Studying the effects of siloxane poisoning on a SnO₂ metal oxide semiconductor gas sensor in temperature cycled operation enabling self-monitoring and self-compensation

This work studies poisoning by the cyclic siloxane octamethylcyclotetrasiloxane on a commercially available semiconductor gas sensor in TCO (temperature cycled operation). The data is evaluated using the Sauerwald-Baur model and the DSR method (differential surface reduction). The sensitivity towards several gases (volatile organic compounds, hydrogen and carbon monoxide) is evaluated and compared with a sensor in constant temperature operation mode. The physical and chemical processes on the sensitive layer as well as the resulting selectivity towards hydrogen are discussed. A feature is identified that can be derived from the Sauerwald-Baur model (the differential surface oxidation, DSO) and that quantitatively expresses the sensor condition regarding siloxane poisoning. With the help of this feature, a self-compensation of the sensor signal is demonstrated.