The effects of heat treatment on the gas sensitivity of reactively sputtered SnO₂ films

Tin oxide (SnO₂) films were deposited by d.c. magnetron reactive sputtering and subsequently annealed at 500-900 °C. The effects of the deposition parameters and annealing conditions on the phases, electrical resistivity and gas sensitivity of the SnO₂ films were investigated. The oxygen-to-tin ratio in sputtered films increased with the substrate temperature and flow rate ratio of oxygen to argon in the physical vapour deposition process. An amorphous phase and metallic tin were observed in as-sputtered films. These were converted into the SnO₂ phase after heat treatment, however. The grain size, electrical resistivity and gas sensitivity increased with the annealing temperature.