Curved thin film pressure sensor based on micromachining and manufacturing method thereof

Abstract

The present invention relates to the field of micromachining technology, and specifically to a curved thin film pressure sensor based on micromachining and a manufacturing method thereof, comprising a silicon base, a sensitive thin film structure covering the silicon base, and a glass cover bonded to the sensitive thin film structure, wherein the sensitive thin film structure has an aspheric profile, a thickness gradient distribution along the radial direction, and a piezoresistive sensitive element and a temperature compensation element integrated on the surface; by adopting a parabolic or hyperbolic aspheric profile, the radial gradient distribution of stress is guided, edge concentration is reduced, and stress uniformity and sensitivity are improved; the gradient thickness of the sensitive film is thin in the center and thick at the edge, combined with a composite layer, enhances overload resistance; a double-layer sacrificial layer stepped etching process accurately controls the surface accuracy and improves the molding quality; an integrated piezoresistive bridge circuit, a thermistor and a platinum shielding layer are combined with vacuum packaging to offset thermal drift, suppress electromagnetic interference, stabilize the vacuum degree, and comprehensively improve environmental adaptability and stability.

Description

Technical Field

[0001] The present invention relates to the technical field of micromachining, and in particular to a curved-surface thin-film pressure sensor based on micromachining and a manufacturing method thereof. Background Art

[0002] Existing micromechanical pressure sensors generally adopt a planar thin film structure. The core technology path is to generate an electrical signal by driving the piezoresistive element through the force deformation of the planar thin film. However, the stress concentration at the edge of the planar thin film is significant under the action of pressure, resulting in limited sensitivity. In addition, the planar structure is prone to failure due to edge cracking under high pressure. Traditional bulk silicon processing technology makes it difficult to accurately control the film thickness. The planar structure cannot adapt to wide-range pressure measurement, which limits its application in different scenarios.

[0003] In view of this, we propose a curved thin film pressure sensor based on micromachining and its manufacturing method. Summary of the Invention

[0004] In response to the above-mentioned shortcomings of the prior art, the present invention provides a curved thin film pressure sensor based on micromachining and a manufacturing method thereof, which can effectively solve the problems of the prior art micromechanical pressure sensor adopting a planar thin film structure and traditional bulk silicon processing technology, resulting in edge stress concentration leading to limited sensitivity, weak overload resistance, low film thickness control accuracy, and limited application scenarios.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0006] The present invention provides a curved surface thin film pressure sensor based on micromachining, comprising a silicon base, a sensitive thin film structure covering the silicon base, and a glass cover bonded to the sensitive thin film structure;

[0007] The sensitive film structure has an aspherical profile, with a gradient thickness distribution along the radial direction, and a piezoresistive sensitive element and a temperature compensation element integrated on the surface;

[0008] The sensitive film structure includes an anti-interference shielding layer arranged under the glass cover and a buried oxide layer covering the silicon base.

[0009] Furthermore, the sensitive film structure is a composite structure of a silicon nitride layer and a polysilicon layer, wherein the silicon nitride layer is located above the polysilicon layer, accounting for 60%-75% of the thickness, and the polysilicon layer accounts for 25%-40% of the thickness;

[0010] The aspheric surface profile is a parabola or a hyperbola, and the radius of curvature is 1-5 mm.

[0011] Furthermore, a P-type piezoresistive bridge circuit is integrated in the polysilicon layer, and the piezoresistive strips are arranged along the principal stress direction of the curved surface, and the angle between the principal stress direction and the radial direction of the film is ≤10°;

[0012] An N-type thermistor is integrated in the edge area of ​​the polysilicon layer and connected in series with a P-type piezoresistive bridge to form a temperature compensation network.

[0013] Furthermore, the anti-interference shielding layer is a platinum or gold layer with a thickness of 30-80 nm, covering the upper surface and side surfaces of the silicon nitride layer, and grounded through the metallized area at the edge of the silicon base.

[0014] Furthermore, the thickness of the central area of ​​the sensitive film structure is 5-10µm, the thickness of the edge area is 15-25µm, and the thickness gradient change rate is the film radius, with a value range of 2-5µm / mm; the glass cover and the silicon base are sealed by an anodic bonding layer, and the pressure in the packaging cavity is controlled at 10 -4 -10 -3 Pa level, and a porous silicon reference air cavity is embedded in the glass cover.

[0015] Furthermore, the buried oxide layer has a thickness of 0.5-1.5µm. After being released through a back-side etching process, the sensitive film structure and the silicon base form a cantilever structure that can freely respond to pressure loads.

[0016] A method for manufacturing a curved thin film pressure sensor, comprising:

[0017] S1. Wafer preparation: Provide <100> Crystalline SOI wafer, whose structure from bottom to top includes silicon base, buried oxide layer and top silicon (thickness 15-25µm);

[0018] S2. Ion implantation: P-type piezoresistive bridge and N-type thermistor are formed in the top silicon by ion implantation, with an implantation dose of 5×10 15 cm -2 and 1×10 15 cm -2 ;

[0019] S3. Deposit and pattern a sacrificial layer: Deposit a double sacrificial layer of phosphosilicate glass and silicon dioxide on the top silicon surface with a thickness ratio of (3-5):(2-3), and define the curved surface area by photolithography.

[0020] S4. Wet etching to form a curved surface: Using a mixed solution of HF:HNO3 = 1:3-1:5, step etching is performed to remove the sacrificial layer in the unprotected area to form a parabolic or hyperbolic profile;

[0021] S5. Depositing structural layers: Using the LPCVD process, silicon nitride and polysilicon layers are deposited on the contours of the sacrificial layer, covering the entire curved surface and forming a composite film.

[0022] S6. Backside etching release film: Etching from the backside of the silicon base to the buried oxide layer, removing the buried oxide layer with HF solution, and separating the sensitive film structure from the silicon base;

[0023] S7. Vacuum packaging: Bond a glass cover plate on top of the sensitive film structure. Treat the bonding surface with oxygen plasma before bonding. The pressure in the packaging cavity is controlled at 10 -4 -10 -3 Pa, and a built-in porous silicon reference air cavity.

[0024] Furthermore, in step S3, the thickness ratio of the sacrificial layer is 4:3, the etching solution uses HF:HNO3=1:4, and the surface roughness Ra formed after etching is less than 5nm.

[0025] Furthermore, in step S5, the deposition temperature of the silicon nitride layer is 700-900° C., and that of the polysilicon layer is 550-650° C., and the step coverage uniformity of the composite layer and the sacrificial layer is ≥95%.

[0026] Furthermore, in step S7, the width of the bonding area between the glass cover plate and the silicon base is 0.5-1 mm, the bonding temperature is 400° C., the voltage is 800 V, and the porous silicon reference air cavity is formed by high temperature annealing with a pore diameter of 20-50 nm.

[0027] Compared with the known public technologies, the technical solution provided by the present invention has the following beneficial effects:

[0028] The present invention adopts a parabolic or hyperbolic aspheric profile, which distributes stress along a radial gradient under pressure. Compared with traditional planar structures, the stress concentration area shifts from the edge to the center, reducing the edge stress concentration problem and improving the uniformity of the overall stress distribution of the film, thereby improving the sensor's response sensitivity to pressure changes.

[0029] The sensitive film adopts a gradient thickness, with a thin center and thick edges. Combined with the composite layer, the center area has strong flexible deformation ability to sense pressure, while the edge area has high rigidity to withstand overload. This forms a "flexible sensing + rigid support" synergistic mechanism, significantly improving the sensor's overload resistance and structural reliability.

[0030] During the manufacturing process, a double sacrificial layer of phosphosilicate glass and silicon dioxide is used, and a smooth curved surface profile is formed through step-by-step wet etching. The film surface accuracy and roughness are precisely controlled, avoiding the step stress concentration in traditional processes, and improving film forming quality and batch consistency.

[0031] A polysilicon piezoresistive bridge, thermistor and platinum shielding layer are integrated on the surface of the thin film, and vacuum packaging is achieved by combining the plasma-activated anodic bonding process. Thermal drift is offset by a temperature compensation network, and electromagnetic interference is suppressed by a metal shielding layer. At the same time, the vacuum degree in the package is stabilized by a porous silicon reference air cavity, comprehensively improving the environmental adaptability and long-term working stability of the sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive effort.

[0033] Figure 1 This is a schematic diagram of the partial disassembly structure of the glass cover plate and the silicon base of the present invention;

[0034] Figure 2 It is a schematic diagram of the local structure of the sensitive film structure plane of the present invention;

[0035] Figure 3 It is a schematic diagram of the partial planar structure of the silicon nitride layer and the anti-interference shielding layer of the present invention;

[0036] Figure 4 It is a schematic diagram of the manufacturing process of the present invention.

[0037] The numbers in the figure represent: 1, glass cover;

[0038] 2. Silicon base;

[0039] 3. Sensitive thin film structure; 301. Silicon nitride layer;

[0040] 302, polysilicon layer; 3021, P-type piezoresistive bridge circuit; 3022, N-type thermistor;

[0041] 303, buried oxide layer; 304, anti-interference shielding layer. DETAILED DESCRIPTION

[0042] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings 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 making any creative efforts shall fall within the scope of protection of the present invention.

[0043] The present invention will be further described below with reference to the embodiments.

[0044] like Figure 1 、 Figure 2 、 Figure 3 and Figure 4As shown, a curved thin film pressure sensor based on micromachining includes a silicon base 2, a sensitive thin film structure 3 covering the silicon base 2, and a glass cover 1 bonded to the sensitive thin film structure 3. The sensitive thin film structure 3 has an aspherical profile and a thickness gradient distribution along the radial direction. A piezoresistive sensitive element and a temperature compensation element are integrated on the surface. The sensitive thin film structure 3 includes an anti-interference shielding layer 304 provided below the glass cover 1 and a buried oxide layer 303 covering the silicon base 2.

[0045] It should be noted that when the parabolic or hyperbolic profile (radius of curvature 1-5 mm) of the sensitive film structure 3 is subjected to a pressure load, the stress diffuses toward the center of the film. Compared with traditional planar structures, the curved surface guides the stress path through the curvature, reducing stress concentration at the edges. For example, according to the parabolic equation z=4fx+y (f is the focal length), finite element simulation optimization can be used to shift the stress concentration area from the edge to the center.

[0046] The film has a center thickness of 5-10µm and an edge thickness of 15-25µm, forming a "central flexible deformation + edge rigid support" structure. When pressure is applied, the central thin layer produces a larger deformation, while the edge thick layer limits excessive deformation.

[0047] The piezoresistive sensing element and temperature compensation element are integrated on the surface of the sensitive film structure 3 to directly sense the film deformation and ambient temperature;

[0048] Specifically, the sensitive film structure 3 is a composite structure of a silicon nitride layer 301 and a polysilicon layer 302, wherein the silicon nitride layer 301 is located above the polysilicon layer 302, with a thickness of 60%-75%, and the polysilicon layer 302 has a thickness of 25%-40%. The aspheric profile is a parabola or a hyperboloid with a curvature radius of 1-5 mm. A P-type piezoresistive bridge 3021 is integrated in the polysilicon layer 302, and the piezoresistive strips are arranged along the principal stress direction of the curved surface, with an angle of ≤10° between the principal stress direction and the radial direction of the film. An N-type thermistor is integrated in the edge region of the polysilicon layer 302. 3022, connected in series with the P-type piezoresistive bridge 3021 to form a temperature compensation network. The anti-interference shielding layer 304 is a 30-80nm thick platinum or gold layer covering the upper surface and side surfaces of the silicon nitride layer 301 and grounded through the metallized area at the edge of the silicon base 2. The thickness of the central area of ​​the sensitive thin film structure 3 is 5-10µm, and the thickness of the edge area is 15-25µm. The thickness gradient change rate is the film radius, and the value range is 2-5µm / mm; the glass cover 1 and the silicon base 2 are sealed by an anodic bonding layer, and the pressure in the packaging cavity is controlled at 10 -4 -10 -3 Pa level, and a porous silicon reference air cavity is embedded in the glass cover 1, and the thickness of the buried oxide layer 303 is 0.5-1.5µm. After being released through the back etching process, the sensitive film structure 3 and the silicon base 2 form a cantilever structure, which can freely respond to the pressure load.

[0049] It should be noted that according to elastic mechanics, the film stress σ∝h1 (h is the thickness). The stress in the thin center area (small h) is large, which is suitable for arranging the P-type piezoresistive bridge 3021 to maximize sensitivity; the stress in the thick edge area (large h) is small, which mainly bears the structural strength. For example, for a film with a center thickness of 8µm and an edge thickness of 20µm, the edge stress is only 16% of that in the center, effectively avoiding edge cracking. The gradient change rate (edge ​​thickness - center thickness) / radius = 2-5µm / mm, ensuring that the stiffness of the film at different radii gradually changes, suppressing high-order vibration modes and improving the consistency of dynamic response. The P-type piezoresistive strips in the polysilicon layer 302 (implantation dose 5×10 15 cm -2 ) resistivity changes under stress, and four piezoresistive strips form a Wheatstone bridge to convert resistance changes into voltage output. The main stress direction of the curved film is approximately radial (the angle with the radial direction is ≤10°). The piezoresistive strips are arranged in this direction to maximize the stress-resistance coupling efficiency. If the angle exceeds 10°, the projection of the stress component on the axial direction of the piezoresistive strip decreases, and the sensitivity decreases. The piezoresistive coefficient and elastic modulus of silicon are temperature-dependent, which will cause the bridge zero point drift and sensitivity drift. After the N-type thermistor 3022 is connected in series with the P-type piezoresistive bridge 3021, its resistance temperature coefficient matches the piezoresistive strip. For example, when the temperature rises, the resistance of the N-type thermistor 3022 increases, and the change in the voltage divider ratio offsets the increase in the resistance of the piezoresistive strip caused by temperature, thereby achieving temperature drift compensation. The N-type thermistor 3022 is arranged in a low stress area at the edge of the film to avoid stress interference with its pure temperature response and ensure compensation accuracy. The anti-interference shielding layer 304 serves as Metal conductors can reflect and absorb external electromagnetic radiation. According to the skin effect, the penetration depth of high-frequency electromagnetic waves in metal is δ=πfμσ1 (f is frequency, μ is magnetic permeability, and σ is electrical conductivity). A thickness of 30-80nm can cover the skin depth of frequencies above 100MHz, effectively suppressing electromagnetic interference and improving the signal-to-noise ratio from 65dB to 85dB. The anti-interference shielding layer 304 is grounded through the metallized area on the edge of the silicon base 2, forming a low-impedance loop to ensure rapid discharge of induced charges and prevent static electricity accumulation from affecting the stability of the piezoresistive signal. The silicon nitride layer 301 is located on the upper layer, providing high hardness and corrosion resistance; the polycrystalline silicon layer 302 is located on the lower layer, supporting the piezoresistive element. The thermal expansion coefficients of the two are similar, and the interface stress is small, which avoids delamination and cracking under thermal cycling. When the silicon nitride accounts for 60%-75%, the composite modulus is 200-280GPa, taking into account rigidity, ensuring controllable deformation, and flexibility, thereby improving sensitivity.

[0050] A method for manufacturing a curved thin film pressure sensor, comprising:

[0051] S1. Wafer preparation: Provide <100> The structure of the crystal-oriented SOI wafer from bottom to top includes a silicon base 2, a buried oxide layer 303 and a top silicon layer (thickness 15-25µm);

[0052] S2. Ion implantation: P-type piezoresistive bridge 3021 and N-type thermistor 3022 are formed in the top silicon layer by ion implantation. The implantation dose is 5×10 15 cm -2 and 1×10 16 cm -2 ;

[0053] S3. Deposit and pattern a sacrificial layer: Deposit a double sacrificial layer of phosphosilicate glass and silicon dioxide on the top silicon surface with a thickness ratio of (3-5):(2-3), and define the curved surface area by photolithography.

[0054] S4. Wet etching to form a curved surface: Using a mixed solution of HF:HNO3 = 1:3-1:5, step etching is performed to remove the sacrificial layer in the unprotected area to form a parabolic or hyperbolic profile;

[0055] S5. Deposition of structural layer: A silicon nitride layer 301 and a polysilicon layer 302 are deposited on the sacrificial layer profile by an LPCVD process to cover the entire curved surface and form a composite film;

[0056] S6 backside etching release film: etching from the back of the silicon base 2 to the buried oxide layer 303, using HF solution to remove the buried oxide layer 303, the sensitive film structure 3 and the silicon base 2 are separated;

[0057] S7. Vacuum packaging: Bond the glass cover plate 1 on top of the sensitive film structure 3. Before bonding, treat the bonding surface with oxygen plasma. The pressure in the packaging cavity is controlled at 10 -4 -10 -3 Pa, and a built-in porous silicon reference air cavity.

[0058] Furthermore, in step S3, the sacrificial layer thickness ratio is 4:3, the etching solution uses HF:HNO3=1:4, the surface roughness Ra formed after etching is <5nm, the deposition temperature of the silicon nitride layer 301 in step S5 is 700-900℃, the polysilicon layer 302 is 550-650℃, the step coverage uniformity of the composite layer and the sacrificial layer is ≥95%, and in step S7, the bonding area width of the glass cover 1 and the silicon base 2 is 0.5-1mm, the bonding temperature is 400℃, the voltage is 800V, and the porous silicon reference air cavity is formed by high-temperature annealing, with a pore size of 20-50nm.

[0059] It should be noted that the silicon base 2 provides mechanical support, and the buried oxide layer 303 serves as an insulating layer. After being released by back etching, the sensitive thin film structure 3 is separated from the silicon base 2 to form a cantilever beam structure. P-type impurities (such as boron) are injected into the top silicon and polysilicon layers 302 to form a P-type piezoresistive bridge 3021, and N-type impurities (such as phosphorus) are injected to form an N-type thermistor 3022. The temperature coefficient of resistance is regulated by different doping concentrations to achieve temperature compensation network matching. The deposited phosphosilicate glass (bottom layer, 5µm thick) has a fast etching rate and is used to quickly form a curved surface profile; the silicon dioxide has a slow etching rate and is used to refine the surface roughness. The stepped etching ensures the surface accuracy of the sensitive thin film structure 3 and avoids the step stress concentration of the traditional single sacrificial layer process. The silicon nitride layer 301 and the polysilicon layer 3 02 The sacrificial layer surface is conformally covered by low-pressure chemical vapor deposition, with a thickness uniformity of ≤±0.5%, ensuring that the mechanical properties of the film are consistent throughout. The silicon nitride layer 301 and the polysilicon layer 302 are conformally covered by low-pressure chemical vapor deposition, with a thickness uniformity of ≤±0.5%, ensuring that the mechanical properties of the film are consistent throughout. DRIE deep etching is performed from the back of the silicon base 2, penetrating the silicon base to the buried oxide layer 303. The buried oxide layer 303 is then dissolved with HF solution to separate the sensitive film structure 3 from the silicon base 2. The structure is connected to the base only through the edge, forming a freely deformable cantilever structure. The bonding surface of the glass cover 1 and the silicon base 2 is treated with oxygen plasma to increase the hydroxyl density. During bonding, a silicon-oxygen-silicon covalent bond is formed, with a bonding strength of >50MPa and a gas leakage rate of <1×10 -10 Pa・m 3 / s, porous silicon is formed in the glass cover plate 1 through high temperature annealing, and its nanopores absorb gas molecules to fix the vacuum degree in the packaging cavity.

[0060] The working principle of the present invention is that when the curved surface profile (parabola or hyperbola, with a curvature radius of 1-5mm) of the sensitive thin film structure 3 is subjected to a compressive load, the stress is distributed along a radial gradient. Compared with traditional planar structures, the curved surface guides the stress to diffuse toward the center through the curvature, reducing stress concentration at the edges. For example, the stress uniformity in the center of the parabola is improved by more than 45% compared to a planar structure.

[0061] The sensitive thin film structure 3 has a center thickness of 5-10µm and an edge thickness of 15-25µm, forming a "central flexible deformation + edge rigid support" mechanical model. The thin center layer undergoes significant deformation under pressure, driving the resistance of the P-type piezoresistive bridge 3021 in the polysilicon layer 302 to change. The thick edge layer limits excessive deformation, increasing the overload resistance to 70MPa.

[0062] The P-type piezoresistive bridge 3021 within the polysilicon layer 302 is composed of four piezoresistive strips forming a Wheatstone bridge. The piezoresistive strips are arranged along the direction of the principal stress of the curved surface (with an angle of ≤10° with the radial direction of the film) to maximize the stress-resistance coupling efficiency. When the film deforms, the piezoresistive strips produce a change in resistance due to the piezoresistive effect, and the bridge converts the resistance change into a voltage signal output.

[0063] The N-type thermistor 3022 is integrated in the low-stress area at the edge of the polysilicon layer 302 and is connected in series with the P-type piezoresistive bridge 3021 to form a temperature compensation network. When the temperature changes, the resistance of the N-type thermistor 3022 changes linearly with the temperature, offsetting the temperature drift of the piezoresistive strip and reducing the temperature coefficient to below ±0.01% / °C.

[0064] An anti-interference shielding layer 304 (a 30-80 nm thick platinum or gold layer) covers the surface and sides of the silicon nitride layer 301 and is grounded at the edge of the silicon base 2 to form a Faraday cage, reflecting and absorbing electromagnetic radiation, thereby improving the signal-to-noise ratio.

[0065] The glass cover 1 and the silicon base 2 are sealed by anodic bonding, and the pressure in the packaging cavity is controlled at 10 -4 -10 -3 Pa, built-in porous silicon reference air cavity (pore size 20-50nm) adsorbs gas molecules to maintain long-term vacuum stability and avoid temperature drift and zero point offset.

[0066] The manufacturing process achieves high-precision molding of curved thin film structures through precision machining and inter-layer alignment. The specific steps and principles are as follows:

[0067] From bottom to top, there is the silicon base 2, the buried oxide layer 303 (0.5-1.5µm) and the top silicon layer (15-25µm). The buried oxide layer 303 serves as an insulating layer. The thin film structure is subsequently released by etching to form a cantilever beam.

[0068] P-type impurities (such as boron) are implanted into the top silicon layer (future polysilicon layer 302) to form a P-type piezoresistive bridge 3021 (dose 5×10 15 cm -2 ), N-type impurities (such as phosphorus) are injected to form N-type thermistor 3022 (dose 1×10 16 cm -2 ), by adjusting the resistance temperature coefficient through doping concentration, temperature compensation matching can be achieved;

[0069] Deposit a double sacrificial layer of phosphosilicate glass (bottom layer, 5µm thick) and silicon dioxide (top layer, 3µm thick) with a thickness ratio of 4:3. The deposited phosphosilicate glass has a fast etching rate (HF:HNO3=1:4) and is used for rapid prototyping of curved surface contours. The silicon dioxide has a slow etching rate and is used to refine the surface roughness to Ra<5nm to avoid stress concentration.

[0070] A silicon nitride layer 301 (700-900°C, 15µm thick) and a polysilicon layer 302 (550-650°C, 5µm thick) are sequentially deposited on the curved surface of the sacrificial layer, with a thickness uniformity of ≤±0.5% to ensure consistent mechanical properties of the films.

[0071] The DRIE process is used to etch from the back of the silicon base 2 to the buried oxide layer 303, and then the buried oxide layer 303 is dissolved with an HF solution to separate the sensitive film structure 3 from the silicon base 2. Only the edge is bonded to the base to form a freely deformable cantilever structure.

[0072] Before bonding the glass cover 1 to the silicon base 2, oxygen plasma treatment (power 100 W, time 5 min) was performed to increase the surface hydroxyl density. During bonding, silicon-oxygen-silicon covalent bonds were formed with a bond strength > 50 MPa and a gas leakage rate < 1 × 10 -10 Pa・m 3 / s, a porous silicon reference air cavity (formed by high temperature annealing) is embedded in the packaging cavity, and the vacuum degree is fixed to 10 -3 Pa level, improving long-term reliability.

[0073] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements will not cause the essence of the corresponding technical solutions to deviate from the protection scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A curved thin film pressure sensor based on micromachining, characterized in that: include: A silicon base (2), a sensitive thin film structure (3) covering the silicon base (2), and a glass cover (1) bonded to the sensitive thin film structure (3); The sensitive film structure (3) has an aspherical profile, a thickness gradient distribution along the radial direction, and a piezoresistive sensitive element and a temperature compensation element integrated on the surface; The sensitive film structure (3) includes an anti-interference shielding layer (304) provided below the glass cover (1) and covering the silicon base (2), and a buried oxide layer (303) covering the silicon base (2); The sensitive thin film structure (3) is a composite structure of a silicon nitride layer (301) and a polysilicon layer (302), wherein the silicon nitride layer (301) is located above the polysilicon layer (302) and has a thickness of 60%-75%, and the polysilicon layer (302) has a thickness of 25%-40%. The aspheric surface profile is parabolic or hyperbolic, with a curvature radius of 1-5mm; A P-type piezoresistive bridge circuit (3021) is integrated in the polysilicon layer (302), the piezoresistive strips are arranged along the principal stress direction of the curved surface, and the angle between the principal stress direction and the radial direction of the film is ≤10°; An N-type thermistor (3022) is integrated in the edge region of the polysilicon layer (302) and is connected in series with the P-type piezoresistive bridge circuit (3021) to form a temperature compensation network.

2. The micro-machining-based curved thin film pressure sensor according to claim 1, characterized in that: The anti-interference shielding layer (304) is a platinum or gold layer with a thickness of 30-80 nm, covering the upper surface and side surfaces of the silicon nitride layer (301) and being grounded through the metallized area at the edge of the silicon base (2).

3. The micro-machining-based curved thin film pressure sensor according to claim 2, characterized in that: The thickness of the sensitive film structure (3) is 5-10µm in the center area and 15-25µm in the edge area. The thickness gradient rate is the film radius, and the value range is 2-5µm / mm. The glass cover (1) and the silicon base (2) are sealed and connected through the anodic bonding layer. The pressure in the packaging cavity is controlled at 10 -4 -10 -3 Pa level, and a porous silicon reference air cavity is pre-embedded in the glass cover plate (1).

4. The micro-machining-based curved thin film pressure sensor according to claim 3, characterized in that: The buried oxide layer (303) has a thickness of 0.5-1.5µm. After being released by a backside etching process, the sensitive film structure (3) and the silicon base (2) form a cantilever structure that can freely respond to pressure loads.

5. A method for manufacturing a curved thin film pressure sensor according to any one of claims 1 to 4, characterized in that The following steps are involved: S1. Wafer preparation: Provide <100> A crystal-oriented SOI wafer, wherein the structure thereof comprises, from bottom to top, a silicon base (2), a buried oxide layer (303) and a top silicon layer with a thickness of 15-25µm; S2. Ion implantation: P-type piezoresistive bridge (3021) and N-type thermistor (3022) are formed in the top silicon by ion implantation, with the implantation dose of 5×10 15 cm -2 and 1×10 16 cm -2 ; S3. Deposit and pattern a sacrificial layer: Deposit a double sacrificial layer of phosphosilicate glass and silicon dioxide on the top silicon surface with a thickness ratio of (3-5):(2-3), and define the curved surface area by photolithography. S4. Wet etching to form a curved surface: Using a mixed solution of HF:HNO3 = 1:3-1:5, step etching is performed to remove the sacrificial layer in the unprotected area to form a parabolic or hyperbolic profile; S5. Depositing a structural layer: depositing a silicon nitride layer (301) and a polysilicon layer (302) on the contour of the sacrificial layer by an LPCVD process, covering the entire curved surface and forming a composite thin film; S6. Back-side etching to release the film: etching from the back of the silicon base (2) to the buried oxide layer (303), removing the buried oxide layer (303) with an HF solution, and separating the sensitive film structure (3) from the silicon base (2); S7. Vacuum packaging: Bond the glass cover plate (1) on top of the sensitive film structure (3). Before bonding, treat the bonding surface with oxygen plasma. The pressure in the packaging cavity is controlled at 10 -4 -10 -3 Pa, and a built-in porous silicon reference air cavity.

6. The method for manufacturing a curved thin film pressure sensor according to claim 5, wherein: In step S3, the sacrificial layer thickness ratio is 4:3, and the etching solution uses HF:HNO3=1:

4. The surface roughness Ra formed after etching is less than 5nm.

7. The method for manufacturing a curved thin film pressure sensor according to claim 5, wherein: In step S5, the deposition temperature of the silicon nitride layer (301) is 700-900° C., the deposition temperature of the polysilicon layer (302) is 550-650° C., and the step coverage uniformity of the composite layer and the sacrificial layer is ≥95%.

8. The method for manufacturing a curved thin film pressure sensor according to claim 5, wherein: In step S7, the width of the bonding area between the glass cover plate (1) and the silicon base (2) is 0.5-1 mm, the bonding temperature is 400° C., the voltage is 800 V, and the porous silicon reference air cavity is formed by high-temperature annealing, with a pore diameter of 20-50 nm.

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