Preparation And Properties Of Thermally Induced Phase Change Material VO₂Film

VO2has a metal-to-insulator phase transition near room temperature, companied by a high relative resistance change and optical transmittance change. Therefore, VO2can be used in infrared detectors, optical storage, optical switches and smart windows.In this dissertation, we synthesized VO2thin films by pulsed laser deposition (PLD) method and studied the impact on VO2thin films in many different parameters like substrate type, temperature, pressure, laser energy and the annealing treatment. Through optimizing process parameters, we prepared high-quality VO2thin film on (0001) SiO2and r-A12O3single crystal substrates. Film quality is determined by testing the physical performance on the phase transition. The electrical properties of the film were measured by the four-probe method. The resistivity changes of single crystal epitaxial VO2film grow on r-Al2O3substrate can reach104orders. And the resistivity changes of the polycrystal VO2film grow on SiO2substrate can reach103orders. The optical properties of the film were tested by visible and infrared spectrophotometer which has a heating platform. The transmittance of single crystal VO2film has a8%change at λ=700nm when the temperature is heated over67℃. Polycrystal VO2films has1%transmittance changes at λ=700nm, but the transmittance of metal phase polycrystal VO2films are only0.1%, so the ratio is more than10times between metal phase and insulating phase transmittance.We also prepared TiO2/VO2composite structure film grow on (0001) SiO2substrate, which have a high contrast in the visible region before and after the phase transition, and can be used on the new uncooled infrared detectors. We measured the transmittance of the TiO2/VO2films in the wavelength of400-1700nm. The transmittance at λ=630nm of VO2/SiO2film at20℃and100℃was35.7%and42%, which has a6.3%change. The transmittance at λ=630nm of TiO2/VO2/SiO2film at20℃and100℃was35.9%and52.1%, which has a17.2%change. This result can be applied in the design of the new type infrared detector. The writing laser light λ=630nm in the visible light range makes the VO2/TiO2thin films on SiO2substrate in a critical phase transition state, and VO2phase transition will occur once the infrared light shining into the detector causing the change of the writing light, thus convert the infrared light signal into a visible signal.