SOL-GEL Materials for Gas-Sensing Applications

High temperature sintering of porous pellets of metal oxides to form flammable gas sensors remains one of the most straightforward and popular fabrication methods in use today, but is unsatisfactory in many ways including lack of control over structure and morphology of the pellets. In addition, the chemical and physical role of catalytic dopants is often unclear and further sintering during operation can lead to long-term drift and unreliable behaviour. We have been exploring the use of alternative fabrication techniques, for the development of highly sensitive flammable ps detectors, based on the sol-gel process. The main advantage of this technique over conventional processing technologies is the use of homogeneous, multi-component systems which can be prepared to a high degree of purity by mixing the molecular precursor solutions, and the reduction in fabrication temperature leading to unusual glasses or ceramics with better-defined properties. Several advantages in the development of highly sensitive flammable gas sensors are to be expected. Deliberate addition of impurities can be carefully controlled and low temperature fabrication should allow greater control over the structure, stoichiometry and morphology of the sensors. Both of these factors will contribute towards low background conductivity and high purity for high sensitivity. Finally the high porosity and large surface area of glassy materials produced by sol-gel methods should enhance sensitivity in mechanisms dominated by surface phenomena. In this paper we present details of the preparation of novel tin oxide thin-film sensors and initial results of response to a variety of organic solvents and common flammable gases. A comparison with conventional, commercially available tin dioxide (Taguchi) flammable gas sensors will be given.