Effect of air humidity on gas response of SnO2 thin film ozone sensors

The peculiarities in the sensor response to ozone are discussed for SnO2 thin films. Films with thickness from 30 to 200 nm were deposited by spray pyrolysis. The study of sensor response kinetics and humidity influence on the gas sensing characteristics was used to understand these unique responses. The response to dry (ozone + air) gas of the films was a multiple-step process, reflecting a complex reaction mechanism. The presence of humidity in the surrounding atmosphere made this process still more complicated. It was found that adsorption/desorption of both water and oxygen controlled the kinetics of gas response of the SnO2-based sensors. Interestingly, higher pyrolysis and operation temperatures both promoted a lowering of the humidity influence on the gas sensor response.This work suggests that the appearance of a slower component in sensor response at higher temperatures, Toper > 400 °C, is connected with the increased influence by diffusion processes in the bulk of the SnO2 grains, which is consistent with reduction/reoxidation processes.