Thin Sn02 films of about 10 nm thickness were prepared by sputtering on Si02/Si substrates, and the effects of an external electric field from the substrate on the conductance of the SnO., film were investigated at 26°C and up to 300°C. The apparent conductance of the Sn02 film increased with a positive substrate bias and decreased with a negative substrate bias. These field effects became more evident with larger bias and in 5n02 films with a lower carrier concentration. By using metal oxide semiconductor theory, the results are attributed to the formation of a depletion and an accumulation layers in the Sn02 film under a negative and a positive bias, respectively. The influence of electron traps in the Sn02 film on its apparent conductance was suggestectfrom calculations of these field effects. At temperatures above 150°C, slow changes in the conductance with time were observed under a constant negative bias. From the results measured in N2 and in air, it was suggested that the amount or types of surface oxygen adsorbates changed under a negative electric field. These results indicate the possibility of controlling the electrical properties and the surface reactions of Sn02 films by an external electric field.

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.

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