Effects of rapid thermal annealing temperature on NO2 gas sensing properties of p-type mixed phase tin oxide thin films

Abstract

Effects of the rapid thermal annealing (RTA) temperature on the NO2 gas sensing properties of p-type SnOX thin films were investigated. The SnOX thin films were deposited using radio-frequency magnetron sputtering and subjected to RTA at 200 °C, 250 °C, and 300 °C. The deposited SnOX thin films contained both p-type SnO and n-type SnO2 components, but the SnO was the dominant phase. The amount of SnO2 components increased with increasing RTA temperature, but the highest amount of oxygen vacancy (OVac) states was observed in the SnOX thin film annealed at 250 °C. The surface roughness of the SnOX thin film decreased as the RTA temperature increased. The SnOX thin film subjected to RTA at 250 °C exhibited a significantly higher maximum sensing response to NO2 (4.25–10 ppm NO2 at 60 °C) than those of the films treated at 200 °C (1.13) or 300 °C (0.92). The higher response was attributed to the larger amount of SnO2 and OVac in the thin film and large number of defects and cracks on the film surface. The experimental results demonstrated that the post-deposition RTA temperature considerably affects the NO2 sensing properties of the p-type SnOX-based gas sensors.