Membrane structure and method for manufacturing a membrane structure, mems piezoelectric microphone

Abstract

The application provides a MEMS structure and a preparation method thereof, and a MEMS piezoelectric microphone. The preparation method comprises the following steps: sequentially depositing a lower electrode layer, a piezoelectric layer and an upper electrode layer on a front surface of a substrate; etching the upper electrode layer and the upper piezoelectric layer from top to bottom to reserve the inner upper electrode layer and the upper piezoelectric layer; and performing deep silicon etching on a back surface of the substrate until the lower electrode layer is reached to form a back cavity of the substrate. The longitudinal section of the piezoelectric layer after etching is in a "convex" shape, the neutral plane of the piezoelectric layer is not coincided with the geometric symmetry plane, the neutral plane is a plane in the piezoelectric layer where the stress and strain are 0, and the geometric symmetry plane is a plane extending along the horizontal direction through the midpoint in the thickness direction of the piezoelectric layer. In the application, the neutral plane is not coincided with the original geometric symmetry plane, the symmetry in the thickness direction is broken, the sensitivity of the structure is greatly improved, the difficulty of adjusting the process parameters to control the residual stress in the structure is reduced, and the accuracy of quantifying the residual stress is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of new electro-acoustic element manufacturing and microelectronic devices, and particularly relates to a MEMS structure and a preparation method thereof, and a MEMS piezoelectric microphone. BACKGROUND

[0002] The MEMS (Micro-Electro-Mechanical System) microphone is a new type of electro-acoustic element manufactured by using micro-machining technology, and has the characteristics of small size, good frequency response characteristics, low noise and the like. With the development of the miniaturization and lightness of intelligent electronic devices, the MEMS microphone is more and more widely used in these devices.

[0003] The MEMS microphone mainly includes a capacitive type and a piezoelectric type. The MEMS piezoelectric microphone is a microphone prepared by using microelectronic mechanical system technology and piezoelectric film technology, and has the advantages of small size, small volume and good consistency due to the adoption of semiconductor planar process and bulk silicon processing technology. Meanwhile, compared with the capacitive microphone, the piezoelectric microphone has the advantages of not needing a bias voltage, a large working temperature range, dustproof and waterproof, but has a relatively low sensitivity, which restricts the development of the MEMS piezoelectric microphone. Residual stress is a main factor restricting the improvement of the sensitivity of the MEMS piezoelectric microphone, and is particularly significant in the circular piezoelectric MEMS structure.

[0004] In the prior art, the MEMS piezoelectric microphone is composed of a vibration support layer and a piezoelectric functional layer, or is directly composed of two piezoelectric functional layers, and the piezoelectric functional layer is composed of a piezoelectric layer and upper and lower electrodes. The residual stress is generated when multiple layers of thin films with different thicknesses and different materials are deposited in the process of manufacturing the MEMS device, and too many layers of thin films with different thicknesses and different materials bring great error to the evaluation of the residual stress and great difficulty to the adjustment of the residual stress. SUMMARY

[0005] (I) Technical problems to be solved

[0006] In order to at least partially solve one of the above technical problems, the present application provides a MEMS structure and a preparation method thereof, and a MEMS piezoelectric microphone.

[0007] (II) Technical solutions

[0008] In the first aspect of the present application, a preparation method of a MEMS structure is provided. The preparation method comprises: step A, sequentially depositing a lower electrode layer, a piezoelectric layer and an upper electrode layer on the front surface of a substrate; step B, etching the upper electrode layer and the upper piezoelectric layer from top to bottom to reserve the inner upper electrode layer and the upper piezoelectric layer; and step D, performing deep silicon etching on the back surface of the substrate until the lower electrode layer to form a back cavity of the substrate; wherein the longitudinal section of the piezoelectric layer after etching is in the shape of a "convex" character, the neutral plane of the piezoelectric layer is not coincident with the original geometric symmetry plane, the neutral plane is a plane in the piezoelectric layer where the stress and strain are 0, and the original geometric symmetry plane is a plane extending along the horizontal direction through the midpoint in the thickness direction of the piezoelectric layer.

[0009] In some embodiments of the present application, in step A, the thickness of the piezoelectric layer is t; and in step B, the thickness of the upper piezoelectric layer is t1, wherein 0.1t≤t1≤0.9t.

[0010] In some embodiments of the present application, in step D, the cross section of the back cavity of the substrate is a first circle with a radius of R; and in step B, the cross section of the reserved upper electrode layer and upper piezoelectric layer after etching is a second circle with a radius of R1 concentric with the first circle; wherein the horizontal plane projection of the second circle falls within the horizontal plane projection of the first circle, and 0.5R≤R1<R.

[0011] In some embodiments of the present application, 0.4t≤t1≤0.6t, and 0.8R≤R1≤0.9R.

[0012] In some embodiments of the present application, 0.1μm≤t≤10μm, and 0.1mm≤R≤3mm.

[0013] In some embodiments of the present application, step A comprises: sub-step A1, depositing the lower electrode layer on the front surface of the substrate; sub-step A2, patterning the lower electrode layer to form N lower electrodes in the shape of a whole circle and individual fan shape; sub-step A3, depositing the piezoelectric layer on the front surface of the substrate containing the N lower electrodes; and sub-step A4, depositing the upper electrode layer on the piezoelectric layer; and after step A, step C is further included, which is patterning the upper electrode layer to form N upper electrodes in the shape of a whole circle and individual fan shape, corresponding to the N lower electrodes one by one; wherein the upper electrode, the lower electrode and the piezoelectric layer therebetween form a parallel-plate capacitor structure, the N parallel-plate capacitor structures on the MEMS structure are connected in series, and N≥2.

[0014] In some embodiments of the present application, the piezoelectric layer is made of one or more of the following materials: aluminum nitride, scandium-doped aluminum nitride, zinc oxide and lead zirconate titanate.

[0015] In some embodiments of the present application, the thickness of the upper electrode layer and the lower electrode layer is between 20nm and 200nm, and the material thereof is selected from one or more of the following: molybdenum, gold, aluminum and chromium.

[0016] In the second aspect of the present application, a MEMS structure is provided. The MEMS structure comprises: a substrate comprising: a peripheral substrate outer ring body; a substrate back cavity formed on the inner side of the substrate outer ring body; a lower electrode layer, a piezoelectric layer, and an upper electrode layer, which are sequentially formed on the substrate outer ring body and the substrate back cavity; wherein the longitudinal section of the piezoelectric layer is in the shape of a "convex" character, comprising: an upper layer piezoelectric layer and a lower layer piezoelectric layer, and the upper electrode layer is formed on the upper layer piezoelectric layer.

[0017] In some embodiments of the present application, the cross section of the substrate back cavity is a first circle with a radius R; the cross section of the upper electrode layer and the upper layer piezoelectric layer is a second circle concentric with the first circle and with a radius R1; wherein the horizontal projection of the second circle falls within the horizontal projection of the first circle; the thickness t1 of the upper layer piezoelectric layer satisfies: 0.4t ≤ t1 ≤ 0.6t, wherein t is the thickness of the piezoelectric layer; the first circle and the second circle satisfy: 0.8R ≤ R1 ≤ 0.9R.

[0018] In the second aspect of the present application, a MEMS piezoelectric microphone is provided. The MEMS piezoelectric microphone comprises: the MEMS structure as above; wherein the upper electrode layer and the lower electrode layer are each independently connected to the output end of the MEMS piezoelectric microphone, outputting an induced electrical signal.

[0019] (Three) beneficial effects

[0020] From the above technical solutions, the present application has at least one of the following beneficial effects relative to the prior art:

[0021] (1) In the MEMS structure of the prior art, the neutral plane of the single-layer piezoelectric layer structure substantially coincides with the geometric symmetry plane. In the present application, the longitudinal section of the etched piezoelectric layer is in the shape of a "convex" character, the neutral plane does not coincide with the original geometric symmetry plane, breaking the symmetry in the thickness direction, greatly improving the sensitivity of the structure, and reducing the difficulty of adjusting the process parameters to control the residual stress in the structure, and also improving the accuracy of quantifying the residual stress.

[0022] (2) Only a single piezoelectric layer and upper and lower electrode layers are needed, as no vibration support layer or second piezoelectric layer is needed, the present application also reduces the process complexity and cost, and improves the practicality of the structure.

[0023] (3) In the MEMS structure, partial etching also reduces the bending stiffness and increases the amplitude. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 、 Figure 2 are respectively a perspective view and a sectional view of an embodiment of the MEMS structure of the present application.

[0025] Figure 3 for preparingFigure 1 , Figure 2 the structure cross-sectional view after each step of the MEMS process shown in FIG.

[0026] Figure 4 the in-plane stress distribution cloud chart on the cross section of the MEMS piezoelectric microphone of the embodiment of the present application and the comparative structure under the action of the uniform sound pressure of 1 Pa.

[0027] Figure 5 the sensitivity frequency response curve of the MEMS structure shown in FIG. Figure 1 , Figure 2 the sensitivity frequency response curve of the MEMS structure shown in FIG. DETAILED DESCRIPTION

[0028] The present application provides a piezoelectric MEMS microphone structure directly composed of a single piezoelectric functional layer, wherein the piezoelectric functional layer is partially etched, the longitudinal section of the piezoelectric layer is in the shape of a "convex" character, so that the neutral plane and the original geometric symmetry plane do not coincide, the neutral plane is the plane in which the stress and strain of the piezoelectric layer are 0, and the original geometric symmetry plane is the plane extending along the horizontal direction through the midpoint of the thickness direction of the piezoelectric layer.

[0029] In order to make the purpose, technical scheme and advantages of the present application more clear and apparent, the present application is further described in detail below in combination with specific embodiments and with reference to the accompanying drawings.

[0030] According to the first and second aspects of the present application, a MEMS structure and a preparation method thereof are provided. Figure 1 , Figure 2 respectively are the perspective view and the cross-sectional view of the MEMS structure embodiment of the present application. As shown in FIG. Figure 1 and Figure 2 the MEMS structure of the embodiment comprises:

[0031] a substrate 10, comprising: a peripheral substrate outer ring body 11; a substrate back cavity 12 formed on the inner side of the substrate outer ring body;

[0032] a piezoelectric functional layer 20, comprising: a lower electrode layer 20a, a piezoelectric layer 20b, and an upper electrode layer 20c, sequentially formed on the substrate outer ring body and the substrate back cavity;

[0033] wherein the longitudinal section of the piezoelectric layer is in the shape of a "convex" character, comprising: a lower piezoelectric layer 20b1 and an upper piezoelectric layer 20b2; the upper electrode layer is formed on the upper piezoelectric layer. In other words, the original piezoelectric layer is an integral whole with the same radial thickness from top to bottom, and the outer periphery of the piezoelectric layer is partially etched in the thickness direction and the radial direction, so that the inner part of the piezoelectric layer has a greater thickness than the edge part, and the radius of the middle part of the piezoelectric layer is smaller than the radius of the cavity, and the radius of the upper electrode is equal to the radius of the middle part of the piezoelectric layer.

[0034] In this embodiment, the thickness t of the piezoelectric layer needs to satisfy: 0.1 μm≤t≤10 μm. The cross section of the substrate back cavity is a first circle, and the radius R of the first circle needs to satisfy: 0.1 mm≤R≤3 mm.

[0035] In this embodiment, the cross section of the upper electrode layer and the upper piezoelectric layer after etching is a second circle concentric with the first circle, with a radius R1, and the horizontal projection of the second circle falls within the horizontal projection of the first circle. The thickness of the upper piezoelectric layer is t1. R1 and t1 are determined by the maximum output energy.

[0036] Typically, the thickness t1 of the upper piezoelectric layer satisfies: 0.1t≤t1≤0.9t. Preferably, 0.4t≤t1≤0.6t. The radius R1 of the second circle satisfies: 0.5R≤R1<R. Preferably, 0.8R≤R1≤0.9R.

[0037] In this embodiment, the piezoelectric layer (including: the lower piezoelectric layer 20b1 and the upper piezoelectric layer 20b2) is continuously arranged in the horizontal direction; and the lower electrode layer 20a and the upper electrode layer 20c above the substrate back cavity are each divided into N electrodes that are overall circular and individually sector-shaped, with N≥2. The upper electrodes formed by the upper electrode layer correspond one by one to the lower electrodes formed by the lower electrode layer, and the upper electrodes, the lower electrodes, and the piezoelectric layer sandwiched therebetween form a parallel-plate capacitor structure. In the MEMS structure of this embodiment, N parallel-plate capacitors are formed, and through circuit design, the N parallel-plate capacitors are connected in series.

[0038] In this embodiment, the material of the substrate 10 is silicon. The piezoelectric layer material can be one or more of aluminum nitride (AlN), scandium-doped aluminum nitride (Sc x Al 1-x N), zinc oxide (ZnO), piezoelectric ceramic (PZT), etc. The preferred thickness range of the piezoelectric layer is 0.1 μm-10 μm. The electrode material can be one or more of molybdenum (Mo), gold (Au), aluminum (Al), chromium (Cr), etc. The preferred thickness range of the electrode layer is 20 nm-200 nm.

[0039] Specifically, in this embodiment, the radius R of the substrate back cavity 12 is 500 um, and the radius R1 of the upper piezoelectric layer 20b2 is 440 um. The thickness of the lower piezoelectric layer 20b1 is 400 nm, the thickness of the upper piezoelectric layer 20b2 is 400 nm, and the thickness of the upper and lower electrode layers is 100 nm. The piezoelectric material is selected to be aluminum nitride (AlN), and the upper and lower electrode materials are selected to be molybdenum (Mo). The upper and lower electrodes are equally divided into eight sector-shaped parallel-plate capacitors along the center, and the upper and lower electrodes are connected in series in turn, which can increase the output voltage by 8 times.

[0040] The following is described Figure 1 ,Figure 2 A method for preparing the MEMS structure shown in the figure. Figure 3 To prepare Figure 1 , Figure 2 The structure cross-sectional view after each step of the MEMS process shown in the figure. Please refer to Figure 1 , Figure 2 , Figure 3 The preparation method comprises:

[0041] Step A, sequentially depositing a lower electrode layer, a piezoelectric layer, and an upper electrode layer on the front surface of a substrate;

[0042] The substrate material is Si. The thickness of the piezoelectric layer is t, which satisfies: 0.1 μm≤t≤10 μm.

[0043] Further, step A comprises:

[0044] Sub-step A1, depositing a lower electrode layer on the front surface of the substrate, as shown in (a) of the figure; Figure 3

[0045] Sub-step A2, patterning the lower electrode layer to form N lower electrodes that are circular as a whole and fan-shaped as a single body;

[0046] Sub-step A3, depositing a piezoelectric layer on the front surface of the substrate containing the N fan-shaped lower electrodes, as shown in (b) of the figure; Figure 3

[0047] Sub-step A4, depositing an upper electrode layer on the piezoelectric layer, as shown in (c) of the figure. Figure 3 Step B, etching the peripheral upper electrode layer and the upper piezoelectric layer from top to bottom, leaving the inner upper electrode layer and the upper piezoelectric layer, and the longitudinal cross-section of the etched piezoelectric layer is in the shape of a "convex" character, as shown in (d) and (e) of the figure;

[0048] Figure 3 Unlike the technical solution in the prior art in which the neutral plane of the single-layer piezoelectric layer structure substantially coincides with the geometric symmetry plane, in this step, the longitudinal cross-section of the etched piezoelectric layer is in the shape of a "convex" character, the neutral plane of the piezoelectric layer does not coincide with the original geometric symmetry plane, and the neutral plane is the plane in the piezoelectric layer where the stress and strain are 0, and the original geometric symmetry plane is the plane extending along the horizontal direction through the midpoint of the thickness direction of the piezoelectric layer.

[0049]

[0050] ​​​​The thickness of the upper piezoelectric layer is t1, where 0.1t≤t1≤0.9t. Preferably, 0.4t≤t1≤0.6t. The cross section of the upper electrode layer 20c and the upper piezoelectric layer 20b2 after etching is a second circle concentric with the first circle, with a radius R1. Moreover, the horizontal projection of the second circle falls within the horizontal projection of the first circle, where 0.5R≤R1<R. Preferably, 0.8R≤R1≤0.9R.

[0051] Step C: patterning the upper electrode layer to form N upper electrodes each in the shape of a sector of a circle concentric with the lower electrode.

[0052] The upper electrode, the lower electrode and the piezoelectric layer therebetween form a parallel-plate capacitor structure. The N parallel-plate capacitor structures on the MEMS structure are connected in series, where N≥2.

[0053] In this embodiment, the number of sectors of the lower (or upper) electrode is N=8, but the present application is not limited thereto. In other embodiments of the present application, N can be any integer greater than or equal to 2, and all such embodiments are within the scope of the present application.

[0054] Step D: deep silicon etching on the back of the substrate until the lower electrode layer is reached, forming a back cavity of the substrate, as shown in Fig. (f). Figure 3

[0055] The cross section of the back cavity of the substrate is a first circle with a radius R, where 0.1mm≤R≤3mm.

[0056] It should be noted that the MEMS structure provided above can be applied to any practical scenario for precisely evaluating and regulating the residual stress of the composite vibration layer to provide specific performance. The practical scenario can be, but is not limited to, a microphone, an ultrasonic transducer, a pressure sensor or other actuators, of which the application in a MEMS piezoelectric microphone is the most typical. The following will also take the MEMS piezoelectric microphone as an example for introduction.

[0057] According to a third aspect of the present application, based on the above-mentioned MEMS structure, the present application provides a MEMS piezoelectric microphone. The microphone comprises the above-mentioned MEMS structure, wherein the upper electrode layer and the lower electrode layer are each independently connected to an output terminal of the MEMS piezoelectric microphone, outputting an induced electrical signal.

[0058] Regarding the MEMS structure and the MEMS piezoelectric microphone of this embodiment, the following three points should be noted:

[0059] (1) Difference from the prior art double wafer structure

[0060] ​In the prior art, there is a technical solution of partially etching the piezoelectric layer. However, these technical solutions are all applied to a bimorph structure completely symmetrical in the thickness direction, the neutral plane is located on the geometric neutral plane, the stress of the upper piezoelectric layer and the lower piezoelectric layer is equal in size and opposite in direction, the middle electrode is grounded, and the upper and lower electrodes are connected in parallel to output an electric signal. In this case, the edge partial etching is to reduce the structural bending stiffness, increase the amplitude, and avoid the neutralization of positive and negative charges in the same piezoelectric layer.

[0061] In the present application, the purpose of the edge partial etching is that the neutral plane does not coincide with the original geometric symmetry plane, the symmetry in the thickness direction is broken, the sensitivity of the structure is greatly improved, the difficulty of adjusting the process parameters to control the residual stress in the structure is reduced, and the accuracy of quantifying the residual stress is also improved.

[0062] (2) omitting the vibration support layer, partially etching to improve the vibration amplitude and improve the sensitivity

[0063] In the present application, the vibration support layer is omitted and partially etched, thereby the bending stiffness can be reduced and the amplitude can be increased. In addition, the process is simple, the cost is low, the stress evaluation and adjustment difficulty is greatly reduced,

[0064] (3) difference from the prior art of patterning the vibration support layer and then depositing the piezoelectric layer

[0065] In the prior art, there is a technical solution of patterning the vibration support layer and then depositing the piezoelectric layer. However, due to the asymmetry of the vibration support layer, the asymmetry of the piezoelectric layer itself is affected, and the effect of improving the sensitivity is reduced.

[0066] In the present application, the thickness of the lower and upper electrodes can be ignored, and the thickness of the piezoelectric layer is the main part of the piezoelectric functional layer in the entire MEMS structure, and the asymmetry of the piezoelectric layer has the greatest influence on the entire MEMS structure. In principle, the present application partially etches the piezoelectric layer to break the symmetry in the thickness direction, and the main purpose is to change the distribution position of the neutral plane, so that the stress integral in the piezoelectric layer is not zero, and there is a voltage output

[0067] The sensitivity of the MEMS piezoelectric microphone is discussed in detail as follows.

[0068] The expression of the voltage sensitivity of the piezoelectric microphone is as follows:

[0069]

[0070] wherein d 31 , ε is the transverse piezoelectric coefficient and the dielectric constant of the piezoelectric material, A is the area of the upper electrode, t is the thickness of the piezoelectric layer, σ r +σ θ is the in-plane stress of the piezoelectric layer in polar coordinates.

[0071] Figure 4 The in-plane stress distribution cloud chart on the cross section of the MEMS piezoelectric microphone of the embodiment of the application and the comparative structure under the action of 1 Pa uniform sound pressure. The in-plane stress σ r +σ θ is 0, representing the distribution shape of the neutral plane.

[0072] As Figure 4 shown in the upper diagram, for a single piezoelectric functional layer completely symmetrical in the thickness direction, under the action of external uniform sound pressure, the neutral plane coincides with the geometric symmetry plane, the in-plane stress in the thickness direction of the piezoelectric layer is distributed along the two sides of the neutral plane with equal size and opposite direction, at this time, the stress integral term in the sensitivity expression is 0, representing no voltage output.

[0073] As Figure 4 shown in the lower diagram, in the application, the purpose of the partial etching of the edge of the piezoelectric layer is to break the symmetry in the thickness direction, so that the neutral plane deviates from the original geometric symmetry plane, the stress integral term in the sensitivity expression is not 0, so there is output voltage. The entire MEMS structure is composed of a single piezoelectric functional layer, generally, the thickness of the electrode layer is much smaller than the thickness of the piezoelectric layer, the residual stress in the entire MEMS structure can be considered to be determined by the residual stress of the piezoelectric layer, which reduces the difficulty of adjusting the process parameters to control the residual stress in the structure, and also improves the accuracy of quantifying the residual stress. Since no vibration support layer or second piezoelectric functional layer is needed, the MEMS structure also reduces the process complexity and cost.

[0074] Figure 5 The sensitivity frequency response curve of the MEMS structure shown in Figure 1 , Figure 2 . The corresponding relationship between the radio frequency bias and the average stress of the AlN film can be used to realize the accurate control of the stress of the AlN film between-200 MPa and 200 MPa, and does not affect the stress uniformity, at this time, the residual stress of the piezoelectric functional layer is set to 0. From the frequency response curve, it can be seen that the sensitivity of more than-42 dB is realized in the frequency band of 20-12 kHz. The A-weighted noise in the frequency band of 20-20 kHz is-105.87 dB, and the overall signal-to-noise ratio reaches more than 64 dB.

[0075] So far, the various embodiments of the application have been introduced. According to the above description, those skilled in the art should have a clear understanding of the application.

[0076] It should be noted that the directional terms mentioned in the embodiments, such as "upper", "lower", "front", "back", "left", "right", "inner", "outer", etc., are only the directions of the drawings, and are not intended to limit the protection scope of the present application. Throughout the drawings, the same elements are represented by the same or similar reference numerals. Also, the shapes and sizes of the components in the drawings do not reflect the actual sizes and proportions, but only illustrate the content of the embodiments of the present application.

[0077] It should be noted that unless otherwise explicitly specified and limited, the terms "connected", "connected" should be understood broadly, for example, it can be fixedly connected, or detachably connected, or integrally connected; it can be directly connected, or indirectly connected through an intermediate medium, or the internal communication of two elements. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0078] It should be noted that unless explicitly stated to the contrary, the numerical parameters in the specification and claims of the present application can be approximate values, which can be changed according to the content of the present application. Specifically, all numbers indicating the content of composition, reaction conditions, etc. described in the specification and claims should be understood as being modified by the term "about" in all cases, which means that it includes a variation of ±10% from the specific number in some embodiments.

[0079] For some implementations, if it is not the key content of the present application and is well known to those skilled in the art, it is not described in detail in the drawings or text of the specification due to the limitation of the length, at this time it can be understood by referring to the related prior art. Also, the purpose of providing the above embodiments is only to make the present application meet the legal requirements, and the present application can be implemented in many different forms, and should not be interpreted as being limited to the embodiments described herein. In addition, the above definitions of elements and methods are not limited only to the various specific structures, shapes or ways mentioned in the embodiments, and those skilled in the art can make simple changes or replacements.

[0080] Similarly, it is to be understood that the brans of the application which has been often grouped in a single embodiment, figure or description thereof in the above description of illustrative embodiments of the application, various features of the application sometimes are grouped together in a single embodiment, figure or description thereof. No inference should be drawn however, that the brans of the application has required more features than are explicitly described in each claim. Rather, as is apparent from the claims, a distinct aspect or aspect of the application lies in less than all of the features of the previous single embodiment. Also, aspects of the embodiments can be combined with each other or other embodiments, based on design and / or operational considerations. Thus, the following claims are hereby expressly incorporated into this detailed description of the embodiments of the application, with each claim acting as a separate embodiment of the application.

[0081] The various specific embodiments described above are intended to be illustrative of the principles of the application, technical means of performing the application, and the advantages of the application. It is understood that the detailed description is intended to enable those skilled in the art to better understand the present application, and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method of fabricating a MEMS structure, characterized by, The method comprises the following steps: Step A, sequentially depositing a lower electrode layer, a piezoelectric layer, and an upper electrode layer on the front surface of a substrate, wherein the thickness of the piezoelectric layer is t, and 0.1 μm≤t≤10 μm; Step B, etching the upper electrode layer and the upper piezoelectric layer from top to bottom to reserve the inner upper electrode layer and the upper piezoelectric layer, wherein the thickness of the upper piezoelectric layer is t1, and 0.4t≤t1≤0.6t; Step D, performing deep silicon etching on the back surface of the substrate until the lower electrode layer is exposed to form a substrate back cavity; In the step D, the cross section of the substrate back cavity is a first circle with a radius of R; in the step B, the cross section of the upper electrode layer and the upper piezoelectric layer reserved after etching is a second circle concentric with the first circle with a radius of R1; the horizontal projection of the second circle falls within the horizontal projection of the first circle, and 0.8R≤R1≤0.9R; In the step B, the longitudinal section of the piezoelectric layer after etching is in the shape of a "convex" character, the neutral plane of the piezoelectric layer is not coincident with the original geometric symmetry plane, the neutral plane is a plane in the piezoelectric layer where the stress and strain are zero, and the original geometric symmetry plane is a plane extending along the horizontal direction through the midpoint of the thickness direction of the piezoelectric layer.

2. The production method according to claim 1, characterized by, 0.1mm≤R≤3mm.

3. The method according to claim 1, wherein the step A comprises the following sub-steps: sub-step A1, depositing a lower electrode layer on the front surface of a substrate; sub-step A2, patterning the lower electrode layer to form N lower electrodes in the shape of a whole circle and individual fan shape; sub-step A3, depositing a piezoelectric layer on the front surface of the substrate containing the N lower electrodes; and sub-step A4, depositing an upper electrode layer on the piezoelectric layer. The method further comprises the following step after the step A: step C, patterning the upper electrode layer to form N upper electrodes in the shape of a whole circle and individual fan shape, and corresponding to the N lower electrodes one by one. The upper electrode, the lower electrode, and the piezoelectric layer therebetween form a parallel-plate capacitor structure, the N parallel-plate capacitor structures on the MEMS structure are connected in series, and N≥2.

4. The method according to any one of claims 1 to 3, wherein the piezoelectric layer is made of one or more of the following materials: aluminum nitride, scandium-doped aluminum nitride, zinc oxide, and lead zirconate titanate; and / or the thickness of the upper electrode layer and the lower electrode layer is between 20 nm and 200 nm, and the material thereof is selected from one or more of the following: molybdenum, gold, aluminum, and chromium. The method comprises the following steps: a substrate comprising a substrate outer ring body and a substrate back cavity formed on the inner side of the substrate outer ring body; a lower electrode layer, a piezoelectric layer, and an upper electrode layer sequentially formed on the substrate outer ring body and the substrate back cavity, wherein the thickness of the piezoelectric layer is t, and 0.1 μm≤t≤10 μm; 5. A MEMS structure, characterized by, the longitudinal section of the piezoelectric layer is in the shape of a "convex" character, comprising an upper piezoelectric layer and a lower piezoelectric layer, and the upper electrode layer is formed on the upper piezoelectric layer; the thickness of the upper piezoelectric layer is t1, and 0.4t≤t1≤0.6t. ​ ​ ​ The cross section of the substrate back cavity is a first circle with a radius R; the cross section of the upper electrode layer and the upper piezoelectric layer is a second circle concentric with the first circle and with a radius R1; the horizontal projection of the second circle falls within the horizontal projection of the first circle, and 0.8R≤R1≤0.9R. The neutral plane of the piezoelectric layer is not coincident with the original geometric symmetry plane, the neutral plane is a plane in the piezoelectric layer where the stress and strain are 0, and the original geometric symmetry plane is a plane extending along the horizontal direction through the midpoint of the thickness direction of the piezoelectric layer.

6. A MEMS piezoelectric microphone, characterized by, The MEMS structure of claim 5; The upper electrode layer and the lower electrode layer are each independently connected to an output end of the MEMS piezoelectric microphone to output an induced electrical signal. ​

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