A high-order bending vibration coupling stepped micro-cantilever plate MEMS viscosity sensor chip and a working method thereof

Abstract

The application belongs to the field of MEMS sensors, and particularly relates to a high-order bending vibration coupling ladder micro-cantilever plate MEMS viscosity sensor chip and a working method thereof. The chip comprises a silicon-based fixed support body, a fixed support body cavity is arranged on the silicon-based fixed support body, a ladder micro-cantilever plate suspension structure is connected in the fixed support body cavity, the ladder micro-cantilever plate suspension structure comprises two ladder micro-cantilever plates with different lengths which are oppositely arranged at a free end, the ladder micro-cantilever plate comprises a rectangular fixed support plate and a wide plate cantilever, two ends of the fixed support plate are connected with the silicon-based fixed support body and the wide plate cantilever respectively, the width of the fixed support plate is smaller than that of the wide plate cantilever, and a vibration coupling gap is left between the free ends of the two wide plate cantilevers; piezoelectric driving electrodes and vibration pickup electrodes are symmetrically arranged on the fixed support plate along the width direction; the piezoelectric driving electrodes and the vibration pickup electrodes are located on different sides, and the piezoelectric driving electrodes and the vibration pickup electrodes are connected with metal leads. The viscosity sensor chip can significantly improve the measurement performance such as fluid measurement precision and stability.

Description

Technical Field

[0001] This invention belongs to the field of MEMS (Micro Electromechanical Systems) sensors, specifically relating to a high-order bending vibration coupled stepped microcantilever plate MEMS viscosity sensor chip and its working method. Background Technology

[0002] Viscosity, as one of the important thermophysical parameters of fluids, is fundamental data for scientific research in thermophysical properties and fluid mechanics, as well as engineering applications in energy and power, industrial control, and other fields. While traditional viscometers used in laboratories offer high accuracy, they struggle to achieve real-time online measurement of fluid viscosity, leading to the predominantly on-site sampling and laboratory measurement methods in industrial settings. Accurate measurement of fluid viscosity in the laboratory requires the use of auxiliary instruments to simulate the temperature and pressure of the fluid's actual environment. This method is not only labor-intensive, costly, and time-consuming, but also involves numerous instruments. A malfunction in any of these instruments can result in a significant discrepancy between the laboratory measurement and the actual fluid viscosity. Viscosity sensors based on micromachining technology offer advantages such as small size, fast response, and low power consumption, and are developing towards intelligence and integration. However, due to the limitations of their micro-nano size, these sensors generally suffer from shortcomings in measurement performance, including narrow measurement range and poor stability. Therefore, it is necessary to optimize the design of MEMS viscosity sensors from the perspectives of measurement methods and structural design to improve their fluid measurement performance and technological development. Summary of the Invention

[0003] To address the problems existing in the prior art, the present invention aims to provide a high-order bending vibration coupled stepped microcantilever plate MEMS viscosity sensor chip and its working method, in order to improve the overall performance of MEMS viscosity sensors, such as measurement accuracy, measurement range, and stability.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A high-order bending vibration coupled stepped microcantilever MEMS viscosity sensor chip includes a silicon-based solid support with a cavity. A stepped microcantilever suspension structure is connected within the cavity. The stepped microcantilever suspension structure includes a first stepped microcantilever plate and a second stepped microcantilever plate with their free ends opposite each other. The length of the first stepped microcantilever plate is greater than the length of the second stepped microcantilever plate. The first stepped microcantilever plate includes a rectangular first solid support plate and a first wide plate cantilever. The two ends of the first solid support plate are connected to the silicon-based solid support plate and the first wide plate cantilever, respectively. The width of the first solid support plate is less than that of the first wide plate cantilever. The second stepped microcantilever plate includes a rectangular second solid support plate and a second wide plate. The cantilever has two ends connected to the silicon-based fixed support and the second wide plate cantilever, respectively. The width of the second fixed support is smaller than the width of the second wide plate cantilever. A vibration coupling gap is left between the free ends of the first wide plate cantilever and the free ends of the second wide plate cantilever. The first fixed support is symmetrically provided with a first piezoelectric driving electrode and a first vibration pickup electrode on both sides along the width direction. The second fixed support is symmetrically provided with a second piezoelectric driving electrode and a second vibration pickup electrode on both sides along the width direction. The first piezoelectric driving electrode and the second piezoelectric driving electrode are located on the same side. The first vibration pickup electrode and the second vibration pickup electrode are located on the same side. All of the first piezoelectric driving electrode, the second piezoelectric driving electrode, the first vibration pickup electrode, and the second vibration pickup electrode are connected to metal leads.

[0006] Preferably, the first fixed support plate and the second fixed support plate have the same length, the same width, and the same thickness, and the length of the first wide plate cantilever is greater than the length of the second wide plate cantilever.

[0007] Preferably, the length of the second wide plate cantilever is 80% to 84% of the length of the first wide plate cantilever;

[0008] The length of the first fixed support plate is 37% to 39% of the cantilever length of the first wide plate, and the width of the first fixed support plate is 26% to 29% of the cantilever width of the first wide plate.

[0009] The length of the second fixed support plate is 37% to 39% of the cantilever length of the second wide plate, and the width of the second fixed support plate is 26% to 29% of the cantilever width of the second wide plate.

[0010] Preferably, the width of the vibration coupling gap is 95~105μm.

[0011] Preferably, the length of the first fixed support plate is more than 5 times the thickness, and the width is more than 5 times the thickness;

[0012] The length of the second fixed plate is more than 5 times the thickness, and the width is more than 5 times the thickness.

[0013] The length of the first wide plate cantilever is more than 5 times its thickness, and its width is more than 5 times its thickness;

[0014] The length of the second wide plate cantilever is more than 5 times its thickness, and its width is more than 5 times its thickness.

[0015] The width of the first wide plate cantilever is more than twice the width of the first fixed plate;

[0016] The width of the second wide plate cantilever is more than twice the width of the second fixed plate.

[0017] Preferably, the first piezoelectric driving electrode, the first vibration pickup electrode, the second piezoelectric driving electrode, and the second vibration pickup electrode are all rectangular in shape, and have the same length, width, and thickness.

[0018] Preferably, the width of the first wide plate cantilever is greater than or equal to its length, and the width of the second wide plate cantilever 4 is greater than or equal to its length.

[0019] Preferably, the fixed support cavity is rectangular in shape, and the axes of symmetry of the wide side of the fixed support cavity, the wide side of the first fixed support plate, the wide side of the first wide plate cantilever, the wide side of the second fixed support plate, and the wide side of the second wide plate cantilever are coaxial. The width of the fixed support cavity is greater than the width of the first wide plate cantilever and the width of the second wide plate cantilever. The first piezoelectric driving electrode and the first vibration pickup electrode are located on both sides of the axis of symmetry of the wide side of the first fixed support plate, and the second piezoelectric driving electrode and the second vibration pickup electrode are located on both sides of the axis of symmetry of the wide side of the second fixed support plate.

[0020] Preferably, the silicon-based fixed support includes a monocrystalline silicon substrate, with a thermo-oxidized silicon thin film on both the bottom and top surfaces of the monocrystalline silicon substrate. A piezoelectric layer bottom electrode molybdenum thin film is disposed on the surface of the thermo-oxidized silicon thin film on the top surface of the monocrystalline silicon substrate. A low-stress aluminum nitride piezoelectric thin film is disposed on the surface of the piezoelectric layer bottom electrode molybdenum thin film. An electrode metal layer serving as a first piezoelectric driving electrode, a second piezoelectric driving electrode, a first vibration pickup electrode, and a second vibration pickup electrode is disposed on the surface of the low-stress aluminum nitride piezoelectric thin film and the electrode metal layer. A silicon nitride thin film is disposed on the surfaces of the low-stress aluminum nitride piezoelectric thin film and the electrode metal layer. The plate, the first wide plate cantilever, the rectangular second fixed plate, and the second wide plate cantilever have the same structure in the thickness direction. The first fixed plate, the first wide plate cantilever, the rectangular second fixed plate, and the second wide plate cantilever share the thermo-oxidative silicon thin film, the piezoelectric layer bottom electrode molybdenum thin film, the low-stress aluminum nitride piezoelectric thin film, the silicon nitride thin film, and part of the single crystal silicon substrate on the top surface of the single crystal silicon substrate with the silicon-based fixed support. The thickness of the single crystal silicon substrate on the first fixed plate, the first wide plate cantilever, the rectangular second fixed plate, and the second wide plate cantilever is smaller than that on the single crystal silicon substrate of the silicon-based fixed support.

[0021] The operating method of the high-order bending vibration coupled stepped microcantilever plate MEMS viscosity sensor chip of the present invention, as described above, includes:

[0022] When the high-order bending vibration coupled stepped microcantilever plate MEMS viscosity sensor chip is immersed in fluid, the fluid fills the vibration coupling gap and acts as the vibration coupling medium.

[0023] Using the first stepped microcantilever plate as an active cantilever plate, when an alternating electric field is applied to the first piezoelectric driving electrode, the top electrode of the piezoelectric layer of the first stepped microcantilever plate is energized and the bottom electrode is grounded, causing the first stepped microcantilever plate to generate non-resonant higher-order bending vibration at the frequency of the driving voltage. At the same time, it causes the fluid around the first stepped microcantilever plate to generate corresponding vibration. The vibration of the fluid around the first stepped microcantilever plate generates a vibration driving force on the second stepped microcantilever plate, causing the second stepped microcantilever plate to generate passive higher-order bending vibration at a specific frequency, wherein the vibration direction of the second stepped microcantilever plate is opposite to that of the first microcantilever plate.

[0024] As a passive cantilever plate, the second-step microcantilever plate generates vibration coupling with the first cantilever plate through a fluid medium. The fluid medium in the vibration coupling gap is subjected to shear force between the first and second-step microcantilever plates, so that the vibration amplitude of the second microcantilever plate structure is related to the fluid viscosity and the vibration amplitude of the first microcantilever plate structure.

[0025] When the first and second stepped microcantilever plates are in a non-resonant high-order bending vibration state, the first and second vibration-collecting electrodes form an external electrical output port at the top electrode and a grounded bottom electrode. Through the piezoelectric effect, an alternating voltage detection signal is generated and output. The output voltage ratio of the suspended structure of the stepped microcantilever plate is extracted to realize the measurement of fluid viscosity.

[0026] The present invention has the following beneficial effects:

[0027] The high-order bending vibration coupled microcantilever plate MEMS viscosity sensor chip of the present invention adopts a stepped microcantilever plate structure, which has a higher Reynolds number than the traditional slender microcantilever beam structure. At the same time, the stepped shape design aims to reduce the vibration stiffness of the wide plate cantilever along the width direction by using the width difference between the wide plate cantilever and the fixed support plate, thereby making it easier to generate high-order bending vibrations along both the length and width directions of the stepped microcantilever plate. The stepped microcantilever plate structure has both high Reynolds number and high-order bending vibration, which can significantly improve the fluid damping resistance of the sensor chip immersed in the fluid, increase the vibration stability of the sensor, and thus improve the measurement accuracy of the sensor chip in viscous fluids.

[0028] This invention utilizes a fluid medium to achieve high-order bending vibration coupling in a stepped microcantilever plate suspended structure. Through the coupling effect of the non-resonant high-order bending vibration of the active stepped microcantilever plate with the vibration of the fluid medium, the passive stepped microcantilever plate is driven to generate non-resonant high-order bending vibration at a specific frequency. Compared with existing resonant fluid viscosity measurement methods based on quality factor vibration parameters, the viscosity sensor chip working method proposed in this invention does not require resonance curve fitting. At the same time, it avoids the problem of poor fluid viscosity measurement accuracy or even difficulty in obtaining experimental fluid viscosity values ​​due to the complexity of the quality factor in high-viscosity fluids. By directly measuring the fluid viscosity through the vibration amplitude output by the sensor, the measurement efficiency and accuracy can be significantly improved.

[0029] The high-order bending vibration coupled stepped microcantilever plate MEMS viscosity sensor chip of the present invention realizes the piezoelectric driven vibration and output voltage detection of the stepped microcantilever plate suspended structure through the arrangement of piezoelectric driving electrodes and vibration pickup electrodes. Compared with electromagnetic, electrothermal and electrostatic excitation methods, it has excellent packaging characteristics and anti-interference ability. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a schematic diagram of the overall structure of the MEMS viscosity sensor chip for a high-order bending vibration coupled stepped microcantilever plate in an embodiment of the present invention.

[0032] Figure 2 for Figure 1 A schematic diagram of the cross section along line A-A'.

[0033] Figure 3 This is a simulation diagram of the in-plane vibration mode of the stepped microcantilever plate suspended array structure according to an embodiment of the present invention.

[0034] Figure 4 The simulation diagram shows the vibration amplitude ratio of the stepped microcantilever plate suspended array structure in different fluids according to an embodiment of the present invention.

[0035] In the figure, 1-first wide plate cantilever, 2-first fixed plate, 3-1-first piezoelectric driving electrode, 3-2-first piezoelectric vibration pickup electrode, 4-second wide plate cantilever, 5-second fixed plate, 6-1-second piezoelectric vibration pickup electrode, 6-2-third piezoelectric vibration pickup electrode, 7-silicon-based fixed support, 8-fixed support cavity, 9-metal lead, 10-single crystal silicon substrate, 11-thermo-oxidized silicon thin film, 12-piezoelectric layer bottom electrode molybdenum thin film, 13-low-stress aluminum nitride piezoelectric thin film, 14-electrode metal layer, 15-silicon nitride thin film, 16-vibration coupling gap, 17-first stepped microcantilever plate, 18-second stepped microcantilever plate. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0037] Reference Figure 1This embodiment of a high-order bending vibration coupled stepped microcantilever MEMS viscosity sensor chip includes a silicon-based solid support 7, on which a rectangular solid support cavity 8 is provided. A stepped microcantilever suspension structure is connected within the solid support cavity 8. The stepped microcantilever suspension structure includes a first stepped microcantilever plate 17 and a second stepped microcantilever plate 18. The first stepped microcantilever plate includes a rectangular first solid support plate 2 and a rectangular first wide plate cantilever 1. One end of the first solid support plate 2 is connected to the silicon-based solid support 7, and the other end of the first solid support plate 2 is connected to the first wide plate cantilever 1. The width of the first solid support plate 2 is smaller than the width of the first wide plate cantilever 1. The second stepped microcantilever plate is entirely covered with… The system includes a second fixed support plate 5 and a second wide plate cantilever 4. One end of the second fixed support plate 5 is connected to the silicon-based fixed support 7, and the other end is connected to the second wide plate cantilever 4. The width of the second fixed support plate 5 is less than the width of the second wide plate cantilever 4. The first fixed support plate 2, the first wide plate cantilever 1, the second fixed support plate 5, and the second wide plate cantilever 4 are coaxial with the axis of symmetry on the wide side of the fixed support cavity 8. The length of the second wide plate cantilever 4 is less than the length of the first wide plate cantilever 1. The width and thickness of the second wide plate cantilever 4 and the first wide plate cantilever 1 are the same. The length, width, and thickness of the first fixed support plate 2 and the second fixed support plate 5 are the same. The length of the first fixed support plate 2 is more than 5 times its thickness, and its width is... The first wide plate cantilever 1 has a length and width that are more than 5 times the thickness, and the second wide plate cantilever 4 has a length and width that are more than 5 times the thickness. The width of the first wide plate cantilever 1 is more than twice the width of the first fixed support plate 2, and the width of the second wide plate cantilever 4 is more than twice the width of the second fixed support plate 5. The first wide plate cantilever 1 is coaxially connected to the bottom of the first fixed support plate 2, and the second wide plate cantilever 4 is coaxially connected to the bottom of the second fixed support plate 5. The first stepped micro-cantilever plate and the second stepped micro-cantilever plate are coaxially designed along the length direction. The two wide plate cantilever arms are positioned such that there is a free end gap width between them, that is, there is a vibration coupling gap 16 between the free ends of the first wide plate cantilever arm 1 and the second wide plate cantilever arm 4; piezoelectric electrode pairs are arranged on the fixed support plate structure of the stepped micro cantilever plate suspended structure, wherein the first fixed support plate 2 is provided with a first piezoelectric driving electrode 3-1 and a first vibration picking electrode 3-2, which constitute a piezoelectric vibration picking electrode pair; the second fixed support plate 5 is provided with a piezoelectric vibration picking electrode pair, that is, the second fixed support plate 5 is provided with a second piezoelectric driving electrode 6-1 and a second vibration picking electrode 6-2, and the piezoelectric electrode pairs are used as the top electrodes of the corresponding stepped micro cantilever plate suspended structure;The piezoelectric electrodes on the fixed support plate structure are symmetrically arranged about an axis of symmetry along the length direction. The length of the piezoelectric electrode pair is the same as the length of the fixed support plate. Specifically, the first piezoelectric driving electrode 3-1 and the first vibration pickup electrode 3-2 are symmetrically arranged about an axis of symmetry along the length direction of the first fixed support plate 2. The second piezoelectric driving electrode 6-1 and the second vibration pickup electrode 6-2 are symmetrically arranged about an axis of symmetry along the length direction of the second fixed support plate 5. The first piezoelectric driving electrode 3-1 and the second piezoelectric driving electrode 6-1 are located on the same side of the aforementioned axis of symmetry. The first vibration pickup electrode 3-2 and the second vibration pickup electrode 6-2 are located on... On the same side of the aforementioned axis; the piezoelectric electrode pairs (i.e., the first piezoelectric driving electrode 3-1, the first vibration pickup electrode 3-2, the second piezoelectric driving electrode 6-1, and the second vibration pickup electrode 6-2) have the same length, width, and thickness; in the stepped micro-cantilever plate cantilever structure, the width of the wide plate cantilever is greater than or equal to its length, that is, the width of the first wide plate cantilever 1 is greater than or equal to its length, and the width of the second wide plate cantilever 4 is greater than or equal to its length; the width of the fixed support cavity 8 is greater than the width of the first wide plate cantilever 1 and the second wide plate cantilever 4; each driving electrode and vibration pickup electrode is connected to a metal lead 9. The length direction is along; Figure 1 The X direction is parallel to the axis of the stepped microcantilever plate along its length, and the Y direction is along the width of the stepped microcantilever plate.

[0038] Reference Figure 1 and combined Figure 3 The operating method of the high-order bending vibration coupled stepped microcantilever plate MEMS viscosity sensor chip in this embodiment includes the following steps:

[0039] When the high-order bending vibration coupled stepped microcantilever plate MEMS viscosity sensor chip is immersed in fluid, the fluid fills the free end gaps (i.e., vibration coupling gaps 16) between the suspended structures of the stepped microcantilever plate and acts as a vibration coupling medium. The first stepped microcantilever plate, as an active cantilever plate, generates non-resonant high-order bending vibrations at the frequency of the driving voltage when an alternating electric field is applied to its first piezoelectric driving electrode 3-1, forming a piezoelectric layer with the top electrode energized and the bottom electrode grounded. This causes the first stepped microcantilever plate to vibrate accordingly in the surrounding fluid at the frequency of the driving voltage. Furthermore, the vibration of the surrounding fluid generates a vibration driving force on the second stepped microcantilever plate, causing it to generate passive high-order bending vibrations at a specific frequency. The vibration direction of the second stepped microcantilever plate is opposite to that of the first microcantilever plate, thereby enhancing the vibration coupling effect of the fluid medium.

[0040] The second-step microcantilever plate, acting as a passive cantilever plate, vibrates and couples with the first cantilever plate through a fluid medium. The fluid medium in the gap between the free ends of the cantilevered structure is subjected to shear force between the first and second microcantilever plates, causing the vibration amplitude of the second microcantilever plate structure to be directly related to the fluid viscosity and the vibration amplitude of the first microcantilever plate structure. Under non-resonant high-order bending vibration conditions, the piezoelectric pickup electrodes (first pickup electrode 3-2 and second pickup electrode 6-2) are configured with an external electrical output port at the top electrode and a grounded bottom electrode. Through the piezoelectric effect, an alternating voltage detection signal is generated and output, thereby extracting the output voltage ratio of the cantilevered structure and achieving fluid viscosity measurement.

[0041] This invention relates to a high-order bending vibration coupled stepped microcantilever MEMS viscosity sensor chip. The chip employs a stepped microcantilever structure with a free-end gap to excite the vibration coupling effect of two microcantilever plates through a fluid medium. By utilizing the stepped shape design of the stepped microcantilever plate and the width difference between the wide cantilever and the fixed support plate, the vibration stiffness of the wide cantilever structure along the width direction is reduced. This makes it easier for the overall stepped microcantilever plate to excite non-resonant high-order bending vibrations simultaneously along both length and width directions in the fluid, thereby improving the stability of the stepped microcantilever plate's high-order bending vibration. The use of a double-stepped microcantilever structure in a non-resonant vibration state, along with fluid viscosity measurement based on the sensor's vibration amplitude, avoids the problem of poor fluid viscosity measurement accuracy caused by the difficulty in accurately fitting complex resonance parameters such as the quality factor in high-viscosity fluids. This improves the fluid viscosity measurement accuracy and efficiency of this type of sensor.

[0042] In this embodiment, the dimensions of the first wide cantilever 1 of the stepped microcantilever plate suspension structure are: length × width = (1100±10) × (1400±10) μm 2 The thickness is 20±5μm; the dimensions of the second wide plate cantilever 4 are: length × width = (900±10) × (1400±10)μm 2 The thickness is 20±5μm; the dimensions of the fixed plate (i.e., the first fixed plate 2 or the second fixed plate 5) are: length × width = (420±5) × (380±10)μm 2 The thickness is 20±5μm; the length of the free end gap (i.e. vibration coupling gap 16) between the first and second stepped microcantilever plates is 100±5μm.

[0043] like Figure 2As shown in the cross-sectional view of the high-order bending vibration coupled stepped microcantilever plate MEMS viscosity sensor chip of the present invention, the high-order bending vibration coupled stepped microcantilever plate MEMS viscosity sensor chip of this embodiment is fabricated on a single-crystal silicon substrate 10. Both the top and back surfaces of the single-crystal silicon substrate 10 are covered with a thermo-oxidized silicon oxide film 11, which serves as an electrical insulating layer for the single-crystal silicon substrate 10. A piezoelectric bottom electrode molybdenum film 12 is disposed on the surface of the thermo-oxidized silicon oxide film 11 on the top surface of the single-crystal silicon substrate 10. A low-stress aluminum nitride piezoelectric film 13 is disposed on the surface of the piezoelectric bottom electrode molybdenum film 12. The piezoelectric bottom electrode molybdenum film 12 can be used as the chip bottom electrode grounding layer and also as the substrate layer for the deposition of the low-stress aluminum nitride piezoelectric film 13. The aluminum nitride piezoelectric film 13 serves as the piezoelectric film for the high-order bending vibration coupled stepped microcantilever MEMS viscosity sensor chip in this embodiment. The low-stress aluminum nitride piezoelectric film 13 is used to generate inverse piezoelectric effect and piezoelectric effect to realize the excitation of vibration mode and electrical signal detection. An electrode metal layer 14 is provided on the surface of the low-stress aluminum nitride piezoelectric film 13. The electrode metal layer 14 is used to form a piezoelectric electrode pair (first piezoelectric driving electrode 3-1, first vibration pickup electrode 3-2, second piezoelectric driving electrode 6-1, second vibration pickup electrode 6-2) and metal leads 9. A silicon nitride insulating layer film 15 covers the surface of the sensor chip (i.e., the silicon nitride insulating layer film 15 covers the top surface of the low-stress aluminum nitride piezoelectric film 13 and the electrode metal layer 14) and is used for insulation in the fluid medium. In the cross-sectional view, the area with a larger thickness of the single crystal silicon substrate 11 on the left side represents the silicon-based solid support 1 of the sensor chip, and the area with a smaller thickness of the single crystal silicon substrate represents the double microcantilever plate cantilever structure. Specifically, the first-step microcantilever plate and the silicon-based solid support 1 share the thermally oxidized silicon film 11, the piezoelectric layer bottom electrode molybdenum film 12, the low-stress aluminum nitride piezoelectric film 13, the electrode metal layer 14, the silicon nitride insulating layer film 15, and a portion of the single-crystal silicon substrate 10 (specifically, a part of the top of the single-crystal silicon substrate 10) on the top surface of the single-crystal silicon substrate 10; the second-step microcantilever plate and the silicon-based solid support 1 share the thermally oxidized silicon film 11, the piezoelectric layer bottom electrode molybdenum film 12, the low-stress aluminum nitride piezoelectric film 13, the electrode metal layer 14, the silicon nitride insulating layer film 15, and a portion of the single-crystal silicon substrate 10 (specifically, a part of the top of the single-crystal silicon substrate 10) on the top surface of the single-crystal silicon substrate 10.

[0044] like Figure 3 and Figure 4 In this study, Comsol Multiphysics simulation software was used to perform fluid-structure interaction simulation analysis on the stepped microcantilever plate suspended structure of the above embodiment. Figure 3 The simulation results are for the non-resonant vibration of the first-step microcantilever plate 17 and the second-step microcantilever plate 18 under the coupling of higher-order bending vibration. The simulation liquid is cyclohexane (density 779 kg / m³).3 (The viscosity is 1.0 cP). It can be seen that the first stepped microcantilever plate 17 and the second stepped microcantilever plate 18 undergo bending vibrations of specific amplitudes. These bending vibrations occur simultaneously in both the length and width directions of the stepped microcantilever plates, forming a basic bending vibration pattern distinct from that occurring only along the length direction. Vibration transmission between the stepped microcantilever plates is achieved through the interstitial fluid medium, coupling the active bending vibration of the first stepped microcantilever plate 17 to the second stepped microcantilever plate 18. This causes the second stepped microcantilever plate 18 to undergo passive bending vibration, with the vibration direction opposite to that of the first stepped microcantilever plate 17. The opposing higher-order bending vibrations of the first stepped microcantilever plate 17 and the second stepped microcantilever plate 18 enhance the vibration coupling effect of the fluid medium, thereby improving the accuracy and sensitivity of fluid viscosity measurement.

[0045] Figure 4 In this study, four different liquids were selected for fluid-structure interaction simulation analysis, including n-heptane, cyclohexane, MD2M, and D4 liquids. The variation curves between the vibration amplitude ratio of the stepped microcantilever plate suspended structure (vibration amplitude of the second stepped microcantilever plate 18 / vibration amplitude of the first stepped microcantilever plate 17) and the fluid viscosity were obtained. It can be seen that a univariate correspondence between the vibration amplitude ratio of the stepped microcantilever plate suspended structure and the fluid viscosity can be established through the vibration amplitude ratio, thereby realizing the measurement of fluid viscosity. This verifies the working mode of the viscosity sensor chip proposed in this invention.

[0046] In summary, the stepped microcantilever plate cantilever structure of this invention adopts a free-end gap design, and realizes the high-order bending vibration coupling between the two microcantilever plate cantilever structures through the fluid medium, so that the two stepped microcantilever plates can undergo active and passive non-resonant bending vibrations. The stepped microcantilever plate cantilever structure consists of a fixed support plate and a wide plate cantilever structure, wherein the width of the fixed support plate is smaller than the width of the wide plate cantilever, thus forming the stepped shape of the overall microcantilever plate structure. The stepped shape design is used to increase the bending vibration stiffness of the wide plate cantilever along the width direction, making it easier to excite high-order bending vibrations and improving the vibration stability and measurement accuracy of the sensor chip immersed in the fluid. The sensor chip uses locally arranged piezoelectric driving electrodes to excite non-resonant high-order bending vibrations, and piezoelectric pickup electrodes are used to convert the vibration signal into an electrical signal output through the piezoelectric effect, realizing the self-excitation and self-detection performance of the viscosity sensor chip, which helps to improve the comprehensive measurement performance of the viscosity sensor chip, such as fluid measurement accuracy and stability.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A high-order flexural vibration coupled stepped micro-cantilever plate MEMS viscosity sensor chip, characterized in that, The application relates to a silicon-based fixed support body (7) provided with a fixed support body cavity (8) and a stepped micro-cantilever plate suspended structure connected in the fixed support body cavity (8), wherein the stepped micro-cantilever plate suspended structure comprises first and second stepped micro-cantilever plates (17) and (18) oppositely arranged at free ends, the length of the first stepped micro-cantilever plate (17) is greater than that of the second stepped micro-cantilever plate (18), the first stepped micro-cantilever plate (17) comprises a rectangular first fixed support plate (2) and a first wide plate cantilever (1), the two ends of the first fixed support plate (2) are connected with the silicon-based fixed support body (7) and the first wide plate cantilever (1) respectively, the width of the first fixed support plate (2) is smaller than that of the first wide plate cantilever (1), the second stepped micro-cantilever plate (18) comprises a rectangular second fixed support plate (5) and a second wide plate cantilever (4), the two ends of the second fixed support plate (5) are connected with the silicon-based fixed support body (7) and the second wide plate cantilever (4) respectively, the width of the second fixed support plate (5) is smaller than that of the second wide plate cantilever (4), and a vibration coupling gap (16) is left between the free ends of the first wide plate cantilever (1) and the second wide plate cantilever (4); the first fixed support plate (2) is provided with a first piezoelectric driving electrode (3-1) and a first vibration pickup electrode (3-2) symmetrically arranged along the width direction on both sides, and the second fixed support plate (5) is provided with a second piezoelectric driving electrode (6-1) and a second vibration pickup electrode (6-2) symmetrically arranged along the width direction on both sides; the first piezoelectric driving electrode (3-1) and the second piezoelectric driving electrode (6-1) are located on the same side, the first vibration pickup electrode (3-2) and the second vibration pickup electrode (6-2) are located on the same side, and the first piezoelectric driving electrode (3-1), the second piezoelectric driving electrode (6-1), the first vibration pickup electrode (3-2) and the second vibration pickup electrode (6-2) are all connected with metal leads (9).

2. The high-order flexural vibration coupling stepped micro-cantilever plate MEMS viscosity sensor chip according to claim 1, characterized in that, The length, width and thickness of the first fixed support plate (2) and the second fixed support plate (5) are the same, the width and thickness of the first wide plate cantilever (1) and the second wide plate cantilever (4) are the same, and the length of the first wide plate cantilever (1) is greater than that of the second wide plate cantilever (4).

3. The high-order flexural vibration coupling stepped micro-cantilever plate MEMS viscosity sensor chip according to claim 1, characterized in that, The width of the vibration coupling gap (16) is 95-105 mu m.

4. The high-order flexural vibration coupling stepped micro-cantilever plate MEMS viscosity sensor chip according to claim 1, characterized in that, The first piezoelectric driving electrode (3-1), the first vibration pickup electrode (3-2), the second piezoelectric driving electrode (6-1) and the second vibration pickup electrode (6-2) are all rectangular in shape and have the same length, width and thickness.

5. The high-order flexural vibration coupling stepped micro-cantilever plate MEMS viscosity sensor chip according to claim 1, characterized in that, The width of the first wide plate cantilever (1) is greater than or equal to the length, and the width of the second wide plate cantilever (4) is greater than or equal to the length.

6. The high-order flexural vibration coupling stepped micro-cantilever plate MEMS viscosity sensor chip according to claim 1, characterized in that, The shape of the fixed support body cavity (8) is rectangular, the symmetry axis of the wide side of the fixed support body cavity (8), the symmetry axis of the wide side of the first fixed support plate (2), the symmetry axis of the wide side of the first wide plate cantilever (1), the symmetry axis of the wide side of the second fixed support plate (5) and the symmetry axis of the wide side of the second wide plate cantilever (4) are coaxial, the width of the fixed support body cavity (8) is greater than the width of the first wide plate cantilever (1) and the width of the second wide plate cantilever (4), the first piezoelectric driving electrode (3-1) and the first vibration pickup electrode (3-2) are respectively located on the two sides of the symmetry axis of the wide side of the first fixed support plate (2), and the second piezoelectric driving electrode (6-1) and the second vibration pickup electrode (6-2) are respectively located on the two sides of the symmetry axis of the wide side of the second fixed support plate (5).

7. The high-order flexural vibration coupling stepped micro-cantilever plate MEMS viscosity sensor chip according to any one of claims 1-6, characterized in that, The silicon-based fixed support body (7) comprises a single crystal silicon substrate (10), the bottom surface and the top surface of the single crystal silicon substrate (10) are provided with a thermal oxidation silicon film (11), the surface of the thermal oxidation silicon film (11) on the top surface of the single crystal silicon substrate (10) is provided with a piezoelectric layer bottom electrode molybdenum film (12), the surface of the piezoelectric layer bottom electrode molybdenum film (12) is provided with a low-stress aluminum nitride piezoelectric film (13), the surface of the low-stress aluminum nitride piezoelectric film (13) is provided with an electrode metal layer (14) serving as the first piezoelectric driving electrode (3-1), the second piezoelectric driving electrode (6-1), the first vibration pickup electrode (3-2) and the second vibration pickup electrode (6-2), and the surfaces of the low-stress aluminum nitride piezoelectric film (13) and the electrode metal layer (14) are provided with a silicon nitride film (15); the first fixed support plate (2), the first wide plate cantilever (1), the rectangular second fixed support plate (5) and the second wide plate cantilever (4) are the same in structure in the thickness direction, the first fixed support plate (2), the first wide plate cantilever (1), the rectangular second fixed support plate (5), the second wide plate cantilever (4) and the silicon-based fixed support body (7) share the thermal oxidation silicon film (11) on the top surface of the single crystal silicon substrate (10), the piezoelectric layer bottom electrode molybdenum film (12), the low-stress aluminum nitride piezoelectric film (13), the silicon nitride film (15) and part of the single crystal silicon substrate (10), wherein the thickness of the single crystal silicon substrate (10) on the first fixed support plate (2), the first wide plate cantilever (1), the rectangular second fixed support plate (5) and the second wide plate cantilever (4) is less than the thickness of the single crystal silicon substrate (10) of the silicon-based fixed support body (7).

8. The working method of the high-order flexural vibration coupling ladder micro-cantilever plate MEMS viscosity sensor chip according to any one of claims 1-6, characterized in that, When the high-order bending vibration coupling stepped micro-cantilever plate MEMS viscosity sensor chip is immersed in a fluid, the fluid fills the vibration coupling gap (16) and acts as a vibration coupling medium; ​ The first ladder micro-cantilever plate is used as an active cantilever plate. When an alternating electric field is applied on the first piezoelectric driving electrode (3-1), the piezoelectric layer top electrode of the first ladder micro-cantilever plate is powered and the bottom electrode is grounded, so that the first ladder micro-cantilever plate generates non-resonant high-order bending vibration at the frequency of the driving voltage, and the fluid around the first ladder micro-cantilever plate generates corresponding vibration. The vibration of the fluid around the first ladder micro-cantilever plate generates a vibration driving force on the second ladder micro-cantilever plate, so that the second ladder micro-cantilever plate generates passive high-order bending vibration at a specific frequency, wherein the vibration direction of the second ladder micro-cantilever plate is opposite to the vibration direction of the first micro-cantilever plate; The second ladder micro-cantilever plate is used as a passive cantilever plate. The fluid medium in the vibration coupling gap (16) between the first ladder micro-cantilever plate and the second ladder micro-cantilever plate is subjected to shear force through the vibration coupling effect of the fluid medium and the first cantilever plate, so that the vibration amplitude of the second micro-cantilever plate structure is related to the fluid viscosity and the vibration amplitude of the first micro-cantilever plate structure; In the non-resonant high-order bending vibration state of the first ladder micro-cantilever plate and the second ladder micro-cantilever plate, the first pick-up electrode (3-2) and the second pick-up electrode (6-2) form a top electrode external electrical output port and a bottom electrode grounding mode. Through the piezoelectric effect, an alternating voltage detection signal is generated and outputted, the output voltage ratio of the ladder micro-cantilever plate suspended structure is extracted, and the measurement of the fluid viscosity is realized.

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