Effect of oxygen content and crystallization temperature on the insulator-to-metal transition properties of vanadium oxide thin-films

Abstract

In this article, x-ray photoelectron spectroscopy (XPS) studies indicate increasing concentrations of V4+ and O 1s (V4+) states responsible for a prominent insulator-to-metal transition (IMT) for vanadium oxides (VO) deposited using reactive sputtering at higher pO2 in Ar/O2 plasma and at higher deposition temperatures. The crystallization temperatures of VOs deposited at various Ar/O2 ratios are identified by differential scanning calorimetry (DSC) technique and accordingly, the deposition temperatures were set at above their respective crystallization temperatures. The DSC study further reveals that amorphous-to-crystalline transition temperature (Tc) increases with the increase in pO2. I–V studies reveal ∼4 order IMT for the devices with VO deposited at 60% pO2. An abrupt change in resistance is observed in the 40–50°C temperature range for VO deposited at 40% pO2, accompanied by a large magnitude of IMT for I–V characteristics measured in the same temperature range. Therefore, with increasing deposition temperatures and higher oxygen content in the plasma, crystallization causes an increase in grain size and a simultaneous reduction in the density of grain boundaries, thereby causing a large and sharp IMT.