SOL-GEL MATERIALS FOR GAS-SENSING APPLICATIONS

High temperature sintering of porous pellets of metal oxides to form f lammable gas sensors remains one of the most straightforward and popul ar fabrication methods in use today, but is unsatisfactory in many way s including lack of control over structure and morphology of the pelle ts. In addition, the chemical and physical role of catalytic dopants i s often unclear and further sintering during operation can lead to lon g-term drift and unreliable behaviour. We have been exploring the use of alternative fabrication techniques, for the development of highly s ensitive flammable ps detectors, based on the sol-gel process. The mai n advantage of this technique over conventional processing technologie s is the use of homogeneous, multi-component systems which can be prep ared to a high degree of purity by mixing the molecular precursor solu tions, and the reduction in fabrication temperature leading to unusual glasses or ceramics with better-defined properties. Several advantage s in the development of highly sensitive flammable gas sensors are to be expected. Deliberate addition of impurities can be carefully contro lled and low temperature fabrication should allow greater control over the structure, stoichiometry and morphology of the sensors. Both of t hese factors will contribute towards low background conductivity and h igh purity for high sensitivity. Finally the high porosity and large s urface area of glassy materials produced by sol-gel methods should enh ance sensitivity in mechanisms dominated by surface phenomena. In this paper we present details of the preparation of novel tin oxide thin-f ilm sensors and initial results of response to a variety of organic so lvents and common flammable gases. A comparison with conventional, com mercially available tin dioxide (Taguchi) flammable gas sensors will b e given.