MEMS speaker according to claim 2, wherein The sector structure actuators are in the same plane. The annular structure area can be divided into one to multiple discrete sector parts, and each part of the actuator area is isolated by the fixing column (140) and the air gap. All the sector actuators and the isolation area together form the internal circular area of the support base.
5. The center-clamped piezoelectric MEMS speaker according to claim 1, wherein: It also includes an acoustic isolation layer (130), and the acoustic isolation layer (130) is arranged on the inner wall of the through-hole of the base (110).
6. The center-clamped piezoelectric MEMS speaker according to claim 1, wherein: The air gap between the diaphragm (120) and the base (110) and the rib plates (150) is 4 to 6 micrometers.
7. The center-clamped piezoelectric MEMS speaker according to claim 1, wherein: The diaphragm (120) is composed of four layers of structures, which are, from bottom to top, a structural silicon layer (105), a bottom electrode layer (102), a piezoelectric layer (101), and a top electrode layer (103).
8. The center-clamped piezoelectric MEMS speaker according to claim 6, wherein The circular fixed support end of the cantilever actuator is in the central area of the device. The fixed support end is part of the base and is parallel to other bases.
9. The center-clamped piezoelectric MEMS speaker according to claim 1, wherein The thickness S2 of the piezoelectric layer (101) is twice the thickness S1 of the structural silicon layer (105).
10. The center-clamped piezoelectric MEMS speaker according to claim 1, wherein: The diaphragm (120) is distributed with multiple arc-shaped long holes (160) along the radial direction, and the width of the arc-shaped long holes (160) is 10 - 20 micrometers.
11. The center-clamped piezoelectric MEMS speaker according to claim 10, wherein: The arc-shaped long holes (160) are filled with flexible materials.
12. The center-clamped piezoelectric MEMS speaker according to claim 1, wherein, The manufacturing method uses the exposed area of the bottom electrode as the common ground electrode. The top electrode of the diaphragm (120) is connected to the top electrode of the peripheral substrate through the connecting electrode on the top layer of the substrate where the rib plates (150) that isolate each part of the diaphragm are located, so as to synchronously drive each sector-shaped diaphragm.
13. An electronic device, characterized in that It includes the center-clamped piezoelectric MEMS speaker according to any one of claims 1-11.