Three-stage linkage differential capacitance sensor

Abstract

The invention relates to a three-level linkage differential capacitance sensor, which belongs to the technical field of micro electro mechanical sensors, and comprises a fixed support structure, three polar plates are horizontally arranged at the top of the fixed support structure at equal intervals along the vertical direction, and the polar plates and the fixed support structure as well as the adjacent polar plates are connected in an insulating and sealing manner; according to the invention, gas or liquid on the outer side of the sensor enters the middle cavity by using the vent holes, so that the pressure load of the gas or liquid acts on the three polar plates at the same time, and the pressure load of the gas or liquid is applied to the three polar plates at the same time; the three polar plates can deform at the same time, the gap between the two polar plates on the upper side is reduced, the capacitance between the polar plates is increased, the gap between the two polar plates on the lower side is increased, the capacitance between the polar plates is reduced, and the total output capacitance can be remarkably increased finally through differential output of the capacitance between the upper polar plate and the lower polar plate. And the sensitivity of the three-stage linkage differential capacitance sensor is greatly improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of micro-electromechanical sensors, and in particular relates to a three-stage linkage differential capacitance sensor. Background Art

[0002] Types of pressure sensors include piezoresistive, capacitive, piezoelectric, resonant, and inductive types. Compared with piezoresistive pressure sensors, capacitive pressure sensors have significant advantages such as good temperature stability, high sensitivity, low power consumption, simple and robust structure, and excellent dynamic response. Compared with piezoelectric, resonant, and inductive pressure sensors, capacitive pressure sensors have higher sensitivity and accuracy, can detect tiny pressure changes, and are suitable for use in medical equipment and gas detection equipment.

[0003] Capacitive pressure sensors primarily operate in variable spacing, variable area, and variable dielectric modes. Since variable spacing capacitive pressure sensors sense pressure based on capacitance changes, capacitance changes are only related to changes in spacing, and are less affected by electrode shape and dielectric influences. Therefore, variable spacing capacitive pressure sensors offer greater stability compared to the other two methods. However, the capacitance of a variable spacing capacitive pressure sensor is inversely proportional to the plate spacing. When the plate spacing changes, the relationship between the change in capacitance and the change in plate spacing becomes a high-order nonlinear function. This nonlinearity is primarily influenced by higher-order terms, leading to the inherent defect of large nonlinearity in existing variable spacing capacitive pressure sensors, resulting in low measurement accuracy.

[0004] Currently, in order to improve the measurement accuracy of variable-gap capacitance pressure sensors, existing technologies mostly use differential capacitance structures, such as two-dimensional differential capacitance sensors and 4H-SiC-based differential capacitance vacuum gauges. Variable-gap capacitance pressure sensors with differential capacitance structures can offset high-order nonlinear terms and reduce the impact of edge effects, improving the clarity and stability of sensor signals, thereby enhancing the signal-to-noise ratio, achieving a linear response of the variable-gap capacitance pressure sensor, reducing nonlinear errors, and improving the measurement accuracy of the pressure sensor. However, in the differential capacitance structure of existing variable-gap capacitance pressure sensors, only the middle plate undergoes parallel movement or deformation, causing changes in the upper and lower capacitances, resulting in a small total capacitance output, resulting in low sensitivity of the variable-gap capacitance pressure sensor. Summary of the Invention

[0005] In view of this, the present invention provides a three-stage linkage differential capacitance sensor to address the deficiencies in the prior art. The present invention can significantly increase the total output capacitance, thereby greatly improving the sensitivity of the three-stage linkage differential capacitance sensor.

[0006] The technical solution of the present invention is: a three-stage linkage differential capacitance sensor, including a fixed support structure. Three electrodes are horizontally arranged at equal intervals along the vertical direction on the top of the fixed support structure. The electrodes are insulated and sealedly connected to the fixed support structure and adjacent electrodes. Three cavities are formed between the electrodes and the fixed support structure and adjacent electrodes. The fixed support structure is provided with a ventilation hole. One end of the ventilation hole is communicated with the middle cavity, and the other end is communicated with the outside. The gas or liquid outside the sensor presses the uppermost electrode, and at the same time, the gas or liquid enters the middle cavity through the ventilation hole to press the other two electrodes, so that the three electrodes deform simultaneously.

[0007] Preferably, the fixed support structure includes: a substrate and two annular insulating members. A sunken groove is vertically opened in the middle of the top of the substrate. The three electrodes are arranged directly above the sunken groove. The lowermost electrode is insulated and sealedly fixed to the top of the substrate outside the mouth of the sunken groove. The two annular insulating members are respectively horizontally arranged between adjacent electrodes and are coaxial with the center line of the sunken groove. The annular insulating members are fixedly and sealedly connected to the electrodes. The longitudinal section of the ventilation hole is in an L shape. The vertical section of the ventilation hole is opened on the upper two electrodes and the two annular insulating members connected thereto, and its horizontal section is opened on the middle annular insulating member.

[0008] Preferably, the shape of the electrode is circular.

[0009] Preferably, the radius of the electrode is 145μm - 155μm.

[0010] Preferably, the radius of the electrode is 150μm.

[0011] Preferably, the thickness range of the electrode is 4μm - 5μm.

[0012] Preferably, the thickness of the electrode is 4.5μm.

[0013] Preferably, the thickness range of the annular insulating member is 2μm - 3μm.

[0014] Preferably, the thickness of the annular insulating member is 2.5μm.

[0015] Preferably, the material of the electrode is single crystal silicon.

[0016] Compared with the prior art, the present invention provides a three - stage linked differential capacitance sensor. Through a fixed - support structure, it is insulated and sealedly connected to three electrodes to form three cavities. Then, by using air vents, gas or liquid outside the sensor enters the middle cavity, so that the pressure load of the gas or liquid acts on the three electrodes simultaneously. Compared with the situation in the traditional differential capacitance structure where only the middle electrode undergoes parallel movement or deformation, it can achieve deformation of the three electrodes simultaneously, increasing the relative contact area between the electrodes. When the pressure of the external gas or liquid changes, the gap between the two upper electrodes decreases and the capacitance between the electrodes increases, while the gap between the two lower electrodes increases and the capacitance between the electrodes decreases. Through the differential output of the capacitance between the upper and lower electrodes, the total output capacitance can be significantly increased, thereby greatly improving the sensitivity of the three - stage linked differential capacitance sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a cross - sectional view of the three - stage linked differential capacitance sensor of the present invention; Figure 2 is a schematic diagram of the change in the state of the electrodes of the three - stage linked differential capacitance sensor of the present invention; Figure 3 is a top view of the three - stage linked differential capacitance sensor of the present invention; Figure 4 is a schematic diagram of the change in the state of the two upper electrodes of the sensor of the present invention; Figure 5 is a schematic diagram of the change in the state of the two lower electrodes of the sensor of the present invention; Figure 6 is a stress distribution diagram of the electrodes of the present invention, where (a) is the stress distribution diagram of a circular electrode and (b) is the stress distribution diagram of a square electrode; Figure 7 is a sensor output characteristic curve graph of circular and square electrodes of the present invention; Figure 8 is a sensor output characteristic curve graph of a circular electrode with a changed radius of the present invention, where (a) is the deflection curve graph of circular electrodes with different radii and (b) is the total capacitance curve graph of circular electrodes with different radii; Figure 9 is a sensor output characteristic curve of a circular electrode with a changed thickness of the present invention, where (a) is the deflection curve graph of circular electrodes with different thicknesses and (b) is the total capacitance curve graph of circular electrodes with different thicknesses; Figure 10 is a sensor output characteristic curve graph of an annular insulating part with a changed thickness of the present invention, where (a) is the deflection curve graph of annular insulating parts with different thicknesses and (b) is the total capacitance curve graph of annular insulating parts with different thicknesses; Figure 11 is a sensor sensitivity curve graph of an annular insulating part with different heights of the present invention; Figure 12 is the sensitivity curve graph of the sensor with different materials for the plate of the present invention; Figure 13 is the comparison schematic diagram of the sensitivity and linear response range of the sensor with different film thicknesses of the present invention; Figure 14 is the graph of the measuring range, linear response range and sensitivity of the sensor of the present invention; Figure 15 is the schematic diagram of the state change of the plate of the comparative analog differential capacitance structure; Figure 16 is the comparative graph of the linear response range and sensitivity between the sensor of the present invention and the existing differential capacitance structure sensor; Figure 17 is the stress nephogram when a pressure load is applied to the circular plate of the present invention. Specific embodiments

[0018] The present invention provides a three-stage linkage differential capacitance sensor. The following combines Figures 1 to 7 the structural schematic diagram to illustrate the present invention.

[0019] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "axial", "radial", "circumferential", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the technical solutions of the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention.

[0020] The working modes of capacitive pressure sensors mainly include variable spacing, variable area, and variable medium. Since the variable-spacing capacitive pressure sensor is a pressure sensing method based on capacitance change, the change in capacitance is only related to the change in spacing, and has a relatively small relationship with the shape of the electrode and the influence of the medium. Therefore, the variable-spacing capacitive pressure sensor has better stability than the other two methods. However, the capacitance of the variable-spacing capacitive pressure sensor is inversely proportional to the plate spacing. When the plate spacing changes, the relationship between the capacitance change amount and the plate spacing change amount is a high-order non-linear function, and the non-linearity is mainly affected by the high-order terms, which in turn leads to the inherent defect of large non-linearity in the existing variable-spacing capacitive pressure sensors, resulting in low measurement accuracy of the variable-spacing capacitive pressure sensors.

[0021] The capacitance is inversely proportional to the plate spacing. When the plate spacing changes, the relationship between the capacitance change amount and the spacing change amount is a high-order non-linear function, and the non-linearity is mainly affected by the high-order terms. The specific relationship formula is as follows: The capacitance is inversely proportional to the distance between the plates: In the above formula: C is the capacitance, is the permittivity, is the relative contact area between the plates, is the distance between the plates.

[0022] When the plate moves by the capacitance expression is: In the above formula: C is the capacitance, Ɛ is the absolute permittivity of the plate material, A is the relative contact area of the plates, d0 is the distance between the plates in the unloaded state, and x is the displacement of the plate when it is stressed.

[0023] Among them, the presence of quadratic and higher-order terms indicates its non-linear characteristics, and it can be approximated as linear if and only if is satisfied.

[0024] Therefore, there is a large non-linearity between the distance and the capacitance change of the existing variable-gap capacitance pressure sensor, which in turn affects the measurement accuracy of the variable-gap capacitance pressure sensor.

[0025] Currently, in order to improve the measurement accuracy of variable-gap capacitance pressure sensors, most sensors in the prior art adopt a differential capacitance structure, such as two-dimensional differential capacitance sensors, differential capacitance vacuum gauges based on 4H-SiC, etc. The variable-gap capacitance pressure sensor with a differential capacitance structure can cancel out the higher-order non-linear terms and reduce the influence of the edge effect, improve the clarity and stability of the sensor signal, thereby enhancing the signal-to-noise ratio, achieving a linear response of the variable-gap capacitance pressure sensor, reducing the non-linear error, and improving the measurement accuracy of the pressure sensor. Among them, the symmetry of the differential capacitance structure makes the distance change directions of the upper and lower capacitors opposite and approximately equal in magnitude. This complementary change makes the even-order non-linear terms in their capacitance change functions have the same sign. In the final difference output, these non-linear terms with the same sign cancel each other out, while the linear terms with opposite signs are enhanced, canceling the influence of the higher-order non-linear terms and improving the linearity. At the same time, the symmetry of the differential capacitance structure also ensures that the influence of the edge effect caused by environmental factors and manufacturing factors on the two sensing capacitors is highly similar. The differential signal suppresses or cancels the common-mode edge capacitance signal, reducing the influence of the edge effect on the measurement accuracy. However, in the differential capacitance structure of the existing variable-gap capacitance pressure sensor, only the middle plate moves parallel or deforms to cause changes in the upper and lower capacitances, resulting in a relatively small total capacitance output, and thus the sensitivity of the variable-gap capacitance pressure sensor is relatively low.

[0026] Based on the above problems, a three-stage linkage differential capacitance sensor provided by an embodiment of the present invention forms three cavities through an insulating and sealed connection of a fixed support structure with three electrode plates. Then, through vent holes, gas or liquid outside the sensor enters the middle cavity, so that the pressure load of the gas or liquid acts on the three electrode plates simultaneously. Compared with the situation where only the middle electrode plate undergoes parallel movement or deformation in the traditional differential capacitance structure, it is possible to achieve deformation of the three electrode plates simultaneously, increasing the relative contact area between the electrode plates. When the pressure of the external gas or liquid changes, the gap between the two upper electrode plates decreases and the capacitance between the electrode plates increases, while the gap between the two lower electrode plates increases and the capacitance between the electrode plates decreases. Through the differential output of the capacitance between the upper and lower electrode plates, the total output capacitance can be significantly increased, thereby greatly improving the sensitivity of the three-stage linkage differential capacitance sensor. The three-stage linkage differential capacitance sensor of the present invention has high sensitivity, high precision, and strong practicability, and is worthy of promotion.

[0027] Referring to Figure 1 , Figure 1 is a cross-sectional view of the three-stage linkage differential capacitance sensor of this embodiment. A three-stage linkage differential capacitance sensor includes a fixed support structure. Three electrode plates 2 are horizontally arranged at equal intervals in the vertical direction on the top of the fixed support structure. The electrode plates 2 are insulated and sealedly connected to the fixed support structure and adjacent electrode plates 2. The electrode plates 2 and the fixed support structure and adjacent electrode plates 2 form three cavities 7. The fixed support structure is provided with vent holes 1. One end of the vent hole 1 is communicated with the middle cavity 7, and the other end is communicated with the outside. The gas or liquid outside the sensor presses the uppermost electrode plate 2, and at the same time, the gas or liquid enters the middle cavity 7 through the vent hole 1 to press the other two electrode plates 2, so that the three electrode plates 2 deform simultaneously.

[0028] The three-stage linkage differential capacitance sensor in the above embodiment is a three-stage linkage differential capacitance sensing structure. The difference between this structure and the traditional differential capacitance structure is that all three electrode plates 2 are movable electrode plates. Gas or liquid such as silicone oil is introduced into the middle cavity 7 through the vent hole 1. When the pressure of the external gas or liquid such as silicone oil changes, the pressure load of the gas or liquid acts on the uppermost electrode plate 2. After the gas or liquid such as silicone oil enters the middle cavity 7, the pressure load acts on the other two electrode plates 2 simultaneously, so that the three electrode plates are subjected to the same pressure. Compared with the situation where only the middle electrode plate undergoes parallel movement or deformation in the existing differential capacitance structure, referring to Figure 2 , Figure 2This is a schematic diagram showing the state change of the plates of a three - stage linked differential capacitance sensor. This three - stage linked differential capacitance sensing structure has the following advantages: First, the three plates deform simultaneously, significantly increasing the relative contact area between the plates; Second, the gap between the two upper plates 2 decreases, increasing the capacitance between the plates, while the gap between the two lower plates 2 increases, reducing the capacitance between the plates. Through the differential output of the capacitance between the upper and lower plates, the total output capacitance is significantly increased, thereby greatly improving the sensitivity of the three - stage linked differential capacitance sensor.

[0029] In the above - mentioned embodiment, the total capacitance output by the three - stage linked differential capacitance sensor: The deflection function of the circular plate is: Among them, ω(r, θ) is the deflection function, r is the radial distance (radial coordinate), which is used to describe the distance from a certain point to the center (pole) in structures such as circular plates; θ is the polar angle (circumferential coordinate), which is used to describe the angular position of this point relative to a certain reference direction (such as the polar axis). By combining r and θ, the position of any point on the plane of the circular plate can be determined, so as to analyze the deflection conditions at different positions, thereby enabling the study of the deformation of the plate to be accurate to each specific point within the plane, P is the pressure load acting on the plate, D is the bending stiffness of the plate, R1 is the outer diameter of the plate, and R2 is the inner diameter of the plate (the radius located inside the cavity 7).

[0030] The bending stiffness D of the plate: Among them, E is the Young's modulus of the plate material, h1 is the thickness of the plate, and v is the Poisson's ratio of the plate material.

[0031] The maximum deflection occurs at the center point and its value is: Among them, ω max is the maximum deflection after the plate deforms, the negative sign represents the direction, W is the equivalent load, , m is the reciprocal of the Poisson's ratio, , h is the thickness of the plate, and R2 is the inner diameter of the circular plate.

[0032] For a two - plate linked non - contact pressure sensor with a circular plate, when the upper plate is subjected to a uniform pressure load, it will bend into a curved surface, and the displacement offsets at each point are different. Applying the mathematical differential idea, the plate is divided into a set of countless small regions. At this time , the tiny area of each small region is: Among them, dA is the area element of the circular plate, r is the radial distance, and dr is the element of the radial distance on the circular plate.

[0033] The tiny capacitance generated by each small area is: (1.12) where dC （P） is the tiny capacitance generated on a microelement at a certain point on the circular plate under the action of the pressure load, Ɛ0 is the absolute permittivity of vacuum, Ɛ r is the relative permittivity, representing the dielectric ability of the material relative to vacuum, d is the plate spacing, ω(r, θ) is the deflection function of the circular plate, dr is the microelement of the radial distance on the circular plate, dθ is the microelement of the polar angle on the circular plate, and C out is the total output capacitance of the sensor.

[0034] For the non-contact pressure sensor with two-plate linkage circular plates, when calculating the double integral of the output capacitance generated by the deformed circular plate, as shown in Equation (1.10), it is equivalent to calculating the volume of a volume column formed by projecting a two-dimensional circular surface onto the XOY plane in a three-dimensional coordinate system, as Figure 3 shown. However, for the three-stage linkage differential capacitance sensor structure proposed in the above embodiment, when the plate deforms, the projection of the two-dimensional circular surface is not a plane but a curved surface. If calculated according to Equation (1.12) above, the error will be very large and it is not applicable to the calculation of the output capacitance of the three-stage linkage differential capacitance pressure sensor.

[0035] Therefore, a method is proposed to fictitiously create a plane at the middle position between the upper two cavities 7 when the plate deformation reaches the maximum within the sensor range, and approximate calculations are made as if there is a hypothetical plate at this position.

[0036] Referring to Figure 4 、 Figure 5 , Figure 4 is a schematic diagram of the state change of the upper two plates of the sensor, Figure 5 is a schematic diagram of the state change of the lower two plates of the sensor. The differential capacitance structure is abstracted into two capacitors, upper and lower. The dotted line in the figure represents the fictitiously created plate plane at the middle position between the two cavities.

[0037] The distance between the center points of the upper two plates and the fictitiously created plate plane is ,the distance between the center points of the upper two plates and the fictitiously created plate plane is ,the distance between the center points of the upper two plates is ,the distance between the center points of the lower two plates is ,where d is the plate spacing and ω is the deflection magnitude of the plate at a certain moment under the action of the pressure load.

[0038] The output capacitance of the upper two plates: Output capacitance of the two lower plates: Total output capacitance: Among them, C 12 is the output capacitance of the two upper plates, C 23 is the output capacitance of the two lower plates, C out is the total output capacitance of the sensor, R2 is the inner diameter of the circular plate, Ɛ0 is the absolute permittivity of vacuum, Ɛ r is the relative permittivity, representing the dielectric ability of the material relative to vacuum, r is the radial distance, 1 / 2d is half of the plate spacing, ω(r, θ) is the deflection function of the circular plate, dr is the differential element of the radial distance on the circular plate, and dθ is the differential element of the polar angle on the circular plate.

[0039] As a further optimization scheme, a specific composition of a fixed support structure is given in this embodiment. The fixed support structure includes a substrate 6 and two annular insulating members 5. A sinking groove 61 is vertically opened in the middle of the top of the substrate 6. Three plates 2 are arranged directly above the sinking groove 61. The lowermost plate 2 is fixedly connected to the top of the substrate 6 outside the mouth of the sinking groove 61 in an insulating and sealed manner. The two annular insulating members 5 are respectively horizontally arranged between adjacent plates 2 and are coaxial with the center line of the sinking groove 61. The annular insulating members 5 are fixedly and sealedly connected to the plates 2. The longitudinal section of the ventilation hole 1 is in an L shape. The vertical section of the ventilation hole 1 is opened on the two upper plates 2 and the two annular insulating members 5 connected thereto, and its horizontal section is opened on the middle annular insulating member 5.

[0040] In this embodiment, the fixed support structure is composed of a substrate 6 and two annular insulating members 5. Three plates 2 are horizontally arranged at equal intervals along the vertical direction on the sinking groove 61 opened on the top of the substrate 6. Among them, the lowermost plate 2 is fixedly and sealedly connected to the top of the substrate 6 outside the mouth of the sinking groove 61 in an insulating manner. The lowermost cavity 7 is formed by the sinking groove 61 opened on the top of the substrate 6 and the lowermost plate 2. The two annular insulating members 5 are used to fixedly and sealedly connect the three plates 2, thereby obtaining the other two cavities 7. The longitudinal section of the ventilation hole 1 is in an L shape. Its vertical section is opened on the two upper plates 2 and the two annular insulating members 5 connected thereto, and the horizontal section is opened on the middle annular insulating member 5, realizing the connection between the ventilation hole 1 and the cavity 7 in the middle, and the cavities 7 on the upper and lower sides are in a vacuum state.

[0041] In the above embodiment, the longitudinal section of the ventilation hole 1 is in an L shape. When the pressure load of gas or liquid such as silicone oil outside the sensor acts on the uppermost plate 2, it quickly enters the middle cavity 7 through the vertical section of the ventilation hole 1, further improving the synchronization of the pressure load acting on the three plates.

[0042] Analysis of the structural characteristics of the three-stage linkage differential capacitance sensor: As a further optimization solution, the shape of the electrode plate 2 in this embodiment is circular.

[0043] The influence of plate shape on output characteristics: In the optimized design of electrode plates, the choice of geometric shape directly influences the stress distribution characteristics, which in turn determines the sensitivity performance of the sensor. In the structural design system of three-stage differential capacitance sensors, circular and square electrode plates are two typical geometric configurations and are widely used in various design schemes. This example compares the stress and sensitivity of circular and square electrode plates of the same size to determine the performance characteristics corresponding to the two electrode shapes.

[0044] The dimensions of the structural model are as follows: the plate diameter and side length are 200 μm, the plate thickness is 3 μm, and the spacing between the upper and lower plates is 4 μm. The material selection for each area of the structural model is shown in Table 3-2. The stress distribution diagrams of the circular and square plates are obtained by simulation. Figure 6 , Figure 6 The stress distribution diagrams of the plates of this embodiment are shown in Figure 2. (a) is the stress distribution diagram of a circular plate, and (b) is the stress distribution diagram of a square plate.

[0045] Table 3-2 Materials in various areas of the structural model Under the action of external pressure load, the stress distribution of the square plate shows completely different characteristics from that of the circular plate. Through finite element analysis and stress testing, it can be seen that the stress distribution of the square plate has obvious non-uniformity. The stress in the central area is relatively small, and as the distance from its center increases, the stress value gradually increases. The maximum stress of the plate is concentrated in the central part of the edge of the plate, and its value is measured to be about 335MPa. At the same time, the stress level in the four corner areas of the plate is low. In contrast, the stress distribution of the circular plate of the same size shows significant uniformity, and the overall stress level is significantly lower than that of the square plate. It can be seen that in the design of the three-stage linkage differential capacitance sensor chip, the use of circular plates can effectively reduce the stress level compared to square plates, and achieve a more uniform stress distribution, thereby improving the stability and reliability of the sensitive structure.

[0046] Reference Figure 7 , Figure 7 The following graph shows the sensor output characteristic curves for circular and square plates in this embodiment. The circular and square plates have identical dimensions. As can be seen from the graph, when the plates are subjected to pressure loads, they remain in a non-contact state. The pressure sensor output capacitance increases slowly with increasing pressure, with the square plate having a higher output capacitance than the circular plate.

[0047] By calculation, in the range of 0~200kPa, the output capacitance change of the circular plate is 0.04pF, the sensitivity is 0.22fF / kPa, and the output capacitance change of the square plate is 0.05pF, and the sensitivity is 0.28fF / kPa. It can be seen that under the same size conditions, the sensitivity of pressure sensor chips with different plate shapes is not much different. As mentioned above, the circular plate exhibits a more uniform stress distribution characteristic, and the maximum stress value is significantly lower than that of the square plate. The maximum stress of the square plate is about 1.5 times that of the circular plate, that is, the overload protection capability is about 1.5 times higher than that of the square plate, and as the plate size continues to increase, the overload capacity gap between the circular and square plates shows a trend of further expansion.

[0048] Therefore, the circular electrode plate has higher reliability when subjected to pressure overload, so the electrode plate of the three-stage linkage differential capacitance sensor in this embodiment is circular.

[0049] The influence of plate radius on output characteristics Reference Figure 8 , Figure 8 The output characteristic curves of the sensor with different circular plates of this embodiment are obtained by changing the radius of the plates without changing other conditions of the sensitive structure. (a) is the deflection curve of circular plates with different radii, and (b) is the total capacitance curve of circular plates with different radii. Figure 8 It can be seen that different plate radii result in different deflections, linear working ranges, and output characteristic curves.

[0050] When other structural parameters remain unchanged, the larger the plate radius, the higher the sensitivity. This is because an increase in the plate radius will increase the relative contact area between the plates. Furthermore, plates with larger radii will have greater deflection when subjected to the same pressure load, resulting in differences in the electric field distribution between the plates, thereby increasing the output capacitance. Therefore, the larger the plate radius, the greater the sensitivity of the sensitive structure. However, when other conditions remain unchanged, the larger the radius, the greater the stress on the circular plate under the influence of the pressure load, and the worse the overload characteristics will be. Therefore, it is necessary to comprehensively consider these two factors to determine the plate radius.

[0051] Through finite element simulation and data processing, we obtained the data shown in Table 3-3. When R1=150μm, the linear working range is 0~170kPa; when R1=170μm, the linear working range is 30kPa~110kPa.

[0052] Table 3-3 Effect of changing only the plate radius on output characteristics Through comparative analysis and comprehensive consideration of two factors, the radius range of the electrode plate 2 is 145 μm to 155 μm.

[0053] In this embodiment, the radius of the electrode plate 2 is 145 μm.

[0054] In this embodiment, the radius of the electrode plate 2 is 150 μm.

[0055] In this embodiment, the radius of the electrode plate 2 is 155 μm.

[0056] As a further optimization scheme, in this embodiment, the radius of the electrode plate 2 is 150 μm considering the sensitivity and linear response range of the electrode plate 2 comprehensively.

[0057] Influence of the electrode plate thickness on the output characteristics The thickness of the electrode plate affects the deflection of the electrode plate, and the change of the deflection will affect the electrode plate spacing and the electric field distribution between the electrode plates, and further affect the output characteristics of the sensitive structure. Therefore, in this embodiment, other parameters of the structure are controlled to be unchanged, and by comparing the output characteristics of the sensitive structures composed of electrode plates with different thicknesses, a suitable electrode plate thickness is selected.

[0058] When the radius of the electrode plate is 150 μm and the thickness of the annular insulating part 5 is 6 μm, finite element simulations are carried out on different electrode plate thickness models, and the following results are obtained: Refer to Figure 9 , Figure 9 is the output characteristic curve of the sensor with the circular electrode plate of this embodiment changing the thickness. Among them, (a) is the deflection curve graph of the circular electrode plates with different thicknesses, and (b) is the total capacitance curve graph of the circular electrode plates with different thicknesses. Through Figure 9 It can be seen that the deflections at the center positions of the electrode plates with different thicknesses, the output capacitance, sensitivity, and linearity of the sensitive structure will all be different. The data is shown in Table 3-4: Table 3-4 Influence of changing the electrode plate thickness on the output characteristics As can be seen from Table 3-4, without changing other parameters of the structure, the smaller the thickness of the electrode plate, the higher the sensitivity, but a certain linear response range will be sacrificed, and appropriately increasing the thickness of the electrode plate can improve the stability of the sensing structure and extend the service life of the sensor.

[0059] Comprehensively considering the sensitivity and linear response range performance indicators of the sensitive structure, the thickness range of the electrode plate 2 is 4 μm to 5 μm.

[0060] In this embodiment, the thickness of the electrode plate 2 is 4 μm.

[0061] In this embodiment, the thickness of the electrode plate 2 is 4.5 μm.

[0062] In this embodiment, the thickness of the electrode plate 2 is 5 μm.

[0063] As a further optimization scheme, in this embodiment, considering the sensitivity and linear response range of the electrode plate 2 comprehensively, the thickness of the electrode plate 2 is 4.5 μm.

[0064] Influence of the thickness of the annular insulating part (spacing height between the electrode plates) on the output characteristics For a variable-gap capacitive sensor, the thickness of the annular insulating part is the determining factor affecting the spacing between the electrode plates, and thus affects the output capacitance and other output characteristics of the structure.

[0065] Establish a pressure sensor simulation model: the radius of the electrode plate is 150 μm, the thickness of the electrode plate is 4.5 μm, and other conditions are kept unchanged. The thicknesses of the annular insulating parts are set to 3 μm, 4 μm, 5 μm, and 6 μm respectively. By comparing the output characteristics of the sensitive structures with different thicknesses of the annular insulating parts, select the annular insulating part with a suitable thickness.

[0066] Refer to Figure 10 , Figure 10 is the output characteristic curve graph of the sensor with the thickness of the annular insulating part changed in this embodiment. Among them, (a) is the deflection curve graph of the annular insulating parts with different thicknesses, and (b) is the total capacitance curve graph of the annular insulating parts with different thicknesses. It can be seen that the change in the thickness of the annular insulating part does not affect the deflection. Under the action of the maximum pressure load, the deflection is 1.0071 μm, and at this time, no contact occurs between the three electrode plates. Through data processing, Table 3-6 is obtained:

[0067] Table 36 Sensitivity and linear response range corresponding to different thicknesses of the annular insulating part with other dimensional parameters being the same Refer to Figure 11 , Figure 11 is the sensitivity curve graph of the sensor with different thicknesses of the annular insulating part in this embodiment. When the other dimensional parameters of the sensitive structure remain unchanged, the sensitivity decreases with the increase in the thickness of the annular insulating part. In order to improve the sensitivity and accuracy of the structure. Therefore, the thickness range of the annular insulating part 5 is 2 μm to 3 μm.

[0068] In this embodiment, the thickness of the annular insulating part 5 is 2 μm.

[0069] In this embodiment, the thickness of the annular insulating part 5 is 2.5 μm.

[0070] In this embodiment, the thickness of the annular insulating part 5 is 3 μm.

[0071] As a further optimization scheme, in this embodiment, considering the sensitivity and linear response range of the electrode plate 2 comprehensively, the thickness of the annular insulating part 5 is 2.5 μm.

[0072] As described above, when the radius of the electrode plate 2 ranges from 145 μm to 155 μm, the difference between the inner and outer diameters of the annular insulating member 5 ranges from 5 μm to 155 μm, that is, the radius of the inner part of the electrode plate 2 inside the annular insulating member 5 ranges from 130 μm to 150 μm, and the height of the substrate is 8 μm.

[0073] In addition, the diameter of the vent hole 1 is smaller than the thickness of the annular insulating member.

[0074] Influence of different electrode plate materials on output characteristics: Selection of materials: In the design of the sensitive structure, the output characteristics of the structure are closely related to the electrode plate material. Under the condition that other conditions are controlled unchanged, the smaller the Young's modulus, the greater the sensitivity of the sensitive structure, and the greater the Poisson's ratio, the greater the sensitivity of the sensitive structure. This is because both the Young's modulus and the Poisson's ratio will affect the deformation degree of the electrode plate.

[0075] Therefore, in this embodiment, structures with exactly the same size are established, and the electrode plate materials are respectively selected as Si<100>, SiC, and Si3N4. The specific parameters of the materials are shown in Table 3-7: Table 3-7 Specific parameters of different materials As shown in Table 3-7, the density of single-crystalline silicon with <100> crystal orientation is lower than the latter two. As the electrode plate material, it has good flexibility, lower local yield strength, and allows a larger range of elastic deformation. At the same time, the relative dielectric constant of single-crystalline silicon with <100> crystal orientation is higher, and a larger capacitance change can be generated under the same deformation amount. It can also suppress the interference of edge effects and parasitic capacitance on measurement. Refer to Figure 12 , Figure 12 This is the sensitivity curve graph of the sensor with different materials used for the electrode plate in this embodiment.

[0076] By processing the data, Table 3-8 is obtained: Table 3-8 Comparison of sensitivity performance when changing the thickness with different electrode plate materials Through comparative analysis, it is obtained that when other parameters of the structure remain unchanged, when using single-crystalline silicon, silicon carbide, and silicon nitride as the electrode plate materials and only changing the film thickness, the sensitivity performance of the single-crystalline silicon electrode plate is significantly better than the latter two. Therefore, the electrode plate is selected to be made of single-crystalline silicon material.

[0077] In the above embodiment, the material of the substrate 6 is single-crystalline silicon, and the material of the annular insulating member is silicon dioxide.

[0078] Influence of single-crystalline silicon crystal orientation on output characteristics: <100>oriented single-crystalline silicon has good interface quality, is easy to process, and the surfaces of <100> and <111> oriented single-crystalline silicon are flat, with small surface energy and stable structure, which are suitable for the manufacture of large-scale integrated circuit devices. Mechanically, compared with <111> oriented single-crystalline silicon, <100> oriented single-crystalline silicon has a smaller Young's modulus and a larger Poisson's ratio. When used as the plate material, it has a smaller bending stiffness, which can make the plate deflection larger and the output capacitance value larger. For the differential structure, <100> oriented single-crystalline silicon can increase the change amount of the differential capacitance signal and improve the sensitivity of the pressure sensor. Therefore, <100> oriented single-crystalline silicon is selected as the plate material of the sensitive structure.

[0079] Optimal Design of the Chip Size of the Pressure Sensor In order to obtain a more sensitive sensitive structure, in this embodiment, the thickness of the annular insulator is made to the limit so that the plates do not touch and there is a small distance margin. The deflections of the center points of the plates at different thicknesses are obtained through simulation, as shown in Table 39:

[0080] Table 39 Thicknesses of the Limit Annular Insulators Corresponding to Different Plate Thicknesses When the thicknesses of the annular insulators at each film thickness in the above table are taken as the limit values, a simulation model is established, and the respective output characteristic curves are obtained. Through linear fitting, the approximate sensitivity and linear response range are obtained. Refer to Figure 13 , Figure 13 which is the comparison diagram of the sensitivities and linear response ranges of the sensors with different film thicknesses in this embodiment. It can be seen that obtaining high-sensitivity performance requires sacrificing a certain linear response range. Therefore, the plate thickness of this structure is selected as 4.5 μm, and the depth of the sinking groove is selected as 2.5 μm.

[0081] Final Dimensions of the Structure, Comparison with the Traditional Structure, and Feasibility Analysis: Final Dimensions of the Structure: Based on the above research and analysis, considering the application scenarios of the three-stage linked differential capacitance pressure sensor, the structural parameters of the optimized sensitive structure with a measuring range of 0~200 kPa are given in Table 3-10: Table 310 Optimized Sensitive Structure Dimension Parameters Through simulation with the COMSOL finite element analysis software, the optimized output characteristic curve is obtained. Refer to Figure 14 , Figure 14This is the graph of the measurement range, linear response range, and sensitivity of the sensor in this embodiment. The electrodes of the pressure sensor are always in a non-contact state. When the applied pressure is in the range of 0 - 120 kPa, it is in the linear response range, and the output capacitance increases linearly with the increase of the pressure load. When the applied pressure is in the range of 120 kPa - 200 kPa, it enters the non-linear range, and the output capacitance increases rapidly with the increase of the pressure load.

[0082] After data processing, the following results are obtained. The measurement range of the three-stage linked differential capacitance sensitive structure of the present invention is 0 - 200 kPa, the linear response range is 0 - 120 kPa, and the sensitivity is 0.57 fF / kPa.

[0083] Comparison with the traditional differential variable pole distance capacitive sensitive structure: For the convenience of comparison, a traditional variable distance differential capacitance structure with the same conditions is established in the embodiment. The upper and lower electrodes are simulated and set as fixed structures (non-deformable), and the pressure load is applied to the lower surface of the middle electrode. All other simulation settings are the same as those of the three-stage linked differential capacitance sensor structure of the present invention. Refer to Figure 15 , Figure 15 This is the schematic diagram of the change in the state of the electrodes of the traditional variable distance differential capacitance structure in the comparative example.

[0084] Through finite element simulation, it is obtained that, referring to Figure 16 , Figure 16 This is the graph comparing the linear response range and sensitivity of the three-stage linked differential capacitance sensor of the present invention with the traditional variable distance differential capacitance structure sensor in the comparative example. It can be seen from the graph that within the measurement range of 0 - 200 kPa, the total output capacitance change range of the three-stage linked differential capacitance sensor of the present invention is larger, which is 0.12 pF, while the output capacitance change range of the traditional variable distance differential capacitance structure sensor in the comparative example is smaller, which is 0.04 pF. This shows that the three-stage linked differential capacitance sensor of the present invention can obtain higher sensitivity performance. Within the measurement range, both sensor structures show good linear responses in the range of 0 - 120 kPa, and the total output capacitance increases linearly with the increase of the pressure. However, when it exceeds 120 kPa, the output capacitance of the three-stage linked differential capacitance sensor of the present invention increases rapidly and becomes non-linear, while the traditional variable distance differential capacitance structure sensor in the comparative example still maintains a good linear response.

[0085] By processing the data, Table 4-1 is obtained: Table 41 Performance parameters of the pressure sensor chips with three-stage linked differential capacitance structure and traditional structure According to the results of finite element simulation, the sensitivity of the three-stage linked differential capacitance sensor of the present invention is about 2.4 times that of the traditional variable pitch differential capacitance structure sensor in the comparative example, but the linear working range is smaller than that of the traditional structure. Therefore, for high-sensitivity measurement within a small pressure range, the three-stage linked differential capacitance sensor of the present invention is a better choice.

[0086] Feasibility analysis: Analysis of the overload characteristics of the electrode plate: The overload capacity of the sensitive structure depends on the maximum stress on the surface of the electrode plate and the tensile strength of the electrode plate material. The maximum stress of the electrode plate increases as the stress of the electrode plate increases. When the maximum stress exceeds the tensile strength, the electrode plate will break, and the overload capacity is the maximum applied pressure that the sensing electrode plate can withstand.

[0087] The fracture strength of single-crystal silicon material is not fixed. When the size changes, the fracture strength also changes. Since the radius size of the electrode plate is much larger than its thickness, the influence of the radius on the tensile strength can be ignored. The tensile strength of the electrode plate is mainly affected by its thickness. The relationship function between the tensile strength of the circular electrode plate and its thickness is as follows:

[0088] Among them, is the tensile strength of the electrode plate, is the thickness of the single-crystal silicon electrode plate.

[0089] Substituting the electrode plate thickness h = 4.5 μm into the above formula (1.23), the tensile strength of the three-stage linked differential capacitance sensitive structure can be obtained as 6.88 GPa.

[0090] When a pressure load of 200 kPa is applied to the optimized-sized circular electrode plate, the maximum stress on the surface of the electrode plate is 100 MPa. Referring to Figure 17 , Figure 17 which is the stress nephogram when the pressure load is applied to the circular electrode plate in this embodiment, and it is less than its tensile strength. Therefore, the three-stage linked differential capacitance sensor of the present invention will not break during normal operation.

[0091] Verification of the correctness of the theoretical formula: According to the formula derivation of the sensitivity formula of the traditional sensitive structure described above, it can be obtained that So Among them, C 12 (traditional) is the output capacitance of the upper two electrode plates of the traditional variable pitch differential capacitance structure sensor in the comparative example, and C 23 (traditional) is the output capacitance of the lower two electrode plates of the traditional variable pitch differential capacitance structure sensor in the comparative example, and C out(Traditional) is the total output capacitance of the proportional traditional variable pitch differential capacitance structure sensor, R2 is the inner diameter of the circular plate, Ɛ0 is the absolute permittivity of vacuum, Ɛ r is the relative permittivity, representing the dielectric ability of the material relative to vacuum, r is the radial distance, d is the plate spacing, ω(r, θ) is the deflection function of the circular plate, dr is the differential element of the radial distance on the circular plate, dθ is the differential element of the polar angle on the circular plate, S is the sensitivity of the three-stage linked differential capacitance sensor, and S(Traditional) is the sensitivity of the proportional traditional variable pitch differential capacitance structure sensor.

[0092] Calculated by Matlab, the sensitivity of the three-stage linked differential capacitance sensor in this embodiment is about 2.3 times that of the traditional differential sensitive structure, and the result obtained by simulation is about 2.4 times. The difference between the two is not significant. It can be concluded that the sensitivity formula and output capacitance formula derived from the foregoing embodiments are true and reliable.

[0093] Using the finite element method, the performance of the three-stage linked differential capacitance sensor constructed in this embodiment is simulated and analyzed. The results show that the sensitivity of the three-stage linked differential capacitance sensor in this embodiment is about 2.4 times that of the traditional differential capacitance structure, and the linear response range is 0~120 kPa, which has been significantly improved. It can be used for meteorological monitoring in high-altitude and low-pressure environments, human respiration, pulse, blood pressure monitoring, etc., and has high application value.

[0094] The above-disclosed are only the preferred specific embodiments of the present invention. However, the embodiments of the present invention are not limited thereto, and any changes that can be thought of by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A three - stage linked differential capacitance sensor, characterized in that, Comprising: Fixed support structure; Three electrodes (2), horizontally arranged at equal intervals in the vertical direction on the top of the fixed support structure. The electrodes (2) are insulated and sealedly connected to the fixed support structure and adjacent electrodes (2). Three cavities (7) are formed between the electrodes (2) and the fixed support structure and adjacent electrodes (2). An air vent hole (1) is provided on the fixed support structure. One end of the air vent hole (1) communicates with the middle cavity (7), and the other end communicates with the outside. The gas or liquid outside the sensor presses the uppermost electrode (2), and at the same time, the gas or liquid enters the middle cavity (7) through the air vent hole (1) to press the other two electrodes (2), so that the three electrodes (2) are deformed simultaneously.

2. The triple-linked differential capacitance sensor according to claim 1, characterized in that The fixed support structure includes: a substrate (6) and two annular insulating members (5). A sunken groove (61) is vertically provided in the middle of the top of the substrate (6). The three electrodes (2) are arranged directly above the sunken groove (61). The lowermost electrode (2) is insulated and fixedly sealedly connected to the top of the substrate (6) outside the mouth of the sunken groove (61). The two annular insulating members (5) are respectively horizontally arranged between adjacent electrodes (2) and are coaxial with the center line of the sunken groove (61). The annular insulating members (5) are fixedly and sealedly connected to the electrodes (2). The longitudinal section of the air vent hole (1) is L-shaped. The vertical section of the air vent hole (1) is provided on the upper two electrodes (2) and the two annular insulating members (5) connected thereto, and its horizontal section is provided on the middle annular insulating member (5).

3. The triple-linked differential capacitance sensor according to claim 2, characterized in that, The shape of the electrode (2) is circular.

4. The three-stage linked differential capacitance sensor according to claim 3, characterized in that, The radius range of the electrode (2) is 145 μm to 155 μm.

5. The triple-linked differential capacitance sensor according to claim 4, wherein, The radius of the electrode (2) is 150 μm.

6. The triple-linked differential capacitance sensor according to claim 2, wherein The thickness range of the electrode (2) is 4 μm to 5 μm.

7. The triple-linked differential capacitance sensor according to claim 6, wherein The thickness of the electrode (2) is 4.5 μm.

8. The three-stage linkage differential capacitance sensor according to claim 2, wherein The thickness range of the annular insulating member (5) is 2 μm to 3 μm.

9. The triple-linked differential capacitance sensor according to claim 8, characterized in that The thickness of the annular insulating member (5) is 2.5 μm.

10. The triple-linked differential capacitance sensor according to claim 2, wherein, The material of the electrode (2) is single crystal silicon.

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