PT symmetry-based three-degree-of-freedom weak-coupling high-sensitivity MEMS sensor and preparation method thereof

Abstract

The invention discloses a PT symmetry-based three-degree-of-freedom weak-coupling high-sensitivity MEMS sensor and a preparation method thereof, and the sensor comprises double-end fixed tuning fork resonators which are in mirror symmetry pairwise and are equal in mass and size; the three double-end fixed tuning fork resonators are positioned on the same straight line; the adjustable mechanical weak coupling structure is used for coupling and connecting the adjacent double-end fixed tuning fork resonators; the movable comb tooth capacitor structures are located on the two sides of each double-end fixed tuning fork resonator. The detection comb teeth and the driving comb teeth are located on the outer sides of the movable comb tooth capacitor structures corresponding to the two double-end fixed tuning fork resonators. The two adjustable damping circuits are correspondingly connected with the electrode layer and the two double-end fixed tuning fork resonators through leads; glass serves as a substrate of the sensor. According to the invention, a new principle and a new idea are provided for the design of a micro-electro-mechanical system, and the ultra-sensitive measurement of the resonance type MEMS sensor on weak signals is facilitated.

Description

Technical Field

[0001] The present invention relates to a technology in the field of semiconductor sensors, in particular to a three-degree-of-freedom weak-coupling high-sensitivity MEMS sensor based on PT symmetry and a preparation method thereof. Background Art

[0002] MEMS resonators are widely used in the field of sensing. They are mainly used to change the physical properties of the MEMS resonator, such as the effective mass and equivalent stiffness, thereby changing the corresponding eigenfrequency of the resonator, and using the frequency shift as the sensor output metric to achieve signal sensing. At present, MEMS resonators can be used to measure physical quantities such as pressure, acceleration, mass, gas concentration, and flow field. However, the accuracy and sensitivity of MEMS resonators still need to be improved. Therefore, it is of great significance to develop MEMS resonant sensors with low interference to sensor signals, high spatial resolution, fast response, and high measurement accuracy.

[0003] In 1998, Bender CM and Boettcher S of the University of Washington first proposed the PT symmetry theory, proving that under the combined action of parity (P) transformation and time (T) transformation, the Hamiltonian of the PT symmetric non-Hermitian system can also have real eigenvalues. Since the PT symmetric system can greatly enhance the sensitivity of weak perturbation sensing, the design of sensors based on the PT symmetric system has attracted widespread attention and has been applied to the sensing research of various physical parameters. At present, the PT symmetric system has been widely studied and applied in the fields of optical systems, atomic systems, electronic systems, etc., providing new ideas for the design of devices with new functions.

[0004] Current research results show that the PT-symmetric third-order system has higher perturbation sensitivity than the second-order system, but there are few research reports on the third-order MEMS sensors based on PT symmetry, and there are no research reports on the three-degree-of-freedom weak-coupled high-sensitivity MEMS sensor based on PT symmetry and the gas sensor based on this structure. Summary of the invention

[0005] In view of the defects in the prior art, the object of the present invention is to provide a three-degree-of-freedom weak-coupling high-sensitivity MEMS sensor based on PT symmetry and a sensing and manufacturing method thereof.

[0006] According to one aspect of the present invention, a three-degree-of-freedom weakly coupled high-sensitivity MEMS sensor based on PT symmetry is provided, comprising:

[0007] A double-ended fixed tuning fork resonator, wherein the tuning forks are mirror-symmetrical, and the mass and size of each tuning fork are equal; three of the double-ended fixed tuning fork resonators are located on the same straight line;

[0008] An adjustable mechanical weak coupling structure connects the adjacent two-end fixed tuning fork resonators in a weak coupling manner;

[0009] Movable comb teeth connected to both sides of each of the double-ended fixed tuning fork resonators;

[0010] Detection comb teeth, arranged outside the movable comb teeth corresponding to the two double-ended fixed tuning fork resonators;

[0011] A driving comb tooth, arranged outside the movable comb teeth corresponding to the two double-ended fixed tuning fork resonators;

[0012] An electrode layer connected to the detection comb teeth and the driving comb teeth;

[0013] An adjustable damping circuit, wherein the two adjustable damping circuits are connected to the electrode layer through leads to achieve corresponding connection with the two double-ended fixed tuning fork resonators; the two adjustable damping circuits make the equivalent damping acting on the two double-ended fixed tuning fork resonators have opposite signs and equal magnitudes, thereby achieving PT symmetry;

[0014] Glass, as the substrate for the sensor.

[0015] Preferably, the adjustable mechanical weak coupling structure comprises:

[0016] A coupling beam connecting two adjacent double-ended fixed tuning fork resonators to form a closed area;

[0017] A tuning coupling structure stiffness electrode, wherein four of the tuning coupling structure stiffness electrodes are distributed in a mirror-symmetrical manner in the closed area surrounded by the coupling beam;

[0018] A gas sensitive material thin layer, wherein two gas sensitive material thin layers are symmetrically distributed on the coupling beam.

[0019] Preferably, movable beams are provided on both sides of the double-ended fixed tuning fork resonator, the movable comb teeth are located on the movable beams, and the side of the movable beam close to the double-ended fixed tuning fork resonator is called the inner side, and the other side is called the outer side;

[0020] The detection comb teeth are fixedly constrained on the inner side of the movable beam; and the driving comb teeth are fixedly constrained on the outer side of the movable beam.

[0021] Preferably, the movable comb teeth are connected to the double-ended fixed tuning fork resonator as a whole, and vibrate along with the vibration of the double-ended fixed tuning fork resonator;

[0022] The detection comb teeth detect the capacitance change between themselves and the movable comb teeth, and the capacitance change reflects the vibration frequency and vibration speed of the double-ended fixed tuning fork resonator;

[0023] The driver provides a driving voltage to drive the double-ended fixed tuning fork resonator; and also provides a damping voltage so that the damping satisfies PT symmetry.

[0024] Preferably, the adjustable damping circuit comprises a transimpedance amplifier, an analog-to-digital converter ADC, a programmable gate array FPGA and a digital-to-analog converter DAC connected in sequence; wherein the programmable gate array FPGA sequentially implements bandpass filtering, gain control and phase control;

[0025] The detection comb teeth are connected to the transimpedance amplifier through leads, and the driving comb teeth are connected to the digital-to-analog converter DAC through leads.

[0026] Preferably, the detection principle of the sensor is:

[0027] When there is no perturbation input, by adjusting the adjustable damping circuit, the equivalent damping acting on the two double-ended fixed tuning fork resonators has opposite signs and equal magnitudes, and the third-order double-ended fixed tuning fork resonator works at the singular point of PT symmetry;

[0028] After a perturbation voltage / perturbation gas is input, the perturbation causes the stiffness of the adjustable mechanical weak coupling structure to change, thereby changing the eigenfrequency of the PT-symmetric third-order double-ended fixed tuning fork resonator;

[0029] Using a calibration instrument to calibrate the third-order double-ended fixed tuning fork resonator, and establish the relationship between its eigenfrequency and different input perturbations;

[0030] The perturbation to be measured is input into the sensor, the eigenfrequency of the third-order double-ended fixed tuning fork resonator is read out, and the perturbation value to be measured is obtained according to the established relationship.

[0031] Preferably, after the perturbation gas is input, the perturbation causes the stiffness of the adjustable mechanical weak coupling structure to change, thereby changing the eigenfrequency of the PT-symmetric third-order double-ended fixed tuning fork resonator, including:

[0032] The thin layer of gas sensitive material adsorbs the perturbation gas, and the equivalent stiffness of the adjustable mechanical weak coupling structure changes, which triggers the fission of the eigenfrequency of the PT-symmetric third-order double-ended fixed tuning fork resonator; the change in the eigenfrequency is proportional to the concentration of the adsorbed gas.

[0033] Preferably, after the perturbation voltage is input, the perturbation causes the stiffness of the adjustable mechanical weak coupling structure to change, thereby changing the eigenfrequency of the PT-symmetric third-order double-ended fixed tuning fork resonator, including:

[0034] A perturbation voltage is applied to the stiffness electrode of the tuned coupling structure, and the electrostatic force of the adjustable mechanical weak coupling structure changes, and its equivalent stiffness changes, which triggers the fission of the eigenfrequency of the PT-symmetrical third-order double-ended fixed tuning fork resonator; the change in its eigenfrequency is proportional to the perturbation voltage.

[0035] Preferably, the step of reading out the eigenfrequency of the third-order double-ended fixed tuning fork resonator comprises:

[0036] The vibration change of the movable comb teeth causes the capacitance between the comb teeth to change. The detection comb teeth detect the capacitance change and read out the eigenfrequency after processing through the C / V conversion circuit.

[0037] According to a second aspect of the present invention, a method for preparing a three-degree-of-freedom weakly coupled high-sensitivity MEMS sensor based on PT symmetry is provided, comprising:

[0038] Spin coating a first photoresist on the silicon wafer and photolithography an anchor block pattern of the sensor;

[0039] Using the first photoresist after photolithography as a mask, DRIE or wet etching to form anchor blocks, and then removing the photoresist;

[0040] Anodic bonding the glass substrate and the back side of the etched silicon wafer;

[0041] Grinding the front side of the silicon wafer to a set thickness;

[0042] sputtering a Cr layer and an Au layer on the front side of the silicon wafer;

[0043] Spin-coating a second photoresist on the sputtered Cr layer and Au layer and photolithography the electrode layer and the tuning coupling structure stiffness electrode pattern;

[0044] Using the second photoresist after photolithography as a mask, etching Cr and Au, and removing the resist;

[0045] Spin coating a third photoresist and photolithography a device main body pattern; the device main body comprises: a double-ended fixed tuning fork resonator, an adjustable mechanical weak coupling structure and movable comb teeth;

[0046] Using the third photoresist after photolithography as a mask, DRIE etching is performed to form a device body, and then the resist is removed;

[0047] A gas sensitive material film is plated on the adjustable mechanical weak coupling structure;

[0048] The whole is laser sliced ​​to finally obtain the sensor structure.

[0049] Compared with the prior art, the embodiments of the present invention have at least one of the following beneficial effects:

[0050] The three-degree-of-freedom weak-coupling high-sensitivity MEMS sensor structure based on PT symmetry in the embodiment of the present invention is a system based on the PT symmetry principle, compared with the traditional MEMS resonator based on the Hermitian principle. The third-order PT symmetric MEMS resonator is a system based on the PT symmetry principle, and the constructed sensing system can exhibit new physical phenomena or effects; the sensitivity of the third-order PT symmetric MEMS resonator at the singular point will be orders of magnitude higher than that of the traditional non-PT symmetric system, and it also has higher perturbation sensitivity than the second-order PT system.

[0051] According to the PT symmetric mechanical theory, the three-degree-of-freedom weak-coupling high-sensitivity MEMS sensor based on PT symmetry in the embodiment of the present invention has a 1 / 3 power relationship with the perturbation when it is biased near a singularity, which is more conducive to the MEMS sensor's detection of weak signals.

[0052] The PT-symmetric three-degree-of-freedom weak-coupling high-sensitivity MEMS sensor in the embodiment of the present invention has differential capacitance detection comb teeth, and differential detection can improve the stability and accuracy of frequency signal detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 It is a three-dimensional schematic diagram of a three-degree-of-freedom weak-coupling high-sensitivity MEMS sensor based on PT symmetry in one embodiment of the present invention;

[0054] Figure 2 It is a partial enlarged schematic diagram of the comb teeth in a preferred embodiment of the present invention;

[0055] Figure 3 It is a partial enlarged schematic diagram of an adjustable mechanical weak coupling structure in a preferred embodiment of the present invention;

[0056] Figure 4 A diagram of a PT symmetric lumped parameter model in a preferred embodiment of the present invention;

[0057] Figure 5 This is a schematic diagram of an adjustable damping circuit used in a preferred embodiment of the present invention;

[0058] In the figure: 1-first double-ended fixed tuning fork resonator, 2-second double-ended fixed tuning fork resonator, 3-third double-ended fixed tuning fork resonator, 4-movable comb teeth, 51-first adjustable mechanical weak coupling structure, 52-second adjustable mechanical weak coupling structure, 6-driving comb teeth, 7-detecting comb teeth, 8-substrate, 9-electrode layer, 10a-first tuning coupling structure stiffness electrode, 10b-second tuning coupling structure stiffness electrode, 10c-third tuning coupling structure stiffness electrode, 10d-fourth tuning coupling structure stiffness electrode, 11a-first gas sensitive material thin layer, 11b-second gas sensitive material thin layer, 12a-first adjustable damping circuit, 12b-second adjustable damping circuit, 13-lead; 122-transimpedance amplifier, 123-analog-to-digital conversion ADC, 124-bandpass filter, 125-gain controller, 126-phase controller, 127-digital-to-analog conversion DAC. DETAILED DESCRIPTION

[0059] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several variations and improvements may be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0060] In one embodiment of the present invention, a three-degree-of-freedom weak-coupling high-sensitivity MEMS sensor based on PT symmetry is provided, comprising: a double-ended fixed tuning fork resonator, an adjustable mechanical weak-coupling structure, movable comb teeth, detection comb teeth, drive comb teeth, an electrode layer, an adjustable damping circuit and a substrate. Among them:

[0061] A double-ended fixed tuning fork resonator, wherein the tuning forks are mirror-symmetrical, and the mass and size of each tuning fork are equal; the three double-ended fixed tuning fork resonators are located on the same straight line. An adjustable mechanical weak coupling structure connects the adjacent double-ended fixed tuning fork resonators by weak coupling; a movable comb tooth is connected to both sides of each double-ended fixed tuning fork resonator. The detection comb tooth is arranged outside the movable comb tooth corresponding to the two double-ended fixed tuning fork resonators. The driving comb tooth is arranged outside the movable comb tooth corresponding to the two double-ended fixed tuning fork resonators. An electrode layer is connected to the detection comb tooth and the driving comb tooth. The two adjustable damping circuits are connected to the electrode layer through leads to realize corresponding connection with the two double-ended fixed tuning fork resonators; the two adjustable damping circuits make the equivalent damping acting on the two double-ended fixed tuning fork resonators have opposite signs and equal sizes, realizing PT symmetry. Glass is used as the substrate of the sensor.

[0062] In the above embodiment, the third order mentioned refers to three double-ended fixed tuning fork resonators, and the eigenfrequencies merge at the PT symmetric singular point EP. The principle of this sensor is to detect the eigenfrequencies and obtain perturbation information. Weak coupling refers to the equivalent coupling stiffness of the two resonators being much less than 1. In the process of deriving the theoretical formula, it is found that when the two satisfy weak coupling, the system Hamiltonian satisfies PT symmetry.

[0063] In the above embodiment, the third-order PT symmetric MEMS resonator is a system based on the PT symmetry principle, and the constructed sensing system can show new physical phenomena or effects. The sensitivity of the third-order PT symmetric MEMS resonator at the singular point will be an order of magnitude higher than that of the traditional non-PT symmetric system, and it also has a higher perturbation sensitivity than the second-order PT system.

[0064] In some specific embodiments, Figure 1 As shown, this embodiment involves a PT-symmetric three-degree-of-freedom weak-coupling high-sensitivity MEMS sensor, including: a first double-ended fixed tuning fork resonator 1, a second double-ended fixed tuning fork resonator 2, a third double-ended fixed tuning fork resonator 3, a movable comb-tooth capacitor structure 4 located on both sides of the double-ended fixed tuning fork, a first adjustable mechanical weak coupling structure 51, a second adjustable mechanical weak coupling structure 52, a driving comb tooth 6, a detection comb tooth 7, a substrate 8, an electrode layer 9 at the edge of the substrate, a tuning coupling structure stiffness electrode 10, a gas sensitive material thin layer 11, a first adjustable damping circuit 12a and a second adjustable damping circuit 12b. The first adjustable damping circuit 12a is connected to the first double-ended fixed tuning fork resonator 1 through the lead 13; the second adjustable damping circuit 12b is connected to the second double-ended fixed tuning fork resonator 2 through the lead 13; the first double-ended fixed tuning fork resonator 1 is coupled to the third double-ended fixed tuning fork resonator 3 through the first adjustable mechanical weak coupling structure 51; the second double-ended fixed tuning fork resonator 2 is coupled to the third double-ended fixed tuning fork resonator 3 through the second adjustable mechanical weak coupling structure 52; the third double-ended fixed tuning fork resonator 3 is located between the first double-ended fixed tuning fork resonator 1 and the second double-ended fixed tuning fork resonator 2, and the two are mirror-symmetrical, with equal mass and size, so as to better form a third-order PT symmetrical structure. Among them: the movable comb teeth 4 and the detection comb teeth 7 located on both sides of the double-ended fixed tuning fork constitute a group of detection capacitors, which are used to reflect the vibration frequency and vibration speed of the double-ended fixed tuning fork, realize the regulation and control of the resonator damping and frequency detection, and calculate the perturbation size through the change of the eigenfrequency.

[0065] Continuing with the above embodiment, the enlarged schematic diagram of the comb capacitor is as follows: Figure 2As shown, movable beams are provided on both sides of the double-ended fixed tuning fork resonator, 4 is a movable comb-teeth capacitor structure located on both sides of the double-ended fixed tuning fork, and is located on the movable beam. 7 is a comb-teeth structure constituting a detection comb-teeth capacitor, and is located on the inner side of the movable beam. 6 is a comb-teeth structure constituting a driving capacitor, and is located on the outer side of the movable beam. The first double-ended fixed tuning fork resonator 1 and the second double-ended fixed tuning fork resonator 2 are provided with detection comb teeth 7 and driving comb teeth 6 on both sides.

[0066] The movable comb teeth 4 are located on the double-ended fixed tuning fork resonator, and vibrate with the vibration of the double-ended fixed tuning fork resonator; the detection comb teeth 7 detect the capacitance change between the movable comb teeth 4, and reflect the vibration frequency and vibration speed of the double-ended fixed tuning fork resonator through the capacitance change; the driving comb teeth provide electrostatic force to drive the double-ended fixed tuning fork resonator. Damping is related to the vibration rate of the resonator. Therefore, the movable comb teeth 4 and the detection comb teeth 7 can reflect the vibration frequency and vibration speed of the double-ended fixed tuning fork, realize the regulation and control of the resonator damping and frequency detection, facilitate the detection of the C / V conversion circuit, and detect the size of the perturbation information through frequency detection. More specifically, its functions are: first, detect the capacitance change, so as to obtain the vibration frequency change of the fixed tuning fork resonator; the vibration frequency change is used as the data basis for the subsequent acquisition of the eigenfrequency of the third-order PT symmetric MEMS resonator; second, since the damping is related to the vibration speed of the resonator, the damping size can be obtained from the obtained vibration speed, so as to adjust the damping based on this damping size so that the entire sensor satisfies the PT symmetry.

[0067] In some specific embodiments, the movable comb teeth 4 located on both sides of the double-ended fixed tuning fork, the first double-ended fixed tuning fork 1, the second double-ended fixed tuning fork 2, the third double-ended fixed tuning fork 3, the first adjustable mechanical weak coupling structure 51, the second adjustable mechanical weak coupling structure 52, the driving comb teeth 6, and the detection comb teeth 7 are made of conductive silicon.

[0068] In some other specific embodiments, the substrate 8 is made of glass material, and is anodic bonded to the silicon material of the anchor block in the device. The glass material can reduce the parasitic capacitance of the device and avoid affecting the measurement.

[0069] And, in some other specific embodiments, the electrode layer 9 and the tuning coupling structure stiffness electrode 10 are obtained by Cr / Au metal sputtering. Figure 1 As shown in , the electrode layer 9 is connected to the detection comb teeth, such as the first detection comb tooth electrode layer 91, the second detection comb tooth electrode layer 92, the third detection comb tooth electrode layer 93, the fourth detection comb tooth electrode layer 94, the fifth detection comb tooth electrode layer 95, the sixth detection comb tooth electrode layer 96, the seventh detection comb tooth electrode layer 97, and the eighth detection comb tooth electrode layer 98. The electrode layer 9 is also connected to the drive comb teeth, such as the first drive comb tooth electrode layer 9a, the second drive comb tooth electrode layer 9b, the third drive comb tooth electrode layer 9c, and the fourth drive comb tooth electrode layer 9d.

[0070] In a preferred embodiment of the present invention, the adjustable mechanical weak coupling structure 5 is as follows: Figure 3 As shown, the first tuning coupling structure stiffness electrode 10a, the second tuning coupling structure stiffness electrode 10b, the third tuning coupling structure stiffness electrode 10c, and the fourth tuning coupling structure stiffness electrode 10d are distributed in a mirror surface in the adjustable mechanical weak coupling structure 5.

[0071] Furthermore, the first gas sensitive material thin layer 11 a and the second gas sensitive material thin layer 11 b are respectively located on the coupling beams of the adjustable mechanical weak coupling structure 5 .

[0072] This embodiment relates to the above-mentioned three-degree-of-freedom weak-coupling high-sensitivity MEMS sensor based on PT symmetry, and its working mode is compatible with capacitive and resonant sensing. Specifically, when the adjustable mechanical weak-coupling structure 5 is acted upon by the tuned coupling structure stiffness electrode 10 or the gas sensitive material thin layer 11 is acted upon by gas perturbation, the equivalent stiffness of the adjustable mechanical weak-coupling structure 5 will change, causing its eigenfrequency to change, and the detection capacitance to change, so that the change in the eigenfrequency is obtained by measuring the comb capacitance, and the size of the external perturbation is known.

[0073] The thin layer of gas sensitive material in the above embodiment is used to adsorb the perturbation gas, and the equivalent stiffness of the adjustable mechanical weak coupling structure changes, which triggers the fission of the eigenfrequency of the PT symmetric structure; the change in the eigenfrequency is proportional to the concentration of the adsorbed gas.

[0074] The tuning coupling structure stiffness electrode in the above embodiment is used to be applied with a perturbation voltage, and the electrostatic force of the adjustable mechanical weak coupling structure changes, its equivalent stiffness changes, and the change of its eigenfrequency is proportional to the perturbation voltage.

[0075] In a preferred embodiment of the present invention, the first adjustable damping circuit acts 12a on the first double-end fixed tuning fork resonator 1, and the second adjustable damping circuit acts 12b on the second double-end fixed tuning fork resonator 2. The equivalent damping of the first double-end fixed tuning fork resonator 1 and the equivalent damping of the second double-end fixed tuning fork resonator have opposite signs and equal magnitudes, forming a PT symmetrical structure.

[0076] Further, such as Figure 4 As shown, the third-order PT symmetric weakly coupled resonator can be analyzed using a lumped parameter model, the first double-ended fixed tuning fork resonator 1 has a negative equivalent damping, the second double-ended fixed tuning fork resonator 2 has an equivalent damping of approximately 0, and the third double-ended fixed tuning fork resonator 3 has a positive equivalent damping.

[0077] like Figure 5The double-ended fixed tuning fork adjustable damping circuit includes: a detection comb 7, a transimpedance amplifier 122, an analog-to-digital conversion (Analog-to-Digital Conversion) ADC123, a bandpass filter 124, a gain controller 125, a phase controller 126, a digital-to-analog conversion (Digital-to-Analog Conversion) DAC127 and a driving comb 6; the detection comb 7 is connected to the input of the transimpedance amplifier 122, the output of the transimpedance amplifier 122 is connected to the input of the ADC123, and the bandpass filter 124, the gain controller 125, and the phase controller 126 are respectively implemented through a field programmable gate array (Field Programmable Gate Array) FPGA to perform gain adjustment and phase adjustment, thereby adjusting the equivalent damping coefficient of the double-ended tuning fork, and the realization of positive and negative damping is realized by phase adjustment. The output of the phase controller 126 is connected to the digital-to-analog conversion (Digital-to-Analog Conversion) DAC127, and the output of the DAC127 is connected to the driving comb 6.

[0078] Based on the adjustable damping circuit of the above embodiment, in a preferred embodiment of the present invention, the eigenfrequency of the double-ended fixed tuning fork can be obtained in the following manner: the arrangement of the detection comb teeth on both sides of the double-ended fixed tuning fork forms a pair of differential detection capacitors, which are converted into voltages for frequency detection by a CV conversion circuit. A C / V conversion circuit is a circuit that converts a capacitance value into a voltage signal. When the capacitance of the sensor changes with perturbation, the change in capacitance can be converted into a voltage signal by a C / V conversion circuit so as to be input into subsequent analog or digital signal processing.

[0079] In one embodiment of the present invention, the above-mentioned sensor is used for detection, and the following steps may be adopted:

[0080] S1, when there is no perturbation input, by adjusting the damping magnitudes of the first double-ended fixed tuning fork resonator and the second double-ended fixed tuning fork resonator to be equal and opposite in sign, the third-order double-ended fixed tuning fork resonator works at a PT symmetric singular point;

[0081] S2, after the perturbation voltage / perturbation gas input, the perturbation induces the change of the stiffness of the adjustable mechanical weak coupling structure, thereby changing the eigenfrequency of the PT-symmetric third-order double-ended fixed tuning fork resonator;

[0082] S3, calibrating the resonator using a calibration instrument to establish the relationship between its eigenfrequency and different input perturbations;

[0083] S4, input the perturbation to be measured into the sensor, read the eigenfrequency of the sensor, and obtain the perturbation value to be measured based on the established relationship.

[0084] In a preferred embodiment, a thin layer of gas-sensitive material will adsorb a specific gas, which causes a certain equivalent stiffness change in the adjustable mechanical weak coupling structure. Similarly, after a voltage is applied to the tuning coupling structure stiffness electrode, an electrostatic force will be generated on the adjustable mechanical weak coupling structure. The greater the voltage, the greater the electrostatic force, and the stiffness of the adjustable mechanical weak coupling structure will change. After being perturbed, the working state of the third-order PT symmetric resonator deviates from the singularity point, and the system eigenfrequency will split. Based on the eigenfrequency and frequency splitting amount of S1 when it is PT symmetric, the stiffness perturbation amount Δk is derived, and finally, the weak information to be measured can be obtained based on the relationship between the stiffness perturbation amount and the perturbation to be measured.

[0085] According to a third aspect of the present invention, a method for preparing a three-degree-of-freedom weakly coupled high-sensitivity MEMS sensor based on PT symmetry is provided, wherein a substrate and an anchor block structure are integrated on a silicon wafer substrate by an anodic bonding technique, specifically:

[0086] Step 1, spin-coating a first photoresist on a silicon wafer and photolithography anchor block patterns of all sensor structures such as detection comb teeth and drive comb teeth;

[0087] Step 2, using the first photoresist after photolithography as a mask, DRIE or wet etching to form anchor blocks, and removing the photoresist;

[0088] Step 3, anode bonding the glass substrate and the back side of the etched silicon wafer;

[0089] Step 4, grinding the front side of the silicon wafer to a set thickness;

[0090] Step 5: sputtering a Cr layer and an Au layer on the front of the silicon wafer. Specifically, the Cr metal is sputtered first, and then the Au metal is sputtered. The purpose is to make the Au metal better connected to the silicon and prevent the Au metal from falling off.

[0091] Step 6, spin-coating a second photoresist on the sputtered Cr layer and Au layer and photolithography the electrode layer and the tuning coupling structure stiffness electrode pattern;

[0092] Step 7, using the second photoresist after photolithography as a mask, etching Cr and Au, and removing the resist;

[0093] Step 8, spin-coating a third photoresist and photolithography a device main body pattern; the device main body includes: a double-ended fixed tuning fork resonator, an adjustable mechanical weak coupling structure, and movable comb teeth;

[0094] Step 9, using the third photoresist after photolithography as a mask, DRIE etching is performed to form the device body, and the resist is removed;

[0095] Step 10, coating a gas sensitive material film layer on the adjustable mechanical weak coupling structure;

[0096] Step 11, laser slice the whole to finally obtain the sensor structure.

[0097] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various modifications or variations within the scope of the claims, which does not affect the essence of the present invention. The above preferred features can be used in any combination without conflicting with each other.

Claims

1. A three-degree-of-freedom weakly coupled high-sensitivity MEMS sensor based on PT symmetry, characterized in that: include: A double-ended fixed tuning fork resonator, wherein the tuning forks are mirror-symmetrical, and the mass and size of each tuning fork are equal; three of the double-ended fixed tuning fork resonators are located on the same straight line; An adjustable mechanical weak coupling structure connects the adjacent two-end fixed tuning fork resonators in a weak coupling manner; Movable comb teeth connected to both sides of each of the double-ended fixed tuning fork resonators; Detection comb teeth, arranged outside the movable comb teeth corresponding to the two double-ended fixed tuning fork resonators; A driving comb tooth, arranged outside the movable comb teeth corresponding to the two double-ended fixed tuning fork resonators; An electrode layer connected to the detection comb teeth and the driving comb teeth; An adjustable damping circuit, wherein the two adjustable damping circuits are connected to the electrode layer through leads to achieve corresponding connection with the two double-ended fixed tuning fork resonators; the two adjustable damping circuits make the equivalent damping acting on the two double-ended fixed tuning fork resonators have opposite signs and equal magnitudes, thereby achieving PT symmetry; Glass, as the substrate for the sensor.

2. A three-degree-of-freedom weakly coupled high-sensitivity MEMS sensor based on PT symmetry according to claim 1, characterized in that: The adjustable mechanical weak coupling structure comprises: A coupling beam connecting two adjacent double-ended fixed tuning fork resonators to form a closed area; A tuning coupling structure stiffness electrode, wherein four of the tuning coupling structure stiffness electrodes are distributed in a mirror-symmetrical manner in the closed area surrounded by the coupling beam; A gas sensitive material thin layer, wherein two gas sensitive material thin layers are symmetrically distributed on the coupling beam.

3. The three-degree-of-freedom weakly coupled high-sensitivity MEMS sensor based on PT symmetry according to claim 1, characterized in that: A movable beam is provided on both sides of the double-ended fixed tuning fork resonator, the movable comb teeth are located on the movable beam, the side of the movable beam close to the double-ended fixed tuning fork resonator is called the inner side, and the other side is called the outer side; The detection comb teeth are fixedly constrained on the inner side of the movable beam; and the driving comb teeth are fixedly constrained on the outer side of the movable beam.

4. A three-degree-of-freedom weakly coupled high-sensitivity MEMS sensor based on PT symmetry according to claim 3, characterized in that: The movable comb teeth are connected to the double-ended fixed tuning fork resonator as a whole, and vibrate along with the vibration of the double-ended fixed tuning fork resonator; The detection comb teeth detect the capacitance change between themselves and the movable comb teeth, and the capacitance change reflects the vibration frequency and vibration speed of the double-ended fixed tuning fork resonator; The driver provides a driving voltage to drive the double-ended fixed tuning fork resonator; and also provides a damping voltage so that the damping satisfies PT symmetry.

5. The three-degree-of-freedom weakly coupled high-sensitivity MEMS sensor based on PT symmetry according to claim 1, characterized in that: The adjustable damping circuit comprises a transimpedance amplifier, an analog-to-digital converter ADC, a programmable gate array FPGA and a digital-to-analog converter DAC connected in sequence; wherein the programmable gate array FPGA sequentially realizes bandpass filtering, gain control and phase control; The detection comb teeth are connected to the transimpedance amplifier through leads, and the driving comb teeth are connected to the digital-to-analog converter DAC through leads.

6. The three-degree-of-freedom weakly coupled high-sensitivity MEMS sensor based on PT symmetry according to claim 1, characterized in that: The detection principle of the sensor is: When there is no perturbation input, by adjusting the adjustable damping circuit, the equivalent damping acting on the two double-ended fixed tuning fork resonators has opposite signs and equal magnitudes, and the third-order double-ended fixed tuning fork resonator works at the singular point of PT symmetry; After a perturbation voltage / perturbation gas is input, the perturbation causes the stiffness of the adjustable mechanical weak coupling structure to change, thereby changing the eigenfrequency of the PT-symmetric third-order double-ended fixed tuning fork resonator; Using a calibration instrument to calibrate the third-order double-ended fixed tuning fork resonator, and establish the relationship between its eigenfrequency and different input perturbations; The perturbation to be measured is input into the sensor, the eigenfrequency of the third-order double-ended fixed tuning fork resonator is read out, and the perturbation value to be measured is obtained according to the established relationship.

7. A three-degree-of-freedom weakly coupled high-sensitivity MEMS sensor based on PT symmetry according to claim 6, characterized in that: After the perturbation gas is input, the perturbation causes the stiffness of the adjustable mechanical weak coupling structure to change, thereby changing the eigenfrequency of the PT-symmetric third-order double-ended fixed tuning fork resonator, including: The thin layer of gas sensitive material adsorbs the perturbation gas, and the equivalent stiffness of the adjustable mechanical weak coupling structure changes, which triggers the fission of the eigenfrequency of the PT-symmetric third-order double-ended fixed tuning fork resonator; the change in the eigenfrequency is proportional to the concentration of the adsorbed gas.

8. The three-degree-of-freedom weakly coupled high-sensitivity MEMS sensor based on PT symmetry according to claim 6, characterized in that: After the perturbation voltage is input, the perturbation causes the stiffness of the adjustable mechanical weak coupling structure to change, thereby changing the eigenfrequency of the PT-symmetric third-order double-ended fixed tuning fork resonator, including: A perturbation voltage is applied to the stiffness electrode of the tuned coupling structure, and the electrostatic force of the adjustable mechanical weak coupling structure changes, and its equivalent stiffness changes, which triggers the fission of the eigenfrequency of the PT-symmetrical third-order double-ended fixed tuning fork resonator; the change in its eigenfrequency is proportional to the perturbation voltage.

9. The three-degree-of-freedom weakly coupled high-sensitivity MEMS sensor based on PT symmetry according to claim 6, characterized in that: The step of reading out the eigenfrequency of the third-order double-ended fixed tuning fork resonator comprises: The vibration change of the movable comb teeth causes the capacitance between the comb teeth to change. The detection comb teeth detect the capacitance change and read out the eigenfrequency after processing through the C / V conversion circuit.

10. A method for preparing a three-degree-of-freedom weakly coupled high-sensitivity MEMS sensor based on PT symmetry, characterized in that: include: Spin coating a first photoresist on the silicon wafer and photolithography an anchor block pattern of the sensor; Using the first photoresist after photolithography as a mask, DRIE or wet etching to form anchor blocks, and then removing the photoresist; Anodic bonding the glass substrate and the back side of the etched silicon wafer; Grinding the front side of the silicon wafer to a set thickness; sputtering a Cr layer and an Au layer on the front side of the silicon wafer; Spin-coating a second photoresist on the sputtered Cr layer and Au layer, and photolithography the electrode layer and the electrode pattern of the tuning coupling structure stiffness; Using the second photoresist after photolithography as a mask, etching Cr and Au, and removing the resist; Spin coating a third photoresist and photolithography a main body pattern of the device; The device body comprises: a double-ended fixed tuning fork resonator, an adjustable mechanical weak coupling structure and movable comb teeth; Using the third photoresist after photolithography as a mask, DRIE etching is performed to form a device body, and then the resist is removed; A gas sensitive material film is plated on the adjustable mechanical weak coupling structure; The whole is laser sliced ​​to finally obtain the sensor structure.

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