A highly tunable vanadium dioxide nanowire sensor and its preparation method and application

Abstract

The application discloses a highly-tunable vanadium dioxide nanowire sensor and a preparation method and application thereof, which comprises a substrate and electrodes, vanadium dioxide nanowires, fixed ends and power supply ends, a voltmeter and a sensitive layer on a resonator; two fixed ends are located on two electrodes of a source electrode and a drain electrode and are connected with two ends of the vanadium dioxide nanowires; the two electrodes of the source electrode and the drain electrode are connected with the vanadium dioxide nanowires and the two fixed ends on the substrate and support and fix one vanadium dioxide nanowire; the power supply end is connected with the electrode of the source electrode, and phase transition of the vanadium dioxide nanowire is caused by changing a circuit voltage so as to change a resonant frequency of the nanowire. The application forms an electric circuit on the vanadium dioxide nanowire, makes the two ends of the nanowire form a potential difference, causes the vanadium dioxide nanowire to gradually change phase by Joule heating, changes the resonant frequency of the nanowire, improves the sensitivity of the nanowire, and simultaneously detects gas molecules through the laid sensitive layer.

Description

Technical Field

[0001] This invention belongs to the field of nanowire resonant sensor technology, specifically relating to a vanadium dioxide nanowire sensor with significant tunability, its preparation method, and its application. Background Technology

[0002] Resonant gas sensors, due to their high sensitivity and selectivity, have broad application prospects in biochemical reaction monitoring and environmental monitoring. Among these, ultrasensitive detection technology for biochemical reactions is crucial for mass spectrometry, atomic physics, and a wide range of clinical and environmental applications, including disease diagnosis, drug discovery, pathogen detection in food, environmental toxin detection, and bioprocess control. However, the realization of single-molecule detection technology for biochemical reactions remains a key challenge in many application areas due to insufficient precision in detecting very low concentrations of biochemical molecules.

[0003] Nanowire resonators offer numerous advantages, including small size, high frequency, and high quality factor, making them ideal for high-frequency precision measurement and sensors. Among these, resonant mass sensors can reveal the interaction forces and biochemical reaction kinetics between minute masses, representing one of the most significant applications of mechanics-based micro / nano sensors. One-dimensional nanowire resonant mass sensors, with their small equivalent mass and high resonant frequency, generally exhibit high sensitivity. Primarily used for measuring small masses, they can reveal the interaction forces and biochemical reaction kinetics between small masses, serving as a potential source for atomic or molecular-scale dynamic detection.

[0004] With the increasing precision requirements for biochemical reaction detection, higher demands are placed on the sensitivity of resonant sensors. Resonators have evolved from the micrometer scale to the nanometer scale to continuously improve resonant frequencies and meet the sensitivity measurement requirements of sensors. However, current resonator sensitivities have not yet reached the precision required for biochemical reactions. Furthermore, existing resonator technologies, such as those based on piezoelectric materials, typically require high driving voltages to generate sufficient mechanical vibration, limiting their application in low-power devices. Additionally, many current resonators have fixed resonant frequencies, making them difficult to adjust according to actual needs, further restricting their application range. Therefore, there is an urgent need for a novel, highly tunable nanowire resonator using a novel driving method to overcome the limitations of existing nanowire resonators.

[0005] We learned that vanadium dioxide nanowires are a typical phase change material, undergoing a phase transition from semiconductor to metal when the temperature rises to 68℃. During the phase transition, the resistance of the vanadium dioxide nanowires decreases by several orders of magnitude, accompanied by a significant increase in the axial force of the nanowires. This leads to a 33% increase in the resonant frequency, thereby improving the sensor's sensitivity by 33%. Furthermore, vanadium dioxide nanowires can be used with electrostatic excitation and resistance detection methods, which have low power consumption and simple detection circuitry. Summary of the Invention

[0006] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0007] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0008] Therefore, the object of this invention is to overcome the shortcomings of the prior art and provide a vanadium dioxide nanowire sensor that can be significantly tunable. Its structure includes...

[0009] Substrate silicon wafer;

[0010] Vanadium dioxide nanowires are located above the silicon substrate and in contact with the metal electrodes at both ends.

[0011] The metal electrode includes a source, a drain, and a gate. The source and drain are used to provide support and fixation for the vanadium dioxide nanowires, and are also responsible for connecting to external circuits to realize the input of excitation signals and the output of response signals.

[0012] The gate, located below the vanadium dioxide nanowire, is not connected to the vanadium dioxide nanowire and is used to apply a bias electrostatic force to the vanadium dioxide nanowire.

[0013] The fixing end includes a first fixing end and a second fixing end, which fix the vanadium dioxide nanowires onto the electrode.

[0014] The power supply includes an AC power supply and a DC power supply. The AC power supply is connected to the source, and the DC power supply is connected to the gate.

[0015] A voltmeter is connected in parallel with the nanowire via wires to the first and second fixed terminals, and is used to detect changes in the voltage of the vanadium dioxide nanowire.

[0016] The sensitive layer is located at the midpoint of the vanadium dioxide nanowire, and different sensitive materials can be replaced to detect different gas molecules.

[0017] Another object of the present invention is to provide a method for preparing a vanadium dioxide nanowire sensor that can be significantly tunable.

[0018] To solve the above-mentioned technical problems, the present invention provides the following technical solution: including,

[0019] After activation, the silicon wafers with polished and oxidized surfaces are sequentially cleaned, dehydrated, and surface film formed to obtain pretreated substrate silicon wafers.

[0020] A layer of polymethyl methacrylate (PMMA) photoresist is uniformly coated on the surface of the substrate silicon wafer, and a pre-baking process is performed to form the first photoresist layer;

[0021] The first photoresist layer is exposed on a photolithography machine using a first mask, and then the substrate silicon wafer is developed and dry etched to form a trench with a depth of 1-5μm and a width of 4-7μm on the substrate silicon wafer, which serves as the gate of the sensor.

[0022] A second photoresist layer is formed by coating a layer of PMMA onto the etched silicon substrate.

[0023] The second photoresist layer is exposed on the photolithography machine using the second mask, and then the substrate silicon wafer is developed to reserve the position of the electrode.

[0024] Metal is sputtered onto the electrode region of the photolithographically ...

[0025] The synthesis of vanadium dioxide nanowires involved placing 0.2 g of commercially available vanadium dioxide powder (99% purity) in a quartz boat and then placing it in the center of a horizontal tube furnace. An unpolished (rough) quartz substrate was placed 5 mm above the bottom of the quartz boat to achieve higher vapor density and deposition temperature. The furnace tube was first evacuated to a basic pressure of 1.33 Pa and then purged with argon (Ar). The temperature was then increased at a rate of 15 °C / min and maintained at the target temperature of 700 °C-800 °C for 5-6 hours. Throughout the process, the pressure was maintained at 1333 Pa. After the reaction was complete, the unpolished (rough) quartz substrate with vanadium dioxide nanowires grown on it was removed after the tube furnace cooled to room temperature.

[0026] A vanadium dioxide nanowire grown on a quartz substrate was transferred using a tungsten probe to ensure that the two ends of the vanadium dioxide nanowire were mounted on the source and drain electrodes and perpendicular to the gate.

[0027] Among them, the vanadium dioxide nanowires with a diameter of 180-240nm, a length of 5-8μm, and an aspect ratio of 28-33 serve as the resonant beam;

[0028] Platinum (Pt) was deposited on both ends of vanadium dioxide nanowires using focused ion beam (FIB) technology, forming two rectangular platinum metal blocks that smoothly fix the vanadium dioxide nanowires, forming the first fixed end and the second fixed end.

[0029] First, a layer of PMMA photoresist with a thickness of about 200 nm is spin-coated on the surface of the fixed vanadium dioxide nanowire. Then, the midpoint of the vanadium dioxide nanowire is exposed at the midpoint of a scanning electron microscope. Then, a sensitive layer is deposited by vapor deposition, and a lift-off process is used to obtain a vanadium dioxide nanowire sensor with a midpoint coated sensitive layer.

[0030] Next, connect the AC power supply to the source electrode with a wire, connect the DC power supply to the gate electrode, and connect the voltmeter to the first fixed terminal and the second fixed terminal to obtain a vanadium dioxide nanowire sensor that can be greatly tunable.

[0031] In a preferred embodiment of the method for preparing the tunable vanadium dioxide nanowire sensor described in this invention, the activation temperature of the silicon wafer is 500-700K and the activation time is 20-40min.

[0032] In a preferred embodiment of the method for preparing the tunable vanadium dioxide nanowire sensor described in this invention, the pre-baking treatment is carried out at a temperature of 373-383 K for a time of 50-60 s.

[0033] In a preferred embodiment of the method for preparing the vanadium dioxide nanowire sensor with significant tunability described in this invention, the vanadium dioxide nanowires are prepared by chemical vapor deposition.

[0034] In a preferred embodiment of the fabrication method of the vanadium dioxide nanowire sensor with significant tunability described in this invention, the vanadium dioxide nanowires are first peeled off from the quartz substrate using a tungsten probe, then a voltage of 5V is applied to adsorb the vanadium dioxide nanowires for transfer, the vanadium dioxide nanowires are placed on the source and drain electrodes perpendicular to the gate, then the applied voltage is turned off to release the vanadium dioxide nanowires, and finally the transfer is completed.

[0035] In a preferred embodiment of the method for fabricating the tunable vanadium dioxide nanowire sensor described in this invention, the sputtered metal material includes gold, silver, or copper, and the sputtering speed is... Vacuum degree less than 1×10 -2 Pa.

[0036] In a preferred embodiment of the method for fabricating the vanadium dioxide nanowire sensor with significant tunability described in this invention, the thickness of the source, drain, and gate is 400-600 nm.

[0037] In a preferred embodiment of the fabrication method of the tunable vanadium dioxide nanowire sensor described in this invention, the photoresist is AZ5214 photoresist, and the exposure dose is 3.6mW / cm². 2 The development time is 60-100 seconds.

[0038] In a preferred embodiment of the method for fabricating the vanadium dioxide nanowire sensor with significant tunability described in this invention, the first and second fixed ends are formed by depositing metal Pt using FIB technology, forming a rectangular block with a length of 2 micrometers, a width of 200 nanometers, and a thickness of 200 nanometers.

[0039] In a preferred embodiment of the method for preparing the tunable vanadium dioxide nanowire sensor described in this invention, the sensitive layer 111 can be replaced with different materials, such as copper phthalocyanine, platinum, or tin oxide, for detecting different gas molecules.

[0040] In a preferred embodiment of the method for preparing the vanadium dioxide nanowire sensor with significantly tunable impedance described in this invention, the resonant frequency f of the vanadium dioxide nanowire 102 is 27.1 MHz at a temperature T = 295 K and 36 MHz at a temperature T = 360 K.

[0041] In a preferred embodiment of the method for preparing the vanadium dioxide nanowire sensor that can be significantly tunable according to the present invention, the sensitive layer is coated at the midpoint of the vanadium dioxide nanowire.

[0042] Another object of the present invention is to provide an application of a vanadium dioxide nanowire sensor that can be greatly tunable in the construction of ultra-high sensitivity sensors.

[0043] This invention discloses a varyingly tunable vanadium dioxide nanowire sensor. The sensor includes a substrate, electrodes on the substrate, vanadium dioxide nanowires, fixed terminals and a power supply terminal, a voltmeter, and a sensitive layer on a resonator. Two fixed terminals are located on the source and drain electrodes, connected to both ends of the vanadium dioxide nanowire, for fixing a single vanadium dioxide nanowire. The source and drain electrodes are located on the substrate, connected to the vanadium dioxide nanowire and the two fixed terminals, supporting the vanadium dioxide nanowire and forming a current path with it. Another electrode is located on the gate electrode and connected to a power supply terminal to apply an electrostatic bias force to cause the vanadium dioxide nanowire to vibrate. The other power supply terminal is connected to the source electrode to provide the sensor with an operating voltage. Changing the circuit voltage can cause a phase transition in the vanadium dioxide nanowire, thereby changing the resonant frequency of the nanowire and improving its sensitivity. A voltmeter is connected in parallel to detect voltage changes in the nanowire. A sensitive layer is deposited on the vanadium dioxide nanowire for detecting gas molecules. This invention discloses a varyingly tunable vanadium dioxide nanowire sensor. By constructing an electrical circuit on the vanadium dioxide nanowire, a potential difference is created at both ends of the nanowire. Joule heating causes a gradual phase transition in the vanadium dioxide nanowire, thereby changing its resonant frequency and increasing its sensitivity. Simultaneously, a sensitive layer can be deposited to detect gas molecules. This invention features simple operation, low driving voltage, wide tuning range, and high sensitivity, demonstrating broad application prospects in numerous fields such as mass detection, mechanical detection, displacement detection, and gas molecule detection.

[0044] Beneficial effects of this invention:

[0045] (1) High sensitivity: The nanowire sensor of the present invention can cause a phase transition of vanadium dioxide nanowires by changing the voltage. During the phase transition, the resistance of vanadium dioxide nanowires will decrease by several orders of magnitude, and the axial force of the nanowires will increase significantly, thereby changing its resonant frequency and increasing its sensitivity by 33%.

[0046] (2) Wide detection range: The nanowire sensor of the present invention can change its resonant frequency and sensitivity to different gases by changing the voltage so that the vanadium dioxide nanowires can work in the insulating phase and the metallic phase respectively, thus giving it a wider detection range. Attached Figure Description

[0047] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0048] Figure 1This is a flowchart of the vanadium dioxide nanowire sensor that can be greatly tunable, prepared according to Example 1 of the present invention.

[0049] Figure 2 This is a schematic planar view of the vanadium dioxide nanowire sensor that can be greatly tunable, prepared according to Example 1 of the present invention.

[0050] Figure 3 This is a three-dimensional structural schematic diagram of the vanadium dioxide nanowire sensor that can be greatly tunable, prepared in Example 1 of the present invention. Detailed Implementation

[0051] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0052] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0053] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0054] Unless otherwise specified, all raw materials used in this invention are commercially available in the field.

[0055] Unless otherwise specified, all processes involved in this invention are conventional processes in the field.

[0056] Example 1

[0057] Reference Figure 1 This embodiment provides a method for fabricating a vanadium dioxide nanowire sensor that can be significantly tunable, specifically:

[0058] Step 1) Substrate pretreatment:

[0059] Using a surface-polished and oxidized silicon wafer as the substrate material, it is activated at 500K for 20 minutes to ensure good electrical insulation. Then, it is cleaned, dehydrated and surface film formed in sequence to enhance the adhesion between the silicon wafer and the photoresist, resulting in a pretreated substrate 100.

[0060] Step 2) Photoresist coating and gate fabrication:

[0061] A layer of PMMA photoresist is uniformly coated on the surface of the pretreated substrate 100 and pre-baked at 373K for 50s to form the first photoresist layer 101.

[0062] The first photoresist layer 101 is exposed on a photolithography machine using a first mask. Then, the substrate 100 is subjected to processes such as development, dry etching, and debonding to process a trench with a depth of 1-5 μm and a width of 4-7 μm on the quartz plate, which serves as the gate of the sensor.

[0063] The photoresist used in this step is AZ5214 photoresist, and the exposure dose is 3.8 W / cm². 2 The development time is 100 seconds. Step 3) Metal electrode sputtering and stripping:

[0064] A second photoresist layer is formed by coating a layer of PMMA onto the etched substrate 100.

[0065] The second photoresist layer is exposed on a photolithography machine using a second mask, and then the substrate 100 is further developed to reserve the positions of the electrodes.

[0066] Metal is sputtered onto the electrode region of the photolithographic substrate 100 by magnetron sputtering. The metal material selected is gold, which has good conductivity and oxidation resistance. Acetone is used to remove excess photoresist and excess metal layer on the photoresist to form source 103, drain 104 and gate 105.

[0067] In this step, the thickness of the source 103, drain 104, and gate 105 is 400 nm, and the sputtering speed is controlled at [missing value]. The vacuum level used is less than 1×10 – 2 Pa, to ensure the continuity and conductivity of the electrodes.

[0068] Step 4) Preparation of vanadium dioxide nanowires:

[0069] Before preparing vanadium dioxide nanowires using vapor deposition technology, the quartz boat and the unpolished (rough) quartz substrate must be cleaned. The cleaning process follows the standard procedure for electronic cleaning, which mainly includes sonication with acetone, alcohol, isopropanol, and distilled water for 5 minutes each, followed by drying with nitrogen (N2).

[0070] 0.2g of commercially available vanadium dioxide powder with a purity of 99% was placed in a quartz boat and then placed in the center of a horizontal tube furnace; an unpolished (rough) quartz substrate was placed 5mm above the reaction source to obtain higher vapor density and deposition temperature.

[0071] First, the furnace tube was evacuated to a basic pressure of 1.33 Pa, and then purged multiple times with argon gas. Then, the temperature was increased at a rate of 15 °C / min and maintained at the target temperature of 700 °C for 5 hours. Throughout the process, the pressure was maintained at 1333 Pa and the argon gas rate was 50 sccm. After the reaction was completed, the unpolished (rough) quartz substrate with vanadium dioxide nanowires 102 grown on it was removed after the tube furnace cooled to room temperature.

[0072] Step 5) Transfer and fixation of vanadium dioxide nanowires:

[0073] After the vanadium dioxide nanowires 102 are prepared in step 4), they are initially embedded in the quartz substrate. A tungsten probe is used to peel the vanadium dioxide nanowires 102 off the quartz substrate. Then, a voltage of 5V is applied to adsorb the vanadium dioxide nanowires 102 for transfer. The vanadium dioxide nanowires 102 are placed on the source electrode 103 and the drain electrode 104 perpendicular to the gate electrode 105. Then, the applied voltage is turned off to release the vanadium dioxide nanowires 102, and finally the transfer is completed.

[0074] Vanadium dioxide nanowires 102 grown on a quartz substrate are transferred using a tungsten probe, ensuring that the two ends of the vanadium dioxide nanowires 102 are mounted on the source electrode 103 and the drain electrode 104 and are perpendicular to the gate electrode 105; wherein the vanadium dioxide nanowires are in a free state, and residual strain is released by overcoming the adhesion force between the nanowires and the electrodes.

[0075] Then, using FIB technology, metallic Pt is deposited on the interface between vanadium dioxide nanowire 102 and the electrode. Two rectangular Pt blocks are deposited on both sides of the vanadium dioxide nanowire 102 on the electrode to smoothly fix the vanadium dioxide nanowire 102, forming the first fixed end 106 and the second fixed end 107.

[0076] Specifically, in this step, the metal block deposited by the first fixed end 106 and the second fixed end 107 using FIB technology is a rectangular block with a length of 2 micrometers, a width of 200 nanometers, and a thickness of 200 nanometers.

[0077] Step 6) Preparation of the sensitive layer:

[0078] In step 5), the surface of the fixed vanadium dioxide nanowire 102 is first spin-coated with a layer of PMMA photoresist of about 200 nm. Then, the midpoint of the vanadium dioxide nanowire 102 is exposed at the midpoint of a scanning electron microscope. Then, a sensitive layer 111 is deposited by vapor deposition, and a vanadium dioxide nanowire sensor with a dot-coated sensitive layer 111 is obtained by using a lift-off process.

[0079] Step 7) Circuit connection:

[0080] Next, connect the AC power supply 108 to the source 103 with a wire, connect the DC power supply 109 to the gate 105, and connect the voltmeter 110 to the first fixed terminal 106 and the second fixed terminal 107 to obtain a vanadium dioxide nanowire sensor that can be greatly tunable.

[0081] The tunable vanadium dioxide nanowire sensor prepared according to this embodiment has excellent sensitivity and a wide detection range, and can be widely used in the field of gas detection. At the same time, the present invention also has the characteristics of being tunable, initializeable, and having different sensitive layers that can be replaced.

[0082] Comparative Example 1

[0083] The difference between this comparative example and Example 1 is that the FIB method was used to fabricate first and second fixed ends of different thicknesses on vanadium dioxide nanowires of the same size, resulting in the vanadium dioxide nanowire sensor of this comparative example. Under the same testing environment, open-loop testing was performed on the vanadium dioxide nanowire sensor, and five sets of experimental data were read and averaged. The results are shown in Table 1.

[0084] Table 1

[0085] Thickness of deposited metal quality factor Example 1 200nm 1366 Comparative Example 1 100nm 1145

[0086] As shown in Table 1, the average overall quality factor of the vanadium dioxide nanowire sensor with a fixed end thickness of 200 nm deposited using the FIB method in Example 1 of this invention is 1366, while the average overall quality factor of the vanadium dioxide nanowire sensor with a fixed end thickness of 100 nm deposited using the FIB method is 1145. Clearly, the thickness of the metal deposited using the FIB method should not be too thin, which is beneficial for improving the resonant characteristics of the resonator and making the resonator's detection easier.

[0087] In Embodiment 1 of this invention, the vanadium dioxide nanowire sensor with a fixed end thickness of 200 nm deposited using the FIB method has an average overall quality factor of 1366, while the vanadium dioxide nanowire sensor with a fixed end thickness of 100 nm deposited using the FIB method has an average overall quality factor of 1145. Clearly, the 200 nm thickness of the fixed end provides better clamping for the resonant beam, resulting in lower clamping losses during resonance. This is beneficial for improving the resonant's resonance characteristics and sensitivity.

[0088] Example 2

[0089] The difference between this embodiment and Embodiment 1 is that:

[0090] The sputtering metal type was adjusted to silver, and the sputtering rate was...

[0091] The pre-baking treatment was carried out at a temperature of 383K for 60 seconds.

[0092] The photoresist exposure dose is 3.6 mW / cm. 2 The development time is 60 seconds;

[0093] The target temperature for preparing vanadium dioxide nanowires was 800℃, the holding time was 6 hours, and the argon gas rate was 100 sccm.

[0094] The remaining steps and processes were all the same as in Example 1, and the vanadium dioxide nanowire sensor of this example was obtained. Open-loop testing was performed on it, and the results were comparable to those of Example 1.

[0095] Example 3

[0096] The difference between this embodiment and Embodiment 1 is that:

[0097] The sputtering metal type was adjusted to silver, and the sputtering rate was...

[0098] The pre-baking treatment was carried out at a temperature of 378K for 55 seconds.

[0099] The photoresist exposure dose is 4.0 mW / cm. 2 The development time is 80 seconds;

[0100] The target temperature for preparing vanadium dioxide nanowires was 750℃, the holding time was 5.5 hours, and the argon gas rate was 75 sccm.

[0101] The remaining steps and processes were all the same as in Example 1, and the vanadium dioxide nanowire sensor of this example was obtained. Open-loop testing was performed on it, and the results were comparable to those of Example 1.

[0102] Comparative Example 2

[0103] The difference between this comparative example and Example 1 is that, in step 6) of Example 1, the portion of the sensitive layer 111 to be deposited on the vanadium dioxide nanowire 102 is changed from the midpoint of the vanadium dioxide nanowire to the entire vanadium dioxide nanowire. The remaining steps are the same as in Example 1, thus obtaining the vanadium dioxide nanowire sensor of this comparative example.

[0104] Under the same testing environment, open-loop tests were performed on the zinc oxide nanowire resonator. Five sets of experimental data were read and the average value was taken. The results are shown in Table 2.

[0105] Table 2

[0106] Sensitive layer location resonant frequency Example 1 midpoint 36MHz Comparative Example 2 overall 30MHz

[0107] As shown in Table 2, the average resonant frequency of the vanadium dioxide nanowire sensor with the sensitive layer deposited at the midpoint of the vanadium dioxide nanowire in Embodiment 1 of the present invention is 36 MHz, while the average resonant frequency of the vanadium dioxide nanowire sensor with the sensitive layer deposited throughout the entire vanadium dioxide nanowire is 30 MHz. Clearly, depositing the sensitive layer at the midpoint of the vanadium dioxide nanowire is beneficial for improving the resonator's resonant frequency and sensitivity, and also facilitates detection. The average resonant frequency of the vanadium dioxide nanowire sensor with the sensitive layer deposited at the midpoint of the vanadium dioxide nanowire in Embodiment 1 of the present invention is 36 MHz, while the average resonant frequency of the vanadium dioxide nanowire sensor with the sensitive layer deposited throughout the entire vanadium dioxide nanowire is 30 MHz. Clearly, depositing the sensitive layer at the midpoint of the vanadium dioxide nanowire ensures a uniform adsorption position for gas molecules, which is beneficial for improving the resonator's measurement accuracy and sensitivity.

[0108] Comparative Example 3

[0109] The difference between this comparative example and Example 1 is that the operating temperature of the vanadium dioxide nanowire resonator in Example 1 was adjusted to obtain the vanadium dioxide nanowire sensor of this comparative example.

[0110] Under the same testing environment, the vanadium dioxide nanowire sensor was subjected to open-loop testing. Five sets of experimental data were read and the average value was taken. The results are shown in Table 3.

[0111] Table 3

[0112] Operating temperature resonant frequency Example 1 360K 36MHz Comparative Example 1 295K 27.1MHz

[0113] As shown in Table 3, the average resonant frequency of the vanadium dioxide nanowire sensor in Embodiment 1 of the present invention is 36 MHz when the operating temperature of the vanadium dioxide nanowire resonator is 360 K, while the average resonant frequency is 36 MHz when the operating temperature of the vanadium dioxide nanowire resonator is 295 K. Clearly, an operating temperature of 360 K for the vanadium dioxide nanowire resonator is beneficial for increasing the resonant frequency of the resonator, thereby improving the sensor sensitivity.

[0114] In Embodiment 1 of this invention, the average resonant frequency of the vanadium dioxide nanowire sensor is 36 MHz when the operating temperature of the vanadium dioxide nanowire resonator is 360 K, and the average resonant frequency is also 36 MHz when the operating temperature of the vanadium dioxide nanowire resonator is 295 K. Clearly, the significant increase in the axial force of the nanowires at 360 K compared to 295 K is beneficial for increasing the resonant frequency of the resonator, thereby improving the sensor sensitivity.

[0115] In summary, this invention utilizes vanadium dioxide nanowires to improve sensor sensitivity and expand its detection range by leveraging their phase transition properties, allowing the sensor to transition from an insulating phase to a metallic phase. Furthermore, uniform adsorption sites are achieved by depositing the sensitive layer at the midpoint of the vanadium dioxide nanowires, further enhancing sensor sensitivity. All these optimizations contribute to improving sensor performance.

[0116] In addition to the optimization measures mentioned above, the manufacturing method of this invention can be appropriately adjusted to adapt to different application scenarios and needs. For example, different electrode materials and sensitive layers can be selected according to actual needs to reduce the manufacturing cost of the resonator and change the performance indicators of the sensor, such as the detected gas. Electrode materials can be metals such as copper, aluminum, and nickel to reduce the manufacturing cost of the resonator. Sensitive layers can be sensitive materials such as copper phthalocyanine, platinum, and tin oxide to detect gases such as ethanol, oxygen, and methane, respectively.

[0117] Therefore, the fabrication method of the tunable vanadium dioxide nanowire sensor of the present invention is characterized by flexibility and adjustability, and can be optimized and adjusted according to actual needs to meet different application scenarios and requirements. The resonator prepared by the fabrication method of the present invention has excellent sensitivity and stability, and can be widely used in gas detection and related fields, providing strong support for research and development in these fields.

[0118] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for fabricating a vanadium dioxide nanowire sensor with significantly tunable impedance, characterized in that: include, After the surface-polished and oxidized silicon wafer is activated, it is sequentially cleaned, dehydrated and surface film formed to obtain a pretreated substrate silicon wafer (100). A layer of polymethyl methacrylate photoresist is uniformly coated on the surface of the substrate silicon wafer (100), and a pre-baking process is performed to form a first photoresist layer (101). The first photoresist layer (101) is exposed on a photolithography machine using a first mask, and then the substrate silicon wafer (100) is developed and dry etched to form a trench with a depth of 1-5 μm and a width of 4-7 μm on the substrate silicon wafer, and metal is deposited inside as the gate of the sensor. A second photoresist layer is formed by coating a layer of PMMA onto the etched substrate silicon wafer (100). The second photoresist layer is exposed on a photolithography machine using a second mask, and then the substrate silicon wafer (100) is further developed to reserve the position of the electrode. Metal is deposited in the electrode region of the photolithographically etched substrate silicon wafer (100) through a lift-off process to form the source (103), drain (104) and gate (105). The synthesis of vanadium dioxide nanowires (102) involved placing 0.2 g of commercially available vanadium dioxide powder with a purity of 99% in a quartz boat and then placing it in the center of a horizontal tube furnace. An unpolished quartz substrate was placed 5 mm above the bottom of the quartz boat to obtain a higher vapor density and deposition temperature. The furnace tube was first evacuated to a basic pressure of 1.33 Pa and then purged with argon. The temperature was then increased at a rate of 15 °C / min and maintained at the target temperature of 700 °C-800 °C for 5-6 hours. Throughout the process, the pressure was maintained at 1333 Pa. After the reaction was completed, the unpolished quartz substrate with vanadium dioxide nanowires (102) was removed after the tube furnace cooled to room temperature. Vanadium dioxide nanowires (102) grown on a quartz substrate were transferred using a tungsten probe to ensure that the two ends of the vanadium dioxide nanowires (102) were mounted on the source (103) and drain (104) and perpendicular to the gate (105); Among them, the vanadium dioxide nanowires (102) with a diameter of 180-240nm, a length of 5-8μm, and an aspect ratio of 28-33 serve as the resonant beam; Platinum was deposited on both ends of vanadium dioxide nanowires (102) using focused ion beam technology to form two rectangular platinum metal blocks as the first fixed end (106) and the second fixed end (107) to smoothly fix the vanadium dioxide nanowires (102); First, a 200 nm layer of polymethyl methacrylate photoresist is spin-coated onto the surface of the fixed vanadium dioxide nanowire (102). Then, the midpoint of the vanadium dioxide nanowire (102) is exposed at the midpoint of a scanning electron microscope. Then, a sensitive layer (111) is deposited by vapor deposition, and a vanadium dioxide nanowire sensor with a midpoint coated sensitive layer (111) is obtained by using a lift-off process. Next, connect the AC power supply (108) to the source (103) with a wire, connect the DC power supply (109) to the gate (105), and connect the voltmeter (110) to the first fixed terminal (106) and the second fixed terminal (107) to obtain a vanadium dioxide nanowire sensor that can be greatly tunable.

2. The method for preparing the vanadium dioxide nanowire resonator with significant tunability as described in claim 1, characterized in that: The activation temperature for silicon wafer activation is 500-700K, and the activation time is 20-40min; the pre-baking treatment temperature is 373-383K, and the time is 50-60s.

3. The method for preparing the tunable vanadium dioxide nanowire sensor as described in claim 1, characterized in that: The vanadium dioxide nanowires (102) were prepared by chemical vapor deposition.

4. The method for preparing the tunable vanadium dioxide nanowire sensor as described in claim 1, characterized in that: The vanadium dioxide nanowires (102) are transferred by first peeling the vanadium dioxide nanowires (102) off the quartz substrate with a tungsten probe, then applying a voltage of 5V to adsorb the vanadium dioxide nanowires (102) for transfer. The vanadium dioxide nanowires (102) are placed on the source (103) and drain (104) perpendicular to the gate (105), and then the applied voltage is turned off to release the vanadium dioxide nanowires (102), and finally the transfer is completed.

5. The method for preparing the tunable vanadium dioxide nanowire sensor as described in claim 1, characterized in that: The source (103), drain (104), and gate (105) are fabricated using a magnetron sputtering method; the metal material used for magnetron sputtering includes gold, silver, or copper, the sputtering velocity is 0.1-0.4 Å / s, and the vacuum level is less than 1×10⁻⁶. -2 Pa.

6. The method for preparing the varyingly tunable vanadium dioxide nanowire sensor as described in claim 1, characterized in that: The photoresist is AZ5214 photoresist, and the exposure dose is 3.6mW / cm. 2 The development time is 60-100 seconds.

7. The method for preparing the tunable vanadium dioxide nanowire sensor as described in claim 1, characterized in that: The first fixed end (106) and the second fixed end (107) are formed by depositing metal Pt using focused ion beam technology. The length is 2µm, the width is 200nm, and the thickness is 200nm.

8. The method for preparing the tunable vanadium dioxide nanowire sensor as described in claim 1, characterized in that: The resonant frequency of the vanadium dioxide nanowires (102) f The frequency is 27.1 MHz at temperature T=295 K, and at temperature T Frequency at 360K f The amplitude tuning is 36MHz.

9. A vanadium dioxide nanowire sensor with significantly tunable impedance obtained based on the preparation method according to any one of claims 1-8, characterized in that: include, Substrate silicon wafer (100); Vanadium dioxide nanowires (102) are located above the substrate silicon wafer (100) and in contact with the metal electrodes at both ends; The metal electrode includes a source (103), a drain (104), and a gate (105). The source (103) and drain (104) are used to provide support and fixation for the vanadium dioxide nanowire (102) and are also responsible for connecting to external circuits to realize the input of excitation signal and the output of response signal, respectively. The gate (105) is located below the vanadium dioxide nanowire (102) and is not connected to the vanadium dioxide nanowire (102). It is used to apply a bias electrostatic force to the vanadium dioxide nanowire (102). The fixing end includes a first fixing end (106) and a second fixing end (107), which fix the vanadium dioxide nanowire (102) on the electrode. The power supply includes an AC power supply (108) and a DC power supply (109). The AC power supply (108) is connected to the source (103), and the DC power supply (109) is connected to the gate (105). A voltmeter (110) is connected in parallel with the nanowire via a wire to the first fixed terminal (106) and the second fixed terminal (107) to detect changes in the voltage of the vanadium dioxide nanowire (102). The sensitive layer (111) is located at the midpoint of the vanadium dioxide nanowire (102) for detecting different gas molecules.

10. The application of the tunable vanadium dioxide nanowire sensor prepared by any one of claims 1-8 in the construction of ultra-high sensitivity sensors.

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