Gas sensing characteristics in ZnO thin film explicated through the analysis of conductance transients and the concept of activation energy

ZnO thin film structures have been widely investigated for sensing gases such as carbon monoxide, hydrogen, H2S, NOx and volatile organic compounds. Selectivity, however, remains a challenge and had not been addressed for a long time. Current research involves the synthesis of ZnO thin film sensor and its use in the detection of hydrogen and carbon monoxide. Carbon monoxide shows a maximum response of 65% at 250 degrees C and hydrogen shows a maximum response of 68% at 300 C. Both gases can be detected over a wide temperature range of 350 - 200 degrees C and the response varies between 36 68% for 500 ppm H2 and 36 - 65% for 500 ppm CO. Assuming Langmuir adsorption kinetics, cross sensitivity of ZnO sensor has been addressed in terms of activation energy of these gases by the analysis of conductance transients. Fast fourier transform analyses of the resistance transients in conjunction with principal component analyses has also been successfully demonstrated to distinguish the gases at their operating temperatures.