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

Highly hydrogen $(H2)$-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 $H2$ $(S=12700)$⁠; 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 $H2$ 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 $H2$ 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 $H2$ selectivity behavior.