Nano-electro-mechanical resonant magnetometer based on two-dimensional graphene and preparation and detection method of nano-electro-mechanical resonant magnetometer

Abstract

The invention belongs to the field of MEMS sensors and magnetic field detection, and particularly relates to a nano-electromechanical resonant magnetometer based on two-dimensional graphene. The structure of the sensor mainly comprises a two-dimensional graphene resonance band which is used as a sensitive element for converting mechanical quantity into electrical quantity and outputting the electrical quantity. The drain electrode is placed in the center of the substrate, and the two insulating bases are fixed to the two sides of the substrate and tangent to the wide side of the substrate. The left end and the right end of the two-dimensional graphene resonance band are orthogonally arranged on the upper surfaces of the middles of the top ends of the left insulating base and the right insulating base respectively, the source electrode and the grid electrode are fixed to the tops of the two insulating bases, and the two-dimensional graphene resonance band is pressed over the source electrode and the grid electrode, so that the whole device is of a bilateral symmetry structure. The magnetometer is installed in a magnetic field environment to be measured, and the magnetic field intensity can be calculated according to the resonant frequency change of the two-dimensional graphene resonant band measured by an external circuit. While ultra-high sensitivity and ultra-high precision measurement of a micro magnetic field is realized, the core size of the device is reduced to a nanometer level. The sensor can be combined with electronic products such as a mobile phone to be used as a sensor, or the sensor can be integrated in high-precision devices such as a gyroscope and an aircraft inertial navigation device, so that the blank of related fields in China is filled.

Description

Technical Field

[0001] The present invention belongs to the technical field of MEMS sensors and magnetic field detection, and in particular relates to a nanoelectromechanical resonant magnetometer based on two-dimensional graphene and a preparation and detection method thereof. Background Art

[0002] Magnetometer, also known as Gaussmeter, is a sensor widely used in scientific research, medical imaging, navigation systems and industrial fields. Its main function is to measure the size and direction of the magnetic field in the surrounding environment. The working principle of magnetometer is usually based on different physical effects. There are two main physical effects of magnetometers that can be used to detect magnetic fields: one is the Hall effect magnetometer, which uses Hall sensors to measure the deflection of the current by the magnetic field; the other is the magnetoresistance effect magnetometer. The magnetoresistance effect is used to measure the effect of the magnetic field on the resistance change of the conductor. However, both are restricted by the size of the equipment and the properties of the materials. Magnetometers with high sensitivity are often large in size, high in power consumption and expensive; on the contrary, small portable magnetometers often have poor performance indicators such as sensitivity, accuracy, and linearity. Summary of the invention

[0003] In order to solve the above problems, the present invention faces the urgent need for small-size, high-precision, and low-power magnetic field detection, and proposes a nanoelectromechanical resonant magnetometer based on two-dimensional graphene and its preparation and detection method, using the relevant principles of nanoelectromechanical resonators and new magnetostrictive materials, through the "force-electricity" coupling of the resonator and the "magnetic-force" coupling of the magnetostrictive material, to achieve the conversion of magnetic field signals into electrical signals, and to measure the magnetic field strength by measuring the relevant electrical quantities, breaking through the shortcomings of the existing pure electrical detection method, and achieving small-size, high-precision, and low-power magnetic field detection at the micron level. To achieve the above purpose, the present invention provides the following technical solutions:

[0004] 1. Structural design of a nanoelectromechanical resonant magnetometer based on two-dimensional graphene:

[0005] The present invention adopts the basic principle and structure of field effect tube. Specifically, it includes basic components such as source, gate, drain, and conductive groove. The difference is that the gate of the device is at the bottom of the whole structure, called back gate, and a two-dimensional graphene resonant strip is used instead of the conductive groove to play a conductive role.

[0006] The basic shape of the present invention is a cuboid, and the basic size is 50μm×30μm×20μm. The functional components include a two-dimensional graphene resonance strip 1, a gate 2, a source 3, two insulating bases 4, a drain 5, and a substrate 6. The two insulating bases 4 are fixed on the substrate 6, tangent to the wide side of the substrate 6, and the left and right ends of the two-dimensional graphene resonance strip 1 are orthogonally placed on the upper surface of the middle of the top of the left and right insulating bases 4, respectively. The gate 2 and the drain 3 are fixed on the top of the two insulating bases, and the two-dimensional graphene resonance strip 1 is pressed directly above, so that the overall device presents a left-right symmetrical structure.

[0007] The two-dimensional graphene resonance strip 1 is a resonance strip made of two-dimensional graphene material, and its lower surface is in direct contact with the upper surfaces of the left and right insulating bases 3 , and its upper surface is in direct contact with the lower surfaces of the left and right electrodes 2 .

[0008] The source electrode 2 and the drain electrode 3 are conductive electrodes of the present invention, and are made of Au.

[0009] The drain electrode 5 is located in the center of the substrate.

[0010] The insulating base 4 is a rectangular parallelepiped. Its bottom surface is vertically fixed to the left and right tops of the base 6. The two insulating bases are parallel to each other. The left end of the two-dimensional graphene resonance strip 1 is fixed to the middle of the upper surface of the left insulating base 4. The right end of the two-dimensional graphene resonance strip 1 is fixed to the middle of the upper surface of the right insulating base 4. The gate 2 and the source 3 are respectively fixed to the top of the insulating base 4, and the material is SiO2.

[0011] The substrate 6 is made of magnetostrictive material, is the main supporting structure and functional structure of the structure, and also participates in the conduction as the gate of the device. The material is magnetostrictive material, such as Terfenol-D.

[0012] 2. Process design of a nanoelectromechanical resonant magnetometer based on two-dimensional graphene

[0013] The first step is the preparation and configuration of the two-dimensional graphene resonance strip. The present invention provides two MEMS process methods.

[0014] One is the mechanical stripping method. First, place the prepared graphene sheet in a tray and use tape to strip it multiple times to obtain a single layer of graphene two-dimensional graphene resonance band. At this time, the shape of the obtained graphene two-dimensional graphene resonance band is irregular, which seriously affects the stability of the device. Therefore, the graphene is configured by electron beam etching. The specific method is as follows: first, a layer of electron beam photoresist polymethyl methacrylate (PMMA) is evenly coated on the graphene two-dimensional graphene resonance band, and then the PMMA on the graphene two-dimensional graphene resonance band to be removed is exposed using electron beam etching technology. After development, the chip is placed in a plasma etcher, and the exposed position is etched with oxygen. Finally, the chip is placed in acetone to dissolve PMMA, and then washed with isopropanol to obtain the graphene two-dimensional graphene resonance band of the desired shape.

[0015] The second is the reduction method. First, a certain mass of graphene oxide is weighed and dispersed in distilled water by ultrasound to obtain a graphene oxide dispersion with a concentration of 5 mg / mL. Then, the graphene oxide dispersion is spin-coated on a polytetrafluoroethylene substrate using a vacuum spin coating device, dried naturally and the substrate is peeled off to obtain a two-dimensional graphene resonance band of graphene oxide. Finally, the two-dimensional graphene resonance band of graphene oxide is placed in a graphitization furnace, heated to 1000°C at a rate of 5°C / min in an argon atmosphere, kept warm for 1h, and then heated to 2800°C at a rate of 2°C / min, kept warm for 2h, to complete the graphitization treatment, and mechanically compacted to obtain a two-dimensional graphene resonance band of graphene.

[0016] The second step is the preparation of the substrate and the transfer of the two-dimensional graphene resonance band. It mainly includes: (1) the preparation of the gate and the insulating base; (2) the preparation and transfer of the two-dimensional graphene resonance band; (3) the preparation of the source and drain electrodes.

[0017] The gate electrode is made using standard photolithography technology. A layer of photoresist is first spin-coated on the magnetostrictive material, and then the device is exposed under a mask printed with the desired gate electrode shape. After development, Cr (1nm) / Au (20nm) is grown by thermal evaporation, and the desired gate electrode is obtained after separation. After the gate electrode is completed, SiO2 is thermally grown to obtain an insulating base.

[0018] At this point, the two-dimensional graphene resonance band needs to be transferred. Since the two-dimensional graphene resonance band obtained by mechanical exfoliation is relatively small, transferring the two-dimensional graphene resonance band to the top of the insulating base is one of the key steps. The main process is: (1) spin-coating PMMA on the prepared graphene; (2) placing the graphene / PMMA in a potassium hydroxide solution to etch SiO2, and the PMMA with graphene will float on the surface of the solution; (3) using a glass slide to transfer the graphene / PMMA two-dimensional graphene resonance band from the solution to deionized (DI) water; (4) using a substrate to pick up the graphene / PMMA two-dimensional graphene resonance band from the water, and using a glass needle under a microscope to move the two-dimensional graphene resonance band until the graphene is located directly above the local back gate.

[0019] Finally, drain-source electrodes are made, and the excess parts are etched by BOE to obtain the device.

[0020] 3. A method for detecting magnetic field strength using a nanoelectromechanical resonant magnetometer based on two-dimensional graphene

[0021] A method for detecting magnetic field strength using a two-dimensional graphene-based nanoelectromechanical resonant magnetometer as described in claim 1, comprising the following steps:

[0022] The first step is to obtain the vibration frequency of the n-order mode of the two-dimensional graphene resonance band during free vibration according to the following formula:

[0023]

[0024] in

[0025]

[0026] is the instantaneous inertia, for a rectangular cross section,

[0027]

[0028] l is the length of the two-dimensional graphene resonance band, w is the width of the two-dimensional graphene resonance band, t is the thickness of the two-dimensional graphene resonance band, ω n is the resonance frequency of the nth order mode, E is the Young's modulus of the two-dimensional graphene resonance band, and ρ is the density of the two-dimensional graphene resonance band.

[0029] The second step is to use an external circuit to apply a pre-voltage V to the gate and drain of the magnetometer. g , so that the two-dimensional graphene resonance band of the magnetometer is in a non-measurement initial vibration state. At this time, the charge amount is:

[0030] q=C g V g

[0031] Electrostatic force

[0032]

[0033] in, C g is the capacitance between the gate and the measurement.

[0034] If the modulation voltage

[0035] in, is the DC component, For the exchange quantity.

[0036] but

[0037]

[0038] The electrostatic force mainly consists of two parts: the DC term and the AC term. The DC term controls the tension of the two-dimensional graphene resonance band, and the AC term acts as a periodic force to drive the vibration of the two-dimensional graphene resonance band. When the driving frequency is close to the intrinsic mechanical vibration frequency of the two-dimensional graphene resonance band, the two-dimensional graphene resonance band resonates, and its vibration amplitude also increases accordingly.

[0039] The third step is to apply a magnetic field with a magnetic field strength of B outside the device. At this time, the magnetic coupling effect generated can be expressed by the following two equations:

[0040]

[0041]

[0042] in,

[0043] σ is the prestress of the material. When the prestress is compressive stress, σ<0, when the prestress is tensile stress, σ>0;

[0044] d 33 is the piezomagnetic coefficient, is the magnetomechanical coefficient. If only the magnetoelectric coupling effect in the length direction is considered, the two are equal; is the Young's modulus of the magnetostrictive material when the magnetic field intensity is a constant;

[0045] μ σ is the magnetic permeability of the magnetostrictive material when the stress is a certain constant;

[0046] ε is the strain of the material;

[0047] H is the magnetic field strength to be measured.

[0048] Then, according to the one-dimensional Euler-Bernoulli equation for a uniform beam

[0049]

[0050] Where A represents the cross-sectional area of ​​the two-dimensional graphene resonance band.

[0051] Utilizing parameters

[0052]

[0053] The equation degenerates into

[0054]

[0055] Its general solution is

[0056] x(y)=A1sin(k n +x)+A2cos(k n x)+A3sinh(k n x)+A4cosh(k n x)

[0057] Then, using the boundary conditions

[0058] cos(k n l)·cosh(k n l)=1

[0059] Perform numerical solution.

[0060] k n The three eigenvalues ​​of l are fundamental mode: 4.730; second-order high-order mode: 7.853; third-order high-order mode: 10.996.

[0061] The k n Bring back

[0062]

[0063] The natural frequency of the resonant band can be obtained.

[0064] The fourth step is to generate electromechanical coupling with the electrical quantity and read the magnitude of the magnetic field through the electrical quantity.

[0065] Relationship between conductivity and capacitance:

[0066]

[0067] And there are

[0068]

[0069] Assume that z0 is an example between the gate and the two-dimensional graphene resonance band, is the vibration amplitude of the two-dimensional graphene resonance band, and the distance between the gate and the two-dimensional graphene resonance band is

[0070]

[0071] Then, the corresponding conductance modulation is

[0072]

[0073] It can be seen that the conductance of the two-dimensional graphene resonance band is modulated by the driving frequency and is related to the vibration amplitude.

[0074] Finally, we get

[0075]

[0076] Based on the measured current, the required magnetic induction can be inversely calculated. Furthermore, two orthogonal components can measure the magnitude and direction of the measured induction.

[0077] Beneficial effects of the present invention:

[0078] 1. By using nano-scale two-dimensional graphene resonance strips and magnetic coupling, the existing purely electrical measurement form is changed to achieve ultra-high sensitivity and ultra-high precision measurement of magnetic field strength.

[0079] 2. The core size of the device has been reduced to the nanometer level. It can be combined with various electronic products to be used as a sensor. It is very portable and has the advantages of ultra-low power consumption and fast response.

[0080] 3. Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0081] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0082] Figure 1 The three-view diagram of the nanoelectromechanical resonant magnetometer based on two-dimensional graphene according to an embodiment of the present invention;

[0083] Figure 2 This is a structural diagram of a nanoelectromechanical resonant magnetometer based on two-dimensional graphene according to an embodiment of the present invention;

[0084] Figure 3 This is a working principle diagram of a nanoelectromechanical resonant magnetometer based on two-dimensional graphene according to an embodiment of the present invention;

[0085] Figure 4This is a simulation diagram of the elongation of the two-dimensional graphene resonance band caused by the deformation of the device substrate under a constant magnetic field according to an embodiment of the present invention;

[0086] Figure 5 This is a simulation diagram of the change of the natural frequency of the two-dimensional graphene resonance band of the device under different magnetic fields according to an embodiment of the present invention;

[0087] Figure 6 This is a measurement circuit diagram of a nanoelectromechanical resonant magnetometer based on two-dimensional graphene according to an embodiment of the present invention;

[0088] Figure 7 The overall process flow chart of the embodiment of the present invention;

[0089] Figure 8 This is a process flow chart of a two-dimensional graphene resonance band configuration after mechanical peeling according to an embodiment of the present invention;

[0090] Fig. 9 This is a process flow chart of preparing a two-dimensional graphene resonance band by a reduction method according to an embodiment of the present invention.

[0091] Fig.10 A process flow chart of two-dimensional graphene resonance band transfer according to an embodiment of the present invention;

[0092] Figure numerals: 1 - two-dimensional graphene resonance strip, 2 - gate, 3 - source, 4 - insulating base, 5 - drain, 6 - substrate. DETAILED DESCRIPTION

[0093] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0094] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0095] The same or similar reference numerals in the drawings of the embodiments of the present invention correspond to the same or similar components; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "back" and the like indicate an orientation or positional relationship based on the orientation or positional relationship shown in the drawings, it is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the terms describing the positional relationship in the drawings are only used for exemplary description and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances. The present invention will be described in detail below in conjunction with the drawings; it should be understood that the preferred embodiments are only for illustrating the present invention, not for limiting the scope of protection of the present invention.

[0096] The present invention designs a nanoelectromechanical resonant magnetometer based on two-dimensional graphene. Its structure is as follows Figure 1 and Figure 2 As shown. The functional components include a two-dimensional graphene resonance strip 1, a gate 2, a source 3, two insulating bases 4, a drain 5, and a substrate 6. Among them, the two insulating bases 4 are fixed on the substrate 6, tangent to the wide side of the substrate 6, and the left and right ends of the two-dimensional graphene resonance strip 1 are orthogonally placed on the upper surface of the middle part of the top of the left and right insulating bases 4, respectively. The gate 2 and the drain 3 are fixed on the top of the two insulating bases, and the two-dimensional graphene resonance strip 1 is pressed directly on the top, so that the overall device presents a left-right symmetrical structure. The lower surface of the two-dimensional graphene resonance strip 1 is in direct contact with the upper surfaces of the left and right insulating bases 3, and its upper surface is in direct contact with the lower surfaces of the gate 2 and the source 3. The gate 2 and the source 3 are conductive electrodes made of Au. The insulating base 4 is a rectangular parallelepiped. Its bottom surface is vertically fixed to the left and right tops of the base 6, the two insulating bases are parallel to each other, the left end of the two-dimensional graphene resonance strip 1 is fixed to the middle of the upper surface of the left insulating base 4, the right end of the two-dimensional graphene resonance strip 1 is fixed to the middle of the upper surface of the right insulating base 4, the gate 2 and the source 3 are respectively fixed to the top of the insulating base 4, and the material is SiO2. The base 6 is made of magnetostrictive material, which is the main supporting mechanism and functional structure of this structure, and also participates in the conduction as the gate of this device, and the material is magnetostrictive material, such as Terfenol-D.

[0097] Its working principle is as follows Figure 3 shown. Figure 3 The plane shown is the XY plane, and the coordinate system is marked in the figure. During the measurement, a magnetic field is applied along the X direction. Under the action of the magnetic field, the substrate produces magnetostriction and stretches along the magnetic field direction. Due to the elongation of the substrate, according to the coordination condition of the deformation, the two-dimensional graphene resonance band is forced to stretch. The device is warped due to the internal stress, such as Figure 4 As shown in (A), the warping increases with the increase of magnetic field. Figure 4 (C) shows that the length of the two-dimensional graphene resonance band also increases in the X direction, as shown in Figure 4 (B). Its length increases with the increase of magnetic field. The specific changes are shown in Figure 4 (D) It should be noted that Figure 4 In the figure, all electrodes are hidden. As the length of the two-dimensional graphene resonance band changes, the force on the membrane changes, and its natural frequency changes, such as Figure 5 As shown. Through the closed-loop feedback circuit, the magnitude of the magnetic field can be measured. Figure 6 As shown, the movement of the resonant strip is detected using the capacitive method. The change in capacitance of the driving electrode generates a current, which is introduced into an amplifier. The amplifier produces a voltage output proportional to the oscillation amplitude, which is phase-shifted by an active analog implementation of an all-pass filter, and then the voltage is used as the input of the phase-locked loop in the lock-in amplifier. The reference output of the lock-in amplifier is phase-locked to the input reference, whose amplitude is set to a fixed value by an internal function generator. Therefore, the signal at the output of the phase-locked loop is phase-locked to the detection signal, but the signal has been phase-shifted and has a constant amplitude that can be set independently of the oscillation amplitude. The generated signal is used to drive the resonator and measure the oscillation frequency using a digital frequency meter. The phase shift between the excitation signal and the detection signal determines the point in the resonance curve. In addition, if two orthogonal devices are connected in parallel, the magnitude and direction of the magnetic field can be measured simultaneously. After simulation, the device is accurate and effective in the magnetic field range of 1000A / m-10000A / m. It should be noted that although Figure 3 The working principle of this device is divided into multiple steps, but in fact they occur almost simultaneously without obvious order.

[0098] Specifically, the mathematical model of its working principle is as follows.

[0099] The vibration frequency of the n-order mode of the two-dimensional graphene resonance band during free vibration:

[0100]

[0101] in

[0102]

[0103] is the instantaneous inertia, for a rectangular cross section,

[0104]

[0105] is the length of the two-dimensional graphene resonance band, w is the width of the two-dimensional graphene resonance band, t is the thickness of the two-dimensional graphene resonance band, and w n is the resonance frequency of the nth order mode, E is the Young's modulus of the two-dimensional graphene resonance band, and ρ is the density of the two-dimensional graphene resonance band.

[0106] At this time, a pre-voltage V is applied to the gate and drain of the magnetometer. g , so that the two-dimensional graphene resonance band of the magnetometer is in a non-measurement initial vibration state. At this time, the charge amount is:

[0107] q=C g V g

[0108] Electrostatic force

[0109]

[0110] in, C g is the capacitance between the gate and the measurement.

[0111] If the modulation voltage

[0112] in, is the DC component, For the exchange quantity.

[0113] but

[0114]

[0115] The electrostatic force mainly consists of two parts: the DC term and the AC term. The DC term controls the tension of the two-dimensional graphene resonance band, and the AC term acts as a periodic force to drive the vibration of the two-dimensional graphene resonance band. When the driving frequency is close to the intrinsic mechanical vibration frequency of the two-dimensional graphene resonance band, the two-dimensional graphene resonance band resonates, and its vibration amplitude also increases accordingly.

[0116] When a magnetic field with a magnetic field strength of B is applied to the outside of the device, the magnetic coupling effect generated can be expressed by the following two equations:

[0117]

[0118] in,

[0119] σ is the prestress of the material. When the prestress is compressive stress, σ<0; when the prestress is tensile stress, σ>0;

[0120] d 33 is the piezomagnetic coefficient, is the magnetomechanical coefficient. If only the magnetoelectric coupling effect in the length direction is considered, the two are equal;

[0121] is the Young's modulus of the magnetostrictive material when the magnetic field intensity is a constant;

[0122] μ σis the magnetic permeability of the magnetostrictive material when the stress is a certain constant;

[0123] ε is the strain of the material;

[0124] H is the magnetic field strength to be measured.

[0125] Then, according to the one-dimensional Euler-Bernoulli equation for a uniform beam

[0126]

[0127] Where A represents the cross-sectional area of ​​the two-dimensional graphene resonance band.

[0128] Utilizing parameters

[0129]

[0130] The equation degenerates into

[0131]

[0132] Its general solution is

[0133] x(y)=A1sin(k n x)+A2cos(k n x)+A3sinh(k n x)+A4cosh(k n x)

[0134] Then, using the boundary conditions

[0135] cos(k n l)·cosh(k n l)=1

[0136] Perform numerical solution.

[0137] k n The three eigenvalues ​​of l are fundamental mode: 4.730; second-order high-order mode: 7.853; third-order high-order mode: 10.996.

[0138] The fourth step is to generate electromechanical coupling with the electrical quantity and read the magnitude of the magnetic field through the electrical quantity.

[0139] Relationship between conductivity and capacitance:

[0140]

[0141] And there are

[0142]

[0143] Assume that z0 is an example between the gate and the two-dimensional graphene resonance band, is the vibration amplitude of the two-dimensional graphene resonance band, and the distance between the gate and the two-dimensional graphene resonance band is

[0144]

[0145] Then, the corresponding conductance modulation is

[0146]

[0147] It can be seen that the conductance of the two-dimensional graphene resonance band is modulated by the driving frequency and is related to the vibration amplitude.

[0148] Finally, we get

[0149]

[0150] The manufacturing process of this device is as follows. Figure 7 shown.

[0151] The first step is the preparation and configuration of the two-dimensional graphene resonance strip. The present invention provides two MEMS process methods.

[0152] The first is the mechanical peeling method. First, the prepared graphene sheet is placed on a tray and peeled off multiple times with tape to obtain a single layer of graphene two-dimensional graphene resonance band. At this time, the shape of the obtained graphene two-dimensional graphene resonance band is irregular, which seriously affects the stability of the device. Therefore, the graphene is configured using electron beam etching, such as Figure 8 As shown. The specific method is as follows: First, a layer of electron beam photoresist polymethyl methacrylate (PMMA) is evenly coated on the graphene two-dimensional graphene resonance band, and then the PMMA on the graphene two-dimensional graphene resonance band to be removed is exposed using electron beam etching technology. After development, the chip is placed in a plasma etcher, and the exposed position is etched using oxygen. Finally, the chip is placed in acetone to dissolve the PMMA, and then washed with isopropanol to obtain the graphene two-dimensional graphene resonance band of the desired shape.

[0153] The second is the reduction method, such as Fig. 9 As shown. First, a certain mass of graphene oxide is weighed and dispersed in distilled water by ultrasound to obtain a graphene oxide dispersion with a concentration of 5 mg / mL. Then, the graphene oxide dispersion is spin-coated on a polytetrafluoroethylene substrate using a vacuum spin coating device, dried naturally and the substrate is peeled off to obtain a graphene oxide two-dimensional graphene resonance band. Finally, the graphene oxide two-dimensional graphene resonance band is placed in a graphitization furnace, heated to 1000°C at a rate of 5°C / min in an argon atmosphere, and then heated to 2800°C at a rate of 2°C / min and kept warm for 2h to complete the graphitization treatment and obtain a graphene two-dimensional graphene resonance band.

[0154] The second step is the preparation of the substrate and the transfer of the two-dimensional graphene resonance band. It mainly includes: (1) the preparation of the gate and the insulating base; (2) the preparation and transfer of the two-dimensional graphene resonance band; (3) the preparation of the source and drain electrodes.

[0155] The gate electrode is made using standard photolithography technology. A layer of photoresist is first spin-coated on the magnetostrictive material, and then the device is exposed under a mask printed with the desired gate electrode shape. After development, Cr (1nm) / Au (20nm) is grown by thermal evaporation, and the desired gate electrode is obtained after separation. After the gate electrode is completed, SiO2 is thermally grown to obtain an insulating base.

[0156] At this point, the two-dimensional graphene resonance band needs to be transferred, such as Fig.10 As shown. Since the two-dimensional graphene resonance band of graphene obtained by mechanical exfoliation is small, transferring the two-dimensional graphene resonance band to the upper side is one of the key steps. The main process is: (1) spin-coating PMMA on the prepared graphene; (2) placing graphene / PMMA in potassium hydroxide solution to etch SiO2, and the PMMA with graphene will float on the surface of the solution; (3) using a glass slide to transfer the graphene / PMMA two-dimensional graphene resonance band from the solution to deionized (DI) water; (4) using a substrate to pick up the graphene / PMMA two-dimensional graphene resonance band from the water, and using a glass needle under a microscope to move the two-dimensional graphene resonance band until the graphene is located directly above the local back gate.

[0157] Finally, drain-source electrodes are made, and the excess parts are etched by BOE to obtain the device.

[0158] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions, which should be included in the scope of the claims of the present invention.

Claims

1. A nanoelectromechanical resonant magnetometer based on two-dimensional graphene, characterized in that There is one resonant strip 1, two electrodes 2, two insulating bases 3, and one substrate 4.

2. A nanoelectromechanical resonant magnetometer based on two-dimensional graphene according to claim 1, characterized in that Two insulating bases 3 are fixed on the substrate 1 and are tangent to the wide side of the substrate 1. The left and right ends of the resonance band 1 are orthogonally placed on the upper surface of the middle part of the top of the left and right insulating bases 3. The electrode 2 fixes the top of the two insulating bases and presses the resonance band 1 directly above, so that the overall device presents a left-right symmetrical structure.

3. A nanoelectromechanical resonant magnetometer based on two-dimensional graphene according to claim 2, characterized in that The resonance strip 1 is a graphene film, the lower surface of which is in direct contact with the upper surfaces of the left and right insulating bases 3 , and the upper surface of which is in direct contact with the lower surfaces of the left and right electrodes 2 .

4. The nanoelectromechanical resonant magnetometer based on two-dimensional graphene according to claim 3, characterized in that The electrodes 3 are the source and drain of the present invention and are used as conductive electrodes, and are made of Au.

5. The nanoelectromechanical resonant magnetometer based on two-dimensional graphene according to claim 4, characterized in that The insulating base 3 is a rectangular parallelepiped. Its bottom surface is vertically fixed to the left and right tops of the base 4. The two insulating bases are parallel to each other. The left end of the resonance belt 1 is fixed to the middle of the upper surface of the left insulating base 3, and the right end of the resonance belt 1 is fixed to the middle of the upper surface of the right insulating base 3. The two electrodes 2 are respectively fixed to the top of the insulating base 3, and the material is SiO2.

6. According to the two-dimensional graphene-based nanoelectromechanical resonant magnetometer of claim 5, the substrate 4 is made of magnetostrictive material, is the main supporting mechanism and functional structure of the structure, and also participates in the conduction as the gate of the device, and is made of magnetostrictive material, such as Terfenol-D.

7. A method for preparing a nanoelectromechanical resonant magnetometer based on two-dimensional graphene according to claim 1, comprising the following steps: The first step is the preparation and configuration of the resonance strip. The present invention provides two MEMS process methods. One is the mechanical stripping method. First, place the prepared graphene sheet in a tray and use tape to strip it multiple times to obtain a single-layer graphene film. At this time, the shape of the obtained graphene film is irregular, which seriously affects the stability of the device. Therefore, the graphene is configured using electron beam etching. The specific method is as follows: first, a layer of electron beam photoresist polymethyl methacrylate (PMMA) is evenly coated on the graphene film, and then the PMMA on the graphene film to be removed is exposed using electron beam etching technology. After development, the chip is placed in a plasma etcher, and the exposed position is etched with oxygen. Finally, the chip is placed in acetone to dissolve the PMMA, and then washed with isopropanol to obtain a graphene resonance band of the desired shape. The second is the reduction method. First, a certain mass of graphene oxide is weighed and dispersed in distilled water by ultrasound to obtain a graphene oxide dispersion with a concentration of 5 mg / mL. Then, the graphene oxide dispersion is spin-coated on a polytetrafluoroethylene substrate using a vacuum spin coating device, dried naturally and the substrate is peeled off to obtain a graphene oxide film. Finally, the graphene oxide film is placed in a graphitization furnace, heated to 1000°C at a rate of 5°C / min in an argon atmosphere, kept warm for 1h, and then heated to 2800°C at a rate of 2°C / min and kept warm for 2h to complete the graphitization treatment and obtain a graphene film. The second step is the preparation of the substrate and the transfer of the resonance band. It mainly includes: (1) the preparation of the gate and the insulating base; (2) the preparation and transfer of the resonance band; (3) the preparation of the source and drain electrodes. The gate electrode is made using standard photolithography technology. A layer of photoresist is first spin-coated on the magnetostrictive material, and then the device is exposed under a mask printed with the desired gate electrode shape. After development, Cr (1nm) / Au (20nm) is grown by thermal evaporation, and the desired gate electrode is obtained after separation. After the gate electrode is completed, SiO2 is thermally grown to obtain an insulating base. At this point, the resonant band needs to be transferred. Since the graphene film obtained by mechanical exfoliation is relatively small, transferring the resonant band to the top of the insulating base is one of the key steps. The main process is: (1) spin-coating PMMA on the prepared graphene; (2) placing the graphene / PMMA in a potassium hydroxide solution to etch SiO2, and the PMMA with graphene will float on the surface of the solution; (3) using a glass slide to transfer the graphene / PMMA film from the solution to deionized (DI) water; (4) using a substrate to pick up the graphene / PMMA film from the water, and using a glass needle to move the film under a microscope until the graphene is located directly above the local back gate.

8. Finally, the drain-source electrodes are made, and the excess parts are etched away by BOE to obtain the device.

9. A method for measuring magnetic field strength using a two-dimensional graphene-based nanoelectromechanical resonant magnetometer according to claim 1, comprising the following steps: The first step is to obtain the vibration frequency of the n-order mode of the resonant band during free vibration according to the following formula: in I is the instantaneous inertia. For a rectangular cross section, l is the length of the resonance belt, w is the width of the resonance belt, t is the thickness of the resonance belt, ω n is the resonant frequency of the nth-order mode, E is the Young's modulus of the resonant band, and ρ is the density of the resonant band. The second step is to use an external circuit to apply a pre-voltage V to the gate and drain of the magnetometer. g , so that the magnetometer resonance belt is in a non-measurement initial vibration state. At this time, the charge amount is: q=C g V g Electrostatic force in, C g is the capacitance between the gate and the measurement. If the modulation voltage in, is the DC component, For the exchange quantity. but The electrostatic force mainly consists of two parts: the DC term and the AC term. The DC term controls the tension of the film, and the AC term acts as a periodic force to drive the film to vibrate. When the driving frequency is close to the intrinsic mechanical vibration frequency of the resonant band, the resonant band resonates and its vibration amplitude increases accordingly. The third step is to apply a magnetic field with a magnetic field strength of B outside the device. At this time, the magnetic coupling effect generated can be expressed by the following two equations: in, σ is the prestress of the material. When the prestress is compressive stress, σ<0, when the prestress is tensile stress, σ>0; d 33 is the piezomagnetic coefficient, is the magnetomechanical coefficient. If only the magnetoelectric coupling effect in the length direction is considered, the two are equal; is the Young's modulus of the magnetostrictive material when the magnetic field intensity is a constant; μ σ is the magnetic permeability of the magnetostrictive material when the stress is a certain constant; ε is the strain of the material; H is the magnetic field strength to be measured. Then, according to the one-dimensional Euler-Bernoulli equation for a uniform beam Where A represents the cross-sectional area of ​​the resonant band. Utilizing parameters The equation degenerates into Its general solution is x(y)=A1sin(k n x)+A2cos(k n x)+A3sinh(k n x)+A4cosh(k n x) Then, using the boundary conditions cos(k n l)·cosh(k n l)=1 Perform numerical solution. k n The three eigenvalues ​​of l are fundamental mode: 4.730; second-order high-order mode: 7.853; third-order high-order mode: 10.

996. The fourth step is to generate electromechanical coupling with the electrical quantity and read the magnitude of the magnetic field through the electrical quantity. Relationship between conductivity and capacitance: And there are Assume that z0 is an example between the gate and the resonant band, is the vibration amplitude of the resonance band, then the distance between the gate and the resonance band is Then, the corresponding conductance modulation is It can be seen that the conductance of the resonant band is modulated by the driving frequency and is related to the vibration amplitude. Finally, we get Based on the measured current, the required magnetic induction can be inversely calculated. Furthermore, two orthogonal components can measure the magnitude and direction of the measured induction.

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