Investigating On The Effect Of Ti、Y-doping On The Structure And Properties Of Vanadium Oxide Thin Films

Because of outstanding change of optical and electrical properties of vanadium dioxides resulting from semiconductor-metal phase transition(SMPT) at about room temperature(~ 68 ℃), it has great applications in many fields such as optical switches, smart windows, optical storage, etc. However, the wide hysteresis width of vanadium dioxide polycrystalline thin film is a big problem. This limits its application where high temperature-sensitivity is necessary, Therefore, the regulation of vanadium dioxide film polycrystalline phase transition has attracted many scholars’ attention in recent years. This paper focuses on phase transition properties of vanadium dioxide polycrystalline thin film, by means of SEM, XRD, Raman, XPS analysis and other characterization techniques to explore impact of Ti、Y-doping on the microstructure and phase transition features of vanadium oxide thin films. In addition, due to the excellent performance, vanadium oxide thin films can be widely used in high-sensitivity uncooled infrared detector. Further enhancing its temperature coefficient of resistance(TCR) will help improve the sensitivity of devices. This paper will try to seek new methods to prepare high TCR vanadium oxide films without SMPT based on the results about the impact of Ti、Y-doping on the electrical properties of vanadium oxide thin films. The main work and innovations are summarized as follows:(1) The influence of Ti-doping on the microstructure and phase transition characteristics of vanadium dioxide polycrystalline films was investigated. Ti-doping can decrease the grain size. For the lower concentration of Ti-doped(≤7.7at%), Ti-doping changes the morphologies of films from the short-worm-like particles to spherical or spherical particles. With further increasing the concentration of Ti-doping, vanadium oxide thin films shows mixed rod and spherical morphology. Ti-doping will significantly inhibit SMPT of vanadium oxide thin films: hysteresis width and transition amplitude are significantly reduced due to the introduction of Ti. As a result, high-TCR(-4.42%/K) vanadium oxide films without SMPT can be prepared with high Ti concentration. This provides a new method for preparation of high-TCR vanadium oxide thermal films without SMPT.(2) We firstly realize preparation high-TCR vanadium oxide thin films without SMPT through Y-doping. Different concentration of Y-doped vanadium oxide thin films was prepared by low-temperature reactively sputtering process. As-prepared vanadium oxide thin films are amorphous and no SMPT. Y-doping significantly enhances its TCR: from-2.67%/K to-3.63%/K. Moreover, Y-doping also greatly improvs the environmental stability of resistance of vanadium oxide thin films.(3) The effect of Y-doping on the microstructure and phase transition characteristics of vanadium dioxide polycrystalline thin films. Y-doped vanadium dioxide polycrystalline thin film with Y3 + form was fabricated by low-temperature reactively sputtering followed by annealing at high temperature. Y-doped and undoped vanadium dioxide films both have a typical monoclinic structure and typical SMPT feature. Y-doping significantly inhibits particle scale and grain size of films. The introduction of Y increases the heterogeneous nucleation density during SMPT, the appropriate concentration of Y can decrease hysteresis width of vanadium oxide thin film from 10.6 ℃ to 4.6 ℃. With further increasing the concentration of Y, the hysteresis width gradually increases and even becomes close to the one of undoped vanadium oxide thin films.