Microcrack tunneling gas pressure sensor for near space exploration and manufacturing method thereof

Abstract

The application provides a micro crack tunneling air pressure sensor for near space exploration and a manufacturing method thereof, and belongs to the technical field of near space environment exploration.The application comprises a tunneling micro crack graphene film, a deformation silicon film, a reference cavity and an insulating layer, different tunneling effects are induced according to the interval change of the micro crack under different air pressure conditions, the micro deformation detection capability of the deformation silicon film under different air pressures is improved, the transmission capability of the sensor to ultra-low air pressure is improved to 0.01Pa; meanwhile, the deformation silicon film itself is used as a piezoresistive sensor to detect and supplement the high air pressure section, the resolution capability of the sensor in the high air pressure section is improved, and the full pressure range of the near space is covered.The micro crack tunneling air pressure sensor has the characteristics of a large range, a low detection limit, high measurement precision, strong anti-radiation capability and high overload resistance, and solves the problems of the range, precision and response time of the air pressure detection of the near space rocket.

Description

Technical Field

[0001] This invention belongs to the field of near-space environment detection technology, and particularly relates to a microcrack tunneling pressure sensor for near-space detection and its manufacturing method. Background Technology

[0002] Near space (typically referring to the airspace 20-100 kilometers above the Earth's surface, including the stratosphere, mesosphere, and thermosphere) is a crucial transitional region connecting the troposphere and outer space, and its environmental detection has unique scientific value and application significance. Near space environmental parameters are important boundary conditions affecting the development of tropospheric weather systems. The upper boundary of current numerical weather prediction models is typically around 10-30 kilometers; the lack of near space data with spatiotemporal continuity leads to uncertainty in the model's top boundary conditions, affecting the accuracy of medium- and long-term forecasts. Furthermore, as a core parameter for satellite drag calculations, pressure detection across the entire altitude range of near space can effectively influence satellite orbital decay prediction and collision avoidance.

[0003] Because the near space spans a large area, has a wide range of air pressure, and involves the detection of ultra-low air pressure, the current mainstream method is to use remote sensing to detect the near space environment. In-situ detection is generally limited to a range of less than 30km and cannot achieve continuous and effective detection of air pressure in higher airspaces. Summary of the Invention

[0004] To address the aforementioned shortcomings in the existing technology, this invention provides a microcrack tunneling barometric pressure sensor for near-space exploration and its fabrication method, which solves the problems of large range and extremely low detection limit in in-situ barometric pressure measurement across all elevations in near-space.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a microcrack tunneling pressure sensor for near-space exploration, wherein the microcrack tunneling pressure sensor uses a silicon diaphragm reference cavity as a substrate and includes a graphene layer, an insulating layer, a deformable silicon film, an electrode, a reference cavity substrate, tunneling microcracks in the graphene layer, and a reference cavity. The insulating layer covers the deformable silicon film, and the graphene layer is disposed on the insulating layer. A defect layer induced by a femtosecond laser is disposed in the middle of the graphene layer, and microcracks with tunneling effect are generated under stress. The reference cavity is located between the reference cavity substrate and the deformable silicon film, and the length of the graphene layer is equal to the diameter of the reference cavity. The graphene layer covers a local strip-shaped sensitive area in the center of the silicon film. The electrode is in direct electrical contact with the silicon film. The gas value in the near-space environment is detected by the change of the crack spacing of the tunneling microcracks under different gas pressures.

[0006] Furthermore, the resistance of the graphene layer as a function of air pressure is expressed by the following formula:

[0007] in, Indicates the resistance of the graphene layer. This indicates the sheet resistance of the graphene layer. Indicates the width of the graphene layer. Indicates the length of the graphene layer. Indicates the anode contact resistance. Indicates the cathode contact resistance. This indicates the total number of microcracks. This indicates the microcrack count. Indicates the first The initial tunneling resistance of a microcrack. Indicates the reference coefficient. Indicates the initial gap of the microcrack. This represents the magnification factor of a single crack opening. This represents the strain on the local diaphragm surface in response to air pressure. This indicates the pressure difference across the silicon diaphragm.

[0008] Furthermore, the sensitivity formula for the graphene layer is as follows:

[0009] in, This indicates the sensitivity to tunneling through microcracked graphene layers. Indicates the reference coefficient. This represents the equivalent average microcrack opening magnification factor. This indicates the strain-pressure sensitivity of the silicon diaphragm.

[0010] Furthermore, the formula for the response of the resistance of the deformed silicon film to air pressure is as follows:

[0011]

[0012]

[0013] in, This represents the resistance of the deformed silicon film (3). This represents the initial resistance when there is no pressure difference. This represents the longitudinal piezoresistive coefficient. This represents the lateral piezoresistive coefficient. This represents the stress along the direction of the current. This represents the stress perpendicular to the direction of the current. This indicates the pressure difference across the silicon diaphragm. Indicates the thickness of the silicon film. This represents the Poisson's ratio of silicon. This represents the radius of the circular silicon film. This indicates the radius of the distance from the center of the membrane.

[0014] Furthermore, the sensitivity formula for the deformed silicon film is as follows:

[0015] in, The sensitivity of the deformable silicon film (3) is indicated. This represents the longitudinal piezoresistive coefficient. This represents the lateral piezoresistive coefficient. This represents the stress along the direction of the current. This represents the stress perpendicular to the direction of the current. This indicates the pressure difference across the silicon diaphragm.

[0016] This invention also provides a method for fabricating a microcrack tunneling barometric pressure sensor for near-space exploration, comprising the following steps: Silicon-on-insulator wafers were selected as the device substrate and were sequentially cleaned and dried with acetone, isopropanol, and deionized water to remove surface organic matter and particulate contamination. Photoresist is spin-coated on the front side of the SOI silicon wafer, and silicon piezoresistive strips, electrode leads or metal contact areas are defined by photolithography, while the insulating layer in non-silicon piezoresistive strip areas is etched. Deposit metal electrodes to form the anode and cathode of the silicon piezoresistive strip; A graphene film is deposited on the front side of a silicon wafer, covering a local strip-shaped sensitive area in the center of the silicon wafer and contacting the anode and cathode electrodes. The graphene layer is defined as a strip-shaped conductive bridge structure by photolithography and oxygen plasma etching, which restricts the main current path and allows the microcrack tunneling channel to dominate the resistance change. Among them, a defect layer induced by femtosecond laser is set in the middle of the graphene layer, and microcracks with tunneling effect are generated under stress. Multiple parallel fully fractured microcracks are fabricated in the strip-shaped graphene sensitive area of ​​the graphene layer using femtosecond lasers, with the direction of the microcracks perpendicular to the direction of the main current, forming a graphene-air-graphene tunneling structure. Photoresist is spin-coated on the back of the SOI silicon wafer. The circular film release window is defined by photolithography with the back side aligned, and the radius and position of the pressure-sensitive film are determined. The silicon substrate is etched from the back of the SOI silicon wafer, and the etching stops at the SOI buried oxide layer to form a circular thin silicon deformation film structure with fixed support on all sides. Using another SOI silicon wafer as a packaging base, the chip is bonded to the packaging base to form a reference cavity (7) structure.

[0017] Furthermore, the length of the graphene layer is equal to the diameter of the reference cavity.

[0018] The beneficial effects of this invention are: This invention provides a microcrack tunneling barometric pressure sensor for near-space exploration. The main sensing structure is graphene microcracks with tunneling effect. Different tunneling effects are induced by the change in the spacing of the microcracks under different pressure conditions, which improves the ability of deformable silicon films to detect microdeformation under different pressures and improves the sensor's ability to sense ultra-low pressures down to 0.01 Pa.

[0019] The microcrack tunneling pressure sensor provided by this invention uses a deformable silicon film that supports the graphene layer. This film itself has a piezoresistive effect and works in synergy with the graphene tunneling microcrack sensitive structure to detect the microcracks. This serves as a supplement to the detection of high-pressure sections, improving the sensor's resolution in high-pressure sections and covering the entire pressure range of near space.

[0020] This invention primarily employs the tunneling microcrack detection mechanism, supplemented by a piezoresistive sensing mechanism, resulting in high response speed and high accuracy. Structurally, it uses a silicon diaphragm as a substrate, exhibiting strong overload resistance, effectively resisting the overload of sounding rocket launches, reducing the impact of environmental interference, and meeting the sensing requirements of high-speed descent of sounding rockets.

[0021] In this invention, the tunneling microcracks are generated by femtosecond laser induction, the microcrack size is controllable, and the measurement repeatability is high. Attached Figure Description

[0022] Figure 1 A schematic diagram of the microcrack tunneling pressure sensor of the present invention is shown; Figure 2 A cross-sectional structural schematic diagram of the microcrack tunneling pressure sensor of the present invention is shown; Figure 3 A schematic diagram of the reference cavity of the microcrack tunneling pressure sensor in this invention is shown; Figure 4 The method for fabricating the microcrack tunneling pressure sensor of the present invention is shown; Wherein, 1-graphene layer; 2-insulating layer; 3-deformed silicon film; 4-electrode; 5-reference cavity substrate; 6-microcrack; 7-reference cavity. Detailed Implementation

[0023] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0024] Example 1 like Figure 1 , Figure 2 and Figure 3As shown, this invention provides a microcrack tunneling pressure sensor for near-space exploration. The microcrack tunneling pressure sensor uses a silicon diaphragm reference cavity (the reference cavity is formed by bonding an upper silicon wafer and a lower silicon wafer; when the upper silicon wafer is etched to deform the diaphragm, the space below the diaphragm forms a cavity after bonding another silicon wafer; the pressure in the cavity is equal to the pressure during the bonding process, and this pressure is the reference pressure) as a substrate. It includes a graphene layer 1, an insulating layer 2, a deformable silicon film 3, an electrode 4, a reference cavity substrate 5, tunneling microcracks 6 in the graphene layer 1, and a reference cavity 7; the insulating layer 2 covers... A graphene layer 1 is disposed on an insulating layer 2 on a deformable silicon film 3. A defect layer induced by a femtosecond laser is disposed in the middle of the graphene layer 1, and microcracks 6 with tunneling effect are generated under stress. A reference cavity 7 is located between the reference cavity substrate 5 and the deformable silicon film 3. The length of the graphene layer 1 is equal to the diameter of the reference cavity 7. The graphene layer 1 covers a local strip-shaped sensitive area in the center of the silicon film. The electrode 4 is in direct electrical contact with the silicon film. The gas pressure in the near-space environment is detected by the change in the crack spacing of the tunneling microcracks 6 under different gas pressures. The gas pressure in the reference cavity 7 is determined during bonding, and the optimal sensitivity gas pressure measurement range of the tunneling response of the microcracks 6 is adjusted accordingly.

[0025] The resistance of graphene layer 1 as a function of air pressure is expressed by the following formula:

[0026] in, This represents the resistance of graphene layer 1. This indicates the sheet resistance of the graphene layer. This indicates the width of graphene layer 1. This indicates the length of graphene layer 1. Indicates the anode contact resistance. Indicates the cathode contact resistance. This indicates the total number of microcracks. This indicates the microcrack count. Indicates the first The initial tunneling resistance of a microcrack. Indicates the reference coefficient. Indicates the initial gap of the microcrack. This represents the magnification factor of a single crack opening. This represents the strain on the local diaphragm surface in response to air pressure. This indicates the pressure difference across the silicon diaphragm.

[0027] Among them, the Initial tunneling resistance of a microcrack The formula is as follows: R 00,i =1 / (G 0,i A i ) Among them, G 0,i Indicates the first The initial conductivity of the crack, A i This indicates the effective tunnel area.

[0028]

[0029] in, Indicates electron mass, Indicates the effective barrier height. Represents Planck's constant In this embodiment, the sensitivity formula for graphene layer 1 is as follows:

[0030] in, This indicates the sensitivity to tunneling through microcracked graphene layers. Indicates the reference coefficient. This represents the equivalent average microcrack opening magnification factor. This indicates the strain-pressure sensitivity of the silicon diaphragm.

[0031] In this embodiment, the response formula of the resistance of the deformed silicon film 3 with air pressure is as follows:

[0032]

[0033]

[0034] in, This represents the resistance of the deformed silicon film 3. This represents the initial resistance when there is no pressure difference. This represents the longitudinal piezoresistive coefficient. This represents the lateral piezoresistive coefficient. This represents the stress along the direction of the current. This represents the stress perpendicular to the direction of the current. This indicates the pressure difference across the silicon diaphragm. Indicates the thickness of the silicon film. The Poisson's ratio for silicon is typically approximated as 0.275. This represents the radius of the circular silicon film. This indicates the radius of the distance from the center of the membrane.

[0035] In this embodiment, the sensitivity formula for the deformed silicon film 3 is as follows:

[0036] in, This indicates the sensitivity of the deformable silicon film 3. This represents the longitudinal piezoresistive coefficient. This represents the lateral piezoresistive coefficient. This represents the stress along the direction of the current. This represents the stress perpendicular to the direction of the current. This indicates the pressure difference across the silicon diaphragm.

[0037] In this embodiment, the microcrack tunneling pressure sensor detects the air pressure in the near-space environment by measuring the change in the crack spacing of the microcracks 6 exhibiting a tunneling effect under different air pressures. The silicon diaphragm of the microcrack tunneling pressure sensor itself has a piezoresistive effect, enabling detection in higher-pressure environments and compensating for the decrease in sensitivity of the microcrack pressure sensor under higher pressure conditions. This works in conjunction with the microcrack tunneling graphene film to detect the air pressure in the near-space environment. The tunneling microcracks 6 in the graphene layer of the microcrack tunneling pressure sensor are first induced to generate defects through femtosecond laser, and then, under prestress, nanoscale microcracks are produced. The maximum sensitivity detection range of the pressure sensor can be adjusted by regulating the air pressure value within the reference cavity 7. The length of the graphene layer 1 is equal to the diameter of the reference cavity 7.

[0038] Example 2 like Figure 4 As shown, this invention provides a method for fabricating a microcrack tunneling barometric pressure sensor for near-space exploration, the implementation of which is as follows: Silicon-on-insulator (SOI) wafers were selected as the device substrate and were sequentially cleaned and dried with acetone, isopropanol, and deionized water to remove surface organic matter and particulate contamination. Photoresist is spin-coated on the front side of the SOI silicon wafer. Photolithography is used to define the silicon piezoresistive strip, electrode leads, or metal contact areas. The insulating layer 2 in the non-silicon piezoresistive strip areas is etched. The silicon-on-insulator (SOI) wafer has an insulating layer embedded in the middle of a regular pure silicon wafer at the factory. The thickness of the silicon above the insulating layer 2 can be customized as needed. When etching the deformable silicon film, the silicon wafer below the insulating layer 2 is etched. The cavity formed after the material is removed by etching is the reference cavity. However, the reference cavity is not closed at this time, so another silicon wafer needs to be bonded below to close the cavity. The silicon layer above the insulating layer 2 is subsequently used as the material layer for the silicon piezoresistive strip. Metal electrodes 4 are deposited using vapor deposition or sputtering processes, and the anode and cathode of the silicon piezoresistive strip are formed by lift-off photolithography. A graphene film is deposited on the front side of a silicon wafer using CVD or a pre-fabricated graphene film transfer method, so that the graphene layer 1 covers the local strip-shaped sensitive area in the center of the silicon wafer and contacts the anode and cathode electrodes. The graphene layer 1 is defined as a strip-shaped conductive bridge structure by photolithography and oxygen plasma etching, which restricts the main current path and makes the tunneling channel of the microcrack 6 dominate the resistance change. Among them, a defect layer induced by femtosecond laser is set in the middle of the graphene layer 1, and microcracks 6 with tunneling effect are generated under stress. Multiple parallel fully fractured microcracks 6 are processed in the strip-shaped graphene sensitive area of ​​graphene layer 1 using femtosecond laser, so that the direction of microcracks 6 is perpendicular to the direction of the main current, forming a graphene-air-graphene tunneling structure. Photoresist is spin-coated on the back of the SOI silicon wafer. The circular film release window is defined by back-side alignment photolithography. The radius and position of the pressure-sensitive film are determined. The silicon substrate is etched from the back side using DRIE deep silicon etching, and the etching stops at the SOI buried oxide layer to form a circular thin silicon deformation film structure with fixed support on all sides. Using another SOI silicon wafer as a packaging substrate, the chip is bonded to the packaging substrate to form a reference cavity 7 structure; the length of the graphene layer 1 is equal to the diameter of the reference cavity 7.

[0039] The working principle of a pressure sensor based primarily on the microcrack tunneling mechanism and supplemented by silicon piezoresistive resistance is described below: When external pressure is applied to the silicon diaphragm, the diaphragm deforms, resulting in axial tensile deformation. This causes a change in the gap size of microcrack 6, leading to a change in tunneling resistance. When the pressure is too high, causing microcrack 6 to become too large and exceed the optimal sensitivity range of the tunneling resistance, the piezoresistive effect of the silicon diaphragm itself can still be used as a pressure measurement value. This value is cross-validated with the pressure value measured by the microcrack 6 tunneling through the graphene, compensating for the decrease in sensitivity of the microcrack graphene under excessive atmospheric pressure conditions.

[0040] The above detailed description further illustrates the purpose, technical solution, and beneficial effects of the invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A microcrack tunneling barometric pressure sensor for near-space exploration, characterized in that, The microcrack tunneling barometric sensor is based on a silicon diaphragm reference cavity and includes a graphene layer (1), an insulating layer (2), a deformable silicon film (3), an electrode (4), a reference cavity substrate (5), tunneling microcracks (6) in the graphene layer (1), and a reference cavity (7). The insulating layer (2) covers the deformable silicon film (3), the graphene layer (1) is disposed on the insulating layer (2), a defect layer generated by femtosecond laser is disposed in the middle of the graphene layer (1), and microcracks (6) with tunneling effect are generated under stress. The reference cavity (7) is located between the reference cavity substrate (5) and the deformable silicon film (3). The length of the graphene layer (1) is equal to the diameter of the reference cavity (7). The graphene layer (1) covers the local strip-shaped sensitive area in the center of the silicon film. The electrode (4) is in direct electrical contact with the silicon film. The gas value in the near space environment is detected by the change of the crack spacing of the microcracks (6) with tunneling effect under different gas pressures.

2. The microcrack tunneling barometric pressure sensor for near-space exploration according to claim 1, characterized in that, The resistance of the graphene layer (1) as a function of air pressure is expressed by the following formula: in, This represents the resistance of the graphene layer (1). Indicates the sheet resistance of graphene layer (1), Indicates the width of graphene layer (1), Indicates the length of the graphene layer (1), Indicates the anode contact resistance. Indicates the cathode contact resistance. This indicates the total number of microcracks. This indicates the microcrack count. Indicates the first The initial tunneling resistance of a microcrack. Indicates the reference coefficient. Indicates the initial gap of the microcrack. This represents the magnification factor of a single crack opening. This represents the strain on the local diaphragm surface in response to air pressure. This indicates the pressure difference across the silicon diaphragm.

3. The microcrack tunneling barometric pressure sensor for near-space exploration according to claim 1, characterized in that, The sensitivity formula for the graphene layer (1) is as follows: in, This indicates the sensitivity to tunneling through microcracked graphene layers. Indicates the reference coefficient. This represents the equivalent average microcrack opening magnification factor. This indicates the strain-pressure sensitivity of the silicon diaphragm.

4. The microcrack tunneling barometric pressure sensor for near-space exploration according to claim 1, characterized in that, The resistance of the deformed silicon film (3) as a function of air pressure is expressed by the following formula: in, This represents the resistance of the deformed silicon film (3). This represents the initial resistance when there is no pressure difference. This represents the longitudinal piezoresistive coefficient. This represents the lateral piezoresistive coefficient. This represents the stress along the direction of the current. This represents the stress perpendicular to the direction of the current. This indicates the pressure difference across the silicon diaphragm. Indicates the thickness of the silicon film. This represents the Poisson's ratio of silicon. This represents the radius of the circular silicon film. This indicates the radius of the distance from the center of the membrane.

5. The microcrack tunneling barometric pressure sensor for near-space exploration according to claim 1, characterized in that, The sensitivity formula for the deformed silicon film (3) is as follows: in, The sensitivity of the deformable silicon film (3) is indicated. This represents the longitudinal piezoresistive coefficient. This represents the lateral piezoresistive coefficient. This represents the stress along the direction of the current. This represents the stress perpendicular to the direction of the current. This indicates the pressure difference across the silicon diaphragm.

6. A method for fabricating a microcrack tunneling barometric pressure sensor for near-space exploration, characterized in that, Includes the following steps: Silicon-on-insulator wafers were selected as the device substrate and were sequentially cleaned and dried with acetone, isopropanol, and deionized water to remove surface organic matter and particulate contamination. Photoresist is spin-coated on the front side of the SOI silicon wafer, and silicon piezoresistive strips, electrode leads or metal contact areas are defined by photolithography. The insulating layer (2) in the non-silicon piezoresistive strip area is etched. Deposit metal electrodes (4) and form the anode and cathode of the silicon piezoresistive strip; A graphene film is deposited on the front side of a silicon film, so that the graphene layer (1) covers the local strip-shaped sensitive area in the center of the silicon film and contacts the anode and cathode electrodes. The graphene layer (1) is defined as a strip-shaped conductive bridge structure by photolithography and oxygen plasma etching, which restricts the main current path and makes the tunneling channel of the microcrack (6) dominate the resistance change. Among them, a defect layer induced by femtosecond laser is set in the middle of the graphene layer (1), and microcracks (6) with tunneling effect are generated under stress. Multiple parallel full-fracture microcracks (6) are processed in the strip-shaped graphene sensitive area of ​​the graphene layer (1) using a femtosecond laser, so that the direction of the microcracks (6) is perpendicular to the direction of the main current, forming a graphene-air-graphene tunneling structure. Photoresist is spin-coated on the back of the SOI silicon wafer. The circular film release window is defined by photolithography with the back side aligned, and the radius and position of the pressure-sensitive film are determined. The silicon substrate is etched from the back of the SOI silicon wafer, and the etching stops at the SOI buried oxide layer to form a circular thin silicon deformation film structure with fixed support on all sides. Using another SOI silicon wafer as a packaging base, the chip is bonded to the packaging base to form a reference cavity (7) structure.

7. The method for fabricating a microcrack tunneling barometric pressure sensor for near-space exploration according to claim 6, characterized in that, The length of the graphene layer (1) is equal to the diameter of the reference cavity (7).

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