A MEMS accelerometer, seismic detector and preparation method

Abstract

The present application belongs to the field of MEMS devices, and specifically discloses a MEMS accelerometer, a seismic detector, and a preparation method. The sensitive unit of the accelerometer is prepared on SOI, and includes: an outer frame, a mass block, a spring structure, a pickup structure, a first feedback capacitor structure, and a second feedback capacitor structure; the spring structure is prepared on the first layer of SOI, and the first feedback capacitor structure and the second feedback capacitor structure are prepared on the third layer of SOI, and the first layer and the third layer are any combination of a substrate layer and a device layer; the first feedback capacitor structure and the second feedback capacitor structure are respectively arranged on the sensitive axis and the perpendicular sensitive axis of the mass block, and are variable area capacitors and variable spacing capacitors respectively; the pickup structure is arranged above the mass block on the first layer of SOI. Through this application, the area occupied by the MEMS accelerometer is reduced based on the SOI process, and the sensing signal and the feedback signal can be isolated through the insulating layer of SOI, thereby improving the detection accuracy of the accelerometer and regulating the linearity of the accelerometer feedback execution.

Description

Technical Field

[0001] The present application relates to the field of micro-electromechanical system (MEMS) devices, and more specifically, to a MEMS accelerometer, a seismic detector, and a preparation method thereof. Background Art

[0002] A MEMS accelerometer is a miniaturized acceleration sensor implemented using a combination of micromechanical structures and microelectronics. Due to its compact size, low power consumption, high resolution, and high precision, MEMS accelerometers are widely used in mobile devices, automobiles, drones, spacecraft, and other fields. Their operating principle is based on the micromass-spring system employed in microelectromechanical systems (MEMS) technology. When acceleration acts on an accelerometer, the micromass within the accelerometer displaces, causing the microspring system to vibrate, which in turn changes the output signals of sensor elements such as capacitors, piezoresistors, and magnetoresistors. These output signals are processed and calculated to determine the magnitude and direction of the acceleration. With the continuous advancement of MEMS technology, MEMS accelerometers have been optimized and improved in terms of size, power consumption, and accuracy. They have become an indispensable key technology in various smart devices, smart sensors, and the Internet of Things (IoT). However, accelerometer accuracy is a key constraint on their development.

[0003] Therefore, how to improve the measurement accuracy of MEMS accelerometers is an urgent problem to be solved. Summary of the Invention

[0004] In view of the defects of the existing technology, the purpose of this application is to provide a MEMS accelerometer, a seismic detector and a preparation method, aiming to solve the problem that the measurement accuracy of the existing MEMS accelerometer cannot be guaranteed.

[0005] To achieve the above objectives, in a first aspect, the present application provides a MEMS accelerometer, comprising: a sensitive unit;

[0006] The sensitive unit includes: an outer frame, a mass block, a spring structure, a pickup structure, a first feedback capacitor structure and a second feedback capacitor structure;

[0007] The upper end of the outer frame, the upper end of the mass block, and the spring structure are fabricated on a first layer of silicon-on-insulator (SOI) substrate; the spring structure connects the mass block to the outer frame;

[0008] The middle end of the outer frame and the middle end of the mass block are prepared on the second layer of SOI;

[0009] The lower end of the outer frame, the lower end of the mass block, the first feedback capacitor structure, and the second feedback capacitor structure are fabricated on the third layer of SOI; the second layer is an insulating layer, and the first and third layers are any combination of a substrate layer and a device layer; the first feedback capacitor structure and the second feedback capacitor structure are respectively arranged in the sensitive axis and perpendicular sensitive axis directions of the mass block, and are variable area capacitors and variable spacing capacitors, respectively; the moving plates of the two feedback capacitor structures are connected to the mass block, and the fixed plates are connected to the outer frame; the outer frame is provided with a plurality of isolation grooves penetrating the third layer of SOI, for electrically isolating the fixed plates of different polarities and types in the first feedback capacitor structure and the second feedback capacitor structure;

[0010] The pickup structure is arranged above the upper end of the mass block and is used to sense the input acceleration and convert it into a sensing signal output;

[0011] The first feedback capacitor structure and the second feedback capacitor structure are used to generate electrostatic force under the action of different feedback signals to adjust the position of the mass block.

[0012] It should be noted that the above-mentioned first feedback capacitor structure and second feedback capacitor structure are used to adjust the position of the mass block, and can also be called feedback actuators; wherein, the first feedback capacitor structure corresponds to feedback actuator A, and the second feedback capacitor structure corresponds to feedback actuator B. The above-mentioned pickup structure is a sensor of a sensitive unit. The present application adopts SOI to prepare the sensitive unit of the MEMS accelerometer, so that the sensor and the actuator are at the same horizontal position and arranged vertically, which greatly reduces the horizontal area occupied by the device, and can isolate the electrical signals of the two through the insulating layer of SOI, thereby eliminating the crosstalk between the two. Furthermore, the present application combines a variable area feedback actuator with a variable spacing feedback actuator, and realizes the separation of the two types of actuators by an electrical isolation method of an etched isolation groove in the SOI where the actuator is located, thereby avoiding crosstalk between the electrical signals of the two types of actuators, changing the weight of different actuators in the feedback force, and regulating the linearity of their feedback.

[0013] In summary, the present application prepares the sensitive unit of the MEMS accelerometer based on SOI, which can not only greatly reduce the horizontal area occupied by the device, but also isolate the electrical signals between the sensor and the actuator, as well as between two different actuators through the SOI insulating layer. There is no need for additional complex design or matching related circuit algorithms. In a simple way, the isolation of the three electrical signals can be achieved on the basis of reducing the horizontal area of ​​the device, effectively eliminating crosstalk between different electrical signals, and greatly improving the measurement accuracy of the MEMS accelerometer.

[0014] In a possible implementation, the accelerometer further includes: an upper cover plate and a lower cover plate; the upper cover plate is arranged above the sensitive unit, and the lower cover plate is arranged below the sensitive unit.

[0015] In a possible implementation, a first metal shielding layer is provided between the pickup structure and the upper end of the mass block;

[0016] An excitation structure is provided at the lower end of the upper cover plate; a second metal shielding layer is provided between the lower end of the upper cover plate and the excitation structure; the excitation structure is opposite to the pickup structure; insulating layers are provided at the upper and lower ends of the first and second metal shielding layers.

[0017] It should be noted that the metal shielding layer can enclose the sensor composed of the excitation structure and the pickup structure, thereby effectively isolating the sensor from the influence of the external environment and improving the measurement accuracy of the internal sensing unit.

[0018] In a possible implementation, a cavity is provided at the lower end of the upper cover plate and the upper end of the lower cover plate.

[0019] In a possible implementation, scribing lanes are provided on the lower end of the upper cover plate, the upper and lower ends of the sensitive unit, and the upper end of the lower cover plate;

[0020] The upper cover plate, the sensitive unit and the lower cover plate are connected by bonding metal and sealed by the dicing lanes.

[0021] In a second aspect, the present application provides a MEMS seismic detector, comprising the MEMS accelerometer provided in the first aspect above.

[0022] In a third aspect, the present application provides a method for preparing a MEMS accelerometer, comprising preparing a sensitive unit:

[0023] Deep silicon etching is performed on the SOI substrate layer or one of the device layers to obtain the lower end of the outer frame, the lower end of the mass block, a first feedback capacitor structure, and a second feedback capacitor structure; the first feedback capacitor structure and the second feedback capacitor structure are respectively arranged in the sensitive axis and perpendicular sensitive axis directions of the mass block, and are variable area capacitors and variable spacing capacitors, respectively; the moving plates of the two feedback capacitor structures are connected to the mass block, and the fixed plates are connected to the outer frame;

[0024] Performing deep silicon etching on the SOI device layer or another layer in the substrate layer to obtain the upper end of the outer frame, the upper end of the mass block, and the spring structure, and connecting the mass block to the outer frame through the spring structure;

[0025] The SOI insulating layer between the spring structure and the first feedback capacitor structure and the second feedback capacitor structure is removed to obtain the middle end of the outer frame and the middle end of the mass block on the SOI insulating layer;

[0026] Deep silicon etching is performed on the SOI substrate layer or the device layer to obtain a plurality of isolation trenches; the isolation trenches are used to electrically isolate fixed electrodes of different polarities and types in the first feedback capacitor structure and the second feedback capacitor structure;

[0027] A pickup structure is prepared on the top of the SOI device layer or another layer in the substrate layer.

[0028] In one possible implementation, a transmission channel for a feedback signal is provided above one of the SOI substrate layers or the device layer; a transmission channel for a sensing signal is provided above another of the SOI substrate layers or the device layer; the feedback signal is applied to a first feedback capacitor structure and a second feedback capacitor structure to generate a response electrostatic force and adjust the position of the mass block; the sensing signal is a signal output by the pickup structure sensing the input acceleration.

[0029] In one possible implementation, a pickup structure is prepared on an upper end of another layer in the SOI device layer or the substrate layer, including:

[0030] Sequentially preparing a first insulating layer, a first metal shielding layer, and a second insulating layer on the upper end of the other layer; then etching a deep hole; the deep hole sequentially penetrates the second insulating layer, the first metal shielding layer, the first insulating layer, and the SOI;

[0031] Depositing a pickup metal layer on the upper end of the second insulating layer, and electrically connecting another SOI layer to the first metal shielding layer by depositing the metal into the deep hole;

[0032] The pickup metal layer is patterned and etched to obtain a positive pickup plate, a negative pickup plate, scribe lines, and punch holes; the punch holes serve as electrical connections between the first feedback capacitor structure, the second feedback capacitor structure, and the first metal shielding layer and the outside world;

[0033] Performing patterned etching on the second insulating layer to obtain an etched second insulating layer, which corresponds to the etched pickup metal layer and is used to insulate the etched pickup metal layer;

[0034] Performing patterned etching on the first metal shielding layer to obtain an etched first metal shielding layer corresponding to the etched second insulating layer, and grounding the etched first metal shielding layer;

[0035] The first insulating layer is pattern-etched to obtain an etched first insulating layer corresponding to the etched metal shielding layer, and an etching groove is formed for deep silicon etching of the other layer.

[0036] In a possible implementation, the method further includes preparing an upper cover plate:

[0037] Etching a cavity in the middle of the lower end of the first silicon wafer;

[0038] After etching, a third insulating layer is deposited at the lower end of the first silicon wafer for the first time and patterned to obtain electrical connection holes;

[0039] Depositing a second metal shielding layer at the lower end of the first silicon wafer for the second time, and patterning the second metal shielding layer to obtain metal shielding electrodes, metal connecting lines, scribe lines, and electrical connection holes;

[0040] depositing a fourth insulating layer at the lower end of the first silicon wafer for a third time and patterning the fourth insulating layer, wherein the patterned fourth insulating layer corresponds to the second metal shielding layer;

[0041] Depositing an excitation metal layer at the bottom of the first silicon wafer for the fourth time and patterning the layer to obtain an excitation metal substrate, metal connecting lines, electrical connecting lines, and scribe lines;

[0042] An electrical connection hole is obtained by etching the upper end of the first silicon wafer.

[0043] In general, the above technical solutions conceived by this application have the following beneficial effects compared with the existing technologies:

[0044] The present application provides a MEMS accelerometer, a seismic detector, and a preparation method. The sensitive unit of the MEMS accelerometer is prepared using SOI, so that the sensor and actuator are at the same horizontal position and arranged vertically, which greatly reduces the horizontal area occupied by the device. The electrical signals of the two can be isolated through the insulating layer of SOI, thereby eliminating the crosstalk between the two. Furthermore, the present application combines a variable-area feedback actuator with a variable-pitch feedback actuator. By electrically isolating the actuators in a layer of etched isolation grooves in the SOI, the two types of actuators are separated, avoiding crosstalk between the electrical signals of the two types of actuators, changing the weight of different actuators in the feedback force, and thus regulating the linearity of their feedback. Therefore, the present application prepares the sensitive unit of the MEMS accelerometer based on SOI, which can not only greatly reduce the horizontal area occupied by the device, but also isolate the electrical signals between the sensor and the actuator, as well as between two different actuators through the SOI insulation layer. There is no need for additional complex design or matching related circuit algorithms. The isolation of the three electrical signals can be achieved in a simple way while reducing the horizontal area of ​​the device, effectively eliminating crosstalk between different electrical signals, and greatly improving the measurement accuracy of the MEMS accelerometer.

[0045] This application provides a MEMS accelerometer, a seismic detector, and a method for fabricating the same. A metal shielding layer is provided within the MEMS accelerometer to enclose the sensor, which comprises both an excitation structure and a pickup structure. This effectively isolates the sensor from the effects of the external environment and improves the measurement accuracy of the internal sensing unit. Furthermore, bonding metal and scribe lines allow the MEMS accelerometer to be completely sealed, further enhancing measurement accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 is a side view of a MEMS device provided in an embodiment of the present application;

[0047] Figure 2 Schematic diagram of the lower cover of the MEMS device provided in an embodiment of the present application;

[0048] Figure 3 This is a schematic diagram of a metal layer above the SOI substrate layer of a MEMS device provided in an embodiment of the present application;

[0049] Figure 4 Schematic diagram of the capacitor plate of the SOI substrate layer feedback actuator of the MEMS device provided in an embodiment of the present application;

[0050] Figure 5 This is a schematic diagram of a MEMS device electrical conduction deep hole provided in an embodiment of the present application;

[0051] Figure 6 This is a schematic diagram of a sensing pickup metal layer above the SOI device layer of a MEMS device provided in an embodiment of the present application;

[0052] Figure 7 This is a schematic diagram of the first insulating layer above the SOI device layer of the MEMS device provided in an embodiment of the present application;

[0053] Figure 8 This is a schematic diagram of a metal shielding layer above the SOI device layer of a MEMS device provided in an embodiment of the present application;

[0054] Figure 9 This is a schematic diagram of a second insulating layer above the SOI device layer of a MEMS device provided in an embodiment of the present application;

[0055] Figure 10 This is a schematic diagram of a spring oscillator system in a SOI device layer of a MEMS device provided in an embodiment of the present application;

[0056] Figure 11 is a side view of a sensitive unit in a MEMS device provided in an embodiment of the present application;

[0057] Figure 12 This is a schematic diagram of the cavity on the upper cover of the MEMS device provided in an embodiment of the present application;

[0058] Figure 13 This is a schematic diagram of the insulating layer of the upper cover of the MEMS device provided in an embodiment of the present application;

[0059] Figure 14 This is a schematic diagram of the metal shielding layer on the upper cover of the MEMS device provided in an embodiment of the present application;

[0060] Figure 15This is a schematic diagram of the metal insulation layer on the upper cover of the MEMS device provided in an embodiment of the present application;

[0061] Figure 16 This is a schematic diagram of the excitation metal layer of the upper cover plate of the MEMS device provided in an embodiment of the present application;

[0062] Figure 17 This is a schematic diagram of the back of the upper cover of the MEMS device provided in an embodiment of the present application;

[0063] Figure 18 The embodiment of the present application provides a top view of an existing MEMS device;

[0064] Figure 19 The embodiment of the present application provides a schematic diagram of closed-loop feedback of an existing MEMS device;

[0065] In all the drawings, the same reference numerals are used to represent the same elements or structures, wherein: 1 is an upper cover silicon wafer, 2, 4, 7, 9, 15, 61 are insulating layers distributed at different positions, 3, 8, 71 are metal shielding layers distributed at different positions, 5 is an excitation metal layer, 6 is a pickup metal layer, 10 is an SOI device layer, 11 is an SOI insulating layer, 12 is an SOI substrate layer, 13 is a substrate bonding metal layer; 14 is a lower cover bonding metal layer, 16 is a lower cover silicon wafer; 21, 31 are bonding metal pads distributed at different positions, 22, 31, 54, 132, 152 are dicing streets distributed at different positions, 23 is a lower cover cavity, 401 is a deep hole, 402 is an isolation groove, 403 is an outer frame, 41 is a fixed circuit of the feedback actuator A+ Pole, 42 is the movable electrode of feedback actuator A+, 43 is the fixed electrode of feedback actuator A-, 44 is the movable electrode of feedback actuator A-, 45 is the fixed electrode of feedback actuator A+, 46 is the movable electrode of feedback actuator B+, 47 is the fixed electrode of feedback actuator A-, 48 is the movable electrode of feedback actuator B-; 51 and 55 are wire holes distributed at different positions, 52 is the positive pickup plate, 53 is the negative pickup plate; 91 is the movable mass block, 92 is the spring beam, and 93 is the spring connecting beam; 111 is the upper cover cavity, 121, 134, 154, and 161 are electrical connection holes distributed at different positions, 131 is the metal shielding plate, 133 and 153 are metal connecting wires distributed at different positions; 151 is the excitation metal plate. DETAILED DESCRIPTION

[0066] In order to make the purpose, technical solutions and advantages of this application more clear, the following further describes this application in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0067] The embodiments of the present application are described below in conjunction with the drawings in the embodiments of the present application.

[0068] In one embodiment, the present application provides a MEMS accelerometer including: an upper cover plate, a sensitive unit, and a lower cover plate in a sandwich structure.

[0069] Specifically, the sensitive unit includes: an outer frame, a mass block, a spring structure, a pickup structure, a first feedback capacitor structure, and a second feedback capacitor structure;

[0070] The upper end of the outer frame, the upper end of the mass block and the spring structure are prepared on the first layer of SOI; the spring structure connects the mass block to the outer frame;

[0071] The middle end of the outer frame and the middle end of the mass block are prepared on the second layer of SOI;

[0072] The lower end of the outer frame, the lower end of the mass block, the first feedback capacitor structure, and the second feedback capacitor structure are fabricated on the third layer of SOI; the second layer is an insulating layer, and the first and third layers are any combination of a substrate layer and a device layer; the first feedback capacitor structure and the second feedback capacitor structure are respectively arranged in the sensitive axis and perpendicular sensitive axis directions of the mass block, and are variable area capacitors and variable spacing capacitors, respectively; the moving plates of the two feedback capacitor structures are connected to the mass block, and the fixed plates are connected to the outer frame; the outer frame is provided with a plurality of isolation grooves penetrating the third layer of SOI, for electrically isolating the fixed plates of different polarities and types in the first feedback capacitor structure and the second feedback capacitor structure;

[0073] The pickup structure is arranged above the upper end of the mass block and is used to sense the input acceleration and convert it into a sensing signal output;

[0074] The first feedback capacitor structure and the second feedback capacitor structure are used to generate electrostatic force under the action of different feedback signals to adjust the position of the mass block.

[0075] The different types mentioned above refer to different feedback capacitor structures. Different polarities refer to a feedback capacitor structure in which the spacing or area of ​​the capacitor plates increases or decreases, respectively, where the increase or decrease corresponds to capacitor plates of different polarities.

[0076] It is understandable that the upper cover is arranged above the sensitive unit and the lower cover is arranged below the sensitive unit. The upper and lower cover are used to provide an activity space for the sensitive unit and to seal the sensitive unit.

[0077] Furthermore, a first metal shielding layer is provided between the pickup structure and the upper end of the mass block;

[0078] An excitation structure is provided at the lower end of the upper cover plate; a second metal shielding layer is provided between the lower end of the upper cover plate and the excitation structure; the excitation structure is opposite to the pickup structure; insulating layers are provided at the upper and lower ends of the first and second metal shielding layers.

[0079] Furthermore, a cavity is provided at the lower end of the upper cover plate and the upper end of the lower cover plate.

[0080] Furthermore, scribing lanes are provided on the lower end of the upper cover plate, the upper and lower ends of the sensitive unit, and the upper end of the lower cover plate;

[0081] The upper cover plate, the sensitive unit and the lower cover plate are connected by bonding metal and sealed by the dicing lanes.

[0082] It is understandable that the MEMS accelerometer provided in the embodiment of the present application can also be used as a MEMS seismic detector when it is capable of performing seismic detection measurements. Therefore, the embodiment of the present application also protects the MEMS seismic detector corresponding to the above-mentioned MEMS accelerometer.

[0083] The following describes the preparation process of the above-mentioned MEMS accelerometer:

[0084] The MEME accelerometer provided in the embodiment of the present application is a uniaxial accelerometer (only measures acceleration in the direction of the sensitive axis) and adopts a sandwich structure. The sandwich structure requires two pieces of single crystal silicon and one piece of SOI to complete the device production. The two pieces of single crystal silicon are used to prepare the upper and lower cover plates respectively, and the SOI is used to prepare the sensitive unit. Figure 1 As shown:

[0085] like Figure 1 As shown, the upper cover includes a silicon wafer 1, an insulating layer 2, a metal shielding layer 3, a metal insulating layer 4 and a sensing excitation metal layer 5; the SOI includes a sensing pickup metal layer 6, a metal insulating layer 7, a metal shielding layer 8, an insulating layer 9, an SOI device layer 10, an SOI insulating layer 11, an SOI substrate layer 12, and a substrate bonding metal layer 13; the lower cover includes a bonding metal layer 14, an insulating layer 15, and a silicon wafer 16.

[0086] A silicon wafer 16 is taken out to make the lower cover plate. An insulating layer 15 is deposited on the lower cover plate to isolate the metal layer 14 from the silicon wafer 16. A metal film is then deposited to serve as the bonding metal layer 14 for bonding to the SOI wafer. The metal layer is then etched to obtain the bonding metal pad 21, the scribe line 22, and the cavity 23 that provides space for the mass block to move. The insulating layer 15 and the silicon wafer 16 are then etched and patterned to increase the depth of the cavity 23. Figure 2 shown.

[0087] In one embodiment, taking the fabrication of a feedback actuator on the SOI substrate layer and a spring structure on the device layer as an example (those skilled in the art may also arrange the feedback actuator on the device layer and the spring structure on the substrate layer according to actual needs), the following examples are provided for illustration:

[0088] The following is the production of the middle layer. Take a piece of SOI wafer, deposit a metal layer on the SOI substrate layer 12, and then etch and pattern the metal to obtain a metal layer 14 bonded to the lower cover, including a bonding metal pad 31 and a dicing road 31, as shown in FIG. Figure 3 shown.

[0089] Then, the substrate layer 12 is subjected to deep silicon etching to obtain a feedback actuator structure, including feedback actuator A and feedback actuator B, as shown in FIG. Figure 4 shown.

[0090] It should be noted that feedback actuators are usually set in pairs. Taking feedback actuator A as an example, it includes two pairs of feedback capacitor plates. When acceleration in one direction is input, the distance between one pair of plates becomes smaller, and the actuator provides a force opposite to the direction of acceleration, which can be marked as A+. The distance between the other pair of plates becomes larger, and the actuator provides a force opposite to the direction of acceleration, which can be marked as A-.

[0091] Fixed electrode 41 and movable electrode 42 form feedback actuator A+, fixed electrode 43 and movable electrode 44 form feedback actuator A-, fixed electrode 45 and movable electrode 46 form feedback actuator B+, and fixed electrode 47 and movable electrode 48 form feedback actuator B-. The center portion is a movable mass block 49. The outer frame is 403, and the outer frame has multiple isolation slots 402. The capacitor plates can be comb-shaped or other shapes, as long as one of the feedback actuators is a variable area capacitor and the other is a variable spacing capacitor.

[0092] The fixed electrodes 41, 43, 45, 47 are separated from each other by deep silicon etching, which can be achieved by etching a plurality of isolation grooves in the substrate layer (eg, Figure 4As shown, the outer frame includes multiple isolation slots 402, allowing actuators A+, A-, B+, and B- to be connected to different loops. The weight of each feedback actuator's contribution to the feedback force can be externally adjusted. Along the sensitive axis, feedback A+ and feedback B+ generate electrostatic driving forces in the same direction, and similarly, feedback A- and feedback B- generate electrostatic driving forces in the same direction. This design reduces the rotational torque generated by electrostatic force feedback. The actuators in feedback group A can be comb-tooth linear actuators (where the driving force is proportional to the square of the voltage and is independent of the travel), while the actuators in feedback group B can be parallel-plate nonlinear actuators. To reduce the nonlinear relationship between the electrostatic feedback force and travel, the actuators in feedback groups A and B can be connected to different feedback control loops, allowing for flexible adjustment of the linearity of the feedback system. The higher the proportion of feedback group A actuators connected to the electrostatic feedback force, the greater the reduction in the nonlinear relationship, and the lower the rotational torque generated by the electrostatic force feedback. To reduce the risk of plate adhesion caused by the pull-in effect, the MEMS accelerometer / MEMS seismic sensor structure is designed with displacement-blocking bumps (sloppcrs). In addition, the plate adhesion problem of feedback group B can be solved by adjusting the driving voltage of feedback group A actuator separately.

[0093] The following is the process of manufacturing the device layer of SOI. First, the device layer 10 of SOI is coated in sequence, which is the insulating layer 9, the metal shielding layer 8, and the metal insulating layer 7. Then, the upper surface is etched to obtain a deep hole 401, which is used as the electrical connection of the movable mass block of the substrate layer. Figure 5 shown.

[0094] On this basis, a film is formed to form a sensing pickup metal layer 6. At this time, the sidewalls of 401 are filled with metal to realize the electrical connection between the metal shielding layer 8 and the SOI substrate layer 12. Then the SOI device layer is made, which includes a spring beam, a movable mass block, a metal shielding structure, and a sensing pickup metal. Figure 6 As shown, the topmost sensing pickup metal layer 6 is first etched and patterned to obtain: a sensing positive pickup plate 52, a sensing negative pickup plate 53, a dicing road 54, and a punching hole 51 and a punching hole 55. The punching hole 51 is an electrical connection window between the feedback actuator and the outside world, and the punching hole 51 is an electrical connection window between the metal shielding layer 8 and the outside world.

[0095] Then, the metal insulating layer 7 is patterned and etched to obtain an insulating layer 61, as shown in FIG. Figure 7 As shown, it corresponds to the sensing pickup metal layer 6.

[0096] Then, the metal shielding layer 8 is patterned and etched to obtain a metal shielding layer 71 corresponding to the insulating layer 61. The metal shielding layer 71 is grounded to achieve the electromagnetic shielding effect of the sensing positive pickup plate 52 and the sensing negative pickup plate 53. Figure 8shown.

[0097] Then, the insulating layer 9 is patterned and etched to obtain an insulating layer 81, which corresponds to the metal shielding layer 71 and completely isolates the metal shielding layer 71 from the SOI device layer. At the same time, an etching groove 82 is formed for deep silicon etching of the SOI device layer. Figure 9 shown.

[0098] Further, the SOI device layer 10 is subjected to deep silicon etching to obtain a spring oscillator system, such as Figure 10 As shown, it includes a spring beam 92, a movable mass block 91, and a spring connecting beam 93, wherein the spring connecting beam 93 connects the spring beams 92 to improve the cross-axis suppression ratio of the sensor.

[0099] Finally, the device is released from the substrate layer, and the SOI insulating layer 11 between the device layer spring and the actuator plate can be removed by HF vapor release. Figure 11 As shown in the side view of the SOI, the movable mass of the device layer is connected to the movable mass of the actuator via the SOI insulating layer. The insulating layer between the spring beam 92 and the actuator's electrode plates 42 / 44 / 46 / 48 is etched, allowing the movable mass to move freely. Compared to the prior art, the actuator and sensor of this structure are stacked and share the same surface area, effectively saving the total device area and significantly improving device integration and miniaturization. Furthermore, the sensor and actuator are completely electrically isolated. Since capacitive sensors cause voltage changes through capacitance changes, and the external circuit detects the magnitude of the voltage change to obtain seismic wave signals, this completely isolated structure prevents the actuator's feedback voltage from coupling to the sensor voltage, thereby ensuring high accuracy of the sensor voltage and stable feedback voltage from the actuator.

[0100] Finally, the upper cover is made. First, take the silicon wafer 1 and use release etching to etch out a trapezoidal cavity 111, as shown in FIG. Figure 12 As shown, it can provide distance for the movement of the outer mass block while limiting the spacing between the sensing capacitor plates. The trapezoidal slope is to allow metal to connect to the outer frame from the cavity (if deep silicon etching is used, the steepness is too good and metal cannot be deposited on the sidewalls).

[0101] An insulating layer 2 is deposited on the silicon wafer and then patterned to obtain electrical connection holes 121, which are used to connect the electrical signals of all metal plates to the outside world.

[0102] Then deposit a metal shielding layer 3 and then pattern it, as shown in FIG. Figure 14 As shown, a metal shielding plate 131 , a metal connecting line 133 , a dicing street 132 , and an electrical connection hole 134 are obtained.

[0103] Then deposit a metal insulating layer 4 and then pattern it, see Figure 15 As shown, the metal insulating layer 144 is obtained corresponding to the metal shielding layer 3.

[0104] Then deposit a sensing excitation metal layer 5 and pattern it, see Figure 16 , obtaining the sensing excitation metal plate 151 and the metal connecting line 153, the electrical connection hole 154 and the dicing street 152.

[0105] Finally, the upper cover is etched back to obtain the electrical connection hole 161, see Figure 17 .

[0106] In the final step, the three-layer structure is metal-bonded, such as gold-gold bonding, to obtain a corresponding MEMS accelerometer or MEMS seismic detector.

[0107] It should be noted that Figure 18 The embodiment of the present application provides a top view of an existing MEMS device; Figure 18 As shown in the figure, when the sensor (pickup structure) and the feedback actuator (feedback capacitor plate) are laid flat (set on a horizontal plane), Figure 18 As can be seen in the figure, the dark color is the movable mass block and the light color is the fixed structure. It can be seen that the area of ​​the existing accelerometer is the area of ​​the sensing electrode plus the area of ​​the feedback electrode and the area of ​​the movable mass block. This setting greatly increases the size of the device.

[0108] Further, Figure 19 The embodiment of the present application provides a schematic diagram of the closed-loop feedback of the existing MEMS device; for the existing technology, the movable mass block serves as the driving electrode part, and the output voltage Vf of the feedback electrode. Therefore, the slight capacitance change of the feedback actuator will cause the charge at both ends of the capacitor to change. Since the entire mass block is a conductor, this will affect the capacitive charge detection of the sensor, causing crosstalk between the feedback signal and the sensing signal, thereby reducing the measurement accuracy of the accelerometer.

[0109] Furthermore, if two feedback capacitor plates (two actuators) are set in an existing MEMS device, crosstalk between the feedback signals of the two feedback actuators also needs to be considered; since the SOI insulation layer cannot be used for insulation, crosstalk cannot be avoided through electrical isolation. On this basis, the design of the MEMS device will become more complicated, and the corresponding measurement accuracy may be further reduced.

[0110] It should be understood that expressions such as "include" and "may include" used in this application indicate the existence of the disclosed functions, operations, or constituent elements, and do not limit one or more additional functions, operations, and constituent elements. In this application, terms such as "include" and / or "have" may be interpreted as indicating specific characteristics, numbers, operations, constituent elements, components, or combinations thereof, but may not be interpreted as excluding the existence or possibility of adding one or more other characteristics, numbers, operations, constituent elements, components, or combinations thereof.

[0111] In addition, in this application, the expression "and / or" includes any and all combinations of the associated listed words. For example, the expression "A and / or B" may include A, may include B, or may include both A and B.

[0112] In the description of the embodiments of the present application, it should be noted that, unless otherwise clearly specified and limited, the term "connection" should be understood in a broad sense. For example, "connection" can be a detachable connection or a non-detachable connection; it can be a direct connection or an indirect connection through an intermediate medium. Among them, "fixed connection" means that the two are connected to each other and the relative position relationship after the connection remains unchanged. "Rotational connection" means that the two are connected to each other and can rotate relative to each other after the connection. "Sliding connection" means that the two are connected to each other and can slide relative to each other after the connection. The directional terms mentioned in the embodiments of the present application, such as "top", "bottom", "inside", "outside", "left", "right", etc., are only reference to the directions of the accompanying drawings. Therefore, the directional terms used are for better and clearer explanation and understanding of the embodiments of the present application, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of the present application.

[0113] In addition, in the embodiments of the present application, the mathematical concepts mentioned include symmetry, equality, parallelism, and perpendicularity. These limitations are all for the current state of the art, rather than being absolutely strict definitions in a mathematical sense. A small amount of deviation is allowed, and it is possible to be approximately symmetric, approximately equal, approximately parallel, or approximately perpendicular. For example, A and B are parallel, which means that A and B are parallel or approximately parallel, and the angle between A and B can be between 0 and 10 degrees. A and B are perpendicular, which means that A and B are perpendicular or approximately perpendicular, and the angle between A and B can be between 80 and 100 degrees.

[0114] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of this application. Therefore, the scope of protection of this application should be based on the scope of protection of the claims.

Claims

1. A MEMS accelerometer, characterized in that: include: sensitive units; The sensitive unit includes: an outer frame, a mass block, a spring structure, a pickup structure, a first feedback capacitor structure and a second feedback capacitor structure; The upper end of the outer frame, the upper end of the mass block and the spring structure are prepared on the first layer of SOI; the spring structure connects the mass block to the outer frame; The middle end of the outer frame and the middle end of the mass block are prepared on the second layer of SOI; The lower end of the outer frame, the lower end of the mass block, the first feedback capacitor structure, and the second feedback capacitor structure are fabricated on the third layer of SOI; the second layer is an insulating layer, and the first and third layers are any combination of a substrate layer and a device layer; the first feedback capacitor structure and the second feedback capacitor structure are respectively arranged in the sensitive axis and perpendicular sensitive axis directions of the mass block, and are variable area capacitors and variable spacing capacitors, respectively; the moving plates of the two feedback capacitor structures are connected to the mass block, and the fixed plates are connected to the outer frame; the outer frame is provided with a plurality of isolation grooves penetrating the third layer of SOI, for electrically isolating the fixed plates of different polarities and types in the first feedback capacitor structure and the second feedback capacitor structure; The pickup structure is arranged above the upper end of the mass block.

2. The accelerometer according to claim 1, wherein Also includes: An upper cover plate and a lower cover plate; the upper cover plate is arranged above the sensitive unit, and the lower cover plate is arranged below the sensitive unit.

3. The accelerometer according to claim 2, wherein: A first metal shielding layer is provided between the pickup structure and the upper end of the mass block; An excitation structure is provided at the lower end of the upper cover plate; a second metal shielding layer is provided between the lower end of the upper cover plate and the excitation structure; the excitation structure is opposite to the pickup structure; insulating layers are provided at the upper and lower ends of the first and second metal shielding layers.

4. The accelerometer according to claim 2, wherein: The lower end of the upper cover plate and the upper end of the lower cover plate are both provided with cavities.

5. The accelerometer according to claim 2, wherein: The lower end of the upper cover plate, the upper and lower ends of the sensitive unit and the upper end of the lower cover plate are provided with scribing paths; The upper cover plate, the sensitive unit and the lower cover plate are connected by bonding metal and sealed by the dicing lanes.

6. A MEMS geophone, characterized in that: The MEMS accelerometer comprises the MEMS accelerometer according to any one of claims 1 to 5.

7. A method for preparing a MEMS accelerometer, characterized in that: Including, preparing sensitive units: Deep silicon etching is performed on the SOI substrate layer or one of the device layers to obtain the lower end of the outer frame, the lower end of the mass block, a first feedback capacitor structure, and a second feedback capacitor structure; the first feedback capacitor structure and the second feedback capacitor structure are respectively arranged in the sensitive axis and perpendicular sensitive axis directions of the mass block, and are variable area capacitors and variable spacing capacitors, respectively; the moving plates of the two feedback capacitor structures are connected to the mass block, and the fixed plates are connected to the outer frame; Performing deep silicon etching on the SOI device layer or another layer in the substrate layer to obtain the upper end of the outer frame, the upper end of the mass block, and the spring structure, and connecting the mass block to the outer frame through the spring structure; The SOI insulating layer between the spring structure and the first feedback capacitor structure and the second feedback capacitor structure is removed to obtain the middle end of the outer frame and the middle end of the mass block on the SOI insulating layer; Performing deep silicon etching on the SOI substrate layer or the device layer to obtain a plurality of isolation trenches; The isolation groove is used to electrically isolate fixed plates of different polarities and types in the first feedback capacitor structure and the second feedback capacitor structure; A pickup structure is prepared on the top of the SOI device layer or another layer in the substrate layer.

8. The method according to claim 7, characterized in that A transmission channel for a feedback signal is provided above one of the SOI substrate layers or the device layer; a transmission channel for a sensing signal is provided above another layer of the SOI substrate layer or the device layer; the feedback signal is applied to the first feedback capacitor structure and the second feedback capacitor structure to generate a response electrostatic force to adjust the position of the mass block; the sensing signal is a signal output by the pickup structure sensing the input acceleration.

9. The method according to claim 7, characterized in that A pickup structure is prepared on an upper end of another layer in the SOI device layer or the substrate layer, comprising: Sequentially preparing a first insulating layer, a first metal shielding layer, and a second insulating layer on the upper end of the other layer; then etching a deep hole; the deep hole sequentially penetrates the second insulating layer, the first metal shielding layer, the first insulating layer, and the SOI; Depositing a pickup metal layer on the upper end of the second insulating layer, and electrically connecting another SOI layer to the first metal shielding layer by depositing the metal into the deep hole; The pickup metal layer is patterned and etched to obtain a positive pickup plate, a negative pickup plate, scribe lines, and punch holes; the punch holes serve as electrical connections between the first feedback capacitor structure, the second feedback capacitor structure, and the first metal shielding layer and the outside world; Performing patterned etching on the second insulating layer to obtain an etched second insulating layer, which corresponds to the etched pickup metal layer and is used to insulate the etched pickup metal layer; Performing patterned etching on the first metal shielding layer to obtain an etched first metal shielding layer corresponding to the etched second insulating layer, and grounding the etched first metal shielding layer; The first insulating layer is pattern-etched to obtain an etched first insulating layer corresponding to the etched metal shielding layer, and an etching groove is formed for deep silicon etching of the other layer.

10. The method according to claim 7, characterized in that Also includes the preparation of the upper cover: Etching a cavity in the middle of the lower end of the first silicon wafer; After etching, a third insulating layer is deposited at the lower end of the first silicon wafer for the first time and patterned to obtain electrical connection holes; Depositing a second metal shielding layer at the lower end of the first silicon wafer for the second time, and patterning the second metal shielding layer to obtain metal shielding electrodes, metal connecting lines, scribe lines, and electrical connection holes; depositing a fourth insulating layer at the lower end of the first silicon wafer for a third time and patterning the fourth insulating layer, wherein the patterned fourth insulating layer corresponds to the second metal shielding layer; Depositing an excitation metal layer at the bottom of the first silicon wafer for the fourth time and patterning the layer to obtain an excitation metal substrate, metal connecting lines, electrical connecting lines, and scribe lines; An electrical connection hole is obtained by etching the upper end of the first silicon wafer.

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