Undoped and 0.1Â wt.% Ca-doped Pt-catalyzed SnO2 sensors for CH4 detection

Thin films of undoped and 0.1 wt.% Ca-doped SnO2 with 30-60 Å Pt layers deposited by ion beam sputtering have been structured on Si substrates. CH4 sensitivities for those Pt-covered undoped and Ca-doped SnO2 sensors are compared in terms of root-mean-square surface roughnesses measured by the scanning probe microscopy in the AFM mode. There is an optimal Pt thickness of 45 Å for maximum CH4 sensitivity. Pt catalysts lead to increase in methane sensitivity for the undoped sensor. However, coating of a Pt catalyst layer on the Ca-doped SnO2 results in an inverse effect on CH4 sensitivity. All the fabricated sensors exhibited relatively small humidity dependencies and excellent long-term stabilities for 90 days.