A field-polished MEMS electric field sensor based on piezoelectric micro-mirror

Abstract

This invention relates to a field-polished MEMS electric field sensor based on a piezoelectric micromirror, comprising a substrate, a piezoelectric driving structure, a sensing electrode, and a shielding electrode. The shielding electrode includes a shielding electrode plate and first comb-like structures disposed on both sides of the shielding electrode plate. The sensing electrode includes one or more pairs of second comb-like structures symmetrically disposed on both sides of the shielding electrode. The combs on the sensing electrode and the shielding electrode are interdigitated. The piezoelectric driving structure includes two centrally symmetrically arranged driving arms, each driving arm having a fixed end and a free end. The fixed end is mounted on the substrate, and the free ends of the two driving arms are connected to two centrally symmetrical positions on the shielding electrode, respectively. When the sensor is working, the operating mode of the shielding electrode is set, and the piezoelectric driving structure causes the shielding electrode to vibrate periodically, collecting the induced signal carrying the measured electric field information generated on the sensing electrode. Compared with the prior art, this invention has the advantages of higher frequency detection and higher accuracy.

Description

Technical Field

[0001] This invention belongs to the field of micro electric field sensors, and relates to a MEMS electric field sensor, and more particularly to a field-milled MEMS electric field sensor based on a piezoelectric micromirror. Background Technology

[0002] With economic and social development, power systems are evolving towards intelligence, efficiency, and integration. To effectively capture information from equipment within the power grid, electric field measurement is not only a crucial monitoring target on the equipment but also a vital state variable for network nodes and lines. Electric field measurement has significant applications in various power grid scenarios, such as electromagnetic environment monitoring along transmission line corridors and non-contact voltage measurement of lines. Currently, traditional electric field sensors are outdated and have significant drawbacks, such as large size, high power consumption, and limited measurement range. In contrast, MEMS (Micro-Electro-Mechanical Systems) employ miniature structures, achieving intelligent functionality within a very small space. Non-contact electric field sensors manufactured using MEMS offer advantages that traditional sensors lack, including small size, light weight, low cost, high reliability, and mass production capability. These advantages meet the requirements of power grid development and enable large-scale deployment and comprehensive information sensing for power grid condition monitoring.

[0003] Currently, piezoelectric MEMS systems offer significant advantages due to the high electromechanical energy conversion efficiency of piezoelectric materials and the high resolution and high driving capability resulting from the direct and inverse piezoelectric effects. Compared to complex electrostatic MEMS systems and the difficult-to-control electrothermal and electromagnetic MEMS systems, integrated piezoelectric MEMS systems offer advantages in high performance, miniaturization, and low cost, making them an important research direction in the MEMS field. However, current research on piezoelectric micromirror field-polished MEMS electric field sensors is still immature, easily limited by their operating mode, and suffers from low accuracy and sensitivity. Further research is needed on novel adapted piezoelectric driving structures and MEMS sensing structures. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art by providing a field-milled MEMS electric field sensor based on a piezoelectric micromirror, which can perform higher frequency detection and has high sensor accuracy.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] A field-polished MEMS electric field sensor based on a piezoelectric micromirror includes a substrate, a piezoelectric driving structure, a sensing electrode, and a shielding electrode. The sensing electrode and the piezoelectric driving structure are mounted on the substrate. The shielding electrode includes a shielding electrode plate and a first comb-shaped structure disposed on both sides of the shielding electrode plate. The sensing electrode includes one or more pairs of second comb-shaped structures symmetrically disposed on both sides of the shielding electrode. The comb teeth on the sensing electrode and the shielding electrode are interdigitated. The piezoelectric driving structure includes two driving arms arranged in a centrally symmetrical manner. Each driving arm includes a fixed end and a free end. The fixed end is mounted on the substrate, and the free ends of the two driving arms are connected to two centrally symmetrical positions on the shielding electrode, respectively.

[0007] When the sensor is working, the working mode of the shielding electrode is set, and the shielding electrode is periodically vibrated by the piezoelectric drive structure to collect the sensing signal carrying the measured electric field information generated on the sensing electrode.

[0008] Furthermore, by changing the driving voltage applied to the two driving arms of the piezoelectric drive structure, the shielding electrodes are placed in different operating modes.

[0009] Furthermore, the sensing electrode is mounted on the substrate via sensing electrode solder joints.

[0010] Furthermore, the piezoelectric drive structure is a sandwich structure, comprising a bottom electrode, a piezoelectric material, and a top electrode arranged sequentially. The bottom electrode is mounted on the substrate via a bottom electrode solder joint, and the top electrode is mounted on the substrate via a top electrode solder joint.

[0011] Furthermore, the piezoelectric material is an inorganic piezoelectric material or an organic piezoelectric material.

[0012] Furthermore, the piezoelectric drive structure is an L-shaped beam, an S-shaped beam, or a double S-shaped beam.

[0013] Furthermore, the substrate comprises a bottom layer, a buried oxide layer, and a top layer disposed sequentially.

[0014] Furthermore, the materials of the bottom and top layers are SOI.

[0015] Furthermore, the operating modes include a torsional operating mode and an up-and-down operating mode. When the driving voltage applied to the two driving arms of the piezoelectric driving structure has equal amplitude and opposite phase, the shielding electrode is in the torsional operating mode. When the driving voltage signal applied to the two driving arms of the piezoelectric driving structure has equal amplitude and a phase difference of 90°, the shielding electrode is in the up-and-down operating mode.

[0016] Furthermore, in the initial state, the comb teeth on the sensing electrode and the shielding electrode are on the same plane.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] (1) This invention utilizes a combination of a field-milled MEMS electric field sensor and a piezoelectric MEMS micromirror to improve the structure of the three sensors, thereby increasing their resonant frequency to a certain extent. This enables the designed MEMS electric field sensor to perform higher frequency detection, further improving the accuracy of the sensor.

[0019] (2) By setting a piezoelectric drive structure, the present invention can easily enable the shielding electrode to work in different working modes, including a torsional working mode and an up-and-down working mode. In the torsional working mode, the torsional displacement of the shielding electrode is used to increase the induced charge of the sensing electrode, thereby improving the sensor sensitivity. In the up-and-down working mode, the resonant frequency of the sensor can be increased, thereby improving the accuracy.

[0020] (3) Compared with current MEMS electric field sensors, the present invention can realize multiple working modes. Without adding other materials and processes, the sensor manufacturing process is simple and low cost, which is conducive to mass production. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the sensor structure of the present invention;

[0022] Figure 2 This is a schematic diagram of the sensor of the present invention in torsional working mode;

[0023] Figure 3 This is a schematic diagram of the sensor of the present invention in the up-down working mode;

[0024] Figure 4 A schematic diagram illustrating the working principle of a single-layer thin-film piezoelectric microcantilever beam.

[0025] Figure 5 This is a schematic diagram illustrating the principle of the inverse piezoelectric effect.

[0026] In the figure, 1-bottom silicon layer of SOI substrate, 2-buried oxide layer of SOI substrate, 3-top silicon layer of SOI substrate, 4-top electrode solder joint, 5-bottom electrode solder joint, 6-induction electrode solder joint, 7-induction electrode, 8-shielding electrode, 9-piezoelectric drive structure. Detailed Implementation

[0027] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0028] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention. For example, "horizontal" simply means that its direction is more horizontal relative to "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0029] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0030] like Figure 1 As shown, this embodiment provides a field-polished MEMS electric field sensor based on a piezoelectric micromirror, including a substrate, a piezoelectric driving structure 9, a sensing electrode 7, and a shielding electrode 8. The sensing electrode 7 and the piezoelectric driving structure 9 are mounted on the substrate, and the piezoelectric driving structure is sleeved around the sensing electrode and the shielding electrode. There is an electrical insulation relationship between the substrate and the sensing electrode 7 and the shielding electrode 8. The shielding electrode 8 includes a shielding electrode plate and a first comb-shaped structure disposed on both sides of the shielding electrode plate. The sensing electrode 7 includes one or more pairs of second comb-shaped structures symmetrically disposed on both sides of the shielding electrode. The comb teeth on the sensing electrode 7 and the shielding electrode 8 are interdigitated. The piezoelectric driving structure 9 includes two driving arms arranged in a centrally symmetrical manner. Each driving arm includes a fixed end and a free end. The fixed end is mounted on the substrate, and the free ends of the two driving arms are connected to two centrally symmetrical positions on the shielding electrode, respectively. When the sensor is working, the working mode of the shielding electrode is set, and the piezoelectric driving structure 9 causes the shielding electrode 8 to vibrate periodically, so as to cause the shielding electrode 8 and the sensing electrode 7 to generate displacement, and to collect the sensing signal carrying the measured electric field information generated on the sensing electrode 7. In addition, the sensor can also change the driving voltage applied to the two driving arms of the piezoelectric drive structure 9, so that the shielding electrode 8 is in different working modes.

[0031] In the initial state, the comb teeth on the sensing electrode and the shielding electrode are on the same plane. To ensure a symmetrical and uniform distribution of the induced electric field on the electrodes, the number of comb teeth on the sensing electrode located on one side of the shielding electrode should be greater than or less than the number of comb teeth on that side. In this embodiment, the sensing electrode uses multiple pairs of comb teeth, which helps to improve the driving capability.

[0032] The sensing electrode 7 is mounted on the substrate via the sensing electrode solder joint 6 and is fixedly connected to the substrate. At the same time, the current is detected through the sensing electrode solder joint 6 to analyze and calculate the external electric field.

[0033] The substrate is a multilayer composite structure, comprising a bottom layer, a buried oxide layer, and a top layer arranged sequentially. In this embodiment, the bottom and top layers are made of SOI, i.e., the substrate includes an SOI substrate bottom silicon layer 1, an SOI substrate buried oxide layer 2, and an SOI substrate top silicon layer 3, wherein the thickness of the top silicon layer depends on the thickness of the silicon substrate of the piezoelectric drive structure.

[0034] The piezoelectric drive structure 9 is a sandwich structure, comprising a bottom electrode, a piezoelectric material, and a top electrode arranged sequentially. The bottom electrode is mounted on the substrate via a bottom electrode solder joint 5, and the top electrode is mounted on the substrate via a top electrode solder joint 4. A driving voltage is applied through the bottom electrode solder joint 5. The piezoelectric material can be an inorganic or organic piezoelectric material. In specific embodiments, the piezoelectric material includes, but is not limited to, the following: barium titanate (BT), lead zirconate titanate (PZT), modified lead zirconate titanate, lead metaniobate, lead barium lithium niobate (PBLN), modified lead titanate (PT), and polyvinylidene fluoride (PVDF).

[0035] In specific embodiments, the piezoelectric drive structure includes, but is not limited to, L-shaped beams, S-shaped beams, and double S-shaped beams. In this embodiment, the drive arm of the piezoelectric drive structure is an L-shaped beam structure.

[0036] In the aforementioned sensor, the piezoelectric drive structure 9 is used to drive the shielding electrode 8 to generate displacement. By applying a DC bias voltage and a sinusoidal AC drive voltage to the upper and lower electrodes, an electric field is generated on the piezoelectric material, thereby controlling the vibration of the piezoelectric drive structure and consequently the vibration of the shielding electrode. Simultaneously, by controlling the shielding electrode, the piezoelectric drive structure can achieve both a torsional operating mode (torsional modulation mode) and an up-and-down operating mode (up-and-down displacement modulation mode) for the shielding electrode. Specifically, when the driving voltage applied to the two drive arms of the piezoelectric drive structure has equal amplitude and opposite phase, the shielding electrode is in the torsional operating mode, such as... Figure 2 As shown; when the amplitudes of the driving voltage signals applied to the two driving arms of the piezoelectric drive structure are equal and the phase difference is 90°, the shielding electrode is in the up-and-down working mode, as shown. Figure 3 As shown.

[0037] The piezoelectric drive structure described above is designed based on the working principle and piezoelectric effect of a piezoelectric cantilever beam. The working principle and piezoelectric effect of the piezoelectric cantilever beam are as follows:

[0038] Currently, there are two main structural forms of piezoelectric microcantilever beams: one consists of a single layer of piezoelectric thin film material, a support layer, and upper and lower electrodes, typically functioning only as a sensor or actuator; the other consists of two layers of piezoelectric thin films and a support layer, typically functioning as both a sensor and an actuator. Each of these cantilever beam structures has its advantages: compared to the second type, the single-layer piezoelectric thin film microcantilever beam is relatively simple to manufacture, widely applicable, and exhibits high sensitivity and fast response when used as a sensor; while the double-layer piezoelectric thin film microcantilever beam, although more difficult to manufacture, offers unique advantages in certain applications due to its simultaneous sensor and actuator functionality.

[0039] The working principle of a single-layer thin-film piezoelectric microcantilever beam is as follows: Figure 4 As shown: The free end of the cantilever beam converts the force it receives into an electrical signal through a piezoelectric film. Based on the information transmitted by the electrical signal, the magnitude of the force is calculated. When the piezoelectric cantilever beam is used as an actuator, its working principle is as follows: When a certain electrical signal is applied to the cantilever beam, stress and deformation will occur at the free end of the cantilever beam due to the inverse piezoelectric effect of the piezoelectric film.

[0040] The principle of the inverse piezoelectric effect in piezoelectric materials: When an electric field E with the same polarization direction is applied to a piezoelectric material, the electric field force increases the polarization intensity. This means the distance between the positive and negative bound charges within the piezoelectric material increases along the direction of the electric field, causing the piezoelectric material to elongate along the polarization direction. If the direction of the applied electric field is opposite to the polarization direction, the piezoelectric material will undergo compressive deformation along the polarization direction. Figure 5 As shown.

[0041] Its piezoelectric equation can be simply expressed as:

[0042] σ=cγ-eE

[0043] D=εE+eγ

[0044] In the formula, σ is the stress of the piezoelectric material, c is the elastic modulus of the piezoelectric material, γ is the strain of the piezoelectric material, e is the piezoelectric constant, E is the electric field strength, D is the electric displacement, and ε is the dielectric constant of the material.

[0045] The principle of inverse piezoelectricity is used to drive the vibration of a microcantilever beam sensor using piezoelectric materials. When a positive electric field is applied along the Z-axis of the microcantilever beam, the piezoelectric film contracts, and the microcantilever beam deflects downwards; when a negative electric field is applied along the Z-axis of the microcantilever beam, the piezoelectric film expands, and the microcantilever beam deflects upwards; when the electric field direction alternates, the piezoelectric film alternately "contracts-expands," and the microcantilever beam vibrates along the Z-axis.

[0046] Based on the above principles, the sensor of the present invention can achieve switching of working modes and accurate measurement of signals by controlling the piezoelectric drive structure.

[0047] The basic principle of the piezoelectric micromirror field-polished MEMS electric field sensor of this invention is based on charge induction design. A piezoelectric driving structure periodically shields the sensing electrodes to obtain a constantly changing electric field, which is then modulated to measure the AC / DC electric field. The sensor's quality factor is maximized when operating at its resonant frequency; therefore, different resonant frequencies are required for different operating modes when different driving voltage frequencies are applied. When the driving voltage amplitudes applied to both sides of the piezoelectric driving structure are equal but opposite in phase, the electric field sensor's shielding electrodes operate in a torsional modulation mode. When the driving voltage signals applied to both sides of the piezoelectric driving structure have equal amplitudes and a 90° phase, the electric field sensor's shielding electrodes operate in a vertical displacement modulation mode.

[0048] When the field-milled electric field sensor is working, a piezoelectric drive structure causes the grounded shielding electrode to vibrate periodically. This periodic shielding of the sensing electrode in the electric field generates an alternating induced signal. According to Gauss's law, the electric field strength on the sensing electrode changes periodically with the periodic vibration of the shielding electrode, leading to a periodic change in the induced charge on the electrode and thus inducing a current. By detecting the solder joints of the sensing electrode, the current signal can be measured, allowing for the analysis and calculation of the external electric field.

[0049] i s =ε0AdE / dt (1)

[0050] Where ε0 is the vacuum permittivity, A is the sensing area of ​​the sensing electrode, and E is the electric field around the sensing electrode. s The voltage V is converted by a differential amplifier circuit. OUT The electric field strength is inverted by measuring the voltage magnitude.

[0051] External excitation voltage V d ±V a sin(ω s Under the action of t), the shielding electrode moves at a frequency ω s Periodic oscillations will convert the measured electric field into a voltage signal carrying information about the measured electric field. If the external electric field signal is a DC signal, the modulated signal V... EDC It is an AC sinusoidal signal with an amplitude proportional to the external electric field, and its frequency is the same as the AC part of the driving voltage.

[0052]

[0053] Where k q X represents the change in charge on the induced electrode under unit amplitude when an electric field of 1 kV / m is applied.r E0 is the amplitude of the shielding electrode; E0 is the amplitude of the external electric field to be measured; ω s The frequency of the AC drive voltage; The phase of the AC drive voltage; R f This is the resistor in the I / V conversion circuit.

[0054] If the external electric field signal is an AC signal, then the modulated signal V EAC The mixed AC signal is:

[0055]

[0056] Where ω e The frequency of the external electric field to be measured is denoted as .

[0057] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A field-milled MEMS electric field sensor based on a piezoelectric micromirror, characterized in that, The system includes a substrate, a piezoelectric driving structure, a sensing electrode, and a shielding electrode. The sensing electrode and the piezoelectric driving structure are mounted on the substrate. The shielding electrode includes a shielding electrode plate and first comb-like structures disposed on both sides of the shielding electrode plate. The sensing electrode includes one or more pairs of second comb-like structures symmetrically disposed on both sides of the shielding electrode. The combs on the sensing electrode and the shielding electrode are interdigitated. In the initial state, the combs on the sensing electrode and the shielding electrode are on the same plane. The number of combs on one side of the shielding electrode is different from the number of combs on that side of the shielding electrode. The piezoelectric driving structure includes two driving arms arranged centrally symmetrically. Each driving arm includes a fixed end and a free end. The fixed end is mounted on the substrate. The free end of the two driving arms... The sensor is connected to two centrally symmetrical positions on the shielding electrodes. When the sensor is working, the working mode of the shielding electrodes is set, and the shielding electrodes are periodically vibrated by the piezoelectric drive structure. The sensor collects the induced signal carrying the measured electric field information generated on the sensing electrode. The driving voltage applied to the two driving arms of the piezoelectric drive structure is changed to make the shielding electrodes work in different working modes. The working modes include a torsional working mode and an up-and-down working mode. When the driving voltage applied to the two driving arms of the piezoelectric drive structure has equal amplitude and opposite phase, the shielding electrodes are in the torsional working mode. When the driving voltage signal applied to the two driving arms of the piezoelectric drive structure has equal amplitude and a phase difference of 90°, the shielding electrodes are in the up-and-down working mode.

2. The field-polished MEMS electric field sensor based on a piezoelectric micromirror according to claim 1, characterized in that, The sensing electrode is mounted on the substrate via sensing electrode solder joints.

3. The field-polished MEMS electric field sensor based on a piezoelectric micromirror according to claim 1, characterized in that, The piezoelectric drive structure is a sandwich structure, comprising a bottom electrode, a piezoelectric material, and a top electrode arranged sequentially. The bottom electrode is mounted on the substrate via a bottom electrode solder joint, and the top electrode is mounted on the substrate via a top electrode solder joint.

4. The field-polished MEMS electric field sensor based on a piezoelectric micromirror according to claim 3, characterized in that, The piezoelectric material is either an inorganic piezoelectric material or an organic piezoelectric material.

5. The field-polished MEMS electric field sensor based on a piezoelectric micromirror according to claim 1, characterized in that, The piezoelectric drive structure is an L-shaped beam, an S-shaped beam, or a double S-shaped beam.

6. The field-polished MEMS electric field sensor based on a piezoelectric micromirror according to claim 1, characterized in that, The substrate comprises a bottom layer, a buried oxide layer, and a top layer arranged sequentially.

7. The field-polished MEMS electric field sensor based on a piezoelectric micromirror according to claim 6, characterized in that, The bottom and top layers are made of SOI.

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