High-order bending vibration coupling stepped micro-cantilever slab MEMS viscosity sensor chip and working method thereof

Abstract

The invention belongs to the field of MEMS sensors, and particularly relates to a high-order bending vibration coupling step micro-cantilever plate MEMS viscosity sensor chip and a working method thereof.The chip comprises a silicon-based clamped support, a clamped support cavity is formed in the silicon-based clamped support, a step micro-cantilever plate suspension structure is connected in the clamped support cavity, and a micro-cantilever plate is arranged in the step micro-cantilever plate suspension structure. The stepped micro-cantilever plate suspension structure comprises two stepped micro-cantilever plates with different lengths and free ends oppositely arranged, each stepped micro-cantilever plate comprises a rectangular fixed support plate and a wide plate cantilever, two ends of each fixed support plate are respectively connected with the silicon-based fixed support body and the wide plate cantilever, the width of each fixed support plate is smaller than that of the wide plate cantilever, and the width of each wide plate cantilever is smaller than that of the silicon-based fixed support body. A vibration coupling gap is reserved between the free ends of the two wide plate cantilevers; a piezoelectric driving electrode and a vibration pick-up electrode are symmetrically arranged on the two sides of the fixed support plate in the width direction; the piezoelectric driving electrode and the vibration pick-up electrode are positioned on different sides and are connected with metal leads. The viscosity sensor chip can significantly improve measurement performances such as fluid measurement precision and stability.

Description

Technical Field

[0001] The present invention belongs to the field of MEMS (Micro Electromechanical Systems) sensors, and in particular relates to a high-order bending vibration coupled step micro-cantilever plate MEMS viscosity sensor chip and a working method thereof. Background Art

[0002] As one of the important thermophysical parameters of fluids, viscosity is the basic data for scientific research such as thermophysical properties and fluid mechanics, and engineering applications such as energy and power, and industrial control. Although the traditional viscometers currently used in laboratories have high accuracy, it is difficult to achieve real-time online measurement of fluid viscosity, so most of the industrial fields adopt the method of on-site sampling laboratory measurement. In order to complete the accurate measurement of fluid viscosity in the laboratory, other auxiliary instruments are needed to simulate the temperature and pressure in the actual environment of the fluid. This method is not only labor-intensive, costly, and time-consuming, but also involves many instruments. If there is a problem with the accuracy of any of the instruments, it can lead to a large gap between the laboratory measurement value and the actual value of the fluid viscosity. Viscosity sensors based on micromachining technology have the advantages of small size, fast response, and low power consumption, and are developing in the direction of intelligence and integration. However, due to the limitations of micro-nano size conditions, such sensors generally have measurement performance deficiencies such as measurement accuracy, narrow measurement range, and poor stability. Therefore, it is necessary to optimize the design of MEMS viscosity sensors from the perspective of measurement method and structural design to improve the fluid measurement performance of such sensors and their technological development. Summary of the invention

[0003] In order to solve the problems existing in the prior art, the purpose of the present invention is to provide a high-order bending vibration coupled step micro-cantilever plate MEMS viscosity sensor chip and its working method, in order to improve the comprehensive performance of the MEMS viscosity sensor such as measurement accuracy, measurement range and stability.

[0004] In order to achieve the above object, the present invention adopts the following technical solution: A high-order bending vibration coupled step micro-cantilever plate MEMS viscosity sensor chip, comprising a silicon-based fixed support body, a fixed support body cavity is provided on the silicon-based fixed support body, a step micro-cantilever plate suspension structure is connected in the fixed support body cavity, the step micro-cantilever plate suspension structure comprises a first step micro-cantilever plate and a second step micro-cantilever plate which are arranged opposite to each other at free ends, the length of the first step micro-cantilever plate is greater than the length of the second step micro-cantilever plate, the first step micro-cantilever plate comprises a rectangular first fixed support plate and a first wide plate cantilever, the two ends of the first fixed support plate are respectively connected to the silicon-based fixed support body and the first wide plate cantilever, the width of the first fixed support plate is less than the first wide plate cantilever, the second step micro-cantilever plate comprises a rectangular second fixed support plate and a second wide plate cantilever, the two ends of the second fixing plate are respectively connected to the silicon-based fixing body and the second wide plate cantilever, the width of the second fixing plate is smaller than the width of the second wide plate cantilever, and a vibration coupling gap is left between the free end of the first wide plate cantilever and the free end of the second wide plate cantilever; the first piezoelectric driving electrode and the first vibration pickup electrode are symmetrically arranged on both sides of the first fixing plate in the width direction, and the second piezoelectric driving electrode and the second vibration pickup electrode are symmetrically arranged on both sides of the second fixing plate in 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, and the first piezoelectric driving electrode, the second piezoelectric driving electrode, the first vibration pickup electrode and the second vibration pickup electrode are all connected with metal leads.

[0005] Preferably, the first fixing plate and the second fixing plate have the same length, width and thickness, the length of the first wide plate cantilever is greater than the length of the second wide plate cantilever.

[0006] Preferably: the length of the second wide plate cantilever is 80% to 84% of the length of the first wide plate cantilever; The length of the first fixing plate is 37% to 39% of the length of the cantilever of the first wide plate, and the width of the first fixing plate is 26% to 29% of the width of the cantilever of the first wide plate; The length of the second fixing plate is 37% to 39% of the length of the second wide plate cantilever, and the width of the second fixing plate is 26% to 29% of the width of the second wide plate cantilever.

[0007] Preferably, the width of the vibration coupling gap is 95-105 μm.

[0008] Preferably: the length of the first fixing plate is more than 5 times the thickness, and the width is more than 5 times the thickness; The length of the second fixing plate is more than 5 times the thickness, and the width is more than 5 times the thickness; The length of the first wide plate cantilever is more than 5 times the thickness, and the width is more than 5 times the thickness; The length of the second wide plate cantilever is more than 5 times the thickness and the width is more than 5 times the thickness; The width of the first wide plate cantilever is more than twice the width of the first fixed support plate; The width of the second wide plate cantilever is more than twice the width of the second fixing plate.

[0009] 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.

[0010] 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.

[0011] Preferably, the shape of the solid support body cavity is rectangular, the symmetry axis of the wide side of the solid support body cavity, the symmetry axis of the wide side of the first solid support plate, the symmetry axis of the wide side of the first wide plate cantilever, the symmetry axis of the wide side of the second solid support plate and the symmetry axis of the wide side of the second wide plate cantilever are coaxial, the width of the solid support body cavity is greater than the width of the first wide plate cantilever and the width of the second wide plate cantilever, the first piezoelectric drive electrode and the first vibration pickup electrode are respectively located on both sides of the symmetry axis of the wide side of the first solid support plate, and the second piezoelectric drive electrode and the second vibration pickup electrode are respectively located on both sides of the symmetry axis of the wide side of the second solid support plate.

[0012] Preferably, the silicon-based fixed support body comprises a single crystal silicon substrate, a thermally oxidized silicon film is provided on the bottom and top surfaces of the single crystal silicon substrate, a piezoelectric layer bottom electrode molybdenum film is provided on the surface of the thermally oxidized silicon film on the top surface of the single crystal silicon substrate, a low-stress aluminum nitride piezoelectric film is provided on the surface of the piezoelectric layer bottom electrode molybdenum film, an electrode metal layer used as a first piezoelectric driving electrode, a second piezoelectric driving electrode, a first vibration pickup electrode, and a second vibration pickup electrode is provided on the surface of the low-stress aluminum nitride piezoelectric film, and a silicon nitride film is provided on the surfaces of the low-stress aluminum nitride piezoelectric film and the electrode metal layer; the first fixed support The plate, the first wide plate cantilever, the rectangular second fixing plate and the second wide plate cantilever have the same structure in the thickness direction, and the first fixing plate, the first wide plate cantilever, the rectangular second fixing plate, the second wide plate cantilever and the silicon-based fixing body share the thermally oxidized silicon film on the top surface of the single crystal silicon substrate, the molybdenum film on the bottom electrode of the piezoelectric layer, the low stress aluminum nitride piezoelectric film, the silicon nitride film and part of the single crystal silicon substrate, wherein the thickness of the single crystal silicon substrate on the first fixing plate, the first wide plate cantilever, the rectangular second fixing plate and the second wide plate cantilever is less than the single crystal silicon substrate of the silicon-based fixing body.

[0013] The working method of the high-order bending vibration coupled step micro-cantilever plate MEMS viscosity sensor chip of the present invention as described above comprises: When the high-order bending vibration coupled step micro-cantilever plate MEMS viscosity sensor chip is immersed in a fluid, the fluid fills the vibration coupling gap and acts as a vibration coupling medium; The first step micro-cantilever plate is used 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 step micro-cantilever plate is energized and the bottom electrode is grounded, so that the first step micro-cantilever plate generates non-resonant high-order bending vibration at the frequency of the driving voltage, and at the same time drives the fluid around the first step micro-cantilever plate to generate corresponding vibration. The vibration of the fluid around the first step micro-cantilever plate generates a vibration driving force on the second step micro-cantilever plate, so that the second step micro-cantilever plate generates passive high-order bending vibration at a specific frequency, wherein the vibration direction of the second step micro-cantilever plate is opposite to that of the first micro-cantilever plate; The second step micro-cantilever plate acts as a passive cantilever plate, and generates vibration coupling with the first cantilever plate through the fluid medium. The fluid medium in the vibration coupling gap is subjected to shear force between the first step micro-cantilever plate and the second step micro-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. When the first step micro-cantilever plate and the second step micro-cantilever plate are in a state of non-resonant high-order bending vibration, the first vibration pickup electrode and the second vibration pickup electrode constitute a top electrode externally connected to an electrical output port and a bottom electrode grounded. The piezoelectric effect is used to generate and output an alternating voltage detection signal, and the output voltage ratio of the suspended structure of the step micro-cantilever plate is extracted to achieve the measurement of fluid viscosity.

[0014] The present invention has the following beneficial effects: The high-order bending vibration coupled micro-cantilever plate MEMS viscosity sensor chip of the present invention adopts a stepped micro-cantilever plate structure, which has a higher Reynolds number than the traditional slender micro-cantilever beam structure. At the same time, the purpose of the stepped shape design is to reduce the vibration stiffness of the wide plate cantilever along the width direction through the width difference between the wide plate cantilever and the fixed support plate, so that it is easier to generate high-order bending vibrations along the length and width directions of the stepped micro-cantilever plate. The stepped micro-cantilever 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 thereby achieve the improvement of the measurement accuracy of the sensor chip in the viscous fluid.

[0015] The present invention utilizes a fluid medium to realize high-order bending vibration coupling of a suspended structure of a stepped micro-cantilever plate. Through the coupling effect of the non-resonant high-order bending vibration of an active stepped micro-cantilever plate and the vibration of a fluid medium, a passive stepped micro-cantilever plate is driven to generate non-resonant high-order bending vibration of a specific frequency. Compared with the existing resonant fluid viscosity measurement method based on quality factor vibration parameters, the viscosity sensor chip working method proposed in the present invention does not require resonance curve fitting, and at the same time avoids the problem of poor fluid viscosity measurement accuracy caused by the complexity of the quality factor of the sensor in high-viscosity fluids, and even difficulty in measuring the experimental value of the fluid viscosity. Direct measurement of the fluid viscosity is achieved by outputting the vibration amplitude of the sensor, which can significantly improve the measurement efficiency and accuracy.

[0016] The high-order bending vibration coupled step micro-cantilever plate MEMS viscosity sensor chip of the present invention realizes piezoelectric driven vibration and output voltage detection of the suspended structure of the step micro-cantilever plate 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 capabilities. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0018] Figure 1 Schematic diagram of the overall structure of the high-order bending vibration coupled step micro-cantilever plate MEMS viscosity sensor chip in an embodiment of the present invention.

[0019] Figure 2 for Figure 1 Schematic diagram of the cross section along A-A'.

[0020] Figure 3 This is a simulation diagram of the in-plane vibration form of the stepped micro-cantilever plate suspended array structure according to an embodiment of the present invention.

[0021] Figure 4 It is a simulation diagram of the vibration amplitude ratio of the stepped micro-cantilever plate suspended array structure in different fluids according to an embodiment of the present invention.

[0022] In the figure, 1-first wide plate cantilever, 2-first fixed support plate, 3-1-first piezoelectric driving electrode, 3-2-first piezoelectric vibration pickup electrode, 4-second wide plate cantilever, 5-second fixed support plate, 6-1-second piezoelectric vibration pickup electrode, 6-2-third piezoelectric vibration pickup electrode, 7-silicon-based fixed support body, 8-fixed support body cavity, 9-metal lead, 10-single crystal silicon substrate, 11-thermal oxide silicon film, 12-piezoelectric layer bottom electrode molybdenum film, 13-low stress aluminum nitride piezoelectric film, 14-electrode metal layer, 15-silicon nitride film, 16-vibration coupling gap, 17-first step micro-cantilever plate, 18-second step micro-cantilever plate. DETAILED DESCRIPTION

[0023] To make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0024] Reference Figure 1The high-order bending vibration coupled step micro-cantilever plate MEMS viscosity sensor chip of this embodiment includes a silicon-based fixed support body 7, a rectangular fixed support body cavity 8 is provided on the silicon-based fixed support body 7, a step micro-cantilever plate suspended structure is connected in the fixed support body cavity 8, and the step micro-cantilever plate suspended structure includes a first step micro-cantilever plate 17 and a second step micro-cantilever plate 18; the first step micro-cantilever plate includes a rectangular first fixed support plate 2 and a rectangular first wide plate cantilever 1, one end of the first fixed support plate 2 is connected to the silicon-based fixed support body 7, and the other end of the first fixed support plate 2 is connected to the first wide plate cantilever 1, and the width of the first fixed support plate 2 is less than the width of the first wide plate cantilever 1; the second step micro-cantilever plate includes a rectangular first fixed support plate 2 and a rectangular first wide plate cantilever 1. The second fixing plate 5 and the second wide plate cantilever 4 are included, one end of the second fixing plate 5 is connected to the silicon-based fixing body 7, and the other end of the second fixing plate 5 is connected to the second wide plate cantilever 4. The width of the second fixing plate 5 is smaller than the width of the second wide plate cantilever 4. The first fixing plate 2, the first wide plate cantilever 1, the second fixing plate 5, the second wide plate cantilever 4 and the symmetry axis on the wide side of the fixing body cavity 8 are coaxial; the length of the second wide plate cantilever 4 is smaller than the length of the first wide plate cantilever 1, and the width and thickness of the second wide plate cantilever 4 are the same as those of the first wide plate cantilever 1; the length, width and thickness of the first fixing plate 2 and the second fixing plate 5 are the same; the length of the first fixing plate 2 is more than 5 times the thickness, and the width is more than 10 times the thickness. The length of the first wide plate cantilever 1 is more than 5 times the thickness, the length of the second fixed support plate 5 is more than 5 times the thickness, and the width is more than 5 times the thickness; the length of the first wide plate cantilever 1 is more than 5 times the thickness, and the width is more than 5 times the thickness; the length of the second wide plate cantilever 4 is more than 5 times the thickness, and the width is more than 5 times the thickness; the width of the first wide plate cantilever 1 is more than 2 times the width of the first fixed support plate 2, and the width of the second wide plate cantilever 4 is more than 2 times the width of the second fixed support plate 5; the first wide plate cantilever 1 is coaxially connected to the lower bottom of the first fixed support plate 2, and the second wide plate cantilever 4 is coaxially connected to the lower bottom of the second fixed support plate 5; the first step micro cantilever plate and the second step micro cantilever plate are coaxially arranged along the length direction The two wide plate cantilevers are arranged, and there is a free end gap width between them, that is, a vibration coupling gap 16 is provided between the free ends of the first wide plate cantilever 1 and the second wide plate cantilever 4; a piezoelectric electrode pair is arranged on the fixed support plate structure of the step micro-cantilever plate suspension structure, wherein the first fixed support plate 2 is arranged with a first piezoelectric driving electrode 3-1 and a first vibration pickup electrode 3-2, the first piezoelectric driving electrode 3-1 and the first vibration pickup electrode 3-2 constitute a piezoelectric vibration pickup electrode pair, and the second fixed support plate 5 is arranged with a piezoelectric vibration pickup electrode pair, that is, the second fixed support plate 5 is arranged with a second piezoelectric driving electrode 6-1 and a second vibration pickup electrode 6-2, and the piezoelectric electrode pair is used as the top electrode of the corresponding step micro-cantilever plate suspension structure;The piezoelectric electrode pair on the fixed support plate structure is symmetrically arranged about the symmetry axis in the length direction, and 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 the symmetry axis in the length direction of the first fixed support plate 2, and the second piezoelectric driving electrode 6-1 and the second vibration pickup electrode 6-2 are symmetrically arranged about the symmetry axis in 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 above-mentioned symmetry axis, and the first vibration pickup electrode 3-2 and the second vibration pickup electrode 6-2 are located On the same side of the above-mentioned axis; the piezoelectric electrode pair (i.e., the first piezoelectric drive electrode 3-1, the first vibration pickup electrode 3-2, the second piezoelectric drive electrode 6-1, and the second vibration pickup electrode 6-2) have the same length, width, and thickness; the width of the wide plate cantilever in the step micro-cantilever plate suspension structure is greater than or equal to the length, that is, 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; the width of the fixed support body cavity 8 is greater than the width of the first wide plate cantilever 1 and the second wide plate cantilever 4; each drive electrode and vibration pickup electrode is connected to a metal lead 9. The length direction is along; Figure 1 In the X direction, the X direction is parallel to the axial direction of the length direction of the step micro cantilever plate, and the Y direction is along the width direction of the step micro cantilever plate.

[0025] Reference Figure 1 Combined with Figure 3 The working method of the high-order bending vibration coupled step micro-cantilever plate MEMS viscosity sensor chip of this embodiment includes the following steps: When the high-order bending vibration coupled step micro-cantilever plate MEMS viscosity sensor chip is immersed in the fluid, the fluid will fill the free end gap (i.e., vibration coupling gap 16) between the suspended structures of the step micro-cantilever plate and act as a vibration coupling medium. The first step micro-cantilever plate is used as an active cantilever plate. When an alternating electric field is applied to the first piezoelectric driving electrode 3-1 of the first micro-cantilever plate, the top electrode of the piezoelectric layer of the first step micro-cantilever plate is energized and the bottom electrode is grounded, so that the first step micro-cantilever plate generates non-resonant high-order bending vibration at the frequency of the driving voltage, and drives the surrounding fluid to generate corresponding vibration. Further, the surrounding fluid vibration generates a vibration driving force on the second step micro-cantilever plate, so that the second step micro-cantilever plate generates passive high-order bending vibration at a specific frequency, wherein the vibration direction of the second step micro-cantilever plate is opposite to that of the first micro-cantilever plate, thereby enhancing the vibration coupling effect of the fluid medium.

[0026] The second step micro-cantilever plate acts as a passive cantilever plate, and generates vibration coupling with the first cantilever plate through the fluid medium, and the fluid medium in the gap at the free end of the suspended structure of the step micro-cantilever plate is subjected to shear force between the first step micro-cantilever plate and the second step micro-cantilever plate, so that the vibration amplitude of the second micro-cantilever plate structure is directly related to the fluid viscosity and the vibration amplitude of the first micro-cantilever plate structure. When the first step micro-cantilever plate and the second step micro-cantilever plate are in a non-resonant high-order bending vibration state, the piezoelectric pickup electrodes (the first pickup electrode 3-2 and the second pickup electrode 6-2) also form a top electrode externally connected to the electrical output port and the bottom electrode is grounded, and an alternating voltage detection signal is generated and output through the piezoelectric effect, and then the output voltage ratio of the suspended structure of the step micro-cantilever plate is extracted to achieve the measurement of fluid viscosity.

[0027] The high-order bending vibration coupled step micro-cantilever plate MEMS viscosity sensor chip of the present invention adopts a step micro-cantilever plate structure with a free end gap to excite the vibration coupling effect of the double micro-cantilever plates through a fluid medium; through the step shape structure design of the step micro-cantilever plate, through the width difference between the wide plate cantilever and the fixed support plate, the vibration stiffness of the wide plate cantilever structure along the width direction is reduced, so that the overall step micro-cantilever plate is easier to excite non-resonant high-order bending vibrations along the length and width directions in the fluid, so as to improve the high-order bending vibration stability of the step micro-cantilever plate; a double-step micro-cantilever plate structure in a non-resonant vibration state is adopted, and the fluid viscosity is measured by the sensor vibration amplitude, so as to avoid the problem of poor fluid viscosity measurement accuracy caused by the difficulty in accurately fitting complex resonant parameters such as quality factor in high-viscosity fluids, thereby improving the performance of this type of sensor such as fluid viscosity measurement accuracy and measurement efficiency.

[0028] The size of the first wide plate cantilever 1 of the step micro cantilever plate suspension structure in this embodiment is: length × width = (1100 ± 10) × (1400 ± 10) μm 2 , thickness is 20±5μm; the size of the second wide plate cantilever 4 is: length × width = (900±10) × (1400±10) μm 2 , thickness is 20±5μm; the size of the fixing plate (i.e., the first fixing plate 2 or the second fixing plate 5) is: length × width = (420±5) × (380±10) μm 2 , the thickness is 20±5μm; the free end gap (ie, the vibration coupling gap 16) between the first step micro-cantilever plate and the second step micro-cantilever plate is 100±5μm in length.

[0029] like Figure 2As shown in the cross-sectional view of the high-order bending vibration coupled step micro-cantilever plate MEMS viscosity sensor chip of the present invention, the high-order bending vibration coupled step micro-cantilever plate MEMS viscosity sensor chip of this embodiment is prepared by a single crystal silicon substrate 10, and the upper and lower surfaces (i.e., the top surface and the back surface) of the single crystal silicon substrate 10 are covered with a thermal oxide silicon film 11, and the thermal oxide silicon film 11 is used as an electrical insulation layer of the single crystal silicon substrate 10; a piezoelectric layer bottom electrode molybdenum film 12 is provided on the surface of the thermal oxide silicon film 11 on the top surface of the single crystal silicon substrate 10, and a low stress aluminum nitride piezoelectric film 13 is provided on the surface of the piezoelectric layer bottom electrode molybdenum film 12, wherein the piezoelectric layer bottom electrode molybdenum film 12 can be used as the chip bottom electrode grounding, and can also be used as a substrate layer for the deposition of the low stress aluminum nitride piezoelectric film 13; the low stress nitride The aluminum nitride piezoelectric film 13 is used as the piezoelectric film of the high-order bending vibration coupled step micro cantilever plate MEMS viscosity sensor chip in this embodiment. The low stress aluminum nitride piezoelectric film 13 is used to generate the inverse piezoelectric effect and the piezoelectric effect to realize the excitation of the vibration mode and the detection of the electrical signal; the surface of the low stress aluminum nitride piezoelectric film 13 is provided with an electrode metal layer 14, and the electrode metal layer 14 is used to form a piezoelectric electrode pair (the first piezoelectric drive electrode 3-1, the first vibration pickup electrode 3-2, the second piezoelectric drive electrode 6-1, and the second vibration pickup electrode 6-2) and the metal lead 9; the silicon nitride insulating layer film 15 covers the surface of the sensor chip (that is, 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. The area with a larger thickness of the single crystal silicon substrate 11 on the left side of the cross-sectional view represents the silicon-based fixed support 1 of the sensor chip, and the area with a smaller thickness of the single crystal silicon substrate represents the double micro cantilever plate suspended structure. Specifically, the first-step micro-cantilever plate and the silicon-based fixed support body 1 share the thermally oxidized silicon film 11 on the top surface of the single-crystalline silicon substrate 10, the molybdenum film 12 at the bottom electrode of the piezoelectric layer, the low-stress aluminum nitride piezoelectric film 13, the electrode metal layer 14, the silicon nitride insulating layer film 15 and a part of the single-crystalline silicon substrate 10 (specifically, a part of the top of the single-crystalline silicon substrate 10); the second-step micro-cantilever plate and the silicon-based fixed support body 1 share the thermally oxidized silicon film 11 on the top surface of the single-crystalline silicon substrate 10, the molybdenum film 12 at the bottom electrode of the piezoelectric layer, the low-stress aluminum nitride piezoelectric film 13, the electrode metal layer 14, the silicon nitride insulating layer film 15 and a part of the single-crystalline silicon substrate 10 (specifically, a part of the top of the single-crystalline silicon substrate 10).

[0030] like Figure 3 and Figure 4 In the embodiment, Comsol Multiphysics multi-physics field simulation software is used to perform fluid-solid coupling simulation analysis on the suspended structure of the stepped micro-cantilever plate of the above-mentioned embodiment size. Figure 3 The non-resonant vibration simulation results of the first-step micro-cantilever plate 17 and the second-step micro-cantilever plate 18 under the high-order bending vibration coupling are shown in Figure 1. The simulation liquid is cyclohexane (density 779 kg / m3 , viscosity is 1.0 cP). It can be seen that the first step micro-cantilever plate 17 and the second step micro-cantilever plate 18 respectively undergo bending vibrations of specific amplitudes, and the bending vibrations occur simultaneously in the length and width directions of the step micro-cantilever plate, forming a basic bending vibration form different from that only along the length direction. The vibration between the step micro-cantilever plates is transmitted through the gap fluid medium, and the active bending vibration of the first step micro-cantilever plate 17 is coupled to the second step micro-cantilever plate 18, so that the second step micro-cantilever plate 18 undergoes passive bending vibration, and the vibration direction is opposite to the vibration direction of the first step micro-cantilever plate 17. The reverse high-order bending vibrations of the first step micro-cantilever plate 17 and the second step micro-cantilever plate 18 can enhance the vibration coupling effect of the fluid medium, thereby enhancing the accuracy and sensitivity of fluid viscosity measurement.

[0031] Figure 4 In the present invention, four different liquids are selected for fluid-solid coupling simulation analysis, including n-heptane, cyclohexane, MD2M, and D4 liquids, and a variation curve between the ratio of the vibration amplitude of the suspended structure of the step micro-cantilever plate (the vibration amplitude of the second step micro-cantilever plate 18 / the vibration amplitude of the first step micro-cantilever plate 17) and the viscosity of the fluid is obtained. It can be seen that a univariate corresponding relationship between the vibration amplitude ratio of the suspended structure of the step micro-cantilever plate and the viscosity of the fluid can be established, thereby realizing the measurement of the viscosity of the fluid, thereby verifying the working mode of the viscosity sensor chip proposed in the present invention.

[0032] In summary, the step micro-cantilever plate suspension structure of the present invention adopts a free end gap design, and realizes the high-order bending vibration coupling between the double micro-cantilever plate suspension structures through the fluid medium, so that the two step micro-cantilever plates undergo active and passive non-resonant bending vibrations; the step micro-cantilever plate suspension structure is composed 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, thereby forming a stepped shape of the overall micro-cantilever plate structure, and the stepped shape is designed to increase the bending vibration stiffness of the wide plate cantilever along the width direction, so that it is easier to excite high-order bending vibrations, and improve the vibration stability and measurement accuracy of the sensor chip immersed in the fluid; the sensor chip adopts locally arranged piezoelectric drive electrodes to excite non-resonant high-order bending vibrations, and the piezoelectric pickup electrodes are used to convert vibration signals into electrical signal outputs through the piezoelectric effect, thereby 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.

[0033] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does 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 bending vibration coupled step micro-cantilever plate MEMS viscosity sensor chip, characterized in that: The invention comprises a silicon-based fixed support body (7), a fixed support body cavity (8) is provided on the silicon-based fixed support body (7), a stepped micro-cantilever plate suspended structure is connected in the fixed support body cavity (8), the stepped micro-cantilever plate suspended structure comprises a first stepped micro-cantilever plate (17) and a second stepped micro-cantilever plate (18) whose free ends are arranged opposite to each other, the length of the first stepped micro-cantilever plate (17) is greater than the length 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 respectively connected to the silicon-based fixed support body (7) and the first wide plate cantilever (1), the width of the first fixed support plate (2) is smaller than that of the first wide plate cantilever (1), and 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 respectively connected to the silicon-based fixed support body (7) and the second wide plate cantilever (4). The second fixing plate (5) is connected to the wide plate cantilever (4), the width of the second fixing plate (5) is smaller than the width of the second wide plate cantilever (4), and a vibration coupling gap (16) is left between the free end of the first wide plate cantilever (1) and the free end of the second wide plate cantilever (4); the first piezoelectric driving electrode (3-1) and the first vibration pickup electrode (3-2) are symmetrically arranged on both sides of the first fixing plate (2) along the width direction, and the second piezoelectric driving electrode (6-1) and the second vibration pickup electrode (6-2) are symmetrically arranged on both sides of the second fixing plate (5) along the width direction; 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 to metal leads (9).

2. The high-order bending vibration coupled step micro-cantilever plate MEMS viscosity sensor chip according to claim 1 is characterized in that: The first fixing plate (2) and the second fixing plate (5) have the same length, width and thickness, the length of the first wide plate cantilever (1) is greater than the width of the second wide plate cantilever (4), and the length of the first wide plate cantilever (1) is greater than the length of the second wide plate cantilever (4).

3. The high-order bending vibration coupled step micro-cantilever plate MEMS viscosity sensor chip according to claim 2, characterized in that: The length of the second wide plate cantilever (4) is 80% to 84% of the length of the first wide plate cantilever (1); The length of the first fixing plate (2) is 37% to 39% of the length of the first wide plate cantilever (1), and the width of the first fixing plate (2) is 26% to 29% of the width of the first wide plate cantilever (1); The length of the second fixing plate (5) is 37% to 39% of the length of the second wide plate cantilever (4), and the width of the second fixing plate (5) is 26% to 29% of the width of the second wide plate cantilever (4).

4. The high-order bending vibration coupled step micro-cantilever plate MEMS viscosity sensor chip according to claim 3 is characterized in that: The width of the vibration coupling gap (16) is 95-105 μm.

5. The high-order bending vibration coupled step micro-cantilever plate MEMS viscosity sensor chip according to claim 1, characterized in that: The length of the first fixing plate (2) is more than 5 times its thickness, and the width is more than 5 times its thickness; The length of the second fixing plate (5) is more than 5 times the thickness, and the width is more than 5 times the thickness; The length of the first wide plate cantilever (1) is more than 5 times the thickness, and the width is more than 5 times the thickness; The length of the second wide plate cantilever (4) is more than 5 times the thickness, and the width is more than 5 times the thickness; The width of the first wide plate cantilever (1) is more than twice the width of the first fixing plate (2); The width of the second wide plate cantilever (4) is more than twice the width of the second fixing plate (5).

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

7. The high-order bending vibration coupled step 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 its length, and the width of the second wide plate cantilever 4 is greater than or equal to its length.

8. The high-order bending vibration coupled step micro-cantilever plate MEMS viscosity sensor chip according to claim 1, characterized in that: The shape of the support body cavity (8) is rectangular; the symmetry axis of the wide side of the support body cavity (8), the symmetry axis of the wide side of the first 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 support plate (5), and the symmetry axis of the wide side of the second wide plate cantilever (4) are coaxial; the width of the 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 drive electrode (3-1) and the first vibration pickup electrode (3-2) are respectively located on both sides of the symmetry axis of the wide side of the first support plate (2); and the second piezoelectric drive electrode (6-1) and the second vibration pickup electrode (6-2) are respectively located on both sides of the symmetry axis of the wide side of the second support plate (5).

9. A high-order bending vibration coupled step micro-cantilever plate MEMS viscosity sensor chip according to any one of claims 1 to 8, characterized in that: The silicon-based fixed support body (7) comprises a single crystal silicon substrate (10), the bottom and top surfaces of the single crystal silicon substrate (10) are both provided with a thermally oxidized silicon film (11), the surface of the thermally oxidized 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) used as a first piezoelectric driving electrode (3-1), a second piezoelectric driving electrode (6-1), a first vibration pickup electrode (3-2) and a 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); a first fixed support plate (2), the first wide plate cantilever (1), the rectangular second fixing plate (5) and the second wide plate cantilever (4) have the same structure in the thickness direction; the first fixing plate (2), the first wide plate cantilever (1), the rectangular second fixing plate (5), the second wide plate cantilever (4) and the silicon-based fixing body (7) share the thermally oxidized 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 single crystal silicon substrate (10) on the first fixing plate (2), the first wide plate cantilever (1), the rectangular second fixing plate (5) and the second wide plate cantilever (4) is thinner than the single crystal silicon substrate (10) of the silicon-based fixing body (7).

10. The working method of a high-order bending vibration coupled step micro-cantilever plate MEMS viscosity sensor chip according to any one of claims 1 to 9, characterized in that: include: When the high-order bending vibration coupled step 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 step micro-cantilever plate is used as an active cantilever plate. When an alternating electric field is applied to the first piezoelectric driving electrode (3-1), the top electrode of the piezoelectric layer of the first step micro-cantilever plate is energized and the bottom electrode is grounded, so that the first step micro-cantilever plate generates non-resonant high-order bending vibration at the frequency of the driving voltage, and at the same time drives the fluid around the first step micro-cantilever plate to generate corresponding vibration. The vibration of the fluid around the first step micro-cantilever plate generates a vibration driving force on the second step micro-cantilever plate, so that the second step micro-cantilever plate generates passive high-order bending vibration at a specific frequency, wherein the vibration direction of the second step micro-cantilever plate is opposite to the vibration direction of the first micro-cantilever plate; The second step micro-cantilever plate acts as a passive cantilever plate, and generates vibration coupling with the first cantilever plate through the fluid medium. The fluid medium in the vibration coupling gap (16) is subjected to shear force between the first step micro-cantilever plate and the second step micro-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; When the first step micro-cantilever plate and the second step micro-cantilever plate are in a non-resonant high-order bending vibration state, the first vibration pickup electrode (3-2) and the second vibration pickup electrode (6-2) form a top electrode externally connected to an electrical output port and a bottom electrode grounded, and an alternating voltage detection signal is generated and output through the piezoelectric effect, and the output voltage ratio of the suspended structure of the step micro-cantilever plate is extracted to achieve the measurement of fluid viscosity.

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