Moisture influence and geometry effect of Au and Pt electrodes on CO sensing response of SnO2 microsensors based on sol–gel thin film

Undoped tin oxide-based gas microsensors have been prepared by the sol–gel deposition technique. The influence of the gaseous atmosphere (humidity and carbon monoxide) on the electrical conductance of the samples has been investigated. Then, the variation of the geometry and the nature of the electric contacts has been considered as interesting factor that can modulate the selectivity. SEM observations of the surface have shown a good quality of the electrodes. A pre-deposited Ti thin layer improves the adhesion of the contacts to the SnO2 film. A diversification of the sensors, when exposed to CO, was observed depending on two different electrodes materials (Au and Pt) arranged in two different geometric configurations of the interdigitated fingers. Preliminary results have shown that CO response is enhanced by the use of interdigitated electrodes with a short separation gap (200 μm) as compared to those with wider one (400 μm) for both Pt and Au electrodes, while the use of gold contacts seems to reduce the working temperature of our sensors, probably due to some effects related to the diffusion of Au into the Ti and/or the active layer, but other drawbacks could also arise.