Density-controllable growth of SnO2 nanowire junction-bridging across electrode for low-temperature NO2 gas detection

The junction-bridging structure of metal oxide nanowires (NWs) improves gas-sensing properties. In this study, an on-chip growth method was used to fabricate gas sensors, it easily and effectively controls NW junctions. SnO2 NWs were synthesized by thermal evaporation at 800 °C with tin powder as the source. The density of the NW junctions was controlled by changing the mass of the source material. A source material with large mass yielded high-density NW junctions. With electrode spacing of 20 μm, NW junctions were formed from the source material of larger than 2 mg. Gas sensing results revealed that the junction sensors exhibited a good response to NO2 gas at a concentration of 1–10 ppm. The sensors exhibited a good response to NO2 gas at low temperature of up to 100 °C and short response–recovery time (~20 s). The sensors also had good selectivity to NO2 gas. The response (R gas /R air) to 1 ppm NO2 was as high as 22 at 100 °C, whereas the cross gas responses (R air /R gas) to 10 ppm CO, 10 ppm H2S, 100 ppm C2H5OH, and 100 ppm NH3 were negligible (1.1–1.3).