Three-degree-of-freedom weakly coupled high-sensitivity MEMS sensor based on PT symmetry and preparation method thereof

Abstract

The application discloses a three-degree-of-freedom weak-coupling high-sensitivity MEMS sensor based on PT symmetry and a preparation method thereof, comprising double-end fixed tuning fork resonators which are mirror-symmetrical in pairs and equal in mass and size; three double-end fixed tuning fork resonators are located on the same straight line; an adjustable mechanical weak-coupling structure is used for coupling and connecting adjacent double-end fixed tuning fork resonators; movable comb-tooth capacitor structures are located on both sides of each double-end fixed tuning fork resonator; detection combs and driving combs are located outside movable comb-tooth capacitor structures corresponding to two double-end fixed tuning fork resonators; two adjustable damping circuits are connected with electrode layers through lead wires and are connected with the two double-end fixed tuning fork resonators in correspondence; and glass is used as the substrate of the sensor. The application provides a new principle and a new idea for the design of a micro-electro-mechanical system and is favorable for the realization of super-sensitive measurement of weak signals by a resonant MEMS sensor.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor sensors, and particularly relates to a three-degree-of-freedom weakly coupled high-sensitivity MEMS sensor based on PT symmetry and a preparation method thereof. BACKGROUND

[0002] MEMS resonators have wide applications in the field of sensing. By changing the physical properties such as effective mass and equivalent stiffness of the MEMS resonator, the intrinsic frequency of the resonator is changed, and the frequency shift is taken as the sensing output metric to realize 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 precision and sensitivity of the MEMS resonator still need to be improved. Therefore, it is of great significance to develop a MEMS resonator sensor with small interference to the sensing signal, high spatial resolution, fast response and high measurement precision.

[0003] In 1998, Bender C M and Boettcher S of the University of Washington first proposed the PT symmetry theory, which proved that the Hamiltonian of the PT symmetric non-hermitian system can also have real eigenvalues under the joint action of the parity (P) transformation and the time (T) transformation. Since the PT symmetric system can greatly enhance the sensitivity of weak perturbation sensing, the design of the sensor 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 and electronic systems, providing a new idea for the design of devices with new functions.

[0004] Current research results show that the third-order PT symmetric system has higher perturbation sensitivity than the second-order system, but there are few reports on the third-order MEMS sensor based on PT symmetry, and the three-degree-of-freedom weakly coupled high-sensitivity MEMS sensor based on PT symmetry and the gas sensor based on the structure have not been reported. SUMMARY

[0005] In view of the defects in the prior art, the present application aims to provide a three-degree-of-freedom weakly coupled high-sensitivity MEMS sensor based on PT symmetry and a sensing and preparation method thereof.

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

[0007] Double-end fixed tuning fork resonators, the tuning forks are mirror-symmetric to each other, and the mass and size of each tuning fork are equal; the three double-end fixed tuning fork resonators are located on the same straight line;

[0008] Adjustable mechanical weak coupling structure, which weakly couples adjacent double-ended fixed tuning fork resonators;

[0009] Movable comb teeth, which are connected to both sides of each double-ended fixed tuning fork resonator;

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

[0011] Driving comb teeth, which are arranged outside the movable comb teeth corresponding to two double-ended fixed tuning fork resonators;

[0012] Electrode layers, which are connected to the detection comb teeth and the driving comb teeth;

[0013] Adjustable damping circuits, which are connected to the electrode layers through leads and correspondingly connected to two double-ended fixed tuning fork resonators; the two adjustable damping circuits make the equivalent damping signs acting on the two double-ended fixed tuning fork resonators opposite and the sizes equal, realizing PT symmetry;

[0014] Glass, which is used as a substrate of the sensor.

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

[0016] Coupling beams, which connect two adjacent double-ended fixed tuning fork resonators and enclose a closed area;

[0017] Tuning coupling structure stiffness electrodes, which are mirror-symmetrically distributed in the closed area enclosed by the coupling beams;

[0018] Gas-sensitive material thin layers, which are symmetrically distributed on the coupling beams.

[0019] Preferably, the double-ended fixed tuning fork resonator is provided with movable beams on both sides, the movable comb teeth are located on the movable beams, and the side of the movable beams 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 beams, and the driving comb teeth are fixedly constrained on the outer side of the movable beams.

[0021] Preferably, the movable comb teeth are integrated with the double-ended fixed tuning fork resonator and vibrate 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 vibration frequency and vibration speed of the double-ended fixed tuning fork resonator are reflected through the capacitance change;

[0023] The driving 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, in sequence, a transimpedance amplifier, an analog-to-digital converter (ADC), a field programmable gate array (FPGA), and a digital-to-analog converter (DAC); wherein the FPGA realizes band-pass filtering, gain control, and phase control in sequence.

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

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

[0027] When there is no perturbation input, by adjusting the adjustable damping circuit, the equivalent damping signs of the two double-ended fixed tuning fork resonators are opposite and equal in size, and the third-order double-ended fixed tuning fork resonator works at a PT symmetric singular point.

[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] The third-order double-ended fixed tuning fork resonator is calibrated using a calibration instrument to establish a relationship between the eigenfrequency and different input perturbations.

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

[0031] Preferably, after a 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, which comprises:

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

[0033] Preferably, after a 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, which comprises:

[0034] The tuning coupling structure stiffness electrode applies a perturbation voltage, the adjustable mechanical weak coupling structure changes in electrostatic force, the equivalent stiffness changes, and the third-order double-end fixed tuning fork resonator with PT symmetry causes fission of the intrinsic frequency; the change amount of the intrinsic frequency is proportional to the perturbation voltage.

[0035] Preferably, the reading of the intrinsic frequency of the third-order double-end fixed tuning fork resonator comprises:

[0036] The vibration change of the movable comb teeth causes the capacitance between the comb teeth to change, and the comb teeth detect the capacitance change, and the intrinsic frequency is read after processing by the C / V conversion circuit.

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

[0038] Spin-coat a first photoresist on a silicon wafer and photoetch an anchor block pattern of the sensor;

[0039] Take the photoetched first photoresist as a mask, DRIE or wet etch the anchor block, and remove the photoresist;

[0040] Anodically bond a glass substrate and the etched back of the silicon wafer;

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

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

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

[0044] Take the photoetched second photoresist as a mask, etch the Cr and Au, and remove the photoresist;

[0045] Spin-coat a third photoresist and photoetch a device body pattern; the device body comprises a double-end fixed tuning fork resonator, an adjustable mechanical weak coupling structure, and movable comb teeth;

[0046] Take the photoetched third photoresist as a mask, DRIE etch the device body, and remove the photoresist;

[0047] Plate a gas-sensitive material film layer on the adjustable mechanical weak coupling structure;

[0048] Laser slice the whole, and finally obtain a sensor structure.

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

[0050] Compared with the traditional MEMS resonator based on the Hermite principle, the three-order PT symmetric MEMS resonator based on the PT symmetric principle is a system, and the sensing system constructed can exhibit new physical phenomena or effects; the sensitivity of the three-order PT symmetric MEMS resonator at the singular point will be improved by an order of magnitude compared with the traditional non-PT symmetric system, and the perturbation sensitivity is also higher than that of the two-order PT system.

[0051] The three-degree-of-freedom weakly coupled high-sensitivity MEMS sensor based on PT symmetry in the embodiment of the application has a 1 / 3 power relationship between the eigenfrequency splitting amount of the system and the perturbation when it is biased near the singular point according to the PT symmetric mechanical theory, which is more beneficial to the detection of weak signals by the MEMS sensor.

[0052] The three-degree-of-freedom weakly coupled high-sensitivity MEMS sensor based on PT symmetry in the embodiment of the application has a differential capacitance detection comb, and the differential detection can improve the stability and accuracy of the frequency signal detection. BRIEF DESCRIPTION OF DRAWINGS

[0053] Figure 1 It is a three-dimensional schematic view of the three-degree-of-freedom weakly coupled high-sensitivity MEMS sensor based on PT symmetry in the embodiment of the application.

[0054] Figure 2 It is a local enlarged schematic view of the comb in the preferred embodiment of the application.

[0055] Figure 3 It is a local enlarged schematic view of the adjustable mechanical weak coupling structure in the preferred embodiment of the application.

[0056] Figure 4 It is a PT symmetric lumped parameter model diagram in the preferred embodiment of the application.

[0057] Figure 5 It is a schematic diagram of the adjustable damping circuit used in the preferred embodiment of the application.

[0058] In the figure: 1 - first double-end fixed tuning fork resonator, 2 - second double-end fixed tuning fork resonator, 3 - third double-end fixed tuning fork resonator, 4 - movable comb, 51 - first adjustable mechanical weak coupling structure, 52 - second adjustable mechanical weak coupling structure, 6 - driving comb, 7 - detection comb, 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 wire; 122 - transimpedance amplifier, 123 - analog-to-digital converter ADC, 124 - band-pass filter, 125 - gain controller, 126 - phase controller, 127 - digital-to-analog converter DAC. DETAILED DESCRIPTION

[0059] The application will be described in detail below with specific embodiments. The following examples will help those skilled in the art to further understand the application, but do not limit the application in any form. It should be pointed out that for those skilled in the art, without departing from the concept of the application, a number of modifications and improvements can be made. These all belong to the protection scope of the application.

[0060] In one embodiment of the application, a PT-symmetry-based three-degree-of-freedom weakly coupled high-sensitivity MEMS sensor is provided, comprising: double-end fixed tuning fork resonators, adjustable mechanical weak coupling structures, movable combs, detection combs, driving combs, electrode layers, adjustable damping circuits, and substrates. Among them:

[0061] The double-end fixed tuning fork resonators are mirror-symmetric in pairs, and each tuning fork has equal mass and size; the three double-end fixed tuning fork resonators are located on the same straight line. The adjustable mechanical weak coupling structures weakly couple and connect adjacent double-end fixed tuning fork resonators; the movable combs are connected to both sides of each double-end fixed tuning fork resonator. The detection combs are arranged outside the movable combs corresponding to two double-end fixed tuning fork resonators. The driving combs are arranged outside the movable combs corresponding to two double-end fixed tuning fork resonators. The electrode layers are connected with the detection combs and the driving combs. The two adjustable damping circuits are connected with the electrode layers through lead wires, realizing corresponding connection with the two double-end fixed tuning fork resonators; the two adjustable damping circuits make the equivalent damping acting on the two double-end fixed tuning fork resonators opposite in sign and equal in size, realizing PT symmetry. Glass is used as the substrate of the sensor.

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

[0063] In the above embodiment, the third-order PT symmetric MEMS resonator is a system based on the principle of PT symmetry, 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 improved by an order of magnitude compared with the traditional non-PT symmetric system, and the perturbation sensitivity will be higher than that of the second-order PT system.

[0064] In some specific embodiments, as shown in Figure 1 The embodiment relates to a PT symmetric three-degree-of-freedom weakly coupled high-sensitivity MEMS sensor, which comprises 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, movable comb teeth capacitive structures 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 6, a detection comb 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 with the first double-ended fixed tuning fork resonator 1 through a lead 13; the second adjustable damping circuit 12b is connected with the second double-ended fixed tuning fork resonator 2 through a lead 13; the first double-ended fixed tuning fork resonator 1 is coupled with 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 with 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-symmetric, equal in mass and size, so as to better form a third-order PT symmetric structure. The movable comb teeth 4 located on both sides of the double-ended fixed tuning fork and the detection comb 7 constitute a detection capacitor, which is used for reflecting the vibration frequency and vibration speed of the double-ended fixed tuning fork, realizing the regulation and control of the resonator damping and the frequency detection, and calculating the perturbation size through the change of the eigenfrequency.

[0065] In the above embodiment, the amplification schematic diagram of the comb capacitors is as shown in Figure 2As shown, the two sides of the double-ended fixed tuning fork resonator are provided with movable beams, 4 is the movable comb tooth capacitor structure located on the two sides of the double-ended fixed tuning fork and on the movable beam. 7 is the comb tooth structure for detecting the comb tooth capacitor, located on the inner side of the movable beam. 6 is the comb tooth structure for constituting the driving capacitor, 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 have detection combs 7 and driving combs 6 on the left and right 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 7 detects the change of the capacitance between the movable comb teeth 4, and the change of the capacitance reflects the vibration frequency and vibration speed of the double-ended fixed tuning fork resonator; the driving comb provides electrostatic force to drive the double-ended fixed tuning fork resonator. The damping is related to the vibration speed of the resonator. Therefore, the movable comb teeth 4 and the detection comb 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 the frequency detection, facilitate the detection of the C / V conversion circuit, and detect the perturbation information size through the frequency detection. More specifically, its role is: 1. Detecting the change of the capacitance to obtain the change of the vibration frequency of the fixed tuning fork resonator; the change of the vibration frequency is used as the data basis for obtaining the intrinsic frequency of the third-order PT symmetric MEMS resonator; 2. 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 the damping size, so that the entire sensor satisfies the PT symmetry.

[0067] In some embodiments, the movable comb teeth 4 located on the two 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 6, and the detection comb 7 are made of conductive silicon.

[0068] In other embodiments, the substrate 8 is made of glass material, which is anodically bonded with 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] In addition, in some other embodiments, the electrode layer 9 and the tuning coupling structure stiffness electrode 10 are obtained by sputtering Cr / Au metal. As shown in Figure 1 As shown in FIG. 1, the electrode layer 9 is connected with the detection comb, such as the first detection comb electrode layer 91, the second detection comb electrode layer 92, the third detection comb electrode layer 93, the fourth detection comb electrode layer 94, the fifth detection comb electrode layer 95, the sixth detection comb electrode layer 96, the seventh detection comb electrode layer 97, and the eighth detection comb electrode layer 98. The electrode layer 9 is also connected with the driving comb, such as the first driving comb electrode layer 9a, the second driving comb electrode layer 9b, the third driving comb electrode layer 9c, and the fourth driving comb 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 tuned coupling structure stiffness electrode 10a, the second tuned coupling structure stiffness electrode 10b, the third tuned coupling structure stiffness electrode 10c, and the fourth tuned coupling structure stiffness electrode 10d are mirror-distributed within the adjustable mechanical weak coupling structure 5.

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

[0072] This embodiment relates to the above-mentioned three-degree-of-freedom weakly coupled high-sensitivity MEMS sensor based on PT symmetry. Its working mode is compatible with capacitive and resonant sensing. Specifically, when the adjustable mechanical weak coupling structure 5 is subjected to the stiffness electrode 10 of the tuned coupling structure or the gas-sensitive material thin layer 11 is subjected to gas perturbation, the equivalent stiffness of the adjustable mechanical weak coupling structure 5 will change, causing its intrinsic frequency to change. The detection capacitance changes, and the change in intrinsic frequency can be obtained by measuring the comb capacitance, thereby determining the magnitude of the external perturbation.

[0073] The gas-sensitive material thin layer in the above embodiments is used to adsorb perturbed gases, and the equivalent stiffness of the adjustable mechanical weak coupling structure is changed, which triggers the fission of the intrinsic frequency of the PT symmetric structure; the change in intrinsic frequency is proportional to the concentration of the adsorbed gas.

[0074] The tuned coupling structure stiffness electrode in the above embodiment is used to be subjected to a perturbation voltage. The electrostatic force of the adjustable mechanical weak coupling structure changes, its equivalent stiffness changes, and the change in its intrinsic frequency 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-ended fixed tuning fork resonator 1, and the second adjustable damping circuit acts 12b on the second double-ended fixed tuning fork resonator 2. The equivalent damping of the first double-ended fixed tuning fork resonator 1 and the equivalent damping of the second double-ended fixed tuning fork resonator have opposite signs and equal magnitudes, forming a PT symmetrical structure.

[0076] Furthermore, 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 negative equivalent damping, the second double-ended fixed tuning fork resonator 2 has approximately zero equivalent damping, and the third double-ended fixed tuning fork resonator 3 has positive equivalent damping.

[0077] like Figure 5The adjustable damping circuit of the double-end fixed tuning fork includes a detection comb 7, a transimpedance amplifier 122, an analog-to-digital conversion (ADC) 123, a band-pass filter 124, a gain controller 125, a phase controller 126, a digital-to-analog conversion (DAC) 127, 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 ADC 123, the band-pass filter 124, the gain controller 125, and the phase controller 126 are realized by a field programmable gate array (FPGA), gain adjustment and phase adjustment are performed, so as to adjust the equivalent damping coefficient of the double-end tuning fork, positive and negative damping are realized by phase adjustment, the output of the phase controller 126 is connected to the DAC 127, and the output of the DAC 127 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 application, the eigenfrequency of the double-end fixed tuning fork can be obtained in the following manner: the arrangement mode of the detection combs on both sides of the double-end fixed tuning fork forms a pair of differential detection capacitors, and the capacitors are converted into voltages by a C-V conversion circuit for frequency detection. The C / V conversion circuit is a circuit for converting the capacitance value into a voltage signal. When the capacitance of the sensor changes with the perturbation, the change of the capacitance can be converted into a voltage signal by the C / V conversion circuit, so as to be input to subsequent analog or digital signal processing.

[0079] In an embodiment of the present application, the above sensor is used for detection, and the following steps can be adopted:

[0080] S1, when there is no perturbation input, the damping sizes of the first double-end fixed tuning fork resonator and the second double-end fixed tuning fork resonator are adjusted to be equal and opposite in sign, so that the third-order double-end fixed tuning fork resonator works at the singular point of PT symmetry;

[0081] S2, after the perturbation voltage / perturbation gas is input, the perturbation causes the change of the stiffness of the adjustable mechanical weak coupling structure, and further changes the eigenfrequency of the PT symmetric third-order double-end fixed tuning fork resonator;

[0082] S3, the resonator is calibrated by using a calibration instrument, and the relationship between the eigenfrequency and different input perturbations is established;

[0083] S4, the sensor is input with a to-be-measured perturbation, the eigenfrequency of the sensor is read out, and the to-be-measured perturbation value is obtained according to the established relationship.

[0084] In a preferred embodiment, the thin layer of gas sensitive material will adsorb a specific gas, which makes the adjustable mechanical weak coupling structure produce a certain equivalent stiffness change. 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, and the greater the voltage, the greater the electrostatic force, and the stiffness of the adjustable mechanical weak coupling structure changes. After the perturbation, the working state of the third-order PT symmetric resonator deviates from the singular point, and the system eigenfrequency will split. According to the eigenfrequency and frequency splitting amount of S1 in the PT symmetric state, the stiffness perturbation amount Δk is derived, and finally the weak information to be measured can be obtained according to the relationship between the stiffness perturbation amount and the perturbation to be measured.

[0085] According to a third aspect of the present application, a preparation method of a PT symmetric-based three-degree-of-freedom weak coupling high-sensitivity MEMS sensor is provided, which integrates the substrate and anchor block structure into one by anodic bonding technology on a silicon wafer substrate, specifically comprising:

[0086] Step 1: spin-coat a first photoresist on the silicon wafer and photoetch the anchor block pattern of all sensor structures such as detection comb teeth and drive comb teeth;

[0087] Step 2: take the first photoresist after photoetching as a mask, DRIE or wet etch the anchor block, and remove the photoresist;

[0088] Step 3: anodically bond the glass substrate and the etched silicon wafer back;

[0089] Step 4: grind the front surface of the silicon wafer to a specified thickness;

[0090] Step 5: sputter a Cr layer and an Au layer on the front surface of the silicon wafer, specifically: sputter Cr metal first, and then sputter Au metal, which aims to better connect the Au metal with the silicon and prevent the Au metal from falling off

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

[0092] Step 7: take the second photoresist after photoetching as a mask, etch the Cr and Au, and remove the photoresist;

[0093] Step 8: spin-coat a third photoresist and photoetch the device body pattern; the device body includes: a double-end fixed tuning fork resonator, an adjustable mechanical weak coupling structure, and a movable comb tooth;

[0094] Step 9: take the third photoresist after photoetching as a mask, DRIE to etch the device body, and remove the photoresist;

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

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

[0097] The specific embodiments of the present application have been described. It is to be understood that the application is not limited to particular details of the embodiments described above, as modifications and variations can be made therein without departing from the spirit or scope of the application. The specific features of the above preferred embodiments can be used in any combination without mutual conflict.

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 in pairs, and each tuning fork has the same mass and size; three such double-ended fixed tuning fork resonators are located on the same straight line; An adjustable mechanical weak coupling structure is used to weakly couple adjacent double-ended fixed tuning fork resonators. Movable comb teeth are connected to both sides of each of the aforementioned double-ended fixed tuning fork resonators; The detection comb teeth are positioned outside the movable comb teeth corresponding to the two double-ended fixed tuning fork resonators; The driving comb teeth are located outside the movable comb teeth corresponding to the two double-ended fixed tuning fork resonators; An electrode layer is connected to the detection comb teeth and the drive comb teeth; The adjustable damping circuits are connected to the electrode layer via leads to correspond 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, thus achieving PT symmetry. Glass, used as the substrate for the sensor; The adjustable mechanically weakly coupled structure includes: A coupling beam connects two adjacent double-ended fixed tuning fork resonators and encloses a closed region; Tuned coupling structure stiffness electrodes, four of which are mirror-symmetrically distributed within the closed region enclosed by the coupling beam; Two thin layers of gas-sensitive material are symmetrically distributed on the coupling beam.

2. The three-degree-of-freedom weakly coupled high-sensitivity MEMS sensor based on PT symmetry according to claim 1, characterized in that, The double-ended fixed tuning fork resonator has movable beams on both sides, and the movable comb teeth are located on the movable beams. The side of the movable beam closest 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 to the inner side of the movable beam; the drive comb teeth are fixedly constrained to the outer side of the movable beam.

3. The three-degree-of-freedom weakly coupled high-sensitivity MEMS sensor based on PT symmetry according to claim 2, characterized in that, The movable comb teeth are integrated with the double-ended fixed tuning fork resonator and vibrate as the double-ended fixed tuning fork resonator vibrates. The detection comb tooth detects the capacitance change between itself and the movable comb tooth, and the capacitance change reflects the vibration frequency and vibration velocity of the double-ended fixed tuning fork resonator. The drive provides a driving voltage to drive the double-ended fixed tuning fork resonator; it also provides a damping voltage so that the damping satisfies PT symmetry.

4. 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 includes 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 FPGA sequentially implements bandpass filtering, gain control, and phase control. The detection comb teeth are connected to the transimpedance amplifier via leads, and the drive comb teeth are connected to the digital-to-analog converter (DAC) via leads.

5. A 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 as follows: When there is no perturbation input, by adjusting the adjustable damping circuit, the equivalent damping of the two double-ended fixed tuning fork resonators has opposite signs and equal magnitude, and the third-order double-ended fixed tuning fork resonator operates at a PT-symmetric singularity. When a perturbation voltage / perturbation gas is input, the perturbation causes a change in the stiffness of the adjustable mechanical weak coupling structure, which in turn changes the eigenfrequency of the PT-symmetric third-order double-ended fixed tuning fork resonator. The third-order double-ended fixed tuning fork resonator was calibrated using a calibration instrument to establish the relationship between its intrinsic frequency 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, and the value of the perturbation to be measured is obtained according to the established relationship.

6. A three-degree-of-freedom weakly coupled, high-sensitivity MEMS sensor based on PT symmetry according to claim 5, characterized in that, After the perturbation gas is introduced, the perturbation causes a change in the stiffness of the adjustable mechanically weakly coupled structure, thereby altering the eigenfrequency of the PT-symmetric third-order double-ended fixed tuning fork resonator, including: A thin layer of gas-sensitive material adsorbs perturbed gas, and the equivalent stiffness of the adjustable mechanical weak coupling structure changes, causing a fission of the intrinsic frequency of the PT-symmetric third-order double-ended fixed tuning fork resonator; the change in intrinsic frequency is proportional to the concentration of the adsorbed gas.

7. A three-degree-of-freedom weakly coupled, high-sensitivity MEMS sensor based on PT symmetry according to claim 5, characterized in that, After a perturbation voltage is input, the perturbation causes a change in the stiffness of the adjustable mechanically weakly coupled structure, thereby altering the eigenfrequency of the PT-symmetric third-order double-ended fixed tuning fork resonator, including: When a perturbation voltage is applied to the stiffness electrode of the tuned coupling structure, the electrostatic force of the adjustable mechanical weak coupling structure changes, its equivalent stiffness changes, and this causes the fission of the intrinsic frequency of the PT-symmetric third-order double-ended fixed tuning fork resonator; the change in its intrinsic frequency is proportional to the perturbation voltage.

8. A three-degree-of-freedom weakly coupled, high-sensitivity MEMS sensor based on PT symmetry according to claim 5, characterized in that, The reading of the eigenfrequency of the third-order double-ended fixed tuning fork resonator includes: The vibration of the movable comb teeth causes a change in the capacitance between the comb teeth. The detection comb teeth detect this change in capacitance, and the intrinsic frequency is read out after processing by the C / V conversion circuit.

9. A method for fabricating a three-degree-of-freedom weakly coupled, high-sensitivity MEMS sensor based on PT symmetry as described in any one of claims 1-8, characterized in that, include: The first photoresist is spin-coated onto the silicon wafer, and the anchor block pattern of the sensor is photolithographically patterned. Using the first photoresist after photolithography as a mask, anchor blocks are etched out by DRIE or wet etching, and then the photoresist is removed. Anode bonding is performed between the glass substrate and the etched back side of the silicon wafer; Grind the front side of the silicon wafer to a set thickness; A Cr layer and an Au layer are sputtered on the front side of the silicon wafer; After sputtering, spin-coat the Cr and Au layers with a second photoresist and then photo-etch the electrode layer and the stiffness electrode pattern of the tuned coupling structure. Using the second photoresist after photolithography as a mask, Cr and Au are etched, and the photoresist is removed. Spin-coat the third photoresist and then photolithographically pattern the main body of the device; The main body of the device includes: 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, the device body is etched out by DRIE, and then the photoresist is removed. A gas-sensitive material film is deposited on an adjustable mechanically weakly coupled structure; The entire structure is laser-cut to obtain the final sensor structure.

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