Trace level detection of NO2 gas using SnO2 thin films

Thin films of semiconducting SnO₂ were deposited by using RF sputtering technique under 30% oxygen and 70% argon in the reactive (Ar+O₂) gas mixture using a metallic tin (Sn) target at 16 mTorr deposition pressure. The SnO₂ thin film deposited at optimized sputtering conditions was found to be highly sensitive (sensing response ~1.4 × 10⁴) to NO₂ 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 Al₂O₃ and NiO nano clusters over SnO₂ surface using E-beam evaporation and sputtering techniques respectively. Thickness of Al₂O₃ nano clusters was varied from 10 to 18nm to get the best sensing characteristics. The quality of SnO₂ film and reaction kinetics of NO₂ with SnO₂ surface at the Sn sites play an important role in enhancing the sensing response and response speed at low temperatures (<;60; 200°C).