Sputtered Ultra-Thin Wo3 for Realizing Room Temperature High Sensitive No2 Gas Sensors

Abstract

In this work, we used commercial manufacturing process to form WO3 semiconductor gas sensor to realize NO2 detection in parts-per-billion concentration at room temperature (25-27 °C). Radio-frequency (RF) sputtering process was used to deposit ultrathin WO3 sensing layer down to 5 nm. With a suitable control of the deposition ambient and the post-annealing condition, the WO3 ultra-thin-film resistor with a 50-μm-linewidth can detect 100 ppb NO2 without any heating set-up. Noted that no nanometer process is required, hence the production can be realized by current display technology. By modulating the deposition condition, we investigated the influences of surface roughness, crystalline condition, and the surface hydroxyl group levels on the sensing response. To achieve ppb-level detection, the ultrathin thickness is essential and the high level crystalline together with low level surface hydroxyl group also enhance the sensitivity and the recovery. The humidity effect was also discussed to show almost unchanged response in RH = 30% to 70%. Finally, a good enough selectivity, stability, and the non-decayed sensing after 14 days were demonstrated.

Keywords: Gas Sensor, NO2, Tungsten Oxide, ppb Level Sensing, Ultra-Thin Sensing Layer, Room temperature sensor