A study of hydrogen sensing properties and microstructure for highly dispersed Pd SnO2 thin films with high response magnitude

A series of SnO2-based thin films were prepared for hydrogen sensor fabrication. Pure, Pd-doped and Pd-surface-modified SnO2 thin films were deposited by magnetron sputtering. One Fe-doped, PEG-400-added, Pd-surface-modified SnO2 thin film was prepared by the sol-gel method. The structure, surface morphology and composition of the as-prepared SnO2 thin films were analyzed, and the H2 sensing performance of these films toward hydrogen gas in concentration of 100-2000 ppm at operation temperature of RT-275 °C were investigated. The Fe-doped, PEG-400-added, Pd-surface-modified SnO2 thin film prepared by the sol-gel method had a response magnitude of about 288 toward 2000 ppm H2 at 275 °C. It was the first time that Pd-surface-modified SnO2 thin films fabricated by magnetron sputtering exhibited a high response magnitude of 4636 and an extremely fast response time of about 1 s to 2000 ppm H2 at 175 °C. Additionally, this sensor also showed a response magnitude of 738 toward 2000 ppm H2 at the low temperature of 75 °C. The influence of the annealing process on the Pd-surface-modified SnO2 thin films was discussed for the first time. The abnormal phenomenon of Pd modified SnO2 thin films that the initial resistance reaches a peak with increasing operation temperature was observed and explained.