Resonant flow MEMS sensor based on PT symmetry and preparation method thereof

Abstract

The application discloses a resonant flow field MEMS sensor based on PT symmetry and a preparation method thereof, and comprises two double-end fixed tuning fork resonators which are coupled, mirror-symmetric in structure and equal in mass; the two double-end fixed tuning fork resonators are located on the same straight line; comb tooth capacitors are symmetrically distributed on the two sides of each double-end fixed tuning fork resonator; two adjustable damping circuits are connected with an electrode layer through lead wires, realizing corresponding connection with the two double-end fixed tuning fork resonators; the equivalent dampings of the two adjustable damping circuits are equal in size and opposite in sign; a cilium support structure is suspended at one end of one double-end fixed tuning fork resonator; a micro lever connects the cilium support structure and the double-end fixed tuning fork resonator; a cilium is arranged on the cilium support structure; and glass is used as the substrate of the sensor. The application can make the resonant flow field MEMS sensor obtain higher sensitivity of perturbation response performance, and realize sensitive measurement on weak flow rate.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of semiconductor sensors, and in particular to a PT-symmetry-based resonant flow field MEMS sensor and a preparation method thereof. BACKGROUND

[0002] Flow rate sensors, as irreplaceable elements for obtaining flow rate information in many engineering scenarios, are attracting more and more attention in the fields of aerospace engineering, environmental engineering, sustainable energy development, consumer electronics, gas monitoring systems, microelectronic technology, etc. In particular, for aircraft design, the change of flow rate directly affects the distribution of lift and drag of the aircraft, thereby relating to the operation efficiency and safety of the aircraft. Precise measurement of the flow rate and movement direction of the flow field in which the aircraft is located is the key to enhancing the operation safety, speed, comfort and fuel efficiency of the aircraft. However, the flow field involved in the operation of the aircraft has high complexity, small scale and short life cycle, and is uncertain in time and space. Therefore, it is of great significance to develop a high-performance MEMS flow rate micro sensor with small disturbance to the flow field, high spatial resolution, fast response and high measurement accuracy.

[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 a PT-symmetric non-Hermitian system can also have real eigenvalues under the joint action of the parity (P) transformation and the time (T) transformation. This theory is an analytical extension of the traditional theory from real space to complex space, opens up a new perspective for the study of non-Hermitian Hamiltonians, and becomes a new method for designing open physical systems (i.e. systems interacting with the environment). PT-symmetric systems have been widely studied and applied in optical systems, atomic systems, electronic systems, etc. This not only deepens the understanding of basic quantum physics laws, but also promotes breakthroughs in application technologies and provides new design strategies for devices with new functions. PT-symmetric systems based on mechanical systems are rarely reported, and PT-symmetric flow field microstructures and flow field sensors based on the structures have not been reported, and the theory of introducing perturbation into only one resonator is lacking. SUMMARY

[0004] In view of the defects in the prior art, the purpose of the present application is to provide a PT-symmetry-based resonant flow field MEMS sensor and a preparation method thereof.

[0005] According to one aspect of the present application, a PT-symmetry-based resonant flow field MEMS sensor is provided, comprising:

[0006] Double-end fixed tuning fork resonators, the tuning forks of which are mirror-symmetric to each other, and the mass and size of each tuning fork are equal; and two double-end fixed tuning fork resonators are located on the same straight line.

[0007] Mechanical coupling structure, weakly coupling two of the double-ended fixed tuning fork resonators;

[0008] Cilia support structure, provided at one end of one of the double-ended fixed tuning fork resonators;

[0009] Connecting beam, connecting the cilia support structure, making it suspended;

[0010] Micro-lever, connecting the cilia support structure and the double-ended fixed tuning fork resonator in the vicinity;

[0011] Cilia, provided on the cilia support structure;

[0012] Comb tooth capacitance, symmetrically distributed on both sides of each of the double-ended fixed tuning fork resonators;

[0013] Electrode layer, connected with the comb tooth capacitance and the cilia;

[0014] Adjustable damping circuit, two of which are connected with the electrode layer through lead wires, realizing corresponding connection with two of the double-ended fixed tuning fork resonators; the two adjustable damping circuits can make the equivalent damping acting on the two double-ended fixed tuning fork resonators have opposite signs and equal magnitude, realizing PT symmetry;

[0015] Glass, as the substrate of the sensor.

[0016] Preferably, the comb tooth capacitance comprises:

[0017] Movable comb tooth, integrated with both sides of the double-ended fixed tuning fork resonator, vibrating with the vibration of the double-ended fixed tuning fork resonator; the side of the movable comb tooth close to the double-ended fixed tuning fork resonator is called the inner side, and the other side is called the outer side;

[0018] Detection comb tooth, fixedly constrained on the inner side of the movable comb tooth; the detection comb tooth detects the change of its own capacitance with the movable comb tooth, reflecting the vibration frequency and vibration rate of the double-ended fixed tuning fork resonator;

[0019] Driving comb tooth, fixedly constrained on the outer side of the movable comb tooth; the driving comb tooth provides a driving voltage to drive the double-ended fixed tuning fork resonator, and also provides a damping voltage to make the damping satisfy PT symmetry.

[0020] Preferably, the electrode layer comprises:

[0021] Detection comb tooth electrode layer, connected with the anchor point of the detection comb tooth;

[0022] Driving comb tooth electrode layer, connected with the anchor point of the driving comb tooth;

[0023] A cilia electrode layer is connected to the anchor points on both sides of the cilia.

[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 cilia support structure is a plate structure provided with a plurality of recessed holes for reducing the mass of the support structure and the influence of gravity on the sensor.

[0027] Preferably, the detection principle of the sensor is as follows:

[0028] When there is no flow field input, the adjustable damping circuit is adjusted so that the equivalent damping acting on the two double-ended fixed tuning fork resonators is opposite in sign and equal in size, and the two double-ended fixed tuning fork resonators work at a PT-symmetric singular point.

[0029] After the flow field input, the cilia will be subjected to the flow field force and will drive its support structure, which will amplify the force through a micro-lever and act on one end of the double-ended fixed tuning fork resonator connected thereto, thereby causing the equivalent stiffness of the double-ended fixed tuning fork resonator to change, and thus changing the eigenfrequency of the PT-symmetric system composed of the two double-ended fixed tuning fork resonators.

[0030] Based on the comb teeth capacitance, the electrode layer, and the adjustable damping circuit, the eigenfrequency after the change of the equivalent stiffness is obtained.

[0031] The sensor is calibrated using a flow field calibration instrument to establish the relationship between the eigenfrequency and the input flow field.

[0032] When the to-be-measured flow field is input, the eigenfrequency of the sensor is read out, and the to-be-measured flow field value is obtained according to the relationship between the eigenfrequency and the input flow field.

[0033] Preferably, the double-ended fixed tuning fork resonator adopts a lumped parameter model, and its Hamiltonian is as follows:

[0034]

[0035] wherein μ = kc / k represents the coupling strength, Wherein, g represents the gain intensity, γ represents the loss intensity, when PT is symmetrical, the gain intensity and the loss intensity are equal in value; k c represents the equivalent stiffness of the weakly coupled mechanical structure, k represents the equivalent stiffness of the double-ended fixed tuning fork, m represents the equivalent mass of the double-ended fixed tuning fork, and i represents a complex number.

[0036] Preferably, after the flow field is input, the equivalent stiffness of the double-ended fixed tuning fork resonator becomes k1=k+Δk=k(1+Δk / k)=k(1+δ), wherein Δk is a stiffness perturbation quantity, which is related to the input flow field;

[0037] The normalized relationship between the eigenfrequency and the stiffness perturbation quantity is: The normalized relationship between the eigenfrequency and the stiffness perturbation quantity is: That is, the relationship between the eigenfrequency and the input flow field.

[0038] Preferably, the eigenfrequency of the readout sensor is specifically:

[0039] 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 through C / V conversion, input a current signal into a transimpedance amplifier;

[0040] The transimpedance amplifier converts the current signal into a voltage signal to obtain the perturbed eigenfrequency.

[0041] According to a second aspect of the present application, a preparation method of a PT-symmetry-based resonant flow field MEMS sensor is provided, comprising:

[0042] Spin-coat a first photoresist on a silicon wafer and photoetch an anchor block pattern of a sensor structure;

[0043] Use the photoetched first photoresist as a mask to DRIE or wet etch the anchor block and remove the photoresist;

[0044] Anodically bond a glass substrate and the etched silicon wafer back surface;

[0045] Grind the front surface of the silicon wafer to a set thickness;

[0046] Sputter a Cr layer and an Au layer on the silicon wafer in sequence;

[0047] Spin-coat a second photoresist and photoetch an electrode layer pattern;

[0048] Use the photoetched second photoresist as a mask to etch Cr and Au and remove the photoresist;

[0049] Spin-coat a third photoresist and photoetch a device main body pattern, wherein the device main body comprises a double-ended fixed tuning fork resonator, an adjustable mechanical weak coupling structure, a movable comb tooth, a cilium support structure, a connecting beam, and a micro lever;

[0050] Taking the third photoresist after photoetching as a mask, a device main body is etched by DRIE, and photoresist is removed;

[0051] SU-8 dry film is pasted on the silicon wafer;

[0052] The SU-8 dry film is photoetched to form a cilia pattern, and photoresist is removed;

[0053] The whole is laser sliced, and finally a sensor is obtained.

[0054] Compared with the prior art, the embodiment of the present application has at least one of the following beneficial effects:

[0055] The PT-symmetry-based resonant flow field MEMS sensor in the embodiment of the present application has a PT-symmetry structure. Compared with a conventional flow rate sensor based on the Ehrenfest principle, the PT-symmetry MEMS flow field sensor is based on a PT-symmetry principle system, and thus the constructed flow field sensing system exhibits new physical phenomena or effects. The sensitivity of the PT-symmetry MEMS flow field sensor at a singular point is improved by an order of magnitude compared with a conventional non-PT-symmetry system.

[0056] The PT-symmetry-based resonant flow field MEMS sensor in the embodiment of the present application, according to the PT-symmetry theory, when biased near a singular point, the change amount of the eigenfrequency of the system has a 1 / 2 power relationship with the perturbation, and the smaller the perturbation amount, the higher the system sensitivity, which is more conducive to the detection of weak flow rate by the sensor.

[0057] The PT-symmetry-based resonant flow field MEMS sensor in the embodiment of the present application provides a new principle and new ideas for the design of a micro-electro-mechanical system. Each resonator has a differential capacitance detection comb tooth, and differential detection can improve the damping control efficiency and improve the stability and accuracy of frequency signal detection. BRIEF DESCRIPTION OF DRAWINGS

[0058] Figure 1 It is a three-dimensional schematic view of the PT-symmetry-based resonant flow field MEMS sensor in the embodiment of the present application.

[0059] Figure 2 It is a local enlarged schematic view of the comb tooth in the preferred embodiment of the present application.

[0060] Figure 3 It is a PT-symmetry lumped parameter model diagram in the preferred embodiment of the present application.

[0061] Figure 4 It is a non-symmetry perturbation frequency theory principle curve diagram in the preferred embodiment of the present application.

[0062] Figure 5 It is a principle diagram of an adjustable damping circuit adopted in the preferred embodiment of the present application.

[0063] Fig. 1-First double-ended fixed tuning fork resonator, 2-Second double-ended fixed tuning fork resonator, 3-Micro lever, 4-Connecting beam, 5-Cilium support structure, 6-Cilium, 7-Hollow structure, 8-Substrate, 9-Comb capacitor 9, 9a-Detection comb, 9b-Movable comb, 9c-Drive comb, 10-Mechanical coupling structure, 11-Electrode layer, 111-First detection comb electrode layer, 112-Second detection comb electrode layer, 113-Third detection comb electrode layer, 114-Fourth detection comb electrode layer, 115-Fifth detection comb electrode layer, 116-Sixth detection comb electrode layer, 117-Seventh detection comb electrode layer, 118-Eighth detection comb electrode layer, 119-Cilium electrode layer, 11a-First drive comb electrode layer, 11b-Second drive comb electrode layer, 11c-Third drive comb electrode layer, 11d-Fourth drive comb electrode layer, 12a-First adjustable damping circuit, 12b-Second adjustable damping circuit, 13-Lead wire. DETAILED DESCRIPTION

[0064] The application will be described in detail below with specific examples. 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 noted that for those skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made. These are within the scope of the present application.

[0065] In one embodiment of the present application, a PT-symmetry-based resonant flow field MEMS sensor is provided, comprising: a double-ended fixed tuning fork resonator, a mechanical coupling structure, a cilium support structure, a connecting beam, a micro lever, a cilium, a comb capacitor, an electrode layer, an adjustable damping circuit and a substrate. Wherein:

[0066] A double-ended fixed tuning fork resonator, wherein the tuning forks are mirror-symmetrical in pairs, and each tuning fork has equal mass and size. Two of the double-ended fixed tuning fork resonators are located on the same straight line. A mechanical coupling structure weakly couples the two double-ended fixed tuning fork resonators. A fibrous support structure is disposed at one end of one of the double-ended fixed tuning fork resonators. A connecting beam connects the fibrous support structure, suspending it in mid-air. A micro-lever connects the fibrous support structure and the nearby double-ended fixed tuning fork resonator. Fibers are disposed on the fibrous support structure. Comb capacitors are symmetrically distributed on both sides of each double-ended fixed tuning fork resonator. An electrode layer is connected to the comb capacitors and the fibrous structure. An adjustable damping circuit is provided, with two such circuits connected to the electrode layer via leads to correspond with the two double-ended fixed tuning fork resonators. The two adjustable damping circuits ensure that the equivalent damping acting on the two double-ended fixed tuning fork resonators has opposite signs and equal magnitudes, achieving PT symmetry. Glass serves as the substrate of the sensor.

[0067] In the above embodiments, weak coupling means that the equivalent coupling stiffness of the two resonators is much less than 1. In the process of deriving the theoretical formula, it was found that when the two satisfy weak coupling, the Hamiltonian of the system satisfies PT symmetry.

[0068] The PT-symmetric resonant flow field MEMS sensor in this embodiment of the invention, based on the PT symmetry principle, enables the constructed flow field sensing system to exhibit novel physical phenomena or effects. Utilizing the sensitivity of the PT-symmetric system to the splitting of its eigenfrequency at extremely small perturbations near singular points, high-precision and high-sensitivity measurement of minute flow velocity changes is achieved. Changes in the airflow field are captured by cilia on the sensor, and capacitance detection enables damping control and eigenfrequency measurement, thereby obtaining flow field velocity information.

[0069] like Figure 1 The diagram shown is a schematic representation of a preferred embodiment of a resonant MEMS flow sensor based on PT symmetry. It includes: a substrate 8, a fibrous support structure 5 suspended by a connecting beam 4, fibrous strands 6 disposed on the support structure, a first double-ended fixed tuning fork resonator 1, a second double-ended fixed tuning fork resonator 2, a micro-lever 3, a mechanical coupling structure 10, a first adjustable damping circuit 12a, a second adjustable damping circuit 12b, and comb-tooth capacitors 9 located on both sides of the double-ended fixed tuning fork and an electrode layer 11 at the edge of the substrate. The adjustable damping circuit is connected to the first double-ended fixed tuning fork resonator 1 and the second double-ended fixed tuning fork resonator 2 via leads 13. The first double-ended fixed tuning fork resonator 1 and the second double-ended fixed tuning fork resonator 2 are coupled through the mechanical coupling structure 10, and the coupling is weak. Wherein: Figure 2As shown, the fixed comb teeth 9a and the movable comb teeth 9b located on both sides of the double-ended fixed tuning fork form a set of capacitors for reflecting the vibration frequency and vibration speed of the double-ended fixed tuning fork in the X-axis direction, realizing the regulation of the resonator damping and the detection of the frequency, and reflecting the size and direction of the flow velocity of the flow field in the Y-axis direction.

[0070] The resonant MEMS flow velocity sensor in the above embodiment can work at the PT-symmetric singular point by the regulation of the adjustable damping circuit 12 when there is no flow field input; after the flow field input, the cilia 6 will be subjected to the flow field force and drive the support structure 5 to amplify the force through the micro-lever 3 to act on one end of the first double-ended fixed tuning fork resonator 1 to change the equivalent stiffness, thereby changing the eigenfrequency of the PT-symmetric MEMS system; the sensor is calibrated by using a flow field calibration instrument to establish the relationship between the eigenfrequency and different input flow fields; when the to-be-measured flow field is input, the eigenfrequency of the sensor is read out, the stiffness change is calculated, and compared with the calibration value, so that the to-be-measured flow field value can be obtained.

[0071] The amplification schematic diagram of the comb capacitor in the above embodiment is as shown in Figure 2 As shown, 9a is a comb structure (referred to as a detection comb) for forming a detection comb capacitor, located on the inner side and symmetrically distributed upward and downward; 9c is a comb structure (referred to as a driving comb) for forming a driving capacitor, located on the outer side. 9b is a movable comb, connected to the left and right sides of the double-ended fixed tuning fork, and both have detection combs and driving combs. The entire comb capacitor is used to reflect the vibration frequency of the double-ended fixed tuning fork in the X-axis direction, realize the regulation of the resonator damping and the frequency detection, facilitate the detection of the C / V conversion circuit, and is used for detecting the size and direction of the flow velocity of the flow field in the Y-axis direction. Specifically, the movable comb 9b is connected to the two sides of the double-ended fixed tuning fork resonator to form an integral body, and vibrates with the vibration of the double-ended fixed tuning fork resonator; the side of the movable comb close to the double-ended fixed tuning fork resonator is referred to as the inner side, and the other side is referred to as the outer side. The detection comb 9a is fixedly constrained on the inner side of the movable comb; the detection comb detects the change of the capacitance of itself and the movable comb, and reflects the vibration frequency and vibration speed of the double-ended fixed tuning fork resonator. The driving comb 9c is fixedly constrained on the outer side of the movable comb; the driving comb provides a driving voltage to drive the double-ended fixed tuning fork resonator; and also provides a damping voltage to make the damping satisfy the PT symmetry.

[0072] In some specific embodiments, the comb capacitor 9, the cilia support structure 5, the first double-ended fixed tuning fork 1, the second double-ended fixed tuning fork 2, the mechanical coupling structure 10, and the connecting beam 4 are made of conductive silicon.

[0073] In other specific embodiments, the substrate 8 is made of glass material, and the silicon material of the anchor block in the device is anodically bonded. The glass material can reduce the parasitic capacitance of the device and avoid affecting the measurement.

[0074] In some specific embodiments, the electrode layer 11 is obtained by Cr / Au metal sputtering. In some specific embodiments, the electrode layer is connected to the anchor point of the detection comb teeth, such as... Figure 1 As shown, there are, for example, a first detection comb electrode layer 111, a second detection comb electrode layer 112, a third detection comb electrode layer 113, a fourth detection comb electrode layer 114, a fifth detection comb electrode layer 115, a sixth detection comb electrode layer 116, a seventh detection comb electrode layer 117, and an eighth detection comb electrode layer 118. The electrode layers are also connected to anchor points of the driving comb teeth, such as the first driving comb electrode layer 11a, the second driving comb electrode layer 11b, the third driving comb electrode layer 11c, and the fourth driving comb electrode layer 11d. The electrode layers also have cilia connections, such as the cilia electrode layer 119.

[0075] To reduce the impact of inertia on the sensor, in some preferred embodiments, the fibrous support structure 7 is provided with recessed holes to reduce the mass of the support structure, thereby reducing inertia.

[0076] To better achieve PT symmetry, in some preferred embodiments, the first double-ended fixed tuning fork resonator and the second double-ended fixed tuning fork resonator are mirror-symmetrical, with equal mass and size, which facilitates the formation of a better PT symmetrical structure.

[0077] Similarly, to achieve the purpose of forming PT symmetry, in some other preferred embodiments, the equivalent damping of the adjustable damping circuit acting on the first double-ended fixed tuning fork resonator and the equivalent damping of the second double-ended fixed tuning fork resonator have opposite signs and equal magnitudes, forming a PT symmetric structure.

[0078] Based on the PT-symmetric weakly coupled resonator constructed in the above embodiments, in a preferred embodiment, such as Figure 3 As shown, the resonator is analyzed using a lumped parameter model, and the system Hamiltonian is:

[0079]

[0080] Where μ = kc / k represents the coupling strength. γ represents the gain intensity, and γ represents the loss intensity. When PT is symmetrical, the values ​​of the gain intensity and the loss intensity are equal. kc represents the equivalent stiffness of the weakly coupled mechanical structure, k refers to the equivalent stiffness of the double-ended fixed tuning fork, m refers to the equivalent mass of the double-ended fixed tuning fork, and i represents a complex number.

[0081] After the flow field is input, the equivalent stiffness of the first resonator changes. In a preferred embodiment, the equivalent stiffness of the first resonator becomes: k1=k+Δk=k(1+Δk / k)=k(1+δ), where Δk is the small variable of stiffness. Then, with The normalized eigenfrequency is: This formula can be used as the relationship between stiffness microvariable and eigenfrequency. Since stiffness microvariable is related to the input flow field, this formula can also be used as the relationship between eigenfrequency and flow field.

[0082] like Figure 4 As shown, the theoretical frequency response curves are presented. For a PT-symmetric MEMS resonator system biased around a singularity (specifically, two weakly coupled, fixed-end tuning fork resonators), the real part of the eigenfrequency exhibits a square-root dependence on the externally induced asymmetric perturbation. Due to the perturbation, the eigenfrequency becomes two complex numbers; this perturbation is provided by the flow field. Since the sensing system operates in the singularity region, the eigenfrequency changes drastically with the asymmetric perturbation; that is, the eigenfrequency of the sensing system at the singularity changes drastically with the input flow field.

[0083] This embodiment relates to the above-mentioned MEMS resonator sensor with PT symmetry, whose working mode is compatible with capacitive sensing and resonant sensing. Specifically, when the cilia are subjected to external force, they will generate a certain displacement, which is applied to one end of the double-ended fixed tuning fork via a micro lever, causing its intrinsic frequency to change. The detection capacitance changes, and the change in intrinsic frequency is obtained by measuring the comb capacitance, thereby determining the magnitude and direction of the external force.

[0084] In a preferred embodiment of the present invention, a preferred structure for the adjustable damping circuit is provided. For example... Figure 5 The adjustable damping circuit for a double-ended fixed tuning fork includes: a detection comb 9a, a transimpedance amplifier 122, an analog-to-digital converter (ADC) 123, a bandpass filter 124, a gain controller 125, a phase controller 126, a digital-to-analog converter (DAC) 127, and a driving comb 6. The detection comb 7 is connected to the input of the transimpedance amplifier 122, and the output of the transimpedance amplifier 122 is connected to the input of the ADC 123. The bandpass filter 124, the gain controller 125, and the phase controller 126 are implemented through a field-programmable gate array (FPGA) to adjust the gain and phase, thereby adjusting the equivalent damping coefficient of the double-ended tuning fork. Positive and negative damping are achieved through phase adjustment. The output of the phase controller 126 is connected to the ADC 127, and the output of the ADC 127 is connected to the driving comb 9a.

[0085] Based on the adjustable damping circuit of the above embodiment, in a preferred embodiment of the present application, the eigenfrequency of the double-ended fixed tuning fork can be obtained by the following method: 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 voltage by a C-V conversion circuit for frequency detection. The C / V conversion circuit is a circuit that converts 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 the subsequent analog or digital signal processing.

[0086] In other embodiments of the present application, the sensor detection process can adopt the following steps:

[0087] S1, when there is no flow field input, the two double-ended fixed tuning fork resonators work at the singular point of PT symmetry through the regulation of the adjustable damping circuit;

[0088] S2, after the flow field input, the cilia will be subjected to the flow field force and will drive its support structure, and the force will be amplified by the micro-lever and applied to one end of the double-ended fixed tuning fork resonator connected thereto to induce the change of the equivalent stiffness, so as to change the eigenfrequency of the PT symmetric MEMS system;

[0089] S3, the eigenfrequency after the change of the equivalent stiffness is obtained through the comb tooth capacitor, the electrode layer and the adjustable damping circuit;

[0090] S4, the sensor is calibrated by using a flow field calibration instrument to establish the relationship between the eigenfrequency and different input flow fields;

[0091] S5, when the flow field to be measured is input, the eigenfrequency of the sensor is read out, the stiffness change is calculated, and compared with the calibration value, so as to obtain the value of the flow field to be measured.

[0092] In step S1, the damping of the first double-ended fixed tuning fork resonator and the second double-ended fixed tuning fork resonator is adjusted to be equal and opposite in sign. The PT symmetric resonator works at the singular point, and at this time the eigenfrequency of the PT symmetric resonator is combined.

[0093] In step S2, the PT symmetric resonator working at the singular point is placed in the flow rate environment to be measured. When the cilia are subjected to external force, they will produce a certain displacement, which will act on one end of the double-ended fixed tuning fork through the micro-lever, and perturb the stiffness of the first resonator. At this time, the working state of the PT symmetric resonator deviates from the singular point. The eigenfrequency of the PT symmetric system at this time can be obtained by the sensor.

[0094] In step S4, the formula of the eigenfrequency is as the relationship between the stiffness micro-variable and the eigenfrequency.

[0095] In step S5, the perturbed eigenfrequency is substituted into the above relationship to obtain the stiffness perturbation, and then the input flow field to be measured is obtained according to the relationship between the perturbation and the input flow field.

[0096] In some other embodiments, in step S2, the stiffness of the first resonator is perturbed, the system eigenfrequencies are not the same, and the resonator frequency splitting is:

[0097]

[0098] The above relationship can also be used as a correlation between the eigenfrequencies and different input flow fields. As long as the frequency splitting is obtained, the stiffness perturbation Δk can be derived, and finally the information of the flow field to be measured can be obtained according to the relationship between the stiffness perturbation and the flow rate to be measured.

[0099] Based on the same inventive concept, in some other embodiments of the present application, a preparation method of a PT-symmetry-based resonant MEMS flow field sensor is provided, which specifically comprises:

[0100] Step 1: spin-coating a first photoresist on a silicon wafer and photoetching an anchor block pattern of the sensor structure;

[0101] Step 2: taking the photoetched first photoresist as a mask, etching the anchor block by DRIE or wet etching, and removing the photoresist;

[0102] Step 3: anodically bonding a glass substrate and the etched silicon wafer back;

[0103] Step 4: grinding the front surface of the silicon wafer to a set thickness;

[0104] Step 5: sputtering a Cr layer and an Au layer on the silicon wafer in sequence; specifically, sputtering Cr metal first, and then sputtering Au metal, so that the Au metal can be better connected with the silicon and prevent the Au metal from falling off.

[0105] Step 6: spin-coating a second photoresist and photoetching an electrode layer pattern;

[0106] Step 7: taking the photoetched second photoresist as a mask, etching Cr and Au, and removing the photoresist;

[0107] Step 8: spin-coating a third photoresist and photoetching a device main body pattern, the device main body comprising: a double-end fixed tuning fork resonator, an adjustable mechanical weak coupling structure, a movable comb tooth, a cilium support structure, a connecting beam, and a micro lever;

[0108] Step 9: taking the photoetched third photoresist as a mask, etching the device main body by DRIE, and removing the photoresist;

[0109] Step 10: pasting an SU-8 dry film on the silicon wafer;

[0110] Step 11, SU-8 dry film photoetching cilia pattern, glue removal;

[0111] Step 12, laser cutting the whole body, finally obtaining the sensor.

[0112] The specific embodiments of the present application are described above. It needs to be understood that the present application is not limited to the specific embodiments described above, and various modifications or changes can be made by those skilled in the art within the scope of the claims, which does not affect the essential content of the present application. The above preferred features can be used in combination as long as they are not in conflict with each other.

Claims

1. A resonant flow field 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; The two double-ended fixed tuning fork resonators are located on the same straight line; A mechanical coupling structure is used to weakly couple the two double-ended fixed tuning fork resonators. A fibrous support structure is disposed at one end of the double-ended fixed tuning fork resonator; A connecting beam connects to the fibrillary support structure, suspending it in mid-air. A micro-lever, which connects the cilia support structure and the nearby double-ended fixed tuning fork resonator; Cilia, the cilia being disposed on the cilia support structure; Comb capacitors, wherein the comb capacitors are symmetrically distributed on both sides of each of the double-ended fixed tuning fork resonators; An electrode layer, wherein the electrode layer is connected to the comb-tooth capacitor and the fibers; The adjustable damping circuits are connected to the electrode layer via leads to achieve corresponding connections with the two double-ended fixed tuning fork resonators. The two adjustable damping circuits enable the equivalent damping acting on the two double-ended fixed tuning fork resonators to have opposite signs and equal magnitudes, thus achieving PT symmetry. Glass serves as the substrate for the sensor.

2. The PT-symmetric resonant flow field MEMS sensor according to claim 1, characterized in that, The comb capacitor includes: The movable comb teeth are integrated with both sides of the double-ended fixed tuning fork resonator and vibrate in accordance with the vibration of the double-ended fixed tuning fork resonator; the side of the movable comb teeth 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 inside the movable comb teeth; the detection comb teeth detect the capacitance change of themselves and the movable comb teeth, reflecting the vibration frequency and vibration rate of the double-ended fixed tuning fork resonator. The drive comb teeth are fixedly constrained to the outside of the movable comb teeth; the drive provides a drive voltage to drive the double-ended fixed tuning fork resonator; it also provides a damping voltage so that the damping satisfies PT symmetry.

3. The PT-symmetric resonant flow field MEMS sensor according to claim 1, characterized in that, The electrode layer includes: The detection comb electrode layer is connected to the anchor point of the detection comb tooth; The drive comb electrode layer is connected to the anchor point of the drive comb teeth; The fibrous electrode layer is connected to the anchor points extending from both sides of the fibrous strands.

4. A resonant flow field MEMS sensor based on PT symmetry according to claim 3, 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 resonant flow field MEMS sensor based on PT symmetry according to claim 1, characterized in that, The fibrous support structure is a plate-like structure with multiple recessed holes to reduce the mass of the support structure and minimize the impact of gravity on the sensor.

6. A resonant flow field 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 flow field input, the adjustable damping circuit is adjusted so that the equivalent damping of the two double-ended fixed tuning fork resonators has opposite signs and equal magnitude, and the two double-ended fixed tuning fork resonators operate at the PT-symmetric singular point. When a flow field is input, the cilia will be subjected to the flow field force and drive their supporting structure. Through micro-lever, the force is amplified and applied to one end of the double-ended fixed tuning fork resonator connected to it, causing the equivalent stiffness of the double-ended fixed tuning fork resonator to change, thereby changing the eigenfrequency of the PT symmetric system composed of two double-ended fixed tuning fork resonators. Based on comb capacitors, electrode layers, and adjustable damping circuits, the intrinsic frequency after the change in equivalent stiffness is obtained. The sensor was calibrated using a flow field calibration instrument to establish the relationship between the intrinsic frequency and the input flow field. When the flow field to be measured is input, the intrinsic frequency of the sensor is read out, and the value of the flow field to be measured is obtained based on the relationship between the intrinsic frequency and the input flow field.

7. A PT-symmetric resonant flow field MEMS sensor according to claim 6, characterized in that, The double-ended fixed tuning fork resonator adopts a lumped parameter model, and its Hamiltonian is: Where μ = kc / k represents the coupling strength. γ represents the gain intensity, γ represents the loss intensity, and when PT is symmetrical, the values ​​of the gain intensity and the loss intensity are equal; kc represents the equivalent stiffness of the weakly coupled mechanical structure, k refers to the equivalent stiffness of the double-ended fixed tuning fork, m refers to the equivalent mass of the double-ended fixed tuning fork, and i represents a complex number.

8. A PT-symmetric resonant flow field MEMS sensor according to claim 7, characterized in that, After the flow field is input, the equivalent stiffness of the double-ended fixed tuning fork resonator becomes k1=k+Δk=k(1+Δk / k)=k(1+δ), where Δk is the stiffness perturbation, which is related to the input flow field; by After normalization, the relationship between the eigenfrequency and the stiffness perturbation is obtained as follows: That is, the relationship between the eigenfrequency and the input flow field.

9. The PT-symmetric resonant flow field MEMS sensor according to claim 7, characterized in that, The intrinsic frequency of the readout sensor is specifically: The vibration of the movable comb teeth causes a change in the capacitance between the comb teeth. The detection comb teeth detect this capacitance change and, through C / V conversion, input a current signal to the transimpedance amplifier. The transimpedance amplifier converts the current signal into a voltage signal to obtain the perturbation-reduced intrinsic frequency.

10. A method for fabricating a PT-symmetric resonant flow field MEMS sensor as described in claim 2, characterized in that, include: The first photoresist is spin-coated onto the silicon wafer, and the anchor block pattern of the sensor structure 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 sequentially onto the silicon wafer; Spin-coat the second photoresist and then photo-etch the electrode layer pattern; Using the second photoresist after photolithography as a mask, Cr and Au are etched, and the photoresist is removed. Spin-coating a third photoresist and photolithographically patterning the main body of the device, the main body of the device includes: a double-ended fixed tuning fork resonator, a mechanical coupling structure, movable comb teeth, a hair support structure, a connecting beam, and a micro lever; Using the third photoresist after photolithography as a mask, DRIE etches out the main body of the device, and then removes the photoresist. SU-8 dry film is attached to the silicon wafer; The photolithographic fiber pattern on the SU-8 dry film is then removed; The entire structure is laser-sliced ​​to obtain the final sensor.

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