The sensor response of tin oxide thin films to different gas concentration and the modification of the gas diffusion theory

SnO2 thin films on alumina and silicon substrates are prepared by sol–gel technique using dip-coating method. The films are sensitive to H2S gas and the one on alumina exhibits response of 81 at low concentration of 3.4 ppm. The sensor response and film conductance are measured in the atmosphere with different reducing gas concentration and furthermore the relationship between film conductance variation and gas concentration is summarized as a linear curve in a logarithmic coordinate with the slope of 1/2, coinciding with the power law. Based on this relationship, the modification of the gas diffusion theory is performed by substituting the former linear assumption with a new one. The modified expression is validated by correlations of experimental sensor response versus film thickness and gas concentration. The probable application of the modified expression on explaining response of thin films to various reducing and oxidizing gases is proposed.