Low-temperature-drift MEMS resonant pressure sensor sensitive chip and preparation method thereof

Abstract

The invention belongs to the field of MEMS sensors, and particularly relates to a low-temperature-drift MEMS resonant pressure sensor sensitive chip and a preparation method thereof. Comprising a cap layer, a resonance layer, a pressure sensing layer and an isolation base which are sequentially bonded and connected from top to bottom, the cap layer is provided with an electrode through hole and a vacuum cavity groove, and a getter is sputtered in the vacuum cavity groove; two Si-SiO2 composite resonators and a plurality of lead wire discs are arranged on the resonance layer, and a metal electrode is arranged on each lead wire disc; the number of the metal electrodes is equal to that of the cap layer electrode through holes, and the metal electrodes are located under the electrode through holes; two groups of silicon islands are arranged on the front surface of the pressure sensing layer, and three rectangular sensitive films with the same size are arranged on the back surface; the isolation base is a glass table; according to the invention, the output sensitivity of the sensor is greatly improved, the chip processing complexity is reduced, and the introduction of additional stress and materials is reduced.

Description

Technical Field

[0001] The invention belongs to the field of micro-electromechanical sensors, and in particular relates to a low-temperature drift MEMS resonant pressure sensor sensitive chip and a preparation method thereof. Background Art

[0002] With the development of micro-electromechanical (MEMS) technology, MEMS silicon resonant pressure sensors are based on the working principle of mechanical vibration, and have the characteristics of high precision and high stability. At the same time, the output is a resonant frequency signal, without the need for analog-to-digital conversion, with a high signal-to-noise ratio and excellent anti-interference ability. It has been widely used in precision measurement fields such as aerospace, industrial control, and meteorological measurement. The temperature drift of MEMS silicon resonant pressure sensors is an important factor restricting the accuracy of the sensor. The current mainstream temperature compensation structure adopts stress isolation, multi-resonator differential output, and all-silicon process methods to effectively reduce the temperature drift caused by thermal stress. However, less attention has been paid to the sensitivity temperature drift caused by the Young's modulus of silicon materials. In addition, most resonant pressure sensors that use a multi-resonator differential output structure arrange multiple resonators on the same sensitive membrane, which has the problem of large sensitive membrane area and low sensitivity.

[0003] In view of the temperature drift mechanism of silicon resonant pressure sensors, a new resonant pressure sensor sensitive chip is urgently needed, which can compensate and optimize the sensor temperature drift caused by thermal stress and Young's modulus drift. At the same time, the piezoresistive output detection structure is improved to reduce the stress caused by the introduction of additional materials and steps in complex processes. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention proposes a low-temperature drift MEMS resonant pressure sensor sensitive chip and a preparation method thereof, comprising:

[0005] A cap layer, a resonance layer, a pressure-sensing layer and an isolation base are bonded and connected in sequence from top to bottom;

[0006] The cap layer is provided with an electrode through hole and a vacuum cavity groove, and a getter is sputtered in the vacuum cavity groove;

[0007] The resonance layer is provided with two Si-SiO2 composite resonators and a plurality of lead plates, each lead plate is provided with a metal electrode; the number of the metal electrodes is equal to the number of the electrode through holes of the cap layer and the metal electrodes are located directly below the electrode through holes;

[0008] The pressure-sensitive layer has two groups of silicon islands on the front side and three rectangular sensitive films of the same size on the back side;

[0009] The isolation base is a glass table.

[0010] Preferably, the Si-SiO2 composite resonator is formed by growing an oxide layer through thermal oxidation of the resonator, and the resonator includes a symmetrical X-shaped torsional piezoresistive structure, a resonant beam, a vibration pickup beam, hollow comb teeth, fixed comb teeth, a connecting beam and a movable anchor point; the middle parts of all the resonant beams, vibration pickup beams and hollow comb teeth are connected by a connecting beam, and the two ends of each resonant beam are respectively connected to the suspended torsion structure on the movable anchor point, and the two ends of each vibration pickup beam are respectively connected to two symmetrical X-shaped torsional piezoresistive structures; the hollow comb teeth cooperate with the fixed comb teeth on both sides of the resonator to form a driving capacitor.

[0011] Furthermore, two groups of silicon islands are arranged in the area where the horizontal displacement of the sensitive membrane is the largest under pressure, the center of one rectangular sensitive membrane is located directly below a Si-SiO2 composite resonator, and the centers of the other two rectangular sensitive membranes are located directly below another Si-SiO2 composite resonator.

[0012] Preferably, the lead pads on the resonance layer are divided into a DC bias lead pad, an AC drive lead pad and an output detection lead pad.

[0013] Preferably, a groove is provided on the glass platform, and the groove is in the shape of a cross, so that four rectangular glass protrusions are formed on the glass platform.

[0014] A method for preparing a low-temperature drift MEMS resonant pressure sensor sensitive chip, comprising:

[0015] S1: A clean double-sided polished SOI silicon wafer is used to prepare the silicon island of the pressure-sensitive layer;

[0016] S2: Prepare a clean double-sided polished SOI silicon wafer as the resonance layer substrate, and bond the silicon island surface of the pressure-sensitive layer to the resonance layer substrate;

[0017] S3: preparing a Si-SiO2 composite resonator and a lead plate of a resonance layer on a resonance layer substrate to obtain a resonance layer;

[0018] S4: using a single crystal silicon double-polished wafer to prepare a cap layer, and bonding the cap layer to the resonance layer silicon-silicon low-temperature vacuum bonding;

[0019] S5: preparing a rectangular sensitive film on the reverse side of the pressure-sensitive layer;

[0020] S6: preparing an isolation base, and anodically bonding the isolation base to the reverse side of the pressure-sensitive layer;

[0021] S7: etching silicon oxide on the resonance layer through the electrode through-hole of the cap layer, and sputtering metal through the electrode through-hole of the cap layer to form an ohmic contact on the resonance layer, thereby completing the preparation of the metal electrode.

[0022] Furthermore, the process of preparing the silicon island includes:

[0023] S11: prepare a clean double-sided polished SOI silicon wafer;

[0024] S12: thermally oxidizing and growing silicon oxide on the double-sided polished SOI silicon wafer as an etching mask;

[0025] S13: photolithographically etching silicon oxide on the surface of the SOI silicon wafer device layer to form a silicon island pattern etching mask;

[0026] S14: Perform DRIE etching on the device layer to form a silicon island.

[0027] Further, the process of preparing the Si-SiO2 composite resonator and the lead plate includes:

[0028] S31: using a CMP process to thin the substrate layer of the SOI silicon wafer to 50 μm, and then using KOH or TMAH wet etching to etch the remaining silicon to expose the oxide layer of the SOI silicon wafer;

[0029] S32: photolithographically etching silicon oxide to obtain a resonance layer device pattern etching mask;

[0030] S33: DRIE etches the device layer of the SOI silicon wafer to obtain a resonator and a lead disk structure;

[0031] S34: removing the oxide layer on the surface of the resonance layer by dry etching to complete the preparation of the resonator-silicon island integrated structure;

[0032] S35: thermally oxidizing and growing an oxide layer on the surface of the resonator to form a Si-SiO2 composite resonator.

[0033] Furthermore, the process of preparing the capping layer includes:

[0034] S41: performing laser drilling on the single crystal silicon double polished wafer to obtain an electrode through hole;

[0035] S42: thermally oxidizing and growing silicon oxide on a single crystal silicon double-polished wafer, and photolithographically etching the silicon oxide to obtain a vacuum cavity groove pattern etching mask;

[0036] S43: RIE etching of vacuum cavity grooves;

[0037] S44: Magnetron sputtering of Ti getter in the vacuum chamber groove.

[0038] The beneficial effects of the present invention are:

[0039] (1) The present invention grows silicon oxide on the surface of a single crystal silicon resonator to form a Si-SiO2 composite resonant beam, and uses the positive frequency temperature coefficient of silicon oxide to offset the negative frequency temperature coefficient of single crystal silicon, thereby compensating for the temperature drift of the Young's modulus of the silicon material and significantly reducing the temperature drift of the sensor sensitivity.

[0040] (2) The X-shaped torsional piezoresistive structure is designed, which eliminates the need for additional varistors and corresponding metal wiring, reducing chip processing complexity and the introduction of additional stress and materials.

[0041] (3) The dual resonator anchor points in the present invention are both located in the area where the horizontal displacement of the sensitive film is the largest under the action of pressure, which differentially offsets the drift caused by thermal stress while maximizing the stress transfer effect of the sensitive film-silicon island. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a schematic diagram of the overall structure of the low temperature drift MEMS resonant pressure sensor sensitive chip of the present invention;

[0043] Figure 2 Schematic diagram of the front and back structures of the capping layer in the present invention;

[0044] Figure 3 It is a schematic diagram of the resonance layer structure in the present invention;

[0045] Figure 4 It is a schematic diagram of the front and back structures of the pressure-sensitive layer in the present invention;

[0046] Figure 5 It is a schematic diagram of the isolation base structure in the present invention;

[0047] Figure 6 This is a schematic diagram of the silicon island process flow in the present invention;

[0048] Figure 7 It is a schematic diagram of the process flow of the resonance layer in the present invention;

[0049] Figure 8 This is a schematic diagram of the process flow of the capping layer and the sensitive film in the present invention;

[0050] Fig. 9 It is a schematic diagram of the isolation base process flow in the present invention. DETAILED DESCRIPTION

[0051] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0052] The present invention proposes a low temperature drift MEMS resonant pressure sensor sensitive chip and a preparation method thereof, such as Figure 1 As shown, the chip includes: a cap layer (Layer 1), a resonance layer (Layer 2), a pressure sensing layer (Layer 3) and an isolation base (Layer 4) which are bonded and connected in sequence from top to bottom.

[0053] like Figure 2 As shown, the cap layer is provided with an electrode through hole (1) and a vacuum cavity groove (2), and a getter (3) is sputtered in the vacuum cavity groove. The cap layer (Layer 1) uses a single crystal silicon wafer laser to process the electrode through hole (1) and RIE to etch the vacuum cavity groove (2), and the getter (3) is sputtered in the groove, and the vacuum cavity is formed after bonding with the resonance layer (Layer 2).

[0054] like Figure 3 As shown, two Si-SiO2 composite resonators (4) and a plurality of lead plates (5, 6, 7) are provided on the resonance layer, and a metal electrode (8) is provided on each lead plate; the number of the metal electrodes is equal to the number of the electrode through holes of the cap layer, and the metal electrodes are located directly below the electrode through holes.

[0055] The Si-SiO2 composite resonator is formed by growing an oxide layer through thermal oxidation of the resonator. The resonator comprises a symmetrical X-shaped torsional piezoresistive structure (10), a resonant beam (11), a vibration pickup beam (12), hollow comb teeth (13), fixed comb teeth (22), a connecting beam (14) and a movable anchor point (9); all the resonant beams, vibration pickup beams and the middle parts of the hollow comb teeth are connected by a connecting beam, and the two ends of each resonant beam are respectively connected to the suspended torsional structure (21) on the movable anchor point, and the two ends of each vibration pickup beam are respectively connected to two symmetrical X-shaped torsional piezoresistive structures; the hollow comb teeth cooperate with the fixed comb teeth on both sides of the resonator to form a driving capacitor.

[0056] The resonator is the core structure of the sensitive chip of the MEMS resonant pressure sensor. Based on the principle of electrostatic excitation / piezoresistive detection, the present invention designs a double-ended fixed-support resonant beam structure. The structure is mainly composed of two groups of beams, namely the resonant beam and the vibration pickup beam. The two groups of beams are connected together through the middle connecting beam. The two ends of the resonant beam are connected to the suspended torsion structure on the movable anchor point, and the two ends of the vibration pickup beam are connected to the X-shaped torsion piezoresistive structure in the fixed area of ​​the chip. On the outside of the beam is a driving comb structure. The driving comb teeth (hollow comb teeth) cooperate with the fixed comb teeth to form a driving capacitor. A layer of silicon oxide grows on the surface of the single crystal silicon of the resonator to form a Si-SiO2 composite resonant beam. The negative frequency temperature coefficient of the single crystal silicon is offset by the positive frequency temperature coefficient of silicon oxide to compensate for the temperature drift of the Young's modulus of the silicon material, which can greatly reduce the temperature drift of the sensor sensitivity.

[0057] Conventional piezoresistive detection methods prepare diffused varistors by ion implantation on the resonant beam or the vibration pickup beam, and output resistance changes through metal wiring. The present invention directly uses heavily doped wafers to etch out long strip structures as varistors to form an X-shaped torsional piezoresistive structure. When the vibration pickup beam vibrates with the resonant beam, the end connected to the X-shaped piezoresistive structure drives the X-shaped piezoresistive structure to torsion, and the total resistance of the series-parallel network composed of the X-shaped piezoresistive structure produces alternations of the same frequency with the vibration. In addition, the X-shaped torsional piezoresistive structure is located in the fixed area of ​​the chip, and the connection of the vibration pickup beam to it effectively reduces the out-of-plane displacement of the drive comb teeth under pressure, thereby improving the stability of the drive.

[0058] When the width of the driving comb tooth connection block is insufficient, due to the small lateral stiffness, the movable comb teeth are prone to synchronous vibration during the vibration of the resonator, affecting the driving stability. Therefore, the present invention designs a hollow comb tooth structure, increases the width of the comb tooth connection block to improve the vibration stiffness, and prevents the comb teeth from deforming with the vibration of the resonance beam. In addition, an overly large comb tooth connection block causes the effective mass of the resonator vibration to be too large, which greatly reduces the natural frequency and causes the sensor sensitivity to decrease. Therefore, designing it as a hollow structure can reduce the effective mass while ensuring the vibration stiffness, increase the resonant frequency of the resonator, and improve the sensor sensitivity.

[0059] The lead pads on the resonance layer are divided into a DC bias lead pad, an AC drive lead pad and an output detection lead pad, and the lead pads are formed by etching.

[0060] like Figure 4 As shown, two groups of silicon islands (15, 16) are arranged on the front side of the pressure-sensitive layer, and three rectangular sensitive films (17, 18, 19) of the same size are etched on the back side by DRIE; the two groups of silicon islands are arranged in the area where the horizontal displacement of the sensitive film is the largest under the action of pressure, the center of one rectangular sensitive film is located directly below a Si-SiO2 composite resonator, and the centers of the other two rectangular sensitive films are located directly below another Si-SiO2 composite resonator.

[0061] The three-membrane-dual-resonator differential output structure of the present invention arranges two resonators with exactly the same materials and structural parameters, one in the center of a sensitive membrane and the other between two outer sensitive membranes. Under the action of pressure, tensile stress and compressive stress are respectively generated on the two resonant beams, so that the resonant frequency increases and decreases respectively, while the drift caused by temperature is the same. The difference in the output frequency of the two offsets the drift caused by thermal stress, and at the same time improves the sensitivity of the sensor. The anchor points of the two resonators are both located in the area with the maximum horizontal displacement of the sensitive membrane, maximizing the use of the stress transfer effect of the sensitive membrane-silicon island, and the sensitive membrane is designed to be rectangular, which greatly increases the horizontal displacement of the sensitive membrane compared to the square membrane.

[0062] Preferably, Figure 5As shown, the isolation base (20) is a glass table. Specifically, the isolation base (Layer 4) is borosilicate glass that is grinded and grooved by a thick glass grinding wheel to form four rectangular glass protrusions (20) that are anodically bonded to the pressure-sensitive layer to isolate assembly stress.

[0063] The working principle of the low temperature drift MEMS resonant pressure sensor sensitive chip designed by the present invention is:

[0064] The present invention adopts an electrostatic drive / piezoresistive detection method, applies an anti-phase AC voltage to the comb capacitors on both sides of the resonator, generates an alternating electrostatic force to drive the resonator to vibrate in the same direction in the plane, and the vibration of the resonant beam drives the vibration pickup beam to twist around the center point of the X-shaped torsion piezoresistive detection structure, so that the resistance value of the piezoresistive detection structure changes at the same frequency. When pressure acts on the sensitive film, the deformation of the sensitive film is converted into axial stress on the resonant beam through the silicon island, thereby changing the stiffness of the resonant beam and causing its natural frequency to change linearly. The alternating frequency of the output resistance value during resonance can be measured to achieve pressure measurement.

[0065] The present invention adopts an electrostatic drive / piezoresistive detection method when working, a DC bias voltage is applied to a DC bias lead disk (5), an output detection lead disk (7) is externally connected to a resistor and then grounded, and the potential of the hollow comb teeth (13) is suspended, so there is no voltage drop on each comb tooth, and the potential is the same. An anti-phase AC voltage is applied to the two AC drive lead disks (6), so that an alternating electrostatic force is generated on the comb tooth capacitors on both sides of the resonator to drive the resonator to vibrate in the same direction within the plane, and the vibration of the resonance beam (11) drives the vibration pickup beam to twist around the center point of the X-shaped torsion piezoresistive structure (10), so that the resistance value of the piezoresistive detection structure changes at the same frequency. The pressure acting on the sensitive film (17) converts the deformation of the sensitive film into tensile stress on the resonance beam through the silicon island, thereby increasing the resonator frequency. The pressure acting on the sensitive films (18, 19) converts the deformation of the sensitive films into compressive stress on the resonance beam through the silicon island, thereby reducing the resonator frequency. Two completely identical resonators are completely affected by thermal stress. The difference in the frequencies of the two resonators offsets the influence of thermal stress and increases the output sensitivity.

[0066] The present invention also provides a method for preparing a low-temperature drift MEMS resonant pressure sensor sensitive chip, comprising:

[0067] S1: Use a clean double-sided polished SOI silicon wafer to prepare the silicon island of the pressure-sensitive layer.

[0068] like Figure 6 As shown, the process of preparing the silicon island includes:

[0069] S11: Prepare a clean double-sided polished SOI silicon wafer.

[0070] Prepare double-sided polished SOI silicon wafers and perform standard RCA cleaning. The SOI silicon wafer is divided into three layers: device layer, oxide layer, and substrate layer.

[0071] S12: thermally oxidizing and growing silicon oxide on the double-sided polished SOI silicon wafer as an etching mask;

[0072] S13: photolithographically etching silicon oxide on the surface of the device layer to obtain a silicon island pattern etching mask;

[0073] S14: Perform DRIE etching on the device layer to form a silicon island.

[0074] S2: Prepare a clean double-sided polished SOI silicon wafer as the resonance layer substrate, and bond the silicon island surface of the pressure-sensitive layer to the resonance layer substrate.

[0075] like Figure 7 As shown, the resonant layer is prepared by double-sided polished SOI silicon wafer, the thickness of the device layer of the SOI silicon wafer used is the designed thickness of the resonant layer device, and standard RCA cleaning is performed to serve as the resonant layer substrate. The silicon island surface of the pressure-sensitive layer and the resonant layer substrate are silicon-silicon bonded.

[0076] S3: preparing a Si-SiO2 composite resonator and a lead plate of the resonance layer on the resonance layer substrate to obtain the resonance layer.

[0077] like Figure 7 As shown, the process of preparing Si-SiO2 composite resonator and lead disk includes:

[0078] S31: The substrate layer of the SOI silicon wafer is thinned to 50 μm using a CMP process, and then the remaining silicon is wet-etched using KOH or TMAH to expose the oxide layer of the SOI silicon wafer.

[0079] S32: photolithographically etching silicon oxide to obtain a resonance layer device pattern etching mask;

[0080] S33: DRIE etches the device layer of the SOI silicon wafer to obtain a resonator and a lead disk structure;

[0081] The lead pads etched around the resonator include a DC bias lead pad, an AC drive lead pad, and an output detection lead pad.

[0082] S34: removing the oxide layer on the surface of the resonance layer by dry etching to complete the preparation of the resonator-silicon island integrated structure;

[0083] S35: thermally oxidizing and growing an oxide layer on the surface of the resonator to form a Si-SiO2 composite resonator.

[0084] S4: Use a single crystal silicon double-polished wafer to prepare a cap layer, and bond the cap layer to the resonance layer silicon-silicon low-temperature vacuum bonding.

[0085] like Figure 8 As shown, the process of preparing the capping layer includes:

[0086] S41: performing laser drilling on the single crystal silicon double polished wafer to obtain an electrode through hole;

[0087] S42: thermally oxidizing and growing silicon oxide on a single crystal silicon double-polished wafer, and photolithographically etching the silicon oxide to obtain a vacuum cavity groove pattern etching mask;

[0088] S43: RIE etching of vacuum cavity grooves;

[0089] S44: Magnetron sputtering of Ti getter in the vacuum chamber groove.

[0090] S5: preparing a rectangular sensitive film on the reverse side of the pressure-sensitive layer.

[0091] like Figure 8 As shown, in the pressure-sensitive layer, the bottom silicon oxide is etched to obtain a sensitive film pattern etching mask. Then, the silicon of the pressure-sensitive layer is etched to the silicon oxide self-stop layer by dry etching. Finally, dry etching is used to remove the silicon oxide at the bottom of the pressure-sensitive layer.

[0092] S6: Prepare an isolation base, and anodically bond the isolation base to the reverse side of the pressure-sensitive layer.

[0093] like Fig. 9 As shown, the process of preparing the isolation base includes: preparing a thick glass table and using a grinding wheel to grind and groove it, the groove is in the shape of a cross, and four rectangular bosses are prepared on the glass table.

[0094] S7: etching silicon oxide on the resonance layer through the electrode through-hole of the cap layer, and sputtering metal through the electrode through-hole of the cap layer to form an ohmic contact on the resonance layer, thereby completing the preparation of the metal electrode.

[0095] like Fig. 9 As shown, the silicon oxide on the resonance layer in the electrode through hole of the cap layer is etched, and a metal is evaporated or sputtered on the resonance layer using a hard mask to form an ohmic contact, thereby completing the preparation of the metal electrode.

[0096] After the metal electrode is prepared, a prepared low-temperature drift MEMS resonant pressure sensor sensitive chip is obtained.

[0097] In summary, the present invention aims at the temperature drift caused by the Young's modulus and thermal stress of the MEMS resonant pressure sensor, and the problem of low sensitivity in the existing thermal stress compensation method, and designs and proposes a low-temperature drift resonant pressure sensor sensitive chip based on Si-SiO2 composite resonator and three-film-double resonator structure. Compared with the existing MEMS resonant pressure sensor, the present invention adopts Si-SiO2 composite resonator to realize the compensation of the temperature drift of the Young's modulus of silicon material, which can greatly reduce the sensitivity temperature drift of the sensor. At the same time, the three-film-double resonator structure is designed to separate and place two identical resonators on the maximum displacement area of ​​different sensitive diaphragms, maximizing the use of the deformation of the sensitive film, and greatly improving the output sensitivity of the sensor under the same size conditions. At the same time, the present invention designs an X-shaped torsional piezoresistive structure, which does not require additional production of piezoresistors and corresponding metal wiring, reduces the complexity of chip processing, and reduces the introduction of additional stress and materials. In addition, the present invention uses a silicon cap layer and a resonant layer to bond to form a vacuum cavity, seals the resonator in a vacuum environment, improves the quality factor of the resonator, and bonds an isolation base to reduce assembly stress.

[0098] The above embodiments further illustrate the purpose, technical solutions and advantages of the present invention in detail. It should be understood that the above embodiments are only preferred implementation modes of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made to the present invention within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A low temperature drift MEMS resonant pressure sensor sensitive chip, characterized in that: include: A cap layer, a resonance layer, a pressure-sensing layer and an isolation base are bonded and connected in sequence from top to bottom; The cap layer is provided with an electrode through hole and a vacuum cavity groove, and a getter is sputtered in the vacuum cavity groove; The resonance layer is provided with two Si-SiO2 composite resonators and a plurality of lead plates, each lead plate is provided with a metal electrode; the number of the metal electrodes is equal to the number of the electrode through holes of the cap layer and the metal electrodes are located directly below the electrode through holes; The pressure-sensitive layer has two groups of silicon islands on the front side and three rectangular sensitive films of the same size on the back side; The isolation base is a glass table.

2. A low temperature drift MEMS resonant pressure sensor sensitive chip according to claim 1, characterized in that: The Si-SiO2 composite resonator is formed by growing an oxide layer through thermal oxidation of the resonator. The resonator includes a symmetrical X-shaped torsional piezoresistive structure, a resonant beam, a vibration pickup beam, hollow comb teeth, fixed comb teeth, a connecting beam and a movable anchor point. The middle parts of all the resonant beams, vibration pickup beams and hollow comb teeth are connected by a connecting beam, and the two ends of each resonant beam are respectively connected to the suspended torsion structure on the movable anchor point, and the two ends of each vibration pickup beam are respectively connected to two symmetrical X-shaped torsional piezoresistive structures. The hollow comb teeth cooperate with the fixed comb teeth on both sides of the resonator to form a driving capacitor.

3. A low temperature drift MEMS resonant pressure sensor sensitive chip according to claim 2, characterized in that: Two groups of silicon islands are set in the area where the horizontal displacement of the sensitive membrane is the largest under pressure. The center of one rectangular sensitive membrane is located directly below a Si-SiO2 composite resonator, and the centers of the other two rectangular sensitive membranes are located directly below another Si-SiO2 composite resonator.

4. The low temperature drift MEMS resonant pressure sensor sensitive chip according to claim 1, characterized in that: The lead pads on the resonance layer are divided into a DC bias lead pad, an AC drive lead pad and an output detection lead pad.

5. The low temperature drift MEMS resonant pressure sensor sensitive chip according to claim 1, characterized in that: The glass platform is provided with a groove in a cross shape, so that four rectangular glass protrusions are formed on the glass platform.

6. A method for preparing a low-temperature drift MEMS resonant pressure sensor sensitive chip, characterized in that: include: S1: A clean double-sided polished SOI silicon wafer is used to prepare the silicon island of the pressure-sensitive layer; S2: Prepare a clean double-sided polished SOI silicon wafer as the resonance layer substrate, and bond the silicon island surface of the pressure-sensitive layer to the resonance layer substrate; S3: preparing a Si-SiO2 composite resonator and a lead plate of a resonance layer on a resonance layer substrate to obtain a resonance layer; S4: using a single crystal silicon double-polished wafer to prepare a cap layer, and bonding the cap layer to the resonance layer silicon-silicon low-temperature vacuum bonding; S5: preparing a rectangular sensitive film on the reverse side of the pressure-sensitive layer; S6: preparing an isolation base, and anodically bonding the isolation base to the reverse side of the pressure-sensitive layer; S7: etching silicon oxide on the resonance layer through the electrode through-hole of the cap layer, and sputtering metal through the electrode through-hole of the cap layer to form an ohmic contact on the resonance layer, thereby completing the preparation of the metal electrode.

7. The method for preparing a low temperature drift MEMS resonant pressure sensor sensitive chip according to claim 6, characterized in that: The process of preparing silicon islands includes: S11: prepare a clean double-sided polished SOI silicon wafer; S12: thermally oxidizing and growing silicon oxide on the double-sided polished SOI silicon wafer as an etching mask; S13: photolithographically etching silicon oxide on the surface of the SOI silicon wafer device layer to form a silicon island pattern etching mask; S14: Perform DRIE etching on the device layer to form a silicon island.

8. The method for preparing a low-temperature drift MEMS resonant pressure sensor sensitive chip according to claim 6, characterized in that: The process of preparing Si-SiO2 composite resonator and lead disk includes: S31: using a CMP process to thin the substrate layer of the SOI silicon wafer to 50 μm, and then using KOH or TMAH wet etching to etch the remaining silicon to expose the oxide layer of the SOI silicon wafer; S32: photolithographically etching silicon oxide to obtain a resonance layer device pattern etching mask; S33: DRIE etches the device layer of the SOI silicon wafer to obtain a resonator and a lead disk structure; S34: removing the oxide layer on the surface of the resonance layer by dry etching to complete the preparation of the resonator-silicon island integrated structure; S35: thermally oxidizing and growing an oxide layer on the surface of the resonator to form a Si-SiO2 composite resonator.

9. The method for preparing a low temperature drift MEMS resonant pressure sensor sensitive chip according to claim 6, characterized in that: The process of preparing the capping layer includes: S41: performing laser drilling on the single crystal silicon double polished wafer to obtain an electrode through hole; S42: thermally oxidizing and growing silicon oxide on a single crystal silicon double-polished wafer, and photolithographically etching the silicon oxide to obtain a vacuum cavity groove pattern etching mask; S43: RIE etching of vacuum cavity grooves; S44: Magnetron sputtering of Ti getter in the vacuum chamber groove.

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