Electrical behavior of SnO2 thin films in humid atmosphere

This paper presents results of research of the temperature dependence of resistance (R) of thin film gas sensors (TFGS) in a humid atmosphere. It was shown that the R(T) dependencies, measured in the usual atmospheric conditions (relative humidity is in the range of 40-100% and ambient temperature similar to 20 degrees C), had some maximums and significant hysteresis, the form and area of which depends on the maximum temperature reached in the measurement. A critical temperature (T-CR = 410-430 degrees C) was observed for the maximum temperature. Upon exceeding T-CR, the second loop of hysteresis appears. It was established that such behavior of R(T) is connected with the influence of water on the SnO2 surface state. These anomalies disappear in a dry atmosphere. The explanation of the observed effects is given and the mechanism of interaction of the SnO2 surface with H2O explaining such behavior of R(T), is proposed. (C) 1999 Elsevier Science S.A. All rights reserved.