Long-Term Stability of Oxide Nanowire Sensors via Heavily Doped Oxide Contact

Long-term stability of a chemical sensor is an essential quality for long-term collection of data related to exhaled breath, environmental air, and other sources in the Internet of things (IoT) era. Although an oxide nanowire sensor has shown great potential as a chemical sensor, the long-term stability of sensitivity has not been realized yet due to electrical degradation under harsh sensing conditions. Here, we report a rational concept to accomplish long-term electrical stability of metal oxide nanowire sensors via introduction of a heavily doped metal oxide contact layer. Antimony-doped SnO2 (ATO) contacts on SnO2 nanowires show much more stable and lower electrical contact resistance than conventional Ti contacts for high temperature (200 degrees C) conditions, which are required to operate chemical sensors. The stable and low contact resistance of ATO was confirmed for at least 1960 h under 200 degrees C in open air. This heavily doped oxide contact enables us to realize the long-term stability of SnO2 nanowire sensors while maintaining the sensitivity for both NO2 gas and light (photo) detections. The applicability of our method is confirmed for sensors on a flexible polyethylene naphthalate (PEN) substrate. Since the proposed fundamental concept can be applied to various oxide nanostructures, it will give a foundation for designing long-term stable oxide nanomaterial-based IoT sensors.