Exploring the role of substrate temperature in tailoring the gas sensing performance of sputter-deposited WO3 films

Due to the increasing demand for gas sensors, particularly in the oil and gas industry for accurate detection and safe operation, the present study is centered on the synthesis process of WO3 thin-films, as WO3 is a promising material for sensitive gas detection. Using pulsed DC magnetron sputtering, WO3 films were coated on silicon (100) and ITO-coated glass substrates at different substrate temperatures varying from room temperature to 800oC in 200oC intervals. The XRD pattern revealed that increasing the substrate temperature beyond 400oC led to a phase transformation from monoclinic to hexagonal WO3. The surface morphological studies using FESEM showed a transition from a fine granular structure at room temperature to larger grains at higher temperatures, reflecting enhanced grain growth. Gas sensing measurements were conducted at 200oC in a static test chamber, demonstrating that the sensitivity is strongly depending on the substrate temperature and corresponding microstructure. Gas sensing performance was evaluated for gases like hydrogen (H2), methane (CH4), and carbon monoxide (CO). The films coated at 800oC showed the highest sensitivity to CH4, with a rapid response time of 20 seconds and a recovery time of 25 seconds. Notably, the thin film sensor demonstrated excellent repeatable sensitivity to 25 ppm of CH4. These findings emphasize the critical role of substrate temperature in tailoring the phase composition and grain structure of WO3 thin films for CH4 sensing applications.