Application of thin-film materials in solid state gas sensors

Abstract

The mode of operation of metal–insulator–semiconductor (MIS) hydrogen sensors, which contain Langmuir–Blodgett solid ultrathin films as the insulator layer, has been examined. The device response to low concentrations (0–6 ppm) of hydrogen in nitrogen at 373 K was observed to correlate with analyte concentration according to the Lundström model, while at lower temperatures or in the presence of air, no such correlation was evident. Results from transient response and operating stability tests, taken together with previously reported analyses using X-ray photoelectron spectroscopy, indicate significant differences, compared with conventional (oxide I-layer) MIS devices, in the mechanism of interaction of hydrogen with the sensor. The palladium M-layer in the present device does not appear to be porous, according to carbon monoxide interference tests and it is proposed that there is no significant permeation of oxygen through the device.