Capacitance floating unit shear stress chip with acceleration detection and compensation functions

Abstract

The invention discloses a capacitance floating unit shear stress chip with acceleration detection and compensation functions, and relates to a shear stress measurement chip. According to the chip, the displacement response of the floating unit under the action of incoming flow shear stress is detected by using the differential capacitor comb teeth, and then the shear stress is calculated. The chip comprises a capacitance sensitive layer, a shielding layer and a shear stress sensitive layer from top to bottom. The chip is provided with two groups of floating units, one group of floating units senses the shear stress, and the other group of floating units senses the acceleration, so that the synchronous detection and compensation function of the shear stress and the acceleration in a single chip can be realized. And the influence of the external environment on the comb tooth structure of the differential capacitor is avoided through the buried design, and the range is widened and the detection stability is improved through the closed-loop electrostatic driving force. The chip has the characteristics of high-precision shear stress detection, internal acceleration detection and decoupling.

Description

Technical Field

[0001] This invention relates to shear stress measurement chips, and more particularly to a capacitive floating unit shear stress chip with acceleration detection and compensation functions. Background Technology

[0002] Shear stress sensors are crucial measurement tools in aerodynamic experiments, playing an irreplaceable role in boundary layer flow analysis, precise measurement of surface friction drag, and aerodynamic optimization of aircraft. This technology facilitates in-depth research into complex phenomena such as laminar-turbulent transition, shock wave / boundary layer interaction, and separated flows, thereby improving the performance of hypersonic vehicles. Shear stress measurement methods are divided into indirect and direct methods. The shear stress detection using a capacitive floating unit shear stress chip with acceleration detection and compensation functions, as described in this invention, falls under the category of direct measurement methods. It boasts advantages such as high accuracy, high sensitivity, and ease of miniaturization through microelectromechanical processes, making it a promising candidate for application in the aerospace field.

[0003] In the existing floating unit shear stress chip technology, there is often only one set of floating units used to sense shear stress, ignoring the external acceleration coupling effect. However, when the floating unit shear stress chip senses external shear stress, the acceleration coupling field acts on the floating unit, and the inertial force is incorrectly included in the shear stress measurement value, resulting in the problem that the measurement error is difficult to eliminate and the flight-borne limitation is large. These problems together hinder the practical application of floating unit shear stress detection technology. [1] V. Chandrasekharan, J. Sells, J. Meloy, DP Arnold, and M. Sheplak, "A Microscale Differential Capacitive Direct Wall-Shear-Stress Sensor," J. Microelectromech. Syst., vol. 20, no. 3, pp. 622-635, June. 2011, doi:10.1109 / jmems.2011.2140356. Summary of the Invention

[0004] The purpose of this invention is to solve the problem of acceleration decoupling in the measurement of fluid wall shear stress by floating unit shear stress sensors, and to provide a capacitive floating unit shear stress chip with acceleration detection and compensation functions for direct measurement of wall shear stress. This chip uses differential capacitance comb teeth to detect the displacement response of the floating unit under the action of incoming flow shear stress, and then calculates the magnitude of the shear stress. This chip can directly achieve acceleration decoupling of shear stress measurement within a single chip, effectively eliminating the interference of inertial force on the shear stress measurement value, and has the advantages of wide measurement range, good stability, and strong environmental adaptability.

[0005] To achieve the above-mentioned objectives, the present invention provides the following parameters.

[0006] A shear stress chip with capacitor floating unit and acceleration detection and compensation functions comprises, from top to bottom, a capacitor-sensitive layer, a shielding layer, and a shear stress-sensitive layer, fabricated using the multilayer material properties of silicon-on-insulator (SOI). The capacitor-sensitive layer is made of silicon, the shielding layer of silicon dioxide, and the shear stress-sensitive layer of silicon. When shear stress acts on the surface of the floating unit, the floating unit causes displacement of the folded beam-capacitor comb structure, inducing a symmetrical change in the gap between the differential capacitor plates. The capacitance signal, after demodulation by an ASIC circuit, enables accurate detection of shear stress. The chip of this invention, by arranging two sets of floating units—one set sensing shear stress and the other sensing acceleration—achieves decoupling of shear stress and acceleration within a single chip, and can also measure shear stress and acceleration independently. Furthermore, the embedded design avoids the influence of the external environment on the differential capacitor comb structure.

[0007] The capacitance-sensitive layer consists of shear stress floating units, acceleration floating units, fixed differential comb teeth, shear stress floating unit differential comb teeth, acceleration floating unit differential comb teeth, force feedback differential comb teeth, upper shear stress folded beams, lower shear stress folded beams, upper acceleration folded beams, lower acceleration folded beams, and anchor points. The shear stress floating units and acceleration floating units are located on the left and right sides of the chip, respectively connected to the anchor points via shear stress folded beams, lower shear stress folded beams, upper acceleration folded beams, and lower acceleration folded beams. Release holes are distributed on the acceleration floating units. The fixed differential comb teeth, along with the shear stress floating unit differential comb teeth, acceleration floating unit differential comb teeth, and force feedback differential comb teeth, form three sets of capacitance comb tooth detection structures. The anchor points are located on the upper and lower sides of the other structures. The capacitance-sensitive layer is made of silicon and is fabricated using an SOI (silicon-on-insulator) device layer.

[0008] The shielding layer is located between the capacitance-sensitive layer and the shear stress-sensitive layer, and includes an anchor connection area and a floating unit connection area. The shielding layer is made of silicon oxide material and is prepared by SOI buried oxide layer etching to support the chip structure.

[0009] The shear stress sensitive layer consists of a floating unit pressure-sensitive membrane and a support layer. The floating unit pressure-sensitive membrane is located on the side of the shear stress sensitive layer, directly opposite the shear stress floating unit. There is an movable gap between the floating unit pressure-sensitive membrane and the support layer. The shear stress sensitive layer is made of silicon material and is fabricated through an SOI substrate.

[0010] The chip is equipped with two sets of floating units. One set of floating units senses shear stress, and the other set senses acceleration. By adjusting the comb structure and inertial mass of the two sets of floating units, the two sets of differential signals after the two sets of floating units are subjected to acceleration cancel each other out, thus achieving acceleration decoupling.

[0011] The shear stress floating unit of the chip can detect the shear stress of the external fluid wall independently, or it can be used in conjunction with the acceleration floating unit to achieve acceleration decoupling.

[0012] The chip's acceleration floating unit can detect uniaxial acceleration and can also be used in conjunction with a shear stress floating unit to achieve acceleration decoupling.

[0013] The chip's shear stress floating unit has force feedback differential comb teeth arranged on its upper and lower sides to provide electrostatic driving force, which can realize closed-loop driving and expand the detection range and detection stability.

[0014] The areas where the fixed differential comb teeth, shear stress floating unit differential comb teeth, acceleration floating unit differential comb teeth, and force feedback differential comb teeth are located are separated by etching silicon material for subsequent capacitance detection.

[0015] The shear stress floating unit of the capacitance sensitive layer and the floating unit pressure-sensitive membrane of the shear stress sensitive layer are on the same axis but arranged in layers. They are connected by the floating unit connection area of ​​the shielding layer. The floating unit is exposed to the flow field upward, and the capacitance detection sensitive comb is buried downward in the encapsulation shell.

[0016] Shear stress floating unit, acceleration floating unit, fixed differential comb teeth, shear stress floating unit differential comb teeth, acceleration floating unit differential comb teeth, force feedback differential comb teeth, upper shear stress folded beam, lower shear stress folded beam, upper acceleration folded beam, lower acceleration folded beam, and a grounding layer is arranged around the anchor point.

[0017] The chip thickness is 200-500 mm. The radius is 4000-6000 .

[0018] The shielding layer thickness is 2-6 mm. .

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] 1) Eliminating the effects of acceleration coupling: By adjusting the comb structure and inertial mass of the two sets of floating units (shear stress floating unit and acceleration floating unit), the two floating units generate differential capacitance signals with equal amplitude and opposite polarity in response to acceleration. In the detection circuit, these two signals cancel each other out, thus enabling the accurate separation of the pure shear stress signal from the complex coupling signal, fundamentally solving the problem of measurement inaccuracy of traditional sensors under vibration or high overload conditions.

[0021] 2) Expanding the measurement range and improving detection stability: By integrating force feedback differential comb teeth on both sides of the shear stress floating unit, a highly efficient closed-loop control mechanism is introduced. When the floating unit is displaced due to shear stress, the system dynamically stabilizes it near the equilibrium position by applying an opposite electrostatic feedback force in real time. This closed-loop working mode not only expands the linear measurement range of the sensor by an order of magnitude, but also significantly suppresses the nonlinearity and transient oscillations of the mechanical structure, thereby ensuring high accuracy and high stability in measurements over a wide range.

[0022] 3) Achieving Multifunctional Integration and High Environmental Adaptability: This invention integrates shear stress measurement, acceleration measurement, and acceleration compensation functions on a single chip, achieving multifunctionality and miniaturization of the device. Simultaneously, an embedded design protects the sensitive capacitor comb structure within the package, and a complete grounding layer is provided to effectively shield against external electromagnetic interference and flow field contamination. This enables the chip to withstand the harsh testing environments of the aerospace field, improving its reliability and lifespan in engineering applications. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the overall structure of an embodiment of the present invention.

[0024] Figure 2 This is an exploded view diagram of an embodiment of the present invention.

[0025] Figure 3 This is a schematic diagram of the capacitance-sensitive layer structure according to an embodiment of the present invention.

[0026] Figure 4 This is one of the magnified views of the capacitance-sensitive layer in an embodiment of the present invention.

[0027] Figure 5 This is a magnified view of the capacitance-sensitive layer in an embodiment of the present invention, number 2.

[0028] Figure 6 This is a schematic diagram of the shielding layer structure according to an embodiment of the present invention.

[0029] Figure 7 This is a schematic diagram of the shear stress sensitive layer structure according to an embodiment of the present invention.

[0030] exist Figures 1-7 In the middle, each is marked as:

[0031] 1-Capacitance-sensitive layer; 2-Shielding layer; 3-Shear stress-sensitive layer; 4-Upper shear stress folded beam; 5-Shear stress floating unit; 6-Fixed differential comb teeth; 7-Shear stress floating unit differential comb teeth; 8-Lower shear stress folded beam; 9-Force feedback differential comb teeth; 10-Upper acceleration folded beam; 11-Acceleration floating unit; 12-Acceleration floating unit differential comb teeth; 13-Lower acceleration folded beam; 14-Anchor point; 15-Anchor point connection area; 16-Floating unit connection area; 17-Support layer; 18-Floating unit pressure-sensitive membrane. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the following embodiments will be used in conjunction with the accompanying drawings to further illustrate the invention. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. Existing conventional techniques can be used for aspects not described in detail.

[0033] See Figures 1-7 A shear stress chip for a capacitor floating unit with acceleration detection and compensation functions includes a capacitor-sensitive layer 1, a shielding layer 2, and a shear stress-sensitive layer 3. The capacitor-sensitive layer 1, shielding layer 2, and shear stress-sensitive layer 3 are respectively the device layer, buried oxide layer, and substrate layer of SOI (silicon-on-insulator) material. The capacitor-sensitive layer 1 is made of silicon, the shear stress-sensitive layer 3 is made of silicon, and the shielding layer 2 is made of silicon oxide. In one specific embodiment, the capacitor-sensitive layer 1 uses resistivity... The N-type single-crystal silicon material, with shear stress sensitive layer 3 using resistivity The shielding layer 2 is made of N-type monocrystalline silicon material, and the shielding layer 2 is made of thermally oxidized silicon dioxide material. The three layers are connected by silicon-silicon direct bonding process.

[0034] The capacitance-sensitive layer 1 is located on the top layer of the chip. Through photolithography patterning and dry etching, upper shear stress folded beam 4, shear stress floating unit 5, fixed differential comb teeth 6, shear stress floating unit differential comb teeth 7, lower shear stress folded beam 8, force feedback differential comb teeth 9, upper acceleration folded beam 10, acceleration floating unit 11, acceleration floating unit differential comb teeth 12, lower acceleration folded beam 13, and anchor point 14 are fabricated on its surface. The fixed differential comb teeth 6, together with the shear stress floating unit differential comb teeth 7, acceleration floating unit differential comb teeth 12, and force feedback differential comb teeth 9, form three sets of differential capacitor structures used to detect changes in capacitance. The gap between the comb teeth should be at least three times the maximum expected displacement to avoid comb tooth adsorption. The width of the comb teeth should be determined based on the required stiffness and process capability, typically 3–8 μm. The number of comb teeth should be as large as possible within the chip size constraints to improve detection sensitivity. The upper shear stress folding beam 4 and the lower shear stress folding beam 8 are connected at one end to the anchor point 14 and at the other end to the shear stress floating unit 5, respectively, for transmitting displacement and providing restoring force. The upper acceleration folding beam 10 and the lower acceleration folding beam 13 are connected at one end to the anchor point 14 and at the other end to the acceleration floating unit 11, respectively, for transmitting displacement and providing restoring force. Force feedback differential comb teeth are arranged on the upper and lower sides of the shear stress floating unit 5. An electrostatic driving voltage is provided through a closed-loop detection circuit to generate an electrostatic driving force opposite to the displacement direction of the shear stress floating unit 5, which is used to widen the measurement range and improve the detection stability. The closed-loop control logic is as follows: when the displacement of the shear stress floating unit 5 due to shear stress is detected, the ASIC circuit generates a feedback voltage and applies it to the force feedback differential comb teeth 9. The electrostatic force generated by this voltage is opposite to the direction of the shear stress, thereby pulling the floating unit back or close to the equilibrium position. At this time, the magnitude of the feedback voltage directly corresponds to the magnitude of the measured shear stress.

[0035] The shielding layer 2 is located between the capacitance-sensitive layer 1 and the shear stress-sensitive layer 3. It is etched using a 50% HF etching solution to remove some silicon oxide, leaving behind anchor point connection regions 15 and floating unit connection regions 16. The anchor point connection region 15 connects the anchor point 14 of the capacitance-sensitive layer 1 to the support layer 17 of the shear stress-sensitive layer 3 via a bonding process. The floating unit connection region 16 connects the shear stress floating units 5 of the capacitance-sensitive layer 1 to the floating unit pressure-sensitive film 18 of the shear stress-sensitive layer 3 via a bonding process. The shear stress-sensitive layer 3 is located at the bottom of the chip, and its surface includes the support layer 17 and the floating unit pressure-sensitive film 18. The floating unit pressure-sensitive membrane 18 is patterned by photolithography and dry etching on the front side to sense external shear stress. When subjected to an external flow, the shear stress acts on the floating unit pressure-sensitive membrane 18, causing the shear stress floating unit 5 to displace through the floating unit connection area 16. This displacement is then caused by the stiffness-displacement relationship between the upper shear stress folding beam 4 and the lower shear stress folding beam 8, resulting in displacement of the differential comb teeth 7 of the shear stress floating unit. The differential capacitor formed by the fixed differential comb teeth 6 and the differential comb teeth 7 of the shear stress floating unit detects the capacitance change, thereby calculating the displacement and the magnitude of the shear stress. The displacement can be calculated using the capacitance-displacement conversion formula. Estimation: Among them The vacuum permittivity, Let be the relative permittivity of air, S be the overlap area of ​​the comb teeth, and d be the gap between the comb teeth. The formula for calculating shear stress is τ = kδ / Where k is the stiffness of the folded beam, and δ is the displacement. This represents the effective area of ​​the pressure-sensitive membrane. When subjected to external acceleration, the inertial force acts on the acceleration floating unit 11, which in turn causes the differential comb teeth 12 of the acceleration floating unit to shift due to the stiffness-displacement relationship between the upper acceleration folding beam 10 and the lower acceleration folding beam 13. The differential capacitor formed by the fixed differential comb teeth 6 and the differential comb teeth 12 of the acceleration floating unit detects the capacitance change, thereby calculating the magnitude of the acceleration or directly decoupling the shear stress output value through a differential circuit. The differential capacitance signals of the shear stress floating unit 5 and the acceleration floating unit 11 can be differentially processed by the circuit. Since their responses to acceleration are designed to be equal in magnitude and opposite in direction, the measurement error introduced by acceleration can be canceled, achieving acceleration decoupling and thus obtaining a pure shear stress signal.

[0036] The chip is equipped with two sets of floating units: a shear stress floating unit 5 to sense shear stress and an acceleration floating unit 11 to sense acceleration. By adjusting the comb structure and inertial mass of the two sets of floating units, the two sets of differential signals after the two sets of floating units are subjected to acceleration cancel each other out, thus achieving acceleration decoupling.

[0037] The shear stress floating unit 5 of the chip can detect the shear stress of the external fluid wall independently, or it can be used in conjunction with the acceleration floating unit 11 to achieve acceleration decoupling.

[0038] The acceleration floating unit 11 of the chip can detect uniaxial acceleration and can also be used in conjunction with the shear stress floating unit 5 to achieve acceleration decoupling.

[0039] The shear stress floating unit 5 of the chip has force feedback differential comb teeth 9 arranged on the upper and lower sides to provide electrostatic driving force, which can realize closed-loop driving and expand the detection range and detection stability.

[0040] The regions where the fixed differential comb teeth 6, shear stress floating unit differential comb teeth 7, acceleration floating unit differential comb teeth 12, and force feedback differential comb teeth 9 are located are separated by etching silicon material for subsequent capacitance detection.

[0041] The upper shear stress folding beam 4, shear stress floating unit 5, fixed differential comb teeth 6, shear stress floating unit differential comb teeth 7, lower shear stress folding beam 8, force feedback differential comb teeth 9, upper acceleration folding beam 10, acceleration floating unit 11, acceleration floating unit differential comb teeth 12, lower acceleration folding beam 13 and anchor point 14 are surrounded by a grounding layer and electrically grounded.

[0042] The overall thickness of the chip is 200-500 mm. The radius is 4000-6000 .

[0043] The thickness of shielding layer 2 is 2-6 mm. .

[0044] In one specific embodiment, the chip uses a thickness of 400 mm. SOI wafer fabrication. The thickness of the capacitor-sensitive layer 1 is 50 μm. The thickness of shear stress sensitive layer 3 is 340 mm. The thickness of shielding layer 2 is 5. The folded beams of both shear stress floating unit 5 and acceleration floating unit 11 have a design stiffness of 0.1 N / m. By adjusting the mass block size, the mass-stiffness ratio of both units satisfies the acceleration decoupling condition. The comb tooth gap is designed to be 4. Finite element simulation analysis shows that, under a shear stress of 100 Pa and an acceleration of 5 g, this embodiment can reduce the shear stress measurement error from ±20% before decoupling to within ±0.5%. Through force feedback closed-loop control, the linear measurement range of the sensor can be increased from ±50 Pa in the open-loop state to ±200 Pa.

[0045] This invention is based on microelectromechanical systems (MEMS) and differential capacitance detection technology, and is fabricated using silicon-on-insulator (SOI) multilayer material. From top to bottom, it comprises a capacitance-sensitive layer, a shielding layer, and a shear stress-sensitive layer. The invention utilizes the collaborative operation of two floating units in the capacitance-sensitive layer: a shear stress floating unit, working in conjunction with the pressure-sensitive membrane of the shear stress-sensitive layer, receives the shear stress from the flow field and converts it into relative displacement of the comb teeth and capacitance signals; an acceleration floating unit responds to inertial forces, generating a reverse cancellation signal to decouple acceleration coupling errors. This, combined with a force feedback closed-loop control mechanism, broadens the detection range and improves measurement stability. This invention not only completely solves the acceleration interference problem of traditional chips but also integrates shear stress measurement, acceleration measurement, and compensation functions. It is applicable to diverse scenarios, and its embedded structure and grounding layer design provide strong anti-interference capabilities. Based on mature MEMS technology, it is easy to mass-produce and can accurately meet the high-precision shear stress measurement needs of aerospace and other fields.

[0046] The above embodiments are merely preferred embodiments of the present invention and should not be considered as limiting the scope of the present invention. All equivalent variations and improvements made within the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A capacitive floating unit shear stress chip with acceleration detection and compensation function, characterized in that, From top to bottom, it includes a capacitance-sensitive layer, a shielding layer, and a shear stress-sensitive layer; The capacitance-sensitive layer consists of a shear stress floating unit, an acceleration floating unit, fixed differential comb teeth, shear stress floating unit differential comb teeth, acceleration floating unit differential comb teeth, force feedback differential comb teeth, an upper shear stress folded beam, a lower shear stress folded beam, an upper acceleration folded beam, a lower acceleration folded beam, and anchor points. The shear stress floating unit and the acceleration floating unit are located on the left and right sides of the chip, respectively connected to the anchor points through the shear stress folded beam, the lower shear stress folded beam, the upper acceleration folded beam, and the lower acceleration folded beam. Release holes are distributed on the acceleration floating unit. The fixed differential comb teeth are interleaved with the shear stress floating unit differential comb teeth, the acceleration floating unit differential comb teeth, and the force feedback differential comb teeth to form three sets of capacitance comb tooth detection structures. The anchor points are located on the upper and lower sides of the other structures. The capacitance-sensitive layer is made of silicon material and is fabricated through the SOI device layer. The shielding layer is located between the capacitance-sensitive layer and the shear stress-sensitive layer, and includes an anchor connection area and a floating unit connection area. The shielding layer is made of silicon oxide material and is prepared by SOI buried oxide layer etching to support the chip structure. The shear stress sensitive layer consists of a floating unit pressure-sensitive membrane and a support layer. The floating unit pressure-sensitive membrane is located on the side of the shear stress sensitive layer, directly opposite the shear stress floating unit. There is an movable gap between the floating unit pressure-sensitive membrane and the support layer. The shear stress sensitive layer is made of silicon material and is fabricated through an SOI substrate.

2. The capacitive floating unit shear stress chip with acceleration detection and compensation function as described in claim 1, characterized in that... By arranging two sets of floating units, one set of floating units senses shear stress and the other set senses acceleration, and by adjusting the comb structure and inertial mass of the two sets of floating units, the two sets of differential signals cancel each other out when the two sets of floating units are subjected to acceleration, thus achieving acceleration decoupling.

3. The capacitive floating unit shear stress chip with acceleration detection and compensation function as described in claim 1, characterized in that... The shear stress floating unit is used to detect the shear stress on the wall of the external fluid alone, or to work with the acceleration floating unit to achieve acceleration decoupling.

4. The capacitive floating unit shear stress chip with acceleration detection and compensation function as described in claim 1, characterized in that... The acceleration floating unit is used to detect uniaxial acceleration, or in conjunction with the shear stress floating unit to achieve acceleration decoupling.

5. The capacitive floating unit shear stress chip with acceleration detection and compensation function as described in claim 1, characterized in that... The shear stress floating unit has force feedback differential comb teeth arranged on its upper and lower sides to provide electrostatic driving force, thereby expanding the detection range and detection stability.

6. The capacitive floating unit shear stress chip with acceleration detection and compensation function as described in claim 1, characterized in that... The areas where the fixed differential comb teeth, shear stress floating unit differential comb teeth, acceleration floating unit differential comb teeth, and force feedback differential comb teeth are located are separated by etching silicon material for subsequent capacitance detection.

7. The capacitive floating unit shear stress chip with acceleration detection and compensation function as described in claim 1, characterized in that... The shear stress floating unit of the capacitance sensitive layer and the floating unit pressure-sensitive membrane of the shear stress sensitive layer are on the same axis but arranged in layers. They are connected by the floating unit connection area of ​​the shielding layer. The floating unit is exposed to the flow field upward, and the capacitance detection sensitive comb is buried downward in the encapsulation shell.

8. The capacitive floating unit shear stress chip with acceleration detection and compensation function as described in claim 1, characterized in that... Shear stress floating unit, acceleration floating unit, fixed differential comb teeth, shear stress floating unit differential comb teeth, acceleration floating unit differential comb teeth, force feedback differential comb teeth, upper shear stress folded beam, lower shear stress folded beam, upper acceleration folded beam, lower acceleration folded beam, and a grounding layer is arranged around the anchor point.

9. A capacitive floating unit shear stress chip with acceleration detection and compensation function as described in claim 1, characterized in that... The chip thickness is 200-500 mm. The radius is 4000-6000 .

10. A capacitive floating unit shear stress chip with acceleration detection and compensation function as described in claim 1, characterized in that... The shielding layer thickness is 2-6 mm. .

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