Built-in active filter for an improved response to carbon monoxide combining thin- and thick-film technologies

A thick-film Pd-catalysed tin oxide layer is used as active built-in filter for ethanol when it is deposited on the surface of a thin-film tin oxide layer fabricated by sputtering and catalysed with Pt. The latter film has been previously optimised for carbon monoxide detection. The structure, morphology and composition of each layer, as well as their electric response to carbon monoxide, methane and ethanol have been studied separately first. Subsequently, the filtering effect of the thick micro-dropped layer on the thin sputtered layer is studied by means of the electrical response to the sample gases. The novelty of the proposed gas sensor structure is the combination of two different technologies resulting in an improved solution to get a selective response to carbon monoxide in the presence of ethanol or methane. (C) 2002 Elsevier Science B.V. All rights reserved.