Room temperature ultra-sensitive resistive humidity sensor based on single zinc oxide nanowire

A highly sensitive relative humidity (RH) sensor is fabricated by a low-cost and scalable dielectrophoresis method that places a single crystalline zinc oxide nanowire (ZnO NWs) between pre-patterned electrodes in a freestanding device structure. The resistive device demonstrates an exponential sensitivity of more than 5 decades to changes from dry air to 60% RH at room temperature, indebted to a subthreshold carrier modulation due to the high surface-to-volume-ratio and completely exposed NW surface that facilitates surface physisorption of water molecules. Transient and temperature-dependence measurements signify a reproducible sensing performance and an Arrhenius behavior with activation energy of 0.6 eV, expected for these metal oxide semiconductors. These results demonstrate the potential of such nanoscale devices for accurate monitoring of RH in different applications, including fuel cells and automotive sensors, smart clothing, smart food packaging and sensor networks.