A MEMS structure and a method for forming the same

Abstract

The present application discloses a MEMS structure, including: a substrate having a cavity; a first unit layer connected to the substrate and covering the cavity, the first unit layer including a first electrode layer, a first piezoelectric layer and a second electrode layer stacked in sequence from bottom to top, and the first piezoelectric layer and the second electrode layer have a through opening; a second unit layer formed above or below the first unit layer, the second unit layer including a second piezoelectric layer and a third electrode layer adjacent to the second piezoelectric layer, the second piezoelectric layer being located below the first electrode layer or the second piezoelectric layer being located above the second electrode layer, and the projection area of ​​the second piezoelectric layer being smaller than the projection area of ​​the cavity and larger than the projection area of ​​the through opening. The dual-chip structure in the MEMS structure reduces residual stress, reduces the warping of the diaphragm, and improves the sensitivity of the MEMS structure. In addition, a method for forming a MEMS structure is also provided.

Description

Technical Field

[0001] The present application relates to the technical field of micro-electromechanical systems, and in particular to a MEMS structure and a method for forming the same. Background Art

[0002] MEMS (Micro-Electro-Mechanical Systems) microphones mainly include capacitive and piezoelectric types. MEMS piezoelectric microphones are made using micro-electro-mechanical system technology and piezoelectric film technology. Due to the use of semiconductor planar technology and bulk silicon processing technology, they are small in size, small in volume, and have good consistency. At the same time, compared with capacitive microphones, they also have the advantages of not requiring bias voltage, a wide operating temperature range, and being dustproof and waterproof. However, their sensitivity is relatively low, which restricts the development of MEMS piezoelectric microphones.

[0003] Regarding the problem of how to improve the sensitivity of the MEMS structure in the related art, a common solution currently is to divide the electrode layer into multiple parts, but this method of dividing the electrode has a limited scope for improving the sensitivity. Summary of the invention

[0004] In response to the problem of how to improve the sensitivity of MEMS structures in related technologies, the present application proposes a MEMS structure and a method for forming the same, which can effectively output higher sensitivity.

[0005] The technical solution of this application is implemented as follows:

[0006] According to one aspect of the present application, a MEMS structure is provided, comprising:

[0007] a substrate having a cavity;

[0008] A first unit layer, connected to the substrate and covering the cavity, the first unit layer comprising a first electrode layer, a first piezoelectric layer and a second electrode layer stacked in sequence from bottom to top, and the first piezoelectric layer and the second electrode layer have through openings;

[0009] A second unit layer is formed above or below the first unit layer, the second unit layer includes a second piezoelectric layer and a third electrode layer adjacent to the second piezoelectric layer, the second piezoelectric layer is located below the first electrode layer or the second piezoelectric layer is located above the second electrode layer, and the projection area of ​​the second piezoelectric layer is smaller than the projection area of ​​the cavity and larger than the projection area of ​​the through opening.

[0010] Wherein, when the second piezoelectric layer is located below the first electrode layer, the MEMS structure further includes a first isolation layer, the first isolation layer is used to separate the first electrode layer from the third electrode layer, and the first electrode layer covers the second piezoelectric layer.

[0011] The wire portion of the third electrode layer is fixedly connected to the substrate, and the first isolation layer covers the third electrode layer.

[0012] The wire portion of the second electrode layer extends outward and is arranged in a staggered manner with the wire portion of the third electrode layer.

[0013] The first electrode layer, the second electrode layer and the third electrode layer have at least two mutually isolated partitions, and the mutually corresponding partitions of the first electrode layer, the second electrode layer and the third electrode layer constitute electrode layer pairs, and a plurality of the electrode layer pairs are sequentially connected in series.

[0014] The first electrode layer, the second electrode layer and the third electrode layer have corresponding 12 equal-angle partitions.

[0015] The outer edge of the first piezoelectric layer is located outside the outer edge of the first electrode layer, and the first piezoelectric layer wraps the outer edge of the first electrode layer.

[0016] The MEMS structure further includes a sacrificial layer, which is formed above the substrate, and the first electrode layer is connected to the substrate through the sacrificial layer.

[0017] Wherein, when the second piezoelectric layer is located above the second electrode layer, the MEMS structure further includes a second isolation layer, the second isolation layer is used to separate the third electrode layer from the second electrode layer, and the second piezoelectric layer covers the second electrode layer.

[0018] Wherein, the MEMS structure includes a piezoelectric MEMS microphone.

[0019] According to another aspect of the present application, a method for forming a MEMS structure is provided, comprising:

[0020] Providing a substrate, forming a first sacrificial material over the substrate, and patterning the first sacrificial material to form a first sacrificial layer having a groove;

[0021] Conformally forming a first electrode material on the first sacrificial layer, and patterning the first electrode material to form a first electrode layer, wherein the first electrode layer is formed at the bottom and sidewalls of the groove;

[0022] Conformally forming an isolation material above the first electrode layer, and patterning the isolation material to form an isolation layer;

[0023] Filling the groove, forming a first piezoelectric material above the isolation layer, retaining the first piezoelectric material in the groove to form a first piezoelectric layer, so that the upper surface of the first piezoelectric layer is coplanar with the upper surface of the isolation layer;

[0024] forming a second electrode material over the isolation layer and the first piezoelectric layer, and patterning the second electrode material to form a second electrode layer;

[0025] Sequentially forming a second piezoelectric material and a third electrode material on the second electrode layer, and sequentially patterning the third electrode material and the second piezoelectric material to form a second piezoelectric layer and a third electrode layer having through openings;

[0026] The bottom etching releases the substrate and the first sacrificial layer to form a cavity, so that a projection area of ​​the first piezoelectric layer is smaller than a projection area of ​​the cavity and larger than a projection area of ​​the through opening.

[0027] According to another aspect of the present application, a method for forming a MEMS structure is provided, comprising:

[0028] Providing a substrate, forming a first sacrificial material over the substrate, and patterning the first sacrificial material to form a first sacrificial layer having a groove;

[0029] Conformally forming a first electrode material on the first sacrificial layer, and patterning the first electrode material, wherein the first electrode layer is formed on the bottom and outer sidewall of the groove;

[0030] Filling the groove, forming a first piezoelectric material above the first electrode layer, retaining the first piezoelectric material in the groove to form a first piezoelectric layer, so that the upper surface of the first piezoelectric layer is coplanar with the upper surface of the first electrode layer;

[0031] forming a second electrode material over the first piezoelectric layer and the first electrode layer, and patterning the second electrode material to form a second electrode layer, wherein an outer edge of the second electrode layer is separated from the first electrode layer;

[0032] forming a second piezoelectric material above the second electrode layer, and patterning the second piezoelectric material to form a second piezoelectric layer;

[0033] forming an isolation material on a side of the second piezoelectric layer, and patterning the isolation material to form an isolation layer;

[0034] forming a third electrode material over the isolation layer and the second piezoelectric layer, and patterning the third electrode material to form a third electrode layer, wherein the isolation layer separates the second electrode layer from the third electrode layer;

[0035] Bottom etching releases the substrate and the first sacrificial layer to form a cavity and a through opening, wherein the through opening is located between the first piezoelectric layer and the first electrode layer, wherein the projection area of ​​the second piezoelectric layer is smaller than the projection area of ​​the cavity and larger than the projection area of ​​the through opening.

[0036] In summary, the dual-chip structure in the above MEMS structure reduces residual stress, reduces the warping of the diaphragm, and improves the sensitivity of the MEMS structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can also be obtained based on these drawings without paying creative work. It should be emphasized that according to the standard practice of the industry, the various components are not drawn to scale and are only used for illustration purposes. In fact, for the sake of clear discussion, the size of each component can be increased or decreased arbitrarily.

[0038] Figures 1 to 9 A cross-sectional schematic diagram showing an intermediate stage of a method for forming a MEMS structure according to some embodiments;

[0039] Fig.10 An exploded schematic diagram of a MEMS structure according to some embodiments is shown at a first viewing angle;

[0040] Fig.11 An exploded schematic diagram of a MEMS structure according to some embodiments is shown at a second viewing angle;

[0041] Fig.12 shows a perspective view of a MEMS structure according to some embodiments;

[0042] Fig.13 Shows Fig.12 A cross-sectional perspective view of a MEMS structure;

[0043] Fig.14 shows a perspective view of a MEMS structure according to some embodiments;

[0044] Fig.15 Shows Fig.14 A cross-sectional perspective view of a MEMS structure;

[0045] Fig.16 The sensitivity frequency response curve of the MEMS structure is shown;

[0046] Figures 17 to 25 A cross-sectional schematic diagram shows an intermediate stage of a method for forming a MEMS structure according to some other embodiments. DETAILED DESCRIPTION

[0047] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments in the present application belong to the scope of protection of this application.

[0048] The following disclosure provides many different embodiments or examples to realize different features of the present application. Specific examples of components and arrangements will be described below to simplify the present application. Of course, these are only examples and are not intended to be limiting. For example, the size of the component is not limited to the disclosed range or value, but may depend on the process conditions and / or the performance required for the device. In addition, in the following description, forming a first component above or on a second component may include an embodiment in which the first component and the second component are directly contacted, and may also include an embodiment in which an additional component may be formed between the first component and the second component, so that the first component and the second component may not be in direct contact. For simplicity and clarity, the various components may be arbitrarily drawn with different sizes.

[0049] Embodiment 1:

[0050] According to an embodiment of the present application, a MEMS structure and a method for forming the same are provided, and the MEMS structure will be described in detail below through the method for forming the MEMS structure. The MEMS structure can be used for sensors or actuators, such as microphones, speakers, and hydrophones.

[0051] In step S101, see Figure 1 and Figure 2, provide a substrate 10, form a first sacrificial material on the substrate 10, and pattern the first sacrificial material to form a first sacrificial layer 20 having a groove 21. Wherein, the substrate 10 includes silicon or any suitable silicon-based compound or derivative (such as silicon wafer, SOI, polysilicon on SiO2 / Si). The first sacrificial material includes silicon dioxide, phosphorus-doped silicon oxide (PSG for short), zinc oxide or other suitable sacrificial materials. The first sacrificial material can be formed by a CVD (Chemical Vapor Deposition) process, and then the first sacrificial material is dry-etched to form a groove 21. For example, when the first sacrificial material is silicon dioxide, it can be formed by thermal oxidation at a temperature of 1075°C, with source gases of oxygen and hydrogen, and flow rates of 6slm and 10slm respectively.

[0052] In step S102, see Figure 3 , a first electrode material is conformally formed on the first sacrificial layer 20, and the first electrode material is patterned to form a first electrode layer 31, and the first electrode layer 31 is formed on the bottom and sidewalls of the groove 21. The first electrode material can be formed by electron beam evaporation and magnetron sputtering. The first electrode material includes aluminum, gold, platinum, molybdenum, titanium, chromium, and composite films composed of them or other suitable materials. For example, when the first electrode material is aluminum, an aluminum electrode layer can be formed by magnetron sputtering at a power of 300 W, a pressure of 300 MPa, and room temperature.

[0053] In step S103, see Figure 4 , conformally forming a first isolation material on the first electrode layer 31, and patterning the first isolation material to form a first isolation layer 32. The first isolation material includes silicon dioxide, silicon nitride, phosphorus-doped silicon oxide or other suitable materials. The first isolation material can be formed by a CVD process. When silicon dioxide is used as an isolation layer, it can be obtained by a PECVD (Plasma Enhanced Chemical Vapor Deposition) method at a temperature of 300°C, gases SiH4 and N2O, and a pressure of 1 Torr.

[0054] In step S104, see Figure 5, fill the groove 21, form a first piezoelectric material above the first isolation layer 32, retain the first piezoelectric material in the groove 21 to form a first piezoelectric layer 33, so that the upper surface of the first piezoelectric layer 33 is coplanar with the upper surface of the first isolation layer 32. The first piezoelectric material includes one or more layers of zinc oxide, aluminum nitride, organic piezoelectric film, lead zirconate titanate (PZT), perovskite piezoelectric film, or other suitable materials. The first piezoelectric material can be formed by a CVD process or a magnetron sputtering process or other suitable process. When zinc oxide is used as the first piezoelectric material, a radio frequency magnetron sputtering method can be used, with a target material of ZnO, a radio frequency power of 80W, a pressure of 2Pa, and a substrate temperature of room temperature to form a zinc oxide film. When aluminum nitride is used as the first piezoelectric material, an radio frequency magnetron sputtering method can be used, with a target material of aluminum, a radio frequency power of 200W, a pressure of 0.27Pa, a bias voltage of 0 to -320V, and a substrate temperature of room temperature to 80°C to form an aluminum nitride film. The flat upper surfaces of the first piezoelectric layer 33 and the first isolation layer 32 may be obtained by CMP (Chemical Mechanical Polishing). When the first isolation layer 32 is exposed, the CMP process is stopped.

[0055] In step S105, see Figure 6 and Figure 7 A second electrode material is formed over the first isolation layer 32 and the first piezoelectric layer 33, and the second electrode material is patterned to form a second electrode layer 34. The material and formation process of the second electrode layer 34 may be the same as those of the first electrode layer 31.

[0056] In step S106, a second piezoelectric material and a third electrode material are sequentially formed on the second electrode layer 34, and the third electrode material and the second piezoelectric material are sequentially patterned to form a second piezoelectric layer 35 and a third electrode layer 36 having a through opening 37. The material and the forming process of the second piezoelectric layer 35 may be the same as the material and the forming process of the first piezoelectric layer 33. The material and the forming process of the third electrode layer 36 may be the same as the material and the forming process of the first electrode layer 31.

[0057] In step S107, see Figure 8 and Fig. 9, the substrate 10 and the first sacrificial layer 20 are released by bottom etching to form a cavity 11, so that the projection area of ​​the first piezoelectric layer 33 is smaller than the projection area of ​​the cavity 11 and larger than the projection area of ​​the through opening 37. Specifically, an insulating material and a photoresist are sequentially deposited on the back of the substrate 10 by a standard photolithography process, the photoresist is patterned to form a mask layer, and the exposed insulating material and substrate 10 are dry-etched until the first sacrificial layer 20 is exposed, thereby forming a cavity 11. Then, wet etching is used to remove the exposed first sacrificial layer 20. Finally, the insulating material on the back of the substrate 10 is removed. At this point, the MEMS structure is manufactured.

[0058] exist Fig. 9 In the MEMS structure shown, the first electrode layer 31, the first piezoelectric layer 33, the second electrode layer 34, the second piezoelectric layer 35 and the third electrode layer 36 constitute a dual-chip structure. The first piezoelectric layer 33 and the second piezoelectric layer 35 realize the conversion of acoustic energy into electrical energy under the piezoelectric effect. The first electrode layer 31, the second electrode layer 34 and the third electrode layer 36 transmit the generated electrical energy to other circuit elements.

[0059] The MEMS structure in Embodiment 1 will be described in detail below.

[0060] See also Fig.10 , Fig.11 , Fig.12 and Fig.13 , the MEMS structure includes a substrate 10, a first unit layer and a second unit layer.

[0061] The substrate 10 has a cavity 11. Figures 10 to 13 The substrate 10 is shown to be circular. Figure 14 to Figure 15 The substrate 10 is shown as a square. The substrate 10 may also include a pentagon, a hexagon, or other regular or irregular shapes.

[0062] The first unit layer is connected to the substrate 10 and covers the cavity 11 . The first unit layer includes a second electrode layer 34 , a second piezoelectric layer 35 and a third electrode layer 36 stacked in sequence from bottom to top. The second piezoelectric layer 35 and the third electrode layer 36 have through openings 37 .

[0063] The second unit layer is formed below the first unit layer. The second unit layer includes a first piezoelectric layer 33 and a first electrode layer 31 adjacent to the first piezoelectric layer 33. The first piezoelectric layer 33 is located below the second electrode layer 34. The projection area of ​​the first piezoelectric layer 33 is smaller than the projection area of ​​the cavity 11 and larger than the projection area of ​​the through opening 37.

[0064] In the MEMS structure, the second piezoelectric layer 35 and the third electrode layer 36 have through openings 37, which helps to reduce the internal residual stress of the second piezoelectric layer 35 and the third electrode layer 36. In addition, the first electrode layer 31 and the first piezoelectric layer 33 are suspended below the through openings 37, which is equivalent to the first electrode layer 31 and the first piezoelectric layer 33 being suspended in the air, further releasing the residual stress. As a result, this dual-chip structure reduces the residual stress, reduces the warping of the diaphragm, and improves the sensitivity of the MEMS structure.

[0065] Preferably, the wire portion of the first electrode layer 31 is fixedly connected to the substrate 10, and the first isolation layer 32 covers the first electrode layer 31. The first isolation layer 32 is conducive to leading out the wire portion of the suspended first electrode layer 31, and the first isolation layer 32 is used to separate the first electrode layer 31 from the second electrode layer 34 to avoid short circuit between the first electrode layer 31 and the second electrode layer 34.

[0066] Preferably, the wire portion of the third electrode layer 36 extends outward and is arranged offset from the wire portion of the first electrode layer 31 .

[0067] Preferably, the first electrode layer 31, the second electrode layer 34 and the third electrode layer 36 have at least two mutually isolated partitions, and the mutually corresponding partitions of the first electrode layer 31, the second electrode layer 34 and the third electrode layer 36 constitute electrode layer pairs, and multiple electrode layer pairs are sequentially connected in series. Preferably, the first electrode layer 31, the second electrode layer 34 and the third electrode layer 36 have corresponding 12 equal-angle partitions. By adopting the method of dividing the electrode layer, the sensitivity of the MEMS structure can be improved.

[0068] Preferably, the outer edge of the second piezoelectric layer 35 is located outside the outer edge of the second electrode layer 34, and the second piezoelectric layer 35 wraps the outer edge of the second electrode layer 34 to avoid short circuit between the second electrode layer 34 and the third electrode layer 36. Moreover, the second electrode layer 34 does not need to lead out the charge through a wire.

[0069] Preferably, the MEMS structure further includes a first sacrificial layer 20, which is formed above the substrate 10, and the first electrode layer 31 is connected to the substrate 10 through the first sacrificial layer 20. The first sacrificial layer 20 is conducive to forming a suspended structure of the first electrode layer 31 and the second piezoelectric layer 35.

[0070] Preferably, the MEMS structure comprises a piezoelectric MEMS microphone.

[0071] See also Fig.16, shows the sensitivity frequency response curve of the MEMS structure under specific dimensions and parameters. Among them, the radius of the cavity 11 is 543μm, the radius of the first electrode layer 31 and the first piezoelectric layer 33 is 390μm, the radius of the second electrode layer 34 is 600μm, the outer radius of the second piezoelectric layer 35 and the third electrode layer 36 is 600μm, and the inner radius is 385μm. Among them, the thickness of the first electrode layer 31, the second electrode layer 34 and the third electrode layer 36 is 100nm, and the material is molybdenum (Mo). The thickness of the first piezoelectric layer 33 and the second piezoelectric layer 35 is 600nm, and the material is aluminum nitride (AlN). From the sensitivity frequency response curve, it can be seen that the sensitivity of the MEMS structure is above -34dB in the frequency range of 100Hz to 20000Hz, and it is very flat within 10kHz.

[0072] Embodiment 2:

[0073] According to an embodiment of the present application, another MEMS structure and a method for forming the same are provided. The MEMS structure will be described in detail below through the method for forming the MEMS structure. The difference between the MEMS structure in Example 2 and the MEMS structure in Example 1 is that the middle suspended piezoelectric layer in Example 1 is located below the through opening 37, while the middle suspended piezoelectric layer in Example 2 is located above the through opening 37.

[0074] The method for forming the MEMS structure in this embodiment will be described in detail below. Since each material layer and the corresponding process method in the MEMS structure have been described in Embodiment 1, they will not be repeated here. It is worth noting that the same reference numerals in Embodiment 2 and Embodiment 1 represent the same material layer or element.

[0075] In step S201, see Fig.17 and Fig.18 , providing a substrate 10 , forming a first sacrificial material over the substrate 10 , and patterning the first sacrificial material to form a first sacrificial layer 20 having a groove 21 .

[0076] In step S202, see Fig.19 , a first electrode material is conformally formed on the first sacrificial layer 20 , and the first electrode material is patterned to form a first electrode layer 31 , wherein the first electrode layer 31 is formed on the bottom and outer sidewall of the groove 21 .

[0077] In step S203, see Fig. 20 , filling the groove 21, forming a first piezoelectric material above the first electrode layer 31, retaining the first piezoelectric material in the groove 21 to form a first piezoelectric layer 33, so that the upper surface of the first piezoelectric layer 33 is coplanar with the upper surface of the first electrode layer 31.

[0078] In step S204, see Fig.21, forming a second electrode material over the first piezoelectric layer 33 and the first electrode layer 31 , and patterning the second electrode material to form a second electrode layer 34 , wherein an outer edge of the second electrode layer 34 is separated from the first electrode layer 31 .

[0079] In step S205, see Fig. 22 , forming a second piezoelectric material above the second electrode layer 34 , and patterning the second piezoelectric material to form a second piezoelectric layer 35 .

[0080] In step S206 , a first isolation material is formed on the side of the second piezoelectric layer 35 , and the first isolation material is patterned to form a first isolation layer 32 .

[0081] In step S207, see Fig.23 A third electrode material is formed over the first isolation layer 32 and the second piezoelectric layer 35 , and the third electrode material is patterned to form a third electrode layer 36 . The first isolation layer 32 separates the second electrode layer 34 from the third electrode layer 36 .

[0082] In step S208, see Fig.24 and Fig.25 , the release substrate 10 and the first sacrificial layer 20 are bottom etched to form a cavity 11 and a through opening 37, wherein the through opening 37 is located between the first piezoelectric layer 33 and the first electrode layer 31, wherein the projection area of ​​the second piezoelectric layer 35 is smaller than the projection area of ​​the cavity 11 and larger than the projection area of ​​the through opening 37. Thus, the MEMS structure is manufactured.

[0083] The following will describe in detail the embodiment 2 Fig.25 Since the MEMS structure has been described in detail in Example 1, the same technical features of Example 2 as those of Example 1 will not be described here, and only the technical features different from those of Example 1 will be described below.

[0084] The substrate 10 has a cavity 11 .

[0085] The first unit layer is connected to the substrate 10 and covers the cavity 11 , and includes a second electrode layer 34 , a second piezoelectric layer 35 and a third electrode layer 36 stacked in sequence from bottom to top.

[0086] The second unit layer is formed below the first unit layer, and the second unit layer includes a first piezoelectric layer 33 and a first electrode layer 31 adjacent to the first piezoelectric layer 33. The first piezoelectric layer 33 is located below the second electrode layer 34. The first piezoelectric layer 33 and the first electrode layer 31 have a through opening 37. The projection area of ​​the second piezoelectric layer 35 is smaller than the projection area of ​​the cavity 11 and larger than the projection area of ​​the through opening 37.

[0087] In the MEMS structure, the first piezoelectric layer 33 and the first electrode layer 31 have a through opening 37, which helps to reduce the internal residual stress of the first piezoelectric layer 33 and the first electrode layer 31. In addition, the third electrode layer 36 and the second piezoelectric layer 35 are suspended above the through opening 37, which is equivalent to the third electrode layer 36 and the second piezoelectric layer 35 being suspended in the air, further releasing the residual stress. As a result, this dual-chip structure reduces the residual stress, reduces the warping of the diaphragm, and improves the sensitivity of the MEMS structure.

[0088] Preferably, the MEMS microphone further includes a first isolation layer 32 , wherein the first isolation layer 32 is used to separate the third electrode layer 36 from the second electrode layer 34 , and the second piezoelectric layer 35 covers the second electrode layer 34 .

[0089] Preferably, the MEMS structure further includes a first sacrificial layer 20 , which is formed above the substrate 10 , and the first electrode layer 31 is connected to the substrate 10 through the first sacrificial layer 20 .

[0090] In summary, the MEMS structure of the present application reduces residual stress and improves sensitivity by penetrating the opening 37 and the suspended piezoelectric layer. Then, the first electrode layer 31, the second electrode layer 34 and the third electrode layer 36 are divided into multiple parts, further improving the sensitivity of the MEMS structure.

[0091] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A MEMS structure, characterized in that: include: a substrate having a cavity; A first unit layer, connected to the substrate and covering the cavity, the first unit layer comprising: a second electrode layer, a second piezoelectric layer and a third electrode layer stacked in sequence from bottom to top, and the second piezoelectric layer and the third electrode layer have through openings; a second unit layer, formed below the first unit layer, the second unit layer comprising: a first piezoelectric layer and a first electrode layer adjacent to the first piezoelectric layer, the first piezoelectric layer being located below the second electrode layer, a projection area of ​​the first piezoelectric layer being smaller than a projection area of ​​the cavity and larger than a projection area of ​​the through opening; Wherein, the substrate includes: silicon or silicon-based compounds.

2. The MEMS structure according to claim 1, characterized in that: When the first piezoelectric layer is located below the second electrode layer, the MEMS structure further includes a first isolation layer, wherein the first isolation layer is used to separate the first electrode layer from the second electrode layer, and the second electrode layer covers the first piezoelectric layer.

3. The MEMS structure according to claim 2, characterized in that: The wire portion of the first electrode layer is fixedly connected to the substrate, and the first isolation layer covers the first electrode layer.

4. The MEMS structure according to claim 3, characterized in that: The wire portion of the third electrode layer extends outward and is arranged in a staggered manner with the wire portion of the first electrode layer.

5. The MEMS structure according to claim 4, characterized in that: The first electrode layer, the second electrode layer and the third electrode layer have at least two mutually isolated partitions, and the mutually corresponding partitions of the first electrode layer, the second electrode layer and the third electrode layer constitute electrode layer pairs, and a plurality of the electrode layer pairs are sequentially connected in series.

6. The MEMS structure according to claim 5, characterized in that: The first electrode layer, the second electrode layer and the third electrode layer have corresponding 12 equal-angle divisions.

7. The MEMS structure according to claim 2, characterized in that: The outer edge of the second piezoelectric layer is located outside the outer edge of the second electrode layer, and the second piezoelectric layer wraps the outer edge of the second electrode layer.

8. The MEMS structure according to claim 1, characterized in that: The MEMS structure further includes a sacrificial layer formed above the substrate, and the first electrode layer is connected to the substrate through the sacrificial layer.

9. The MEMS structure according to claim 1, characterized in that: The MEMS structure includes a piezoelectric MEMS microphone.

10. A MEMS structure, characterized in that: include: a substrate having a cavity; A first unit layer, connected to the substrate and covering the cavity, the first unit layer comprising: a second electrode layer, a second piezoelectric layer and a third electrode layer stacked in sequence from bottom to top; A second unit layer is formed below the first unit layer, the second unit layer comprising: a first piezoelectric layer and a first electrode layer adjacent to the first piezoelectric layer, the first piezoelectric layer is located below the second electrode layer, The first piezoelectric layer and the first electrode layer have through openings, and a projection area of ​​the second piezoelectric layer is smaller than a projection area of ​​the cavity and larger than a projection area of ​​the through openings; Wherein, the substrate includes: silicon or silicon-based compounds.

11. The MEMS structure according to claim 10, characterized in that: When the second piezoelectric layer is located above the second electrode layer, the MEMS structure further includes a second isolation layer, the second isolation layer is used to separate the third electrode layer from the second electrode layer, and the second piezoelectric layer covers the second electrode layer.

12. The MEMS structure according to claim 10, characterized in that: The MEMS structure includes a piezoelectric MEMS microphone.

13. A method for forming a MEMS structure, characterized in that: include: Providing a substrate, forming a first sacrificial material over the substrate, and patterning the first sacrificial material to form a first sacrificial layer having a groove; Conformally forming a first electrode material on the first sacrificial layer, and patterning the first electrode material to form a first electrode layer, wherein the first electrode layer is formed at the bottom and sidewalls of the groove; Conformally forming an isolation material above the first electrode layer, and patterning the isolation material to form an isolation layer; Filling the groove, forming a first piezoelectric material above the isolation layer, retaining the first piezoelectric material in the groove to form a first piezoelectric layer, so that the upper surface of the first piezoelectric layer is coplanar with the upper surface of the isolation layer; forming a second electrode material over the isolation layer and the first piezoelectric layer, and patterning the second electrode material to form a second electrode layer; Sequentially forming a second piezoelectric material and a third electrode material on the second electrode layer, and sequentially patterning the third electrode material and the second piezoelectric material to form a second piezoelectric layer and a third electrode layer having through openings; The bottom etching releases the substrate and the first sacrificial layer to form a cavity, so that a projection area of ​​the first piezoelectric layer is smaller than a projection area of ​​the cavity and larger than a projection area of ​​the through opening.

14. A method for forming a MEMS structure, characterized in that: include: Providing a substrate, forming a first sacrificial material over the substrate, and patterning the first sacrificial material to form a first sacrificial layer having a groove; Conformally forming a first electrode material on the first sacrificial layer, and patterning the first electrode material, wherein the first electrode layer is formed on the bottom and outer sidewall of the groove; Filling the groove, forming a first piezoelectric material above the first electrode layer, retaining the first piezoelectric material in the groove to form a first piezoelectric layer, so that the upper surface of the first piezoelectric layer is coplanar with the upper surface of the first electrode layer; forming a second electrode material over the first piezoelectric layer and the first electrode layer, and patterning the second electrode material to form a second electrode layer, wherein an outer edge of the second electrode layer is separated from the first electrode layer; forming a second piezoelectric material above the second electrode layer, and patterning the second piezoelectric material to form a second piezoelectric layer; forming an isolation material on a side of the second piezoelectric layer, and patterning the isolation material to form an isolation layer; forming a third electrode material over the isolation layer and the second piezoelectric layer, and patterning the third electrode material to form a third electrode layer, wherein the isolation layer separates the second electrode layer from the third electrode layer; Bottom etching releases the substrate and the first sacrificial layer to form a cavity and a through opening, wherein the through opening is located between the first piezoelectric layer and the first electrode layer, wherein the projection area of ​​the second piezoelectric layer is smaller than the projection area of ​​the cavity and larger than the projection area of ​​the through opening.

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