Development of gas sensors based on tungsten oxide nanowires in metal/SiO2/metal structure and their sensing responses to NO 2

In this work, the fabrication of gas sensors utilizing self-synthesized tungsten oxide nanowires (TONWs) and their response to NO₂ are reported. The gas sensor is based on a sputter-deposited WC_x/SiO ₂/WC_x triple-layer structure with the periphery of the SiO₂ layer etched chemically. Self-synthesized TONWs with crystalline W₁₈O₄₉(010) were grown by simple thermal annealing in nitrogen ambient, which linked, in parallel, the upper and lower WC_x electrodes for gas sensing. The TONW-based sensors increased in resistance in NO₂ because the surface of TONWs comprised oxygen adsorbates and the adjacent space charge region was electron-depleted. The amount of enlargement in resistance increased with increasing temperature. To improve the detectability of the parallel-connected TONW-based sensor, a connection of several individual sensors in series was proposed to enlarge the number of TONWs for gas sensing. For the 8-series-connected sensor, a sensitivity as high as 9.3. a response time as low as about 9 s, and a detectability as low as 2 ppm for NO₂ were obtained.