Effects of the External Electric Field from a Substrate on Conductance Changes of SnO2 Thin Films by CO Gas

Thin SnO2 films were sputtered on SiO2/Si substrates. The effects of the external electric field from the substrate on the film conductance and on CO gas reactions at the film surface were studied. The conductance of the film increased with a positive substrate bias, and decreased with a negative substrate bias. A gradual increase in conductance was observed at 250 and 300° C in air, which suggested a change in the amount of adsorbed oxygen ions on the film surface. A positive substrate bias induced a larger increase in conductance due to CO gas at 250 and 300° C, which indicates enhancement of the adsorption of negatively charged oxygen ions and subsequent CO oxidation. In contrast, a negative bias induced a larger increase in conductance due to CO gas at 47° C, which indicates enhancement of the adsorption of positively charged CO. The results suggest that it is possible to control surface gas reactions and gas sensitivity using this external electric field.