Graphene micro-cantilever resonator and preparation method thereof

Abstract

The application discloses a graphene micro-cantilever beam resonator and a preparation method thereof, and relates to the technical field of micro-nano mechanical and electrical system sensing, which comprises the following steps: transferring a graphene film to a silicon wafer, performing annealing treatment to obtain a graphene film silicon wafer, and etching to obtain a patterned graphene film silicon wafer; plating a source electrode and a drain electrode on both sides of the patterned graphene of the patterned graphene film silicon wafer respectively to obtain a graphene film silicon wafer with electrodes; after silicon corrosion is performed on the graphene film silicon wafer with electrodes, the graphene film silicon wafer with electrodes is placed in isopropyl alcohol, and a double-end suspended graphene resonator is obtained by taking out; and the double-end suspended graphene resonator is disconnected through electric heating annealing to obtain a graphene micro-cantilever beam resonator. The graphene cantilever beam resonator disclosed by the application can reach a maximum resonance frequency of 58 Mhz, a quality factor of 600 at 300K room temperature, and the thermal noise power spectral density of the graphene cantilever beam is measured at 300K room temperature.

Description

TECHNICAL FIELD

[0001] The present application relates to a graphene micro-cantilever resonator and a preparation method thereof, and belongs to the technical field of micro-nano mechanical and electrical system sensing. BACKGROUND

[0002] The micro-cantilever resonator mainly realizes the detection of target substances through the change of the vibration signal of the micro-cantilever, and the development of new functional sensitive materials will be beneficial to improve the sensitivity of the micro-cantilever resonator and increase its application field.

[0003] The current mainstream silicon-based or polymer cantilever resonator sensor (such as AFM probe, biomolecule detection chip) has disadvantages such as thickness limitation of cantilever material sensitivity, performance degradation caused by cantilever surface functionalization, and high test environment requirements.

[0004] However, as a single-atom layer two-dimensional material micro-cantilever, graphene has a theoretical mass detection limit of angstrom, which is 6 orders of magnitude higher than that of a silicon beam; the synergistic improvement of ultra-high stiffness and low density improves the frequency response, so that the resonance fundamental frequency is greater than 10 MHz; and the intrinsic high quality factor value resists environmental interference. However, the technical difficulties lie in the complex manufacturing process of the graphene cantilever, which is prone to deformation and rupture; the resonant signal is weak and difficult to efficiently pick up. SUMMARY

[0005] The present application aims to overcome the deficiencies in the prior art, and provides a graphene micro-cantilever resonator and a preparation method thereof. The graphene cantilever resonator prepared by the method can achieve a maximum resonance frequency of 58 Mhz, a quality factor of 600, and the thermal noise power spectral density of the graphene cantilever is measured at room temperature.

[0006] To achieve the above-mentioned purpose, the present application is realized by using the following technical scheme:

[0007] On the one hand, the present application provides a preparation method of a graphene micro-cantilever resonator, comprising:

[0008] transferring a graphene film to a silicon wafer, and obtaining a graphene film silicon wafer after annealing treatment;

[0009] etching the graphene film silicon wafer to obtain a patterned graphene film silicon wafer;

[0010] plating a source electrode and a drain electrode on both sides of the patterned graphene of the patterned graphene film silicon wafer, respectively, to realize ohmic contact between the source electrode and the drain electrode and the patterned graphene, and obtain a graphene film silicon wafer with electrodes;

[0011] placing the graphene film silicon wafer with electrodes in isopropyl alcohol after silicon etching, and taking out to obtain a double-end suspended graphene resonator;

[0012] The graphene micro-cantilever resonator is obtained by disconnecting the double-end suspended graphene resonator through electric heating annealing.

[0013] Further, the silicon wafer surface is provided with an oxide layer with a thickness ranging from 300 to 445 nm, and four gold marker points are arranged on the oxide layer, which are arranged at four azimuth angles respectively, and are used for realizing fixed-point transfer and photolithography of the graphene film.

[0014] Further, the annealing treatment comprises placing the graphene film silicon wafer in a protective atmosphere of argon and hydrogen, and heating the graphene film silicon wafer at 300-400℃ for 55-65 min.

[0015] Further, the etching of the graphene film silicon wafer to obtain a patterned graphene film silicon wafer comprises:

[0016] Uniformly applying electron beam photoresist on the graphene film silicon wafer;

[0017] Exposing, developing and fixing the graphene film silicon wafer by using an electron beam lithography process to obtain a graphene pattern, wherein the graphene pattern is divided into a photoresist removal part and a photoresist covering part, and the photoresist covering part serves as a mask;

[0018] Ion etching the graphene pattern to etch the photoresist removal part, and cleaning and removing the photoresist to obtain a patterned graphene film silicon wafer.

[0019] Further, the patterned graphene comprises end portions and a middle portion, and the width of the end portions on both sides is greater than the width of the middle portion.

[0020] Further, the source electrode and the drain electrode are respectively plated on both sides of the patterned graphene of the patterned graphene film silicon wafer to realize ohmic contact between the source electrode, the drain electrode and the patterned graphene, and obtain a graphene film silicon wafer with electrodes, comprising:

[0021] Uniformly applying electron beam photoresist on the surface of the patterned graphene film silicon wafer;

[0022] Exposing, developing and fixing the patterned graphene film silicon wafer by using an electron beam lithography process to obtain a double-electrode pattern;

[0023] Plating titanium and gold as the source electrode and the drain electrode on the double-electrode pattern by electron beam plating, and peeling off the excess photoresist to obtain a graphene film silicon wafer with electrodes.

[0024] Further, the silicon etching comprises: placing the graphene film silicon wafer with electrodes in hydrofluoric acid, and then sequentially placing it in water and acetone, and then blowing it dry with nitrogen.

[0025] Further, the isopropyl alcohol is in a near-boiling state, and a method for determining the near-boiling state is as follows:

[0026] A silicon wafer is placed in isopropyl alcohol, and after being immersed, the silicon wafer is taken out, and the isopropyl alcohol on the surface of the silicon wafer is in a near-boiling state when the isopropyl alcohol can be gasified without residue.

[0027] Further, the graphene micro-cantilever resonator is obtained by disconnecting the double-end suspended graphene resonator through electric heating annealing.

[0028] A gradually increasing direct current voltage is applied to the source electrode and the drain electrode of the double-end suspended graphene resonator until the middle part of the graphene is broken, and the graphene micro-cantilever resonator is obtained.

[0029] In another aspect, the application also provides a graphene micro-cantilever resonator prepared by the preparation method of the graphene micro-cantilever resonator.

[0030] Compared with the prior art, the application has the following beneficial effects:

[0031] The application provides a triangular patterned graphene micro-cantilever resonator, and the suspended graphene cantilever is buried below the source electrode and the drain electrode. -5 The resonant frequency of the graphene micro-cantilever resonator reaches the order of 58 MHz under the driving of a 3V gate direct current voltage and a 20dBm alternating current voltage, which is three orders of magnitude higher than the resonant frequency of a conventional silicon cantilever such as an atomic force microscope probe, and the quality factor reaches 600, which indicates that the energy loss of the system is at a low level.

[0032] Meanwhile, the graphene micro-cantilever resonator is used as a super-sensitive force detector, and the power spectral density of thermal noise is measured through three basic data processing methods of RMS (root mean square), SAMPLE (sample value) and AVERAGE (average value) in a room temperature environment, and the thermal vibration signal of the graphene cantilever is measured through the three methods, which verifies that the device has super-sensitive force detection performance and greatly reduces the measurement error, and provides a basis for developing other two-dimensional material cantilever resonator devices and super-sensitive force detectors. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 FIG. 1 is a flowchart of a preparation method of a graphene micro-cantilever resonator according to an embodiment of the application;

[0034] Figure 2 FIG. 2 is a scanning electron microscope diagram of a double-end suspended graphene resonator according to an embodiment of the application;

[0035] Figure 3 A structure schematic diagram for applying a direct current voltage to a graphene micro-cantilever resonator in an embodiment of the present application;

[0036] Figure 4 A scanning electron microscope schematic diagram of a graphene micro-cantilever resonator in an embodiment of the present application;

[0037] Figure 5 A laser interferometry system structure schematic diagram of a graphene micro-cantilever resonator in an embodiment of the present application;

[0038] Figure 6 A resonance signal test result schematic diagram of a graphene micro-cantilever resonator in an embodiment of the present application;

[0039] Figure 7 A resonance signal quality factor test result schematic diagram of a graphene micro-cantilever resonator in an embodiment of the present application;

[0040] Figure 8 A thermal noise test result schematic diagram of a graphene micro-cantilever resonator in an embodiment of the present application. DETAILED DESCRIPTION

[0041] The present application will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present application, and cannot be used to limit the protection scope of the present application.

[0042] Embodiment 1

[0043] As shown in the drawings, the present embodiment provides a preparation method of a graphene micro-cantilever resonator, comprising the following steps: Figure 1

[0044] S1, preparing a patterned graphene film

[0045] A target graphene sheet is obtained by a mechanical exfoliation method, and the target graphene sheet is transferred to an oxide layer silicon wafer with gold marker points. After annealing at 400℃ for one hour, a graphene film silicon wafer is obtained.

[0046] In the present embodiment, the thickness of the oxide layer is 300-445nm, and the gold marker points are located at four azimuth angles, thereby surrounding a rectangle. The gold marker points are equivalent to coordinates, which are used for the fixed-point position transfer of the graphene film and also facilitate the position guidance for subsequent fixed-point photolithography.

[0047] ​A layer of electron beam resist (PMMA 950A4, 120-160 nm thick) is uniformly coated on the surface of the graphene film silicon wafer, which is then baked at 140°C for 2 minutes. The graphene pattern is exposed using electron beam lithography (process parameters: 10 kV accelerating voltage, 30 diaphragm, 200 uC / cm 2 dose), developed (methyl isobutyl ketone and isopropyl alcohol mixed solution in a ratio of 1:3, 40 s), and fixed (isopropyl alcohol, 30 s) to obtain the graphene pattern.

[0048] The graphene pattern is divided into a resist-removed part and a resist-covered part, and the resist-covered part is used as a mask to perform ion etching on the resist-removed part for 50 s to obtain the etched graphene film silicon wafer. The etching parameters include argon and oxygen at 20 sccm, power of 50 W, and pressure of 20 mTorr.

[0049] The etched graphene film silicon wafer is placed in acetone for one hour to remove the resist on the surface of the silicon wafer, and then isopropanol (IPA) is used to clean the surface to remove the residual acetone, and nitrogen is used to dry the graphene film silicon wafer to obtain the patterned graphene film silicon wafer.

[0050] In this embodiment, atomic force microscopy is also used to characterize the patterned graphene film silicon wafer to ensure that the patterned graphene meets the expectations. The patterned graphene in this embodiment is shown in FIG. 1, which includes end portions and a middle portion, and the width of the two end portions is 1 μm, and the width of the middle portion is 130 nm, and the overall structure is a symmetric structure of two similar triangles. Figure 1

[0051] It should be noted that the patterned graphene in this patent must be narrow in the middle and wide at both ends, because the strong local current heat effect will occur after the current passes through the narrow middle, which will burn off the suspended patterned graphene film, thereby achieving the purpose of forming a single cantilever beam structure.

[0052] S2, preparation of source electrode and drain electrode

[0053] A layer of electron beam resist (PMMA 950A4, 120-160 nm thick) is uniformly coated on the surface of the graphene film silicon wafer, which is then baked at 140°C for 2 minutes. The graphene pattern is exposed using electron beam lithography (process parameters: 10 kV accelerating voltage, 30 diaphragm, 200 uC / cm 2 dose), developed (methyl isobutyl ketone, isopropyl alcohol 40 s), and fixed (isopropyl alcohol 30 s), and the double electrode pattern is also divided into a resist-removed part and a resist-covered part.

[0054] ​Then, 5 nm titanium and 50 nm gold are respectively plated on the debonding part of the double electrode pattern by electron beam evaporation as the source electrode and the drain electrode to realize ohmic contact between the source electrode and the drain electrode and the patterned graphene, and then the photoresist covered part and the titanium and gold metal layer plated on the photoresist covered part are stripped to obtain a graphene thin film silicon wafer with electrodes, and the source electrode and the drain electrode are used for subsequent electric heating annealing and as a grounding electrode for device testing.

[0055] S3, preparation of a double-end suspended graphene resonator

[0056] The graphene thin film silicon wafer with electrodes is placed in a 1:10 concentration hydrofluoric acid solution for 4 min, since the hydrofluoric acid only etches silicon dioxide and hardly reacts with the titanium electrode, the gold electrode and the graphene, and then it is placed in clean water and acetone to remove the residual hydrofluoric acid.

[0057] The graphene thin film silicon wafer with electrodes is placed in isopropyl alcohol in a near boiling state and then quickly removed, so that the isopropyl alcohol on the surface of the silicon wafer is quickly heated and vaporized to obtain a double-end suspended graphene resonator, and the electron microscope structure is as shown in Figure 2 .

[0058] The determination method of the isopropyl alcohol in a near boiling state is that a silicon wafer without structure is placed in it and quickly taken out, and if the isopropyl alcohol on the surface of the silicon wafer is quickly vaporized without residue, it is the isopropyl alcohol in a near boiling state.

[0059] S4, preparation of a graphene micro-cantilever resonator

[0060] In order to prepare a single cantilever graphene resonator, the double-end suspended graphene resonator needs to be disconnected, and in this embodiment, the electric heating annealing method is adopted, and Figure 3 a slowly increasing direct current voltage is applied to the source electrode and the drain electrode, and the heat generated by the current at the 130 nm middle slit of the patterned graphene thin film is greater than that on both sides, so after a certain voltage is applied, the graphene at the slit is burned off, a short circuit is formed between the source electrode and the drain electrode, and the two are not connected, thereby forming two independent suspended graphene cantilevers, and the electron microscope structure is as shown in Figure 4 .

[0061] Embodiment 2

[0062] This embodiment provides a graphene micro-cantilever resonator prepared by the preparation method of the graphene micro-cantilever resonator of embodiment 1.

[0063] The performance of the graphene micro-cantilever resonator is tested as follows:

[0064] Firstly, the resonance signal of the graphene micro-cantilever resonator is characterized by optical interference and electrical driving method, and the test principle is as follows:

[0065] The application of voltage on the silicon substrate (gate) produces a capacitive effect, and the potential energy stored between the graphene film and the gate can be expressed as:

[0066]

[0067] wherein, represents the potential energy stored between the graphene film and the gate, is the capacitance between the graphene film and the gate, represents the applied voltage.

[0068] The electrostatic force between the graphene film and the gate is expressed as:

[0069]

[0070] wherein, represents the electrostatic force between the graphene film and the gate, , represents the distance between the graphene film and the gate.

[0071] The alternating electrostatic force between the graphene film and the gate generated by the superposition of the direct current voltage and the alternating current voltage is expressed as:

[0072]

[0073] wherein, represents the alternating electrostatic force between the graphene film and the gate, represents the direct current voltage, represents the alternating current voltage.

[0074] Since the amplitude of the alternating current voltage is small, the square term can be ignored. The direct current voltage causes the film to be statically offset towards the gate, and the alternating current voltage provides a periodic driving force. When the driving frequency approaches the natural frequency, the resonator will resonate.

[0075] The test method is realized by using a laser interferometric measurement system as shown in Figure 5 . The graphene micro-cantilever resonator is placed in a vacuum cavity. A He-Ne laser emits linearly polarized light with a wavelength of 632.8 nm, which successively passes through a polarization beam splitting cube (P-polarized light is transmitted), a λ / 4 wave plate (P-polarized light is changed to circularly polarized light), and then is focused on the surface of the graphene micro-cantilever resonator through a 100x objective lens in the vacuum cavity.

[0076] The modulated reflected light successively passes through the objective lens, the λ / 4 wave plate (circularly polarized light is changed to S-polarized light), the polarization beam splitting cube (S-polarized light is reflected), and then is received by a photodetector and converted into an electrical signal which is transmitted to a vector analyzer.

[0077] ​​​The source electrode and the drain electrode are grounded, a direct current and an alternating current voltage are synchronously applied to the silicon substrate of the graphene micro-cantilever beam resonator through a biasing device, a resonance signal spectrum is obtained through a vector network analyzer, as shown in Figure 6 The red marked area is a vibration peak value, and the second maximum resonance mode signal of the cantilever beam resonator reaches 58 MHz, and the fitting result of the resonance signal quality factor is as shown in Figure 7 The first maximum resonance mode signal with the strongest resonance signal is selected f 0 14.15 MHz, and the corresponding half width Δf 23 KHz, and the quality factor is calculated by the calculation formula Q = f 0 / Δf The quality factor of the device is 600.

[0078] Then, the graphene micro-cantilever beam resonator is tested for thermal noise:

[0079] The thermal noise of graphene is essentially a random electric signal fluctuation caused by the thermal motion of the internal carrier (electron), also known as Johnson-Nyquist noise. The direct current voltage source is grounded, and only an alternating current voltage of -20 dBm is applied, and the thermal noise signal of the graphene cantilever beam is obtained through the power spectrum density of the reflected light intensity, and the thermal noise signal of the graphene cantilever beam is analyzed by three different data processing methods (root mean square, sampling value and average value), as shown in Figure 8 1200 groups of thermal noise data are measured, and the data are processed by three calculation methods of root mean square, sampling value and average value, wherein the root mean square calculation can be used to measure and calculate the strength or power of the measured thermal noise, the sampling value calculation can retain the noise spectrum details of the full frequency band Figure 8 The spurious signal of the noise spectrum details is obviously more than the root mean square and average value, and more noise spectrum details are retained), and the average value calculation can significantly reduce the measurement uncertainty, the peak position of the thermal noise resonance peak obtained by the three methods does not shift, the multi-method verification strategy provides a holographic diagnostic tool for the intrinsic noise analysis of the resonator, and the accurate measurement of the thermal noise spectrum is a key basis for evaluating the limit sensing potential.

[0080] The above only describes the preferred embodiments of the present application, and it should be noted that for ordinary skilled persons in the technical field, several improvements and modifications can be made without departing from the technical principles of the present application, and these improvements and modifications should also be considered as the protection scope of the present application.

Claims

1. A method for fabricating a graphene microcantilever beam resonator, characterized in that, The application relates to a graphene micro-cantilever resonator preparation method. The graphene film is transferred to a silicon wafer, and a graphene film silicon wafer is obtained after annealing treatment; The graphene film silicon wafer is etched to obtain a patterned graphene film silicon wafer, which comprises the following steps: Uniformly applying electron beam photoresist on the graphene film silicon wafer; Exposing, developing and fixing the graphene film silicon wafer by using an electron beam lithography process to obtain a graphene pattern, wherein the graphene pattern is divided into a photoresist removal part and a photoresist covering part, and the photoresist covering part is used as a mask; Ion etching the graphene pattern to etch the photoresist removal part, and cleaning and removing the photoresist to obtain a patterned graphene film silicon wafer; Plating a source electrode and a drain electrode on both sides of the patterned graphene of the patterned graphene film silicon wafer to realize ohmic contact between the source electrode and the drain electrode and the patterned graphene, and obtaining a graphene film silicon wafer with electrodes; After silicon etching of the graphene film silicon wafer with electrodes, the graphene film silicon wafer with electrodes is placed in isopropyl alcohol to obtain a double-end suspended graphene resonator; The double-end suspended graphene resonator is disconnected by electric heating annealing to obtain a graphene micro-cantilever resonator.

2. The method of claim 1, wherein the graphene micro-cantilever resonator is prepared by the steps of: providing a graphene sheet; providing a substrate; and transferring the graphene sheet onto the substrate. The silicon wafer surface is provided with an oxide layer with a thickness range of 300-445 nm, and four gold marker points are arranged on the oxide layer, and the four gold marker points are arranged at four azimuth angles and are used for realizing fixed-point transfer and photoetching of the graphene film.

3. The method of claim 1, wherein the graphene micro-cantilever resonator is prepared by the steps of: providing a graphene sheet; providing a substrate; and transferring the graphene sheet onto the substrate. The annealing treatment comprises the following steps: placing the graphene film silicon wafer in a protective atmosphere of argon and hydrogen, and heating at 300-400 DEG C for 55-65 min.

4. The method of claim 1, wherein the graphene micro-cantilever resonator is prepared by the steps of: providing a graphene sheet; providing a substrate; and transferring the graphene sheet onto the substrate. The patterned graphene comprises end portions and a middle portion, and the width of the end portions on both sides is greater than that of the middle portion.

5. The method of claim 1, wherein the graphene micro-cantilever resonator is prepared by a process comprising: The graphene film silicon wafer with electrodes is placed in isopropyl alcohol to obtain a double-end suspended graphene resonator. ​ The silicon etching comprises the following steps: placing the graphene film silicon wafer with electrodes in hydrofluoric acid, and then sequentially placing the graphene film silicon wafer with electrodes in water and acetone, and then taking out the graphene film silicon wafer with electrodes and blowing dry with nitrogen. The isopropyl alcohol is in a near-boiling state, and the near-boiling state is determined by the following method: A silicon wafer is placed in isopropyl alcohol, and after immersion, the silicon wafer is taken out, and when the isopropyl alcohol on the surface of the silicon wafer can be gasified without residue, the isopropyl alcohol is in a near-boiling state.

6. The method of claim 1, wherein the graphene micro-cantilever resonator is prepared by a process comprising: The double-end suspended graphene resonator is disconnected by electric heating annealing to obtain a graphene micro-cantilever resonator. ​ 7. The method of claim 1, wherein the graphene micro-cantilever resonator is prepared by a process comprising: providing a graphene sheet; providing a substrate; and transferring the graphene sheet onto the substrate. The graphene micro-cantilever resonator is prepared by the graphene micro-cantilever resonator preparation method in any one of claims 1-8. ​ 8. The method of claim 1, wherein the graphene micro-cantilever resonator is prepared by a process comprising: ​ ​ ​ 9. A graphene micro-cantilever resonator, characterized by, ​

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