A MEMS acoustic wave sensor with a marker vector composite sensing function and a manufacturing method thereof

Abstract

The application discloses a MEMS sound wave sensor with scalar and vector composite sensing and a manufacturing method thereof, and belongs to the technical field of micro-electro-mechanical systems. The piezoelectric film, the scalar lower lead wire area and the scalar upper lead wire area constitute a piezoelectric MEMS sensor for sensing scalar sound wave information; the upper plate vector lead wire area, the upper plate, the upper plate lower insulating layer, the upper plate limiting concave frame, the upper plate anti-collision convex point, the back-shaped upper cantilever beam group, the vector lead wire area, the back-shaped lower cantilever beam group, the mass block, the support frame, the lower plate upper insulating layer, the lower plate limiting concave frame, the lower plate anti-collision convex point, the lower plate, the lower plate vector lead wire area constitute a sandwich type differential capacitance MEMS sensor for sensing vector sound wave information. The application has the advantages of scalar and vector composite sensing, small volume, large range, high sensitivity, high reliability, high integration, low cost, low noise, stable performance and the like.

Description

Technical Field

[0001] This invention belongs to the field of microelectromechanical systems (MEMS) technology, and specifically relates to a standard vector composite sensing MEMS acoustic wave sensor and its fabrication method. Technical Background

[0002] With the continuous development and progress of microelectronics, microdevices, and micromachining technologies, microsensors, with micro and nanofabrication processes as their core technology, have become an important development direction for microelectromechanical systems (MEMS). MEMS microsensors are among the most widely used microsensors and have been mass-produced and applied in transportation, medical devices, robotic systems, national defense, home appliances, and other related industries and fields.

[0003] Sound waves are generated by the mechanical vibration of objects and are chaotic, intermittent, or statistically random acoustic oscillations. Sound waves propagate through media such as air, solids, or liquids. Sound wave sensors, based on their working principles, are classified into: piezoelectric sound wave sensors, piezoresistive sound wave sensors, capacitive sound wave sensors, and electret sound wave sensors, among others.

[0004] Patent CN111142153B discloses a combined volumetric array of acoustic bar hydrophones and vector hydrophones. It includes a cylindrical mesh support frame, inside which is a narrow-waisted drum-shaped array of multiple acoustic bar hydrophone linear arrays; and outside the support frame, a cylindrical array of multiple circumferentially uniformly arranged vector hydrophone linear arrays. A watertight electronics compartment connected to watertight cables is mounted on top of the support frame, and all signal cables for the acoustic bar hydrophone linear arrays and vector hydrophone linear arrays are connected to the watertight electronics compartment. This invention achieves scalar and vector information perception of sound waves, but suffers from problems such as large size, high cost, and limited applicability.

[0005] A MEMS monolithically integrated scalar-vector composite acoustic wave sensor, disclosed in publication number CN112903087A, includes a substrate on which a scalar detection module and a vector detection module made of silicon-based material are disposed. The vector detection module includes a support body disposed within a first cavity, suspended from a frame by a connecting beam, with a first piezoresistive resistor disposed on the connecting beam, and sensitive cilia disposed on the support body. The scalar detection module includes a second cavity containing a sensitive thin film and a second piezoresistive resistor. This patent achieves the sensing of both scalar and vector acoustic wave information and can be integrated into a single process, but it suffers from problems such as low sensitivity and large horizontal area. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a scalar-vector composite sensing MEMS acoustic wave sensor and its fabrication method. This sensor has the advantages of scalar-vector composite sensing, small size, large range, high sensitivity, high reliability, high integration, low cost, low noise, and stable performance.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A MEMS acoustic wave sensor with scalar-vector composite sensing includes a three-layer structure: upper, middle, and lower. The main body of the upper layer is an upper plate 26. The upper surface of the upper plate 26 is covered with an upper plate insulating layer 21. A piezoelectric film 23 is located on the surface of the insulating layer, and scalar lower lead area 24 and scalar upper lead area 25 for detecting the piezoelectric film 23 extend from the sides of the piezoelectric film 23, respectively. The insulating layer is also provided with a cutout as an upper plate vector lead area 22. The lower surface of the upper plate is provided with an upper limit groove 32 and an upper plate lower insulating layer 31. The upper plate lower insulating layer 31 has a ring structure. The upper limit groove 32 is located in the area enclosed by the upper plate lower insulating layer 31. The upper plate anti-collision protrusion 33 is provided in the upper limit groove 32.

[0009] The main body of the middle layer structure is a support frame 45. Inside the support frame, there is a mass block 44. The top and bottom of the mass block are connected to the inner edge of the support frame by corresponding loop cantilever beams. The edge of the support frame 45 is also provided with a vector lead area 42.

[0010] The main body of the lower structure is the lower plate 54. The upper surface of the lower plate is provided with a lower limiting groove 52 and an upper insulating layer 51. The upper insulating layer 51 of the lower plate has a ring structure. The lower limiting groove is located in the area enclosed by the upper insulating layer 51 of the lower plate. The lower limiting groove 52 is provided with lower plate anti-collision protrusions 53. The lower surface of the lower plate is provided with a lower insulating layer 61 of the lower plate. The edge of the lower insulating layer 61 of the lower plate is hollowed out to form a vector lead area 62 of the lower plate.

[0011] According to claim 1, a MEMS acoustic wave sensor with scalar-vector composite sensing is characterized in that the piezoelectric thin film 23 is a piezoelectric ceramic material, and the scalar lower lead region 24 and the scalar upper lead region 25 are both used as leads to detect the electrical signal generated by the piezoelectric thin film 23; the piezoelectric MEMS sensor composed of the piezoelectric thin film 23, the scalar lower lead region 24, and the scalar upper lead region 25 is used to sense the scalar value of the acoustic wave.

[0012] Furthermore, the insulating layer 21 on the upper board is a silicon oxide insulating layer, used to isolate the scalar sensing MEMS sensor from the vector sensing MEMS sensor.

[0013] Furthermore, the lower surface of the scalar upper lead region 25 is bonded to the upper surface of the piezoelectric film 23, and the lower surface of the piezoelectric film 23 is bonded to the upper surface of the scalar lower lead region 24.

[0014] Furthermore, the mass block 44 is made of low-resistivity silicon material, and the upper plate vector lead area 22, vector lead area 42 and lower plate vector lead area 62 are connected to detect differential capacitance signals.

[0015] Furthermore, the loop-shaped cantilever beam includes a loop-shaped upper cantilever beam group 41 and a loop-shaped lower cantilever beam group 43, both of which are elastically movable structures. The upper and lower surfaces of the mass block 44 are square. The inner ends of each beam in the loop-shaped upper cantilever beam group 41 are connected to the upper surface layer of the mass block 44, and the outer ends of each beam are connected to the upper surface layer of the support frame 45. The inner ends of each beam in the loop-shaped lower cantilever beam group 43 are connected to the lower surface layer of the mass block 44, and the outer ends of each beam are connected to the lower surface layer of the support frame 45. The loop-shaped upper cantilever beam group 41 and the loop-shaped lower cantilever beam group 43 are arranged in parallel and centrally symmetrical.

[0016] Furthermore, there are gaps between the mass block 44 and the upper plate 26 and between the mass block 44 and the lower plate 54. The outer surfaces of the anti-collision protrusions 33 of the upper plate and the anti-collision protrusions 53 of the lower plate are covered with an insulating layer to prevent the mass block 44 from being attracted to the upper plate 26 and the lower plate 54 when it moves up and down.

[0017] A method for fabricating a scalar-vector composite sensing MEMS acoustic wave sensor, used to fabricate a scalar-vector composite sensing MEMS acoustic wave sensor as described above.

[0018] The specific steps for creating the upper structure are as follows:

[0019] Step 101: Perform the first oxidation on the double-sided polished low-resistivity silicon wafer;

[0020] Step 102: The upper-level board vector lead area 22 groove and the scalar lower lead area 24 groove are etched on the front side of the oxidized low-resistivity silicon wafer, and the upper limit positioning recess 32 is etched on the back side.

[0021] Step 103: Gold plating is performed in the groove of vector lead area 22 on the upper board;

[0022] Step 104: Perform a second oxidation on the low-resistivity silicon wafer;

[0023] Step 105: Gold plating is performed in the groove 24 of the scalar lower lead area;

[0024] Step 106: Grow a piezoelectric thin film 23 on the front side of the low-resistivity silicon wafer;

[0025] Step 107: Perform a third oxidation on the low-resistivity silicon wafer;

[0026] Step 108: A scalar upper lead area 25 groove is etched on the front side of the oxidized low-resistivity silicon wafer, and an upper board limiting recess 32 is etched on the back side while retaining the upper board anti-collision bump 33.

[0027] Step 109: Gold plating is performed in the groove 25 of the scalar lead area;

[0028] The specific steps for creating the middle layer structure are as follows:

[0029] Step 201: Wet deep etching is performed on the front side of two double-sided polished low-resistivity silicon wafers to obtain the lower cavity of the upper cantilever beam group 41 and the lower cantilever beam group 43.

[0030] Step 202: Perform silicon-silicon bonding on the two low-resistivity silicon wafers, face to face.

[0031] Step 203: Etch the upper cantilever beam group 41 and the lower cantilever beam group 43 in a spiral shape on the front and back sides of the bonded silicon wafer.

[0032] Step 204: Gold plating is performed at position 42 of the vector lead area;

[0033] The specific steps for creating the lower layer structure are as follows:

[0034] Step 301: Perform the first oxidation on the double-sided polished low-resistivity silicon wafer;

[0035] Step 302: A lower limit recess 52 is etched on the front side of the oxidized low-resistivity silicon wafer, and a groove for the vector lead area 62 of the lower stage board is etched on the back side.

[0036] Step 303: Gold plating is performed in the groove 62 of the vector lead area of ​​the lower-level board;

[0037] Step 304: Perform a second oxidation on the low-resistivity silicon wafer;

[0038] Step 305: Perform a third oxidation on the low-resistivity silicon wafer;

[0039] Step 306: Etch the lower board limiting recess 52 on the front side of the oxidized low-resistivity silicon wafer and retain the lower board anti-collision bump 53.

[0040] The upper structure 11, the middle structure 12, and the lower structure 13 are bonded together in a three-layer silicon-silicon bonded manner according to their corresponding relationship.

[0041] The present invention has the following beneficial effects:

[0042] 1. This invention uses a piezoelectric MEMS sensor and a sandwich-type differential capacitance MEMS sensor stacked vertically, which effectively improves the utilization rate of silicon wafers in the vertical direction, increases integration, reduces size, and ensures the sensor's range and sensitivity.

[0043] 2. This invention uses a piezoelectric MEMS sensor, which has the advantages of flat frequency response curve, simple structure and low cost.

[0044] 3. The present invention uses a sandwich-type differential capacitor MEMS sensor, which has the advantages of low inherent noise, flat frequency response curve and high sensitivity.

[0045] 4. This invention employs a sandwich-type differential capacitance MEMS sensor, which utilizes a spiral beam structure to effectively increase the movable range of the mass block, thereby increasing the capacitance change and thus improving the acceleration sensitivity.

[0046] 5. The structure of each layer of the present invention adopts silicon-silicon bonding, which effectively ensures the bonding strength of the sensor and improves the reliability of the sensor.

[0047] 6. The present invention uses low-resistivity silicon material for each layer, which is easy to lead wires, effectively reducing the manufacturing cost and reducing the difficulty of manufacturing electrodes for each layer.

[0048] 7. The present invention provides an insulating layer on the upper board to isolate the piezoelectric MEMS sensor and the sandwich-type differential capacitor MEMS sensor, preventing conduction between the sensors and improving the reliability of the sensors.

[0049] 8. The present invention is equipped with anti-collision frame and anti-collision protrusions to prevent sensor damage or failure during bonding, scratching and use. Attached Figure Description

[0050] Figure 1 This is a schematic diagram of the overall structure of the MEMS acoustic wave sensor with vector composite sensing in an embodiment of the present invention.

[0051] Figure 2 for Figure 1 A top view of the upper and middle layers.

[0052] Figure 3 for Figure 1 A bottom-view diagram of the upper and middle layers.

[0053] Figure 4a for Figure 1 A schematic diagram of the mid-layer structure.

[0054] Figure 4b for Figure 4a A schematic diagram of a medium-mass block and a cantilever beam.

[0055] Figure 5 for Figure 1 A top view of the middle and lower structure.

[0056] Figure 6 for Figure 1 A bottom-view diagram of the middle and lower structure.

[0057] Figure 7 for Figure 1 A schematic diagram of the construction of the middle and upper layers.

[0058] Figure 8 for Figure 1 A schematic diagram of the fabrication of the mid-layer structure.

[0059] Figure 9 for Figure 1 A schematic diagram of the construction of the middle and lower layers. Detailed Implementation

[0060] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0061] A MEMS acoustic wave sensor with scalar and vector composite sensing includes an upper structure 11, a middle structure 12, and a lower structure 13. The three-layer structure constitutes a MEMS sensor with scalar and vector composite sensing of acoustic waves.

[0062] The upper structure 11 includes an insulating layer 21 on the upper plate, a vector lead area 22 on the upper plate, a piezoelectric film 23, a scalar lower lead area 24, a scalar upper lead area 25, an upper plate 26, a lower insulating layer 31 on the upper plate, a limiting recessed frame 32 on the upper plate, and anti-collision protrusions 33 on the upper plate; the middle structure 12 includes a loop-shaped upper cantilever beam assembly 41, a vector lead area 42, a loop-shaped lower cantilever beam assembly 43, a mass block 44, and a support frame 45; the lower structure 13 includes an insulating layer 51 on the lower plate, a limiting recessed frame 52 on the lower plate, anti-collision protrusions 53 on the lower plate, a lower plate 54, a lower insulating layer 61 on the lower plate, and a vector lead area 62 on the lower electrode plate.

[0063] The piezoelectric MEMS sensor, consisting of the piezoelectric thin film 23, the scalar lower lead region 24, and the scalar upper lead region 25, is used to sense the scalar value of sound waves.

[0064] The sandwich-type differential capacitance MEMS sensor, consisting of the upper plate vector lead area 22, upper plate 26, upper plate lower insulating layer 31, upper plate limiting recess 32, upper plate anti-collision protrusion 33, loop-shaped upper cantilever beam group 41, vector lead area 42, loop-shaped lower cantilever beam group 43, mass block 44, support frame 45, lower plate upper insulating layer 51, lower plate limiting recess 52, lower plate anti-collision protrusion 53, lower plate 54, and lower electrode plate vector lead area 62, is used to sense the sound wave vector value.

[0065] Furthermore, the insulating layer 21 on the upper board is a silicon oxide insulating layer, used to isolate the scalar sensing MEMS sensor from the vector sensing MEMS sensor;

[0066] Furthermore, the piezoelectric thin film 23 is made of piezoelectric ceramic material, and the scalar lower lead area 24 and the scalar upper lead area 25 are used to detect the electrical signal generated by the piezoelectric thin film 23.

[0067] Furthermore, the lower surface of the scalar upper lead area 25 is attached to the upper surface of the piezoelectric film 23, and the lower surface of the piezoelectric film 23 is attached to the upper surface of the scalar lower lead area 24. The piezoelectric film 23, the scalar lower lead area 24, and the scalar upper lead area 25 are all parallel plates with flat surfaces.

[0068] Furthermore, the mass block 44 is made of low-resistivity silicon material, and the vector lead area 22 of the upper plate, the vector lead area 42, and the vector lead area 62 of the lower plate are led out to detect differential capacitance signals.

[0069] Furthermore, the spiral upper cantilever beam group 41 and the spiral lower cantilever beam group 43 are elastic and movable structures. The upper and lower surfaces of the mass block 44 are square. The inner ends of each beam of the spiral upper cantilever beam group 41 are connected to the upper surface layer of the mass block 44, and the outer ends of each beam are connected to the upper surface layer of the support frame 45. The inner ends of each beam of the spiral lower cantilever beam group 43 are connected to the lower surface layer of the mass block 44, and the outer ends of each beam are connected to the lower surface layer of the support frame 45. The spiral upper cantilever beam group 41 and the spiral lower cantilever beam group 43 are arranged in parallel and centrally symmetrical.

[0070] Furthermore, there are gaps between the mass block 44 and the upper plate 26, and between the mass block 44 and the lower plate 54. The outer surfaces of the anti-collision protrusions 33 of the upper plate and the anti-collision protrusions 53 of the lower plate are covered with an insulating layer to prevent the mass block 44 from being attracted to the upper plate 26 and the lower plate 54 when it moves up and down.

[0071] The following is a more specific example:

[0072] like Figures 1-9 As shown, the sensor includes an insulating layer 21 on an upper plate, a vector lead area 22 on an upper plate, a piezoelectric film 23, a scalar lower lead area 24, a scalar upper lead area 25, an upper plate 26, a lower insulating layer 31 on an upper plate, a limiting recessed frame 32 on an upper plate, anti-collision protrusions 33 on an upper plate, a loop-shaped upper cantilever beam assembly 41, a vector lead area 42, a loop-shaped lower cantilever beam assembly 43, a mass block 44, a support frame 45, an insulating layer 51 on a lower plate, a limiting recessed frame 52 on a lower plate, anti-collision protrusions 53 on a lower plate, a lower plate 54, a lower insulating layer 61 on a lower plate, and a vector lead area 62 on a lower electrode plate.

[0073] The vector lead area 22 of the upper plate is located on the upper plate 26 and is attached and conductive. The insulating layer 21 on the upper plate is located on the upper plate 26 but is not conductive. The scalar lower lead area 24, the piezoelectric film 23, and the scalar upper lead area 25 are located on the upper plate above the insulating layer 21 and are arranged from bottom to top. The lower insulating layer 31 and the anti-collision protrusions 33 of the upper plate are located on the lower layer of the upper plate 26 and are not conductive. The spiral upper cantilever beam group 41 and the spiral lower cantilever beam group 43 are both connected to the mass block 44 and the support frame 45. The inner ends of each beam on the upper plate are connected to the mass block 44. The upper surface layer is connected, and the outer ends of each beam in the upper layer are connected to the upper surface layer of the support frame 45. The inner ends of each beam in the lower layer are connected to the lower surface layer of the mass block 44. The outer ends of each beam in the lower layer are connected to the lower surface layer of the support frame 45. The loop-shaped upper cantilever beam group 41 and the loop-shaped lower cantilever beam group 43 are arranged in parallel and centrally symmetrically. The insulation layer 51 and the anti-collision protrusion 53 on the lower plate are located on the upper layer of the lower plate 54 but are not conductive. The lower insulation layer 61 on the lower plate is located on the lower layer of the lower plate 54 but is not conductive. The vector lead area 62 on the lower plate is located on the lower layer of the lower plate 54 and is conductive.

[0074] Both the upper cantilever beam group 41 and the lower cantilever beam group 43 are elastic movable beams, providing elasticity for the forced motion of the mass block 44.

[0075] Scalar upper lead area 25 and scalar lower lead area 24 are on the same side but their projected positions do not overlap. Upper plate vector lead area 22, vector lead area 42 and lower plate vector lead area 62 are on the same side but their projected positions do not overlap.

[0076] The sensor achieves scalar and vector information perception of sound waves through the upper structure 11, the middle structure 12, and the lower structure 13.

[0077] The MEMS sensor for scalar information perception is located in the upper structure 11 and consists of a piezoelectric thin film 23, a scalar lower lead area 24, and a scalar upper lead area 25. The MEMS sensor for vector information perception consists of an upper plate vector lead area 22, an upper plate 26, an upper plate lower insulating layer 31, an upper plate limiting recess 32, an upper plate anti-collision protrusion 33, a loop-shaped upper cantilever beam group 41, a vector lead area 42, a loop-shaped lower cantilever beam group 43, a mass block 44, a support frame 45, an upper plate insulating layer 51, a lower plate limiting recess 52, a lower plate anti-collision protrusion 53, a lower plate 54, and a lower electrode plate vector lead area 62.

[0078] The insulating layer 21 on the upper board provides insulation isolation between the scalar MEMS acoustic wave sensor and the vector MEMS acoustic wave sensor.

[0079] The upper plate 26, the upper cantilever beam assembly 41, the lower cantilever beam assembly 43, the mass block 44, the support frame 45, and the lower plate 54 are all made of low-resistivity silicon; the upper plate insulation layer 21, the upper plate lower insulation layer 31, the upper plate anti-collision bump 33, the lower plate upper insulation layer 51, the lower plate anti-collision bump 53, and the lower plate lower insulation layer 61 are all made of silicon oxide; the piezoelectric film 23 is piezoelectric ceramic; the upper plate vector lead area 22, the scalar lower lead area 24, the scalar upper lead area 25, the vector lead area 42, and the lower plate vector lead area 62 are all made of gold.

[0080] During the fabrication of this sensor, except for the cavities under the upper cantilever beam group 41 and the lower cantilever beam group 43 which are etched by wet etching, all other etching is done by dry etching. The three-layer structure uses silicon-silicon bonding, which effectively improves the reliability of the sensor.

[0081] The upper plate anti-collision protrusion 33 and the lower plate anti-collision protrusion 53 are formed by three oxidation processes. This setting prevents the mass block 44 from being attracted to the upper plate 26 and the lower plate 54 when it is forced to move, which would cause the sensor to fail. The two consecutive oxidation processes of the lower structure 13 can ensure that the gap formed between the lower plate 54 and the mass block 44 is consistent with the gap formed between the upper plate 26 and the mass block 44.

[0082] The working principle of this invention is as follows:

[0083] This scalar-vector composite sensing MEMS acoustic wave sensor consists of a piezoelectric MEMS sensor that senses the scalar quantity of acoustic waves and a sandwich-type differential capacitance MEMS sensor that senses the vector quantity of acoustic waves.

[0084] Acoustic wave scalar information sensing utilizes a piezoelectric MEMS sensor, consisting of a piezoelectric thin film and upper and lower leaded regions. When the piezoelectric thin film deforms under the influence of a sound wave, a potential difference is created within it. The scalar information value of the sound wave can be obtained using the piezoelectric effect equation. Acoustic wave vector information sensing utilizes a sandwich-type differential capacitance MEMS sensor, consisting of an upper electrode, a lower electrode, and a mass layer. When the mass mass moves in the Z-direction under the influence of a sound wave, the capacitance of the parallel-plate capacitor formed by the upper and lower electrodes changes. The vector information value of the sound wave can be obtained using the differential capacitance.

[0085] The working principle of acoustic scalar information sensing is as follows:

[0086] Piezoelectric thin films are only affected by sound waves and are not driven by voltage. The equation for the piezoelectric effect is:

[0087] D m =d mj T j

[0088] In the formula D m Let d be the electric displacement vector. mj piezoelectric constant matrix, Tj Stress tensor.

[0089] Because the piezoelectric thin film is polarized and extremely thin, a large electric displacement signal is obtained only in the Z direction, and its piezoelectric equation can be simplified to:

[0090] D3=d 31 T1+d 32 T2+d 33 T3

[0091] In the formula d 31 d 32 d 33 These are the piezoelectric coefficients of the piezoelectric film in the X, Y, and Z directions, respectively.

[0092] The working principle of acoustic vector information sensing is as follows:

[0093] Ideally, the mass is located between the upper and lower plates. Without acceleration, the mass remains stationary, and the expression for the capacitance values ​​is:

[0094]

[0095] In the formula, C1 and C2 are the capacitance values ​​of the upper and lower parts, respectively, S is the area of ​​the mass block and the upper and lower plates facing each other, and d0 is the initial distance between the mass block and the upper and lower plates.

[0096] When the vector-sensing MEMS acoustic sensor detects an acoustic wave, the mass block is forced to move, resulting in a displacement x. Therefore, the capacitance difference of the sandwich-type differential capacitance MEMS sensor is:

[0097]

[0098] The acceleration value is then calculated from the capacitance value obtained when acceleration is sensed in the Z direction:

[0099]

[0100] In the formula, m is the mass of the mass block, and k is the elastic stiffness of the system.

[0101] The creation of the upper structure 11 includes the following steps:

[0102] 1) Perform the first oxidation on the double-sided polished low-resistivity silicon wafer to form a smooth oxide layer on the upper and lower surfaces of the low-resistivity silicon wafer;

[0103] 2) The surface oxide layer of the low-resistivity silicon wafer is removed by dry etching, and the grooves where the vector lead area 22 of the upper board and the scalar lower lead area 24 are located are formed on the front side, and the upper board limiting recess 32 is formed on the back side.

[0104] 3) Gold plating is performed in the groove of the vector lead area 22 of the upper board, and the vector lead area 22 of the upper board is connected to the upper board 26.

[0105] 4) The low-resistivity silicon wafer is oxidized a second time to form an insulating layer 21 on the upper board used to isolate the scalar sensing MEMS sensor and the vector sensing MEMS sensor.

[0106] 5) Gold plating is applied to the groove of the scalar lower lead area 24. Due to the insulation effect of the insulating layer 21 on the upper board, the scalar lower lead area 24 is not conductive to the upper board 26.

[0107] 6) A piezoelectric thin film 23 is grown on the front side of the low-resistivity silicon wafer, and the piezoelectric thin film 23 is connected to the scalar lower lead region 24.

[0108] 7) Perform a third oxidation on the low-resistivity silicon wafer;

[0109] 8) The surface oxide layer of the low-resistivity silicon wafer is removed by dry etching, and a groove is formed on the front side where the scalar upper lead area 25 is located, and an upper board limiting recess 32 and an upper board anti-collision bump 33 are formed on the back side.

[0110] 9) Gold is plated in the groove of the scalar upper lead area 25, and the scalar upper lead area 25 is connected to the piezoelectric thin film 23. At this time, a piezoelectric MEMS sensor for sensing acoustic wave scalar information has been formed.

[0111] The fabrication of the middle layer structure 12 includes the following steps:

[0112] 1) The silicon material of the double-sided polished low-resistivity silicon wafer is removed by wet etching, and the lower cavity of the upper cantilever beam group 41 and the lower cantilever beam group 43 in the loop shape is formed on the front side.

[0113] 2) Two low-resistivity silicon wafers are bonded together face to face to form a mass block structure of an unreleased loop cantilever beam.

[0114] 3) The silicon material of the bonded silicon wafer is removed by dry etching to form a spiral upper cantilever beam group 41 and a spiral lower cantilever beam group 43 on the front and back sides.

[0115] 4) Gold plating is applied to the vector lead area 42, and the vector lead area 42 is connected to the mass block 44;

[0116] The creation of the lower layer structure 13 includes the following steps:

[0117] 1) Perform the first oxidation on the double-sided polished low-resistivity silicon wafer to form a smooth oxide layer on the upper and lower surfaces of the low-resistivity silicon wafer;

[0118] 2) The surface oxide layer of the low-resistivity silicon wafer is removed by dry etching, forming a lower-level board limiting recess 52 on the front side and a groove where the lower-level board vector lead area 62 is located on the back side.

[0119] 3) Gold plating is performed in the groove of the vector lead area 62 of the lower-level board, and the vector lead area 62 of the lower-level board is connected to the lower-level board 54;

[0120] 4) Perform a second oxidation on the low-resistivity silicon wafer;

[0121] 5) Perform a third oxidation on the low-resistivity silicon wafer to ensure that the gap between the middle layer structure 12 and the upper layer structure 11 is consistent with the gap between the middle layer structure 12 and the upper layer structure 11.

[0122] 5) The surface oxide layer of the low-resistivity silicon wafer is removed by dry etching, and the lower board limiting recess 52 and the lower board anti-collision bump 53 are formed on the front side.

[0123] The fabrication of a MEMS acoustic wave sensor based on vector-based composite sensing includes the following steps:

[0124] After the upper structure 11, the middle structure 12, and the lower structure 13 are prepared, three-layer silicon-silicon bonding is performed according to the corresponding relationship.

[0125] This invention can sense both scalar and vector information values ​​of sound waves. It has advantages such as scalar-vector composite sensing, small size, large range, high sensitivity, high reliability, high integration, low cost, low noise, and stable performance. The thickness of the piezoelectric film, piezoelectric material, mass block thickness, and number of loop cantilever beams can be adjusted according to the needs of the application environment to obtain different characteristic frequencies and elastic coefficients.

[0126] It should be noted that the above description is only a specific example of the present invention and does not constitute any limitation on the present invention. Obviously, those skilled in the art, after understanding the content and principle of the present invention, may make various modifications and changes in form and details without departing from the principle and structure of the present invention. However, these modifications and changes based on the concept of the present invention are still within the scope of protection of the claims of the present invention.

Claims

1. A MEMS acoustic wave sensor with vector-based composite sensing, comprising an upper, middle, and lower three-layer structure, characterized in that, The main body of the upper structure is the upper plate (26); the upper surface of the upper plate (26) is covered with an insulating layer (21) on the upper plate, the piezoelectric film (23) is located on the surface of the insulating layer, and the sides of the piezoelectric film (23) extend out scalar lower lead area (24) and scalar upper lead area (25) for detecting the piezoelectric film (23); the insulating layer is also provided with a hollow as the vector lead area (22) of the upper plate; the lower surface of the upper plate is provided with an upper limit groove (32) and an upper plate lower insulating layer (31), the upper plate lower insulating layer (31) is a ring structure, the upper limit groove (32) is located in the area enclosed by the upper plate lower insulating layer (31), and the upper plate anti-collision protrusion (33) is provided in the upper limit groove (32); The main body of the middle layer structure is a support frame (45), and a mass block (44) is provided inside the support frame. The top and bottom of the mass block are connected to the inner edge of the support frame through corresponding loop cantilever beams. The edge of the support frame (45) is also provided with a vector lead area (42). The main body of the lower structure is the lower plate (54). The upper surface of the lower plate is provided with a lower limiting groove (52) and an insulating layer (51) on the lower plate. The insulating layer (51) on the lower plate is a ring structure. The lower limiting groove is located in the area enclosed by the insulating layer (51) on the lower plate. The lower limiting groove (52) is provided with anti-collision protrusions (53) on the lower plate. The lower surface of the lower plate is provided with a lower insulating layer (61). The edge of the lower insulating layer (61) is hollowed out to form the vector lead area (62) of the lower plate.

2. The MEMS acoustic wave sensor with vector-based composite sensing according to claim 1, characterized in that, The piezoelectric thin film (23) is a piezoelectric ceramic material. The scalar lower lead area (24) and the scalar upper lead area (25) are both used as leads to detect the electrical signal generated by the piezoelectric thin film (23). The piezoelectric MEMS sensor composed of the piezoelectric thin film (23), the scalar lower lead area (24), and the scalar upper lead area (25) is used to sense the scalar value of the sound wave.

3. The MEMS acoustic wave sensor with vector-based composite sensing according to claim 1, characterized in that, The insulating layer (21) on the upper plate is a silicon oxide insulating layer, which is used to isolate the scalar sensing MEMS sensor from the vector sensing MEMS sensor.

4. A MEMS acoustic wave sensor with vector-based composite sensing according to claim 1, characterized in that, The lower surface of the scalar upper lead region (25) is attached to the upper surface of the piezoelectric film (23), and the lower surface of the piezoelectric film (23) is attached to the upper surface of the scalar lower lead region (24).

5. A MEMS acoustic wave sensor with vector-based composite sensing according to claim 1, characterized in that, The mass block (44) is made of low-resistivity silicon material. The vector lead area (22), vector lead area (42), and vector lead area (62) of the upper plate are connected to the lead for detecting differential capacitance signals.

6. A MEMS acoustic wave sensor with vector-based composite sensing according to claim 1, characterized in that, The loop-shaped cantilever beam includes a loop-shaped upper cantilever beam group (41) and a loop-shaped lower cantilever beam group (43), both of which are elastically movable structures. The upper and lower surfaces of the mass block (44) are square. The inner ends of each beam in the loop-shaped upper cantilever beam group (41) are connected to the upper surface layer of the mass block (44), and the outer ends of each beam are connected to the upper surface layer of the support frame (45). The inner ends of each beam in the loop-shaped lower cantilever beam group (43) are connected to the lower surface layer of the mass block (44), and the outer ends of each beam are connected to the lower surface layer of the support frame (45). The loop-shaped upper cantilever beam group (41) and the loop-shaped lower cantilever beam group (43) are arranged in parallel and centrally symmetrical.

7. A MEMS acoustic wave sensor with vector-based composite sensing according to claim 1, characterized in that, There are gaps between the mass block (44) and the upper plate (26) and between the mass block (44) and the lower plate (54). The outer surfaces of the anti-collision protrusions (33) of the upper plate and the anti-collision protrusions (53) of the lower plate are covered with an insulating layer to prevent the mass block (44) from being attracted to the upper plate (26) and the lower plate (54) when it moves up and down.

8. A method for fabricating a MEMS acoustic wave sensor with vector-based composite sensing, characterized in that, Used to fabricate a vector composite sensing MEMS acoustic wave sensor as described in any one of claims 1-7. The specific steps for creating the upper structure are as follows: Step 101: Perform the first oxidation on the double-sided polished low-resistivity silicon wafer; Step 102: The upper plate vector lead area (22) groove and the scalar lower lead area (24) groove are etched on the front side of the oxidized low-resistivity silicon wafer, and the upper limit positioning recess (32) is etched on the back side. Step 103: Gold plating is performed in the groove of the vector lead area (22) of the upper board; Step 104: Perform a second oxidation on the low-resistivity silicon wafer; Step 105: Gold plating is performed in the groove of the scalar lower lead area (24); Step 106: Grow a piezoelectric thin film (23) on the front side of the low-resistivity silicon wafer; Step 107: Perform a third oxidation on the low-resistivity silicon wafer; Step 108: A scalar upper lead area (25) groove is etched on the front side of the oxidized low-resistivity silicon wafer, and an upper board limiting recess (32) is etched on the back side, while retaining the upper board anti-collision bump (33). Step 109: Gold plating is performed in the groove of the scalar lead area (25); The specific steps for creating the middle layer structure are as follows: Step 201: Wet deep etching is performed on the front side of two double-sided polished low-resistivity silicon wafers to obtain the lower cavity of the upper cantilever beam group (41) and the lower cantilever beam group (43). Step 202: Perform silicon-silicon bonding on the two low-resistivity silicon wafers, face to face. Step 203: Etch the upper cantilever beam group (41) and the lower cantilever beam group (43) in a spiral shape on the front and back sides of the bonded silicon wafer; Step 204: Gold plating is performed at the vector lead area (42); The specific steps for creating the lower layer structure are as follows: Step 301: Perform the first oxidation on the double-sided polished low-resistivity silicon wafer; Step 302: A lower limiting recess (52) is etched on the front side of the oxidized low-resistivity silicon wafer, and a groove for the vector lead area (62) of the lower stage board is etched on the back side. Step 303: Gold plating is performed in the groove of the vector lead area (62) of the lower-level board; Step 304: Perform a second oxidation on the low-resistivity silicon wafer; Step 305: Perform a third oxidation on the low-resistivity silicon wafer; Step 306: Etch a lower board limiting recess (52) on the front side of the oxidized low-resistivity silicon wafer and retain the lower board anti-collision bump (53); The upper structure (11), the middle structure (12) and the lower structure (13) are bonded together in a three-layer silicon-silicon bonded manner according to the corresponding relationship.

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