Conductive polymer gate FET devices for vapour sensing

The development of ultra low-power CMOS compatible gas sensors has been the goal of many research groups for a number of years. Such sensors benefit from both a low fabrication cost and an ease of integration with any associated transducer or signal processing circuitry. A sensor with these attributes is proposed comprising a novel chemFET sensor, with a conducting polymer gate, that operates at ambient temperature. Both electrochemically deposited and polymer composite materials have been deposited to form the gate electrode of an n-channel enhanced MOSFET (ECFET and PCFET, respectively). The authors present the first full characterisation of these sensors in terms of their response to pulses of ethanol and toluene vapour in air. In addition, environmental effects of temperature and humidity on both the baseline signal (i.e. zero vapour) and vapour response have been investigated. The PCFET and ECFET vapour sensitivities (operating at constant current) were found to be up to 5.5 muV/ppm and -2.3 muV/ppm for toluene and 0.6 muV/ppm and 4.5 muV/ppm for ethanol, respectively. The relative selectivity of the chemFET sensors was observed to be up to 564 for these two organics, with an observed sign change with certain polymers. In addition, the detection limits have been estimated to be below 1 ppm of toluene and ethanol vapour in air. It was also found that increasing temperature resulted in a reduction in both baseline and response signals, which the authors postulate is due to a reduction in the bulk solubility of the polymer. The authors believe that the low power of operation, range of polymers and integration with standard electronics makes these sensors ideal for a new range of hand-held electronic noses.