Conducting polymer FET devices for vapour sensing

Conducting polymer films are employed as the active material in both resistive and acoustic;waves gas sensors. Here we describe the use of an electroactive conducting polymer as the gate material in a gas-sensitive MOSFET sensor run at ambient temperature and compare it to a conventional catalytic metal gate MOSFET run at 180 degrees C. The sensors were operated with both the gate voltage V-GS and drain voltage V-DS set constant, whilst the drain currents were measured. Also V plots were made in order to characterise fully the device properties. The polymer and catalytic MOSFETs were exposed to pulses from 2,000 to 31,000 PPM of ethanol vapour at different humidities. A change in the drain current Delta I-DS was observed, for both types of MOSFET sensors. Their response was found to follow a Langmuir isotherm in ethanol concentration, with a current sensitivity of +0.4 nA and +200 nA per PPM of ethanol in air at room temperature, respectively. We believe that in the case of the polymer MOSFET, the ethanol vapour shifts the threshold voltage V-TO Of the device via a change in work function phi(ms) between the polymer and gate oxide. The polymer MOSFET is operated at room temperature and so offers potential use in a palm-top electronic nose.