Hydrogen-discriminating nanocrystalline doped-tin-oxide room-temperature microsensor

Highly hydrogen (H-2)-selective [relative to carbon monoxide (CO)] sensor, operating at room temperature, has been fabricated using the micronanointegration approach involving the deposition of the nanocrystalline indium oxide (In2O3)-doped tin oxide (SnO2) thin film on microelectromechanical systems device. The present microsensor exhibits high room-temperature sensitivity towards H-2 (S=12 700); however, it is insensitive to CO at room temperature. In view of the different gas selectivity mechanisms proposed in the literature, it is deduced that the In2O3 doping, the presence of InSn4 phase, the low operating temperature (room temperature), the mesostructure, the small sizes of H-2 and H2O molecules, the bulky intermediate and final reaction products for CO, and the electrode placement at the bottom are the critical parameters, which significantly contribute to the high room-temperature H-2 selectivity of the present microsensor over CO. The constitutive equation for the gas sensitivity of the semiconductor oxide thin-film sensor, proposed recently by the authors, has been modified to qualitatively explain the observed H-2 selectivity behavior. (c) 2005 American Institute of Physics.