Fabrication Of VO₂ Thin Films With Low Phase Transition Temperature

Vanadium dioxide (VO₂) is very well known for its sharp metal to insulator transition (MIT) at 68℃which is accompanied by a structural transition from monoclinic (low temperature) to tetragonal (high temperature) phase. This transition also brings with it abrupt changes in the optical and electrical properties. When at low temperature (<20℃) , the infrared transmission of VO₂ thin films is at a high level. When at high temperature (>50℃) , the VO₂ thin films keep its infrared transmission at a very low level. The resistance of VO₂ thin films changes 3⁴ magnitude as the MIT took place. With these two excellent properties, VO₂ thin films have wide range of applications, such as micro-bolometer, smart window, laser protection, optical switches, optical storage and so on. A lot of research is underway world over on VO₂ thin films to bring down the MIT to near room temperature and to improve the visible region transmission.The mainly contents of the thesis are as follows:1. The mechanism of VO₂ thin films'phase transition has been briefly analyzed. By using TFCalc coating design software, we obtained the optimum thickness of each layer which will be grown on glass substrate in the followed experiments; .2. Fabrication processes of VO₂ thin films through reactive ion beam sputtering and magnetron sputtering have been introduced in chapter 3 of the thesis. We obtained VO₂ thin films possess excellent properties by using reactive ion beam sputtering and followed-up post annealing. The key parameters of the fabrication process, such as substrate temperature, annealing temperature, annealing time, flow rate of oxygen and argon have been deeply studied and finally fixed;3. Four-probe setup with a temperature controller, spectrophotometer, X-ray diffractometry(XRD), scanning electron microscope(SEM) and atomic force microscope (AFM) have been applied for the test of the VO₂ thin films'optoelectronic properties, film configuration and crystalline information. The results revealed that the nanostructured VO₂ thin films we obtained not only have shifted its transition temperature down to 30℃, but also possess excellent switch property in infrared light.4. VO₂ thin films'applications on smart windows and micro-bolometer have been briefly introduced at the end of the thesis.