Effect of growth pressure on sulfur content of RF-magnetron sputtered WS2 films and thermal oxidation properties of them toward using Pd decorated WO3 based H2 gas sensor

Obtaining near stoichiometric WS2 films with sputtering is challenging because of high sulfur deficiency during sputtering, which limits the application of these films in different solid-state device applications. In this study, in order to understand the growth pressure effect on the sulfur/tungsten ratio, WS2 films were grown at four different growth pressures, 5, 25, 50, and 100 mTorr, by RF-magnetron sputtering. With increasing growth pressure from 5 to 100 mTorr, it is found that films change from relatively metallic to near stoichiometric WS2 films. The thermal oxidation process of as-deposited WS2 films in the presence of O2 gas was also studied. The study showed that WS2 films were turned into WO3 films without significant change in morphology at a temperature of 400 ℃. The obtained WO3 films were then decorated by Palladium catalysis deposited by RFMS to activate the WO3 films toward H2 gas. The high response of 586-fold at an operating temperature of 200 ℃ for 1000 ppm H2 gas response and recovery times of 360 and 90 s, respectively, has been achieved for the sensor deposited at a growth pressure of 50 mTorr. In addition, a detection limit of 10 ppm was achieved for the sensor.