A Weakly Coupled Double-Ended Tuning Fork MEMS Electric Field Sensor

Abstract

The present invention discloses a weakly coupled double-ended tuning fork MEMS electric field sensor, belonging to the technical field of MEMS sensors. It is provided with a first resonator, a second resonator, a weakly coupled mechanical beam, a first mass block, a second mass block, a driving electrode, a DC bias electrode, a perturbation electrode, an adjustment electrode, a first induction electrode and a second induction electrode; the first resonator and the second resonator are arranged in parallel horizontally and offset in the horizontal direction on the same horizontal plane and are connected by a weakly coupled mechanical beam; the driving electrode and the first induction electrode are respectively arranged on both sides of the first resonator, and the perturbation electrode and the second induction electrode are respectively arranged on both sides of the second resonator; the DC bias electrode and the adjustment electrode are respectively arranged on both sides of the second resonator; first mass blocks are respectively arranged on both sides of the first resonator, and second mass blocks are respectively arranged on both sides of the second resonator. The present invention has the advantages of strong performance, simple manufacturing and low cost.

Description

Technical Field

[0001] The present invention relates to the technical field of MEMS sensors, and particularly to a weakly coupled double-ended tuning fork micro-electro-mechanical systems (MEMS) electric field sensor. Background Art

[0002] Micro-machined electric field sensors, as a core instrument for detecting electric fields, have been widely used in fields such as meteorology, petrochemical industry, aerospace, power grids, and biomedicine. Compared with traditional non-MEMS field mill electric field sensors, MEMS electric field sensors at the micron scale have many advantages such as small size and low power consumption, which have promoted the development of micro-machined sensors. Currently, relatively mature MEMS electric field sensors mainly include micro field mills and electric field sensors based on the electro-optic effect, which have many advantages such as low cost and simple principle. Micro field mill electric field sensors generally use sensing electrodes to sense external electric fields, and detect external electric fields by causing changes in the capacitance gap between the sensing electrodes and the shielding electrodes. With its performance advantages, it has been put into use in the meteorological field, with a resolution of 40 V / m, which can meet the detection requirements of thunderstorm weather. However, the electric field detection changes on sunny days can generally reach several V / m, and the power grid and biomedicine fields have higher performance requirements for electric field sensors. Currently, the existing MEMS electric field sensors still cannot meet the requirements of these fields.

[0003] In recent years, in response to the demand for high-performance sensors, a modal localization phenomenon based on a weakly coupled resonant system has been successfully applied to various sensors, including electrometers, current sensors, and accelerometers. The Chinese invention patent application with application number CN202310806821.3 proposes a modal localization electrometer based on self-adjustment of the modal coupling frequency, which uses electrostatic force to achieve coupling between resonant beams and realize flexible coupling strength control. With the greatly expanded linear working bandwidth, the measurement accuracy, range and other indicators of the electrometer based on the modal localization principle are significantly improved. To a certain extent, the problem of insufficient sensor measurement range has been solved. However, due to the high heat loss of the sensitive structure of the sensor, the improvement of sensitivity and quality factor is limited, and the requirements of high performance have not yet been met. In 2022, Chang Honglong's team from Northwestern Polytechnical University proposed a mode-localized DC electric field sensor based on a weakly coupled resonant system in the paper "A mode-localized DC electric field sensor". The sensor uses a designed capacitor array to sense the electric field and generate stiffness disturbances on the resonator, triggering the mode localization phenomenon, causing the resonator amplitude ratio to change, and achieving accurate measurement of the electric field, which to a certain extent solves the sensitivity and resolution problems of MEMS sensors. However, due to the limitations of the structural design of the resonator itself and the electric field transduction mechanism, it is still impossible to achieve a wider range and high quality factor under low vacuum, which limits the application of lightning detection in the meteorological field and also poses severe challenges to vacuum packaging. Summary of the invention

[0004] The present invention provides a weakly coupled double-end tuning fork MEMS electric field sensor to solve the technical problems of insufficient sensitivity, resolution, range and other performances of existing MEMS electric field sensors.

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0006] A weakly coupled double-ended tuning fork MEMS electric field sensor, comprising a ceramic package tube shell and a silicon-on-insulator resonator chip interconnected by gold wire bonding; the resonator chip is provided with a first resonator, a second resonator, a weakly coupled mechanical beam, a first mass block, a second mass block, a driving electrode, a DC bias electrode, a perturbation electrode, an adjustment electrode, a first sensing electrode and a second sensing electrode; wherein,

[0007] The first resonator and the second resonator are arranged in parallel and staggered in the horizontal direction on the same horizontal plane, and the two resonators overlap to a certain extent in the horizontal direction, and are connected by the weak coupling mechanical beam at the overlapping part;

[0008] In the vertical direction, the driving electrode and the first sensing electrode are respectively arranged on both sides of the first resonator, and the driving electrode and the first sensing electrode are arranged in parallel, the perturbation electrode and the second sensing electrode are respectively arranged on both sides of the second resonator, and the perturbation electrode and the second sensing electrode are arranged in parallel; in the horizontal direction, the DC bias electrode and the adjustment electrode are respectively arranged on both sides of the second resonator;

[0009] Along the vertical direction, the first mass blocks are respectively disposed on both sides of the first resonator, and the second mass blocks are respectively disposed on both sides of the second resonator.

[0010] Furthermore, a parallel plate capacitor is formed between the driving electrode and the first resonator, and an AC driving signal is applied to the driving electrode, the first resonator is periodically excited through the driving electrode, and energy is transferred through the weakly coupled mechanical beam to drive the second resonator, thereby achieving the purpose of driving the entire sensor;

[0011] The DC bias electrode is directly mechanically connected to the second resonator, and a DC voltage is applied to the DC bias electrode so that a stable potential difference exists between the DC bias electrode and the disturbance electrode;

[0012] The disturbance electrode is connected to the input electrode in the electric field to be measured through a wire, and a parallel plate capacitor is formed between the disturbance electrode and the second resonator. The electric field to be measured is converted into a redistribution of charges on the disturbance electrode by using the principle of electrostatic induction, and a negative electrostatic stiffness disturbance is generated on the second resonator, triggering a modal localization effect, thereby causing a redistribution of energy between modes, affecting the amplitude ratio of the second resonator, and achieving the purpose of detecting the electric field by measuring the changes in the amplitude and phase of the first resonator and the second resonator and calculating the amplitude ratio;

[0013] A parallel plate capacitor is formed between the adjustment electrode and the second resonator, and a fixed voltage is applied to the adjustment electrode through a DC power supply to adjust the stiffness of the second resonator so that the second resonator is located in an amplitude ratio sensitivity linear region outside the steering region;

[0014] The first sensing electrode and the first resonator form a parallel plate capacitor for detecting the amplitude of the first resonator; the second sensing electrode and the second resonator form a parallel plate capacitor for detecting the amplitude of the second resonator; the amplitude and phase information of the first resonator and the second resonator are obtained by measuring the change of the capacitance;

[0015] Among them, the length of all electrodes is 200~300μm, the width is 200~300μm, and the thickness is 20~40μm; and the gap of all parallel plate capacitors is 2~4μm.

[0016] Furthermore, the first resonator and the second resonator have the same shape and size, and both are double-ended clamped tuning fork structures; the double-ended clamped tuning fork structure is composed of a rectangular resonant beam and rectangular frames fixed at both ends of the rectangular resonant beam; the length of the rectangular resonant beam is 300-400 μm, the width is 2-4 μm, and the thickness is 20-40 μm.

[0017] Furthermore, the double-ended clamped tuning fork structure adopts an intermediate spaced connection design; and a hollow structure design is adopted.

[0018] Furthermore, the double-ended clamped tuning fork structure adopts an annular or partial annular design.

[0019] Furthermore, there are differences between the first resonator and the second resonator in terms of geometric structure and / or mass distribution.

[0020] Furthermore, the weak coupling mechanical beam is a rectangular coupling beam, with a length of 100-500 μm, a width of 1-5 μm, and a thickness of 20-40 μm; and the distance from the center point of the weak coupling mechanical beam to the first resonator and the second resonator is equal.

[0021] Furthermore, the weak coupling mechanical beam is an annular coupling beam.

[0022] Furthermore, the first mass block includes a rectangular connection block perpendicular to the axis of the first resonator and a rectangular connection block parallel to the axis of the first resonator; and the first mass blocks on both sides of the first resonator are symmetrically arranged;

[0023] The second mass block includes a rectangular connection block perpendicular to the axis of the second resonator and a rectangular connection block parallel to the axis of the second resonator; and the second mass blocks on both sides of the second resonator are symmetrically arranged.

[0024] Furthermore, both the first mass block and the second mass block adopt a circular structural design, and the first mass blocks on both sides of the first resonator are asymmetrically arranged, and the second mass blocks on both sides of the second resonator are asymmetrically arranged.

[0025] The beneficial effects brought by the technical solution provided by the present invention at least include:

[0026] (1) The present invention is a high-resolution, wide-range weak-coupling double-ended tuning fork MEMS electric field sensor based on modal localization. It adopts the structural design of a double-ended tuning fork. Two double-ended tuning fork resonators are placed horizontally and parallel with a horizontal offset on the same plane. While ensuring the structural stability, the middle part of the beam can vibrate freely, enabling the double-ended tuning fork resonator to exhibit resonant characteristics with a high quality factor at a specific frequency, so as to reduce heat loss and compensate for the reduction of the quality factor caused by parasitic feedthrough capacitance;

[0027] (2) The present invention can also adopt an intermediate spacer connection design and introduce microstructures, such as microgrooves, microholes, microgrooves, or design the beam into a honeycomb shape, so that the coupling stiffness between the resonators is much smaller than the coupling stiffness inside the tuning fork while ensuring that a high quality factor can be obtained, thereby avoiding the mode aliasing phenomenon and ensuring that the mode localization phenomenon mainly occurs between the two double-ended tuning fork resonators, and obtaining a better sensitivity, measurement range and quality factor;

[0028] (3) The two resonators of the present invention are coupled by a rectangular slender beam, and the aspect ratio of the slender beam is usually designed to be large, which ensures the weak coupling characteristics between the two double-ended tuning forks. Compared with the resonators with electrical coupling and mechanical coupling, it is more stable and has higher reliability;

[0029] (4) The present invention adopts a parallel plate capacitor structure to effectively transmit the sensor input and output signals. The parallel plate capacitor structure has a simple design and a mature manufacturing process, which helps to reduce production costs and improve product consistency. Since the capacitance value of the parallel plate capacitor is inversely proportional to the square of the distance between the electrodes, it has high stability and low environmental sensitivity, so that it can maintain excellent performance under different environmental conditions.

[0030] (5) The present invention adopts a single-ended driving method to periodically excite the first resonator by driving the electrode, thereby reducing the number of electrodes required and the complexity of chip design. In addition, compared with double-ended driving, higher amplitude ratio sensitivity can be achieved.

[0031] (6) The present invention uses capacitive sensing for detection, and by applying a fixed bias voltage on the resonator, signal detection is made easier, thereby obtaining a higher signal-to-noise ratio and lower noise performance;

[0032] (7) The input electrode of the present invention is located in the electric field to be measured, and the potential on the connected disturbance electrode is changed by electrostatic induction, so that the electric field is converted into a stiffness disturbance of the second resonator. The resonator is regulated by adjusting the voltage applied by the electrode, so that the working mode is in a high-sensitivity linear region, and the measurement range is also expanded;

[0033] (8) The structural size design of the present invention achieves a high quality factor in a low vacuum environment, reducing the requirements for high vacuum packaging;

[0034] (9) The present invention uses SOI wafer as the manufacturing material, which has high compatibility with MEMS technology, simple manufacturing and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the accompanying drawings required for the description of the embodiments. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can be obtained based on these drawings.

[0036] Figure 1 is a schematic structural diagram of a weakly coupled dual - ended tuning fork MEMS electric field sensor provided by an embodiment of the present invention;

[0037] Figure 2 is a schematic working principle diagram of a weakly coupled dual - ended tuning fork MEMS electric field sensor provided by an embodiment of the present invention;

[0038] Figure 3 is a response curve graph of the weakly coupled dual - ended tuning fork MEMS electric field sensor to an electric field provided by an embodiment of the present invention;

[0039] Figure 4 is the relationship between the resonator amplitude and frequency during the occurrence of the modal localization phenomenon under different stiffness perturbations of the weakly coupled dual - ended tuning fork MEMS electric field sensor provided by an embodiment of the present invention; among them, (a) is the relationship between the amplitude and frequency of the first resonator; (b) is the relationship between the amplitude and frequency of the second resonator.

[0040] Description of the reference numerals:

[0041] 1. First resonator; 2. Second resonator; 3. Weakly coupled mechanical beam; 4. First mass block;

[0042] 5. Second mass block; 6. Driving electrode; 7. DC bias electrode; 8. Perturbation electrode;

[0043] 9. Adjusting electrode; 10. First induction electrode; 11. Second induction electrode. Detailed implementation manners

[0044] To make the objectives, technical solutions, and advantages of the present invention clearer, the following will further describe the embodiments of the present invention in detail with reference to the accompanying drawings.

[0045] First of all, it should be noted that in the embodiments of the present invention, words such as "exemplarily" and "for example" are used to represent examples, illustrations, or explanations. Any embodiment or design solution described as "exemplary" in the present invention should not be construed as being more preferred or more advantageous than other embodiments or design solutions. Exactly, the use of the word "exemplarily" is intended to present concepts in a specific manner. In addition, in the embodiments of the present invention, the meaning expressed by "and / or" can be both, or either one of the two.

[0046] This embodiment provides a weakly coupled double-ended tuning fork MEMS electric field sensor based on modal localization, which is an MEMS electric field sensor that can maximize the resolution and measurement range. The MEMS electric field sensor includes a ceramic package shell and a silicon-on-insulator (SOI) resonator chip. The chip and the package shell are interconnected through gold wire bonding to effectively transmit the input and output signals of the resonator and facilitate the stable vibration of the resonator. Among them, the ceramic shell includes a ceramic cavity base with 44 gold-immersed metal pins and a metal cover plate; the SOI resonator chip is composed of a device layer, a buried oxide layer, and a substrate layer, and is used to fabricate a resonant electric field sensing unit; among them, the SOI resonator chip needs to go through a complete set of SOI etching processes starting from an SOI wafer: First, deposit metal pads on the device layer and pattern them using the lift-off technique; Second, perform patterned lithography on the device layer and coat a layer of polyimide to protect its surface; Then, perform deep silicon etching to pattern the underlying silicon to ensure the accuracy and integrity of the structure; Finally, wet-etch the silicon oxide of the buried oxide layer using hydrofluoric acid to release the device layer and remove the top polyimide protective layer; among them, the materials used for the device layer and the substrate layer in the SOI resonator chip are both single-crystalline silicon, which ensures the mechanical strength and stability of the structure, while the material used for the buried oxide layer in the SOI resonator chip is silicon oxide, which provides good electrical isolation and structural support; This process flow is mature and reliable, can effectively manufacture high-precision MEMS electric field sensors, verifies the feasibility of the designed structure, and at the same time ensures the stable performance of the device under high resolution and wide range.

[0047] As Figure 1 shown, a first resonator 1, a second resonator 2, a weakly coupled mechanical beam 3, a first mass block 4, a second mass block 5, a drive electrode 6, a DC bias electrode 7, a perturbation electrode 8, an adjustment electrode 9, a first induction electrode 10, and a second induction electrode 11 are provided in the device layer; the metal pads on the electrodes are interconnected with the package shell through gold wire bonding to achieve the purpose of effectively transmitting the input and output signals of the sensor.

[0048] The first resonator 1 and the second resonator 2 are arranged in parallel in a horizontal direction (i.e., the left-right direction) on the same horizontal plane. While ensuring the structural stability, the middle part of the beam can vibrate freely, so that the double-ended tuning fork resonator exhibits resonant characteristics with a high quality factor at a specific frequency based on the modal localization effect; and the first resonator 1 and the second resonator 2 have a certain overlap in the horizontal direction, and the two resonators are connected through the weakly coupled mechanical beam 3 in the overlapping part to form a weak coupling.

[0049] Furthermore, the first resonator 1 and the second resonator 2 can be designed with a symmetric structure. They can be exactly the same in geometric structure and dimensional parameters, both being double-ended clamped tuning fork structures, so as to ensure that their natural frequencies and modal shapes are exactly the same when not disturbed. This design places the system in the turning region of modal localization. When the system is slightly disturbed, the modal localization phenomenon can be clearly observed without additional adjustment or searching for the turning region, thereby improving the detection accuracy and system stability.

[0050] Specifically, the double-ended clamped tuning fork structure consists of a rectangular resonant beam and rectangular frames fixed at both ends of the rectangular resonant beam to reduce heat loss and compensate for the reduction of the quality factor caused by parasitic feedthrough capacitance. Among them, the length of the rectangular resonant beam is 300 - 400 μm, the width is 2 - 4 μm, and the thickness is 20 - 40 μm. In addition, the double-ended clamped tuning fork structure can also adopt an intermediate spaced connection design, which can ensure a high quality factor while making the coupling stiffness between resonators much smaller than the coupling stiffness inside the tuning fork, avoiding modal aliasing, and ensuring that the modal localization phenomenon mainly occurs between the two double-ended tuning fork resonators, so that the modal localization phenomenon can be clearly and effectively demonstrated. On the basis of the intermediate spaced connection of the tuning fork, microstructures such as microgrooves, micropores, microchannels or the beam can be designed in a honeycomb shape to reduce the influence of heat loss, frequency drift and energy loss caused by thermal effects and environmental changes, and better sensitivity and quality factor can be obtained. In addition, the tuning fork can also adopt an annular or partial annular design, thereby utilizing the continuity and integrity of the annular structure to reduce stress concentration and improve the frequency stability and resonance characteristics of the tuning fork.

[0051] In addition, the first resonator 1 and the second resonator 2 can also adopt an asymmetric structure design, with differences in their geometric structure and / or mass distribution. This structural design makes the initial state of the system in the linear region of amplitude ratio sensitivity (asymmetric state), enabling the sensor to obtain higher sensitivity.

[0052] Among them, the weak coupling mechanical beam 3 can adopt a rectangular slender beam with a length of 100 - 500 μm, a width of 1 - 5 μm, and a thickness of 20 - 40 μm. The aspect ratio of the slender beam is usually designed to be large to ensure the weak coupling characteristics between the two double-ended tuning forks, so that the system can clearly demonstrate the modal localization effect. The distance from the center point of the slender beam to the two resonators is equal, ensuring the symmetry and uniformity of the system. In addition, the weak coupling mechanical beam 3 can also adopt a structure design of an annular coupling beam, which can achieve an ultra-low coupling coefficient, ensure stable vibration modes and effective modal localization, effectively avoid modal aliasing, and thus obtain a higher modal localization amplitude ratio sensitivity and improve the overall performance of the sensor.

[0053] Further, in the vertical direction, the driving electrode 6 and the first sensing electrode 10 are respectively arranged on both sides of the first resonator 1, and the driving electrode 6 and the first sensing electrode 10 are arranged in parallel, the perturbation electrode 8 and the second sensing electrode 11 are respectively arranged on both sides of the second resonator 2, and the perturbation electrode 8 and the second sensing electrode 11 are arranged in parallel; in the horizontal direction, the DC bias electrode 7 and the adjustment electrode 9 are respectively arranged on both sides of the second resonator 2; wherein the metal pads on the electrodes are interconnected with the package shell by gold wire bonding; the driving electrode 6, the perturbation electrode 8, the adjustment electrode 9, the first sensing electrode 10 and the second sensing electrode 11 are all coupled with the corresponding resonator by a parallel plate capacitor structure, so as to effectively transmit the input and output signals of the sensor, and the structure is simple in design and mature in manufacturing process, which helps to reduce production costs and improve product consistency, and has high stability and low environmental sensitivity.

[0054] Specifically, a parallel plate capacitor is formed between the driving electrode 6 and the first resonator 1. The sensor adopts a single-ended driving method. A periodic AC driving signal is applied to the driving electrode 6 to periodically excite the first resonator 1 through the parallel plate capacitor to drive the first resonator 1, and energy is transferred through the weakly coupled mechanical beam 3 to drive the second resonator 2, thereby achieving the purpose of driving the entire sensor.

[0055] The DC bias electrode 7 is directly mechanically connected to the second resonator 2 , and a DC voltage is applied to the DC bias electrode 7 so that a stable potential difference exists between the DC bias electrode 7 and the disturbance electrode 8 .

[0056] The disturbance electrode 8 is connected to the input electrode responsible for inducing the electric field in the electric field to be measured through a wire, and forms a parallel plate capacitor with the second resonator 2. By utilizing the principle of electrostatic induction, the electric field to be measured can be effectively converted into a redistribution of the charge on the disturbance electrode 8, and a negative electrostatic stiffness disturbance is generated on the second resonator 2, thereby achieving the purpose of converting the electric field to be measured into the stiffness disturbance of the resonator, triggering the modal localization effect, and then leading to the redistribution of energy between modes. The modal localization amplitude ratio changes, affecting the amplitude ratio of the second resonator 2, and the purpose of detecting the electric field is achieved by measuring the changes in the amplitude and phase of the first resonator 1 and the second resonator 2 and calculating the amplitude ratio.

[0057] A parallel plate capacitor is formed between the adjustment electrode 9 and the second resonator 2. A fixed voltage is applied to the adjustment electrode 9 through a DC power supply to generate a stiffness disturbance on the stiffness of the second resonator 2, which is used to adjust the stiffness and the initial working point of the second resonator 2 so that it is located in the amplitude ratio sensitivity linear region outside the steering region.

[0058] The first induction electrode 10 and the first resonator 1 form a parallel-plate capacitor, and the second induction electrode 11 and the second resonator 2 form a parallel-plate capacitor. With a DC bias, an open-loop measurement circuit is used to characterize the amplitude-frequency response of the two resonators in the sensor; the amplitude and phase information of the first resonator 1 and the second resonator 2 are obtained by measuring the change in capacitance; and the amplitude ratio of the resonator is calculated.

[0059] Among them, the length of all electrodes is 200 - 300 μm, the width is 200 - 300 μm, and the thickness is 20 - 40 μm; the metal pads on the electrodes are rectangular structures with the same shape as the electrodes but slightly smaller in size, and the side length dimension is 150 - 250 μm; the gap of the parallel-plate capacitor between the resonator and the electrode is 2 - 4 μm.

[0060] Further, along the vertical direction, the first mass blocks 4 are respectively arranged on both sides of the first resonator 1, and the second mass blocks 5 are respectively arranged on both sides of the second resonator 2.

[0061] Among them, the first mass block 4 and the second mass block 5 have the same shape and size. The first mass block 4 includes a rectangular connecting block perpendicular to the axis of the first resonator 1 and a rectangular connecting block parallel to the axis of the first resonator 1. One end of the rectangular connecting block perpendicular to the axis of the first resonator 1 is connected to the first resonator 1, and the other end is connected to the rectangular connecting block parallel to the axis of the first resonator 1; and the first mass blocks 4 on both sides of the first resonator 1 are centrosymmetric about the long axis center of the tuning fork; the second mass block 5 includes a rectangular connecting block perpendicular to the axis of the second resonator 2 and a rectangular connecting block parallel to the axis of the second resonator 2. One end of the rectangular connecting block perpendicular to the axis of the second resonator 2 is connected to the second resonator 2, and the other end is connected to the rectangular connecting block parallel to the axis of the second resonator 2, and the second mass blocks 5 on both sides of the second resonator 2 are centrosymmetric about the long axis center of the tuning fork. This symmetric layout optimizes the mass distribution and enhances the symmetry and stability of the resonator.

[0062] Further, the first mass block 4 and the second mass block 5 can also adopt a circular structural design, and an asymmetric structural design is achieved by changing the position of the mass block on the tuning fork. This structure can make the initial state of the sensor located in the linear region of the amplitude ratio sensitivity, thereby obtaining better sensitivity performance.

[0063] Furthermore, the MEMS electric field sensor is fixed on the front-end amplifier circuit for effectively transmitting the input and output signals of the sensor; the front-end amplifier current includes a transimpedance amplifier, a DC decoupling capacitor, and a voltage amplifier; the transimpedance amplifier is used to convert the weak current signal of the sensor into a voltage signal to improve the anti-interference ability of the signal; the DC decoupling capacitor is used to remove the DC bias in the signal to ensure that only the effective sensor output components are further amplified; the voltage amplifier is used to amplify the output signal twice to facilitate subsequent signal processing and precise measurement.

[0064] Based on the above structural design of the double-ended tuning fork, this embodiment greatly broadens the measurement range of the resonant sensor, improves the measurement resolution, achieves a high quality factor in a low vacuum state, and overcomes the problem that the sensitivity of the resonant electric field sensor is in the non-linear range. Based on the high quality factor in the low vacuum state, the requirement for vacuum packaging of the resonant sensor is reduced; based on the above performance, the sensor can meet the actual application requirements of the wide measurement range of the resonant MEMS electric field sensor, and achieves a significant improvement in the overall performance of the mode-localized sensor.

[0065] Please refer to Figure 2 , for the MEMS electric field sensor of this embodiment, an open-loop characterization circuit is adopted, and an AC signal V ac and a DC bias voltage V dc are used to generate a periodic electrostatic excitation to make the sensor vibrate periodically; by adjusting the voltage V t , the sensitivity of the sensor is adjusted to be in the linear region; due to electrostatic induction, the electric field is converted into a perturbation of the second resonator, resulting in a change in the amplitudes of the two resonators; the change in amplitude means that the induced currents induced by the two induction electrodes change, and the induced current passes through the transimpedance amplifier of the front-end amplifier circuit to convert the current signal into a voltage signal with a relatively strong anti-interference ability, and then the voltage signal is further amplified by the voltage amplifier of the front-end amplifier circuit to improve the signal-to-noise ratio of the voltage signal and facilitate reading; through a series of signal processing such as a mixer, a phase discriminator, a filter, and an amplifier, the amplitudes and phases of the two resonators are obtained respectively.

[0066] Please refer to Figure 3 , which is the amplitude-frequency response diagram of the MEMS electric field sensor of this embodiment after an electric field perturbation is applied, and the resonator transfers from the equilibrium state to the non-equilibrium state.

[0067] Please refer to Figure 4, which is the MEMS electric field sensor of this embodiment. By applying different electric field intensities, the amplitude-frequency responses of the two resonators under different relative perturbations are obtained. It can be seen that as the relative perturbation increases, the amplitude of the first mode of the first resonator decreases, and the amplitude of the second mode increases; the amplitudes of the two modes of the second resonator both decrease. This means that the phenomenon of mode localization occurs, and the energy transfers to the first mode of the first resonator.

[0068] In summary, this embodiment provides a high-resolution, wide-range, weakly coupled double-ended tuning fork MEMS electric field sensor based on mode localization. This sensor is based on the mode localization mechanism of a weakly coupled resonance system. Using the electrostatic induction principle of metal electrodes, the measured electric field is converted into the stiffness perturbation of the resonator, triggering the mode localization phenomenon, resulting in the redistribution of energy between the modes of the resonance system, and using the dimensionless amplitude ratio as the output, achieving an improvement in sensitivity and achieving the effect of anti-temperature drift to a certain extent. And this sensor adopts the design of two double-ended tuning fork resonators coupled by a mechanical beam to reduce heat loss and compensate for the reduction of the quality factor caused by parasitic feed-through capacitance; by converting the electric field into the negative electrostatic stiffness perturbation of the resonator, triggering the mode localization effect, and then affecting the amplitude ratio of the resonator, the superior performance of high quality factor and wide range is achieved. Open-loop and closed-loop experiments are carried out on two double-ended tuning fork resonators with the above structural dimensions for characterization. Under the condition of weak coupling, based on this structural design and the mode localization effect, the harmonic sensor realizes a comprehensive and significant improvement in performance such as wide range, high resolution, and high quality factor under low vacuum. This proves that the sensor has excellent quality factors in a low-vacuum environment, reducing the requirements for high-vacuum packaging. Combining the characteristics that the initial state of the resonator is located in the linear region, the performance such as the resolution and range of the sensor is significantly improved.

[0069] In addition, it should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. The term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or terminal device comprising a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article or terminal device.

[0070] Without further limitations, an element limited by the statement "comprising one..." does not exclude the existence of additional identical elements in the process, method, article, or terminal device that includes the said element. In addition, the term "and / or" merely describes the associated relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: the sole existence of A, the simultaneous existence of A and B, and the sole existence of B. Here, A and B can be singular or plural. Additionally, in this document, the character " / " generally indicates an "or" relationship between the associated objects before and after, but it may also represent an "and / or" relationship, which can be specifically understood by referring to the context. "At least one" means one or more, and "a plurality" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single items or plural items. For example, at least one of a, b, or c can represent: a, b, c, a - b, a - c, b - c, or a - b - c, where a, b, and c can be single or multiple.

[0071] Finally, it should be noted that the above description is only a preferred embodiment of the present invention. It should be pointed out that although the preferred embodiments of the present invention have been described, for those of ordinary skill in the art, once they learn the basic creative concept of the present invention, without departing from the principle described in the present invention, several improvements and refinements can still be made, and these improvements and refinements should also be regarded as the protection scope of the present invention. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the embodiments of the present invention.

Claims

1. A weakly coupled double-ended tuning fork MEMS electric field sensor, comprising a ceramic package housing and a silicon-on-insulator resonator chip interconnected by gold wire bonding; characterized in that, The resonator chip is provided with a first resonator, a second resonator, a weak coupling mechanical beam, a first mass block, a second mass block, a driving electrode, a DC bias electrode, a perturbation electrode, an adjustment electrode, a first sensing electrode and a second sensing electrode; wherein, The first resonator and the second resonator are arranged in parallel with a horizontal offset on the same horizontal plane, and there is a certain overlap between them in the horizontal direction, and the overlapping part is connected by the weak coupling mechanical beam; the weak coupling mechanical beam is a rectangular coupling beam with a length of 100 - 500 μm, a width of 1 - 5 μm, and a thickness of 20 - 40 μm; and the center point of the weak coupling mechanical beam is equidistant from the first resonator and the second resonator; In the vertical direction, the driving electrode and the first sensing electrode are respectively arranged on both sides of the first resonator, and the driving electrode and the first sensing electrode are arranged in parallel. The perturbation electrode and the second sensing electrode are respectively arranged on both sides of the second resonator, and the perturbation electrode and the second sensing electrode are arranged in parallel. In the horizontal direction, the DC bias electrode and the adjustment electrode are respectively arranged on both sides of the second resonator; In the vertical direction, a first mass block is respectively arranged on both sides of the first resonator, and a second mass block is respectively arranged on both sides of the second resonator; A parallel plate capacitor is formed between the driving electrode and the first resonator. By applying an AC driving signal on the driving electrode, the first resonator is periodically excited by the driving electrode, and the energy is transmitted through the weak coupling mechanical beam to drive the second resonator, so as to achieve the purpose of driving the entire sensor; The DC bias electrode is directly mechanically connected to the second resonator. By applying a DC voltage on the DC bias electrode, there is a stable potential difference between it and the perturbation electrode; The perturbation electrode is connected to the input electrode in the measured electric field through a wire, and a parallel plate capacitor is formed between it and the second resonator. Using the principle of electrostatic induction, the measured electric field is converted into a redistribution of charges on the perturbation electrode, generating a negative electrostatic stiffness perturbation on the second resonator, triggering the mode localization effect, and then resulting in a redistribution of energy between modes, affecting the amplitude ratio of the second resonator. By measuring the changes in the amplitudes and phases of the first resonator and the second resonator and calculating the amplitude ratio, the purpose of detecting the electric field is achieved; A parallel plate capacitor is formed between the adjustment electrode and the second resonator. By applying a fixed voltage on the adjustment electrode through a DC power supply, the stiffness of the second resonator is adjusted to make it in the linear region of the amplitude ratio sensitivity outside the turning region; A parallel plate capacitor is formed between the first sensing electrode and the first resonator to detect the amplitude of the first resonator; A parallel plate capacitor is formed between the second sensing electrode and the second resonator to detect the amplitude of the second resonator; the amplitude and phase information of the first resonator and the second resonator are obtained by measuring the change in capacitance; Among them, the length of all electrodes is 200 - 300 μm, the width is 200 - 300 μm, and the thickness is 20 - 40 μm; and the gap of all parallel plate capacitors is 2 - 4 μm.

2. The weakly coupled double-ended tuning fork MEMS electric field sensor according to claim 1, wherein, The first resonator and the second resonator have the same shape and size, and both are double-ended clamped tuning fork structures; the double-ended clamped tuning fork structure is composed of a rectangular resonant beam and rectangular frames fixed at both ends of the rectangular resonant beam; the length of the rectangular resonant beam is 300-400 μm, the width is 2-4 μm, and the thickness is 20-40 μm.

3. The weakly coupled double-ended tuning fork MEMS electric field sensor according to claim 2, wherein The double-ended clamped tuning fork structure adopts an intermediate spaced connection design; and a hollow structure design is adopted.

4. The weakly coupled double-ended tuning fork MEMS electric field sensor according to claim 2, characterized in that, The double-ended clamped tuning fork structure adopts an annular or partial annular design.

5. The weakly coupled double-ended tuning fork MEMS electric field sensor according to claim 1, characterized in that The first resonator and the second resonator are different in geometric structure and / or mass distribution.

6. The weakly coupled double-ended tuning fork MEMS electric field sensor according to claim 1, characterized in that, The first mass block includes a rectangular connection block perpendicular to the axis of the first resonator and a rectangular connection block parallel to the axis of the first resonator; and the first mass blocks on both sides of the first resonator are symmetrically arranged; The second mass block includes a rectangular connection block perpendicular to the axis of the second resonator and a rectangular connection block parallel to the axis of the second resonator; and the second mass blocks on both sides of the second resonator are symmetrically arranged.

7. The weakly coupled double-ended tuning fork MEMS electric field sensor according to claim 1, characterized in that, Both the first mass block and the second mass block adopt a circular structural design, and the first mass blocks on both sides of the first resonator are asymmetrically arranged, and the second mass blocks on both sides of the second resonator are asymmetrically arranged.

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