蒸着形成WO_3薄膜のNOx検知特性に及ぼす酸素の影響

概要

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WO3 thin film was evaporated on substrate provided with Pt interdigitated electrodes and with a heater element. The NO2 and NO sensing properties of the filmprepared by vacuum evaporation with post annealing were measured both in N2 and in air. With increasing operating temperature, NO2 sensitivity in N2 is increased but NO2 sensitivity in air is decreased. Oxygen gas affects the adsorption-site of NO2, that is related to oxygen vacancy of WO3 film, at higher temperature. NO is also adsorbed to WO3 film with electron-attraction in N2 only at lower temperature.Control of oxygen composition of WO3 film was tried by evaporation under vacuum, oxygen gas and oxygen plasma ambient. NOx sensitivities of these WO3 films were measured without post annealing. The film evaporated under oxygen ambient has the highest electrical resistivity and the film evaporated under oxygen plasma has the lowest resistivity. The film evaporated under oxygen plasma ambient, that is expected to have lower density of oxygen vacancy, has low sensitivity for NOx gas. The film evaporated under oxygen ambient has high sensitivity for NOx gas.The NOx sensitivities depend on the injection rate of oxy gen gas. The reason why the WO3 thin film prepared by oxygen gas-evaporation has high sensitivity for NOx seems to be related to the nano-crystalization of WO3.
社団法人電気学会の論文
2000-10-01