Abstract
The effects of various binders added in the solidification process, such as polyvinyl alcohol (PVA), silica sol and Al 2O 3, on the sensing and electrical characteristics of WO 3-based n-type semiconductor gas sensors are investigated. Grain sizes show a slight variation according to the employed binders. In the case of WO 3 films fabricated with silica sol or Al 2O 3 binder, some residue of binders at grain boundary and agglomerates of WO 3 grains are observed. The electron concentration of WO 3 film around room temperature and the temperature dependence of film resistance in normal air do not show any systematic dependence on the employed binders. In NO x gas, however, the optimum operation temperature and the sensitivity of WO 3 sensors at that temperature are observed to depend greatly on the employed binders. The resistance of the WO 3 films shows an exponential temperature dependence in NO x gas in the temperature range of 110–375°C, and the increase of film resistance in NO x gas is observed to depend greatly on the binders added in WO 3 films. Sensitivity to various ambient gases does not show any systematic variation. All these results mean that the binders affect the sensing characteristics of WO 3-based gas sensors mainly through the modification of chemical conditions at grain boundary rather than the modification of grain size and electron concentration.
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