Effect of thickness of ultra-thin tin oxide film based gas sensors

Ultra-thin tin oxide films (of 1-40 nm thickness) for gas sensing were grown by dc-magnetron sputtering. Stoichiometric and stable SnO films were characterized by unexpected dependence of the clean air resistance and the resistance response to H-2, NO2 gases on the average thickness of the film. The response to gas significantly increased in the extremely thin films. The rate of the sensor response to gas was independent of the thickness. The morphology and chemical composition of the films was analysed by scanning probe microscopy (SPM) and X-ray photoelectron spectroscopy (XPS). The mechanism of the thickness effect on the sensor properties is discussed within the context of development of the part per billion-sensitive miniaturized sensors.