Influence of effective surface area on gas sensing properties of WO₃ sputtered thin films

WO₃ thin films having different effective surface areas were deposited under various discharge gas pressures at room temperature by using reactive magnetron sputtering. The microstructure of WO₃ thin films was investigated by X-ray diffraction, scanning electron microscopy, and by the measurement of physical adsorption isotherms. The effective surface area and pore volume of WO₃ thin films increase with increasing discharge gas pressure from 0.4 to 12 Pa. Gas sensors based on WO₃ thin films show reversible response to NO₂ gas and H₂ gas at an operating temperature of 50-300 °C. The peak sensitivity is found at 200 °C for NO₂ gas and the peak sensitivity appears at 300 °C for H₂ gas. For both kinds of detected gases, the sensor sensitivity increases linearly with an increase of effective surface area of WO₃ thin films. The results demonstrate the importance of achieving high effective surface area on improving the gas sensing performance.