MEMS accelerometer, geophone and preparation method

Abstract

The invention belongs to the field of MEMS devices, and particularly discloses an MEMS accelerometer, a geophone and a preparation method, a sensitive unit of the accelerometer is prepared on SOI, and the accelerometer comprises 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 a first SOI layer, the first feedback capacitor structure and the second feedback capacitor structure are prepared on a third SOI layer, 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 in the sensitive axis direction and the vertical sensitive axis direction of the mass block, and are respectively a variable area capacitor and a variable spacing capacitor; the pickup structure is disposed over the SOI first layer mass block. According to the MEMS accelerometer, the area occupied by the MEMS accelerometer is reduced based on the SOI technology, the sensing signal and the feedback signal can be isolated through the SOI insulating layer, the detection precision of the accelerometer is improved, and the linearity of feedback execution of the accelerometer is regulated and controlled.

Description

Technical Field

[0001] The present application belongs 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] MEMS accelerometer is a miniaturized acceleration sensor that is realized by combining micromechanical structure and microelectronic technology. MEMS accelerometer has the advantages of small size, low power consumption, high resolution and high precision, so it is widely used in mobile devices, automobiles, drones, spacecraft and other fields. Its working principle is based on the micro-mass spring system in micro-electromechanical system technology. When acceleration acts on the accelerometer, the micro-mass in the accelerometer will be displaced, causing the micro-spring system to vibrate, which in turn causes the output signal of sensor elements such as capacitance, piezoresistance and magnetoresistance to change. By processing and calculating these output signals, the magnitude and direction of acceleration can be obtained. With the continuous development of MEMS technology, MEMS accelerometers have been continuously optimized and improved in terms of volume, power consumption, precision and other aspects. It has become one of the indispensable key technologies in various smart devices, smart sensors and the Internet of Things. The accuracy of accelerometers is an important indicator that restricts 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 prior art, the purpose of the present 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-mentioned object, in a first aspect, the present application provides a MEMS accelerometer, comprising: a sensitive unit; The sensitive unit comprises: 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 silicon-on-insulator (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 prepared on the third layer of SOI; the second layer is an insulating layer, 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 in the sensitive axis and the vertical sensitive axis direction 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; a plurality of isolation grooves penetrating the third layer of SOI are arranged on the outer frame, which are used to electrically isolate 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 and is used to sense the input acceleration and convert it into a sensing signal output; 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.

[0006] It should be noted that the above-mentioned first feedback capacitor structure and the 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 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-spacing feedback actuator, and realizes the separation of the two types of actuators through the electrical isolation method of an etched isolation groove in the SOI where the actuator is located, thereby avoiding the crosstalk between the electrical signals of the two types of actuators, and changing the weights of different actuators in the feedback force to adjust the linearity of their feedback.

[0007] 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. 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.

[0008] 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.

[0009] In a possible implementation, a first metal shielding layer is provided between the pickup structure and the upper end of the mass block; An excitation structure is arranged at the lower end of the upper cover plate; a second metal shielding layer is arranged between the lower end of the upper cover plate and the excitation structure; the excitation structure is directly opposite to the pickup structure; and insulating layers are arranged at both the upper and lower ends of the first metal shielding layer and the second metal shielding layer.

[0010] It should be noted that the metal shielding layer can enclose the sensor composed of the excitation structure and the pickup structure, which can effectively isolate the influence of the external environment on the sensor and improve the measurement accuracy of the internal sensor unit.

[0011] 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.

[0012] In a possible implementation, a scribe line is provided at 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; The upper cover plate, the sensitive unit and the lower cover plate are connected by bonding metal and sealed by the dicing road.

[0013] In a second aspect, the present application provides a MEMS seismic detector, comprising the MEMS accelerometer provided in the first aspect.

[0014] In a third aspect, the present application provides a method for preparing a MEMS accelerometer, comprising preparing a sensitive unit: Deep silicon etching is performed on a layer of the SOI substrate layer or the device layer to obtain 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; the first feedback capacitor structure and the second feedback capacitor structure are respectively arranged in the sensitive axis and the perpendicular sensitive axis direction of the mass block, and are respectively a variable area capacitor and a variable spacing capacitor; 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 an upper end of the outer frame, an upper end of the mass block and a 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, and the middle end of the outer frame and the middle end of the mass block are obtained on the SOI insulating layer; Performing deep silicon etching on the SOI substrate layer or the one of the device layers to obtain a plurality of isolation grooves; the isolation grooves are used to electrically isolate fixed electrodes 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 another layer in the SOI device layer or the substrate layer.

[0015] In a possible implementation, a transmission channel for a feedback signal is arranged above one layer in the SOI substrate layer or the device layer; a transmission channel for a sensing signal is arranged above another layer in the SOI substrate layer or the device layer; the feedback signal is used to be applied to a first feedback capacitor structure and a second feedback capacitor structure to generate a response electrostatic force to adjust the position of the mass block; the sensing signal is a signal sensed by the pickup structure and outputted by the input acceleration.

[0016] In a possible implementation, a pickup structure is prepared on the top of another layer in the SOI device layer or the substrate layer, including: Sequentially prepare a first insulating layer, a first metal shielding layer, and a second insulating layer on the upper end of the other layer; then etch 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 pick-up metal layer on the upper end of the second insulating layer, and electrically connecting another layer of SOI to the first metal shielding layer through the metal deposited into the deep hole; The pickup metal layer is pattern-etched to obtain a positive pickup electrode, a negative pickup electrode, a scribe line and a punch hole; the punch hole is used as an electrical connection port 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.

[0017] In a possible implementation, the method further includes preparing an upper cover plate: 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 is patterned to obtain an electrical connection hole; 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 connecting holes; Depositing a fourth insulating layer at the lower end of the first silicon wafer for the 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 it to obtain an excitation metal substrate, metal connecting lines, electrical connecting lines and scribe lines; The upper end of the first silicon wafer is etched to obtain an electrical connection hole.

[0018] In general, the above technical solutions conceived by this application have the following beneficial effects compared with the prior art: The present application provides a MEMS accelerometer, a seismic detector and a preparation method, which 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 are arranged vertically, which greatly reduces the horizontal area occupied by the device, and 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, and realizes the separation of the two types of actuators through the electrical isolation method of an etched isolation groove in the SOI where the actuator is located, thereby avoiding the crosstalk between the electrical signals of the two types of actuators, changing the weight of different actuators in the feedback force, and thus adjusting 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 on the basis of reducing the horizontal area of ​​the device in a simple way, effectively eliminating crosstalk between different electrical signals, and greatly improving the measurement accuracy of the MEMS accelerometer.

[0019] The present application provides a MEMS accelerometer, a seismic detector and a preparation method. A metal shielding layer is set in the MEMS accelerometer to enclose the sensor composed of the excitation structure and the pickup structure, which can effectively isolate the influence of the external environment on the sensor and improve the measurement accuracy of the internal sensing unit. In addition, the MEMS accelerometer can be completely sealed by bonding metal and scribe lines to improve the measurement accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a side view of a MEMS device provided in an embodiment of the present application; Figure 2 is a schematic diagram of a lower cover plate of a MEMS device provided in an embodiment of the present application; 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; Figure 4 It is a schematic diagram of the capacitor plate of the SOI substrate layer feedback actuator of the MEMS device provided in the embodiment of the present application; Figure 5 This is a schematic diagram of an electrically conductive deep hole of a MEMS device provided in an embodiment of the present application; Figure 6This 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; 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; 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; Fig. 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; Fig.10 It 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; Fig.11 is a side view of a sensitive unit in a MEMS device provided in an embodiment of the present application; Fig.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; Fig.13 This is a schematic diagram of an insulating layer on a cover plate of a MEMS device provided in an embodiment of the present application; Fig.14 This is a schematic diagram of a metal shielding layer on a MEMS device cover provided in an embodiment of the present application; Fig.15 This is a schematic diagram of a metal insulating layer on a MEMS device cover provided in an embodiment of the present application; Fig.16 This is a schematic diagram of an excitation metal layer on a MEMS device cover provided in an embodiment of the present application; Fig.17 This is a schematic diagram of the back of the upper cover plate of the MEMS device provided in an embodiment of the present application; Fig.18 The embodiment of the present application provides a top view of an existing MEMS device; Fig.19 The embodiment of the present application provides a schematic diagram of closed-loop feedback of an existing MEMS device; 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 lanes 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 punching holes distributed at different positions, 52 is the positive pickup plate, and 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 a metal shielding plate, and 133 and 153 are metal connecting wires distributed at different positions; 151 is an excitation metal plate. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0022] The embodiments of the present application are described below in conjunction with the drawings in the embodiments of the present application.

[0023] In one embodiment, the present application provides a MEMS accelerometer, including: an upper cover plate, a sensitive unit, and a lower cover plate of a sandwich structure.

[0024] 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; 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 prepared on the third layer of SOI; the second layer is an insulating layer, 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 in the sensitive axis and the vertical sensitive axis direction 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; a plurality of isolation grooves penetrating the third layer of SOI are arranged on the outer frame, which are used to electrically isolate 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 and is used to sense the input acceleration and convert it into a sensing signal output; 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.

[0025] The above different types 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 and decreases respectively, wherein the increase and decrease correspond to capacitor plates of different polarities.

[0026] It can be understood that the upper cover plate is arranged above the sensitive unit, and the lower cover plate is arranged below the sensitive unit. The upper and lower cover plates are used to provide an activity space for the sensitive unit and seal the sensitive unit.

[0027] Furthermore, a first metal shielding layer is provided between the pickup structure and the upper end of the mass block; An excitation structure is arranged at the lower end of the upper cover plate; a second metal shielding layer is arranged between the lower end of the upper cover plate and the excitation structure; the excitation structure is directly opposite to the pickup structure; and insulating layers are arranged at both the upper and lower ends of the first metal shielding layer and the second metal shielding layer.

[0028] Furthermore, a cavity is provided at the lower end of the upper cover plate and the upper end of the lower cover plate.

[0029] Furthermore, 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 road.

[0030] 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.

[0031] The following is an introduction to the preparation process of the above-mentioned MEMS accelerometer: The MEME accelerometer provided in the embodiment of the present application is a uniaxial accelerometer (only measuring the acceleration in the sensitive axis direction) and adopts a sandwich structure. The sandwich structure requires two pieces of single crystal silicon and one piece of SOI to complete the device manufacturing. The two pieces of single crystal silicon are used to prepare the upper and lower cover plates respectively, and SOI is used to prepare the sensitive unit. Figure 1 As shown: 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.

[0032] A silicon wafer 16 is taken out to make a lower cover plate, and an insulating layer 15 is deposited on the lower cover plate to isolate the metal layer 14 from the silicon wafer 16, and then a metal film is deposited to serve as the bonding metal layer 14 bonded to the SOI wafer. Then, the metal layer is first etched to obtain a bonding metal pad 21, a scribe line 22, and a cavity 23 that provides a space for the mass block to move, and then the insulating layer 15 and the silicon wafer 16 are etched and patterned to deepen the depth of the cavity 23. Figure 2 shown.

[0033] In one embodiment, taking the preparation of a feedback actuator on the substrate layer of SOI and the preparation of 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 example is given: 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 plate, including a bonding metal pad 31 and a scribe line 31, such as Figure 3 shown.

[0034] Then, the substrate layer 12 is subjected to deep silicon etching to obtain a feedback actuator structure, including a feedback actuator A and a feedback actuator B, such as Figure 4 shown.

[0035] It should be noted that feedback actuators are usually arranged 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-.

[0036] The fixed electrode 41 and the movable electrode 42 constitute the feedback actuator A+, the fixed electrode 43 and the movable electrode 44 constitute the feedback actuator A-, the fixed electrode 45 and the movable electrode 46 constitute the feedback actuator B+, the fixed electrode 47 and the movable electrode 48 constitute the feedback actuator B-, the middle part is the movable mass block 49, the outer frame is 403, and there are multiple isolation grooves 402 on the outer frame. The above-mentioned 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.

[0037] 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 4 As shown, there are multiple isolation slots 402 on the outer frame, so that the actuators A+, A-, B+, and B- can be connected to different loops, and the weight of each feedback actuator on the feedback force can be adjusted externally. Along the sensitive axis direction, 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 can reduce the rotational torque generated during electrostatic force feedback. The feedback group A actuator can be a comb-tooth linear actuator (the driving force is proportional to the square of the voltage and has nothing to do with the motion stroke), and the feedback group B actuator can be a parallel plate nonlinear actuator. In order to reduce the nonlinear relationship between the electrostatic feedback force and the stroke, the feedback group A and feedback group B actuators can be connected to different feedback control loops, and the linearity of the feedback system can be flexibly adjusted; wherein, the higher the proportion of the feedback group A actuator connected to the electrostatic feedback force, the higher the proportion of the above nonlinear relationship reduction, and the lower the rotational torque generated by the above electrostatic force feedback. In order to reduce the risk of plate adhesion caused by the Pull-in effect, the MEMS accelerometer / MEMS seismic sensor structure is designed with displacement prevention bumps (sloppcr). In addition, the feedback group B plate adhesion problem can be solved by adjusting the driving voltage of the feedback group A actuator separately.

[0038] The following is the process of manufacturing the device layer of SOI. First, the device layer 10 of SOI is coated with films in sequence, which are 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, such as Figure 5 shown.

[0039] On this basis, a film is formed to form a sensing pickup metal layer 6. At this time, the side wall of 401 is 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 6As shown, firstly, the topmost sensing pickup metal layer 6 is etched and patterned to obtain: a sensing positive pickup electrode 52, a sensing negative pickup electrode 53, a scribe line 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.

[0040] Then, the metal insulating layer 7 is patterned and etched to obtain an insulating layer 61, such as Figure 7 As shown, it corresponds to the sensing pickup metal layer 6.

[0041] Then, the metal shielding layer 8 is pattern-etched to obtain a metal shielding layer 71, which corresponds to the insulating layer 61. The metal shielding layer 71 is grounded to achieve the effect of electromagnetic shielding of the sensor positive pickup plate 52 and the sensor negative pickup plate 53. Figure 8 shown.

[0042] Then, the insulating layer 9 is pattern-etched to obtain an insulating layer 81, which corresponds to the metal shielding layer 71 and completely isolates the metal shielding layer 71 from contact with the SOI device layer. At the same time, an etching groove 82 is formed for deep silicon etching of the SOI device layer. Fig. 9 shown.

[0043] Further, the SOI device layer 10 is subjected to deep silicon etching to obtain a spring oscillator system, such as Fig.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.

[0044] 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 gas phase release. Fig.11 From the side view of the SOI shown, it can be seen that the movable mass block of the device layer is connected to the movable mass block of the actuator through the SOI insulating layer, and the insulating layer between the spring beam 92 and the electrode plate 42 / 44 / 46 / 48 of the actuator is etched, so that the movable mass block can move freely. Compared with the prior art, the actuator and the sensor of this structure are stacked and share the same area, which can effectively save the total area of ​​the device and greatly improve the integration and miniaturization of the device. At the same time, the sensor and the actuator are completely electrically separated. Since the capacitive sensor causes voltage changes through capacitance changes, the external circuit obtains seismic wave signals by detecting the size of the voltage change. Therefore, this completely separated structure will not allow the feedback voltage of the actuator to be coupled to the sensing voltage, thereby making the accuracy of the sensing voltage high enough and the feedback voltage of the actuator stable.

[0045] Finally, the upper cover plate is made. First, the silicon wafer 1 is taken and a trapezoidal cavity 111 is etched out by release etching. Fig.12 As shown, the outer mass block can be moved to provide distance while limiting the spacing of 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) 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.

[0046] Then a metal shielding layer 3 is deposited and then patterned, such as Fig.14 As shown, a metal shielding plate 131, a metal connecting line 133, a scribe line 132, and an electrical connecting hole 134 are obtained.

[0047] Then deposit a metal insulating layer 4 and then pattern it, see Fig.15 As shown, the metal insulating layer 144 corresponds to the metal shielding layer 3.

[0048] Then deposit a sensing excitation metal layer 5 and then pattern it, see Fig.16 , obtaining a sensing excitation metal plate 151 and a metal connecting line 153 , an electrical connection hole 154 and a dicing road 152 .

[0049] Finally, the upper cover plate is back-etched to obtain electrical connection holes 161, see Fig.17 .

[0050] In the last step, the three-layer structure is metal-bonded, such as gold-gold bonding, to obtain a corresponding MEMS accelerometer or MEMS geophone.

[0051] It should be noted that Fig.18 The embodiment of the present application provides a top view of an existing MEMS device; Fig.18 As shown in Figure 1, when the sensor (pickup structure) and the feedback actuator (feedback capacitor plate) are laid flat (set on a horizontal plane), Fig.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.

[0052] Further, Fig.19 The embodiment of the present application provides a schematic diagram of the closed-loop feedback of the existing MEMS device; for the prior art, 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, it 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.

[0053] Furthermore, if two feedback capacitor plates (two actuators) are set in the existing MEMS device, the crosstalk problem between the feedback signals of the two feedback actuators also needs to be considered; since the SOI insulation layer cannot be used for insulation, the crosstalk cannot be avoided by electrical isolation. On this basis, the design of the MEMS device will be more complicated, and the corresponding measurement accuracy may be further reduced.

[0054] It should be understood that expressions such as "including" and "may include" that may be used in the present 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 the present application, terms such as "including" and / or "having" 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.

[0055] In addition, in the present 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.

[0056] 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 relative position relationship after connection remains unchanged. "Rotational connection" means that the two are connected to each other and can rotate relative to each other after connection. "Sliding connection" means that the two are connected to each other and can slide relative to each other after connection. The directional terms mentioned in the embodiments of the present application, such as "top", "bottom", "inside", "outside", "left", "right", etc., are only reference 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.

[0057] In addition, in the embodiments of the present application, the mathematical concepts mentioned are symmetry, equality, parallelism, verticality, etc. These limitations are all for the current state of the art, rather than being absolutely strict definitions in a mathematical sense, and allow a small amount of deviation, approximation to symmetry, approximation to equality, approximation to parallelism, approximation to verticality, etc. 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.

[0058] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art who is familiar with the present technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A MEMS accelerometer, characterized in that: include: Sensitive unit; The sensitive unit comprises: 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 prepared on the third layer of SOI; the second layer is an insulating layer, 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 in the sensitive axis and the vertical sensitive axis direction 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; a plurality of isolation grooves penetrating the third layer of SOI are arranged on the outer frame, which are used to electrically isolate 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, characterized in that 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, characterized in that A first metal shielding layer is provided between the pickup structure and the upper end of the mass block; An excitation structure is arranged at the lower end of the upper cover plate; a second metal shielding layer is arranged between the lower end of the upper cover plate and the excitation structure; the excitation structure is directly opposite to the pickup structure; and insulating layers are arranged at both the upper and lower ends of the first metal shielding layer and the second metal shielding layer.

4. The accelerometer according to claim 2, characterized in that 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, characterized in that 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 road.

6. A MEMS seismic detector, 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 a layer of the SOI substrate layer or the device layer to obtain 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; the first feedback capacitor structure and the second feedback capacitor structure are respectively arranged in the sensitive axis and the perpendicular sensitive axis direction of the mass block, and are respectively a variable area capacitor and a variable spacing capacitor; 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 an upper end of the outer frame, an upper end of the mass block and a 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, and the middle end of the outer frame and the middle end of the mass block are obtained on the SOI insulating layer; Performing deep silicon etching on the SOI substrate layer or the one of the device layers to obtain a plurality of isolation grooves; The isolation groove is used to electrically isolate fixed pole 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 another layer in the SOI device layer or the substrate layer.

8. The method according to claim 7, characterized in that A transmission channel for a feedback signal is arranged above one of the SOI substrate layers or the device layer; a transmission channel for a sensing signal is arranged above another layer of the SOI substrate layer or the device layer; the feedback signal is used to be applied to a first feedback capacitor structure and a 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 the top of another layer in the SOI device layer or the substrate layer, comprising: Sequentially prepare a first insulating layer, a first metal shielding layer, and a second insulating layer on the upper end of the other layer; then etch 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 pick-up metal layer on the upper end of the second insulating layer, and electrically connecting another layer of SOI to the first metal shielding layer through the metal deposited into the deep hole; The pickup metal layer is pattern-etched to obtain a positive pickup electrode, a negative pickup electrode, a scribe line and a punch hole; the punch hole is used as an electrical connection port 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 It 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 is patterned to obtain an electrical connection hole; 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 connecting holes; Depositing a fourth insulating layer at the lower end of the first silicon wafer for the 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 it to obtain an excitation metal substrate, metal connecting lines, electrical connecting lines and scribe lines; The upper end of the first silicon wafer is etched to obtain an electrical connection hole.

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