C4H10 sensing characteristics of ion beam sputtered SnO2 sensors

Thin films of undoped and 0.1 wt.% Ca-doped SnO2 with 30-60 Å Pt layers deposited by ion beam sputtering and subsequent annealing at 500-700 °C were fabricated to measure butane sensing characteristics such as sensitivity, humidity dependency, and long-term stability in the temperature range of 250-450 °C. There are an optimal annealing temperature, operating temperature and Pt thickness for maximum butane sensitivity of the undoped, and Pt catalyzed sensors. Sensitivity enhancement by catalytic activities of the Pt films with a thickness equivalent to or less than 45 Å was not remarkable. In the case of 0.1 wt.% Ca-doped SnO2 sensors, the Pt catalysts had inverse effect on C4H10 sensitivity due to blocking role of free CaO surrounding SnO2 particles. The humidity dependencies of the 5000 ppm C4H10 sensitivity for all the sensors are relatively large at low level of relative humidity. Ion-beam sputtered SnO2 film sensors with dense structure and single SnO2 phase exhibited excellent long-term stability for 90 days.