Effects of rapid thermal annealing on room temperature NO₂-sensing properties of WO₃ thin film under LED radiation

WO₃ thin films were sputtered onto alumina substrates by DC facing-target magnetron sputtering. One sample was rapid-thermal-annealed (RTA) at 600 ℃ in a gas mixture of N₂:O₂=4:1, and as a comparison, another was conventionally thermal-annealed at 600 ℃ in air. The morphology of both was investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM), and the crystallization structure and phase identification were characterized by X-ray diffraction (XRD). The NO₂-sensing measurements were taken under LED light at room temperature. Sensitivity of the RTA-treated sample is high, up to nearly 100, whereas sensitivity of the conventionally thermal-annealed sample is about 5 under the same conditions. From the much better selectivity and response-recovery characteristics, it can be concluded that, compared to conventional thermal annealing, RTA has a greater effect on the NO₂-sensing properties of WO₃ thin films.