Piezoelectric MEMS vibration sensor based on bent cantilever beam-multi-electrode structure

Abstract

The invention belongs to the technical field of micro electro mechanical systems, and particularly provides a piezoelectric MEMS vibration sensor based on a bent cantilever beam-multi-electrode structure, the piezoelectric MEMS vibration sensor comprises a bent cantilever beam 1, an outer ring anchor area 2, a silicon mass block 3 and a piezoelectric film, when an external vibration signal is transmitted, the silicon mass block can generate inertia force under the action of acceleration, and the piezoelectric film can generate the piezoelectric film; the inertia force further acts on the bent cantilever beam, so that the piezoelectric film attached to the bent cantilever beam deforms, charges are generated through the direct piezoelectric effect, an electric signal is collected by the metal electrode, and an acceleration measurement result is obtained through analysis according to the electric signal; the bending type cantilever beam structure with the 135-degree break angle is adopted, the bending type cantilever beam is arranged around the mass block, the area occupied by the vibration sensor is effectively reduced through the bending type cantilever beam structure with the 135-degree break angle while the electromechanical transduction efficiency is guaranteed, the sensitivity of the device is enhanced, and the reliability of the vibration sensor is improved. And support is provided for development of a miniaturized and low-power-consumption intelligent vibration sensing system.

Description

Technical Field

[0001] This invention belongs to the field of micro-electro-mechanical systems (MEMS) technology, specifically a piezoelectric MEMS vibration sensor based on a bent cantilever beam-multi-electrode structure. Background Technology

[0002] With the rapid development of electronic information technology, sensors have become increasingly prominent in condition monitoring and intelligent sensing systems. Among them, vibration sensors, as a key type of mechanical quantity sensor, are widely used in equipment fault diagnosis, structural health monitoring and safety early warning, playing an irreplaceable role. Currently, the mainstream vibration sensor types include piezoelectric, capacitive, and piezoresistive. Among them, vibration sensors based on the piezoelectric effect have been widely used in industrial vibration measurement. Piezoelectric MEMS vibration sensors typically consist of a micromechanical cantilever beam and a mass block structure, with a piezoelectric material film fabricated at key parts of the beam. When external vibration is transmitted to the sensor, the inertial force causes the mass block to displace, resulting in the cantilever beam bending and generating stress on the piezoelectric material on its surface. This stress is directly converted into a charge signal through the positive piezoelectric effect. The detection circuit collects and processes this charge signal, and by analyzing its changes, the vibration information of the measured object can be accurately reconstructed. Piezoelectric vibration sensors based on MEMS technology not only inherit the advantages of traditional piezoelectric sensors, such as wide frequency response and good dynamic performance, but also have significant advantages such as miniaturization, low power consumption, ease of system integration, and low cost of mass production. They are occupying an increasingly important market position in high-demand scenarios such as industrial IoT and predictive maintenance of high-end equipment.

[0003] Currently, the sensing structure of piezoelectric MEMS vibration sensors mainly adopts a cantilever beam design. This structure responds to external vibrations through a mass block supported at a fixed end, causing strain charges to be generated in the piezoelectric material on the beam surface. Although this design has high sensitivity, its physical structure has obvious defects: First, the stress distribution of the cantilever beam is extremely uneven during vibration, with the maximum stress concentrated at the fixed end, resulting in low utilization of the piezoelectric material and limited electromechanical conversion efficiency. Second, the stiffness of the cantilever beam in the direction perpendicular to the sensing axis is weak, easily generating cross-axis interference, which seriously affects the measurement accuracy. In addition, reducing the beam thickness to obtain sufficient sensitivity will significantly reduce the structure's natural frequency, limiting the sensor's operating bandwidth. These inherent structural contradictions make it difficult to balance dynamic range, linearity, and anti-interference ability in cantilever beam-based piezoelectric MEMS vibration sensors, restricting their application in precision measurement fields. Furthermore, in recent years, the demand for multi-parameter sensing under complex working conditions has made composite vibration sensors a research hotspot, placing more stringent requirements on the miniaturization design of vibration sensors. Based on this, this invention provides a piezoelectric MEMS vibration sensor based on a bent cantilever beam-multi-electrode structure. Summary of the Invention

[0004] The purpose of this invention is to propose a piezoelectric MEMS vibration sensor based on a bent cantilever beam-multi-electrode structure, which reduces the area of ​​the piezoelectric sensing unit and enhances the device sensitivity, providing support for the development of miniaturized, low-power intelligent vibration sensing systems.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A piezoelectric MEMS vibration sensor based on a bent cantilever beam-multi-electrode structure includes: a bent cantilever beam 1, an outer anchor region 2, a silicon mass block 3, and a piezoelectric thin film; characterized in that:

[0007] The piezoelectric MEMS vibration sensor adopts a 90° rotationally symmetrical structure, the outer ring anchor area 2 adopts a square ring structure, and the silicon mass block 3 adopts a regular octagonal structure. The silicon mass block 3 is placed in the hollow area of ​​the outer ring anchor area 2 and is located at the center.

[0008] The silicon mass block 3 is connected to the outer ring anchor area 2 via four bent cantilever beams 1. Each bent cantilever beam 1 is composed of at least two straight cantilever beams connected at a 135° angle. An inner piezoelectric film 402 is provided on the inner connecting section of the bent cantilever beam, and an inner metal electrode 103 is provided on the inner piezoelectric film 402. The inner metal electrode 103 is connected to the inner metal pad 202 via an inner metal wire 104. An outer piezoelectric film 401 is provided on the outer connecting section of the bent cantilever beam, and an outer metal electrode 101 is provided on the outer piezoelectric film 401. The outer metal electrode 101 is connected to the outer metal pad 201 via an outer metal wire 102. The outer metal pad 201 and the inner metal pad 202 are located on the outer ring anchor area 2.

[0009] Furthermore, starting from any vertex of the silicon mass block, the four bent cantilever beams are numbered sequentially, with the first, third, fifth, and seventh vertices of the silicon mass block as the starting points, respectively, and arranged around the silicon mass block; or, the four bent cantilever beams are arranged around the silicon mass block with the second, fourth, sixth, and eighth vertices as the starting points, respectively.

[0010] Furthermore, the outer ring anchor area 2 is divided into an electrode metal pad area and a ground metal pad area, both of which are square rings, with the electrode metal pad area located inside the ground metal pad area. The electrode metal pad area is covered by a second isolation oxide layer 204, and the outer metal pad 201 and the inner metal pad 202 are disposed on the second isolation oxide layer 204. The ground metal pad area is also provided with a ground metal pad 203, which is disposed in a one-to-one correspondence with the outer metal pad 201 and the inner metal pad 202.

[0011] Furthermore, the material of the bent cantilever beam is silicon.

[0012] Furthermore, during the operation of the piezoelectric MEMS vibration sensor: the four inner metal electrodes and the four outer metal electrodes are numbered, and the voltage values ​​of the eight metal electrodes are collected and recorded as follows:

[0013] ,

[0014] Among them, V i This represents the voltage value of the i-th metal electrode, where i = 1, 2, 3, ..., 8;

[0015] Then calculate acceleration for: ,

[0016] in, The sensitivity matrix is ​​represented as follows:

[0017] ,

[0018] Among them, a xi a yi a zi These represent the sensitivity of the i-th metal electrode to the acceleration along the x, y, and z axes, respectively.

[0019] Based on the above technical solution, the beneficial effects of the present invention are as follows:

[0020] This invention proposes a piezoelectric MEMS vibration sensor based on a bent cantilever beam-multi-electrode structure. When an external vibration signal is received, the silicon mass block generates inertial force under acceleration. This inertial force further acts on the bent cantilever beam, causing the piezoelectric film attached to the beam to deform and generate charge through the positive piezoelectric effect. The electrical signal is collected by metal electrodes, and the acceleration measurement result is obtained from the analysis of the electrical signal. In this process, on the one hand, a bent cantilever beam structure with a 135° bend angle is adopted, and the bent cantilever beam is arranged around the mass block. While ensuring electromechanical energy conversion efficiency, the 135° bend angle bent cantilever beam structure effectively reduces the area occupied by the vibration sensor and enhances the device sensitivity. On the other hand, through physical structure optimization, the signals of the inner and outer electrodes on a single bent cantilever beam are collected simultaneously, and the detection of triaxial vibration on the same device is achieved through calculation. Attached Figure Description

[0021] Figure 1 A three-dimensional structural diagram of the piezoelectric MEMS vibration sensor based on a bent cantilever beam-multi-electrode structure provided by the present invention;

[0022] Figure 2 A top view of the piezoelectric MEMS vibration sensor based on a bent cantilever beam-multi-electrode structure provided by the present invention;

[0023] Figure 3 A partially enlarged view of the outer metal electrode provided by the present invention;

[0024] Figure 4 A partially enlarged view of the inner metal electrode provided by the present invention;

[0025] Figure 5 This is a partial enlarged view of the outer anchorage area provided by the present invention;

[0026] Figure 6 The sensitivity of the metal electrode position of this invention to acceleration in the x-axis direction;

[0027] Figure 7 The sensitivity of the metal electrode position of this invention to acceleration in the y-axis direction;

[0028] Figure 8The sensitivity of the metal electrode position of this invention to acceleration in the z-axis direction;

[0029] In the above attached figures:

[0030] 1-Bent cantilever beam; 101-Outer metal electrode; 102-Outer metal wire; 103-Inner metal electrode; 104-Inner metal wire; 105-First isolation oxide layer; 2-Outer ring anchor area; 201-Outer metal pad; 202-Inner metal pad; 203-Grounding metal pad; 204-Second isolation oxide layer; 3-Silicon mass block; 401-Outer piezoelectric film; 402-Inner piezoelectric film. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0032] This embodiment provides a piezoelectric MEMS vibration sensor based on a bent cantilever beam-multi-electrode structure, the structure of which is as follows: Figure 1 and Figure 2 As shown, it specifically includes: a bent cantilever beam 1, an outer ring anchor area 2, a silicon mass block 3, and a piezoelectric film;

[0033] The piezoelectric MEMS vibration sensor adopts a 90° rotationally symmetrical structure, the outer ring anchor area 2 adopts a square ring structure, and the silicon mass block 3 adopts a regular octagonal structure. The silicon mass block 3 is placed upright in the hollow area of ​​the outer ring anchor area 2 and located at the center. Figure 2 As shown, the silicon mass block 3 being placed in the hollow area of ​​the outer ring anchor area 2 means that the presence of the regular octagonal silicon mass block corresponds to four sides parallel to the four sides of the square hollow area, and the other four sides are parallel to the diagonal of the square hollow area.

[0034] The silicon mass block 3 is connected to the outer ring anchor area 2 by four bent cantilever beams 1. Each bent cantilever beam 1 is composed of at least two straight cantilever beams with an angle of 135° (in this embodiment, the bent cantilever beam is composed of five straight cantilever beams connected in sequence with an angle of 135°, and the number of straight cantilever beams usually does not exceed 7). Starting from any vertex of the silicon mass block, the four bent cantilever beams are numbered sequentially from the first vertex to the eighth vertex. The four bent cantilever beams are arranged around the silicon mass block, starting from the first, third, fifth, and seventh vertices (or the second, fourth, sixth, and eighth vertices) of the silicon mass block, respectively.

[0035] For each bent cantilever beam 1, the connection segment between the bent cantilever beam 1 and the mass block 3 is marked as the inner connection segment, and the connection segment between the bent cantilever beam 1 and the outer ring anchor area 2 is marked as the outer connection segment. An inner piezoelectric film 402 is provided on the inner connection segment of the bent cantilever beam, and an inner metal electrode 103 is provided on the inner piezoelectric film 402. The inner metal electrode 103 is connected to the inner metal pad 202 through an inner metal wire 104, and a first spacer is provided between the inner metal wire 104 and the bent cantilever beam 1. An oxide layer 105 is provided; an outer piezoelectric film 401 is provided on the outer connecting section of the bent cantilever beam, and an outer metal electrode 101 is provided on the outer piezoelectric film 401. The outer metal electrode 101 is connected to the outer metal pad 201 through an outer metal wire 102. Similarly, a first isolation oxide layer 105 is provided between the outer metal wire 102 and the bent cantilever beam 1. It should be noted that, in terms of spatial arrangement, the inner metal wire 104 and the outer piezoelectric film 401 are obviously separated.

[0036] The outer ring anchor area 2 is divided into an electrode metal pad area and a ground metal pad area. Both the electrode metal pad area and the ground metal pad area are square rings, with the electrode metal pad area located inside the ground metal pad area. The electrode metal pad area is covered with a second isolation oxide layer 204, and the outer metal pad 201 and the inner metal pad 202 are disposed on the second isolation oxide layer 204. Eight ground metal pads 203 are disposed on the ground metal pad area, and the ground metal pads 203 correspond one-to-one with the outer metal pads 201 and the inner metal pads 202.

[0037] Furthermore, the material of the bent cantilever beam is silicon; the materials of the first isolation oxide layer and the second isolation oxide layer can be silicon dioxide, and the thickness can be 0.3μm to 1.5μm; the metal material includes, but is not limited to, metals such as silver, copper, gold, aluminum, nickel, and lead, and the thickness can be 0.5μm to 2μm; the piezoelectric film includes, but is not limited to, piezoelectric materials such as AlN, ZnO, PZT, PVDF, LiNbO3, and LiTaO3, and the thickness is 0.5μm to 2μm.

[0038] In terms of working principle:

[0039] like Figures 1-5 As shown, in the vibration sensor of this invention, a silicon mass block is connected to the outer anchor area via a bent cantilever beam. A piezoelectric film, a metal electrode, and its wires are correspondingly arranged on the bent cantilever beam. When an external vibration signal is applied, the silicon mass block generates a corresponding acceleration, which will exert a force on the bent cantilever beam, thereby causing the piezoelectric film to deform.

[0040] At the outer metal electrode, the relationship between deformation and applied acceleration is:

[0041] ,

[0042] in, denoted as the deformation of the outer piezoelectric film, m as the mass of the mass block, a as the magnitude of the applied acceleration, L as the equivalent total beam length of the single beam, E as the elastic modulus of the beam, b as the width of the beam, and h as the thickness of the beam.

[0043] To increase the beam length and improve device sensitivity while minimizing device size, this invention employs a physical structure design of a cantilever beam with a 135° bend surrounding a mass block. Calculations show that stress is transferred through the bend of the cantilever beam, which can subsequently be equivalent to a straight beam approximately 92% of its length. This constant is denoted as k, and the equivalent total beam length of a single beam can be denoted as:

[0044] ,

[0045] Where L1, L2, L3, L4, and L5 are the linear lengths of the straight beams that pass through each bend, starting from the first segment of the cantilever beam closest to the mass block.

[0046] At the inner metal electrode, the relationship between deformation and applied acceleration is:

[0047] ,

[0048] in, The deformation of the inner piezoelectric film, The distance from the center point of the inner piezoelectric film to the point where the outer anchor area meets the bent cantilever beam is denoted as ;

[0049] When a cantilever beam is bent and deformed, the piezoelectric film attached to it generates an electrical signal through the piezoelectric effect. The electrical signal at the outer electrode can be expressed in voltage form as follows:

[0050] ,

[0051] in, The voltage at the outer electrode. It is the piezoelectric constant. The thickness of the piezoelectric film. The relative permittivity of the piezoelectric material is... It is the vacuum permittivity;

[0052] Similarly, the electrical signal at the inner electrode can be expressed in voltage form as:

[0053] ,

[0054] in, This is the voltage at the inner electrode;

[0055] like Figure 6 , Figure 7 and Figure 8 The figures show the response of the piezoelectric thin film at the selected metal electrode location to acceleration in the x, y, and z axes. The orientation (up, down, left, right) is described based on... Figure 2 The top view shown; because the invention has a 90° rotationally symmetric pattern in the xy plane, the inner electrode positions of the four cantilever beams have the same acceleration sensitivity in the z-axis direction, and the outer electrodes are also the same, therefore... Figure 8 The data only shows the response of the inner and outer electrode positions on the same cantilever beam to the z-axis acceleration;

[0056] This invention can collect electrical signals from a total of eight locations, and the sensitivity of these eight locations to three axial accelerations is denoted as a. xi a yi a zi For i = 1, 2, 3, ..., 8, the sensitivity matrix is ​​denoted as:

[0057] ,

[0058] The measured voltage is recorded as:

[0059] ,

[0060] The final acceleration of the overdetermined system was calculated using the least squares method. The calculation formula is:

[0061] ,

[0062] As can be seen from the above, the vibration sensor in this invention can be regarded as eight single-ended outputs during operation. The eight ports do not have a specific order. They are usually numbered sequentially in a clockwise or counterclockwise direction, starting from any port.

[0063] In summary, this invention proposes a piezoelectric MEMS vibration sensor based on a bent cantilever beam-multi-electrode structure. By replacing the traditional straight beam with a bent cantilever beam, the device area is significantly reduced, and higher sensitivity is achieved. At the same time, collecting data from multiple points can effectively reduce errors in the final calculation.

[0064] The above description is merely a specific embodiment of the present invention. Any feature disclosed in this specification may be replaced by other equivalent or similar features unless otherwise specified. All disclosed features, or steps in all methods or processes, may be combined in any way except for mutually exclusive features and / or steps.

Claims

1. A piezoelectric MEMS vibration sensor based on a folded cantilever beam - multi electrode structure, comprising: Bent cantilever beam (1), outer ring anchor area (2), silicon mass block (3) and piezoelectric film; It is characterized by: The piezoelectric MEMS vibration sensor adopts a 90° rotationally symmetric structure, the outer ring anchor area (2) adopts a square ring structure, and the silicon mass block (3) adopts a regular octagonal structure, and the silicon mass block (3) is placed in the hollow area of the outer ring anchor area (2) and located at the center position; The silicon mass block (3) is connected to the outer ring anchor area (2) by four bent cantilever beams (1), and the bent cantilever beam (1) is composed of at least two straight cantilever beams with a 135° included angle; The inner side of the bent cantilever beam is provided with an inner side piezoelectric film (402), and the inner side piezoelectric film (402) is provided with an inner side metal electrode (103), and the inner side metal electrode (103) is connected to the inner side metal pad (202) through the inner side metal wire (104); The outer side of the bent cantilever beam is provided with an outer side piezoelectric film (401), and the outer side piezoelectric film (401) is provided with an outer side metal electrode (101), and the outer side metal electrode (101) is connected to the outer side metal pad (201) through the outer side metal wire (102); The outer side metal pad (201) and the inner side metal pad (202) are arranged on the outer ring anchor area (2).

2. The piezoelectric MEMS vibration sensor based on a folded cantilever beam-multi electrode structure according to claim 1, characterized in that, With any vertex of the silicon mass block as the starting point, the four bent cantilever beams are arranged around the silicon mass block with the first, third, fifth and seventh vertices of the silicon mass block as the starting points, respectively; Alternatively, the four bent cantilever beams are arranged around the silicon mass block with the second, fourth, sixth and eighth vertices of the silicon mass block as the starting points, respectively.

3. The piezoelectric MEMS vibration sensor based on a folded cantilever beam-multi electrode structure according to claim 1, wherein, The outer ring anchor area (2) is divided into an electrode metal pad area and a grounding metal pad area, both of which are square rings, and the electrode metal pad area is located inside the grounding metal pad area; The electrode metal pad area is covered with a second isolation oxide layer (204), and the outer side metal pad (201) and the inner side metal pad (202) are arranged on the second isolation oxide layer (204); The grounding metal pad area is also provided with a grounding metal pad (203), and the grounding metal pad (203) is arranged one by one with the outer side metal pad (201) and the inner side metal pad (202).

4. The piezoelectric MEMS vibration sensor based on a folded cantilever beam-multi electrode structure according to claim 1, wherein, The material of the bent cantilever beam is silicon.

5. The piezoelectric MEMS vibration sensor based on a folded cantilever beam-multi electrode structure according to claim 1, wherein, During the working process of the piezoelectric MEMS vibration sensor: number four inner side metal electrodes and four outer side metal electrodes, collect the voltage values of the eight metal electrodes, and record them as: ， wherein V i represents the voltage value of the i-th metal electrode, i = 1, 2, 3, …, 8; Then the acceleration is calculated is: , wherein is the sensitivity matrix, denoted as: ， wherein a xi , a yi , a zi respectively represent the sensitivity of the i-th metal electrode to the x, y, z axis acceleration.

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