NO2 sensing and selectivity characteristics of tungsten oxide thin films

Using sol-gel synthesis, we have synthesized phase pure, porous, WO3 thin film (thickness similar to 70 nm) on optically flat quartz substrates. The deposited films were characterized in terms of their structure, microstructure, and gas sensing characteristics. We have investigated the NO2 (0.2-50 ppm), CO (10-500 ppm), methane, and butane (50-500 ppm) sensing characteristics of the synthesized films. The low ppm NO2 sensing characteristics of these films are found to be superior than most of the nanostructured WO3 sensing elements reported in recent literatures. For higher test gas concentrations, we found these sensing elements are sensitive to carbon monoxide (>10 ppm), methane, and butane gases (>50 ppm). We demonstrated that exponential moving average feature extraction algorithm of the resistance transients in conjunction with pattern recognition analyses is one of the most viable approach to address the cross-sensitivity of WO3 thin film NO2 sensors towards other reducing gases. (C) 2014 Elsevier B.V. All rights reserved.