Quasi-closed octagonal piezoelectric MEMS loudspeaker

Abstract

A quasi-closed octagonal piezoelectric MEMS loudspeaker disclosed by the present invention comprises a supporting substrate, an octagonal vibrating diaphragm, fixed edges and a vibrating cavity, the octagonal vibrating diaphragm is an octagon formed by chamfering four corners of a rectangular vibrating diaphragm, four short edges formed by the chamfers are the fixed edges, and the other four long edges of the edge of the supporting substrate are the free edges. The fixed edge is fixedly connected with the support substrate, and the octagonal diaphragm is located in the upper end plane of the support substrate. According to the design, by reducing the connecting area range of the vibrating diaphragm and the peripheral supporting substrate and increasing the size range between connecting boundaries, boundary constraint is reduced, the average distance between each area in the vibrating diaphragm and the boundary constraint area is increased, and the out-of-plane displacement of the vibrating diaphragm under a low-frequency driving signal can be improved; by adopting a driving mode that the inner and outer ring electrodes have a 180-degree phase difference, the purposes of improving the vibration mode of the vibrating diaphragm and increasing the effective vibration area are achieved; therefore, low-frequency sound pressure level output can be improved, and finally higher full-band sound pressure level output is realized.

Description

Technical Field

[0001] The invention belongs to the field of acoustic MEMS devices, and in particular relates to a quasi-closed octagonal piezoelectric MEMS loudspeaker. Background Art

[0002] Dynamic speakers are driven speakers that operate based on the principle of electromagnetic induction and are widely used in various audio equipment. They are known for their simple structure, mature manufacturing process, and excellent sound quality. However, due to the inclusion of components such as permanent magnets and voice coils, these speakers are typically large and heavy, and perform poorly in terms of transient response and mechanical losses. In recent years, with the growing demand for lightweight and miniaturized speakers in wearable devices such as TWS in-ear headphones, AR / VR auxiliary devices, and hearing aids, dynamic speakers face urgent challenges such as reduced bandwidth and degraded sound quality in their miniaturization process.

[0003] MEMS speakers utilize key components such as a miniaturized diaphragm and drive electrodes. By applying voltage to the diaphragm and employing various drive methods (including piezoelectric, electrostatic, and electromagnetic), the diaphragm vibrates, generating sound waves. MEMS manufacturing technology has enabled ultra-miniaturization, typically measuring just a few millimeters, significantly smaller than conventional dynamic coil speakers. This makes them ideal for miniaturized and lightweight speaker units. Among these designs, electromagnetic MEMS speakers utilize the same drive principle as traditional dynamic coil speakers and offer significant advantages in manufacturing cost, power consumption, and response speed. Electrostatic MEMS speakers, on the other hand, employ a voltage difference between two electrodes to generate electrostatic attraction, causing the diaphragm to move toward a fixed electrode and ultimately generate sound waves. Electrostatic MEMS speakers are compatible with CMOS processes and have a simple structure, but their manufacturing process is more complex and requires a higher drive voltage. Piezoelectric MEMS speakers, on the other hand, use piezoelectric thin film materials (such as PZT and AlN) as the vibrating element. Voltage generates mechanical deformation through the inverse piezoelectric effect, driving the diaphragm and generating sound waves. Compared with other types of MEMS speakers, piezoelectric MEMS speakers have shown great application potential in many electronic products due to their high conversion efficiency, simple structure, high integration, fast response, low power consumption and miniaturization, and have become one of the mainstream directions of current MEMS speaker technology development.

[0004] Output sound pressure level (SPL) is one of the key performance indicators of MEMS speakers. Because 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 often low in the low-frequency range (20Hz to 1kHz). One reason for this is that miniaturized products are limited by size, making it difficult for the diaphragm to achieve large out-of-plane displacement. Therefore, how to achieve large out-of-plane displacement of the diaphragm while maintaining the same size structure has become a key issue that needs to be addressed in piezoelectric MEMS speakers. Summary of the Invention

[0005] The present invention aims to achieve superior vibration characteristics by optimizing the design of the diaphragm and supporting structure while maintaining inherent dimensions and structural area. This allows the diaphragm to achieve greater out-of-plane displacement, thereby producing superior sound pressure level output. The present invention provides a quasi-enclosed octagonal piezoelectric MEMS loudspeaker.

[0006] The proposed weak boundary binding boundary diagonally connected piezoelectric MEMS loudspeaker comprises a supporting base, an octagonal diaphragm, fixed edges, and a vibration cavity. The octagonal diaphragm is formed by chamfering four corners of a rectangular diaphragm surrounded by a supporting base. The chamfered four edges serve as fixed edges, while the remaining four edges remain free and unconnected to the supporting base. The supporting base of the designed loudspeaker diaphragm is equipped with a vibration cavity that matches the diaphragm's shape.

[0007] The fixed edge is fixedly connected to the base, with a gap between the free edge and the base. The diaphragm is located within the plane of the base's upper end surface. A first slit extends from the midpoint of the free edge toward the center, but does not penetrate the diaphragm. The diaphragm is divided into an inner electrode region, defined by a line connecting the midpoints of the fixed edges, and an outer electrode region. The outer electrode region is provided with several slits parallel to the fixed edge. Furthermore, multiple layers of third slits parallel to the fixed edge are provided in the center of the diaphragm. Ultimately, this structural design optimizes vibration characteristics and acoustic performance.

[0008] Compared with the prior art, the present invention has the following beneficial effects:

[0009] 1. The quasi-enclosed octagonal piezoelectric MEMS loudspeaker disclosed in the present invention has a square top dual-electrode diaphragm structure with a central connection area, and adopts a driving method with a 180° phase difference between the inner and outer ring electrodes, thereby improving the low-frequency sound pressure level output effect;

[0010] 2. The effect of weak boundary constraint is achieved by reducing the connection area between the diaphragm and the peripheral supporting base, and the boundary constraint area only exists in the diagonal area of the rectangular supporting base, thereby increasing the average distance from each area in the diaphragm to the boundary constraint area, improving the average out-of-plane displacement of the piezoelectric vibration film, and ultimately achieving a higher sound pressure level output. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a schematic structural diagram of a quasi-enclosed octagonal piezoelectric MEMS loudspeaker provided in Example 1 of the present invention;

[0012] Figure 2 This is a planar schematic diagram of a quasi-closed octagonal piezoelectric MEMS loudspeaker provided in Example 1 of the present invention;

[0013] Figure 3 is the comparison of the out-of-plane displacement distribution of the loudspeaker diaphragm;

[0014] Figure 4 This is a process flow chart of a quasi-closed octagonal piezoelectric MEMS speaker array provided in Example 1 of the present invention;

[0015] Figure 5 This is a schematic structural diagram of a quasi-enclosed octagonal piezoelectric MEMS speaker provided in the second embodiment of the present invention;

[0016] Figure 6 1 is a planar schematic diagram of a quasi-enclosed octagonal piezoelectric MEMS loudspeaker provided in the second embodiment of the present invention;

[0017] Figure 7 This is a process flow chart of a quasi-enclosed octagonal piezoelectric MEMS speaker provided by the second embodiment of the present invention;

[0018] Figure 8 This is a schematic structural diagram of a quasi-enclosed octagonal piezoelectric MEMS speaker provided in Example 3 of the present invention;

[0019] Figure 9 1 is a planar schematic diagram of a quasi-enclosed octagonal piezoelectric MEMS loudspeaker provided in the third embodiment of the present invention;

[0020] Figure 10 This is a process flow chart of a quasi-enclosed octagonal piezoelectric MEMS speaker provided in Example 3 of the present invention;

[0021] Figure 11 This is a structural diagram of a quasi-enclosed octagonal piezoelectric MEMS speaker provided by the fourth embodiment of the present invention;

[0022] Figure 12 1 is a planar schematic diagram of a quasi-closed octagonal piezoelectric MEMS loudspeaker provided in Embodiment 4 of the present invention. DETAILED DESCRIPTION

[0023] In order to better illustrate the purpose and advantages of the present invention, the invention is further described below with reference to the accompanying drawings and examples.

[0024] It should be noted that all directional indications in the embodiments of the present invention (such as up, down, left, right, front, back, inside, outside, top, bottom, etc.) are only used to explain the relative position relationship between the various components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0025] Based on application requirements and design, the shape design of MEMS speaker diaphragm is not fixed, but compared with other diaphragm designs, square diaphragms or rectangular diaphragms have the advantages of high space utilization efficiency, simple diaphragm manufacturing process, and high equivalent diaphragm area.

[0026] Therefore, the design of a square or rectangular diaphragm structure for a piezoelectric MEMS speaker has considerable practical value. However, MEMS speakers struggle to equalize the difference between high-frequency and low-frequency output sound pressure levels. Therefore, it is necessary to increase the low-frequency sound pressure level of the MEMS speaker output, stabilize the high-frequency output sound pressure level, and improve the acoustic output quality of the speaker. To this end, this application provides a quasi-enclosed octagonal piezoelectric MEMS speaker structure design based on a square diaphragm with weak boundary constraints and diagonal connections, as well as an electrical excitation scheme.

[0027] Example 1:

[0028] See also Figure 1 A quasi-closed octagonal piezoelectric MEMS loudspeaker includes a supporting base 110, an octagonal diaphragm 120, a fixed edge 130, and a vibration cavity 140. The octagonal diaphragm 120 is an octagon formed by chamfering the four corners of a rectangular diaphragm. The four sides formed by the chamfers are fixed edges 130, and the other four sides are free edges 150. A vibration cavity 140 that matches the shape of the octagonal diaphragm 120 is machined on the supporting base 110. The fixed edge 130 is fixedly connected to the supporting base 110. There is a gap between the other sides of the octagonal diaphragm 120 and the supporting base 110. The octagonal diaphragm 120 is located in the upper end surface plane of the supporting base 110. Four first elongated slits 21 are opened on the octagonal diaphragm 120, extending from the midpoint of the free edge of the octagonal diaphragm 120 to the center of the diaphragm.

[0029] The rectangular boundary dimensions of the support base are 3 mm x 3 mm, and the rectangular area containing the octagonal diaphragm is 2.5 mm x 2.5 mm. The gap between the free edge (other than the fixed edge) of the octagonal diaphragm and the support base is 3 to 6 microns. The four slits defined by the octagonal diaphragm 120 do not reach the center, forming a connecting area at the center of the octagonal diaphragm. The rectangular area containing the connecting area at the center of the octagonal diaphragm is 0.5 mm x 0.5 mm.

[0030] See also Figure 2 , Figure 2The diagram below shows a schematic plan view of a quasi-enclosed octagonal piezoelectric MEMS loudspeaker design for Example 1. The design includes a peripheral support region 101, an inner electrode region 102, an outer electrode region 104, and a gap region 103. Gap region 103 consists of two parts: the gap between the free edge of the octagonal diaphragm and the supporting base, and the gap defined by the octagonal diaphragm. The area connecting the midpoints of the diaphragm's free edges constitutes inner electrode region 102, while the remaining portion of the diaphragm constitutes outer electrode region 104.

[0031] The diaphragm is connected to the support base 110 only through the fixed edges at the diagonal lines, which serve as fixed ends. The remaining edges are called free ends and are not connected to the support base 110. An air gap region 103 of a certain width exists between the free end edges and the peripheral support base. Compared to a structural design without a free end diaphragm boundary region, the diaphragm connection design using diagonal area connection increases the average distance from the diaphragm center area to the fixed edges, thereby achieving the effect of reducing diaphragm stiffness and increasing the overall out-of-plane displacement of the diaphragm for the same size area.

[0032] Figure 3 a Out-of-plane displacement distribution and Figure 3 b Comparison of the out-of-plane displacement distribution of the center-connected dual-electrode loudspeaker of the square diaphragm in the prior art. The white dotted area is the diaphragm area with the same structure under the two designs. Figure 3 a is the first embodiment with a 2.5 mm diaphragm side length, 1000 Hz driving frequency and 2V pp Effect of external displacement distribution under driving voltage. Figure 3 b Out-of-plane displacement distribution effect under the same driving voltage and 3mm diaphragm side length, and there is no etching gap in the boundary area of the square diaphragm. Simulation research shows that by adopting this design method, the central diaphragm area of the two diaphragm types can achieve the same out-of-plane displacement effect under low-frequency driving, and the area occupied by the diaphragm structure design in Example 1 is significantly smaller than that in Example 1. Figure 3 b shows the square diaphragm design. This design method ultimately improves the output sound pressure level in the low-frequency range of the speaker.

[0033] In one technical solution of this embodiment, the square diaphragm area 102 where the inner electrode is located is arranged in a centrally symmetrical manner with the outer electrode area, and there is an electrode isolation area between the two types of electrode areas, that is, there is no top electrode coverage, and the electrode isolation width is 15 microns. When driven in the low-frequency range (20Hz-3kHz), the brake excitation voltage adopts a dual-channel drive of the inner and outer electrodes with a phase difference of 180°. Unlike the eardrum vibration mode when the inner and outer electrodes are driven by a single-channel excitation, this solution can drive the vibration mode of the entire diaphragm at low frequencies to tend to the center piston vibration mode, effectively improving the average out-of-plane displacement of the diaphragm. In the medium and high frequency range (3kHz-20kHz), since the diaphragm vibration of this embodiment under dual-channel drive transitions from the fundamental frequency center piston vibration mode to the high-order vibration mode, and an output sound pressure level valley will appear, within this frequency band, this embodiment adopts a single-channel excitation mode driven only by the inner electrode.

[0034] like Figure 4 As shown, a method for manufacturing a quasi-closed octagonal piezoelectric MEMS loudspeaker is

[0035] The following steps are involved:

[0036] Step S101, refer to Figure 4 (a)(b), a provided SOI wafer includes at least a buried oxide layer 103, a bulk silicon layer 104, and a device layer 105. First, a bottom electrode layer 102 is deposited on the device silicon layer 105 of the SOI wafer;

[0037] Step S102, refer to Figure 4 (c) depositing a piezoelectric layer 101 on the bottom electrode layer 102;

[0038] Step S103, refer to Figure 4 (d) depositing and patterning a top electrode layer 102 on the piezoelectric layer 101;

[0039] Step S104, see Figure 4 (e) etching the piezoelectric layer 101 to complete the patterning of the piezoelectric layer. During this step, the bottom electrode of the device and the scribe line area of the wafer are etched by a PZT wet etching process.

[0040] Step S105, refer to Figure 4 (f)(g) Based on the segmentation gap and the location of the scribe line, the bottom electrode layer 102 and the bulk silicon layer 101 are etched 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 areas where the above two parts are etched should be slightly smaller than the etching width of the piezoelectric layer 101.

[0041] Step S107, see Figure 4(h) etching the SOI bulk silicon layer 107 from the back side until the etching reaches the silicon oxide layer, thereby forming the vibration cavity, i.e., the region where the diaphragm vibrates;

[0042] Step S108, see Figure 4 (i) Etching the SOI buried oxide layer 106 and separating the individual devices after dicing to complete the preparation of a quasi-enclosed octagonal piezoelectric MEMS speaker.

[0043] In a driving scheme of this embodiment, an electrode isolation region exists between the inner electrode diaphragm region and the outer electrode diaphragm region, and there is a 180° phase delay between the inner and outer electrode AC driving voltages.

[0044] Example 2:

[0045] like Figure 5 、 6 As shown, an air gap structure is added on the basis of Example 1. An air gap structure parallel to the fixed edge of the octagonal diaphragm is designed in the diaphragm area where the top electrode of the four-part outer ring is located, and a second elongated slit 22. The gap width is set to 8 microns. By adding an air gap structure in the peripheral area of the diaphragm, it can be used to improve the frequency response characteristics of the diagonally connected octagonal diaphragm with weak boundary constraints, and the reasonably designed etched gap can adjust the stress state of the diaphragm, optimize the frequency response characteristics of the loudspeaker, and obtain a flatter mid- and low-frequency response. On the other hand, during the manufacturing process, the air gap structure in the peripheral area of the diaphragm can also reduce the deformation of the diaphragm by reducing the local stress concentration when the diaphragm is under stress, which is beneficial to improving the linearity and dynamic range of the loudspeaker.

[0046] See Figure 7 This is a flow chart of the structural design and manufacturing method of a quasi-closed octagonal piezoelectric MEMS speaker of this embodiment. During the manufacturing process, the processing process of the air gap structure described in this embodiment is carried out simultaneously with the manufacturing process of the gap area 103 described in the first embodiment.

[0047] Implementation Example 3:

[0048] like Figure 8 、 9 As shown, a multi-layer air gap structure, a third elongated slit 23, is added to the first embodiment. The multi-layer air gap structure is located at the edge of the central connection area of the diaphragm. The gap width is generally set to 8 microns. This creates a spring-like structure between the outer ring diaphragm area and the central connection area. This spring-like design reduces coupling between diaphragm areas and further reduces the stiffness of the central diaphragm area, thereby increasing the average effective out-of-plane displacement of the entire diaphragm. Since the volume integral of the effective out-of-plane displacement of the diaphragm is positively correlated with the output sound pressure level of the loudspeaker under a fixed diaphragm area, this design ultimately improves the output sound pressure level in the low-frequency range.

[0049] In one technical solution of this embodiment, due to the spring-like structure design of the central connection area, the overall stiffness of the diaphragm and the out-of-plane displacement distribution during low-frequency vibration also change. Therefore, it is necessary to adjust the isolation area between the inner ring electrode and the outer ring electrode to achieve the optimal electrode area configuration. Figure 9 The square area enclosed by the electrode isolation area is tangent to the peripheral supporting substrate. By adjusting the regional distribution of the two parts of the electrode, the output sound pressure level in the low-frequency range is further improved.

[0050] like Figure 10 The figure shows a flow chart of the structural design and manufacturing method for a quasi-enclosed octagonal piezoelectric MEMS speaker according to this embodiment. During the manufacturing process, the processing of the multi-layer air gap structure described in this embodiment is carried out simultaneously with the manufacturing process of the gap region 103 described in the first embodiment.

[0051] Implementation Example 4: Figure 11 、 12 As shown, the difference from the second embodiment is that the octagonal diaphragm 120 of this embodiment does not have a first elongated slit 21 extending from the midpoint of the free edge to the center position of the octagonal diaphragm 120 .

[0052] The outer electrode diaphragm area thus forms a spring cantilever structure design. During the vibration process, the spring cantilever structure design around the diaphragm changes the vibration mode of the diaphragm at low frequencies, further improving the sound pressure level output of the device at medium and low frequencies.

[0053] In a technical solution of this embodiment, the area range of the spring cantilever diaphragm formed by etching the gap can be further adjusted.

[0054] It should be understood that the various forms of the above-described processes can be used to reorder, add, or delete steps. For example, the steps described in the present invention can be performed in parallel, sequentially, or in a different order, as long as the desired results of the technical solution of the present invention can be achieved. This is not limited herein.

[0055] The above specific description further illustrates the purpose, technical solutions and beneficial effects of the invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A quasi-closed octagonal piezoelectric MEMS loudspeaker achieves superior diaphragm vibration characteristics by optimizing the design of a symmetrical octagonal quasi-closed diaphragm shape within a quadrilateral diaphragm area and optimizing the diaphragm fixed support area by designing an air gap at the fixed boundary. The speaker is characterized by: The structural features of the design include a supporting base (110), an octagonal diaphragm (120), a fixed edge (130) and a vibration cavity (140). The octagonal diaphragm (120) is an octagon formed by chamfering the four corners of a rectangular diaphragm. The four short sides formed by the chamfers serve as the fixed edges (130) of the octagonal diaphragm (120). The other four parts, which are parallel to the square base, serve as free edges (150) and an air isolation layer exists between the diaphragm and the octagonal diaphragm. A vibration cavity (140) that is adapted to the shape of the octagonal diaphragm (120) is processed on the supporting base (110). The fixed edge (130) is fixedly connected to the supporting base (110). There is a gap between the free edge (150) and the supporting base (110). The octagonal diaphragm (120) is located in the upper end surface plane of the supporting base (110).

2. The quasi-closed octagonal piezoelectric MEMS loudspeaker according to claim 1, wherein: A first elongated slit (21) is provided on the octagonal diaphragm (120), and the first elongated slit (21) extends from the midpoint of the free edge (150) of the octagonal diaphragm (120) to the center of the diaphragm but does not penetrate through the diaphragm, so that a central connection diaphragm exists in the center of the octagonal piezoelectric MEMS speaker diaphragm.

3. The quasi-closed octagonal piezoelectric MEMS loudspeaker according to claim 1, wherein: The octagonal diaphragm (120) is divided into an inner electrode region (102) and an outer electrode region (104), the region formed by connecting the midpoints of the fixed edge (130) is the inner electrode region (102), and the other regions of the octagonal diaphragm (120) are the outer electrode region (104).

4. The quasi-closed octagonal piezoelectric MEMS loudspeaker according to claim 3, wherein: The outer electrode region (104) and the inner electrode region (102) on the surface of the octagonal diaphragm (120) are driven through different electrode connection regions, respectively, and the phase difference of the driving AC voltage at each operating frequency is 180°.

5. The quasi-closed octagonal piezoelectric MEMS loudspeaker according to claim 3, wherein: A plurality of second elongated slits (22) parallel to each other are provided on the octagonal diaphragm (120). The second elongated slits (22) are located in the outer electrode region (104) and are parallel to the fixed edge (130).

6. The quasi-closed octagonal piezoelectric MEMS loudspeaker according to claim 2, wherein: A plurality of third elongated slits (23) parallel to the fixed edge (130) are provided on the octagonal diaphragm (120). The third elongated slits (23) are located in the central area of the octagonal diaphragm (120) and are arranged in parallel in multiple layers.

7. The quasi-closed octagonal piezoelectric MEMS loudspeaker according to claim 1, wherein: The octagonal diaphragm (120) consists of a four-layer structure, which comprises a structural silicon layer (105), a bottom electrode layer (102), a piezoelectric layer (101) and a top electrode layer (103) from bottom to top, wherein the thickness of the base silicon layer is 300 microns to 400 microns.

8. The method for manufacturing a quasi-closed octagonal piezoelectric MEMS loudspeaker according to claim 1, wherein: The outermost square region of the substrate occupies an area of 16 square micrometers to 25 square micrometers.

9. An electronic device, characterized in that: A quasi-closed octagonal piezoelectric MEMS loudspeaker comprising the quasi-closed octagonal piezoelectric MEMS loudspeaker according to any one of claims 1 to 8.

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