The effects of various binders added in the solidification process, such as
polyvinyl alcohol (PVA), silica sol and Al2O3, on the sensing and electric
al characteristics of WO3-based n-type semiconductor gas sensors are invest
igated. Grain sizes show a slight variation according to the employed binde
rs. In the case of WO3 films fabricated with silica sol or Al2O3 binder, so
me residue of binders at grain boundary and agglomerates of WO3 grains are
observed. The electron concentration of WO3 film around room temperature an
d the temperature dependence of film resistance in normal air do not show a
ny systematic dependence on the employed binders. In NOx gas, however, the
optimum operation temperature and the sensitivity of WO3 sensors at that te
mperature are observed to depend greatly on the employed binders. The resis
tance of the WO3 films shows an exponential temperature dependence in NOx g
as in the temperature range of 110-375 degrees C, and the increase of film
resistance in NOx gas is observed to depend greatly on the binders added in
WO3 films. Sensitivity to various ambient gases does not show any systemat
ic variation. All these results mean that the binders affect the sensing ch
aracteristics of WO3-based gas sensors mainly through the modification of c
hemical conditions at grain boundary rather than the modification of grain
size and electron concentration. (C) 1999 Elsevier Science S.A. All rights
reserved.