Ethanol sensing properties of SnO2 thin films

Tin dioxide thin films have been deposited on alumina substrates by different methods in order to test their reliability as a breath analyser. Despite the obvious simplicity of spray pyrolysis, both the structural and electrical properties of the films thus prepared were strongly dependent to the deposition conditions. The samples exhibited poor crystallinity and porous microstructure. They were sensitive to ethanol vapour but since the resistance of the samples reached several MΩ, antimony doping was performed to fit a more convenient detection range. An alternative method was then used to prepare tin dioxyde thin films by evaporation of metallic tin followed by thermal oxidation. In this case, grain size was enhanced up to 100 nm but films remained highly porous. The ethanol sensitivity of evaporated samples was determined. In order to study more accurately the influence of microstructure on sensing ability, dense thin films were prepared using a CVD method with tetrabutyl tin as precursor. Preliminary results indicated that films with different crystallite sizes could be grown by varying the deposition temperature. Paper presented at the 2nd Euroconference on Solid State Ionics, Funchal, Madeira, Portugal, Sept. 10–16, 1995