A method for preparing a 2.5-inch vanadium dioxide thin film

Abstract

This invention discloses a method for preparing 2.5-inch vanadium dioxide thin films, belonging to the field of vanadium dioxide thin film preparation technology. Addressing the problem in the prior art where the atmosphere inside the tube furnace easily fluctuates during heat treatment in the PAD method for preparing vanadium dioxide thin films, thus affecting the quality of the prepared vanadium dioxide thin films, the purpose of this invention is to provide a rectification method for preparing 2.5-inch vanadium dioxide thin films. This invention designs an airflow homogenization device, which ensures that the airflow entering the tube furnace is stably and uniformly dispersed around the ceramic boat, thereby providing a stable heat treatment atmosphere. This allows for the acquisition of high-quality vanadium dioxide thin films, and the device is simple and easy to operate.

Description

Technical Field

[0001] This invention belongs to the field of vanadium dioxide thin film preparation technology, specifically relating to a rectification method for preparing a 2.5-inch vanadium dioxide thin film. Background Technology

[0002] Vanadium dioxide (VO2) exhibits ultrafast, reversible, and multi-stimulus-responsive phase transition properties. The transition from a monoclinic tetragonal phase to a metallic phase can be achieved through various stimuli, including electrical, thermal, optical, electrochemical, mechanical, and magnetic disturbances. At a critical temperature of 340 K, a reversible metal-insulator (MIT) transition occurs, during which the electrical resistance changes by three to four orders of magnitude. It is an oxide with strong electronic correlation properties. Below the transition temperature, VO2 exists as a monoclinic crystal, while above the transition temperature, it exhibits a tetragonal rutile structure. Due to its unique phase transition characteristics, vanadium dioxide thin films can be widely used in smart windows, memristors, switches, and terahertz modulators.

[0003] Currently, preparing highly reproducible and high-quality vanadium dioxide thin films remains a challenging task because vanadium dioxide has relatively low stability in redox processes, and vanadium ions can remain in a V0 state. 2+ V 3+ V 4+ and V 5+ Vanadium dioxide, in its oxidized state, forms non-stoichiometric vanadium oxides with variable oxygen content. Currently, methods for preparing vanadium dioxide thin films include magnetron sputtering, pulsed laser deposition, chemical vapor deposition, molecular beam epitaxy, and sol-gel methods. Magnetron sputtering offers advantages such as good film uniformity, suitability for large-area preparation, and high deposition efficiency; however, it requires precise control of process parameters such as oxygen partial pressure and temperature, resulting in poor reproducibility of the prepared vanadium dioxide films. Pulsed laser deposition typically requires 450℃ to obtain vanadium dioxide films with good performance, but this extremely high temperature leads to huge energy consumption. Therefore, synthesizing vanadium dioxide films at low temperatures is a major challenge, and precise control of oxygen partial pressure, the distance between the target and the substrate, and laser energy is also required. Chemical vapor deposition can obtain dense and uniform vanadium dioxide films. While vanadium dioxide (vanadium dioxide) films can be grown quickly, the temperature and oxygen partial pressure of the substrate during preparation can affect the V:O stoichiometry of the film, thus affecting its phase purity and physical properties. Molecular beam epitaxy can produce high-quality and homogeneous epitaxial vanadium dioxide films, but due to its high melting point and low saturated vapor pressure, controllable vanadium evaporation is not easy, resulting in vanadium oxide exhibiting multiple valence states. The sol-gel method is widely used for depositing vanadium dioxide films due to its low cost, suitability for large-area deposition, and suitability for metal doping. However, the preparation process usually uses toxic reagents that pollute the environment, and the solution must be prepared and used immediately.

[0004] Polymer-assisted deposition (PAD) is another chemical solution method suitable for large-area deposition, besides the sol-gel method. This method requires only very inexpensive reagents to prepare the precursor, and after annealing, high-performance VO2 films can be prepared. The solution also exhibits high stability; after preparation, the solution can be stored in a refrigerator for up to six months and still be usable, making the preparation process more convenient. However, a crucial step in the PAD method for preparing large-area VO2 films is the annealing of the precursor film to obtain the vanadium dioxide film, which requires a uniform atmosphere. Currently, vanadium dioxide films prepared by the PAD method are easily affected by external environmental factors such as temperature, humidity, and gas composition, resulting in unstable film quality.

[0005] Therefore, developing a simple, low-cost, and highly reproducible rectification method for preparing large-area, high-quality vanadium dioxide thin films is of great significance for the practical application of vanadium dioxide. Summary of the Invention

[0006] To address the problem in the prior art where fluctuations in the atmosphere within the tube furnace during heat treatment, affecting the quality of vanadium dioxide thin films prepared using the PAD method, the present invention aims to provide a rectification method for preparing 2.5-inch vanadium dioxide thin films. This invention designs an airflow homogenization device that stably and uniformly disperses the incoming airflow around the ceramic boat, thereby providing a stable heat treatment atmosphere and enabling the production of high-quality vanadium dioxide thin films. Furthermore, this device is simple and easy to operate.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows: a method for preparing a 2.5-inch vanadium dioxide thin film, the method employing a preparation apparatus including: an airflow generation and control device at the inlet of a tubular furnace, a tubular furnace, an airflow uniformization device inside the tubular furnace, and a sealing and airflow detection device at the outlet of the tubular furnace.

[0008] The airflow generation and control device includes: a high-pressure nitrogen cylinder, a flow meter, a gas conduit, a gas washing bottle, and a water bath device; the nitrogen cylinder provides stable high-purity nitrogen gas, the flow meter is installed on the gas conduit to adjust the nitrogen gas flow rate, the nitrogen gas flow is introduced into the gas washing bottle through the gas conduit, the gas washing bottle contains distilled water, and the water bath device acts as a heat source to heat the gas washing bottle, causing the distilled water to rise in temperature and evaporate into water vapor, which is then introduced into the tube furnace along with the nitrogen gas flow.

[0009] The airflow uniformity device includes two heat-insulating furnace plugs, a honeycomb porous ceramic rectifier, and an inverted ceramic boat. The heat-insulating furnace plugs are placed on both sides of the tube furnace to ensure uniform temperature inside the tube furnace. The inverted ceramic boat is placed in the center of the tube furnace, and a 2.5-inch substrate is placed on the ceramic boat. Inverting the ceramic boat can stabilize the airflow flowing through the substrate. The honeycomb porous ceramic rectifier is placed on both sides of the ceramic boat and between the two heat-insulating furnace plugs to uniformly disperse the nitrogen and water vapor airflow at the air inlet of the tube furnace, so that the airflow flowing through the substrate is uniform.

[0010] The sealing and airflow detection device includes a flange, a steel ring, a rubber ring, a gas conduit, and a beaker containing water. The rubber ring and steel ring are fitted onto the outlet end of the tubular furnace, and then sealed with a flange. The airflow from the outlet of the tubular furnace flows into the beaker through the gas conduit. The sealing effect can be detected by observing the bubbling rate in the beaker, and it also serves to isolate air.

[0011] The water bath temperature is set at 38-44℃;

[0012] The method for preparing vanadium dioxide thin films based on the above-described preparation apparatus includes the following steps:

[0013] Step 1. Prepare a vanadium-containing polymer precursor solution using the PAD method;

[0014] Step 2. After cleaning the substrate with acetone, anhydrous ethanol and deionized water respectively, blow it dry with nitrogen gas, and then spin-coat the polymer precursor solution prepared in step 1 onto the substrate.

[0015] Step 3. Place the substrate with the polymer precursor solution spin-coated in Step 2 on an inverted ceramic boat. Place the ceramic boat containing the sample in the center of a tube furnace and introduce 99.999% pure nitrogen gas at a flow rate of 0.3-0.5 L / min. Perform heat treatment under the set program, and then allow it to cool naturally to room temperature to obtain a vanadium dioxide thin film on the substrate.

[0016] The heat treatment method is as follows: first, raise the temperature to 100-120℃ and hold for 20-30 minutes to remove residual water in the precursor solution, then raise the temperature to 430-450℃ and hold for 120-140 minutes to remove organic matter, and then raise the temperature to 490-550℃ and hold for 2-2.5 hours to obtain vanadium dioxide film.

[0017] Furthermore, the specific process for preparing the vanadium-containing polymer precursor solution using the PAD method in step 1 is as follows: dissolve 0.001-0.002 mol of polyetherimide (PEI) or polyethylene glycol (PEG) in 60-120 ml of water, stir, and then add...

[0018] Add 0.001-0.002 mol of ethylenediaminetetraacetic acid (EDTA), continue stirring until a homogeneous solution is formed, then add...

[0019] 0.001-0.002 mol of ammonium metavanadate is stirred in the solution to form a transparent solution. Finally, the solution is transferred to an ultrafiltration device. During filtration, 0.2 atmospheres of pressure is applied and magnetic stirring is performed to remove water from the solution.

[0020] Furthermore, the specific parameters for spin coating in step 2 are as follows: first, rotate at a lower speed of 900-1000 r / min for 10 seconds, and then rotate at a higher speed of 6000-7000 r / min for 40 seconds.

[0021] Furthermore, the porcelain boat is a quartz porcelain boat or a corundum porcelain boat, and the substrate material is silicon, silicon oxide, or Al2O3.

[0022] Furthermore, the distance between the two porous ceramic rectifiers is 40-60 cm.

[0023] Furthermore, the substrate is sapphire Al2O3 with a crystal orientation of (1 0 - 1 0), and the specific cleaning process is as follows: ultrasonic cleaning is performed sequentially with acetone, anhydrous ethanol, and deionized water.

[0024] The mechanism of this invention is as follows: a vanadium ion polymer precursor solution is prepared using the PAD method, and the precursor solution is spin-coated onto a substrate. Finally, the sample is heat-treated. During the heat treatment process, a mixture of water vapor and high-purity nitrogen is introduced. Due to the interference of humidity and temperature in the external environment, the atmosphere inside the furnace tube is prone to fluctuation. Therefore, this application provides a stable heat treatment atmosphere by setting up an airflow homogenizing device inside the tube furnace to uniformly disperse the airflow at the inlet and setting up a sealing device at the outlet to isolate air, thereby controlling the stoichiometry of vanadium oxide and preparing vanadium dioxide films with high repeatability and high quality. Simultaneously, nitrogen gas is first introduced into the tube furnace through a gas washing bottle. The water-containing gas introduces moisture into the growth environment, establishing a self-regulating process for oxygen partial pressure when the growth temperature changes, which is beneficial for the preparation of high-quality vanadium dioxide films.

[0025] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0026] This invention provides a simple apparatus that improves the repeatability of vanadium dioxide thin films prepared by the PAD method, and produces large-area, high-quality vanadium dioxide thin films. The films exhibit a resistance change of four orders of magnitude before and after the phase transition, making them suitable for a variety of applications. The entire preparation method is low-cost and non-toxic. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the rectifier device used to prepare a 2.5-inch vanadium dioxide thin film according to the present invention.

[0028] Figure 2This is a photograph of the 2.5-inch vanadium dioxide thin film prepared in Example 1.

[0029] Figure 3 This is a resistivity change cloud diagram of the 2.5-inch vanadium dioxide thin film prepared in Example 1.

[0030] Figure 4 This is a photograph of the 2.5-inch vanadium dioxide thin film prepared in Comparative Example 1.

[0031] Figure 5 The resistivity change contour plot is shown for the 2.5-inch vanadium dioxide thin film prepared in Comparative Example 1. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings.

[0033] A rectification method for preparing a 2.5-inch vanadium dioxide thin film, the apparatus of which is shown in the schematic diagram below. Figure 1 As shown, the device consists of an airflow generation and control device, an airflow homogenization device, and a sealing and airflow detection device, from right to left.

[0034] The gas flow generation and control device includes a high-pressure nitrogen cylinder, a flow meter, a gas conduit, a gas washing bottle, and a water bath device. The nitrogen cylinder provides a stable supply of high-purity nitrogen, the flow meter can adjust the flow rate of the nitrogen gas, the nitrogen gas flow is introduced into the gas washing bottle through the gas conduit, the gas washing bottle contains distilled water, and the water bath device acts as a heat source to heat the gas washing bottle, causing the distilled water to rise and evaporate into water vapor, which is then introduced into the tube furnace along with the nitrogen gas flow. During the heat treatment process, the water vapor undergoes a hydrolysis reaction with the polymer to remove carbon.

[0035] The airflow equalization device includes two insulating furnace plugs, a honeycomb porous ceramic rectifier, and an inverted ceramic boat. The insulating furnace plugs are placed on both sides of the tube furnace to ensure uniform temperature inside the furnace, unaffected by external temperature changes. The inverted ceramic boat is placed in the center of the tube furnace, with a 2.5-inch substrate placed on it. Inverting the ceramic boat stabilizes the airflow passing through the substrate. The honeycomb porous ceramic rectifier is placed on both sides of the ceramic boat to evenly disperse the nitrogen and water vapor airflow at the tube furnace inlet, ensuring uniform airflow through the substrate.

[0036] The sealing and airflow detection device includes a flange, a steel ring, a rubber ring, a gas conduit, and a beaker filled with water. The rubber ring and steel ring are fitted onto the outlet end of the tubular furnace, and then sealed with a flange. The airflow flows into the beaker through the gas conduit. The sealing effect can be detected by observing the bubbling rate in the beaker, and it also serves to isolate the air.

[0037] Example 1

[0038] The method for preparing vanadium dioxide thin films based on the above-mentioned apparatus includes the following steps:

[0039] Step 1: Prepare a vanadium ion precursor solution according to the polymer-assisted deposition method;

[0040] Step 2: Clean the 2.5-inch Al2O3 substrate by ultrasonically cleaning it sequentially with acetone, anhydrous ethanol and deionized water, and then drying it with nitrogen gas for later use.

[0041] Step 3: Spin-coating the precursor solution prepared in Step 1 onto a cleaned 2.5-inch sapphire substrate using a spin-coating method. The spin-coating process is as follows: first, maintain a low speed of 1000 r / min for 10 seconds, and then maintain a high speed of 6000 r / min for 40 seconds.

[0042] Step 4: Install the heat-insulating plug and porous ceramic rectifier at the gas inlet of the tube furnace. Place the substrate coated with the precursor solution in Step 3 on an inverted quartz ceramic boat and place it in the center of the tube furnace. Install the porous ceramic rectifier and heat-insulating plug at the gas outlet of the tube furnace and seal it with a flange. Place the gas conduit in a beaker containing water and sinter in a mixed atmosphere of nitrogen and water vapor. Observe the bubbling in the beaker to check the sealing effect. Start the preset tube furnace program: heat up to 100℃ and hold for 30 minutes to remove water from the precursor solution. Heat up to 450℃ and hold for 240 minutes to remove the binder. Then heat up to 495℃ and hold for 240 minutes to nucleate. After the reaction is completed, let it cool naturally to room temperature to obtain a vanadium dioxide film.

[0043] The physical image and resistivity change rate contour plot of the 2.5-inch vanadium dioxide thin film prepared in this embodiment are shown below. Figure 2 , 3 As shown, the prepared 2.5-inch vanadium dioxide is uniform, and the resistivity change rate before and after the phase transition is as high as 10. 4 .

[0044] Comparative Example 1

[0045] A 2.5-inch vanadium dioxide thin film was prepared according to the steps in Example 1, except that the porous ceramic rectifier in step 4 was removed, while the other steps remained unchanged.

[0046] The physical image and resistivity change rate contour plot of the 2.5-inch vanadium dioxide thin film prepared in this embodiment are shown below. Figure 4 , 5 As shown, the prepared 2.5-inch vanadium dioxide is non-uniform, and the resistivity change rate of some vanadium dioxide before and after the phase transition is only 10. 3 .

Claims

1. A method for preparing a 2.5-inch vanadium dioxide thin film, the method employing a preparation apparatus comprising: Airflow generation and control device at the inlet of a tubular furnace, tubular furnace, airflow uniformization device inside the tubular furnace, sealing and airflow detection device at the outlet of a tubular furnace. The airflow generation and control device includes: a high-pressure nitrogen cylinder, a flow meter, a gas conduit, a gas washing bottle, and a water bath device; the nitrogen cylinder provides stable high-purity nitrogen gas, the flow meter is installed on the gas conduit to adjust the nitrogen gas flow rate, the nitrogen gas flow is introduced into the gas washing bottle through the gas conduit, the gas washing bottle contains distilled water, and the water bath device acts as a heat source to heat the gas washing bottle, causing the distilled water to rise in temperature and evaporate into water vapor, which is then introduced into the tube furnace along with the nitrogen gas flow. The airflow uniformity device includes two heat-insulating furnace plugs, a honeycomb porous ceramic rectifier, and an inverted ceramic boat. The heat-insulating furnace plugs are placed on both sides of the tube furnace to ensure uniform temperature inside the tube furnace. The inverted ceramic boat is placed in the center of the tube furnace, and a 2.5-inch substrate is placed on the ceramic boat. Inverting the ceramic boat can stabilize the airflow flowing through the substrate. The honeycomb porous ceramic rectifier is placed on both sides of the ceramic boat and between the two heat-insulating furnace plugs to uniformly disperse the nitrogen and water vapor airflow at the air inlet of the tube furnace, so that the airflow flowing through the substrate is uniform. The sealing and airflow detection device includes a flange, a steel ring, a rubber ring, a gas conduit, and a beaker containing water. The rubber ring and steel ring are fitted onto the outlet end of the tubular furnace, and then sealed with a flange. The airflow from the outlet of the tubular furnace flows into the beaker through the gas conduit. The sealing effect can be detected by observing the bubbling rate in the beaker, and it also serves to isolate air. The water bath temperature is set at 38-44℃; The method for preparing vanadium dioxide thin films based on the above-described preparation apparatus includes the following steps: Step 1. Prepare a vanadium-containing polymer precursor solution using the PAD method; Step 2. After cleaning the substrate with acetone, anhydrous ethanol and deionized water respectively, blow it dry with nitrogen gas, and then spin-coat the polymer precursor solution prepared in step 1 onto the substrate. Step 3. Place the substrate with the polymer precursor solution spin-coated in Step 2 on an inverted ceramic boat. Place the ceramic boat containing the sample in the center of a tube furnace and introduce 99.999% pure nitrogen gas at a flow rate of 0.3-0.5 L / min. Perform heat treatment under the set program, and then allow it to cool naturally to room temperature to obtain a vanadium dioxide thin film on the substrate. The heat treatment method is as follows: first, raise the temperature to 100-120℃ and hold for 20-30 minutes to remove residual water in the precursor solution, then raise the temperature to 430-450℃ and hold for 120-140 minutes to remove organic matter, and then raise the temperature to 490-550℃ and hold for 2-2.5 hours to obtain vanadium dioxide film.

2. The method for preparing a 2.5-inch vanadium dioxide thin film as described in claim 1, characterized in that, The specific process of preparing the vanadium-containing polymer precursor solution using the PAD method in step 1 is as follows: Dissolve 0.001-0.002 mol of polyetherimide or polyethylene glycol in 60-120 ml of water, stir, add 0.001-0.002 mol of ethylenediaminetetraacetic acid, and continue stirring until a homogeneous solution is formed. Then add 0.001-0.002 mol of ammonium metavanadate to the solution and stir to form a transparent solution. Finally, transfer the solution to an ultrafiltration device. During filtration, 0.2 atmospheres of pressure must be applied and magnetic stirring must be performed to remove water from the solution.

3. The method for preparing a 2.5-inch vanadium dioxide thin film as described in claim 1, characterized in that, The specific parameters for spin coating in step 2 are as follows: first, rotate at a lower speed of 900-1000 r / min for 10 seconds, and then rotate at a higher speed of 6000-7000 r / min for 40 seconds.

4. The method for preparing a 2.5-inch vanadium dioxide thin film as described in claim 1, characterized in that, The ceramic boat is a quartz ceramic boat or a corundum ceramic boat, and the substrate material is silicon, silicon oxide or Al2O3.

5. The method for preparing a 2.5-inch vanadium dioxide thin film as described in claim 1, characterized in that, The distance between the two porous ceramic rectifiers is 40-60 cm.

6. The method for preparing a 2.5-inch vanadium dioxide thin film as described in claim 4, characterized in that, The substrate is sapphire Al2O3 with a crystal orientation of (1 0-1 0). The specific cleaning process is as follows: ultrasonic cleaning is performed sequentially with acetone, anhydrous ethanol and deionized water.

Images