Properties of metal doped tungsten oxide thin films for NOx gas sensors grown by PLD method combined with sputtering process

The gas sensors based on tungsten oxide (WO3) thin films and doped with different amount of gold (Au) or palladium (Pd) were synthesized by a new developed preparation system using the pulsed Nd:YAG (532 nm) laser deposition method combined with dc sputtering. The crystalline structure and crystallographic orientation of the prepared Au doped WO3 (WO3–Au) thin films, measured by X-ray diffraction system, suggested that there were distinct peaks of WO3 (0 0 1) and (2 0 1) and weak peaks of WO3 (1 2 0), (1 1 1), (0 0 2) and (1 1 2). The maximum sensitivity for 200 ppm NO2 were approximately 69 for WO3–Au thin film and 24 for WO3–Pd thin film at the operating temperature of 300 °C, respectively. These maximum sensitivities are higher than that of the non-doped WO3 sensor which sensitivity is about 17. This may be due to its electronic and/or chemical sensitization effect.