Chemically deposited zinc oxide thin film gas sensor

Zinc oxide (ZnO) thin films were prepared by a low cost chemical deposition technique using sodium zincate bath. Structural characterizations by X-ray diffraction technique (XRD) and scanning electron microscopy (SEM) indicate the formation of ZnO films, containing 0.05-0.50 μm size crystallites, with preferred c-axis orientation. The electrical conductance of the ZnO films became stable and reproducible in the 300-450 K temperature range after repeated thermal cyclings in air. Palladium sensitised ZnO films were exposed to toxic and combustible gases e.g., hydrogen (H2), liquid petroleum gas (LPG), methane (CH4) and hydrogen sulphide (H2S) at a minimum operating temperature of 150°C; which was well below the normal operating temperature range of 200-400°C, typically reported in literature for ceramic gas sensors. The response of the ZnO thin film sensors at 150°C, was found to be significant, even for parts per million level concentrations of CH4 (50 ppm) and H2S (15 ppm).