Speaker
Description
Metal-insulator transitions (MIT) are reversible changes in the conductivity of materials when the temperature above or below the transition point, which are the smart transitions in advanced material. Vanadium oxide (V$_\text{x}$O$_\text{y}$) demonstrated excellent MIT characteristics at the transition temperature (T$_\text{c}$) due to the lattice distortion. However, V$_\text{x}$O$_\text{y}$ has many phases such as V$_\text{2}$O$_\text{5}$, V$_\text{2}$O$_\text{3}$, VO$_\text{2}$, VO, which have the different transition temperature. In this work, we study the influence of an annealing process to improve the MIT of V$_\text{x}$O$_\text{y}$ thin film on glass substrates. V$_\text{x}$O$_\text{y}$ thin films were prepared by the pulsed DC magnetron sputtering technique at room temperature by various gas ratios between Ar and O$_\text{2}$. Then, the crystal structures of V$_\text{x}$O$_\text{y}$ thin films were investigated by X-ray diffraction. X-ray diffractrograms of as deposited V$_\text{x}$O$_\text{y}$ thin films did not show the crystallinity index of material. To improve the MIT or the crystalinity of V$_\text{x}$O$_\text{y}$ films, the controlled ambient annealing process was applied to deform grains and recrystallize of the material. Consequently, as deposited V$_\text{x}$O$_\text{y}$ thin films were annealed under control N$_\text{2}$ pressure, and the temperature was set at 400$^°$C to avoid the deformation of thin film at the high annealing temperature. After annealing process, the MIT characteristics of V$_\text{x}$O$_\text{y}$ thin films were measured by four points probe technique between 30-150 $^°$C. Surprisingly, the V$_\text{x}$O$_\text{y}$ thin films exhibit the MIT behavior in two orders of magnitude. We found the formation of V$_\text{2}$O$_\text{5}$ from XRD patterns of thin films, and other phases such as V$_\text{2}$O$_\text{3}$, VO$_\text{2}$ also discovered. Moreover, the Raman spectra of thin films show the vibration modes of V$_\text{2}$O$_\text{5}$ to confirm the effect of annealing process on the V$_\text{x}$O$_\text{y}$ crystal formation. Our preliminary study is promising method to improve the crystal formation of V$_\text{x}$O$_\text{y}$ thin film and enhance the MIT for further electronics applications.
