Humidity and temperature compensation in work function gas sensor FETs

Field-effect transistors with suspended gate are able to detect gas species if a sensitive film is used as gate. The FET acts as a transducer which converts adsorption induced changes of work function ΔΦ at the surface to a corresponding change of the drain-source current ΔIDS in the FET channel. At operational temperatures below 80 °C, however, humidity induces contributions to the sensor signal and a base line drift which is not related to the sensitive film but to the transducer FET itself. An explanation will be given for this phenomenon and it will be shown that a guard ring and a second FET can largely suppress the influence of humidity at ambient temperatures.