Methods for preparing MEMS structures

Abstract

This invention provides a MEMS structure and its fabrication method, specifically a MEMS piezoelectric microphone. The fabrication method includes: Step A, forming a thermo-oxidative layer with arc-shaped protrusions on the front side of a substrate; Step B, forming a composite vibration layer with an arc-shaped protrusion on the substrate containing the thermo-oxidative layer arc-shaped protrusions; Step C, performing deep silicon etching on the back side of the substrate and releasing the thermo-oxidative layer to form a substrate back cavity, thus suspending the composite vibration layer with the arc-shaped protrusion. In this invention, the amplitude and precision of the thermo-oxidative layer arc-shaped protrusions are controlled using a dry etching process. This process is simple, convenient, and highly accurate. Furthermore, the subsequently deposited composite vibration layer follows the arc-shaped protrusion of the thermo-oxidative layer, exhibiting a smoother and more natural shape, resulting in more effective stress release.

Description

Technical Field

[0001] This invention relates to the fields of novel electroacoustic component manufacturing and microelectronic devices, and in particular to a method for fabricating a MEMS structure. Background Technology

[0002] MEMS (Micro-Electro-Mechanical System) microphones are a new type of electroacoustic component manufactured using micromachining technology. They are characterized by their small size, good frequency response, and low noise. With the miniaturization and thinning of intelligent electronic devices, MEMS microphones are being used more and more widely in these devices.

[0003] MEMS microphones mainly include two types: condenser and piezoelectric. MEMS piezoelectric microphones are microphones fabricated using microelectromechanical systems (MEMS) technology and piezoelectric thin film technology. Due to the use of semiconductor planar processing and bulk silicon fabrication techniques, they are small in size, compact, and have good consistency. Compared to condenser microphones, they also have advantages such as not requiring a bias voltage, a wide operating temperature range, and dust and water resistance. However, their sensitivity is relatively low, which limits the development of MEMS piezoelectric microphones. Residual stress is a major factor restricting the improvement of the sensitivity of MEMS piezoelectric microphones, especially significant in circular piezoelectric MEMS structures. Summary of the Invention

[0004] (a) Technical problems to be solved

[0005] In order to at least partially solve one of the above-mentioned technical problems, the present invention provides a MEMS structure and its fabrication method, namely a MEMS piezoelectric microphone.

[0006] (II) Technical Solution

[0007] In a first aspect, the present invention provides a method for fabricating a MEMS structure. The method includes: step A, forming a thermo-oxidative layer arc-shaped protrusion on the front side of a substrate; step B, forming a composite vibration layer having an arc-shaped protrusion on the substrate containing the thermo-oxidative layer arc-shaped protrusion; and step C, performing deep silicon etching on the back side of the substrate and releasing the thermo-oxidative layer to form a substrate back cavity, thereby suspending the composite vibration layer having an arc-shaped protrusion.

[0008] In some embodiments of the present invention, in step A, the radius of curvature R of the arcuate protrusion of the thermo-oxidative layer satisfies: 0.1cm≤R≤10cm.

[0009] In some embodiments of the present invention, in step A, the radius of curvature R of the arcuate protrusion of the thermo-oxidative layer satisfies 1cm≤R≤3cm.

[0010] In some embodiments of the present invention, the substrate is a silicon substrate, and step A includes: sub-step A1, forming a silicon oxide layer on the front side of the substrate by a thermal oxidation process; sub-step A2, patterning the silicon oxide layer on the front side of the substrate to form arc-shaped protrusions of the silicon oxide layer.

[0011] In some embodiments of the present invention, in sub-step A1, the thickness of the silicon oxide layer is between 0.1 μm and 20 μm; in sub-step A2, the silicon oxide layer is patterned by dry etching.

[0012] In some embodiments of the present invention, step B includes: sub-step B1a, sequentially depositing a vibration support layer, a lower electrode layer, a piezoelectric layer, and an upper electrode layer on a substrate containing the thermo-oxidative layer protrusion; sub-step B1b, patterning the upper electrode layer, the piezoelectric layer, and the lower electrode layer, wherein the horizontal projection of the patterned upper electrode layer, the piezoelectric layer, and the lower electrode layer is inside the horizontal projection of the substrate back cavity and extends continuously.

[0013] In some embodiments of the present invention, step B includes: sub-step B2a, depositing a lower electrode layer on a substrate containing the thermal oxide layer protrusion; sub-step B2b, patterning the lower electrode layer, retaining only the lower electrode layer on the thermal oxide layer; sub-step B2c, sequentially depositing a lower piezoelectric layer, a middle electrode layer, an upper piezoelectric layer, and an upper electrode layer on a substrate containing the lower electrode layer and the thermal oxide layer protrusion; sub-step B2d, patterning the upper electrode layer; wherein the horizontal projection of the patterned upper electrode layer and lower electrode layer is inside the horizontal projection of the substrate back cavity and extends continuously.

[0014] In some embodiments of the present invention, the radius of the horizontal projection of the substrate back cavity is between 0.1 mm and 3 mm.

[0015] In some embodiments of the present invention, the thickness of the piezoelectric layer, the upper piezoelectric layer, and the lower piezoelectric layer is between 0.1 μm and 10 μm, and the material is selected from one or more of the following: aluminum nitride, scandium-doped aluminum nitride, zinc oxide, and lead zirconate titanate.

[0016] In some embodiments of the present invention, the thickness of the upper electrode layer, the middle electrode layer, and the lower electrode layer is between 20 nm and 200 nm, and the material is selected from one or more of the following: molybdenum, gold, aluminum, and chromium.

[0017] In some embodiments of the present invention, the thickness of the vibration support layer is between 0.1 μm and 10 μm, and its material is selected from one or more of the following: silicon nitride, single crystal silicon, aluminum nitride, scandium-doped aluminum nitride, zinc oxide, and lead zirconate titanate.

[0018] In a second aspect of the present invention, a MEMS structure is provided, comprising: a substrate, including: an outer ring of the substrate; a substrate back cavity formed inside the outer ring of the substrate; and a composite vibration layer formed on the substrate; wherein the portion of the composite vibration layer above the substrate back cavity is an arc-shaped protrusion oriented away from the substrate, and the radius of curvature R of the arc-shaped protrusion satisfies: 0.1cm≤R≤10cm.

[0019] In a second aspect, a MEMS piezoelectric microphone is provided, comprising: the MEMS structure as described above.

[0020] In some embodiments of the present invention, the composite vibration layer includes: a vibration support layer, a lower electrode layer, a piezoelectric layer, and an upper electrode layer sequentially formed on the substrate, wherein the composite vibration layer senses sound waves to generate vibration; the piezoelectric layer converts strain into an electrical signal, which is output to the outside through the upper electrode layer and the lower electrode layer.

[0021] In some embodiments of the present invention, the composite vibration layer includes: a lower electrode layer, a lower piezoelectric layer, a middle electrode layer, an upper piezoelectric layer, and an upper electrode layer sequentially formed on the substrate, wherein the composite vibration layer senses sound waves to generate vibration; the lower piezoelectric layer and the upper piezoelectric layer convert strain into electrical signals, which are output to the outside through the upper electrode layer, the middle electrode layer, and the lower electrode layer.

[0022] (III) Beneficial Effects

[0023] As can be seen from the above technical solution, the present invention has at least one of the following beneficial effects compared to the prior art:

[0024] (1) The composite vibration layer with a prefabricated convex or concave shape has a certain ability to stretch and deform in the horizontal plane, which can effectively release the residual stress of the whole structure.

[0025] (2) First, a thermo-oxidative layer arc-shaped protrusion is formed on the front side of the substrate, and then a composite vibration layer with an arc-shaped protrusion is deposited on the thermo-oxidative layer arc-shaped protrusion. This preparation method controls the amplitude and precision of the thermo-oxidative layer arc-shaped protrusion through a dry etching process. The process is simple and convenient, with high precision. Furthermore, the subsequently deposited composite vibration layer follows the arc-shaped protrusion of the thermo-oxidative layer and presents an arc-shaped protrusion, which is more gentle and natural, and the stress release is more effective.

[0026] (3) The radius of curvature of the arc-shaped protrusion of the thermo-oxidative layer determines the shape of the arc-shaped protrusion of the composite vibration layer. If the radius of curvature is too small, the arc-shaped protrusion will be too abrupt and will have an adverse effect on the strength of the composite vibration layer itself. If the radius of curvature is too large, the residual stress release will not achieve the expected effect. Simulation experiments have shown that when the radius of curvature R satisfies: 0.1cm≤R≤10cm, a good balance can be achieved between the strength of the composite vibration layer and the stress release, and the effect is even better when 1cm≤R≤3cm.

[0027] (4) Using silicon oxide layer to create arc-shaped protrusions of thermo-oxidative layer is a relatively mature process, and it is also more convenient to pattern them by dry etching.

[0028] (5) The radius of the piezoelectric layer is smaller than that of the vibration support layer, which is beneficial to release the bending stiffness of the vibration composite layer to increase the vibration displacement. At the same time, it can effectively avoid the neutralization of positive and negative charges in the electrodes to improve sensitivity.

[0029] (5) It can be applied to MEMS structures with single piezoelectric layers, as well as dual-chip MEMS structures, and its application to other types of MEMS structures is also possible. In addition, it can be used not only in microphones, but also in other MEMS devices to release residual stress, making its application range very wide. Attached Figure Description

[0030] Figure 1 , Figure 2 These are, respectively, a perspective view and a cross-sectional view of the MEMS structure of the first embodiment of the present invention.

[0031] Figures 3A-3E for Figure 1 , Figure 2 The diagram shows a cross-sectional view of the MEMS structure after each step in the fabrication method is completed.

[0032] Figure 4 This is a sensitivity comparison between the MEME structure in this embodiment and the existing MEMS structure.

[0033] Figure 5 This is a cross-sectional view of the MEMS structure according to the second embodiment of the present invention. Detailed Implementation

[0034] The concept of this invention lies in giving the composite vibration layer a pre-formed arc-shaped protrusion. This allows the circular composite functional film to have a certain ability to stretch and deform in-plane, effectively releasing residual stress and significantly improving the sensitivity of the MEMS piezoelectric microphone under the influence of residual stress. Furthermore, by forming a silicon oxide layer through thermal oxidation and etching as the bottom template, the complexity of forming the pre-formed arc-shaped protrusion is reduced, improving process accuracy and reliability.

[0035] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0036] According to the first and second aspects of the present invention, a MEMS structure and a method for fabricating the same are provided. Figure 1 , Figure 2 These are, respectively, a perspective view and a cross-sectional view of the MEMS structure according to the first embodiment of the present invention. Figure 1 and Figure 2 As shown, the MEMS structure in this embodiment includes:

[0037] The substrate 10 includes: an outer ring body 11 of the substrate on the periphery; and a substrate back cavity 12 formed inside the outer ring body of the substrate.

[0038] A composite vibration layer 21 is formed on the substrate;

[0039] Among them, the part of the composite vibration layer located above the back cavity of the substrate has an arc-shaped protrusion that faces away from the substrate, and the radius of curvature R of the arc-shaped protrusion satisfies: 0.1cm≤R≤10cm.

[0040] In this embodiment, the composite vibration layer with a prefabricated convex or concave shape has a certain ability to stretch and deform in the horizontal plane, which can effectively release the residual stress of the overall structure.

[0041] The following sections provide a detailed description of each component of the MEMS structure in this embodiment.

[0042] In this embodiment, the substrate 10 is a silicon substrate. The radius of the horizontal projection of the substrate back cavity 12 is between 0.1 mm and 3 mm, and it is formed by deep silicon etching on the back side of the substrate after the composite vibration layer is formed.

[0043] Please refer to Figure 2 The composite vibration layer 21 further includes: a vibration support layer 21a, a lower electrode layer 21b, a piezoelectric layer 21c, and an upper electrode layer 21d, which are sequentially formed on the vibration support layer. The portions of the four layers located above the substrate back cavity are arc-shaped protrusions facing away from the substrate.

[0044] In this embodiment, the horizontal projections of the upper electrode layer, piezoelectric layer, and lower electrode layer are inside the horizontal projection of the substrate back cavity, meaning the radius of the piezoelectric layer is smaller than the radius of the vibration support layer. This helps to release the bending stiffness of the vibration composite layer to increase vibration displacement, while effectively preventing the neutralization of positive and negative charges in the electrodes to improve sensitivity.

[0045] Furthermore, the upper electrode layer, piezoelectric layer, and lower electrode layer extend continuously and smoothly. Compared to composite vibration layers with periodic protrusions, the entire composite vibration layer in this embodiment has the same radius of curvature, which alleviates stress more gently and avoids the adverse effects of abrupt curvature changes on the strength of the composite vibration layer.

[0046] Existing technologies include methods to modify MEMS structures by introducing corrugated structures in localized areas. However, these methods can only release residual stress through deformation in localized areas, and the degree of stress release is limited. In this invention, the entire composite vibration layer has the same pre-fabricated curvature, allowing the entire structure to release residual stress through deformation, resulting in a more thorough stress release.

[0047] In this embodiment, the preferred range of the radius of curvature is determined based on the distribution of residual stress. If the radius of curvature is too small, the arc-shaped protrusion will be too abrupt, which will have an adverse effect on the strength of the composite vibration layer itself. If the radius of curvature is too large, the residual stress release will not achieve the expected effect. Simulation experiments have shown that when the radius of curvature R satisfies: 0.1cm≤R≤10cm, a good balance can be achieved between the strength of the composite vibration layer and stress release, and the effect is even better when 1cm≤R≤3cm.

[0048] In this embodiment, the support layer is 0.4 μm thick silicon nitride (Si3N4), the piezoelectric layer is 0.5 μm thick aluminum nitride (AlN), the upper and lower electrode layers are 0.1 μm thick molybdenum (Mo), the piezoelectric layer and the upper and lower electrodes have a radius of 460 μm, the substrate back cavity 12 has a radius of 500 μm, and the radius of curvature of the entire composite vibration layer is 2 cm.

[0049] However, this invention is not limited to the materials and parameters described above. In other embodiments of this invention, the preferred thickness range for the support layer and the piezoelectric layer is 0.1 μm-10 μm, and the piezoelectric layer material can be aluminum nitride (AlN) or scandium-doped aluminum nitride (Sc). x Al 1-x Materials for the electrode layer include silicon nitride (Si3N4), zinc oxide (ZnO), and piezoelectric ceramics (PZT). The support layer material can be silicon nitride (Si3N4), single-crystal silicon (Si), or the same piezoelectric material as the piezoelectric layer. The preferred thickness of the electrode layer is 20 nm to 200 nm, and its material can be molybdenum (Mo), gold (Au), aluminum (Al), chromium (Cr), etc.

[0050] The following is an introduction Figure 1 , Figure 2 The fabrication method of the MEMS structure shown. Figures 3A-3E for Figure 1 , Figure 2 The diagram shows cross-sectional views of the MEMS structure after each step of the fabrication method is completed. The fabrication method includes:

[0051] Step A: A thermo-oxidative layer arc-shaped protrusion is formed on the front side of the substrate, wherein the radius of curvature of the thermo-oxidative layer arc-shaped protrusion is consistent with the radius of curvature of the arc-shaped protrusion shape of the preset composite vibration layer.

[0052] In this embodiment, the substrate 10 can be a silicon substrate, an SOI substrate, or polycrystalline silicon on SiO2 / Si.

[0053] In this invention, the radius of curvature R of the arc-shaped protrusion in the thermo-oxidative layer satisfies: 0.1cm ≤ R ≤ 10cm. Preferably, the radius of curvature R of the arc-shaped protrusion in the thermo-oxidative layer satisfies 1cm ≤ R ≤ 3cm.

[0054] In this embodiment, the thermal oxidation layer is a silicon oxide layer, and the thermal oxidation layer protrusions are prepared using a microfabrication process. Step A further includes:

[0055] Sub-step A1 involves forming a silicon oxide layer on the front side of the substrate using a thermal oxidation process, such as... Figure 3A As shown.

[0056] The thickness of the silicon oxide layer is between 0.1 μm and 20 μm; preferably, the height of the silicon oxide layer is between 4 μm and 13 μm.

[0057] Sub-step A2 involves patterning a silicon oxide layer on the front side of the substrate to form arc-shaped protrusions in the silicon oxide layer, such as... Figure 3B As shown.

[0058] The radius of curvature R of the arc-shaped protrusion satisfies 0.1cm ≤ R ≤ 10cm. Preferably, the radius of curvature of the arc-shaped protrusion of the silicon oxide layer satisfies 1cm ≤ R ≤ 3cm.

[0059] In this embodiment, dry etching is used to pattern the silicon oxide layer. Of course, those skilled in the art will understand that other methods, such as wet etching, can also be used to pattern the silicon oxide layer.

[0060] In this embodiment, a thermal oxidation process is first used to form a silicon oxide layer, followed by a patterning method to prepare the arc-shaped protrusions of the thermal oxidation layer. However, this invention is not limited to this. In other embodiments of this invention, other methods such as 3D printing can also be used to prepare the arc-shaped protrusions of the thermal oxidation layer, which are also within the scope of protection of this invention.

[0061] Step B: Form a composite vibration layer with an arc-shaped protrusion on a substrate containing the arc-shaped protrusion of the thermal oxide layer;

[0062] In this embodiment, a microfabrication process is used to prepare the composite vibration layer. Step B further includes:

[0063] Sub-step B1a involves sequentially depositing a vibration support layer, a lower electrode layer, a piezoelectric layer, and an upper electrode layer on a substrate containing the thermal oxide layer protrusions, as follows: Figure 3C As shown;

[0064] Because of the arc-shaped protrusion of the thermo-oxidative layer below, the vibration support layer, lower electrode layer, piezoelectric layer and upper electrode layer deposited on it naturally form an arc-shaped protrusion.

[0065] Sub-step B1b involves patterning the upper electrode layer, piezoelectric layer, and lower electrode layer. The horizontal projections of the patterned upper electrode layer, piezoelectric layer, and lower electrode layer lie inside the horizontal projection of the substrate back cavity and extend continuously, as shown below. Figure 3D As shown.

[0066] Those skilled in the art will understand that the process involves first forming a thermo-oxidative layer with arc-shaped protrusions on the front side of the substrate, and then depositing a composite vibration layer with an arc-shaped protrusion on these protrusions. This fabrication method allows for control of the amplitude and precision of the arc-shaped protrusions in the thermo-oxidative layer using a dry etching process. The process is simple, convenient, and highly precise. Furthermore, the subsequently deposited composite vibration layer follows the arc-shaped protrusions of the thermo-oxidative layer, exhibiting a smoother and more natural shape, resulting in more effective stress release.

[0067] Step C involves deep silicon etching on the back side of the substrate and releasing the thermal oxide layer to form a substrate back cavity, thus suspending the composite vibration layer with its arc-shaped protrusions. Figure 3E As shown.

[0068] It should be noted that in this invention, each thin film layer is patterned into a convex or concave pre-fabricated shape during deposition. The purpose is to release residual stress in the structure through stretching or compressing deformation of this pre-fabricated shape after deep silicon etching, thereby improving sensitivity. Unlike methods that control the positive or negative sign of residual stress to make the originally flat thin film layers convex or concave, the MEMS structure prepared by the method of this invention has more uniform internal material, more stable structural strength, and better device sensitivity.

[0069] Figure 4 This section compares the sensitivity of the MEMS structure in this embodiment with that of existing MEMS structures. The left image shows the sensitivity distribution of the existing MEMS structure under residual stress. The composite vibration layer has an infinite radius of curvature, meaning it is completely flat. The right image shows the sensitivity distribution of the MEMS structure in this embodiment under residual stress. The composite vibration layer has a radius of curvature of 2 cm. In both images, the piezoelectric layer and electrode layer have the same residual stress, ranging from -100 MPa to 100 MPa, while the vibration layer has a residual stress range of 0-300 MPa. Referring to the left image, the MEMS structure with an infinite radius of curvature of the composite vibration membrane only exhibits a sensitivity greater than -80 dB under a few stress conditions. Referring to the right image, the MEMS structure with a 2 cm radius of curvature of the composite vibration membrane exhibits a sensitivity greater than -80 dB under the vast majority of stress conditions, significantly reducing the impact of residual stress on structural performance.

[0070] Those skilled in the art should understand that the above embodiments are MEMS structures with a single piezoelectric layer, but the present invention can also be applied to dual-wafer MEMS structures. Figure 5 This is a cross-sectional view of the MEMS structure according to the second embodiment of the present invention. Figure 5 As shown, the MEMS structure in this embodiment includes:

[0071] The substrate 10 includes: an outer ring body 11 of the substrate on the periphery; and a substrate back cavity 12 formed inside the outer ring body of the substrate.

[0072] The composite vibration layer 22 includes: a lower electrode layer 22a, a lower piezoelectric layer 22b, a middle electrode layer 22c, an upper piezoelectric layer 22d, and an upper electrode layer 22e, which are sequentially formed on the substrate.

[0073] Among them, the lower electrode layer, lower piezoelectric layer, middle electrode layer, upper piezoelectric layer, and upper electrode layer are located above the substrate back cavity and have an arc-shaped protrusion that faces away from the substrate.

[0074] This embodiment and Figure 1 , Figure 2 The difference in the illustrated embodiment is that there is no vibration support layer; instead, the lower piezoelectric layer 22b and the upper piezoelectric layer 22d provide support. In this case, the horizontal projections of the lower electrode layer 22a and the upper electrode layer 22e are inside the horizontal projection of the substrate back cavity and extend continuously.

[0075] Regarding the structural differences mentioned above, the preparation method of this embodiment is the same as... Figures 3A-3E Similarly, the difference lies in step B. In this embodiment, step B includes:

[0076] Sub-step B2a: Deposit an electrode layer on a substrate containing thermal oxide layer protrusions;

[0077] Sub-step B2b: Graphicalize the lower electrode layer, retaining only the lower electrode layer on the thermal oxide layer;

[0078] Sub-step B2c involves sequentially depositing a lower piezoelectric layer, a middle piezoelectric layer, an upper piezoelectric layer, and an upper electrode layer on a substrate containing a lower electrode layer and a thermal oxide layer protrusion.

[0079] Sub-step B2d: Graphicalize the upper electrode layer;

[0080] Step C involves deep silicon etching on the back side of the substrate and releasing the thermal oxide layer to form a substrate back cavity. This leaves the composite resonant layer, comprising the lower electrode layer 22a, lower piezoelectric layer 22b, middle electrode layer 22c, upper piezoelectric layer 22d, and upper electrode layer 22e, suspended, as shown below. Figure 5 As shown.

[0081] It should be noted that the MEMS structures described above can be applied to any practical scenario to release residual stress in the composite vibration layer to improve performance characteristics. This practical scenario can include, but is not limited to, microphones, ultrasonic transducers, pressure sensors, or other actuators, with its application in MEMS piezoelectric microphones being the most typical. The following section will also use a MEMS piezoelectric microphone as an example.

[0082] According to a third aspect of the present invention, a MEMS piezoelectric microphone including a MEMS structure is provided, wherein the MEMS structure may be a first embodiment of the MEMS structure or a second embodiment of the MEMS structure.

[0083] In the first embodiment of the MEMS piezoelectric microphone, a first embodiment of the MEMS structure is adopted. In this embodiment, the composite vibration layer includes: a vibration support layer, a lower electrode layer, a piezoelectric layer, and an upper electrode layer, sequentially formed on a substrate. In the MEMS piezoelectric microphone, the composite vibration layer senses sound waves and generates vibration; the piezoelectric layer converts strain into electrical signals, which are then output to the outside world through the upper and lower electrode layers.

[0084] In the second embodiment of the MEMS piezoelectric microphone, a second embodiment of the MEMS structure is adopted. In this case, the composite vibration layer includes: a lower electrode layer, a lower piezoelectric layer, a middle electrode layer, an upper piezoelectric layer, and an upper electrode layer sequentially formed on a substrate. In the MEMS piezoelectric microphone, the composite vibration layer senses sound waves and generates vibrations; the lower and upper piezoelectric layers convert strain into electrical signals, which are then output to the outside through the upper, middle, and lower electrode layers.

[0085] This concludes the description of the various embodiments of the present invention. Based on the above description, those skilled in the art should have a clear understanding of the present invention.

[0086] Those skilled in the art will understand that the word "comprising" in the claims and specification of this invention does not exclude the presence of elements not listed in the claims.

[0087] It should be noted that, unless explicitly stated otherwise, the numerical parameters in the specification and claims of this invention may be approximate values ​​and can be changed according to the content of this invention. Specifically, all figures in the specification and claims indicating the content of composition, reaction conditions, etc., should be understood to be modified by the term "about" in all cases, which means that they include a specific quantity varying by ±10% in some embodiments.

[0088] It should be noted that the directional terms mentioned in the embodiments, such as "up," "down," "front," "back," "left," "right," "inner," and "outer," are only for reference to the directions in the accompanying drawings and are not intended to limit the scope of protection of the present invention. Throughout the accompanying drawings, the same elements are represented by the same or similar reference numerals. Furthermore, the shapes and dimensions of the components in the drawings do not reflect their actual size and proportions, but are only intended to illustrate the content of the embodiments of the present invention.

[0089] For certain implementations, if they are not key aspects of the present invention and are well-known to those skilled in the art, they have not been described in detail in the accompanying drawings or text due to space limitations. In such cases, reference can be made to relevant prior art for understanding. Furthermore, the purpose of providing the above embodiments is merely to ensure that the present invention meets legal requirements. The present invention can be implemented in many different forms and should not be construed as limited to the embodiments described herein. Moreover, the above definitions of elements and methods are not limited to the various specific structures, shapes, or methods mentioned in the embodiments, and those skilled in the art can make simple modifications or substitutions.

[0090] Similarly, it should be understood that, for the sake of brevity, in the above description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof. However, this method of the invention should not be interpreted as reflecting an intention that the claimed invention requires more features than expressly recited in each claim. Rather, as reflected in the claims, the various inventive aspects consist of fewer than all the features of the preceding single embodiment. Furthermore, embodiments may be used in combination with each other or with other embodiments based on design and reliability considerations; that is, technical features from different embodiments can be freely combined to form more embodiments. Therefore, the claims following the detailed description are hereby expressly incorporated into this detailed description, wherein each claim itself is a separate embodiment of the invention. 2

[0091] The above specific embodiments have provided a detailed description of the purpose, technical means, and beneficial effects of the present invention. It should be understood that the purpose of the detailed description is to enable those skilled in the art to better understand the present invention, and it is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for fabricating a MEMS structure, characterized in that, include: Step A: Form an arc-shaped protrusion of thermal oxide layer on the front side of the substrate; Wherein, the substrate is a silicon substrate, and step A includes: sub-step A1, forming a silicon oxide layer on the front side of the substrate through a thermal oxidation process; sub-step A2, patterning the silicon oxide layer on the front side of the substrate to form an arc-shaped protrusion of the silicon oxide layer, wherein the radius of curvature R of the arc-shaped protrusion of the thermal oxidation layer satisfies 1cm≤R≤3cm. Step B: Form a composite vibration layer with an arc-shaped protrusion on a substrate containing the arc-shaped protrusion of the thermal oxide layer; Step B includes: sub-step B1a, depositing a vibration support layer, a lower electrode layer, a piezoelectric layer, and an upper electrode layer sequentially on a substrate containing the arc-shaped protrusion of the thermo-oxidative layer; sub-step B1b, patterning the upper electrode layer, the piezoelectric layer, and the lower electrode layer, wherein the horizontal projection of the patterned upper electrode layer, the piezoelectric layer, and the lower electrode layer is inside the horizontal projection of the substrate back cavity and extends continuously. Alternatively, step B may include: sub-step B2a, depositing a lower electrode layer on a substrate containing the arcuate protrusions of the thermal oxide layer; sub-step B2b, patterning the lower electrode layer, retaining only the lower electrode layer on the thermal oxide layer; sub-step B2c, sequentially depositing a lower piezoelectric layer, a middle electrode layer, an upper piezoelectric layer, and an upper electrode layer on a substrate containing the lower electrode layer and the arcuate protrusions of the thermal oxide layer; sub-step B2d, patterning the upper electrode layer; wherein the horizontal projections of the patterned upper electrode layer and lower electrode layer are inside the horizontal projection of the substrate back cavity and extend continuously; Step C involves deep silicon etching on the back side of the substrate and releasing the thermal oxide layer to form a substrate back cavity, thereby suspending the composite vibration layer with an arc-shaped protrusion.

2. The preparation method according to claim 1, characterized in that, In sub-step A1, the thickness of the silicon oxide layer is between 0.1 μm and 20 μm; In sub-step A2, the silicon oxide layer is patterned using a dry etching method.

3. The preparation method according to claim 1, characterized in that, The radius of the horizontal projection of the substrate back cavity is between 0.1 mm and 3 mm; and / or The thicknesses of the piezoelectric layer, the upper piezoelectric layer, and the lower piezoelectric layer are between 0.1 μm and 10 μm, and their materials are selected from one or more of the following: aluminum nitride, scandium-doped aluminum nitride, zinc oxide, lead zirconate titanate; and / or The thickness of the upper electrode layer, middle electrode layer, and lower electrode layer is between 20 nm and 200 nm, and their materials are selected from one or more of the following: molybdenum, gold, aluminum, chromium; and / or The thickness of the vibration support layer is between 0.1 μm and 10 μm, and its material is selected from one or more of the following: Silicon nitride, monocrystalline silicon, aluminum nitride, scandium-doped aluminum nitride, zinc oxide, lead zirconate titanate.

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