On-chip growth of wafer-scale planar-type ZnO nanorod sensors for effective detection of CO gas

The facile engineering of sensing devices is an important technological achievement that will lead to large-scale and cost-effective fabrication of gas nanosensors. This study demonstrates the on-chip and selective growth process of zinc oxide (ZnO) nanorods (NRs) for wafer-scale fabrication of planar-type gas sensors using combined lithography and chemical hydrothermal techniques. This facile route can effectively fabricate ZnO NR gas sensors at low temperatures without the requirement of novel metal catalyst. The gas-sensing characteristics of the ZnO NR sensors to carbon monoxide (CO) and ammonia (NH3) were evaluated as a function of growth time in correlation with operating temperature and target gas concentration. The ZnO NR sensors showed good response and recovery characteristics with a maximum response to CO and NH3 gas at 400 °C. The ZnO NR sensors grown at 6 h exhibited the highest response to CO and NH3 gases with sensitivities of 0.37 and 0.05 %/ppm, respectively. Furthermore, the gas-sensing mechanism of the ZnO NR sensors was also discussed in terms of three types NR/NR junctions, namely, point-junctions, across-junctions, and block-junctions.