Suspended CuO nanowires for ppb level H2S sensing in dry and humid atmosphere

The ppb level detection of the toxic gas H2S is of great importance for industrial and safety applications. We report on CuO nanowire gas sensors, which are capable to detect H2S concentrations as low as 10 ppb in dry as well as humid atmosphere. In particular, measurements with different humidity levels up to 65% have been performed, which is of high practical relevance regarding H2S detection in ambient atmosphere. Three different types of conductometric gas sensors have been investigated: a single CuO nanowire configuration and two different multiple CuO nanowire configurations that have been developed in order to optimize sensor performance and to enable CMOS integration of CuO nanowire gas sensors in the future. All sensor devices employ suspended CuO nanowires as gas sensitive components. This is a highly favorable configuration because the nanowires are entirely surrounded by the gas atmosphere. The devices based on multiple CuO nanowires show enhanced H2S response in humid air compared to dry synthetic air. Furthermore, we have found that the sensor design, which employs CuO nanowires with the smallest average diameters around 20 nm, has the highest gas response. The estimated detection limit approaches the ppt range, which shows the excellent sensor performance even in humid atmosphere. These results and the CMOS backend compatibility of the optimized CuO nanowire sensor design are of high importance for the realization of low power silicon integrated gas sensors for daily life applications.