A MEMS capacitive pressure sensor and methods of making and using the same

Abstract

The application provides a MEMS capacitive pressure sensor and a preparation and use method thereof, and relates to the technical field of sensors.The structure of the MEMS capacitive pressure sensor provided by the application mainly comprises a force-sensitive nanofilm, a temperature-sensitive nanofilm, a substrate and a base plate, the substrate and the base plate are separated into two independent sealed cavities, and the surface of the base plate opposite to the force-sensitive nanofilm is etched with a ladder-shaped structure.The application optimizes the capacitive-pressure response characteristics (when the external pressure acts, the force-sensitive nanofilm is deformed, and the linear coupling is generated by the change of the effective overlapping area and the interval between the force-sensitive nanofilm and the ladder-shaped structure), and combines with the in-situ temperature compensation of graphene, so that the MEMS capacitive pressure sensor provided by the application can realize high linearity of pressure measurement in a wide temperature range, and the technical problems of traditional devices, such as serious temperature crosstalk and narrow linear interval, are solved, thereby providing a new solution for high-precision and high-reliability pressure measurement.

Description

Technical Field

[0001] This invention relates to the field of sensor technology, and in particular to a MEMS capacitive pressure sensor and its fabrication and usage methods. Background Technology

[0002] In the field of modern industrial inspection and intelligent sensing, pressure is one of the core parameters of automated control. Industries such as aerospace, oil exploration, weaponry, and precision manufacturing have placed increasingly stringent demands on the measurement accuracy, long-term stability, and environmental adaptability of pressure sensors. Among these, capacitive microelectromechanical systems (MEMS) pressure sensors are widely used due to their advantages such as miniaturization, low power consumption, and high sensitivity.

[0003] However, the core performance of traditional MEMS capacitive pressure sensors has long been constrained by two major bottlenecks: temperature interference and non-ideal linear output. Their force-sensitive elements often use silicon-based or metal thin-film materials, and the mismatch in thermal expansion coefficients between these materials and the packaging structure easily introduces thermal stress when temperatures change. When the ambient temperature changes, this mismatch introduces unpredictable thermal stress into the sensitive structure, causing uncontrolled deformation of the thin film, which is then superimposed on the pressure signal, resulting in severe temperature drift errors. On the other hand, traditional MEMS capacitive pressure sensors use a planar electrode structure, and their capacitance-pressure response is inherently non-linear. The effective linear deformation range is usually limited to a small range, making it difficult to meet the requirements of wide-range, high-precision measurements. These factors combined result in significant non-linear errors in MEMS capacitive pressure sensors over a wide temperature range, severely restricting their application in extreme or precision environments. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a MEMS capacitive pressure sensor and its fabrication and usage methods. The MEMS capacitive pressure sensor provided by this invention can achieve high linearity in pressure measurement over a wide temperature range.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: The present invention provides a MEMS capacitive pressure sensor, including a substrate 1 and a substrate 18 opposite to the substrate 1, wherein the space between the substrate 1 and the substrate 18 is divided into an independent first sealed cavity 19-1 and a second sealed cavity 19-2. A temperature-sensitive nanofilm 2 is disposed inside the first sealed cavity 19-1. The temperature-sensitive nanofilm 2 is disposed on the surface of the substrate 1 and opposite to the substrate 18. The two ends of the temperature-sensitive nanofilm 2 are respectively connected to a first metal electrode 4 and a second metal electrode 5. The first metal electrode 4 is connected to a first interconnect pad 10, and the second metal electrode 5 is connected to a second interconnect pad 11. The first interconnect pad 10 and the second interconnect pad 11 are in contact with the surface of the substrate 18. A force-sensitive nanofilm 3 is disposed within the second sealed cavity 19-2. The force-sensitive nanofilm 3 is disposed on the surface of the substrate 1 and is opposite to the substrate 18. One end of the force-sensitive nanofilm 3 is connected to a third metal electrode 6, which is connected to a third interconnect pad 12. The third interconnect pad 12 is in contact with the surface of the substrate 18. The surface of the substrate 18 within the second sealed cavity is a stepped recessed structure 20, which is directly opposite the force-sensitive nanofilm 3, and the surface of the stepped recessed structure 20 is covered with a metal electrode layer 17. The temperature-sensitive nanofilm 2 and the force-sensitive nanofilm 3 are graphene material films; The first interconnect pad 10, the second interconnect pad 11, the third interconnect pad 12, and the metal electrode layer 17 are electrically connected to an external signal processing circuit.

[0006] Preferably, the cross-sectional profile of the stepped recessed structure 20 is a periodically undulating waveform, including a sine wave, a triangular wave, a trapezoidal wave, or a sawtooth wave.

[0007] Preferably, when the waveform is a sawtooth wave, triangular wave, trapezoidal wave or sine wave, the horizontal distance between corresponding points of adjacent waveform units is 5~50μm, the sidewall tilt angle of the waveform unit is 30°~85°, and the height of the waveform unit is 1~30μm; the overall vertical height of the stepped concave structure is 1~100μm, and the overall vertical height of the stepped concave structure is greater than the height of the waveform unit.

[0008] Preferably, the graphene material film is a graphene layer or a sandwich heterojunction structure. The sandwich heterojunction structure includes a graphene layer 9, a first protective layer 21 and a second protective layer 22. The first protective layer 21 and the second protective layer 22 are stacked on both sides of the graphene layer 9. The first protective layer 21 and the second protective layer 22 independently include a boron nitride layer, an aluminum oxide layer or a silicon oxide layer.

[0009] Preferably, when the graphene material film is a graphene layer, the thickness of the graphene layer is 0.34~10nm; when the graphene material film is a sandwich heterojunction structure, the thickness of the graphene layer 9 in the sandwich heterojunction structure is 0.34~10nm, and the total thickness of the sandwich heterojunction structure is 1~50nm.

[0010] Preferably, the area of ​​the temperature-sensitive nanofilm 2 is smaller than the area of ​​the substrate 1 and the substrate 18 in the first sealed cavity, and the area of ​​the force-sensitive nanofilm 3 is smaller than the area of ​​the substrate 1 and the substrate 18 in the second sealed cavity.

[0011] Preferably, the edges of the temperature-sensitive nanofilm 2 and the force-sensitive nanofilm 3 maintain a distance from the outer periphery of the substrate 1.

[0012] Preferably, the first sealed cavity 19-1 and the second sealed cavity 19-2 are oxygen-free cavities.

[0013] This invention provides a method for fabricating the MEMS capacitive pressure sensor described above, comprising the following steps: A stepped recessed structure 20 is formed by etching a portion of the surface of the substrate 18, and a metal electrode layer 17 is deposited on the surface of the stepped recessed structure 20 to obtain a substrate assembly. A temperature-sensitive nanofilm 2 and a force-sensitive nanofilm 3 are prepared at intervals on the surface of a substrate 1. The two ends of the temperature-sensitive nanofilm 2 are respectively connected to a first metal electrode 4 and a second metal electrode 5, and one end of the force-sensitive nanofilm 3 is connected to a third metal electrode 6. A first interconnect pad 10, a second interconnect pad 11, and a third interconnect pad 12 are respectively prepared on the surfaces of the first metal electrode 4, the second metal electrode 5, and the third metal electrode 6 to obtain a substrate assembly. The substrate assembly and the substrate assembly are bonded to form a separated first sealed cavity 19-1 and a second sealed cavity 19-2. The temperature-sensitive nanofilm 2 is located in the first sealed cavity 19-1, and the force-sensitive nanofilm 3 is located in the second sealed cavity 19-2 and is opposite to the stepped recessed structure 20. During bonding, the first interconnect pad 10, the second interconnect pad 11 and the third interconnect pad 12 are in contact with the surface of the substrate 18.

[0014] This invention provides a method for using the MEMS capacitive pressure sensor described above, comprising the following steps: During pressure measurement, the resistance signal of the temperature-sensitive nanofilm 2 in the MEMS capacitive pressure sensor is connected to an external signal processing circuit to convert the resistance change into a voltage signal; the variable capacitor formed by the force-sensitive nanofilm 3 and the metal electrode layer 17 covering the surface of the stepped recessed structure 20 is connected to an external signal processing circuit to convert the capacitance change into a voltage signal; the two voltage signals are processed by a differential amplifier circuit for temperature compensation to eliminate temperature drift error in the pressure signal, and finally output the pressure measurement result.

[0015] This invention provides a MEMS capacitive pressure sensor, which is a high-linearity MEMS capacitive pressure sensor based on graphene and a stepped electrode structure. The main structure includes a force-sensitive nanofilm, a temperature-sensitive nanofilm, a substrate, and a base plate, with the substrate and base plate separated into two independent sealed cavities. Compared with the prior art, this invention has the following advantages: This invention utilizes graphene as the upper electrode material of a capacitive pressure sensor, fully leveraging its excellent electromechanical properties. Graphene possesses atomic-level thickness, extremely high mechanical strength, and excellent conductivity, significantly reducing the mass and stiffness of the sensitive film and improving the sensor's natural frequency and dynamic response characteristics. Simultaneously, graphene's intrinsic two-dimensional structure enables it to exhibit excellent elastic recovery and fatigue resistance under stress, avoiding the plastic deformation and performance degradation that easily occur in traditional metal or doped silicon films under long-term cyclic loading. This invention uses graphene, with its excellent mechanical and thermoelectric properties, to construct force-sensitive and temperature-sensitive nanofilms, placing them within a sealed cavity in the same temperature range. The temperature-sensitive nanofilm can sense temperature changes in real time and in situ, and its resistance signal is used to synchronously compensate the capacitive pressure signal. This achieves precise adaptive temperature compensation within the system, fundamentally solving the problem of temperature crosstalk in traditional capacitive pressure sensors. This invention innovatively employs a stepped electrode structure. Through its periodic geometric contour, the stepped electrode structure optimizes the capacitance change characteristics between the force-sensitive nanofilm and the electrode during deformation (when external pressure increases, the force-sensitive nanofilm moves closer to the sidewall of the stepped electrode, reducing the electrode spacing and increasing the facing area; the combined effect of these two factors causes the capacitance to increase approximately linearly). Compared to capacitive pressure sensors using traditional planar electrodes, this structure enables linear coupling between the effective overlap area and the spacing change, transforming the original nonlinear response into a highly linear function, thus achieving significantly improved linearity over a wide pressure range. Furthermore, in this invention, the sealing cavity is an oxygen-free cavity, and the graphene material film used as the temperature-sensitive nanofilm and force-sensitive nanofilm adopts a sandwich heterojunction structure of protective layer / graphene layer / protective layer. The graphene layer is sandwiched between the two protective layers, which completely eliminates the influence of oxygen, water vapor erosion and air medium temperature drift, and greatly improves the long-term stability and reliability of the sensor under dynamic and static high-load test environments.

[0016] This invention optimizes the capacitance-pressure response characteristics through a stepped concave structure and combines it with in-situ temperature compensation using graphene, enabling the provided MEMS capacitive pressure sensor to achieve high linearity in pressure measurement over a wide temperature range. This overcomes the technical challenges of severe temperature crosstalk and narrow linear range in traditional devices, providing a novel solution for high-precision and high-reliability pressure measurement. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the overall structure of the pressure sensor in the embodiment; Figure 2 This is a side view of the pressure sensor in the embodiment; Figure 3 This is a top view of the stepped electrode structure in the embodiment; Figure 4 This is a side view of the stepped electrode structure in the embodiment; Figure 5 This is a diagram showing the positional distribution of the force-sensitive and temperature-sensitive nanofilms in the embodiments; Figure 6 This is a diagram showing the location distribution of the external interconnect electrodes in the embodiment; Figure 7 This is a schematic diagram of the graphene material film in the embodiment; Figure 8 This is a schematic diagram of the stepped concave structure when the waveform is a sine wave, a triangular wave, or a sawtooth wave. Figure 8 (a) shows the stepped concave structure when the waveform is a sawtooth wave, (b) shows the stepped concave structure when the waveform is a triangular wave, and (c) shows the stepped concave structure when the waveform is a sine wave. In the figure: 1-Substrate; 2-Thermosensitive nanofilm; 3-Force-sensitive nanofilm; 4-First metal electrode; 5-Second metal electrode; 6-Third metal electrode; 7-First sealing ring; 8-Second sealing ring; 9-Graphene layer; 10-First interconnect pad; 11-Second interconnect pad; 12-Third interconnect pad; 13-First lead post; 14-Second lead post; 15-Third lead post; 16-Fourth lead post; 17-Metal electrode plate (metal electrode layer); 18-Substrate; 19-1-First sealing cavity; 19-2-Second sealing cavity; 20-Stepped recessed structure; 21-First protective layer; 22-Second protective layer; 23-First external interconnect electrode; 24-Second external interconnect electrode; 25-Third external interconnect electrode; 26-Fourth external interconnect electrode. Detailed Implementation

[0018] The present invention provides a MEMS capacitive pressure sensor, including a substrate 1 and a substrate 18 opposite to the substrate 1, wherein the space between the substrate 1 and the substrate 18 is divided into an independent first sealed cavity 19-1 and a second sealed cavity 19-2. A temperature-sensitive nanofilm 2 is disposed inside the first sealed cavity 19-1. The temperature-sensitive nanofilm 2 is disposed on the surface of the substrate 1 and opposite to the substrate 18. The two ends of the temperature-sensitive nanofilm 2 are respectively connected to a first metal electrode 4 and a second metal electrode 5. The first metal electrode 4 is connected to a first interconnect pad 10, and the second metal electrode 5 is connected to a second interconnect pad 11. The first interconnect pad 10 and the second interconnect pad 11 are in contact with the surface of the substrate 18. A force-sensitive nanofilm 3 is disposed within the second sealed cavity 19-2. The force-sensitive nanofilm 3 is disposed on the surface of the substrate 1 and is opposite to the substrate 18. One end of the force-sensitive nanofilm 3 is connected to a third metal electrode 6, which is connected to a third interconnect pad 12. The third interconnect pad 12 is in contact with the surface of the substrate 18. The surface of the substrate 18 within the second sealed cavity is a stepped recessed structure 20, which is directly opposite the force-sensitive nanofilm 3, and the surface of the stepped recessed structure 20 is covered with a metal electrode layer 17. The temperature-sensitive nanofilm 2 and the force-sensitive nanofilm 3 are graphene material films; The first interconnect pad 10, the second interconnect pad 11, the third interconnect pad 12, and the metal electrode layer 17 are electrically connected to an external signal processing circuit.

[0019] Figure 1 and Figure 2 The figures shown below are a schematic diagram of the overall structure of the pressure sensor in the embodiment and a side view. Figure 1 and Figure 2 Please provide a detailed explanation.

[0020] The MEMS capacitive pressure sensor provided by this invention includes a substrate 1. In this invention, the substrate 1 is preferably a silicon wafer or a glass wafer.

[0021] The MEMS capacitive pressure sensor provided by this invention includes a substrate 18 opposite to the substrate 1. The space between the substrate 1 and the substrate 18 is divided into an independent first sealed cavity 19-1 and a second sealed cavity 19-2. In this invention, the substrate 18 is preferably made of silicon. In this invention, the first and second sealed cavities are preferably formed by respectively providing a first sealing ring 7 and a second sealing ring 8 between the substrate 1 and the substrate 18, thus enclosing the substrate 1 and the substrate 18 to form two integrated sealed cavities (the sealed cavities are nested within the internal detection space). In this invention, the first and second sealed cavities are preferably oxygen-free cavities, which are either vacuum-filled or filled with inert gases with low thermal expansion coefficients, such as helium, nitrogen, or argon, to isolate the graphene film from direct contact with the outside world, prevent the external environment (oxygen, water vapor) from corroding the graphene material, and eliminate interference caused by the change in the dielectric constant of air with temperature.

[0022] In this invention, a temperature-sensitive nanofilm 2 is disposed within the first sealed cavity 19-1. The temperature-sensitive nanofilm 2 is disposed on the surface of the substrate 1 and opposite to the substrate 18 (i.e., the side of the substrate 1 facing the detection space). In this invention, the temperature-sensitive nanofilm 2 is a graphene material film, preferably a graphene layer (a single graphene component film) or a sandwich heterojunction structure. The sandwich heterojunction structure (e.g., Figure 7The preferred embodiment (shown) includes a graphene layer 9 (single graphene composition), a first protective layer 21, and a second protective layer 22. The first protective layer 21 and the second protective layer 22 are stacked on both sides of the graphene layer 9. The first protective layer 21 is in direct contact with the surface of the substrate 1 and can also be referred to as the lower protective layer. The second protective layer 22 can also be referred to as the upper protective layer. The sandwich heterojunction structure is represented as lower protective layer / graphene / upper protective layer. In this invention, the first protective layer 21 and the second protective layer 22 preferably independently include a boron nitride layer, an aluminum oxide layer, or a silicon oxide layer. The protective layer is a material with an atomically flat interface, excellent chemical inertness, and high insulation, which can achieve the functions of matching the graphene lattice, isolating environmental erosion, maintaining the intrinsic electromechanical and thermoelectric properties of graphene, and improving the stability and temperature compensation accuracy of sensitive films. As an embodiment of this invention, both the first protective layer 21 and the second protective layer 22 are boron nitride layers. In this invention, when the graphene material film is a graphene layer, the thickness of the graphene layer is preferably 0.34~10nm; when the graphene material film is a sandwich heterojunction structure, the thickness of the graphene layer 9 in the sandwich heterojunction structure is preferably 0.34~10nm, and the total thickness of the sandwich heterojunction structure is preferably 1~50nm.

[0023] In this invention, the area of ​​the temperature-sensitive nanofilm 2 is preferably smaller than the area of ​​the substrate 1 and the base plate 18 opposite each other within the first sealed cavity, and the edges of the temperature-sensitive nanofilm 2 preferably maintain a distance from the outer periphery of the substrate 1. This invention does not have specific requirements regarding this distance. In this invention, the temperature-sensitive nanofilm 2 is used to directly and in real-time sense temperature changes within the cavity to compensate for the pressure sensing signal of the force-sensitive nanofilm 3, thereby achieving real-time and accurate correction of the capacitive pressure sensing signal.

[0024] In this invention, the two ends of the temperature-sensitive nanofilm 2 are respectively connected to a first metal electrode 4 and a second metal electrode 5. The first metal electrode 4 is connected to a first interconnect pad 10, and the second metal electrode 5 is connected to a second interconnect pad 11. The first interconnect pad 10 and the second interconnect pad 11 are in contact with the surface of the substrate 18. In this invention, the interconnect pads are used for signal conduction.

[0025] In this invention, a force-sensitive nanofilm 3 is disposed within the second sealed cavity 19-2. The force-sensitive nanofilm 3 is disposed on the surface of the substrate 1 and opposite to the substrate 18. This invention alternates between the temperature-sensitive nanofilm 2 and the force-sensitive nanofilm 3 within two sealed cavities to ensure functional independence. Figure 5(See diagram showing the positional distribution of the force-sensitive and temperature-sensitive nanofilms). The two sealed cavities form a double airtight barrier, which can more effectively prevent corrosive atmospheres such as external oxygen and water vapor from entering the cavities, reducing the risk of oxidation or contamination of the graphene film. Simultaneously, the area between the two sealed cavities can serve as a stress buffer zone and particle trapping zone, reducing bonding stress and particle damage to the graphene film, thereby better protecting the integrity and long-term stability of the graphene film. In this invention, the force-sensitive nanofilm 3 is a graphene material film. The structure and thickness of the force-sensitive nanofilm 3 are preferably the same as those of the temperature-sensitive nanofilm 2, and will not be repeated here. In this invention, the force-sensitive nanofilm 3 can effectively improve the range and linearity of the sensor, and with variations in its thickness, a series of products with different ranges can be produced, achieving accurate control of the device's range. In this invention, the graphene material film used as both the temperature-sensitive and force-sensitive nanofilms employs a sandwich heterojunction structure of a protective layer / graphene layer / protective layer. This sandwich heterojunction structure utilizes the chemical inertness, high insulation, and perfect lattice matching of the protective layer with graphene to provide graphene with an atomically flat and highly stable interface environment. The double-layer protective layer effectively isolates graphene from direct contact with the external environment, fundamentally suppressing performance drift caused by environmental erosion or contamination, and significantly improving the stability and reliability of the sensor during long-term use. Simultaneously, the high-quality interface allows graphene to maintain its intrinsic high carrier mobility, which not only enhances the mechanical response characteristics of the force-sensitive film but also makes the resistance-temperature response relationship of the temperature-sensitive film more significant and linear. This provides a more accurate reference signal for temperature compensation, ultimately achieving a synergistic improvement in the overall measurement accuracy and long-term stability of the sensor.

[0026] In this invention, both the temperature-sensitive nanofilm 2 and the force-sensitive nanofilm 3 use graphene as the core functional material, responsible for sensing deformation caused by pressure or resistance changes caused by temperature. Graphene has atomic-level thickness, extremely high mechanical strength, and good conductivity, which can significantly reduce the mass and stiffness of the sensitive film and improve the sensor's natural frequency and dynamic response characteristics. Simultaneously, graphene's intrinsic two-dimensional structure gives it excellent elastic recovery and fatigue resistance under stress, avoiding the plastic deformation and performance degradation that easily occur in traditional metal or doped silicon films under long-term cyclic loading. Furthermore, graphene films can be prepared using dry transfer, wet transfer, or direct growth processes, avoiding the inhomogeneities and complex temperature drift problems introduced by traditional semiconductor piezoresistive material doping processes, thus improving the material consistency and temperature stability of the sensitive unit. This invention places functionally independent force-sensitive nanofilm 3 and temperature-sensitive nanofilm 2 side by side on the same surface of the substrate 1, thereby ensuring that they are in the same temperature field; and the graphene temperature-sensitive nanofilm integrated in the same temperature field can sense temperature changes in real time and in situ, and its resistance signal is used to synchronously compensate the capacitive pressure signal, realizing accurate adaptive temperature compensation within the system, fundamentally solving the problem of traditional capacitive pressure sensors being susceptible to temperature crosstalk.

[0027] In this invention, the area of ​​the force-sensitive nanofilm 3 is smaller than the area of ​​the substrate 1 and the substrate 18 opposite each other in the second sealed cavity 19-2, and preferably, a gap is maintained between the edge of the force-sensitive nanofilm 3 and the outer periphery of the substrate 1. This invention does not have a particular requirement for this gap. This invention maintains a gap between the edges of the temperature-sensitive nanofilm 2 and the force-sensitive nanofilm 3 and the outer periphery of the substrate 1, avoiding interference from edge stress on the sensitive units, thereby ensuring that they are in the same temperature environment and providing an accurate reference signal for subsequent temperature compensation. In this invention, one end of the force-sensitive nanofilm 3 is connected to a third metal electrode 6, the third metal electrode 6 is connected to a third interconnect pad 12, and the third interconnect pad 12 is in contact with the surface of the substrate 18.

[0028] In this invention, the surface of the substrate 18 inside the second sealed cavity is a stepped recessed structure 20, which faces the force-sensitive nanofilm 3. The cross-sectional profile of the stepped recessed structure 20 is a periodically undulating waveform, preferably including a sine wave, a triangular wave, a trapezoidal wave, or a sawtooth wave. In this invention, when the waveform is a sine wave, a triangular wave, a trapezoidal wave, or a sawtooth wave, the horizontal distance between corresponding points of adjacent waveform units is preferably 5~50μm, the sidewall tilt angle of the waveform unit is preferably 30°~85°, and the height of the waveform unit is preferably 1~30μm; the overall vertical height of the stepped recessed structure is preferably 1~100μm, and the overall vertical height of the stepped recessed structure is greater than the height of the waveform unit. Figure 1The image shows the stepped depression structure during a trapezoidal wave. Figure 8 This is a schematic diagram of the stepped concave structure when the waveform is a sine wave, a triangular wave, or a sawtooth wave. Figure 8 (a) shows the stepped concave structure when the waveform is a sawtooth wave, (b) shows the stepped concave structure when the waveform is a triangular wave, and (c) shows the stepped concave structure when the waveform is a sine wave. Figure 1 and Figure 8 In the diagram, h is the height of the waveform unit, L is the horizontal distance between corresponding points of adjacent waveform units, H is the overall vertical height of the stepped concave structure, and a is the side wall tilt angle of the waveform unit.

[0029] As an embodiment of the present invention, the cross-sectional profile of the stepped recessed structure 20 is a sawtooth wave (e.g., Figure 8 As shown in (a), the sawtooth wave consists of periodically arranged sharp V-shaped grooves (each groove unit is V-shaped with straight sides, forming periodic undulations with sharp edges in the cross-section). This structure maximizes the edge electric field effect, generating a more significant capacitance change gradient under small displacements, further improving the sensor's sensitivity and linearity. When the waveform is a sawtooth wave, the horizontal distance between corresponding points of adjacent sawtooth units (also known as the period of the V-shaped groove) is... Figure 8 In (a) shown in L), the preferred diameter is 5~50μm, and the inclination angle of the sidewall of the sawtooth unit (the angle between the sidewall of the groove and the horizontal plane) is 5~50μm. Figure 8 In (a) shown in (a), the angle is preferably 30°~85°, and the height of the sawtooth unit is ( Figure 8 The height of the stepped recessed structure (as shown in (a) and h) is preferably 1~30μm; the overall vertical height (also known as the depth) of the stepped recessed structure is 1~30μm. Figure 8 The groove diameter (H in (a)) is preferably 1~100μm. In the design of the stepped recessed structure, the period, depth, and sidewall tilt angle of the groove are the key geometric parameters that determine the sensor performance. These parameters affect the sensor performance through multiple mechanisms: the greater the depth or the smaller the period, the more significant the capacitance change gradient during the deformation of the force-sensitive nanofilm, and the higher the sensitivity. By reasonably configuring the ratio of period to depth, the changes in overlapping area and spacing during film deformation can be synergistically coupled, transforming the nonlinear capacitance-displacement relationship dominated by a single variable under traditional planar electrodes into an approximately linear functional relationship, thereby significantly expanding the linear working range. The greater the depth, the greater the space for film deformation, and the greater the full-scale pressure of the sensor. Meanwhile, a deeper groove provides more deformation space, enhancing the overload resistance. Depending on the specific application requirements, the groove diameter can be optimized within the range of 5~50μm, 1~100μm, and 30°~85° to achieve a synergistic design of sensitivity, linear range, measurement range, and reliability.

[0030] As an embodiment of the present invention, the cross-sectional profile of the stepped recessed structure 20 is a sine wave (e.g., Figure 8 (As shown in (c)). The sinusoidal waveform profile is smooth and continuous, without any sharp edges. Its period, depth, and other dimensional parameters can be optimized according to the size range of the sawtooth wave mentioned above. This continuous wave-shaped stepped concave structure, through its smooth and continuously changing geometric features, can provide a smoother and more continuous capacitance change response when the force-sensitive nanofilm 3 deforms. Compared with the sawtooth shape (V-shaped stepped structure) with sharp edges, the wave-shaped structure avoids the severe concentration of local electric field intensity at the microscopic level. This is beneficial for reducing local stress concentration on the force-sensitive nanofilm 3 during ultra-high overload pressure or long-term dynamic fatigue testing, thereby improving the sensor's overload resistance and long-term mechanical reliability. At the same time, the smooth curved surface allows the stress caused by the difference in the thermal expansion coefficient of the material to be distributed more evenly during the bonding process or temperature cycling, reducing the risk of microcracks or failure at the interface of the structure.

[0031] In this invention, the surface of the stepped recessed structure 20 is covered with a metal electrode layer 17 (the metal electrode layer covers the entire surface of the stepped recessed structure), thereby forming the fixed lower electrode of the sensor. The metal electrode layer is also referred to as a metal plate. The metal electrode layer 17 and the movable graphene force-sensitive nanofilm 3 above it together form a capacitive sensing unit (variable capacitor). In this invention, the stepped recessed structure covered with the metal electrode layer 17 can also be referred to as a stepped electrode structure. Figure 3 and Figure 4 The images shown are a top view and a side view of the stepped electrode structure in the embodiment.

[0032] This invention features a stepped recessed structure on a substrate. The unique geometric configuration of the stepped shape fundamentally optimizes the capacitance-pressure response characteristics. When external pressure is applied to the substrate 1, the force-sensitive nanofilm 3 deforms. The local spacing and overlap area between the nanofilm and the uneven surface of the stepped recessed structure (primarily due to the sidewalls of the stepped recessed structure) change synergistically. This transforms the nonlinear capacitance-displacement relationship, originally dominated by a single variable of spacing, into an approximately linear functional relationship, achieving a high linear response to the capacitance-pressure signal. Compared to traditional planar electrodes, this non-planar electrode design with its stepped recessed structure in this invention achieves significant linearization optimization, ensuring stable sensitivity of the sensor throughout its operating range, thus achieving high linearity output and effectively reducing nonlinear errors.

[0033] In this invention, the first metal electrode 4, the second metal electrode 5, the third metal electrode 6, and the metal electrode layer 17 constitute an electrode assembly for achieving reliable electrical connection and signal extraction. This invention does not impose special requirements on the materials of the metal electrodes; the first metal electrode 4, the second metal electrode 5, and the third metal electrode 6 can be made of one or more of gold, platinum, nickel, copper, titanium, and chromium, and the metal electrode layer 17 can be made of one or more of gold, platinum, aluminum, copper, titanium, and chromium. In this invention, the first metal electrode 4, the second metal electrode 5, and the third metal electrode 6 can be configured as elongated strip structures.

[0034] In this invention, the first interconnect pad 10, the second interconnect pad 11, the third interconnect pad 12, and the metal electrode layer 17 are electrically connected to an external signal processing circuit. To achieve low-loss transmission and high-reliability extraction of sensing signals, a vertical interconnect system is preferably integrated into the substrate 18 and designed in conjunction with an external precision measurement circuit. In this invention, a vertically penetrating lead hole is provided in the substrate 18. Metal lead posts—first lead post 13, second lead post 14, third lead post 15, and fourth lead post 16—are respectively inserted into the corresponding lead hole. The upper ends of the first lead post 13, second lead post 14, third lead post 15, and fourth lead post 16 are respectively connected to the interconnect pads—first interconnect pad 10, second interconnect pad 11, third interconnect pad 12, and metal electrode layer 17 through conductive adhesive or micro solder joints to form a stable electrical connection (the interconnect pads are all located in the inner area of ​​the sealing ring). The lower ends are respectively connected to the external interconnect electrodes on the bottom surface of the substrate 18—first external interconnect electrode 23, second external interconnect electrode 24, third external interconnect electrode 25, and fourth external interconnect electrode 26—to construct a complete physical signal transmission path. Specifically, the capacitance signal formed by the force-sensitive nanofilm 3 and the metal electrode layer 17 on the surface of the stepped recessed structure 20 is extracted through the third metal electrode 6, the third interconnect pad 12, the third lead post 15, the fourth lead post 16, the third external interconnect electrode 25, and the fourth external interconnect electrode 26; the resistance signal of the temperature-sensitive nanofilm 2 is extracted through the first metal electrode 4, the second metal electrode 5, the first interconnect pad 10, the second interconnect pad 11, the first lead post 13, the second lead post 14, the first external interconnect electrode 23, and the second external interconnect electrode 24.

[0035] In this invention, the first interconnect pad 10, the second interconnect pad 11, the third interconnect pad 12, the first lead post 13, the second lead post 14, the third lead post 15, the fourth lead post 16, the first external interconnect electrode 23, the second external interconnect electrode 24, the third external interconnect electrode 25, and the fourth external interconnect electrode 26 constitute an interconnect lead-out assembly. Figure 6 This is a diagram showing the location distribution of the external interconnect electrodes in the embodiment.

[0036] In this invention, the various components work together to form a sealed and fully functional sensing system. This invention provides a high-linearity MEMS capacitive pressure sensor. The core of this invention lies in integrating a force-sensitive unit, a temperature-sensitive unit, and microstructures for improving linearity into a sealed micro-cavity. The sensor uses graphene, which has excellent mechanical and thermoelectric properties, to construct both the force-sensitive and temperature-sensitive nanofilms, placing them within a sealed cavity in the same temperature range. This effectively isolates external interference. During pressure measurement, the temperature-sensitive nanofilm detects temperature interference signals and compensates for temperature errors during the pressure measurement process of the force-sensitive nanofilm, achieving in-situ temperature self-compensation within the sensitive unit. Simultaneously, an innovative stepped substrate structure is used to significantly expand the linear deformation range by optimizing the force-capacitance conversion characteristics. This invention solves the problems of existing capacitive pressure sensors, such as susceptibility to temperature crosstalk over a wide temperature range, narrow linear deformation range, and difficulty in simultaneously achieving measurement accuracy and stability.

[0037] This invention provides a method for fabricating the MEMS capacitive pressure sensor described above, comprising the following steps: A stepped recessed structure 20 is formed by etching a portion of the surface of the substrate 18, and a metal electrode layer 17 is deposited on the surface of the stepped recessed structure 20 to obtain a substrate assembly. A temperature-sensitive nanofilm 2 and a force-sensitive nanofilm 3 are prepared at intervals on the surface of a substrate 1. The two ends of the temperature-sensitive nanofilm 2 are respectively connected to a first metal electrode 4 and a second metal electrode 5, and one end of the force-sensitive nanofilm 3 is connected to a third metal electrode 6. A first interconnect pad 10, a second interconnect pad 11, and a third interconnect pad 12 are respectively prepared on the surfaces of the first metal electrode 4, the second metal electrode 5, and the third metal electrode 6 to obtain a substrate assembly. The substrate assembly and the substrate assembly are bonded to form a separated first sealed cavity 19-1 and a second sealed cavity 19-2. The temperature-sensitive nanofilm 2 is located in the first sealed cavity 19-1, and the force-sensitive nanofilm 3 is located in the second sealed cavity 19-2 and is opposite to the stepped recessed structure 20. During bonding, the first interconnect pad 10, the second interconnect pad 11 and the third interconnect pad 12 are in contact with the surface of the substrate 18.

[0038] In this invention, the etching can be performed using laser etching; the deposition can be performed using magnetron sputtering to form a dense metal electrode layer.

[0039] This invention does not impose any particular requirements on the method for preparing the temperature-sensitive nanofilm 2 and the force-sensitive nanofilm 3 on the surface of the substrate 1. Any preparation method well-known to those skilled in the art can be used. For example, when the temperature-sensitive and force-sensitive nanofilms are single graphene layers, the graphene layer can be transferred to the substrate surface via wet transfer. When the temperature-sensitive and force-sensitive nanofilms are sandwich heterojunction structures (lower protective layer / graphene / upper protective layer), the lower protective layer, graphene layer, and upper protective layer can be prepared on the substrate surface by direct CVD growth, or the lower protective layer, graphene layer, and upper protective layer can be transferred to the substrate respectively by nanofilm transfer. In this invention, the first metal electrode 4, the second metal electrode 5, and the third metal electrode 6 can be prepared using photolithography and magnetron sputtering processes; the first interconnect pad 10, the second interconnect pad 11, and the third interconnect pad 12 can be prepared by magnetron sputtering.

[0040] In this invention, the bonding is preferably performed by bonding the substrate 1 to the substrate 18 through a first sealing ring 7 and a second sealing ring 8, forming a separated first sealed cavity and a second sealed cavity. During the bonding process, the bonding section corresponding to the force-sensitive nanofilm 3 is precisely aligned with the stepped recessed structure 20 of the substrate 18. A high-precision alignment process ensures the relative positional accuracy of the two during bonding, so that the force-sensitive nanofilm 3 and the metal electrode 17 on the surface of the stepped recessed structure 20 are positioned opposite each other, together forming a stable variable capacitance sensing unit. This invention achieves a hermetically sealed connection between the substrate and the substrate through the bonding process. During or after the bonding process, the first and second sealed cavities are evacuated or filled with inert gas and then sealed. The stable structure formed by bonding in this invention provides reliable support for the stepped recessed structure 20 and ensures the structural stability of the area where the temperature-sensitive nanofilm 2 is located, allowing it to accurately sense the cavity temperature without pressure interference, providing a reliable reference for temperature compensation of the pressure signal.

[0041] This invention provides a method for using the MEMS capacitive pressure sensor described above, comprising the following steps: During pressure measurement, the resistance signal of the temperature-sensitive nanofilm 2 in the MEMS capacitive pressure sensor is connected to an external signal processing circuit to convert the resistance change into a voltage signal; the variable capacitor formed by the force-sensitive nanofilm 3 and the metal electrode layer 17 covering the surface of the stepped recessed structure 20 is connected to an external signal processing circuit to convert the capacitance change into a voltage signal; the two voltage signals are processed by a differential amplifier circuit for temperature compensation (differential subtraction) to eliminate the temperature drift error in the pressure signal, and finally output a measurement result that is linearly related to the pressure.

[0042] In this invention, the external signal processing circuit preferably employs a combination of a Wheatstone bridge and a differential amplifier circuit to achieve precise processing of pressure and temperature signals. Specifically, the temperature-sensitive nanofilm 2 is connected to the Wheatstone bridge, converting its resistance change into a voltage signal V. T (T); The variable capacitor formed by the force-sensitive nanofilm 3 and the metal electrode 17 on the stepped structure is connected to a capacitor-to-voltage conversion circuit, which converts the capacitance change into a voltage signal V. P (P,T).

[0043] To further illustrate the present invention, the MEMS capacitive pressure sensor provided by the present invention and its preparation and use methods are described in detail below with reference to examples, but these should not be construed as limiting the scope of protection of the present invention.

[0044] Example 1 A high-linearity MEMS capacitive pressure sensor, the structure of which is as follows: Figures 1-8 As shown, the system mainly includes a substrate 1, a base plate 18, a sealing structure, a sensing unit, an electrode assembly, and an interconnect lead-out assembly. These components work together to form a sealed and fully functional sensing system. The sealing structure includes a first sealing ring 7 and a second sealing ring 8. The sensing unit includes a temperature-sensitive nanofilm 2 and a force-sensitive nanofilm 3. The electrode assembly includes a first metal electrode 4, a second metal electrode 5, a third metal electrode 6, and a metal electrode plate (i.e., a metal electrode layer) 17. The interconnect lead-out assembly includes a first interconnect pad 10, a second interconnect pad 11, a third interconnect pad 12, a first lead post 13, a second lead post 14, a third lead post 15, a fourth lead post 16, a first external interconnect electrode 23, a second external interconnect electrode 24, a third external interconnect electrode 25, and a fourth external interconnect electrode 26. The surface of the base plate 18 opposite to the force-sensitive nanofilm 3 is processed using photolithography and laser etching to form a stepped recessed structure 20. The metal electrode plate (i.e., the metal electrode layer) 17 covers the surface of the stepped recessed structure, forming a stepped electrode.

[0045] The working principle of the MEMS capacitive pressure sensor is as follows: The stepped electrode structure, through its specific periodic geometric contour, optimizes the capacitance change characteristics between the force-sensitive film and the electrode when the film deforms. When external pressure is applied to the substrate 1, the force-sensitive nanofilm 3 deforms. The stepped structure enables linear coupling between the effective overlapping area and the spacing, transforming the original nonlinear response relationship into a highly linear function, thereby achieving significantly improved linearity over a wide pressure range. Furthermore, the temperature-sensitive nanofilm can sense temperature changes in real time and in situ, and its resistance signal is used to synchronously compensate the capacitive pressure signal, achieving precise adaptive temperature compensation within the system.

[0046] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A MEMS capacitive pressure sensor, characterized in that, Includes a substrate (1) and a substrate (18) opposite to the substrate (1), the space between the substrate (1) and the substrate (18) being divided into a first sealed cavity (19-1) and a second sealed cavity (19-2). A temperature-sensitive nanofilm (2) is disposed inside the first sealed cavity (19-1). The temperature-sensitive nanofilm (2) is disposed on the surface of the substrate (1) and opposite to the substrate (18). The two ends of the temperature-sensitive nanofilm (2) are respectively connected to a first metal electrode (4) and a second metal electrode (5). The first metal electrode (4) is connected to a first interconnect pad (10), and the second metal electrode (5) is connected to a second interconnect pad (11). The first interconnect pad (10) and the second interconnect pad (11) are in contact with the surface of the substrate (18). A force-sensitive nanofilm (3) is disposed inside the second sealed cavity (19-2). The force-sensitive nanofilm (3) is disposed on the surface of the substrate (1) and opposite to the substrate (18). One end of the force-sensitive nanofilm (3) is connected to a third metal electrode (6). The third metal electrode (6) is connected to a third interconnect pad (12). The third interconnect pad (12) is in contact with the surface of the substrate (18). The surface of the substrate (18) inside the second sealed cavity is a stepped recessed structure (20). The stepped recessed structure (20) is directly opposite to the force-sensitive nanofilm (3), and the surface of the stepped recessed structure (20) is covered with a metal electrode layer (17). The temperature-sensitive nanofilm (2) and the force-sensitive nanofilm (3) are graphene material films; The first interconnect pad (10), the second interconnect pad (11), the third interconnect pad (12) and the metal electrode layer (17) are electrically connected to an external signal processing circuit.

2. The MEMS capacitive pressure sensor according to claim 1, characterized in that, The cross-sectional profile of the stepped concave structure (20) is a periodically undulating waveform, including sine waves, triangular waves, trapezoidal waves or sawtooth waves.

3. The MEMS capacitive pressure sensor according to claim 2, characterized in that, When the waveform is a sawtooth wave, triangular wave, trapezoidal wave or sine wave, the horizontal distance between corresponding points of adjacent waveform units is 5~50μm, the side wall tilt angle of the waveform unit is 30°~85°, and the height of the waveform unit is 1~30μm; the overall vertical height of the stepped concave structure is 1~100μm, and the overall vertical height of the stepped concave structure is greater than the height of the waveform unit.

4. The MEMS capacitive pressure sensor according to claim 1, characterized in that, The graphene material film is a graphene layer or a sandwich heterojunction structure. The sandwich heterojunction structure includes a graphene layer (9), a first protective layer (21), and a second protective layer (22). The first protective layer (21) and the second protective layer (22) are stacked on both sides of the graphene layer (9). The first protective layer (21) and the second protective layer (22) independently include a boron nitride layer, an aluminum oxide layer, or a silicon oxide layer.

5. The MEMS capacitive pressure sensor according to claim 4, characterized in that, When the graphene material film is a graphene layer, the thickness of the graphene layer is 0.34~10nm; when the graphene material film is a sandwich heterojunction structure, the thickness of the graphene layer (9) in the sandwich heterojunction structure is 0.34~10nm, and the total thickness of the sandwich heterojunction structure is 1~50nm.

6. The MEMS capacitive pressure sensor according to claim 1 or 4, characterized in that, The area of ​​the temperature-sensitive nanofilm (2) is smaller than the area of ​​the substrate (1) and the substrate (18) in the first sealed cavity, and the area of ​​the force-sensitive nanofilm (3) is smaller than the area of ​​the substrate (1) and the substrate (18) in the second sealed cavity.

7. The MEMS capacitive pressure sensor according to claim 1, characterized in that, The edges of the temperature-sensitive nanofilm (2) and the force-sensitive nanofilm (3) maintain a distance from the outer periphery of the substrate (1).

8. The MEMS capacitive pressure sensor according to claim 1, characterized in that, The first sealed cavity (19-1) and the second sealed cavity (19-2) are oxygen-free cavities.

9. A method for fabricating a MEMS capacitive pressure sensor according to any one of claims 1 to 8, characterized in that, Includes the following steps: A stepped recessed structure (20) is formed by etching a portion of the surface of the substrate (18), and a metal electrode layer (17) is deposited on the surface of the stepped recessed structure (20) to obtain a substrate assembly; A temperature-sensitive nanofilm (2) and a force-sensitive nanofilm (3) are prepared at intervals on the surface of a substrate (1). The two ends of the temperature-sensitive nanofilm (2) are respectively connected to a first metal electrode (4) and a second metal electrode (5), and one end of the force-sensitive nanofilm (3) is connected to a third metal electrode (6). A first interconnect pad (10), a second interconnect pad (11), and a third interconnect pad (12) are respectively prepared on the surfaces of the first metal electrode (4), the second metal electrode (5), and the third metal electrode (6) to obtain a substrate assembly. The substrate assembly is bonded to the substrate assembly to form a separated first sealed cavity (19-1) and a second sealed cavity (19-2). The temperature-sensitive nanofilm (2) is located in the first sealed cavity (19-1), and the force-sensitive nanofilm (3) is located in the second sealed cavity (19-2) and is opposite to the stepped recessed structure (20). During bonding, the first interconnect pad (10), the second interconnect pad (11), and the third interconnect pad (12) are in contact with the surface of the substrate (18).

10. A method of using the MEMS capacitive pressure sensor according to any one of claims 1 to 8, characterized in that, Includes the following steps: During pressure measurement, the resistance signal of the temperature-sensitive nanofilm (2) in the MEMS capacitive pressure sensor is connected to an external signal processing circuit to convert the resistance change into a voltage signal; the variable capacitor formed by the force-sensitive nanofilm (3) and the metal electrode layer (17) covering the surface of the stepped recessed structure (20) is connected to an external signal processing circuit to convert the capacitance change into a voltage signal; the two voltage signals are processed by a differential amplifier circuit to compensate for temperature, eliminate the temperature drift error in the pressure signal, and finally output the pressure measurement result.

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