Trace level detection of NO2 gas using SnO2 thin films

Thin films of semiconducting SnO 2 were deposited by using RF sputtering technique under 30% oxygen and 70% argon in the reactive (Ar+O 2 ) gas mixture using a metallic tin (Sn) target at 16 mTorr deposition pressure. The SnO 2 thin film deposited at optimized sputtering conditions was found to be highly sensitive (sensing response ∼ 1.4 × 104) to NO 2 gas (10 ppm) at comparatively low operating temperatures (∼ 100°C), but with moderate response (4.1 minutes) and recovery speeds (33.4 minutes). Further the response and recovery times of the sensor structure were improved by loading Al 2 O 3 and NiO nano clusters over SnO 2 surface using E-beam evaporation and sputtering techniques respectively. Thickness of Al 2 O 3 nano clusters was varied from 10 to 18nm to get the best sensing characteristics. The quality of SnO 2 film and reaction kinetics of NO 2 with SnO 2 surface at the Sn sites play an important role in enhancing the sensing response and response speed at low temperatures (< 200°C).