Pressure sensor and preparation method thereof

Abstract

The invention discloses a pressure sensor and a preparation method thereof, and relates to the technical field of micro electro mechanical system sensors, the pressure sensor comprises a pressure sensitive film and a device layer which are oppositely arranged, the device layer comprises a plurality of piezoresistors, and the piezoresistors form a pressure detection circuit through electrodes connected with the piezoresistors; a functional film is arranged on one side, deviating from the pressure sensitive film, of the device layer; wherein in the first direction, at least part of each piezoresistor is overlapped with the functional thin film, and / or at least part of the pressure sensitive film is overlapped with the functional thin film; the first direction is perpendicular to the plane of the pressure sensor. According to the technical scheme, the environmental interference resistance and the long-term stability of the pressure sensor can be improved through the functional film.

Description

Technical Field

[0001] This application relates to the technical field of microelectromechanical system (MEMS) sensors, and particularly to a pressure sensor and a preparation method thereof. Background Art

[0002] At present, pressure sensors are mainly divided into types such as capacitive pressure sensors, fiber optic pressure sensors, and piezoresistive pressure sensors. Capacitive pressure sensors and fiber optic pressure sensors are limited by their working principles, resulting in relatively complex device structures and detection circuits. Piezoresistive pressure sensors, due to their advantages such as simple structure, no moving parts, low manufacturing cost, and high yield, are widely used in many fields such as medical electronics, the automotive industry, and aerospace.

[0003] Existing conventional piezoresistive pressure sensors have weak anti-environmental interference ability, which affects the long-term stability of the pressure sensor. Summary of the Invention

[0004] In view of the above problems, this application provides a pressure sensor and a preparation method thereof to achieve the purpose of improving the anti-environmental interference ability and long-term stability of the pressure sensor. The specific solutions are as follows:

[0005] In a first aspect of this application, a pressure sensor is provided, including:

[0006] A pressure-sensitive film and a device layer arranged oppositely, the device layer includes a plurality of piezoresistors, and the piezoresistors are configured as a pressure detection circuit through the connected electrodes;

[0007] A functional film is arranged on a side of the device layer facing away from the pressure-sensitive film;

[0008] Wherein, in a first direction, at least a part of each piezoresistor overlaps with the functional film, and / or at least a part of the pressure-sensitive film overlaps with the functional film; the first direction is perpendicular to the plane where the pressure sensor is located.

[0009] Optionally, in the above pressure sensor, the perpendicular projection of each piezoresistor on the plane where the pressure sensor is located is located within the perpendicular projection of the functional film on the plane where the pressure sensor is located, and / or the perpendicular projection of the pressure-sensitive film on the plane where the pressure sensor is located is located within the perpendicular projection of the functional film on the plane where the pressure sensor is located.

[0010] Optionally, in the above pressure sensor, an insulating layer is arranged on a side of the device layer facing away from the pressure-sensitive film, and electrode holes are respectively arranged in regions of the insulating layer corresponding to each piezoresistor;

[0011] A metal layer is arranged on a side of the insulating layer facing away from the device layer, the metal layer includes a plurality of electrodes, and the electrodes are connected to the piezoresistors based on the electrode holes;

[0012] Among them, the functional film also fills the gap region between adjacent electrodes.

[0013] Optionally, in the above pressure sensor, the electrode includes a pad and a trace connected to the pad, and the trace is connected to the piezoresistor through an electrode hole;

[0014] The functional film covers the trace and exposes the pad;

[0015] Or, the electrode includes a pad and a trace connected to the pad, and the trace is connected to the piezoresistor through an electrode hole;

[0016] Each pad is arranged in sequence on the same straight line, and the straight line is parallel and opposite to one side of the pressure-sensitive film; the functional film is filled between adjacent pads.

[0017] Optionally, in the above pressure sensor, the pressure-sensitive film is a square film, and the square film has parallel and opposite first and third sides and parallel and opposite second and fourth sides;

[0018] The device layer includes four piezoresistors, and the four piezoresistors are the first resistor, the second resistor, the third resistor, and the fourth resistor in sequence; the vertical projection of each piezoresistor on the plane where the pressure-sensitive film is located is within the area of the pressure-sensitive film;

[0019] In the first direction, both the first resistor and the fourth resistor are linear resistors; the first resistor is aligned with the first side, and the first resistor is located at the middle position of the first side; the fourth resistor is aligned with the third side, and the fourth resistor is located at the middle position of the third side;

[0020] In the first direction, both the second resistor and the third resistor are U-shaped resistors; for the second resistor, the opening of the U-shaped resistor faces the middle position of the second side; for the third resistor, the opening of the U-shaped resistor faces the middle position of the fourth side.

[0021] Optionally, in the above pressure sensor, in the second direction, there is a set distance between the second resistor and the second side and between the third resistor and the fourth side; the second direction is parallel to the first side.

[0022] Optionally, in the above pressure sensor, half of the length of the U-shaped resistor is L;

[0023] The set distance is not less than 0.1L and less than L.

[0024] Optionally, in the above pressure sensor, the thickness of the pressure-sensitive film is at least ten times the thickness of the device layer;

[0025] Or, the thickness range of the device layer is 0.5 μm to 1 μm;

[0026] Alternatively, in the first direction, the line widths of the respective varistors are the same, and the lengths of the respective varistors are the same.

[0027] A second aspect of the present application provides a method for manufacturing any one of the above pressure sensors, including:

[0028] Forming a patterned device layer, the device layer including a plurality of varistors, and the varistors being configured as a pressure detection circuit through the connected electrodes; wherein, a functional thin film is formed on one side of the device layer;

[0029] Forming a pressure-sensitive film on the other side of the device layer;

[0030] Wherein, in the first direction, at least a part of each varistor overlaps with the functional thin film, and / or at least a part of the pressure-sensitive film overlaps with the functional thin film; the first direction is perpendicular to the plane where the pressure sensor is located.

[0031] Optionally, in the above manufacturing method,

[0032] Wherein, the method for manufacturing the functional thin film includes:

[0033] Providing silicon-on-insulator, including a substrate layer, a buried oxide layer, and a device layer stacked in sequence, patterning the device layer to form a plurality of varistors;

[0034] Forming a patterned insulating layer on the surface of the patterned device layer, and electrode holes being provided in the regions of the insulating layer corresponding to the respective varistors;

[0035] Forming a patterned metal layer on the surface of the insulating layer, the metal layer including a plurality of electrodes, and the electrodes being connected to the varistors based on the electrode holes;

[0036] Forming a functional thin film on the surface of the metal layer;

[0037] Wherein, before forming the pressure-sensitive film, the surface of the substrate layer facing away from the device layer is thinned;

[0038] Wherein, before thinning the substrate layer, a first auxiliary substrate for protecting the functional thin film and the electrodes is formed;

[0039] Wherein, the method for forming the pressure-sensitive film includes:

[0040] Forming a groove on the surface of the substrate layer facing away from the device layer; forming a pressure-sensitive film at the bottom of the groove;

[0041] Fixing a cover plate on the side of the substrate layer facing away from the device layer;

[0042] Wherein, the method for fixing the cover plate includes:

[0043] Based on a second auxiliary substrate having through holes, a getter is formed in the area of the cover plate corresponding to the groove;

[0044] After bonding and fixing the cover plate to the substrate layer, the getter is activated to form a vacuum reference cavity based on the groove;

[0045] Wherein, after fixing the cover plate, it further includes: by annealing treatment, improving the ohmic contact between the electrode and the varistor.

[0046] By means of the above technical solution, a functional film is provided on the side of the varistor away from the pressure-sensitive film of the pressure sensor, at least part of each varistor overlaps with the functional film, and / or at least part of the pressure-sensitive film overlaps with the functional film; the first direction is perpendicular to the plane where the pressure sensor is located. The functional film can effectively buffer the influence of external temperature fluctuations on the pressure-sensitive film and reduce the sensor drift caused by thermal stress; it can also isolate the penetration of water vapor and avoid the resistance shift of the varistor caused by humidity changes.

[0047] Optionally, the functional film can be prepared from a material resistant to chemical corrosion. The material resistant to chemical corrosion has high tolerance to acid-base environments and biological fluids and can protect the underlying film layer from corrosion.

[0048] Optionally, the functional film can be prepared from a material with a high dielectric strength. The material with a high dielectric strength can isolate external electromagnetic interference and ensure the stability of the output signal of the pressure detection circuit.

[0049] Optionally, if it is used as an implantable sensor, the functional film can be prepared from a material with good biocompatibility, which is suitable for long-term implant scenarios and reduces tissue rejection reactions. Description of the Drawings

[0050] In order to more clearly illustrate the technical solutions in the embodiments of the present application or related technologies, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained according to the provided drawings.

[0051] The structures, proportions, sizes, etc. shown in the drawings of this specification are only used to cooperate with the content disclosed in the specification for those skilled in this technology to understand and read, and are not used to limit the limited conditions under which the present application can be implemented. Therefore, they do not have technical essential significance. Any modification of the structure, change in the proportional relationship, or adjustment of the size, without affecting the effects that the present application can produce and the purposes that can be achieved, should still fall within the scope covered by the technical content disclosed in the present application.

[0052] Figure 1A cross-sectional view of a pressure sensor provided by an embodiment of the present application;

[0053] Figure 2 A three-dimensional schematic diagram of a pressure sensor provided by an embodiment of the present application;

[0054] Figure 3 A top view of a pressure sensor provided by an embodiment of the present application;

[0055] Figure 4 is Figure 3 A cross-sectional view of the pressure sensor shown along the A-A' direction;

[0056] Figure 5 is Figure 3 A cross-sectional view of the pressure sensor shown along the B-B' direction;

[0057] Figure 6 is Figure 3 An equivalent circuit diagram of the pressure sensor shown;

[0058] Figure 7 A schematic diagram of the layout principle of a piezoresistor and a pressure-sensitive film in a pressure sensor provided by an embodiment of the present application system;

[0059] Figures 8 - 15 A cross-sectional view of a method for manufacturing a pressure sensor provided by an embodiment of the present application at different process stages.

[0060] Reference numerals:

[0061] 100 - device layer; 101 - pressure-sensitive film; 102 - piezoresistor; 1021 - first resistor; 1022 - second resistor; 1023 - third resistor; 1024 - fourth resistor; 1031 - first electrode; 1032 - second electrode; 1033 - third electrode; 1034 - fourth electrode; 200 - buried oxide layer; 300 - substrate layer; 400 - cover plate; 500 - functional film; 210 - insulating layer; 211 - electrode hole; 212 - electrode; 213 - pad; 214 - trace; 401 - first auxiliary substrate; 402 - getter; Y - first direction; X - second direction; D - preset distance. Detailed implementation manners

[0062] Next, the embodiments in the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Those of ordinary skill in the art will know that with the development of technology and the emergence of new scenarios, the technical solutions provided by the embodiments of the present application are equally applicable to similar technical problems.

[0063] In most craniocerebral diseases, the intracranial pressure value is regarded as an important reference index. The invasive implantable intracranial pressure sensor can be implanted in locations such as the brain parenchyma and subarachnoid space, and it is the gold standard for current clinical intracranial pressure monitoring. Therefore, the demand for intracranial pressure sensors is extremely urgent.

[0064] The MEMS capacitive pressure sensor is a pressure sensor that uses a capacitive structure to convert the pressure to be measured into a change in capacitance value and further converts it into a corresponding electrical signal output through a measurement circuit. It is usually composed of two plates and electrodes made on the plates. The MEMS capacitive pressure sensor has the characteristics of high pressure sensitivity and low power consumption. However, due to the inherent non-linearity of the capacitance value with the change of the plate spacing, the non-linearity of the output of the capacitive pressure sensor is very serious. In addition, the inherent capacitance of the capacitive pressure sensor is small and it is easily affected by parasitic capacitance. Therefore, it is necessary to compensate for non-linearity and parasitic capacitance in the subsequent signal compensation circuit, making its signal detection circuit relatively complex.

[0065] The fiber optic pressure sensor transmits the light emitted by the LED through an optical fiber cable to the surface of a reflector. This reflector is located on the pressure-sensitive membrane and generates displacement under pressure changes, thereby causing a change in the intensity of the reflected light. The reflected light is captured by the sensing optical fiber and converted into an electrical signal output through a photoelectric converter. The fiber optic pressure sensor has high precision and resolution, but its signal processing circuit is very complex, and the bending of the optical fiber will cause signal measurement errors.

[0066] The MEMS piezoresistive pressure sensor uses a piezoresistor made on the pressure-sensitive membrane as the sensitive element. When subjected to pressure, the resistance value of the piezoresistor changes. Through a pressure detection circuit (which can be a Wheatstone bridge structure), the change in the resistance value of the piezoresistor is finally converted into a voltage output. The piezoresistive pressure sensor has a simple structure, no moving parts, low manufacturing cost and high yield; and the Wheatstone bridge can directly output a voltage signal, the signal reading is very convenient, and the interface circuit is simple; in addition, the piezoresistive pressure sensor is small in size and has excellent frequency response performance. Based on this, the MEMS piezoresistive pressure sensor is widely used in various industries such as medical electronics, automotive industry, and aerospace. To meet the detection needs of many fields, the MEMS piezoresistive pressure sensor is constantly developing in the direction of micro-size, high-precision, and high-stability.

[0067] In the field of medical team electronics, a piezoresistive pressure sensor has a chip size of 1150μm × 725μm × 170μm and an accuracy of ±2 mmHg. This type of pressure sensor is a gauge pressure sensor chip. There are two piezoresistors on the pressure-sensitive membrane of the pressure sensor, and they are configured as a Wheatstone half-bridge through three electrodes for voltage output. The piezoresistors and the pressure-sensitive membrane in the pressure sensor are always exposed to the detection environment where the chip is located. Therefore, the long-term stability of the pressure sensor is poor, and there will be a large drift, which is not conducive to the long-term monitoring of intracranial pressure. Since the pressure sensor adopts a Wheatstone half-bridge configuration, the temperature stability of the pressure sensor is poor. In addition, there is still room for improvement in the accuracy of this pressure sensor.

[0068] In view of this, an embodiment of the present application provides a pressure sensor, including:

[0069] A pressure-sensitive membrane and a device layer arranged oppositely, the device layer includes a plurality of piezoresistors, and the piezoresistors are configured as a pressure detection circuit through the connected electrodes;

[0070] A functional thin film is arranged on the side of the device layer facing away from the pressure-sensitive membrane;

[0071] Wherein, in a first direction, at least a part of each piezoresistor overlaps with the functional thin film, and / or at least a part of the pressure-sensitive membrane overlaps with the functional thin film; the first direction is perpendicular to the plane where the pressure sensor is located.

[0072] In the embodiment of the present application, water vapor penetration can be isolated to avoid the resistance shift of the piezoresistor caused by humidity change.

[0073] Optionally, the functional thin film can be prepared from a material resistant to chemical corrosion. The material resistant to chemical corrosion has high tolerance to acid-base environments and biological fluids, and can protect the underlying film layer from corrosion.

[0074] Optionally, the functional thin film can be prepared from a material with a high dielectric strength. The material with a high dielectric strength can isolate external electromagnetic interference and ensure the stability of the output signal of the pressure detection circuit.

[0075] Optionally, if it is used as an implantable sensor, the functional thin film can be prepared from a material with good biocompatibility, which is suitable for long-term implantation scenarios and reduces tissue rejection reactions.

[0076] Optionally, a Wheatstone full-bridge circuit can be constructed by four piezoresistors to improve the temperature stability of the pressure sensor.

[0077] Optionally, the pressure-sensitive membrane can be protected inside a vacuum reference cavity through a cover plate, and the piezoresistors can be sealed through an insulating layer and the functional thin film to improve the long-term stability of the pressure sensor.

[0078] Optionally, the linearity of the pressure sensor can also be improved by optimizing the stress matching between each piezoresistor and the pressure-sensitive film.

[0079] Optionally, the chemical stability and mechanical strength can be further improved by coating the surface of the pressure-sensitive film with a polyimide (PI) film, or a silicon nitride (Si3N4) film, or a stack of a polyimide film and a silicon nitride film, so as to isolate temperature, light, temperature, and acid-base corrosion. Among them, the polyimide film improves the biocompatibility, electromagnetic interference resistance, and chemical corrosion resistance of the pressure-sensitive film. The silicon nitride film can improve the high mechanical strength and thermal stability and protect the pressure-sensitive film as a passivation layer.

[0080] The pressure sensor provided by the embodiment of the present application is a piezoresistive pressure sensor. Compared with a capacitive sensor, the piezoresistive pressure sensor has a smaller volume. If used for intracranial implantation, the damage to brain tissue during the implantation process is smaller. Moreover, the piezoresistive pressure sensor can directly output a voltage signal without the complex signal processing circuit of the capacitive pressure sensor.

[0081] It should be noted that the pressure sensor provided by the embodiment of the present application is not limited to being used as an implantable sensor to measure intracranial pressure, cardiac pressure, abdominal pressure, etc. It can also be used in other application scenarios, such as pressure detection in automobiles, pressure detection in aerospace equipment, and pressure detection in the energy field, etc. The embodiment of the present application does not limit the use scenario of the pressure sensor.

[0082] To make the above objects, features, and advantages of the present application more obvious and understandable, the present application will be further described in detail below with reference to the drawings and specific embodiments.

[0083] Refer to Figure 1 , Figure 1 which is a cross-sectional view of a pressure sensor provided by an embodiment of the present application, including:

[0084] The pressure-sensitive film 101 and the device layer 100 are disposed opposite to each other. The device layer 100 includes a plurality of piezoresistors 102. The piezoresistors 102 are configured as a pressure detection circuit through the connected electrodes 212;

[0085] A functional film 500 is disposed on the side of the device layer 100 away from the pressure-sensitive film 101;

[0086] Wherein, in the first direction Y, at least a part of each piezoresistor 102 overlaps with the functional film 500, and / or at least a part of the pressure-sensitive film overlaps with the functional film 500; the first direction Y is perpendicular to the plane of the pressure sensor, and the first direction Y is the thickness direction of the sensor.

[0087] In the pressure sensor provided by the embodiments of the present application, the functional thin film 500 can improve the ability of the pressure sensor to resist environmental interference and can improve the long-term stability of the pressure sensor in extreme environments such as the intracranial environment.

[0088] As described below, the pressure sensor can further reduce the size by thinning the substrate layer 300 and the relatively thin pressure-sensitive film 101.

[0089] Optionally, the vertical projection of each piezoresistor 102 on the plane where the pressure sensor is located is located within the vertical projection of the functional thin film 500 on the plane where the pressure sensor is located, and / or the vertical projection of the pressure-sensitive film 101 on the plane where the pressure sensor is located is located within the vertical projection of the functional thin film 500 on the plane where the pressure sensor is located.

[0090] If the vertical projection of each piezoresistor 102 on the plane where the pressure sensor is located is located within the vertical projection of the functional thin film 500 on the plane where the pressure sensor is located, in the first direction Y, the functional thin film 500 completely shields each piezoresistor 102, and better sealing protection for each piezoresistor 102 can be achieved through the functional thin film 500. Also, based on the weather resistance of the functional thin film 500 itself, the ability of the piezoresistor 102 to resist environmental interference can be enhanced, and thus the long-term stability of the pressure sensor in extreme environments such as the intracranial environment can be improved.

[0091] If the vertical projection of the pressure-sensitive film 101 on the plane where the pressure sensor is located is located within the vertical projection of the functional thin film 500 on the plane where the pressure sensor is located, in the first direction Y, the functional thin film 500 completely shields the pressure-sensitive film 101, and can better isolate Figure 1 the interference of external environmental factors above on the pressure-sensitive film 101, enhance the ability of the pressure-sensitive film 101 to resist environmental interference, and thus can improve the long-term stability of the pressure sensor in extreme environments such as the intracranial environment.

[0092] In the embodiments of the present application, the functional thin film 500 can be used to improve the long-term stability of the sensor. Optionally, the functional thin film 500 can be a polyimide thin film or a silicon nitride thin film.

[0093] Taking the case where the functional thin film 500 is a polyimide thin film as an example, the polyimide thin film has excellent thermal stability. The polyimide thin film can also isolate water vapor penetration and avoid the shift of the resistance value of the piezoresistor caused by humidity changes. The polyimide thin film can also resist chemical corrosion, has high tolerance to acid-base environments and biological fluids, and can protect the sensitive film from corrosion. The high dielectric strength of the polyimide thin film can also isolate external electromagnetic interference and ensure the stability of the output signal of the Wheatstone full-bridge circuit. The polyimide thin film also has good biocompatibility. When used in the intracranial implantation scenario, it is suitable for long-term implantation in the intracranial environment and can reduce tissue rejection reactions.

[0094] Reference Figures 2 - 6 , Figure 2 is a three-dimensional schematic diagram of a pressure sensor provided by an embodiment of the present application, Figure 3 is a top view of a pressure sensor provided by an embodiment of the present application, Figure 4 is Figure 3 a sectional view of the pressure sensor shown along the A-A' direction, Figure 5 is Figure 3 a sectional view of the pressure sensor shown along the B-B' direction, Figure 6 is Figure 3 an equivalent circuit diagram of the pressure sensor shown. For the convenience of clearly showing the layout of the piezoresistors 102 in the top view shown in Figure 2 , the functional film 500 is not shown in the top view shown in Figure 2 .

[0095] Optionally, in one way, as Figure 3 shown, a pressure sensor can be fabricated with silicon-on-insulator (SOI). The silicon-on-insulator includes a substrate layer 300, a buried oxide layer 200, and a device layer 100 stacked in sequence. After patterning the device layer 100, a plurality of piezoresistors 102 are formed. The four piezoresistors 102 can be the first resistor 1021, the second resistor 1022, the third resistor 1023, and the fourth resistor 1024 in sequence. The pressure sensor has four electrodes 212, and the four electrodes 212 can be the first electrode 1031, the second electrode 1032, the third electrode 1033, and the fourth electrode 1034 in sequence.

[0096] Optionally, in one way, as Figure 4 shown, the surface of the substrate layer 300 facing away from the device layer 100 has a groove, and the pressure-sensitive film 101 is located at the bottom of the groove. Each piezoresistor 102 is located on the surface of the buried oxide layer 200 opposite to the bottom of the groove.

[0097] Optionally, in one way, as Figure 6 shown, the first electrode 1031 can be used as the positive input terminal V OUT+ , the third electrode 1033 can be used as the negative output terminal V OUT- , the second electrode 1032 is used as the positive input terminal V IN+ , and the fourth electrode 1034 is used as the negative input terminal V IN-. The first resistor 1021 is connected between the first electrode 1031 and the second electrode 1032, the second resistor 1022 is connected between the second electrode 1032 and the third electrode 1033, the third resistor 1023 is connected between the first electrode 1031 and the fourth electrode 1034, and the fourth resistor 1024 is connected between the third electrode 1033 and the fourth electrode 1034. In this way, each varistor 102 can form a Wheatstone full-bridge circuit as shown in Figure 6 . Compared with the Wheatstone half-bridge circuit, the Wheatstone full-bridge circuit has better temperature characteristics.

[0098] Optionally, in one way, as shown in Figure 4 and Figure 5 , an insulating layer 210 is provided on the side of the device layer 100 facing away from the pressure-sensitive film 101, and electrode holes 211 are respectively provided in the regions of the insulating layer 210 corresponding to the respective varistors 102; a metal layer is provided on the side of the insulating layer 210 facing away from the device layer 100, and the metal layer includes a plurality of electrodes 212, and the electrodes 212 are connected to the varistors 102 based on the electrode holes 211; wherein, the functional thin film 500 also fills the gap regions between adjacent electrodes 212. In this way, each electrode 212 can be insulated and isolated based on the functional thin film 500. This method can not only improve the anti-interference ability of the pressure sensor to external environmental factors through the functional thin film 500, but also use it as an insulating isolation between the electrodes 212 to avoid the problem of electrode short circuit.

[0099] Optionally, in one way, as shown in Figures 3 - 5 , the electrode 212 includes a pad 213 and a trace 214 connected to the pad 213, and the trace 214 is connected to the varistor 102 through the electrode hole 211; the functional thin film 500 covers the trace 214 and exposes the pad 213. In this method, adjacent pads 213 can be insulated and isolated through the functional thin film 500, the functional thin film 500 covering the trace 214 can be reused, the sealing protection of the trace 214 can be achieved, and the functional thin film 500 can also be reused to insulate and isolate adjacent traces 214 and adjacent pads 213.

[0100] In the top view shown in Figure 3 , in order to facilitate connection with the external circuit, the size of the pad 213 is relatively large. In the miniaturization design scheme, due to the limited area of the pressure sensor chip, the relatively large pad area results in a small distance between adjacent pads 213, and adjacent pads 213 are prone to welding short circuit problems during the welding process between the pad 213 and the external circuit. In the method shown in Figures 3 - 5 , the functional thin film 500 can be reused to achieve insulating isolation between adjacent pads 213, which is convenient for the pressure sensor to further reduce the distance between the pads 213 and is convenient for miniaturization design.

[0101] Optionally, in one way, as Figure 3 shown, each pad 213 is arranged in sequence on the same straight line, and the straight line is parallel and opposite to one side of the pressure-sensitive film 101 ( Figure 3 the left side of the pressure-sensitive film 101 in this case); a functional film 500 is filled between adjacent pads 213. This way can not only reuse the functional film 500 to achieve insulation isolation between adjacent pads 213, but also arrange each pad 213 on the same side of the pressure-sensitive film 101, which is convenient for the unified soldering and fixing of each pad 213 of the pressure sensor to the external circuit, and is also convenient for the encapsulation of the pressure sensor.

[0102] Refer to Figure 7 , Figure 7 which is a schematic layout principle diagram of the piezoresistor and the pressure-sensitive film in a pressure sensor according to an embodiment of the present application. Figure 7 is a top view of the piezoresistor 102 and the pressure-sensitive film 101, and the plane of the top view is perpendicular to the first direction Y. In this way, the pressure-sensitive film 101 is a square film, and the square film has parallel and opposite first sides ( Figure 7 the upper side of the square film in this case) and third sides ( Figure 7 the lower side of the square film in this case) and parallel and opposite second sides ( Figure 7 the left side of the square film in this case) and fourth sides ( Figure 7 the right side of the square film in this case). The perpendicular projections of each piezoresistor 102 on the plane where the pressure-sensitive film 101 is located are all within the area of the pressure-sensitive film 101. In this way, direct stress transfer between the pressure-sensitive film 101 and the piezoresistor 102 can be achieved, and the pressure detection circuit formed by the piezoresistor 102 can accurately collect pressure information based on the pressure-sensitive film 101.

[0103] Among them, the four piezoresistors 102 are all arranged at the corresponding edge positions of the square film along the second direction X, and the second direction X is parallel to the second side and is Figure 7 the horizontal direction in this case. The substrate layer 300 is a silicon crystal. The second direction X is the

[110] direction of the silicon crystal. In the

[110] direction of the silicon crystal, the change amount of the resistance value of the piezoresistor 102 is proportional to the difference between the longitudinal and transverse stresses received by the piezoresistor 102. That is to say, the greater the longitudinal stress received by the piezoresistor 102 and the smaller the transverse stress of the piezoresistor 102, the greater the change amount of the resistance value of the piezoresistor 102, thereby improving the sensitivity of the pressure sensor. Among them, the longitudinal direction of the piezoresistor 102 is its length direction, that is Figure 7 the horizontal direction (the second direction X) in this case, and the transverse direction of the piezoresistor 102 is its width direction, that is Figure 7 the vertical direction in this case.

[0104] The square thin film has a symmetric stress distribution and is also convenient for aligning the edges with the

[110] direction of the silicon crystal, so that the length directions of the respective piezoresistors 102 are all along the

[110] direction of the silicon crystal, thereby improving the sensitivity of the pressure sensor.

[0105] Optionally, the side length of the square thin film can be 400 μm to 600 μm, such as 410 μm, or 421 μm, or 460 μm, or 500 μm, or 550 μm, or 580 μm, etc.

[0106] Optionally, the thickness of the pressure-sensitive film 101 can be 10 μm to 15 μm, such as 11 μm, or 12 μm, or 13.2 μm, or 14 μm, or 14.7 μm, etc.

[0107] As Figure 7 As shown, in the first direction Y, both the first resistor 1021 and the fourth resistor 1024 are linear resistors; the first resistor 1021 is aligned with the first side and is located at the middle position of the first side; the fourth resistor 1024 is aligned with the third side and is located at the middle position of the third side. In the first direction Y, both the second resistor 1022 and the third resistor 1023 are U-shaped resistors; for the second resistor 1022, the opening of the U-shaped resistor faces the middle position of the second side; for the third resistor 1023, the opening of the U-shaped resistor faces the middle position of the fourth side. In this way, the respective piezoresistors 102 are opposite to the center positions of the corresponding sides of the square thin film, so that the respective piezoresistors 102 can be placed in the region with the maximum stress of the pressure-sensitive film 101 (the center position of the edge of the square thin film), and a relatively high sensitivity can be obtained.

[0108] Among them, in the second resistor 1022 and the third resistor 1023 with a U-shaped structure, the openings of the U-shaped resistors face the corresponding sides of the square thin film respectively, which is convenient for connecting the two ends of the U-shaped to the corresponding electrodes 212 respectively.

[0109] The first resistor 1021 and the fourth resistor 1024 are parallel to the corresponding edges. The second resistor 1022 and the third resistor 1023 are U-shaped resistors. The varistors 102 on the upper and lower edges and the varistors 102 on the left and right edges have different positions relative to the edges and different shapes. If the varistors 102 on the upper and lower edges and the left and right edges are all aligned with the corresponding edges, the absolute value of the stress of the first resistor 1021 and the fourth resistor 1024 will be smaller than the absolute value of the stress of the second resistor 1022 and the third resistor 1023, which will lead to a mismatch problem in the resistance change of the four varistors 102, resulting in a poor linearity of the output of the Wheatstone full-bridge circuit, and further affecting the measurement accuracy. In view of this, in one embodiment, in the second direction X, there is a set distance D between the second resistor 1022 and the second side and between the third resistor 1023 and the fourth side.

[0110] As Figure 7 shown, when the first resistor 1021 and the fourth resistor 1024 are respectively edge-aligned with the corresponding edges, and the second resistor 1022 and the third resistor 1023 respectively have a preset distance D from the corresponding edges, the problem of mismatch in the resistance change caused by the different positions and different shapes of the varistors 102 on the upper and lower edges and the varistors 102 on the left and right edges can be solved, avoiding the problem of poor linearity of the output of the Wheatstone full-bridge circuit caused thereby, and improving the measurement accuracy.

[0111] Optionally, in one embodiment, half of the length of the U-shaped resistor is L; the set distance D is not less than 0.1L and less than L. The line widths of the varistors 102 are the same, and the lengths of the varistors 102 are the same. For example, the length of each varistor 102 can be 2L, and the lengths of the first resistor 1021 and the fourth resistor 1024 in the second direction X are 2L. The second resistor 1022 and the third resistor 1023 are U-shaped resistors, which can be approximated as being bent once in length, and their dimensions in the second direction X are half of their total length, that is, L.

[0112] When the first resistor 1021 and the fourth resistor 1024 are both linear resistors and are aligned with the corresponding edges, the second resistor 1022 and the third resistor 1023 are both U-shaped resistors, and the preset distance D from the corresponding edges satisfies: 0.1L ≤ D < L, which can make the varistors 102 of different shapes have the same or similar absolute values of pressure, reduce the degree of mismatch in the resistance change between the varistors 102 on the upper and lower edges and the varistors 102 on the left and right edges, and improve the linearity of the output of the Wheatstone full-bridge circuit to improve the measurement accuracy of the pressure sensor.

[0113] Optionally, the preset distance D can be adjusted according to the design parameters of the pressure sensor. In one way, D can be equal to 12 μm.

[0114] In this application, the varistor 102 is fabricated through the device layer 100. Since the varistor 102 can be regarded as a square structure located above the pressure-sensitive film 101, there are differences in the internal stress of the varistor 102 and the stress on the pressure-sensitive film 101. The thicker the varistor 102, the greater this stress difference. Based on this, the thickness of the pressure-sensitive film 101 can be set to be at least ten times the thickness of the device layer 100, so that the varistor 102 has a relatively thin thickness relative to the pressure-sensitive film 101, which can reduce the stress difference between the internal stress of the varistor 102 and the stress on the pressure-sensitive film 101, and can make the average internal stress of the varistor 102 have the same or similar stress as the pressure-sensitive film 101 to ensure the accuracy of the detection result.

[0115] The thickness range of the device layer 100 can be 0.5 μm to 1 μm, such as 0.5 μm, or 0.61 μm, or 0.8 μm, or 0.95 μm, etc. Within this numerical range, the varistor 102 has a relatively thin thickness to reduce the stress difference between the internal stress of the varistor 102 and the stress on the pressure-sensitive film 101, and can make the average internal stress of the varistor 102 have the same or similar stress as the pressure-sensitive film 101 to ensure the accuracy of the detection result.

[0116] Optionally, on the basis of other embodiments, in the first direction Y, the line widths of the varistors 102 are the same, and the lengths of the varistors 102 are the same, that is, the varistors 102 have the same resistance value, so as to ensure the initial balance of the constructed pressure detection circuit, eliminate zero drift, maximize sensitivity and linearity, suppress temperature drift and process errors, and simplify the manufacturing and calibration processes.

[0117] Based on the pressure sensor provided by the above embodiments, another embodiment of this application also provides a method for preparing a pressure sensor, including:

[0118] Step S11: Form a patterned device layer 100, the device layer 100 includes a plurality of varistors 102, and the varistors 102 are configured as a pressure detection circuit through the connected electrodes 212; wherein, a functional thin film 500 is formed on one side of the device layer 100.

[0119] Step S12: Form a pressure-sensitive film 101 on the other side of the device layer 100.

[0120] Wherein, in the first direction Y, at least a part of each varistor 102 overlaps with the functional thin film 500, and / or at least a part of the pressure-sensitive film overlaps with the functional thin film 500; the first direction Y is perpendicular to the plane where the pressure sensor is located.

[0121] Optionally, in one embodiment, the method for preparing the functional film includes:

[0122] Step A: As Figure 8 shown, provide silicon-on-insulator, which includes a substrate layer 300, a buried oxide layer 200, and a device layer 100 stacked in sequence; pattern the device layer 100 to form a plurality of piezoresistors 102. In this step, using photoresist as a mask, deep reactive ion etching technology is used to etch piezoresistors 102 on the front side of the device layer 100. Since the depth to be etched is relatively shallow and the pattern requires high precision, a relatively thin photoresist needs to be used for photolithography in order to achieve a thinner thickness and a pattern with higher precision.

[0123] Step B: As Figure 9 shown, form a patterned insulating layer 210 on the surface of the patterned device layer 100. The insulating layer 210 is provided with electrode holes 211 corresponding to the regions of the respective piezoresistors 102. In this step, on the front side of the device layer 100, silicon oxide with a thickness of 1 μm to 2 μm is grown as the insulating layer 210 by PECVD (plasma enhanced chemical vapor deposition) technology, and using photoresist as a mask, reactive ion etching technology is used to etch out the electrode holes 211. Since the depth to be etched is relatively shallow and the pattern requires high precision, a relatively thin photoresist needs to be used for photolithography in order to achieve a thinner thickness and a pattern with higher precision.

[0124] Step C: As Figure 10 shown, form a patterned metal layer on the surface of the insulating layer 210. The metal layer includes a plurality of electrodes 212, and the electrodes 212 are connected to the piezoresistors 102 based on the electrode holes 211. In this step, a layer of photoresist is spin-coated and patterned on the front side of the device layer 100, a metal layer with a thickness of 1 μm to 2 μm is evaporated, and the patterning of the metal electrodes is completed by lift-off to form the electrodes 212 with the required pattern structure. Optionally, the electrodes 212 can be aluminum electrodes or gold electrodes.

[0125] Step D: As Figure 11 shown, form a functional film 500 on the surface of the metal layer. In this step, the functional film 500 can be prepared by a spin-coating process, a deposition process, or a Si3N4 film can be prepared by photolithographic patterning or atomic layer deposition process to prepare the functional film 500. The thickness of the functional film 500 can be the same as or approximately the same as that of the insulating layer 210. The thickness error of the functional film 500 is controlled to ±5 nm. If the functional film 500 is a PI film, the PI precursor is added with nano-SiO2 particles to improve the mechanical strength. The functional film 500 can be a PI film, or a Si3N4 film, or a composite layer of the two.

[0126] Optionally, in one embodiment, before forming the pressure-sensitive film 101, the surface of the substrate layer 300 facing away from the device layer 100 is thinned to reduce the product thickness.

[0127] Optionally, in one embodiment, before thinning the substrate layer 300, a first auxiliary substrate 401 for protecting the functional thin film 500 and the electrode 212 is formed. The first auxiliary substrate 401 can be a grooved glass plate. The first auxiliary substrate 401 can protect the front structure and also provide support for subsequent thinning, so as to thin the back surface of the substrate layer 300 to a greater extent.

[0128] Optionally, in one embodiment, the formation of the first auxiliary substrate 401 for protecting the functional thin film 500 and the electrode 212 includes:

[0129] Step E: Sputter a Cr / Au film on the first auxiliary substrate 401 with thicknesses of 10 nm to 30 nm / 250 nm to 350 nm (such as 20 nm / 300 nm). Pattern the Cr / Au film through a photolithography process to form a mask. Based on this mask, etch the surface of the first auxiliary substrate 401 with HF acid to fabricate the first auxiliary substrate 401 with grooves.

[0130] Step F: As Figure 12 shown, use anodic bonding to bond and fix the first auxiliary substrate 401 with grooves on the surface of the side where the electrode 212 and the functional thin film 500 are formed. Protect the electrode 212 and the functional thin film 500 through the grooves in the first auxiliary substrate 401.

[0131] Optionally, in one embodiment, thinning the surface of the substrate layer 300 facing away from the device layer 100 includes:

[0132] Step G: Use CMP (chemical mechanical polishing) to thin the thickness of the substrate layer 300 to 40 μm to 60 μm, such as 50 μm.

[0133] Optionally, in one embodiment, the method for forming the pressure-sensitive film 101 includes:

[0134] Step H: As Figure 13 shown, form grooves on the surface of the substrate layer 300 facing away from the device layer 100; form the pressure-sensitive film 101 at the bottom of the grooves. In this step, use KOH wet etching to complete the fabrication of the pressure-sensitive film 101 with a Cr / Au film as a mask on the back surface of the substrate layer 300.

[0135] Step I: As Figure 14As shown, a cover plate 400 is fixed on the side of the substrate layer 300 facing away from the device layer 100. Optionally, a getter 402 is provided in the area of the cover plate 400 corresponding to the back groove of the substrate layer 300 to form a vacuum reference cavity with the groove, which can isolate the interference of the external environment on the pressure-sensitive film 101 and improve the reliability and stability of the sensor.

[0136] Optionally, in one embodiment, the method for preparing the cover plate 400 includes: forming a getter 402 in the area of the cover plate 400 corresponding to the groove based on a second auxiliary substrate having through holes.

[0137] Among them, forming a getter 402 in the area of the cover plate 400 corresponding to the groove based on a second auxiliary substrate having through holes includes:

[0138] Sub-step I1: The second auxiliary substrate can be another glass plate. Laser processing is used to ablate patterned through holes on another glass plate, and the positions of the through holes correspond to the positions of the getter 402 to be deposited in the cover plate 400. Then, the second auxiliary substrate is cleaned to make a hard mask.

[0139] Sub-step I2: Clean the cover plate 400 for anodic bonding and perform single-sided oxygen injection for surface cleaning and activation.

[0140] Sub-step I3: After pasting the second auxiliary substrate as a mask and the cover plate 400 together with a high-temperature tape, based on the through holes on the second auxiliary substrate, evaporate a Ti / Au thin film on the surface of the cover plate 400 as the getter 402, with thicknesses of 1 μm / 30 nm respectively.

[0141] Optionally, in one embodiment, the method for fixing the cover plate 400 includes:

[0142] Step J: After bonding and fixing the cover plate 400 and the substrate layer 300, activate the getter 402 to form a vacuum reference cavity based on the groove. In this step, the cover plate 400 with the getter 402 is bonded to the substrate layer 300 by anodic bonding to form a vacuum reference cavity.

[0143] Step K: Use laser cutting to remove the first auxiliary substrate 401 bonded on the device layer 100 to complete the preparation of the pressure sensor.

[0144] Optionally, in one embodiment, after fixing the cover plate 400, it further includes: improving the ohmic contact between the electrode 212 and the piezoresistor 102 through annealing treatment. If the electrode 212 is an aluminum electrode, a good ohmic contact can be formed without annealing treatment.

[0145] Based on the above description, it can be known that the pressure sensor provided in any embodiment of the present application can be prepared by using the preparation method provided in the embodiments of the present application.

[0146] In this application, the pressure-sensitive film 101 can be protected inside the vacuum chamber through vacuum packaging. The varistor 102 can also be sealed by the insulating layer 210 and the functional film 500, which can isolate external environmental interferences (such as humidity, temperature fluctuations, and biological fluid corrosion), improving the long-term stability of the pressure sensor. The getter 402 (such as Ti / Au film) inside the vacuum chamber can maintain the vacuum degree of the chamber for a long time, solving the problem of long-term drift of existing gauge pressure sensors.

[0147] In this application, through the optimization of the circuit layout, the configuration of the Wheatstone full-bridge circuit can be achieved without significantly increasing the device size, reducing the temperature drift and improving the temperature stability of the pressure sensor. Moreover, through the design of the U-shaped resistor and its corresponding preset distance D, the stress matching of the four varistors 102 can be optimized, improving the linearity.

[0148] In this application, the linearity of the pressure sensor is improved through the stress matching of the varistor 102.

[0149] In this application, by thinning the substrate layer 300 and optimizing the insulation isolation design of the electrode 212, the size of the pressure sensor can be reduced, and the size can be reduced to 500μm×500μm×12μm. The thickness of the device layer 100 can be reduced to 0.5μm. When used as an intracranial implantable sensor, the overall implant volume is smaller, which can reduce brain tissue damage.

[0150] During the preparation process of this application, silicon-on-insulator can be double-sided bonded with a glass plate (the first auxiliary substrate 401 is bonded on the front side, and the cover plate 400 is bonded on the back side); subsequently, redundant glass plates can be removed by laser cutting to improve the process accuracy.

[0151] In the description of the embodiments of this application, the embodiments are described in a progressive, or parallel, or a combination of progressive and parallel manners. Each embodiment focuses on the differences from other embodiments, and the same or similar parts between the embodiments can be referred to each other. The embodiments provided by the embodiments of this application can be combined with each other without conflict.

[0152] It should be noted that in the description of this application, it should be understood that the descriptions of the drawings and embodiments are illustrative rather than restrictive. The same reference numerals throughout the embodiments of the specification identify the same structures. Additionally, for the sake of understanding and ease of description, the drawings may exaggerate the thickness of some layers, films, panels, regions, etc. At the same time, it can be understood that when an element such as a layer, film, region, or substrate is referred to as being "on" another element, the element can be directly on the other element or there can be intervening elements. Additionally, "on" means positioning the element on or under another element, but does not inherently mean positioning on the upper side of another element according to the direction of gravity.

[0153] The orientation or positional relationship indicated by terms such as "upper", "lower", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing this application and simplifying the description, 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 thus should not be construed as a limitation of this application. When a component is considered to be "connected" to another component, it can be directly connected to the other component or there may be intervening components present at the same time.

[0154] It should also be noted that in this document, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including", or any other variation thereof is intended to cover non-exclusive inclusion, such that an article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or further includes elements inherent to such article or device. Without further limitation, an element defined by the statement "including a..." does not exclude the presence of additional identical elements in the article or device including the above elements.

[0155] The above description of the disclosed embodiments enables those skilled in the art to implement or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application will not be limited to these embodiments shown herein, but rather is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A pressure sensor, characterized in that, Comprising: A pressure-sensitive film and a device layer arranged oppositely, the device layer includes a plurality of varistors, and the varistors are configured as a pressure detection circuit through the connected electrodes; A functional film is provided on a side of the device layer facing away from the pressure-sensitive film; Wherein, in a first direction, at least a part of each of the varistors overlaps with the functional film, and / or at least a part of the pressure-sensitive film overlaps with the functional film; the first direction is perpendicular to the plane where the pressure sensor is located.

2. The pressure sensor according to claim 1, wherein, The perpendicular projection of each of the varistors on the plane where the pressure sensor is located is located within the perpendicular projection of the functional film on the plane where the pressure sensor is located, and / or the perpendicular projection of the pressure-sensitive film on the plane where the pressure sensor is located is located within the perpendicular projection of the functional film on the plane where the pressure sensor is located.

3. The pressure sensor according to claim 1, wherein An insulating layer is provided on a side of the device layer facing away from the pressure-sensitive film, and electrode holes are respectively provided in regions of the insulating layer corresponding to each of the varistors; A metal layer is provided on a side of the insulating layer facing away from the device layer, the metal layer includes a plurality of the electrodes, and the electrodes are connected to the varistors based on the electrode holes; Wherein, the functional film also fills a gap region between adjacent electrodes.

4. The pressure sensor according to claim 3, characterized in that, The electrode includes a pad and a trace connected to the pad, and the trace is connected to the varistor through the electrode hole; The functional film covers the trace and exposes the pad; Or, the electrode includes a pad and a trace connected to the pad, and the trace is connected to the varistor through the electrode hole; The pads are arranged in sequence on the same straight line, and the straight line is parallel and opposite to one side of the pressure-sensitive film; the functional film is filled between adjacent pads.

5. The pressure sensor according to claim 1, characterized in that, The pressure-sensitive film is a square film, and the square film has a first side and a third side that are parallel and opposite, and a second side and a fourth side that are parallel and opposite; The device layer includes four varistors, and the four varistors are successively a first resistor, a second resistor, a third resistor, and a fourth resistor; the perpendicular projection of each of the varistors on the plane where the pressure-sensitive film is located is located within the region of the pressure-sensitive film; In the first direction, both the first resistor and the fourth resistor are linear resistors; the first resistor is aligned with the first side, and the first resistor is located at the middle position of the first side; the fourth resistor is aligned with the third side, and the fourth resistor is located at the middle position of the third side; In the first direction, both the second resistor and the third resistor are U-shaped resistors; for the second resistor, the opening of the U-shaped resistor faces the middle position of the second side; for the third resistor, the opening of the U-shaped resistor faces the middle position of the fourth side.

6. The pressure sensor according to claim 5, wherein In a second direction, there is a set distance between the second resistor and the second side and between the third resistor and the fourth side; the second direction is parallel to the first side.

7. The pressure sensor according to claim 6, characterized in that, Half of the length of the U-shaped resistor is L; The set distance is not less than 0.1L and less than L.

8. The pressure sensor according to any one of claims 1-7, characterized in that, The thickness of the pressure-sensitive film is at least ten times the thickness of the device layer; alternatively, the thickness range of the device layer is 0.5 μm to 1 μm; alternatively, in the first direction, the line widths of the respective piezoresistors are the same, and the lengths of the respective piezoresistors are the same.

9. A method for preparing a pressure sensor according to any one of claims 1-8, characterized in that, Comprising: forming a patterned device layer, the device layer including a plurality of piezoresistors, the piezoresistors being configured as a pressure detection circuit through the connected electrodes; wherein, a functional thin film is formed on one side of the device layer; forming a pressure-sensitive film on the other side of the device layer; wherein, in the first direction, at least a part of each of the piezoresistors overlaps with the functional thin film, and / or at least a part of the pressure-sensitive film overlaps with the functional thin film; the first direction is perpendicular to the plane where the pressure sensor is located.

10. The preparation method according to claim 9, Characterized in that wherein, the preparation method of the functional thin film includes: providing silicon-on-insulator, including a substrate layer, a buried oxide layer, and a device layer stacked in sequence, patterning the device layer to form a plurality of the piezoresistors; forming a patterned insulating layer on the surface of the patterned device layer, the insulating layer being provided with electrode holes corresponding to the regions of the respective piezoresistors; forming a patterned metal layer on the surface of the insulating layer, the metal layer including a plurality of electrodes, the electrodes being connected to the piezoresistors based on the electrode holes; forming the functional thin film on the surface of the metal layer; wherein, before forming the pressure-sensitive film, the surface of the substrate layer facing away from the device layer is thinned; wherein, before thinning the substrate layer, a first auxiliary substrate for protecting the functional thin film and the electrodes is formed; wherein, the method for forming the pressure-sensitive film includes: forming a groove on the surface of the substrate layer facing away from the device layer; forming the pressure-sensitive film at the bottom of the groove; fixing a cover plate on the side of the substrate layer facing away from the device layer; wherein, the method for fixing the cover plate includes: forming a getter on the cover plate corresponding to the region of the groove based on a second auxiliary substrate having a through hole; after bonding and fixing the cover plate to the substrate layer, activating the getter to form a vacuum reference cavity based on the groove; wherein, after fixing the cover plate, further included is: improving the ohmic contact between the electrodes and the piezoresistors through annealing treatment.

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