EFFECT OF CONSTITUENT LAYERS ON THE SENSITIVITY AND SELECTIVITY OF MULTILAYER GAS SENSORS

摘要

Multilayer gas sensors based on a thin metal film (Pt, Au, Mo, Ni, etc.), which is covered with top-layer of SnO_2, were investigated experimentally. Technological possibilities to modify the sensitivity and selectivity of multilayer sensors were revealed.The experimental results obtained for the structures consisting of two and three layers were summarised. An optimum thickness of the top-layer was evaluated for multilayer sensors. The properties of the interface between the bottom- and the top-layer were proved to be dependent on additional inter-layer of Ni, which modified the sensitivity and selectivity of the sensor. The interface was also modified by X-ray radiation. The point defects induced by this radiation produced significant effect on the response of the Pt-based structure.Depth profiles of the chemical composition were obtained for multilayer sensors by combining XPS analysis with Ar~+ etching. It was demonstrated that the three-layer structure consists of a pile of ultra-thin layers, and the bottom-layer is practically metallic. The changes of the electron transport induced by an extra charge on the surface or in the interface seem to be the most probable origin of the resistance response to gases in multilayer sensors.