Nano-Crystalline SnO2 Thin Film Based Surface Acoustic Wave Sensor for Selective and Fast Detection of NO2 Gas

In the present work, nanocrystallite SnO2 thin film based SAW sensors have been utilized for the fast and selective detection of NO2 gas. SnO2 thin film deposited under varying sputtering pressure (8-30 mT) are used as the sensing layer on quartz based SAW resonators. The sensing response of the SAW sensor increases from 25 to 30 MHz with increase in growth pressure of the SnO2 thin film from 8 to 20 ml and it decreases to 13 MHz with further increase in pressure to 30 mT. The response time of all the SAW sensors is found to be relatively small (2 to 6 s). The SAW sensors having SnO2 thin film grown at moderate sputtering pressure (10 to 20 mT) have small recovery time (35 to 40 s). However, the recovery time of SAW gas sensors coated with SnO2 sensing layer deposited at high sputtering pressure (30 mT) is found to be large (>6 min.) and could be due to rough and porous microstructure. The sensing response of SnO2/SAW sensor towards NO2 gas is identified mainly due to change in elasticity of the films due to adsorption of gas molecules.