Effect of O₂ flow rate in the annealing process on metal–insulator transition of vanadium oxide thin films

Vanadium oxide (VO_x) thin films were fabricated on the sapphire substrates by sputtering deposition and subsequent rapid-thermal-annealing (RTA) process. The effect of O₂ flow rate on the crystal structure, surface morphology and phase transition property of thin films was studied. The results indicated that VO_x thin films were polycrystalline structures and consisted of irregular blocky-shaped grains. As the O₂ flow rate increased from 3 to 4.5 slpm, the oxidation was enhanced and the grain size decreased gradually. In addition, when we increased O₂ flow rate, phase transition amplitude increased from 5.4 to 117 and the phase transition temperature decreased from 50.45 °C to 45.37 °C. The hysteresis width almost increased as O₂ flow rate increased. More interesting, we found that the value of \(d\lg {\text{R}}_{\square } /dT\) became big at high temperature which could be attributed to the phase transition and the variation trend of difference was in line with the phase transition amplitude. So, it could be concluded that O₂ flow rate in the RTA process played a significant role in the properties of VO_x thin films.