CMOS-MEMS integrated acoustic transducer and preparation method thereof

Abstract

The present invention provides a CMOS-MEMS integrated acoustic transducer and a preparation method thereof. The sensor can be used as both a microphone sensor and an ultrasonic transducer, and it comprises, from bottom to top, a substrate layer, an alternating dielectric layer and a metal layer, and a passivation layer. A cavity is etched on the nth dielectric layer, and a diaphragm and an upper electrode are formed on the top of the cavity, and a lower electrode is formed on the bottom. During preparation, the back-end (BEOL) layer of the COMS process is used as the structural layer of the MEMS device, the COMS electronic layer is integrated below the MEMS device layer, the metal layers are interconnected by tungsten plugs, and finally a cavity is formed on the dielectric layer by dry etching. The sensor of the present invention has the characteristics of good reliability, small size, wide frequency band, high sensitivity, and easy mass production, and can be applied to many fields such as medicine, military, industry, and agriculture.

Description

Technical Field

[0001] The invention relates to the technical field of CMOS-MEMS integrated sensor manufacturing, in particular to a CMOS-MEMS integrated acoustic transducer and a preparation method thereof. Background Art

[0002] Capacitive microphone sensors and capacitive ultrasonic transducers are currently common sensor devices, and their applications in real life are becoming more and more extensive.

[0003] The capacitive microphone sensor consists of two corresponding (upper and lower) electrodes and a diaphragm. When sound waves act on the diaphragm from the outside, the diaphragm deforms, and the distance between the (upper) electrode attached to the diaphragm and the fixed (lower) electrode changes, thereby changing the capacitance value. The capacitive microphone sensor measures the sound pressure based on the electrical signal generated in the above process.

[0004] Capacitive ultrasonic transducer (CMUT) was created in the 1990s. Its principle is to use ultrasound as a carrier for information transmission and is applied in medical imaging, non-destructive testing, ranging and flow measurement. The integration of capacitive ultrasonic transducer (CMUT) on a single chip has attracted widespread attention.

[0005] In recent years, the rapid development of complementary metal oxide semiconductor (CMOS) and micro-electromechanical system (MEMS) technology has led to the rapid development of sensor monolithic integration. Sensors manufactured using integrated CMOS-MEMS technology have the characteristics of good reliability, small size, high-density array element integration, wide bandwidth, high sensitivity, low manufacturing cost, and easy batch production. They have advantages in preparing small-size, large-scale arrays and low-parasitic ultrasound probes, and are a type of sensor with broad application prospects. Summary of the invention

[0006] An object of the present invention is to provide a CMOS-MEMS integrated acoustic transducer based on the above background technology, wherein the sensor can be used as a microphone sensor and an ultrasonic transducer.

[0007] The present invention is achieved through the following technical solutions:

[0008] A CMOS-MEMS integrated sound transducer, namely: a microphone sensor based on CMOS-MEMS integration, comprising a base layer, on which are arranged in order from bottom to top a first dielectric layer, a first metal layer, a second dielectric layer, a second metal layer, ..., an (n-1)th dielectric layer, an (n-1)th metal layer, an nth dielectric layer, and an nth metal layer, n≥3; adjacent metal layers are interconnected by tungsten plugs, a passivation layer is arranged on the nth metal layer, and an upper electrode soldering point and a lower electrode soldering point are arranged on the passivation layer; a cavity is etched on the nth dielectric layer; the passivation layer and the nth metal layer part at the top of the cavity form a diaphragm, the nth metal layer in the diaphragm serves as an upper electrode, the (n-1)th metal layer at the bottom of the cavity serves as a lower electrode, and the upper electrode at the top of the cavity and the lower electrode at the bottom are interconnected by tungsten plugs; the first metal layer to the (n-2)th metal layer serve as an electronic layer.

[0009] As a preferred technical solution, in the above-mentioned microphone sensor, the cavity is a cylindrical cavity, and the cavity is a vacuum; the diaphragm on the top of the cavity is also a circular diaphragm, and a number of circular through holes arranged in an array are evenly distributed on the diaphragm, and the circular through holes are vacuum; the lower electrode at the bottom of the cavity is a circular electrode, and its radius is half the radius of the cylindrical cavity.

[0010] A CMOS-MEMS integrated acoustic transducer, namely: an ultrasonic transducer based on CMOS-MEMS integration, comprising a substrate layer, on which a first dielectric layer, a first metal layer, a second dielectric layer, a second metal layer, ..., an (n-1)th dielectric layer, an (n-1)th metal layer, an nth dielectric layer, an nth metal layer are sequentially arranged from bottom to top, n ≥ 3; adjacent metal layers are interconnected by tungsten plugs, and a passivation layer is arranged on the nth metal layer. The passivation layer is provided with an upper electrode solder joint and a lower electrode solder joint; a plurality of cavities arranged in an array are etched on the nth dielectric layer; the passivation layer and the nth metal layer portion at the top of each cavity form respective corresponding diaphragms; the nth metal layer in the diaphragm at the top of each cavity serves as an upper electrode, the (n-1)th metal layer at the bottom of each cavity serves as a lower electrode, and the upper electrode at the top of each cavity and the lower electrode at the bottom are interconnected through a tungsten plug; the first metal layer to the (n-2)th metal layer serve as an electronic layer.

[0011] As a preferred technical solution, in the above-mentioned ultrasonic transducer, each cavity is a cylindrical cavity, and there is a vacuum in the cavity; the diaphragm on the top of each cavity is also a circular diaphragm, and each diaphragm is evenly provided with a number of circular through holes arranged in an array, and there is a vacuum in the circular through holes; the lower electrode at the bottom of each cavity is a circular electrode, and its radius is half of the radius of the cylindrical cavity, and the lower electrodes at the bottom of all cavities are interconnected together.

[0012] As a preferred technical solution, in the above-mentioned microphone sensor and ultrasonic transducer, the substrate layer is made of silicon wafer, and the silicon wafer is a lightly doped P-type (100) silicon wafer, with a typical doping concentration of N A ≈10 15 cm -3 ; The dielectric layer is made of silicon oxide, the metal layer is made of aluminum, and the passivation layer is made of silicon nitride.

[0013] As a preferred technical solution, in the above-mentioned microphone sensor and ultrasonic transducer, the electronic layer includes a CMOS signal processing circuit.

[0014] Furthermore, another object of the present invention is to provide a method for preparing the above-mentioned microphone sensor and ultrasonic transducer.

[0015] The present invention is achieved through the following technical solutions:

[0016] The method for preparing a microphone sensor based on CMOS-MEMS integration as described above comprises the following steps:

[0017] 1) A silicon wafer is selected as a starting base layer, and a CMOS process is used to complete the production of a CMOS active area, n dielectric layers, n metal layers and a passivation layer on the base layer, and each metal layer is interconnected through a tungsten (W) plug; wherein the nth metal layer is used as an upper electrode layer, the n-1th metal layer is used as a lower electrode layer, the nth dielectric layer is used as an etching cavity sacrificial layer, the passivation layer and the nth metal layer are used as the main body of the diaphragm structure, and a plurality of circular through holes arranged in an array are formed on the passivation layer and the nth metal layer, and the plurality of circular through holes are evenly distributed within the circular boundary range of the cavity, and the bottom ends of the circular through holes extend to the nth dielectric layer;

[0018] 2) A cavity is formed by etching a circular through hole on the nth dielectric layer using dry etching;

[0019] 3) The entire structure is vacuum packaged, and the cavity on the structure forms a vacuum-sealed cavity.

[0020] The method for preparing an ultrasonic transducer based on CMOS-MEMS integration as described above comprises the following steps:

[0021] 1) A silicon wafer is selected as a starting base layer, and a CMOS process is used to complete the production of a CMOS active area, n dielectric layers, n metal layers and a passivation layer on the base layer, and each metal layer is interconnected through a tungsten (W) plug; wherein the nth metal layer is used as an upper electrode layer, the n-1th metal layer is used as a lower electrode layer, the nth dielectric layer is used as an etching cavity sacrificial layer, the passivation layer and the nth metal layer are used as the main body of the diaphragm structure, and a plurality of through hole groups arranged in an array are formed on the passivation layer and the nth metal layer, each through hole group is composed of a plurality of circular through holes, and the plurality of circular through holes are evenly distributed within the circular boundary range of the cavity, and the bottom end of the circular through hole extends to the nth dielectric layer;

[0022] 2) A cavity is etched on the nth dielectric layer through the circular through holes of each through hole group by dry etching; a cavity is etched below a through hole group, and finally a plurality of cavities arranged in an array are formed on the nth dielectric layer;

[0023] 3) The entire structure is vacuum packaged, and the cavity on the structure forms a vacuum-sealed cavity.

[0024] As a preferred technical solution, in the above-mentioned preparation methods of the microphone sensor and the ultrasonic transducer, the dry etching is performed using hydrofluoric acid gas, and the vacuum packaging forms a vacuum-sealed cavity by depositing parylene.

[0025] The beneficial effects of the present invention are as follows:

[0026] 1) The microphone sensor and ultrasonic transducer of the present invention have the characteristics of high stability, wide operating frequency band, high sensitivity, low operating voltage, low packaging difficulty, adaptability to complex working environment, and easy mass production;

[0027] 2) The radius of the lower electrode of the microphone sensor and ultrasonic transducer of the present invention is half of the radius of the cavity, which not only reduces the parasitic capacitance but also improves the sensitivity of the microphone sensor and ultrasonic transducer;

[0028] 3) In the ultrasonic transducer of the present invention, each cavity, diaphragm and upper and lower electrodes constitute a single microelement, and a number of single microelements form an array structure. Structures of different array sizes can be designed according to actual use requirements, and the structure has strong scalability and applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0030] Figure 1 Schematic diagram of a top view of the microphone sensor in Example 1 (unpackaged).

[0031] Figure 2 Schematic diagram of the cross-sectional structure of the microphone sensor in Example 1 (unpackaged).

[0032] Figure 3 Schematic diagram of a top view of the ultrasonic transducer in Example 2 (not packaged).

[0033] Figure 4 Schematic diagram of a top view of a single microelement in the ultrasonic transducer in Example 2 (not packaged).

[0034] Figure 5 Schematic diagram of the cross-sectional structure of a single microelement in the ultrasonic transducer in Example 2 (unpackaged).

[0035] In the figure: 1-base layer, 2-tungsten plug, 3-passivation layer, 4-upper electrode solder joint, 5-lower electrode solder joint, 6-cavity, 7-circular through hole, 8-single microelement;

[0036] L1-the first dielectric layer, L(n-1)-the (n-1)th dielectric layer, Ln-the nth dielectric layer, M1-the first metal layer, M(n-1)-the (n-1)th metal layer, Mn-the nth metal layer. DETAILED DESCRIPTION

[0037] The following is a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field without creative work, including the embodiments of the present invention, belong to the protection scope of the present invention.

[0038] In the description of the present invention, it is to be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate the orientation or position relationship as shown in the integrated drawings, which are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance, quantity or position.

[0039] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0040] Example 1

[0041] like Figure 1 and Figure 2 As shown, a CMOS-MEMS integrated acoustic transducer, i.e., a microphone sensor based on CMOS-MEMS integration, comprises a substrate layer 1, wherein the substrate layer 1 is made of a silicon wafer, and the silicon wafer is a lightly doped P-type (100) silicon wafer, and a typical doping concentration N A ≈10 15 cm -3 ; The substrate layer 1 is provided with a first dielectric layer L1, a first metal layer M1, a second dielectric layer, a second metal layer, ..., the (n-1)th dielectric layer L(n-1), the (n-1)th metal layer M(n-1), the nth dielectric layer Ln, and the nth metal layer Mn in order from bottom to top, wherein n≥3, the dielectric layer is made of silicon oxide, and the metal layer is made of aluminum; the adjacent metal layers are interconnected through tungsten plugs 2, a passivation layer 3 is provided on the nth metal layer Mn, the passivation layer 3 is made of silicon nitride, and an upper electrode solder joint 4 and a lower electrode solder joint 5 are provided on the passivation layer 3; a cavity 6 is etched on the nth dielectric layer Ln, the cavity 6 is a cylindrical cavity 6, and the cavity 6 is a vacuum; the cavity The passivation layer 3 and the n-th metal layer Mn part on the top of 6 form a diaphragm, the n-th metal layer Mn in the diaphragm serves as an upper electrode, the diaphragm is a circular diaphragm, and a plurality of circular through holes 7 arranged in an array and communicating with the cavity 6 are evenly distributed on it, and the circular through holes 7 are vacuum; the (n-1)-th metal layer M(n-1) at the bottom of the cavity 6 serves as a lower electrode, and the lower electrode is a circular electrode, and its radius is half of the radius of the cylindrical cavity 6; the upper electrode at the top of the cavity 6 and the lower electrode at the bottom are interconnected through a tungsten plug 2, and the edge support of the cavity 6 is metal tungsten and silicon oxide; the first metal layer M1 to the (n-2)-th metal layer M(n-2) serve as an electronic layer, and the electronic layer includes a CMOS signal processing circuit.

[0042] The preparation method of the microphone sensor based on CMOS-MEMS integration uses the back-end-of-line (BEOL) layer of the CMOS process as the structural layer of the MEMS device, the CMOS electronic layer is integrated below the MEMS device layer, and each metal layer is interconnected through a tungsten plug 2, specifically comprising the following steps:

[0043] 1) A silicon wafer is selected as a starting base layer 1, and a CMOS process is used to complete the production of a CMOS active area, an n-layer dielectric layer, an n-layer metal layer and a passivation layer 3 on the base layer 1, and each metal layer is interconnected through a tungsten plug 2; wherein the n-th metal layer Mn is used as an upper electrode layer, the n-1-th metal layer M(n-1) is used as a lower electrode layer, the n-th dielectric layer Ln is used as a sacrificial layer for etching a cavity 6, the passivation layer 3 and the n-th metal layer Mn are used as the main body of the diaphragm structure, and a plurality of circular through holes 7 arranged in an array are formed on the passivation layer 3 and the n-th metal layer Mn, and the plurality of circular through holes 7 are evenly distributed within the circular boundary range of the cavity, and the bottom end of the circular through hole 7 extends to the n-th dielectric layer Ln;

[0044] In this step, the base layer 1 is suitable for almost any flat substrate, such as silicon wafers, glass wafers, etc. In order to adapt to the CMOS process, a silicon wafer is selected as the base layer 1. The silicon wafer uses a lightly doped P-type (100) silicon wafer with a typical doping concentration of N A ≈10 15 cm -3 ;

[0045] The CMOS process includes a 0.18um process and an advanced process with a smaller characteristic line width. The four basic micro-manufacturing technologies of the CMOS process: deposition, photolithography, doping and etching are combined to complete the production of the CMOS active area, n dielectric layers, n metal layers and the passivation layer 3 layer by layer; when depositing the dielectric layer, plasma enhanced chemical vapor deposition (PECVD) can be used to deposit silicon oxide; a metal layer is formed on each dielectric layer by sputtering metal aluminum, a layer of photoresist is coated on the metal layer, and the mask pattern is transferred to the photoresist by photolithography technology. The photoresist pattern is used as a mask and then the pattern of each metal layer is defined by a wet etching process to realize the functions of different metal layers; the metal layer is often used for electrical interconnection, electrode material, resistor, etc. In the present invention, the metal layer is used to make upper and lower electrodes and electronic layers.

[0046] 2) Dry etching is used to form a cavity 6 on the nth dielectric layer Ln through the circular through hole 7; wherein the dry etching is performed using hydrofluoric acid gas, and the silicon oxide in the sacrificial layer is isotropically dry-etched using hydrofluoric acid gas through the circular through hole 7. The hydrofluoric acid gas has a relatively high selectivity for the metal layer and will not corrode the metal layer during the dry etching process.

[0047] 3) The entire structure is vacuum packaged, and the cavity 6 on the structure forms a vacuum-sealed cavity 6; wherein, the vacuum packaging forms the vacuum-sealed cavity 6 by depositing parylene; in order to ensure the airtightness of the working environment of the device, the device needs to be vacuum-sealed, and the circular through hole 7 can be sealed by chemical vapor deposition (CVD) of oxide or nitride, and the device can be sealed by plating parylene.

[0048] Example 2

[0049] like Figures 3 to 5 As shown, a CMOS-MEMS integrated acoustic transducer, that is, an ultrasonic transducer based on CMOS-MEMS integration, includes a substrate layer 1, the substrate layer 1 is made of a silicon wafer, and the silicon wafer is a lightly doped P-type (100) silicon wafer with a typical doping concentration N A ≈10 15 cm -3 ; The substrate layer 1 is provided with a first dielectric layer L1, a first metal layer M1, a second dielectric layer, a second metal layer, ..., the (n-1)th dielectric layer L(n-1), the (n-1)th metal layer M(n-1), the nth dielectric layer Ln, and the nth metal layer Mn in order from bottom to top, wherein n≥3, the dielectric layer is made of silicon oxide, and the metal layer is made of aluminum; the adjacent metal layers are interconnected by tungsten plugs 2, a passivation layer 3 is provided on the nth metal layer Mn, the passivation layer 3 is made of silicon nitride, and an upper electrode solder joint 4 and a lower electrode solder joint 5 are provided on the passivation layer 3; a plurality of cavities 6 arranged in an array are etched on the nth dielectric layer Ln, the cavity 6 is a cylindrical cavity 6, and the cavity 6 is a vacuum; the passivation layer 3 and the nth metal layer Mn part at the top of each cavity 6 are shaped The n-th metal layer Mn in the diaphragm at the top of each cavity 6 serves as an upper electrode. The diaphragm is a circular diaphragm on which six circular through holes 7 communicating with the cavity 6 are evenly distributed, and the circular through holes 7 are filled with vacuum. The (n-1)-th metal layer M(n-1) at the bottom of each cavity 6 serves as a lower electrode. The lower electrode is a circular electrode with a radius that is half the radius of the cylindrical cavity 6, and the lower electrodes at the bottom of all cavities 6 are interconnected. The upper electrode at the top of each cavity 6 and the lower electrode at the bottom are interconnected through a tungsten plug 2, and the edge support of each cavity 6 is metal tungsten and silicon oxide. Each cavity 6, the diaphragm at its top, the upper electrode at its top, and the lower electrode at its bottom form a single microelement 8, and a number of such single microelements 8 are arranged in an array structure. The structure of the single microelement 8 is as follows: Figure 2 and Figure 3 As shown, the first metal layer M1 to the (n-2)th metal layer M(n-2) serve as electronic layers, and the electronic layers include CMOS signal processing circuits.

[0050] The above-mentioned method for preparing the CMUT device based on CMOS-MEMS integration uses the back-end (BEOL) layer of the COMS process as the structural layer of the MEMS device, the COMS electronic layer is integrated below the MEMS device layer, and each metal layer is interconnected through a tungsten plug 2, and specifically includes the following steps:

[0051] 1) A silicon wafer is selected as a starting base layer 1, and a CMOS process is used to complete the production of a CMOS active area, an n-layer dielectric layer, an n-layer metal layer and a passivation layer 3 on the base layer 1, and each metal layer is interconnected through a tungsten plug 2; wherein the n-th metal layer Mn is used as an upper electrode layer, the n-1-th metal layer M(n-1) is used as a lower electrode layer, the n-th dielectric layer Ln is used as a sacrificial layer for etching a cavity 6, the passivation layer 3 and the n-th metal layer Mn are used as the main body of the diaphragm structure, and a plurality of through hole groups arranged in an array are formed on the passivation layer 3 and the n-th metal layer Mn, each through hole group is composed of a plurality of circular through holes 7, and the plurality of circular through holes 7 are evenly distributed within the circular boundary range of the cavity, and the bottom end of the circular through hole 7 extends to the n-th dielectric layer Ln;

[0052] In this step, the base layer 1 is suitable for almost any flat substrate, such as silicon wafers, glass wafers, etc. In order to adapt to the CMOS process, a silicon wafer is selected as the base layer 1. The silicon wafer uses a lightly doped P-type (100) silicon wafer with a typical doping concentration of N A ≈10 15 cm -3 ;

[0053] The CMOS process includes a 0.18um process and an advanced process with a smaller characteristic line width. The four basic micro-manufacturing technologies of the CMOS process: deposition, photolithography, doping and etching are combined to complete the production of the CMOS active area, n dielectric layers, n metal layers and the passivation layer 3 layer by layer; when depositing the dielectric layer, plasma enhanced chemical vapor deposition (PECVD) can be used to deposit silicon oxide; a metal layer is formed on each dielectric layer by sputtering metal aluminum, a layer of photoresist is coated on the metal layer, and the mask pattern is transferred to the photoresist by photolithography technology. The photoresist pattern is used as a mask and then the pattern of each metal layer is defined by a wet etching process to realize the functions of different metal layers; the metal layer is often used for electrical interconnection, electrode material, resistor, etc. In the present invention, the metal layer is used to make upper and lower electrodes and electronic layers.

[0054] 2) Dry etching is used to form a cavity 6 on the n-th dielectric layer Ln through the circular through holes 7 of each through hole group; a cavity 6 is etched below a through hole group, and finally a plurality of cavities 6 arranged in an array are formed on the n-th dielectric layer Ln; wherein, the dry etching is performed using hydrofluoric acid gas, and the silicon oxide in the sacrificial layer is isotropically dry-etched using hydrofluoric acid gas through the circular through holes 7. The hydrofluoric acid gas has a relatively high selectivity for the metal layer and will not corrode the metal layer during the dry etching process.

[0055] 3) The entire structure is vacuum packaged, and the cavity 6 on the structure forms a vacuum-sealed cavity 6; wherein, the vacuum packaging forms the vacuum-sealed cavity 6 by depositing parylene; in order to ensure the airtightness of the working environment of the device, the device needs to be vacuum-sealed, and the circular through hole 7 can be sealed by chemical vapor deposition (CVD) of oxide or nitride, and the device can be sealed by plating parylene.

[0056] The ultrasonic transducer prepared by the present invention has the characteristics of good reliability, small size, high-density array element integration, wide frequency bandwidth, high sensitivity, low manufacturing cost, and easy mass production. It has advantages in preparing small-size and large-scale array ultrasonic probes and can be applied to many fields such as medicine, military, industry, and agriculture.

[0057] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art who is familiar with the present technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A CMOS-MEMS integrated acoustic transducer, characterized in that: The invention comprises a base layer, on which are arranged in order from bottom to top a first dielectric layer, a first metal layer, a second dielectric layer, a second metal layer, ..., an (n-1)th dielectric layer, an (n-1)th metal layer, an nth dielectric layer, and an nth metal layer, n≥3; adjacent metal layers are interconnected via tungsten plugs, a passivation layer is arranged on the nth metal layer, and an upper electrode soldering point and a lower electrode soldering point are arranged on the passivation layer; a cavity is etched on the nth dielectric layer; the passivation layer and the nth metal layer part at the top of the cavity form a diaphragm, the nth metal layer in the diaphragm serves as an upper electrode, the (n-1)th metal layer at the bottom of the cavity serves as a lower electrode, and the upper electrode at the top of the cavity and the lower electrode at the bottom are interconnected via tungsten plugs; the first metal layer to the (n-2)th metal layer serve as an electronic layer.

2. The CMOS-MEMS integrated acoustic transducer according to claim 1, characterized in that: The base layer is made of silicon wafer, which is a lightly doped P-type (100) silicon wafer; the dielectric layer is made of silicon oxide, the metal layer is made of aluminum, and the passivation layer is made of silicon nitride.

3. The CMOS-MEMS integrated acoustic transducer according to claim 1, characterized in that: The electronic layer includes CMOS signal processing circuits.

4. The CMOS-MEMS integrated acoustic transducer according to claim 1, characterized in that: The cavity is a cylindrical cavity, and there is a vacuum inside the cavity; the diaphragm on the top of the cavity is a circular diaphragm, and there are a number of circular through holes arranged in an array evenly distributed on the diaphragm, and there is a vacuum inside the circular through holes; the lower electrode at the bottom of the cavity is a circular electrode, and its radius is half the radius of the cylindrical cavity.

5. A CMOS-MEMS integrated acoustic transducer, characterized in that: The invention comprises a base layer, on which are arranged in order from bottom to top a first dielectric layer, a first metal layer, a second dielectric layer, a second metal layer, ..., an (n-1)th dielectric layer, an (n-1)th metal layer, an nth dielectric layer, and an nth metal layer, n≥3; adjacent metal layers are interconnected by tungsten plugs, a passivation layer is arranged on the nth metal layer, and an upper electrode welding point and a lower electrode welding point are arranged on the passivation layer; a plurality of cavities arranged in an array are etched on the nth dielectric layer, the passivation layer and the nth metal layer part at the top of each cavity form respective corresponding diaphragms, the nth metal layer in the diaphragm at the top of each cavity serves as an upper electrode, the (n-1)th metal layer at the bottom of each cavity serves as a lower electrode, and the upper electrode at the top of each cavity and the lower electrode at the bottom are interconnected by tungsten plugs; the first metal layer to the (n-2)th metal layer serve as electronic layers.

6. The CMOS-MEMS integrated acoustic transducer according to claim 5, characterized in that: The base layer is made of silicon wafer, which is a lightly doped P-type (100) silicon wafer; The dielectric layer is made of silicon oxide, the metal layer is made of aluminum, and the passivation layer is made of silicon nitride.

7. The CMOS-MEMS integrated acoustic transducer according to claim 5, characterized in that: The electronic layer includes CMOS signal processing circuits.

8. The CMOS-MEMS integrated acoustic transducer according to claim 5, characterized in that: Each cavity is a cylindrical cavity, and there is a vacuum inside the cavity; the diaphragm on the top of each cavity is a circular diaphragm, and each diaphragm is evenly provided with a number of circular through holes arranged in an array, and there is a vacuum inside the circular through holes; the lower electrode at the bottom of each cavity is a circular electrode, and its radius is half of the radius of the cylindrical cavity, and the lower electrodes at the bottom of all cavities are interconnected.

9. A method for preparing the CMOS-MEMS integrated acoustic transducer as claimed in claim 4, characterized in that: The steps include: 1) A silicon wafer is selected as a starting base layer, and a CMOS process is used to complete the production of a CMOS active area, n dielectric layers, n metal layers and a passivation layer on the base layer, and each metal layer is interconnected through a tungsten plug; wherein the nth metal layer is used as an upper electrode layer, the n-1th metal layer is used as a lower electrode layer, the nth dielectric layer is used as an etching cavity sacrificial layer, the passivation layer and the nth metal layer are used as the main body of the diaphragm structure, and a plurality of circular through holes arranged in an array are formed on the passivation layer and the nth metal layer, and the plurality of circular through holes are evenly distributed within the circular boundary range of the cavity, and the bottom ends of the circular through holes extend to the nth dielectric layer; 2) A cavity is formed by etching a circular through hole on the nth dielectric layer using dry etching; 3) The entire structure is vacuum packaged, and the cavity on the structure forms a vacuum-sealed cavity.

10. The method for preparing a CMOS-MEMS integrated acoustic transducer according to claim 9, characterized in that: The dry etching is performed using hydrofluoric acid gas, and the vacuum packaging forms a vacuum-sealed cavity by depositing parylene.

11. A method for preparing the CMOS-MEMS integrated acoustic transducer as claimed in claim 8, characterized in that: The steps include: 1) A silicon wafer is selected as a starting base layer, and a CMOS process is used to complete the production of a CMOS active area, n dielectric layers, n metal layers and a passivation layer on the base layer, and each metal layer is interconnected through a tungsten plug; wherein the nth metal layer is used as an upper electrode layer, the n-1th metal layer is used as a lower electrode layer, the nth dielectric layer is used as an etching cavity sacrificial layer, the passivation layer and the nth metal layer are used as the main body of the diaphragm structure, and a plurality of through hole groups arranged in an array are formed on the passivation layer and the nth metal layer, each through hole group is composed of a plurality of circular through holes, and the plurality of circular through holes are evenly distributed within the circular boundary range of the cavity, and the bottom end of the circular through hole extends to the nth dielectric layer; 2) A cavity is etched on the nth dielectric layer through the circular through holes of each through hole group by dry etching; a cavity is etched below a through hole group, and finally a plurality of cavities arranged in an array are formed on the nth dielectric layer; 3) The entire structure is vacuum packaged, and the cavity on the structure forms a vacuum-sealed cavity.

12. The method for preparing a CMOS-MEMS integrated acoustic transducer according to claim 11, characterized in that: The dry etching is performed using hydrofluoric acid gas, and the vacuum packaging forms a vacuum-sealed cavity by depositing parylene.

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