High-sensitivity magnetometer based on double-groove graphene suspended mass block structure and method

Abstract

The invention belongs to the technical field of resonant inertial sensors, and particularly relates to a high-sensitivity magnetometer based on a double-groove graphene suspended mass block structure and a method. Wherein the SOI wafer is provided with an I-shaped groove and square grooves, the graphene ribbon is fixed at the rear end of the SOI wafer, the source electrode is fixed on the SOI wafer at the outer side of the I-shaped groove, and the drain electrode is fixed on the SOI wafer at the outer side of the square groove at the right side; a grid electrode is arranged in the I-shaped groove, and a suspended heavy-weight magnetic mass block is adsorbed at the bottom of the graphene ribbon above the square groove; according to the invention, the resonant frequency and the sensitivity can be improved in order of magnitude, the detection range is widened, and the bottleneck problem that ultra-wide range and high sensitivity are difficult to consider at the same time is solved; the invention further breaks through key processes of a graphene film suspended mass block with atomic layer thickness, graphene patterning and the like, and develops a stable preparation technology of the graphene transconductance device structure.

Description

Technical Field

[0001] The present invention belongs to the technical field of resonant inertial sensors, and particularly relates to a highly sensitive magnetometer and method based on a double-groove graphene suspended mass structure. Background Art

[0002] A magnetometer is a sensor used to measure the magnetic field strength. Its basic working principle is to obtain magnetic field information by sensing the magnetic induction intensity in the environment. Magnetometers have a wide range of applications in fields such as navigation, geophysical exploration, and aerospace.

[0003] Currently, there are many types of magnetic field sensors for measuring magnetic fields, and most of them are based on magnetic and electrical phenomena, such as search coil magnetometers, fluxgate sensors, optical pumping sensors, quantum interference sensors, Hall sensors, magnetoresistive sensors, magnetic diodes, fiber optic sensors, magneto-optical sensors, MEMS magnetic field sensors, etc.

[0004] Among them, the MEMS magnetic field sensor is a new type of micromachined sensor proposed by H.H. Yang et al. in 2002. Its structure consists of electroplated hard magnetic alloy and a pair of polysilicon torsion beams. The main physical principles utilized are: Lorentz force, tunneling effect, torsion, and resonant structure. The ferromagnetic alloy will be magnetized in a magnetic field environment, thus generating a magnetic moment. When the ferromagnetic body undergoes a small-angle rotation under the action of a magnetic field, the polysilicon beam will also twist. By measuring the angle of twist, the magnitude of the magnetic field can be measured. In 2004, Franz Keplinger et al. proposed a new sensor structure. There is metallic lead on its U-shaped Si cantilever beam to conduct current without being affected by the magnetic field. When a magnetic field and current act, there will be a Lorentz force at the base end of the cantilever beam, and the resulting deformation of the beam is detected by an optical method. In 2006, Liu Yufei et al. proposed a high-precision and low-power magnetic field sensor. The structure includes a double-ended fixed MEMS micro-torsion mirror, a magnetic sensitive thin film, and a double fiber collimator part. When the sensor is under the action of an external magnetic field, the magnetic thin film will be affected by the magnetic field and generate a torque. This torque causes the MEMS torsion mirror to generate a certain angle of twist. Then, through the reflection optical path formed by the double fiber collimator and the micro-mirror surface, the optical intensity coupling loss generated by the twist can be detected. Through the coupling loss, the angle of twist of the mirror surface can be calculated, and finally the magnetic field information can be measured. In 2007, Daniel J. Vasquez et al. used this structure as a node of a wireless sensor. In 2007, Liu Jian et al. from the Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, proposed a magnetic field sensor with a cantilever beam structure with self-calibration function. By depositing a layer of Ni thin film at the free end of the cantilever beam and injecting particles at the anchor point of the beam to form piezoresistance, detection is also carried out through piezoresistance. To achieve the self-calibration function, an aluminum coil is made around the cantilever beam. When current flows into the aluminum coil, a magnetic field will be generated, causing the beam to bend and generating a self-calibration output signal. Behraad Bahreyni and Cyrus Shafai first established an analysis model and simulation for the proposed resonant magnetic field sensor structure in 2004, and improved and fabricated the structure in 2007. The sensing method is to measure the drift of the resonant frequency of the electrostatic comb drive, and detection is also carried out through the resonant method. In 2008, Li Chengzhang and Huang Qing'an from the Key Laboratory of MEMS of the Ministry of Education, Southeast University, proposed a new type of comb-shaped micromachined resonant magnetic field sensor. The output signal of the capacitance detection is fed back to the excitation end through an amplification feedback loop at the same time, making the resonance stable at the resonant frequency. The structure was simulated by ANSYS to verify the rationality of the results.

[0005] Although scholars at home and abroad have done a lot of research on MEMS magnetic field sensors, the following problems still need to be solved: the existing MEMS magnetic field sensors are difficult to further reduce in volume size, have a slow response speed, low accuracy, and it is difficult to further improve the key performance indicators such as sensitivity, range, and zero offset. Moreover, it is difficult to balance ultra-wide range and high sensitivity. Summary of the Invention

[0006] In order to overcome the above problems, the present invention proposes a high-sensitivity magnetometer and method based on a double-groove graphene suspended mass structure. For the first time, a nano-magnetometer sensing architecture based on a double-groove graphene suspended large-weight magnetic mass transconductor structure is proposed. Through the sliding boundary condition, a perception-detection separation design scheme is realized. On the one hand, it can overcome the reduction effect of the suspended mass on the resonance frequency and achieve an order-of-magnitude improvement in resonance frequency and sensitivity. On the other hand, it can partially release the large magnetic field force through the sliding boundary condition, broaden the detection range, and solve the bottleneck problem that it is difficult to balance ultra-wide range and high sensitivity. The present invention further breaks through the key processes such as the suspension of graphene thin films with atomic layer thickness and graphene patterning, and develops a stable preparation technology for the graphene transconductor structure.

[0007] The object of the present invention is achieved by the following technical solutions:

[0008] A high-sensitivity magnetometer based on a double-groove graphene suspended mass structure, comprising a graphene strip 1, a source electrode 2, a gate electrode 3, a suspended large-weight magnetic mass 4, a drain electrode 5, and an SOI wafer 6. An I-shaped groove and a square groove are sequentially arranged on the SOI wafer 6 from left to right, and a central support column is left on the SOI wafer 6 between the rear end of the I-shaped groove and the square groove. The graphene strip 1 is fixed at the rear end of the SOI wafer 6 and is located above the I-shaped groove, the central support column, and the square groove. The source electrode 2 is fixed on the SOI wafer 6 outside the I-shaped groove, and its rear end is located above the graphene strip 1. The drain electrode 5 is fixed on the SOI wafer 6 outside the right square groove, and its rear end is located above the graphene strip 1. The middle part of the graphene strip 1 is fixed on the central support column. The gate electrode 3 is installed in the I-shaped groove, and a suspended large-weight magnetic mass 4 is adsorbed on the bottom of the graphene strip 1 above the square groove, and the suspended large-weight magnetic mass 4 is located in the square groove.

[0009] The suspended large-weight magnetic mass 4 is nano-scale magnetic powder.

[0010] The graphene strip 1 is a single-layer graphene.

[0011] The gate electrode 3 is a driving electrode.

[0012] A method for measuring the magnetic field strength to be measured by using a high-sensitivity magnetometer based on a double-groove graphene suspended mass structure, comprising the following steps:

[0013] Step 1: Calibrate the natural frequency of the part of graphene strip 1 suspended above the I-shaped groove on the left side. Denote the part of graphene strip 1 suspended above the I-shaped groove on the left side as the left suspended graphene strip, and the part of graphene strip 1 suspended above the square groove on the right side as the right suspended graphene strip. The specific calibration process is as follows:

[0014] Select the viscoelastic connector equivalent model of the Voigt-Kelvin constitutive relation to equivalently model the graphene strip 1 in the magnetometer that is in contact with the right edge of the source electrode 2 on the left side and the graphene strip 1 in the magnetometer that is in contact with the left edge of the drain electrode 5 on the right side. The spring-damper system formed by the spring and damper connected end to end in the equivalent model is equivalent to the graphene strip 1 in contact with the right edge of the source electrode 2 on the left side or the graphene strip 1 in contact with the left edge of the drain electrode 5 on the right side;

[0015] Near the natural frequency f L0 of the left suspended graphene strip, input an accelerating sweep signal to the gate electrode 3. By changing the magnitude of the voltage applied to the gate electrode 3, drive the entire graphene strip 1 to vibrate. The calibrated natural frequency f L0 of the left suspended graphene strip is calculated according to the following formula:

[0016]

[0017] where E is the Young's modulus, S is the cross-sectional area of the graphene strip 1, ε 0 is the initial pre-strain of the graphene strip 1, L L0 is the length of the left suspended graphene strip, x L0 is the maximum displacement of the suspended magnetic mass 4 in the vertical direction, q L0 is the elongation of the spring-damper system in the viscoelastic connector equivalent model of the Voigt-Kelvin constitutive relation during the calibration process, and m L is the effective mass of the left suspended graphene strip;

[0018] Step 2: Install this magnetometer in the magnetic field environment to be measured. Sweep the frequency of the gate electrode 3 again in the frequency range of 0.8f L0 to 1.2f L0 . Under the action of the magnetic field, the suspended large-weight magnetic mass 4 is subjected to a downward magnetic force, the right suspended graphene strip deforms downward, the graphene strip 1 slides to the right, the left suspended graphene strip is tightened, and the change in the axial stress causes the natural frequency of the left suspended graphene strip to change;

[0019] Step 3: Measure the natural frequency f L of the left suspended graphene strip under the action of the magnetic field. According to the natural frequency offset, inversely deduce the magnetic force F mag of the measured magnetic field environment, the magnetic force F mag is inversely proportional to the natural frequency, where the natural frequency f of the left suspended graphene strip L is calculated according to the following formula:

[0020]

[0021] where, L L is the length of the left suspended graphene strip, q L is the elongation of the spring damping system, x L is the maximum displacement of the suspended magnetic mass 4 in the vertical direction;

[0022] The magnetic force is calculated according to the following formula:

[0023]

[0024] The present invention provides a preparation method of a magnetometer based on a double-groove graphene suspended mass structure, including the following process steps:

[0025] Step a, the SOI wafer 6 is sequentially divided into a silicon device layer, an insulating layer, and a silicon substrate from top to bottom; a 1.4-μm-thick silicon dioxide layer is grown on the upper surface of the silicon device layer of the SOI wafer 6 by the oxidation growth method;

[0026] Step b, spin-coat a photoresist on the silicon dioxide layer and perform mask lithography to pattern the photoresist layer to define an I-shaped groove pattern, then etch away the silicon dioxide layer corresponding to the I-shaped groove pattern with 25% by volume of HF, and the unetched silicon dioxide layer and the photoresist layer are used as a mask layer to etch an I-shaped groove structure on the silicon device layer by reactive ion etching technology, and finally remove the photoresist layer by the lift-off stripping process;

[0027] Spin-coat a photoresist on the silicon dioxide layer again, pattern the photoresist layer to define a square groove pattern, then etch away the silicon dioxide layer corresponding to the square groove pattern with 25% by volume of HF, and the unetched silicon dioxide layer and the photoresist layer are used as a mask layer to etch a square groove structure on the silicon device layer by reactive ion etching technology, and finally remove the photoresist layer by the lift-off stripping process;

[0028] Step c: Use the lift-off process again to remove the photoresist layer, then spin-coat photoresist on the insulating layer within the I-shaped trench, perform mask lithography, pattern the photoresist layer to define an I-shaped cavity pattern, etch a 300-nm deep I-shaped cavity in the insulating layer beneath the silicon device layer through reactive ion etching technology. The I-shaped cavity is located within the I-shaped trench. Then, fill the 300-nm deep I-shaped cavity on the insulating layer with Au by magnetron sputtering to form Gate 3, and use the lift-off process to remove the photoresist layer;

[0029] Step d: Spin-coat photoresist on the surface of the backside of the SOI wafer 6, perform mask lithography on the photoresist layer, pattern the photoresist layer to obtain a square trench pattern corresponding in position and size to the square trench above the SOI wafer 6, and etch from the backside of the SOI wafer 6 to the lower surface of the insulating layer beneath the silicon device layer through reactive ion deep etching technology to form a back cavity beneath the square trench structure above the SOI wafer 6;

[0030] Step e: Spin-coat the photoresist layer on the 1.4-μm thick silicon dioxide layer and perform mask lithography to obtain patterns corresponding to Source 2 and Drain 5 on the photoresist layer. Imprint and transfer graphene strips to span above the two trenches, and then through O 2 Plasma etch the graphene strips to form graphene ribbons 1 of the desired shape; Step f: Use reactive ion etching technology to etch 300-nm deep cavities in the silicon dioxide layer corresponding to the patterns of Source 2 and Drain 5, then fill the cavities with Au by magnetron sputtering to form Source 2 and Drain 5, and use the lift-off process to remove the photoresist layer;

[0031] Step g: Place the SOI wafer 6 in a steam chamber with a temperature set to 40°C, and etch the backside of the SOI wafer 6 with 25% by volume steam HF for 5 - 10 minutes to remove the remaining insulating layer beneath the silicon device layer, forming a square trench structure that completely penetrates the SOI wafer 6 on the right side of the SOI wafer 6;

[0032] Step h: Transfer the suspended large-weight magnetic mass 4 into the square trench, and use van der Waals force to adsorb the suspended large-weight magnetic mass 4 to the bottom of the graphene ribbon 1 above the square trench to complete the transfer of the suspended large-weight magnetic mass 4;

[0033] Step i: Bond Source 2 and Drain 5 to the PCB substrate leads respectively, and perform vacuum packaging to complete the preparation of the magnetometer.

[0034] Advantages of the present invention:

[0035] 1. Achieve the separation of inertial sensing and resonant detection, overcome the negative impact of the inertial mass block on the resonant performance in the traditional single-groove structure, and synchronously improve the detection sensitivity and range by an order of magnitude.

[0036] 2. Realize the partial release of the large magnetic force through the sliding boundary condition, broaden the detection range, and take into account both the ultra-wide range and the ultra-high sensitivity.

[0037] 3. It has the advantages of small volume, low power consumption, high precision, fast response, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings to be used in the description of the embodiments of the present invention. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained according to the content of the embodiments of the present invention and these drawings.

[0039] Figure 1 It is a schematic structural diagram of the magnetometer of the present invention;

[0040] Figure 2 It is a schematic cross-sectional structural diagram of the magnetometer of the present invention;

[0041] Figure 3 It is a front view of the schematic cross-sectional structural diagram of the magnetometer of the present invention;

[0042] Figure 4 It is a schematic enlarged view of the left groove of the magnetometer of the present invention, and a schematic diagram of the viscoelastic connector of the Voigt-Kelvin constitutive relationship;

[0043] Figure 5 It is a one-dimensional string model for calculating the left suspended graphene strip in Embodiment 2 of the present invention;

[0044] Figure 6 It is a physical model of the magnetometer in Embodiment 2 of the present invention;

[0045] Figure 7 It is a preparation process of the double-groove graphene suspended mass block structure in Embodiment 2 of the present invention;

[0046] Figure 8 It is a schematic diagram of the principle of the magnetometer in Embodiment 2 of the present invention;

[0047] Among them: 1 graphene strip, 2 source electrode, 3 gate electrode, 4 large-weight magnetic block, 5 drain electrode, 6 SOI wafer. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0048] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It can be understood that the specific embodiments described herein are only for explaining the present invention, rather than limiting the present invention. In addition, it should be noted that for the convenience of description, only the parts related to the present invention rather than all the structures are shown in the drawings.

[0049] Embodiment 1

[0050] A highly sensitive magnetometer based on a double-groove graphene suspended mass structure, comprising a graphene strip 1, a source electrode 2, a gate electrode 3, a suspended large-weight magnetic mass 4, a drain electrode 5, and an SOI wafer 6. An I-shaped groove and a square groove are sequentially arranged on the SOI wafer 6 from left to right, and a central support column is left on the SOI wafer 6 between the rear end of the I-shaped groove and the square groove. The graphene strip 1 is fixed to the rear end of the SOI wafer 6 and is located above the I-shaped groove, the central support column, and the square groove. The source electrode 2 is fixed to the SOI wafer 6 outside the I-shaped groove, and its rear end is located above the graphene strip 1. The drain electrode 5 is fixed to the SOI wafer 6 outside the right square groove, and its rear end is located above the graphene strip 1. The middle part of the graphene strip 1 is fixed to the central support column; the gate electrode 3 is installed in the I-shaped groove, and a suspended large-weight magnetic mass 4 is adsorbed on the bottom of the graphene strip 1 above the square groove, and the suspended large-weight magnetic mass 4 is located in the square groove.

[0051] The suspended large-weight magnetic mass 4 is nano-scale magnetic powder.

[0052] The graphene strip 1 is monolayer graphene.

[0053] The gate electrode 3 is a driving electrode.

[0054] A method for measuring the magnetic field strength to be measured by using a highly sensitive magnetometer based on a double-groove graphene suspended mass structure, comprising the following steps:

[0055] Step 1: Calibrate the natural frequency of the part of the graphene strip 1 suspended above the I-shaped groove on the left. The part of the graphene strip 1 suspended above the I-shaped groove on the left is denoted as the left suspended graphene strip, and the part of the graphene strip 1 suspended above the square groove on the right is denoted as the right suspended graphene strip. The specific calibration process is as follows:

[0056] Select the viscoelastic connector equivalent model of the Voigt-Kelvin constitutive relation (this model is composed of Figure 4The shown spring (elastic element) and damper (viscous element) are in parallel. They respectively equivalent the graphene strip 1 in the magnetometer that contacts the right edge of the source electrode 2 on the left side (referring to the part of the graphene strip 1 that contacts the source electrode 2) and the graphene strip 1 in the magnetometer that contacts the left edge of the drain electrode 5 on the right side (referring to the part of the graphene strip 1 that contacts the drain electrode 5). Among them, the spring-damper system composed of the spring and damper connected end to end in the equivalent model is equivalent to the graphene strip 1 that contacts the right edge of the source electrode 2 on the left side or the graphene strip 1 that contacts the left edge of the drain electrode 5 on the right side;

[0057] Near the natural frequency f of the left suspended graphene strip L0 , an accelerating sweep signal is input to the gate 3. By changing the magnitude of the voltage applied to the gate 3, the entire graphene strip 1 is driven to vibrate. Among them, the calibrated natural frequency f of the left suspended graphene strip L0 is calculated according to the following formula:

[0058]

[0059] Among them, E is the Young's modulus, S is the cross-sectional area of the graphene strip 1, ε 0 is the initial pre-strain of the graphene strip 1, L L0 is the length of the left suspended graphene strip, x L0 is the maximum displacement of the suspended magnetic mass 4 in the vertical direction, q L0 is the elongation of the spring-damper system in the viscoelastic connector equivalent model during the calibration process according to the Voigt-Kelvin constitutive relation, m L is the effective mass of the left suspended graphene strip;

[0060] Step 2: Install this magnetometer in the magnetic field environment to be measured. Sweep the frequency of the gate 3 again in the frequency range of 0.8f L0 to 1.2f L0 . Under the action of the magnetic field, the suspended large-weight magnetic mass 4 is subjected to a downward magnetic force. The right suspended graphene strip deforms downward, the graphene strip 1 slides to the right, the left suspended graphene strip is tightened, and the change in axial stress causes the natural frequency of the left suspended graphene strip to change;

[0061] Step 3: Measure the natural frequency f of the left suspended graphene strip under the action of the magnetic field L . According to the natural frequency offset, inversely deduce the magnetic force F of the measured magnetic field environment mag . The magnetic force F mag is inversely proportional to the natural frequency. Among them, the natural frequency f of the left suspended graphene strip L is calculated according to the following formula:

[0062]

[0063] Among them, L L is the length of the left suspended graphene strip, and q L is the elongation of the spring-damping system and numerically the same as q L，e , and x L is the maximum displacement of the suspended magnetic mass 4 in the vertical direction;

[0064] The magnetic force is calculated by the following formula:

[0065]

[0066] The present invention provides a preparation method of a magnetometer based on a double-groove graphene suspended mass structure, including the following technological steps:

[0067] Step a, the SOI wafer 6 is divided into a silicon device layer, an insulating layer, and a silicon substrate from top to bottom; a 1.4-μm-thick silicon dioxide layer is grown on the upper surface of the silicon device layer of the SOI wafer 6 by the oxidation growth method;

[0068] Step b, spin-coat photoresist on the 1.4-μm-thick silicon dioxide layer and perform mask lithography to pattern the photoresist layer to define an I-shaped groove pattern for detecting magnetic force (i.e., lithograph the groove pattern on the photoresist layer), and then etch away the silicon dioxide layer corresponding to the I-shaped groove pattern with 25% by volume of HF (under the protection of the patterned photoresist, only the silicon dioxide layer corresponding to the pattern will be etched away). The unetched silicon dioxide layer and the photoresist layer are used as a mask layer, and an I-shaped groove structure is etched on the 15-μm-thick silicon device layer by reactive ion etching technology (RIE), and finally the photoresist layer is removed by the lift-off stripping process;

[0069] Spin-coat photoresist on the 1.4-μm-thick silicon dioxide layer again, pattern the photoresist layer to define a square groove pattern for detecting magnetic force (i.e., lithograph the groove pattern on the photoresist layer), and then etch away the silicon dioxide layer corresponding to the square groove pattern with 25% by volume of HF (under the protection of the patterned photoresist, only the silicon dioxide layer corresponding to the pattern will be etched away). The unetched silicon dioxide layer and the photoresist layer are used as a mask layer, and a square groove structure with a size of 150 μm × 150 μm is etched on the 15-μm-thick silicon device layer by reactive ion etching technology (RIE), and finally the photoresist layer is removed by the lift-off stripping process;

[0070] Step c, use the lift-off process again to remove the photoresist layer, then spin-coat photoresist again on the insulating layer within the I-shaped trench, perform mask lithography, pattern the photoresist layer to define an I-shaped cavity pattern, etch an I-shaped cavity with a depth of 300 nm in the insulating layer below the silicon device layer through reactive ion etching technology. The I-shaped cavity is located within the I-shaped trench. Then, fill the 300-nm-deep I-shaped cavity on the insulating layer with Au by magnetron sputtering to form gate 3, and use the lift-off process to remove the photoresist layer;

[0071] Step d, spin-coat photoresist on the surface of the back side of the SOI wafer 6, perform mask lithography on the photoresist layer, pattern the photoresist layer to obtain a square trench pattern corresponding to the position and size of the square trench above the SOI wafer 6, and etch from the back side of the SOI wafer 6 to the lower surface of the insulating layer below the silicon device layer through reactive ion deep etching technology to form a back cavity below the square trench structure above the SOI wafer 6;

[0072] Step e, spin-coat the photoresist layer on a 1.4-μm-thick silicon dioxide layer and perform mask lithography to obtain patterns corresponding to source 2 and drain 5 on the photoresist layer. Stamp and transfer graphene strips to span above the two trenches, and then through O 2 plasma etch the graphene strips to form graphene ribbons 1 with the desired shape; Step f, use reactive ion etching technology to etch 300-nm-deep cavities corresponding to the patterns of source 2 and drain 5 on the silicon dioxide layer, then fill the cavities with Au by magnetron sputtering to form source 2 and drain 5, and then use the lift-off process to remove the photoresist layer;

[0073] Step g, place the SOI wafer 6 in a steam chamber with a temperature set at 40 °C, etch the back side of the SOI wafer 6 with 25% (by volume fraction) steam HF for 5 - 10 min to remove the remaining insulating layer below the silicon device layer, and form a square trench structure that completely penetrates the SOI wafer 6 on the right side of the SOI wafer 6;

[0074] Step h, transfer the suspended large-weight magnetic mass 4 into the square trench, and make the suspended large-weight magnetic mass 4 adsorb on the bottom of the graphene ribbon 1 above the square trench through van der Waals force to complete the transfer of the suspended large-weight magnetic mass 4;

[0075] Step i, respectively wire-bond source 2 and drain 5 to the PCB substrate leads, and perform vacuum packaging to complete the preparation of the magnetometer.

[0076] Example 2

[0077] As Figure 1 , Figure 2 and Figure 3As shown in the figure, a magnetometer based on a double-groove graphene suspended mass structure includes a graphene strip 1, a source electrode 2, a gate electrode 3, a suspended large-weight magnetic mass 4, a drain electrode 5, and an SOI wafer 6. The source electrode 2 and the drain electrode 5 are fixed at the upper end of the SOI wafer 6. The gate electrode 3 is fixed in the left groove of the SOI wafer 6. The graphene strip 1 is fixed on the SOI wafer 6 and is located below the source electrode 2 and the drain electrode 5, perpendicular to the source electrode 2 and the drain electrode 5 respectively, and is located above the left and right grooves of the SOI wafer 6. The middle part of the graphene strip 1 is fixed by the central support formed between the two grooves. The suspended large-weight magnetic mass 4 is fixed below the graphene strip 1 and is located in the right groove of the SOI wafer 6.

[0078] The SOI wafer 6 is a large-area copper-based single-layer graphene grown from bottom to top by chemical vapor deposition (CVD) process for a double-groove graphene suspended mass transconductor, and combined with the preparation process flow for developing the stability of the double-groove graphene suspended mass transconductor, and is fabricated by micro-nano processing technologies such as electron beam lithography, oxygen plasma etching, reactive ion etching (RIE), and deep reactive ion etching (DRIE). Among them, the silicon device layer is 15 μm thick, the SIO 2 layer is 1.4 μm thick, and the operating substrate is 400 μm thick.

[0079] The suspended large-weight magnetic mass 4 is nano-scale magnetic powder.

[0080] The graphene strip 1 is a single-layer graphene obtained by mechanical exfoliation or wet transfer, and has high uniformity in the width direction.

[0081] The gate electrode 3 is a driving electrode.

[0082] The source electrode 1, the gate electrode 3, and the drain electrode 5 are all gold electrodes or platinum electrodes.

[0083] A method for applying the above magnetometer based on a double-groove graphene suspended mass structure includes the following steps:

[0084] Step 1, calibrate the natural frequency of the part of the graphene strip 1 suspended above the I-shaped groove on the left side of the source electrode 2:

[0085] Figure 4 is the model of the part of the graphene strip suspended above the I-shaped groove on the left side. Near the natural frequency f L0 of the part of the graphene strip 1 suspended above the I-shaped groove on the left side, a frequency-sweeping signal is input to the gate electrode 3 for up-frequency scanning with an acceleration of V g ac cos(Ωt) to drive this part of the graphene strip 1 on the left side, and the electrode driving force is represented by F elec ;

[0086] For the double-groove suspended graphene resonator designed in the present invention, the shape of the two-dimensional graphene resonance band has high uniformity in the width direction, and this study only considers the deformation and movement in the vertical direction x and the horizontal direction y. Therefore, it can be simplified to a one-dimensional string model, as Figure 5 shown.

[0087] The static deformation and dynamic vibration mode φ i (i = L or R) of the left and right suspended parts of graphene strip 1 (the parts of graphene strip 1 located above the two grooves) and the electrostatic force F elec or magnetic force F mag in the vertical direction satisfy the following relationship:

[0088]

[0089] where is the second derivative of the vertical displacement of the left and right suspended parts of graphene strip 1 with respect to the horizontal coordinate, is the first derivative of the vertical displacement of the left and right suspended parts of graphene strip 1 with respect to the horizontal coordinate, and y is the horizontal coordinate.

[0090] We assume that although graphene strip 1 can slide horizontally on the central support column, the left and right suspended graphene strips 1 can still be approximately regarded as a quasi-static doubly clamped string, and its boundary conditions are:

[0091]

[0092] where is the vertical displacement of the left and right suspended graphene strips 1 when the abscissa is 0, is the vertical displacement of the left and right suspended graphene strips 1 when the abscissa is L i and L i represents the length of the left and right suspended graphene strips 1.

[0093] The static deformation and modal vibration mode of the left and right suspended graphene strips 1 Under the action of the electrostatic force and magnetic force in the vertical direction, it has a parabolic form, expressed as:

[0094]

[0095] where y is the horizontal coordinate, and x i is the maximum static displacement or the maximum value of the dynamic vibration displacement of the left and right suspended graphene strips 1 in the vertical direction; we can assume that when the electrostatic force and magnetic force change, the modal vibration mode always maintains a parabolic form.

[0096] Assume that in the absence of any external forces including electrostatic force and magnetic force, the original length of the left and right suspended parts of the graphene strip 1 is L i,0 (i = L or R), and its initial internal strain ε 0 is:

[0097]

[0098] where L tot is the total length of the graphene strip 1 resting on the double-groove transducer, L tot,0 is the initial total length of the graphene strip 1, L L is the length of the left suspended part of the graphene strip 1 above the I-shaped groove when the graphene strip 1 is resting on the double-groove transducer, L R is the length of the right suspended part of the graphene strip 1 above the square groove when the graphene strip 1 is resting on the double-groove transducer, L tot (L tot,0 ) = L L (L L,0 ) + L con + L R (L R,0 ), L con is the width of the central support column.

[0099] The lengths of the left and right suspended graphene strips 1 after being deformed by forces are L i,suspended ±q i,e (i = R, take the - sign, i = L, take the + sign), where the length L i,suspended of the suspended part is expressed as:

[0100]

[0101] where y represents the horizontal coordinate, x i,e represents the maximum static displacement of the left and right suspended graphene strips 1 in the vertical direction, q i,e represents the static slip displacement of any point on the graphene strip 1 corresponding to the upper left and right boundaries of the central support column, θ i are respectively the tangents of the parts of the left and right suspended graphene strips 1 on the left and right boundaries of the left and right grooves (the left suspended graphene strip 1 or the right suspended graphene strip is bent under the influence of gravity and magnetic force at this time, and the tangent here refers to the complete left suspended graphene strip 1 or the right suspended graphene strip) and the angle with the horizontal line; therefore, the axial tensions T i , T C分别 are expressed as functions of x i,e and q i,e :

[0102]

[0103] Among them, E is the Young's modulus of the two-dimensional graphene material, S is the cross-sectional area of graphene ribbon 1, and ε i is the strain of graphene ribbon 1 suspended on the left or right side;

[0104] Regarding graphene ribbon 1 above the central support column and the suspended graphene ribbon 1 on the right side as a whole, as Figure 4 shown, it is approximated as a viscoelastic connector that satisfies the Voigt-Kelvin constitutive relation, and the following mechanical relationship is satisfied at the intersection with the part of graphene ribbon 1 suspended above the I-shaped groove on the left side:

[0105]

[0106] Among them, T 0 represents the axial stress of the viscoelastic connector, k represents the elastic coefficient of the spring in the viscoelastic connector of the constitutive relation, qL represents the static slip displacement of the point corresponding to graphene ribbon 1 above the central support column above the left boundary of the left I-shaped groove, c represents the damping coefficient of the damper in the viscoelastic connector of the constitutive relation, and t represents time;

[0107] Substituting formula (4) and formula (6) into formula (9), we get:

[0108]

[0109] The deflection ω equilibrium equation of the suspended part of the left suspended graphene ribbon is:

[0110]

[0111] Among them, m L represents the effective mass of the left suspended graphene ribbon, is the second derivative of the vertical displacement x of the suspended part of the left suspended graphene ribbon, θ is the angle between the parts of the left suspended graphene ribbon that are respectively placed on the left and right boundaries of the left groove and the horizontal line, C’ represents the first derivative of the capacitance C of gate 3 with respect to the displacement in the vertical direction, V G is the voltage of gate 3, and dc represents direct current;

[0112] Substituting formula (4) and formula (6) into formula (11), we get:

[0113]

[0114] Because q L << L L , ε 0≤ 1, ε 0 is the built-in strain, so there is L L,0 ≈ L L , so the L in formula (10) and formula (12) can be L,0 replaced with L L , to get:

[0115]

[0116] The natural frequency of the left suspended graphene ribbon 1 is related to formula (13) and formula (14). Noticing that formula (14) has the form of a vibration equation. So there is:

[0117]

[0118] where x 0 and ω 2 are the relevant elements of the vibration equation; taking the partial derivative of both sides of formula (15) gives:

[0119]

[0120] Formula (14) can be approximated as:

[0121]

[0122] So the natural frequency of the left suspended graphene ribbon is:

[0123]

[0124] To distinguish from the following text, in step three, calculate the natural frequency f of the left suspended graphene ribbon under the action of a magnetic field L1 , the q in the formula L , x L , L L Here it is rewritten as q L0 , x L0 , L L0 ;

[0125] Near this frequency range, scan the gate 3 with an acceleration up-frequency of V g ac cos(Ωt) (V g is the voltage peak value, Ω is the angular frequency, ac represents alternating current, and t is time) to drive the left graphene ribbon 1, and obtain the amplitude-frequency curve with the driving frequency as the abscissa and the amplitude of the left suspended graphene ribbon as the ordinate. The frequency corresponding to the peak point is the natural frequency f of the left suspended graphene ribbon of the double-groove magnetic field sensor without the action of a magnetic field L0 , to complete the calibration;

[0126] Step 2: Install this sensor in the magnetic field environment to be measured. Under the action of the magnetic field, the large-weight suspended magnetic mass 4 on the right side of the magnetometer is subjected to a downward magnetic force, causing the suspended graphene strip on the right side to deform downward. The graphene strip 1 slides to the right, and the suspended graphene strip on the left side is tightened. The change in the axial gravitational force causes the natural frequency to change. Rescan the frequency in the range of approximately 0.8f L0 to 1.2f L0 That is, scan the gate 3 with an acceleration of V g ac cos(Ωt) in a cyclic frequency increase scan, drive the suspended graphene strip on the left side, and continuously detect the graphene strip 1 during the frequency increase process at a frequency increase interval of 0.0001f L0 to obtain the amplitude-frequency curve. The frequency corresponding to the peak point is the natural frequency f L1 of the suspended graphene strip on the left side of the magnetometer under the action of the magnetic field;

[0127] Step 3: Calculate the natural frequency offset according to the natural frequency f L1 of the suspended graphene strip on the left side under the action of the magnetic field, that is, f L1 -f L0 , and inversely deduce the magnetic force of the measured magnetic field environment;

[0128] When the acceleration magnitude of the suspended large-weight magnetic block 4 caused by the external magnetic force is a, and a DC electrostatic bias voltage V g dc acts on the suspended graphene strip on the left side, the static force balance equation of the system can be expressed as:

[0129] T L = T C = T R = T (19)

[0130] T represents the axial stress of the graphene strip 1.

[0131] Substitute formulas (6)(7)(8) into formula (19), and we can get

[0132]

[0133] At the same time, in the vertical direction, the left and right suspended graphene strips satisfy the force balance relationship. Combining with formula (3), we can get:

[0134]

[0135] Among them, F elec(mag) is the electrostatic force (magnetic force), F mag = (M + m R )a ≈ Ma, where M is the mass of the large-weight suspended magnetic mass 4, and m Ris the effective mass of the right suspended graphene ribbon, and a is the acceleration of the suspended large-weight magnetic block 4. Further, we can obtain

[0136]

[0137] Combining formulas (6), (7), (8), (19), (22), and (23), we can obtain

[0138]

[0139] Therefore, when the system reaches static equilibrium under the action of an external magnetic field force, the axial tension can be solved by the following formula:

[0140]

[0141] Furthermore, when static equilibrium is reached, the static deformations of the left and right suspended graphene ribbons can be obtained as follows:

[0142]

[0143] The sliding displacement q of any point on the graphene ribbon 1 corresponding to the left and right boundaries on the central support column i,e is:

[0144]

[0145] We will further derive the physical expression of k; from the definition of formula (9), we can obtain:

[0146]

[0147] And, from formula (6), we know that

[0148]

[0149] Substituting formula (29) into formula (30), we can obtain

[0150]

[0151] Substituting formula (27) into formula (31), we get

[0152]

[0153] We can obtain

[0154] For the designed double-groove suspended graphene resonator, after the right suspended graphene ribbon reaches the static equilibrium position under the action of an external magnetic field force, the left suspended graphene ribbon is under the driving voltage V g = V g dc + V gac Under the action of cos(Ωt), it performs harmonic motion around the static equilibrium position (the DC voltage Vg makes the left suspended graphene strip reach the static equilibrium state, and the AC voltage Vgac makes it perform harmonic motion around the static equilibrium position). Therefore, assuming that the right suspended graphene strip remains quasi-statically stable, the dynamic coupling between the vertical harmonic motion of the left suspended graphene strip and the sliding motion of graphene strip 1 above the support structure is mainly analyzed.

[0155] Under the condition of considering damping, the left suspended graphene strip satisfies the following mechanical relationship:

[0156]

[0157] That is:

[0158]

[0159] Among them, m L , c L are the effective mass and structural damping of the left suspended graphene strip respectively. Substituting formula (6) into formula (9) gives

[0160]

[0161] Therefore, the coupled motion equation can be expressed as:

[0162]

[0163] It can be obtained that the expression of the natural frequency of the left suspended graphene strip is:

[0164]

[0165] That is

[0166]

[0167] According to the formula:

[0168]

[0169] Combining formulas (25), (26), and (40) further obtains the relationship between the acceleration a of the large-weight suspended magnetic mass 4 under the magnetic force and the natural frequency f L of the left suspended graphene strip:

[0170]

[0171] So there is:

[0172]

[0173] Therefore, the magnitude of the external magnetic force is inversely proportional to the natural frequency of the graphene strip 1. By detecting the offset of the natural frequency of the graphene strip 1, highly sensitive detection of weak magnetic fields can be achieved.

[0174] The preferred embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings. However, the protection scope of the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, any person skilled in the art within the technical scope disclosed by the present invention can make equivalent substitutions or changes according to the technical solution and inventive concept of the present invention. These simple variations all fall within the protection scope of the present invention.

[0175] In addition, it should be noted that, in the case of no contradiction, the various specific technical features described in the above specific embodiments can be combined in any appropriate manner. To avoid unnecessary repetition, the present invention will not separately describe various possible combination methods.

[0176] Furthermore, any arbitrary combination can be made between various different embodiments of the present invention, as long as it does not violate the idea of the present invention, and it should also be regarded as the content disclosed by the present invention.

Claims

1. A high-sensitivity magnetometer based on a double-groove graphene suspended mass block structure, characterized in that: The invention comprises a graphene ribbon (1), a source electrode (2), a gate electrode (3), a suspended heavy magnetic mass block (4), a drain electrode (5) and an SOI wafer (6), wherein the SOI wafer (6) is provided with an I-shaped groove and a square groove in sequence from left to right, and a central support column is left on the SOI wafer (6) between the rear end of the I-shaped groove and the square groove. The graphene ribbon (1) is fixed to the rear end of the SOI wafer (6) and is located above the I-shaped groove, the central support column and the square groove. The source electrode (2) is fixed to the I-shaped groove. The I-shaped groove is mounted on the SOI wafer (6) outside the square groove, and its rear end is located above the graphene strip (1); the drain (5) is fixed on the SOI wafer (6) outside the right square groove, and its rear end is located above the graphene strip (1); the middle part of the graphene strip (1) is fixed on the central support column; the gate (3) is installed in the I-shaped groove, and a suspended heavy-weight magnetic mass block (4) is adsorbed on the bottom of the graphene strip (1) above the square groove, and the suspended heavy-weight magnetic mass block (4) is located in the square groove.

2. A high-sensitivity magnetometer based on a double-groove graphene suspended mass block structure according to claim 1, characterized in that: The suspended heavy-weight magnetic mass block (4) is nano-scale magnetic powder.

3. A high-sensitivity magnetometer based on a double-groove graphene suspended mass block structure according to claim 1, characterized in that: The graphene ribbon (1) is a single-layer graphene.

4. A high-sensitivity magnetometer based on a double-groove graphene suspended mass block structure according to claim 1, characterized in that: The gate (3) is a driving electrode.

5. A method for measuring the magnetic field intensity to be measured using a high-sensitivity magnetometer based on a double-groove graphene suspended mass block structure as described in any one of claims 1 to 4, characterized in that: The following steps are involved: Step 1: calibrate the natural frequency of the portion of the graphene ribbon (1) suspended on the left side above the I-shaped groove, wherein the portion of the graphene ribbon (1) suspended on the left side above the I-shaped groove is recorded as the left suspended graphene ribbon, and the portion of the graphene ribbon (1) suspended on the right side above the square groove is recorded as the right suspended graphene ribbon. The specific calibration process is as follows: The viscoelastic connector equivalent model of the Voigt-Kelvin constitutive relationship is selected to respectively equate the graphene ribbon (1) in contact with the right edge of the source (2) on the left side of the magnetometer and the graphene ribbon (1) in contact with the left edge of the drain (5) on the right side of the magnetometer, wherein the spring damping system composed of the spring and the damper connected end to end in the equivalent model is equivalent to the graphene ribbon (1) in contact with the right edge of the source (2) on the left side or the graphene ribbon (1) in contact with the left edge of the drain (5) on the right side; The natural frequency f of the suspended graphene ribbon on the left L0 Nearby, an acceleration sweep frequency signal is input to the gate (3), and by changing the magnitude of the voltage input to the gate (3), the entire graphene strip (1) is driven to vibrate, wherein the calibrated natural frequency f of the left suspended graphene strip is L0 Calculate as follows: Where, E is Young's modulus, S is the cross-sectional area of ​​the graphene ribbon (1), ε0 is the initial prestrain of the graphene ribbon (1), and L L0 is the length of the suspended graphene ribbon on the left, x L0 is the maximum vertical displacement of the suspended magnetic mass block 4, q L0 is the elongation of the spring-damper system in the viscoelastic connector equivalent model of the Voigt-Kelvin constitutive relation during the calibration process, m L is the effective mass of the suspended graphene ribbon on the left; Step 2: Install the magnetometer in the magnetic field environment to be measured at 0.8f L0 to 1.2f L0 The gate (3) is swept again within the frequency range. Under the action of the magnetic field, the suspended heavy magnetic mass block (4) of the magnetometer is subjected to a downward magnetic force, the right suspended graphene ribbon is deformed downward, the graphene ribbon (1) slides to the right, the left suspended graphene ribbon is tightened, and the change in axial stress causes the natural frequency of the left suspended graphene ribbon to change. Step 3: Measure the natural frequency f of the left suspended graphene ribbon under the magnetic field L , according to the natural frequency offset, the magnetic field force F of the magnetic field environment is measured inversely mag , magnetic field force F mag It is inversely proportional to the natural frequency, where the natural frequency of the suspended graphene strip on the left is f L Calculate as follows: Among them, L L is the length of the suspended graphene ribbon on the left, q L is the extension of the spring-damper system, x L is the maximum displacement of the suspended magnetic mass block 4 in the vertical direction; The magnetic field force is calculated as follows:

6. A method for preparing a high-sensitivity magnetometer based on a double-groove graphene suspended mass block structure according to any one of claims 1 to 4, characterized in that: The process steps include: Step a, the SOI wafer (6) is divided into a silicon device layer, an insulating layer, and a silicon substrate from top to bottom; a 1.4 μm thick silicon dioxide layer is grown on the upper surface of the silicon device layer of the SOI wafer (6) by an oxidation growth method; Step b, spin-coating a photoresist on the silicon dioxide layer and performing mask photolithography, patterning the photoresist layer to define an I-shaped groove pattern, and then etching the silicon dioxide layer at the pattern corresponding to the I-shaped groove using HF with a volume fraction of 25%, using the unetched silicon dioxide layer and the photoresist layer as mask layers, etching the I-shaped groove structure on the silicon device layer by reactive ion etching technology, and finally removing the photoresist layer by a lift-off stripping process; Spin-coat the photoresist on the silicon dioxide layer again, pattern the photoresist layer to define a square groove pattern, then etch the silicon dioxide layer at the pattern corresponding to the square groove using HF with a volume fraction of 25%, use the silicon dioxide layer and the photoresist layer that have not been etched as mask layers, etch the square groove structure on the silicon device layer by reactive ion etching technology, and finally remove the photoresist layer by lift-off stripping process; Step c, removing the photoresist layer again by using a lift-off stripping process, then re-spinning the photoresist on the insulating layer in the I-shaped groove, performing mask photolithography, patterning the photoresist layer to define an I-shaped cavity pattern, etching a 300 nm deep I-shaped cavity in the insulating layer below the silicon device layer by using a reactive ion etching technique, wherein the I-shaped cavity is located in the I-shaped groove, then filling the 300 nm deep I-shaped cavity on the insulating layer by magnetron sputtering Au to form a gate (3), and removing the photoresist layer by using a lift-off stripping process; Step d, spin coating a photoresist on the surface of the back side of the SOI wafer (6), photolithography the photoresist layer with a mask, patterning the photoresist layer to obtain a square groove pattern having a position and size corresponding to the square groove on the top of the SOI wafer (6), etching from the back side of the SOI wafer (6) to the lower surface of the insulating layer below the silicon device layer by a reactive ion deep etching technique, and forming a back cavity below the square groove structure above the SOI wafer (6); Step e, spin-coating a photoresist layer on a 1.4 μm thick silicon dioxide layer and performing mask photolithography to obtain patterns corresponding to the source electrode (2) and the drain electrode (5) on the photoresist layer, transferring the graphene strip by stamp so that it crosses over the two grooves, and then etching the graphene strip by O2 plasma to form a graphene strip (1) of a desired shape; Step f, etching a 300 nm deep cavity corresponding to the source electrode (2) and the drain electrode (5) pattern on the silicon dioxide layer by using reactive ion etching technology, and then filling the cavity by magnetron sputtering Au to form the source electrode (2) and the drain electrode (5), and then removing the photoresist layer by a lift-off stripping process; Step g, placing the SOI wafer (6) in a steam chamber set at a temperature of 40° C., etching the back side of the SOI wafer (6) for 5 to 10 minutes using steam HF with a volume fraction of 25%, so as to remove the remaining insulating layer below the silicon device layer, thereby forming a square groove structure on the right side of the SOI wafer (6) that completely penetrates the SOI wafer (6); Step h, transferring the suspended heavy magnetic mass block (4) into the square groove, and adsorbing the suspended heavy magnetic mass block (4) to the bottom of the graphene strip (1) above the square groove by van der Waals force, thereby completing the transfer of the suspended heavy magnetic mass block (4); Step i, bonding the source electrode (2) and the drain electrode (5) to the PCB substrate wires respectively, vacuum packaging, and completing the preparation of the magnetometer.

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