Tailoring surface and structural properties of WO3 thin films via mixed-gas plasma deposition for optimized H2 gas sensing performance

Detecting hydrogen at low concentration is essential for the early identification of leaks in hydrogen storage and transportation systems, thereby improving operational safety. In this work, thin films of tungsten trioxide (WO 3 ), a well-known hydrogen-sensing material, were deposited via DC reactive magnetron sputtering under systematically varied gas environments to elucidate the role of deposition conditions in tailoring film morphology and sensing performance. Introducing mixed Ar/O 2 , Ar/He/O 2 , and He/O 2 sputtering atmospheres with varying gas flow rates at a substrate temperature of 400 °C produced a marked reduction in grain size and film thickness compared with films grown in an equal flow-rate Ar/O 2 plasma. The film synthesized in the Ar/O 2 environment exhibited superior resistance modulation upon H 2 exposure and significantly enhanced sensitivity compared with the other films. Gas sensing characteristics toward H 2 were evaluated at operating temperatures of 100, 150, and 200 °C, and the optimized film was further investigated for low H 2 concentrations down to 25 ppm. These findings demonstrate a strong correlation between microstructure and sensing response and highlight the critical influence of the deposition environment on the morphological and electronic properties of WO 3 thin films, providing a viable strategy for developing next-generation high-performance hydrogen gas sensors.