Piezoelectric PMUT and preparation method thereof

Abstract

The invention provides a piezoelectric PMUT and a preparation method thereof. The piezoelectric PMUT comprises a substrate, the substrate is provided with a front side and a back side which are opposite, a piezoelectric layer is formed on the front side of the substrate, a back cavity is formed in the substrate in a penetrating mode, a structural layer is formed on the surface of the piezoelectric layer, the thickness of the structural layer is larger than that of a piezoelectric film in the piezoelectric layer, and a neutral plane is located in the transverse projection area range of the structural layer; a vibrating diaphragm area of the structural layer is provided with a gap to form a central structure and a plurality of vibrating structures, the adjacent vibrating structures are connected through a connecting beam, and each vibrating structure is connected with the central structure through the connecting beam; the preparation method comprises the following steps: preparing a substrate; growing a piezoelectric layer; etching the piezoelectric layer; growing a structural layer; etching the structural layer; penetrating through the etching substrate to form a back cavity; silicon oxide is adopted as the structural layer, the Young modulus of the silicon oxide is low, the process stress is low, the resonant frequency can be effectively reduced, meanwhile, the vibration diaphragm is slotted to form a honeycomb structure, the impact energy can be effectively dispersed, and the device stability is high.

Description

Technical Field

[0001] One or more embodiments of the present specification relate to the field of semiconductor process technology, and more particularly, to a piezoelectric PMUT and a method for preparing the same. Background Art

[0002] Ultrasonic sensors are sensors that convert ultrasonic signals into other energy signals (usually electrical signals). Ultrasonic waves are mechanical waves with a vibration frequency higher than 20kHz. They have the characteristics of high frequency, short wavelength, small diffraction phenomenon, especially good directionality, and the ability to propagate in a directional manner as rays. Ultrasonic waves have a great ability to penetrate liquids and solids, especially in solids that are opaque to sunlight. When ultrasonic waves encounter impurities or interfaces, they will produce significant reflections to form reflected echoes, and when they encounter moving objects, they can produce the Doppler effect. Ultrasonic sensors are widely used in industry, national defense, biomedicine, etc.

[0003] In the prior art, low-frequency ultrasonic sensors are needed in technical fields such as long-distance measurement, monitoring, and remote information transmission using ultrasound. Therefore, low-frequency MEMS chip devices also have a large market. However, traditional piezoelectric MEMS chips are composed of a stacked SOI substrate with a back cavity and a piezoelectric layer. The top silicon in the SOI substrate serves as a structural layer and assumes the function of a neutral plane. Silicon has a high Young's modulus and high process stress, which leads to a high resonant frequency, which is not conducive to the production design and manufacturing of low-frequency devices. On this basis, the diaphragm forms a whole and cannot disperse the impact energy, resulting in insufficient device stability.

[0004] In summary, the present application now proposes a piezoelectric PMUT and a preparation method thereof to solve the above-mentioned problems. Summary of the invention

[0005] The present invention aims to solve the problems raised in the background technology. The purpose of one or more embodiments of this specification is to propose a piezoelectric PMUT and a preparation method thereof, using silicon oxide as a structural layer to replace traditional top silicon. Silicon oxide has a low Young's modulus and low process stress, which can effectively reduce the resonant frequency. On this basis, by opening slits on the diaphragm to form a honeycomb structure, the impact energy can be effectively dispersed and the device has high stability.

[0006] Based on the above purpose, one or more embodiments of the present specification provide a piezoelectric PMUT, including a substrate, the substrate having a front side and a back side opposite to each other, a piezoelectric layer formed on the front side of the substrate, a back cavity is formed through the substrate, a structural layer is formed on the surface of the piezoelectric layer, the thickness of the structural layer is greater than the thickness of the piezoelectric film in the piezoelectric layer, so that the neutral plane is located within the lateral projection area of ​​the structural layer;

[0007] The piezoelectric layer and the structural layer within the longitudinal projection area of ​​the back cavity are diaphragms. A gap is opened in the diaphragm area of ​​the structural layer to form a central structure and several vibration structures surrounding the central structure. Adjacent vibration structures are connected by connecting beams, and each vibration structure is connected to the central structure through a connecting beam.

[0008] According to the piezoelectric PMUT provided in the embodiment of the present invention, the cross section of the central structure is a regular hexagon.

[0009] According to the piezoelectric PMUT proposed in an embodiment of the present invention, a plurality of vibration structures are arranged in a ring array around a central structure, the vibration structure has a first side surface adjacent to the central structure, a second side surface and a third side surface adjacent to adjacent vibration structures, the second side surface and the third side surface are located on the same side of the first side surface, and the second side surface and the third side surface are symmetrical with respect to the first side surface, and the first side surface, the second side surface and the third side surface form the upper base and two waist sides of an isosceles trapezoid. .

[0010] According to the piezoelectric PMUT provided by the embodiment of the present invention, the material of the structural layer is silicon oxide.

[0011] According to the piezoelectric PMUT provided in the embodiment of the present invention, the structural layer is a double-layer structure in which silicon nitride and silicon oxide are alternately stacked.

[0012] According to the piezoelectric PMUT provided in the embodiment of the present invention, the structural layer is a three-layer structure in which silicon nitride and silicon oxide are alternately stacked.

[0013] A preparation method according to an embodiment of the present invention is used to prepare the piezoelectric PMUT mentioned above, comprising the following steps:

[0014] preparing a substrate, the substrate having a front side and a back side opposite to each other, and growing a piezoelectric layer on the front side of the substrate;

[0015] etching the piezoelectric layer to pattern the piezoelectric layer;

[0016] growing a structural layer on the surface of the patterned piezoelectric layer;

[0017] Etching the structural layer to pattern the structural layer;

[0018] The substrate is etched through to form a back cavity, and the structural layer and the piezoelectric layer within the longitudinal projection area of ​​the back cavity serve as a diaphragm;

[0019] Wherein, the thickness of the structural layer is greater than the thickness of the piezoelectric film in the piezoelectric layer, so that the neutral plane is located within the lateral projection area of ​​the structural layer;

[0020] Among them, the diaphragm area of ​​the structural layer forms a gap due to etching, thereby forming a central structure and several vibration structures surrounding the central structure, adjacent vibration structures are connected by connecting beams formed by etching, and each vibration structure is connected to the central structure through the connecting beams formed by etching.

[0021] According to the preparation method proposed in an embodiment of the present invention, the cross-section of the central structure is a regular hexagon.

[0022] According to the preparation method proposed in an embodiment of the present invention, the vibration structure is an isosceles trapezoid, and a plurality of vibration structures are arranged in a circular array around a central structure, and two adjacent vibration structures are separated by a gap.

[0023] According to the preparation method proposed in the embodiment of the present invention, etching through the substrate to form a back cavity specifically includes:

[0024] etching a portion of the substrate from the back side of the substrate by a dry process;

[0025] The substrate is etched through by a wet process.

[0026] A piezoelectric PMUT and a preparation method thereof proposed in the present invention can effectively disperse impact energy and improve device stability by opening a slit on a diaphragm and connecting a central structure and a vibration structure through a connecting beam.

[0027] The beneficial effects of the present invention are described in detail below with reference to the embodiments and drawings of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate one or more embodiments of the present specification or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only one or more embodiments of the present specification. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0029] Figure 1 It is a structural schematic diagram of a piezoelectric PMUT proposed in an embodiment of the present invention;

[0030] Figure 2 for Figure 1 Exploded diagram of the structure;

[0031] Figure 3 for Figure 1 A front view of

[0032] Figure 4 for Figure 1 A top view of

[0033] Figure 5 for Figure 4A magnified view of the structure at center A;

[0034] Figure 6 This is a schematic flow chart of step S1 of the preparation method in an embodiment of the present invention;

[0035] Figure 7 This is a schematic flow chart of step S2 of the preparation method in an embodiment of the present invention;

[0036] Figure 8 This is a schematic flow chart of step S3 of the preparation method in an embodiment of the present invention;

[0037] Fig. 9 This is a schematic flow chart of step S4 of the preparation method in an embodiment of the present invention;

[0038] Fig.10 This is a schematic flow chart of step S5 of the preparation method in an embodiment of the present invention;

[0039] In the figure markings: 1. substrate; 2. piezoelectric layer; 21. bottom electrode; 22. piezoelectric film; 23. top electrode; 3. structural layer; 31. first structural layer; 32. second structural layer; 33. third structural layer; 331. connecting beam; 332. vibration structure; 333. central structure. DETAILED DESCRIPTION

[0040] In order to make the objectives, technical solutions and advantages of the present disclosure more clearly understood, the present disclosure is further described in detail below in conjunction with specific embodiments.

[0041] Example 1

[0042] See also Figure 1-Figure 5 The piezoelectric PMUT proposed in the embodiment of the present invention includes a substrate 1, a piezoelectric layer 2 and a structural layer 3 which are stacked in sequence.

[0043] The substrate 1 has a front side and a back side opposite to each other. A back cavity is opened from the back side of the substrate 1 through the substrate 1. The piezoelectric layer 2 and the structural layer 3 within the longitudinal projection range of the back cavity are diaphragms. The back cavity provides a vibration space for the diaphragm.

[0044] The piezoelectric layer 2 includes a bottom electrode 21, a piezoelectric film 22 and a top electrode 23 which are sequentially stacked on the surface of the substrate 1. The thickness of the structural layer 3 is greater than that of the piezoelectric film 12, so that the neutral plane is located within the lateral projection area of ​​the structural layer 3.

[0045] The material of the structural layer 3 is silicon oxide, and the Young's modulus of silicon oxide is lower than that of silicon.

[0046] The MEMS chip-based piezoelectric PMUT proposed in the embodiment of the present invention uses silicon oxide instead of silicon as the material of the structural layer. Silicon oxide has a low Young's modulus and low process stress, which can effectively reduce the resonant frequency and is useful for the design and manufacture of low-frequency devices.

[0047] Optionally, the substrate 1 is a silicon wafer substrate, and the cost is reduced by replacing the SOI substrate with the silicon wafer substrate.

[0048] Optionally, the structure layer 3 includes a first structure layer 31 and a second structure layer 32, and the thickness of the second structure layer 32 is much greater than the thickness of the first structure layer 31. In some embodiments, preferably, the material of the first structure layer 31 is silicon nitride (Si3N4), and the material of the second structure layer 32 is silicon oxide (SiO2).

[0049] Of course, in some embodiments, those skilled in the art may choose, when the material of the first structure layer 31 is silicon oxide, the material of the second structure layer 32 is silicon nitride.

[0050] In some embodiments, preferably, the structural layer 3 includes a first structural layer 31 , a second structural layer 32 and a third structural layer 33 , and the thickness of the second structural layer 32 is much greater than the thickness of the first structural layer 31 and / or the third structural layer 33 .

[0051] In some embodiments, preferably, the material of the first structure layer 31 is silicon nitride (Si3N4), the material of the second structure layer 32 is silicon oxide (SiO2), and the material of the third structure layer 33 is silicon nitride.

[0052] Of course, in some embodiments, those skilled in the art may choose that when the material of the first structure layer 31 is silicon oxide, the material of the second structure layer 32 is silicon nitride, and the material of the third structure layer 33 is silicon oxide.

[0053] The main structure of the structural layer 3 in the embodiment of the present invention is the second structural layer 32. The second structural layer 32 mainly has the function of adjusting the neutral plane of the chip. The device performance is mainly determined by the material and thickness of the second structural layer 32. The main function of the first structural layer 31 is to improve the adhesion of the second structural layer 32 and improve the film forming quality. The third structural layer 33 increases the flexibility of the structural layer 3. The three-layer structure is more stable, more reliable, and improves the yield rate.

[0054] The piezoelectric layer 2 and the structural layer 3 within the longitudinal projection area of ​​the back cavity are diaphragms. A gap is opened in the diaphragm area of ​​the structural layer 3 to form a central structure 333 and a number of vibration structures 332 surrounding the central structure 333. Adjacent vibration structures 332 are connected by connecting beams 331, and each vibration structure 332 is connected to the central structure 333 through the connecting beam 331.

[0055] Specifically, Figure 5As shown, the connecting beam 331 is provided with a first opening and a second opening, and the first opening and the second opening are spaced apart from each other, i.e., there is a connecting portion between the first opening and the second opening. When the connecting beam 331 connects two vibration structures 332, the first opening faces one vibration structure 332 connected to the connecting beam 331, and the second opening faces the other vibration structure 332; when the connecting beam 331 connects the vibration structure 332 and the central structure 333, the first opening faces the central structure 333, and the second opening faces the vibration structure 332 connected to the connecting beam.

[0056] The piezoelectric layer 2 includes a bottom electrode 21, a piezoelectric film 22 and a top electrode 23. The diaphragm area of ​​the bottom electrode 21 and the piezoelectric film 22 is the same as that of the structural layer 3. The longitudinal projection area of ​​the top electrode 23 covers the central structure 333. A groove for embedding the top electrode 23 is provided at the bottom of the structural layer 3 corresponding to the position of the central structure 333. The other positions of the structural layer 3 except the central structure 333 extend to the surface of the piezoelectric film 22.

[0057] Optionally, the cross section of the central structure 333 is a regular hexagon.

[0058] Optionally, a plurality of vibration structures 332 are arranged in a circular array around a central structure 333, wherein the vibration structure 332 has a first side surface adjacent to the central structure 333, and a second side surface and a third side surface adjacent to adjacent vibration structures, wherein the second side surface and the third side surface are located on the same side of the first side surface, and the second side surface and the third side surface are symmetrical with respect to the first side surface, wherein the first side surface, the second side surface and the third side surface form an upper base and two side edges of an isosceles trapezoid, and the vibration structure 332 is a structure similar to an isosceles trapezoid.

[0059] The present invention forms a honeycomb structure by opening slits on the diaphragm, which can effectively disperse the impact energy and improve the stability of the device.

[0060] Example 2

[0061] See also Figure 6 , preparing a substrate 1, the substrate 1 having a front side and a back side opposite to each other, and growing a piezoelectric layer 2 on the front side of the substrate 1, specifically comprising:

[0062] S1-1, sputtering and growing a bottom electrode 21 on the front surface of the substrate 1;

[0063] S1-2, sputtering and growing a piezoelectric film 22 on the surface of the bottom electrode 21;

[0064] S1 - 3 , a top electrode 23 is sputtered and grown on the surface of the piezoelectric film 22 .

[0065] See also Figure 7 , S2, etching the piezoelectric layer 2 to pattern the piezoelectric layer 2, specifically comprising:

[0066] S2-1, using IBE dry etching to pattern the top electrode 23;

[0067] S2-2, wet etching the piezoelectric film 22 to pattern the piezoelectric film 22;

[0068] S2-3, using IBE dry etching to etch the bottom electrode 21, so as to pattern the bottom electrode 21.

[0069] See also Figure 8 , S3, using PECVD process to deposit the structural layer 3 on the surface of the piezoelectric layer 2, the thickness of the structural layer 3 is greater than the thickness of the piezoelectric film 22, so that the neutral plane is located within the lateral projection area of ​​the structural layer 3.

[0070] See also Fig. 9 , S4, etching the structural layer 3 to pattern the structural layer 3.

[0071] The thickness of the structural layer 3 is greater than the thickness of the piezoelectric film 22 , so that the neutral plane is located within the lateral projection area of ​​the structural layer 3 .

[0072] Among them, the diaphragm area of ​​the structural layer 3 forms a gap due to etching, thereby forming a central structure 333 and several vibration structures 332 surrounding the central structure 333, and adjacent vibration structures 332 are connected by connecting beams 331 formed by etching, and each vibration structure 332 is connected to the central structure 333 through the connecting beams 331 formed by etching.

[0073] See also Fig.10 S5, etching the substrate 1 from the back side of the substrate 1 to form a back cavity, the piezoelectric layer 2 and the structural layer 3 within the longitudinal projection area of ​​the back cavity are the diaphragm, and the back cavity provides a vibration space for the diaphragm, specifically including:

[0074] S5-1, etching the back side of the substrate 1 by DIRE. The substrate 1 will not be penetrated here because the piezoelectric layer 2 will be damaged by IBE etching. Therefore, 5-15% of the thickness of the substrate 1 will remain after DIRE etching.

[0075] S5-2, etching the back side of the substrate 1 by a wet process, completely penetrating the remaining 5-15% thickness of the substrate 1, forming a U-shaped support structure, and forming a back cavity.

[0076] The preparation method of the present invention is for a piezoelectric MEMS chip based on a silicon wafer substrate. When the SOI substrate is etched, the buried oxide layer serves as a cutoff line, and a back cavity can be formed by penetrating the buried oxide layer. Pure dry etching may damage the piezoelectric layer 2. In order to improve the yield rate, a part of the silicon wafer substrate is dry-etched, and then the remaining part is etched through by a wet process. The wet process will not affect the piezoelectric layer 2.

[0077] Compared with the traditional preparation process, the preparation method of the piezoelectric PMUT based on the MEMS chip proposed in the embodiment of the present invention first grows the piezoelectric layer 2 and patterns it, then grows the structural layer 3 on the surface of the piezoelectric layer 2, and then patterns the structural layer 3. Therefore, the patterning steps of the piezoelectric layer 2 and the structural layer 3 are independent and do not interfere with each other. The piezoelectric layer 2 does not need to be unnecessary hollowed out due to the pattern of the structural layer 3, thereby ensuring the integrity of the piezoelectric layer 2 to the greatest extent.

[0078] Example 3

[0079] As a preferred solution of Example 2, S4, the structural layer 3 is etched to pattern the structural layer 3, so that the diaphragm region of the structural layer 3 forms a pattern consistent with the diaphragm region of the piezoelectric film 22, and the structural layer 3 is a double-layer structure or a three-layer structure in which silicon nitride and silicon oxide are alternately stacked. Optionally, the structural layer 3 includes a first structural layer 31, a second structural layer 32, and a third structural layer 33, the material of the first structural layer 31 and the third structural layer 33 is silicon nitride, the material of the second structural layer 32 is silicon oxide, and the thickness of the second structural layer 32 is much greater than the thickness of the first structural layer 31 and / or the third structural layer 33.

[0080] The cross section of the central structure 333 is a regular hexagon, the vibration structure 332 is an isosceles trapezoid, and a plurality of vibration structures 332 are arranged in a circular array around the central structure 333 , and two adjacent vibration structures 332 are separated by a gap.

[0081] S5, etching the substrate 1 from the back side of the substrate 1 to form a back cavity, wherein the piezoelectric layer 2 and the structural layer 3 within the longitudinal projection area of ​​the back cavity are the diaphragm, and the back cavity provides a vibration space for the diaphragm, specifically including:

[0082] S5-1, etching the back side of the substrate 1 by DRIE dry etching. The substrate 1 will not be penetrated here because DRIE dry etching may damage the piezoelectric layer 2. Therefore, 5-15% of the thickness of the substrate 1 will remain after DRIE dry etching.

[0083] S5-2, etching the back side of the substrate 1 by a wet process, completely penetrating the remaining 5-15% thickness of the substrate 1, forming a U-shaped support structure, and forming a back-to-back cavity.

[0084] It should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0085] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0086] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection, an electrical connection, or communication with each other; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0087] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0088] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A piezoelectric PMUT, comprising a substrate (1), wherein the substrate (1) has a front side and a back side opposite to each other, and a piezoelectric layer (2) is formed on the front side of the substrate (1), characterized in that: The substrate (1) is penetrated to form a back cavity, and a structural layer (3) is formed on the surface of the piezoelectric layer (2). The thickness of the structural layer (3) is greater than the thickness of the piezoelectric film (22) in the piezoelectric layer (2), so that the neutral plane is located within the lateral projection area of ​​the structural layer (3); The piezoelectric layer (2) and the structural layer (3) within the longitudinal projection area of ​​the back cavity are diaphragms, and a gap is opened in the diaphragm area of ​​the structural layer (3) to form a central structure (333) and a plurality of vibration structures (332) surrounding the central structure (333), and adjacent vibration structures (332) are connected by connecting beams (331), and each vibration structure (332) is connected to the central structure (333) by the connecting beams (331).

2. The piezoelectric PMUT according to claim 1, characterized in that: The cross section of the central structure (333) is a regular hexagon.

3. The piezoelectric PMUT according to claim 2, characterized in that: A plurality of the vibration structures (332) are arranged in a circular array around a central structure (333), and the vibration structure (332) has a first side surface adjacent to the central structure, a second side surface adjacent to an adjacent vibration structure (332), and a third side surface, the second side surface and the third side surface are located on the same side of the first side surface, and the second side surface and the third side surface are symmetrical relative to the first side surface.

4. The piezoelectric PMUT according to claim 3, characterized in that: The material of the structural layer (3) is silicon oxide.

5. The piezoelectric PMUT according to claim 3, characterized in that: The structural layer (3) is a double-layer structure in which silicon nitride and silicon oxide are alternately stacked.

6. The piezoelectric PMUT according to claim 3, characterized in that: The structural layer (3) is a three-layer structure in which silicon nitride and silicon oxide are alternately stacked.

7. A method for preparing the piezoelectric PMUT according to any one of claims 1 to 6, characterized in that: The following steps are involved: A substrate (1) is prepared, wherein the substrate (1) has a front side and a back side opposite to each other, and a piezoelectric layer (2) is grown on the front side of the substrate (1); Etching the piezoelectric layer (2) to pattern the piezoelectric layer (2); Growing a structural layer (3) on the surface of the patterned piezoelectric layer (2); Etching the structural layer (3) to pattern the structural layer (3); A substrate (1) is etched through to form a back cavity, wherein the structural layer (3) and the piezoelectric layer (2) within the longitudinal projection area of ​​the back cavity serve as a diaphragm; The thickness of the structural layer (3) is greater than the thickness of the piezoelectric film (22) in the piezoelectric layer (2), so that the neutral plane is located within the lateral projection area of ​​the structural layer (3); In which, a gap is formed in the diaphragm area of ​​the structural layer (3) due to etching, thereby forming a central structure (333) and a plurality of vibration structures (332) surrounding the central structure (333), adjacent vibration structures (332) are connected by connecting beams (331) formed by etching, and each vibration structure (332) is connected to the central structure (333) by a connecting beam (331) formed by etching.

8. The preparation method according to claim 7, characterized in that: The cross section of the central structure (333) is a regular hexagon.

9. The preparation method according to claim 8, characterized in that: The vibration structure (332) is an isosceles trapezoid, and a plurality of vibration structures (332) are arranged in a circular array around a central structure (333), and two adjacent vibration structures (332) are separated by a gap.

10. The preparation method according to claim 9, characterized in that: Etching through the substrate (1) to form a back cavity, specifically comprising: Etching a portion of the substrate (1) from the back side of the substrate (1) by a dry process; The substrate (1) is etched through by a wet process.

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