Resonance type flow field MEMS sensor based on PT symmetry and preparation method thereof

Abstract

The invention discloses a resonance type flow field MEMS sensor based on PT symmetry and a preparation method thereof, and the method comprises the steps: two double-end fixed tuning fork resonators are coupled, are in mirror symmetry in structure, and are equal in mass; the two double-end fixed tuning fork resonators are positioned on the same straight line; the comb tooth capacitors are symmetrically distributed on two sides of each double-end fixed tuning fork resonator; the two adjustable damping circuits are connected with the electrode layer through leads, so that the two adjustable damping circuits are correspondingly connected with the two double-end fixed tuning fork resonators; the equivalent damping of the two adjustable damping circuits is opposite in sign and equal in size; the cilium supporting structure is suspended at one end of a double-end fixed tuning fork resonator; the micro lever is connected with the cilium supporting structure and the double-end fixed tuning fork resonator; the cilia is arranged on the cilia supporting structure; glass serves as a substrate of the sensor. According to the invention, the resonance type flow field MEMS sensor can obtain perturbation response performance with higher sensitivity, and sensitive measurement of weak flow velocity is realized.

Description

Technical Field

[0001] The invention relates to the field of semiconductor sensors, in particular to a resonant flow field MEMS sensor based on PT symmetry and a preparation method thereof. Background Art

[0002] As an irreplaceable component for obtaining flow velocity information in many engineering scenarios, flow velocity sensors have received increasing attention in the fields of aerospace engineering, environmental engineering, sustainable energy development, consumer electronics, gas monitoring systems, and microelectronics technology. Especially for aircraft design, changes in flow velocity directly affect the distribution of lift and drag of the aircraft, which is related to the operating efficiency and safety of the aircraft. Accurately measuring the flow velocity and direction of movement of the flow field in which the aircraft is located is the key to enhancing its operating safety, speed, comfort, and fuel efficiency. However, the flow field structure involved in the operation of the aircraft is highly complex, small in scale, short in life cycle, and has temporal and spatial uncertainties. Therefore, it is of great significance to develop high-performance MEMS flow velocity microsensors with small interference to the flow field, 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 effects of parity (P) transformation and time (T) transformation, the Hamiltonian of a PT-symmetric non-Hermitian system can also have real eigenvalues. This theory is an analytical extension of the traditional theory from real phase space to complex phase space, which opens up a new perspective for studying non-Hermitian Hamiltonians and becomes a new method for designing open physical systems (i.e., systems that interact with the environment). At present, PT-symmetric systems have been widely studied and applied in the fields of optical systems, atomic systems, and electronic systems. This not only deepens the understanding of the basic laws of quantum physics, but also promotes breakthroughs in applied technologies and provides new design strategies for devices with new functions. There are few studies on PT-symmetric systems based on mechanical systems, and there are no studies on PT-symmetric flow field microstructures and flow field sensors based on the structures. There is also a lack of theoretical research on introducing perturbations into only one of the resonators. Summary of the invention

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

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

[0006] 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 two double-ended fixed tuning fork resonators are located on the same straight line;

[0007] A mechanical coupling structure is used to weakly couple the two double-ended fixed tuning fork resonators;

[0008] A ciliary support structure, arranged at one end of one of the double-ended fixed tuning fork resonators;

[0009] A connecting beam, wherein the connecting beam connects the ciliary support structure to make it suspended;

[0010] A micro lever, the micro lever connecting the ciliary support structure and the nearby double-ended fixed tuning fork resonator;

[0011] Cilia, the cilia being disposed on the ciliary support structure;

[0012] Comb-tooth capacitors, the comb-tooth capacitors are symmetrically distributed on both sides of each of the two-terminal fixed tuning fork resonators;

[0013] An electrode layer, the electrode layer is connected to the comb-tooth capacitor and the cilia;

[0014] 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 can make the equivalent damping acting on the two double-ended fixed tuning fork resonators have opposite signs and equal magnitudes, thereby achieving PT symmetry;

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

[0016] Preferably, the comb-tooth capacitor comprises:

[0017] The movable comb teeth are connected to both sides of the double-ended fixed tuning fork resonator to form an integral body, and vibrate with the vibration of the double-ended fixed tuning fork resonator; the side of the movable comb teeth close to the double-ended fixed tuning fork resonator is called the inner side, and the other side is called the outer side;

[0018] A detection comb tooth is fixedly constrained on the inner side of the movable comb tooth; the detection comb tooth detects the capacitance change between itself and the movable comb tooth, reflecting the vibration frequency and vibration rate of the double-ended fixed tuning fork resonator;

[0019] The driving comb teeth are fixedly constrained on the outer side of the movable comb teeth; 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.

[0020] Preferably, the electrode layer comprises:

[0021] A detection comb electrode layer connected to the anchor points of the detection comb teeth;

[0022] A driving comb electrode layer connected to the anchor points of the driving comb teeth;

[0023] The ciliary electrode layer is connected to the anchor points extending from both sides of the cilia.

[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 ciliary support structure is a plate-like structure provided with a plurality of concave holes to reduce the mass of the support structure and reduce the influence of gravity on the sensor.

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

[0028] When there is no flow field input, the adjustable damping circuit is regulated so that the equivalent damping acting on the two double-ended fixed tuning fork resonators has opposite signs and equal magnitudes, and the two double-ended fixed tuning fork resonators work at the singular points of PT symmetry;

[0029] After the flow field is input, the cilia will be affected by the flow field force and drive its supporting structure, and the force will be amplified through the micro-lever to act on 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;

[0030] Based on the comb capacitance, electrode layer and adjustable damping circuit, the eigenfrequency after the change of 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 flow field to be measured is input, the eigenfrequency of the sensor is read out, and the value of the flow field to be measured is obtained based on 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:

[0034]

[0035] Where μ = kc / k represents the coupling strength, represents the gain intensity, γ represents the loss intensity, and when PT is symmetric, the gain intensity is equal to the loss intensity; kc represents the equivalent stiffness of the weakly coupled mechanical structure, k refers to the equivalent stiffness of the double-ended tuning fork, m refers to the equivalent mass of the double-ended 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), where Δk is the stiffness perturbation, which is related to the input flow field;

[0037] 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.

[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. The detection comb teeth detect the capacitance change and input the current signal into the transimpedance amplifier through C / V conversion.

[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 invention, a method for preparing a resonant flow field MEMS sensor based on PT symmetry is provided, comprising:

[0042] Spin coating a first photoresist on the silicon wafer and photolithography an anchor block pattern of a sensor structure;

[0043] Using the first photoresist after photolithography as a mask, DRIE or wet etching to form anchor blocks, and then removing the photoresist;

[0044] Anodic bonding the glass substrate and the back side of the etched silicon wafer;

[0045] Grinding the front side of the silicon wafer to a set thickness;

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

[0047] Spin coating a second photoresist and photolithography an electrode layer pattern;

[0048] Using the second photoresist after photolithography as a mask, etching Cr and Au, and removing the resist;

[0049] Spin coating a third photoresist and photolithography a device main body pattern, wherein the device main body includes: a double-ended fixed tuning fork resonator, an adjustable mechanical weak coupling structure, movable comb teeth, a cilia support structure, a connecting beam and a micro lever;

[0050] Using the third photoresist after photolithography as a mask, DRIE etches out the device body and removes the resist;

[0051] Pasting a SU-8 dry film on the silicon wafer;

[0052] Photolithography of cilia pattern on the SU-8 dry film, and degumming;

[0053] The whole is laser sliced ​​to finally obtain the sensor.

[0054] Compared with the prior art, the embodiments of the present invention have at least one of the following beneficial effects:

[0055] The PT-symmetric resonant flow field MEMS sensor in the embodiment of the present invention has a PT-symmetric structure. Compared with the traditional flow velocity sensor based on the Hermitian principle, the PT-symmetric MEMS flow field sensor is a system based on the PT-symmetric principle. Therefore, the constructed flow field sensing system exhibits new physical phenomena or effects; the sensitivity of the PT-symmetric MEMS flow field sensor at the singular point is orders of magnitude higher than that of the traditional non-PT-symmetric system.

[0056] According to the PT symmetry theory, the resonant flow field MEMS sensor based on PT symmetry in the embodiment of the present invention has a 1 / 2 power relationship with the perturbation when it is biased near the singularity, and the smaller the perturbation, the higher the system sensitivity, which is more conducive to the sensor's detection of weak flow velocities.

[0057] The PT-symmetric resonant flow field MEMS sensor in the embodiment of the present invention can provide a new principle and new idea for the design of micro-electromechanical systems; each resonator has differential capacitance detection comb teeth, and differential detection can improve the damping control efficiency and improve the stability and accuracy of frequency signal detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 It is a three-dimensional schematic diagram of a resonant flow field MEMS sensor based on PT symmetry in one embodiment of the present invention;

[0059] Figure 2 It is a partial enlarged schematic diagram of the comb teeth in a preferred embodiment of the present invention;

[0060] Figure 3 A diagram of a PT symmetric lumped parameter model in a preferred embodiment of the present invention;

[0061] Figure 4 A graph showing the asymmetric perturbation frequency theory principle in a preferred embodiment of the present invention;

[0062] Figure 5 This is a schematic diagram of an adjustable damping circuit used in a preferred embodiment of the present invention;

[0063] In the figure: 1-first double-ended fixed tuning fork resonator, 2-second double-ended fixed tuning fork resonator, 3-micro lever, 4-connecting beam, 5-ciliary support structure, 6-ciliary, 7-hollow structure, 8-base, 9-comb tooth capacitor 9, 9a-detection comb teeth, 9b-movable comb teeth, 9c-driving comb teeth, 10-mechanical coupling structure, 11-electrode layer, 111-first detection comb tooth electrode layer, 112-second detection comb tooth electrode layer, 113-third detection comb tooth electrode layer, 114- The fourth detection comb tooth electrode layer, 115-the fifth detection comb tooth electrode layer, 116-the sixth detection comb tooth electrode layer, 117-the seventh detection comb tooth electrode layer, 118-the eighth detection comb tooth electrode layer, 119-the cilia electrode layer, 11a-the first drive comb tooth electrode layer, 11b-the second drive comb tooth electrode layer, 11c-the third drive comb tooth electrode layer, 11d-the fourth drive comb tooth electrode layer; 12a-the first adjustable damping circuit, 12b-the second adjustable damping circuit, 13-the lead. DETAILED DESCRIPTION

[0064] 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.

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

[0066] A double-ended fixed tuning fork resonator, wherein the tuning forks are mirror-symmetrical with each other, and the mass and size of each tuning fork are equal. The two double-ended fixed tuning fork resonators are located on the same straight line. A mechanical coupling structure connects the two double-ended fixed tuning fork resonators with weak coupling. A cilia support structure is arranged at one end of one of the double-ended fixed tuning fork resonators. A connecting beam, wherein the connecting beam connects the cilia support structure so that it is suspended in the air. A micro-lever, wherein the micro-lever connects the cilia support structure and the double-ended fixed tuning fork resonator nearby. Cilia, wherein the cilia are arranged on the cilia support structure. A comb-tooth capacitor, wherein the comb-tooth capacitor is 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 cilia. 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 can 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 is used as the substrate of the sensor.

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

[0068] The resonant flow field MEMS sensor based on PT symmetry in the embodiment of the present invention is based on the PT symmetry principle, so the constructed flow field sensing system can show new physical phenomena or effects. By utilizing the eigenfrequency splitting sensitive characteristics of the PT symmetric system to extremely small perturbations near the singular point, high-precision and high-sensitivity measurement of weak flow velocity changes is achieved. The cilia on the sensor capture the changes in the air flow field, and the capacitance detection realizes the damping control and eigenfrequency measurement to obtain the flow field velocity information.

[0069] like Figure 1 As shown, it is a schematic diagram of the structure of a preferred embodiment involving a resonant MEMS flow rate sensor based on PT symmetry. It can be seen that it includes: a substrate 8, a cilia support structure 5 suspended by a connecting beam 4, cilia 6 arranged 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 a comb capacitor 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 through a lead 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 weak coupling is satisfied. Among them: 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 group of capacitors, which are used to reflect the vibration frequency and vibration speed of the double-ended fixed tuning fork in the X-axis direction, realize the regulation of the resonator damping and the detection of the frequency, so as to reflect the size and direction of the flow field velocity in the Y direction.

[0070] The resonant MEMS flow rate sensor in the above embodiment can be adjusted by the adjustable damping circuit 12 to make the two double-ended fixed tuning fork resonators work at the PT symmetric singular point when there is no flow field input; after the flow field is input, the cilia 6 will be affected by the flow field force and drive its supporting structure 5 to amplify the force through the micro-lever 3 on one end of the first double-ended fixed tuning fork resonator 1 to cause a change in its equivalent stiffness, thereby changing the eigenfrequency of the PT symmetric MEMS system; the sensor is calibrated using a flow field calibration instrument to establish the relationship between its eigenfrequency and different input flow fields; 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 to obtain the flow field value to be measured.

[0071] The enlarged schematic diagram of the comb capacitor in the above embodiment is as follows: Figure 2 As shown, 9a is a comb tooth structure (called detection comb teeth) constituting the detection comb tooth capacitor, which is located on the inner side and symmetrically distributed up and down; 9c is a comb tooth structure (called drive comb teeth) constituting the drive capacitor, which is located on the outer side. 9b is a movable comb tooth, which is connected to the left and right sides of the double-ended fixed tuning fork, and has detection comb teeth and drive comb teeth. The entire comb tooth capacitor is used to reflect the vibration frequency of the double-ended fixed tuning fork in the X-axis direction, realize the regulation and frequency detection of the resonator damping, facilitate the detection of the C / V conversion circuit, and is used to detect the size and direction of the flow field velocity in the Y-axis direction. Specifically: the movable comb tooth 9b is connected to both sides of the double-ended fixed tuning fork resonator to form a whole, and vibrates 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. The detection comb tooth 9a is fixedly constrained on the inner side of the movable comb tooth; the detection comb tooth detects the capacitance change between itself and the movable comb tooth, reflecting the vibration frequency and vibration speed of the double-ended fixed tuning fork resonator. The driving comb teeth 9c are fixedly constrained on the outer side of the movable comb teeth; the driving voltage is provided to drive the double-ended fixed tuning fork resonator; and the damping voltage is also provided so that the damping satisfies the PT symmetry.

[0072] In some specific embodiments, the comb capacitor 9, the ciliary 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 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.

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

[0075] In order to reduce the influence of inertia on the sensor, in some preferred embodiments, the ciliary support structure 7 is provided with recessed holes to reduce the mass of the support structure, thereby reducing inertia.

[0076] In order to better form 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, so as to better form a PT symmetrical structure.

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

[0078] Based on the PT symmetric weakly coupled resonator constructed in the above embodiment, in a preferred embodiment, 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, represents the gain intensity, and γ represents the loss intensity. When PT is symmetric, 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 tuning fork, m refers to the equivalent mass of the double-ended 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 stiffness microvariable. Then, The normalized eigenfrequencies are: This formula can be used as the relationship between the stiffness microvariable and the eigenfrequency. Since the stiffness microvariable is related to the input flow field, this formula can also be used as the relationship between the eigenfrequency and the flow field.

[0082] like Figure 4 As shown in the figure, the result of the frequency response theoretical curve is shown. For the PT symmetric MEMS resonator system biased around the singular point (specifically, two weakly coupled double-ended fixed tuning fork resonators), the real part splitting of the eigenfrequency has a square root dependence on the asymmetric disturbance caused by the external. Due to the perturbation, the eigenfrequency becomes two complex numbers. This sensor perturbation is provided by the flow field. Since the sensing system works in the singular point region, the eigenfrequency will change dramatically with the asymmetric disturbance, that is, the eigenfrequency of the sensing system at the singular point will change dramatically with the input flow field.

[0083] The present embodiment relates to the above-mentioned PT-symmetric MEMS resonator sensor, whose working mode is compatible with capacitive sensing and resonant sensing. Specifically, when the cilia are acted upon by external forces, they will produce a certain displacement, which acts on one end of the double-ended fixed tuning fork through a micro-lever, causing its intrinsic frequency to change, and detecting the capacitance change. Thus, by measuring the comb tooth capacitance, the change in the intrinsic frequency is obtained, and the magnitude and direction of the external force are known.

[0084] In a preferred embodiment of the present invention, a preferred structure of an adjustable damping circuit is provided. Figure 5 The double-ended fixed tuning fork adjustable damping circuit includes: a detection comb 9a, a transimpedance amplifier 122, an analog-to-digital conversion (Analog-to-DigitalConversion) 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, and the output of the transimpedance amplifier 122 is connected to the input of AD123. 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 DA127, and the output of DA127 is connected to the driving comb 9c.

[0085] 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 by a CV conversion circuit for frequency detection. 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.

[0086] In other embodiments of the present invention, the sensor detection process may 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 is input, the cilia will be affected by the flow field force and drive its supporting structure, and the force will be amplified by the micro lever to act on one end of the double-ended fixed tuning fork resonator connected to it, causing the change of its equivalent stiffness, thereby changing the eigenfrequency of the PT symmetric MEMS system;

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

[0090] S4, calibrating the sensor using a flow field calibration instrument to establish a 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 solved, and compared with the calibration value, the flow field value to be measured can be obtained.

[0092] In step S1, by adjusting the damping of the first double-ended fixed tuning fork resonator and the second double-ended fixed tuning fork resonator to be equal in magnitude and opposite in sign, the PT symmetric resonator works at a singular point, at which time the eigenfrequencies of the PT symmetric resonator merge.

[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 acted upon by external forces, they will produce a certain displacement, which acts on one end of the double-ended fixed tuning fork through a micro lever, causing a slight disturbance to 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 eigenfrequency is As the relationship between the stiffness microvariable and the eigenfrequency.

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

[0096] In some other embodiments, in step S2, a perturbation is generated on the stiffness of the first resonator, the system eigenfrequency is no longer the same, and the resonator frequency splitting amount is:

[0097]

[0098] The above relationship can also be used as a modified relationship between the eigenfrequency and different input flow fields. As long as the frequency splitting amount is obtained, the stiffness perturbation amount Δk can be derived. Finally, the flow field information to be measured can be obtained based on the relationship between the stiffness perturbation amount and the calibration of the flow velocity to be measured.

[0099] Based on the same inventive concept, in other embodiments of the present invention, a method for preparing a resonant MEMS flow field sensor based on PT symmetry is provided, which specifically includes:

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

[0101] Step 2, using the first photoresist after photolithography as a mask, DRIE or wet etching to form anchor blocks, and removing the photoresist;

[0102] Step 3, anode bonding the glass substrate and the back side of the etched silicon wafer;

[0103] Step 4, grinding the front side 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, the purpose of which is to make the Au metal better connected to the silicon and prevent the Au metal from falling off.

[0105] Step 6, spin coating a second photoresist and photolithography an electrode layer pattern;

[0106] Step 7, using the second photoresist after photolithography as a mask, etching Cr and Au, and removing the resist;

[0107] 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, a movable comb tooth, a cilia support structure, a connecting beam and a micro lever;

[0108] Step 9, using the third photoresist after photolithography as a mask, DRIE etching to form the device body, and removing the resist;

[0109] Step 10, attaching SU-8 dry film on the silicon wafer;

[0110] Step 11, photolithography of cilia pattern on SU-8 dry film, and degumming;

[0111] Step 12, laser slicing the whole to finally obtain the sensor.

[0112] 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 resonant flow field MEMS sensor based on PT symmetry, characterized in that: include: A double-ended fixed tuning fork resonator, in which the tuning forks are mirror-symmetrical, and the mass and size of each tuning fork are equal; 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 ciliary support structure, arranged at one end of one of the double-ended fixed tuning fork resonators; A connecting beam, wherein the connecting beam connects the ciliary support structure to make it suspended; A micro lever, the micro lever connecting the ciliary support structure and the nearby double-ended fixed tuning fork resonator; Cilia, the cilia being disposed on the ciliary support structure; Comb-tooth capacitors, the comb-tooth capacitors are symmetrically distributed on both sides of each of the two-terminal fixed tuning fork resonators; An electrode layer, the electrode layer is connected to the comb-tooth capacitor and the cilia; 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 can 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 resonant flow field MEMS sensor based on PT symmetry according to claim 1, characterized in that: The comb-tooth capacitor comprises: The movable comb teeth are connected to both sides of the double-ended fixed tuning fork resonator to form an integral body, and vibrate with the vibration of the double-ended fixed tuning fork resonator; the side of the movable comb teeth close to the double-ended fixed tuning fork resonator is called the inner side, and the other side is called the outer side; A detection comb tooth is fixedly constrained on the inner side of the movable comb tooth; the detection comb tooth detects the capacitance change between itself and the movable comb tooth, reflecting the vibration frequency and vibration rate of the double-ended fixed tuning fork resonator; The driving comb teeth are fixedly constrained on the outer side of the movable comb teeth; 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.

3. The resonant flow field MEMS sensor based on PT symmetry according to claim 1 is characterized in that: The electrode layer comprises: A detection comb electrode layer connected to the anchor points of the detection comb teeth; A driving comb electrode layer connected to the anchor points of the driving comb teeth; The ciliary electrode layer is connected to the anchor points extending from both sides of the cilia.

4. A resonant flow field MEMS sensor based on PT symmetry according to claim 3, 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.

5. The resonant flow field MEMS sensor based on PT symmetry according to claim 1 is characterized in that: The ciliary support structure is a plate-like structure provided with a plurality of concave holes, so as to reduce the mass of the support structure and reduce the influence of gravity on the sensor.

6. The resonant flow field MEMS sensor based on PT symmetry according to claim 1, characterized in that: The detection principle of the sensor is: When there is no flow field input, the adjustable damping circuit is regulated so that the equivalent damping acting on the two double-ended fixed tuning fork resonators has opposite signs and equal magnitudes, and the two double-ended fixed tuning fork resonators work at the singular points of PT symmetry; After the flow field is input, the cilia will be affected by the flow field force and drive its supporting structure, and the force will be amplified through the micro-lever to act on 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 the comb capacitance, electrode layer and adjustable damping circuit, the eigenfrequency after the change of equivalent stiffness is obtained; The sensor is calibrated using a flow field calibration instrument to establish the relationship between the eigenfrequency and the input flow field; When the flow field to be measured is input, the eigenfrequency of the sensor is read out, and the value of the flow field to be measured is obtained based on the relationship between the eigenfrequency and the input flow field.

7. The resonant flow field MEMS sensor based on PT symmetry 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, represents the gain intensity, γ represents the loss intensity, and when PT is symmetric, the gain intensity is equal to the loss intensity; kc represents the equivalent stiffness of the weakly coupled mechanical structure, k refers to the equivalent stiffness of the double-ended tuning fork, m refers to the equivalent mass of the double-ended tuning fork, and i represents a complex number.

8. The resonant flow field MEMS sensor based on PT symmetry 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 resonant flow field MEMS sensor based on PT symmetry according to claim 7, characterized in that: The eigenfrequency of the readout sensor is specifically: 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 input the current signal into the transimpedance amplifier through C / V conversion. The transimpedance amplifier converts the current signal into a voltage signal to obtain the perturbed eigenfrequency.

10. A method for preparing a resonant flow field 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 a sensor structure; 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 silicon wafer in sequence; Spin coating a second photoresist and photolithography an electrode layer pattern; 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 device main body pattern, wherein the device main body includes: a double-ended fixed tuning fork resonator, an adjustable mechanical weak coupling structure, movable comb teeth, a cilia support structure, a connecting beam and a micro lever; Using the third photoresist after photolithography as a mask, DRIE etches out the device body and removes the resist; Pasting a SU-8 dry film on the silicon wafer; Photolithography of cilia pattern on the SU-8 dry film, and degumming; The whole is laser sliced ​​to finally obtain the sensor.

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