The structure and electrical properties of chemical vapor deposition (CVD)-Ta2O5 thin films on Pt, Ru and poly-Si electrode were studied. With 750°C annealing after Ta2O5 deposition, a 12-nm-thick Ta2O5 on Pt and Ru shows a SiO2 equivalent thickness (t eq) of 0.9 nm. We found that Ta2O5 on Pt and Ru shows (110) and (001) orientation, respectively. There is no interaction between Ta2O5 and these electrodes with 750°C annealing. t eq on Pt and Ru decreases with annealing temperature increase. On the other hand, Ta2O5 on poly-Si is randomly oriented and its t eq does not change with annealing temperature increase. The relative dielectric constant of Ta2O5 on Pt and Ru, which is highly oriented with 750°C annealing, is estimated over 50. It is clear that the Ta2O5 electrical properties are strongly related with its crystallinity.

The resistivity responses of layered compound TiS2 to oxygen and nitrogen gases were measured around room temperature. The resistivity showed a selective and reversible response to oxygen. This may be due to the fact that oxygen intercalates into van der Waals gaps in the layered structure of TiS2. The resistivity showed an increment of 1% oxygen partial pressure in 10 min at 50°C. From the comparison with a commercial oxygen gas sensor, it was shown to operate at a lower temperature with the response time as short as the commercial one.

The electrical resistivity of the layered semiconductor CuFeTe2 is created in response to oxygen concentration intercalated into the van der Waals gaps. An oxygen gas sensor operating around room temperature has been fabricated using this property. The resistivity response to oxygen has been improved by the use of crystal grains of uniform size. The specimen consisting of grains with diameters of 20∼53 µm responds to 20% oxygen mixed into nitrogen in 2 min.

The electrical properties of layered compound CuFeTe2 are studied under intercalation and deintercalation conditions of intercalant gas. The resistivity perpendicular to the layer responds to oxygen gas at room temperature. It is found that CuFeTe2 is a favorable material for oxygen sensors which operate even at low temperatures below 100°C.

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