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.