Study on the sensing mechanism of tin oxide flammable gas sensors using the Hall effect

Measurements were made on the Hall effect of SnO2 thin-film inflammable gas sensors prepared by using the reactive sputtering method. The results revealed that when the electrical conductivity of the sensors changed with a change in the flammable gas concentration in air, the apparent carrier density changed significantly while apparent mobility hardly changed at all. However, detailed analysis revealed that these experimental results could not be explained by using the double Schottky model or the neck model that had been proposed. In order to provide satisfactory explanation of the experimental results, the authors clarified that for SnO2 thin films there exists no distinction between bulk and surface of the grain while the carrier densities of bulk and surface of the grain simultaneously change with a change in oxygen absorption of the SnO2 surface in the presence of flammable gas. This model was in good agreement with the results of transmission electron microscopy observations.