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+O-2) 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 similar to 1.4x 10(4)) to NO2 gas (10 ppm) at comparatively low operating temperatures (similar to 100 degrees 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 (<200 degrees C).