General characteristics of thermally cycled tin oxide gas sensors

Abstract

The response, measured as conductance, of thermally cycled tin oxide gas sensors was studied to determine the potential inherent in this technique with respect to increased selectivity and sensitivity. It was found that the range of cycle temperature as well as the period of the cycle had a critical effect on the amount of information that could be extracted from the conductance versus time curves. Significantly different conductance curve shapes were seen for such gases as propane, carbon monoxide and ethanol when an offset sinusoidal waveform was used to drive the sensor heater. The effect of varying the concentration of the reducing gas was examined both to check the effect on selectivity between gases and to determine the functional relationship between conductance and gas concentration as related to the time in the cycle period. It was found that the conductance change at the low-temperature section of the thermal cycle can vary at a rate faster than linear for low concentrations, and because the clear air conductance is very low in these sections the thermally cycled sensor is extremely sensitive to reducing gas.