DEVELOPMENT OF SEMICONDUCTOR FLUOROCARBON GAS SENSOR

To improve the sensitivity to fluorocarbon, surface-modification effec ts on fluorocarbon detection of a gas sensor based on metal oxides suc h as SnO2, ZnO, In2O3, Fe2O3 and WO3 have been examined. It is proved that SnO2 is the most suitable material for fluorocarbon detection. 39 kinds of elements have been investigated as the additives to SnO2, wh ich significantly affect its sensing characteristics. It is confirmed that sulfur is the most effective modifier to improve the sensitivity. The surface modification of SnO2 with 1.0 mol% of sulfur induced the enhancement of sensitivity by a factor of 6.5 for CCl2FCClF2 (R-113). Furthermore, the selectivity is also improved by this modification. Th e sensor doped with 1.0 mol% of sulfur can even detect gas leakage as low as 5 ppm of CH2FCF3 (R-134a) and shows no impairment in long-term stability. IR results have convinced us that the doped sulfur exists i n bidentate coordinated form as the sulfate ion (SO42-) on the Sn atom . The sulfur acts as an active site to decompose fluorocarbon (the sev erance of C-Cl and C-F bonds in fluorocarbon molecules).