Fast Response Microgas Sensors Based on Platinum Nanoclusters Sputtered on Nanocrystalline tin Oxide Thin Films

Nanocrystalline thin film tin-oxide microsensors were fabricated on Si₃N₄ membranes using standard lithography process for the fast detection of reducing gases. The sensing material was spin-coated over platinum electrode contacts with various thicknesses using a sol-gel method. Subsequently, the spin-coated film was gradually heated up to 200 degC in an extended period of 150 mins. After the preannealing process, various thicknesses of platinum were deposited onto the tin oxide surface. Subsequently, platinum layers sputtered on tin-oxide thin films were annealed at different temperatures up to 850 degC in a quartz tube furnace. Due to the high porosity of the films, Pt nanoclusters are formed on the surface of tin-oxide thin films during the postannealing process. The size of crystallites changes from 20 to 200 nm depending on the platinum thickness and the postannealing process. Conductivity measurements of the sensors annealed at different temperatures have been carried out in dry air and in presence of various concentrations of CO, H₂ and ethanol. The response time of sensors for detection of reducing gases was less than 5s. TEM, SEM and XRD analyses were used to investigate the surface morphology and the crystallinity of SnO₂ films