Thickness effect of constituent layers on gas sensitivity in SnO2[metal]/metal multi-layers

The multi-layer sensors based on the SnO2/[metal]/metal thin layers are produced and investigated at temperatures from 20 degrees C to 300 degrees C in clean and contaminated air (CO, H-2, NOx). Various metals Pt, Au, Mo and Ni were used for the layer at the bottom of the sensor. Thickness of the constituent layers is varied and the electrical resistance and the X-ray photoelectron spectroscopy (XPS) depth profiles are measured. It is determined that the resistance response to gases is dependent on the thickness of each of the constituent layers. The response signal was set to maximum by an optimal thickness of the top- and bottom-layers. The selectivity to gas was changed by the metallic inter-layer grown in the interface between the top- and bottom-layers up to appropriate thickness. The metallic character of the conductance in the base film is associated with a unique response to gas in the sensors tested.