Conduction mechanisms in barium tantalates films and modification of interfacial barrier height

The leakage current-voltage characteristics of rf-magnetron sputtered BaTa₂O₆ film in a capacitor with the top aluminum and the bottom indium-tin-oxide electrodes have been investigated as a function of applied field and temperature. In order to study the effect of the surface treatment on the electrical characteristics of as-deposited film we performed an oxygen plasma treatment on BaTa₂O₆ surface. The dc current-voltage, bipolar pulse charge-voltage, dc current-time, and small ac signal capacitance-frequency characteristics were measured to study the electrical and the dielectric properties of BaTa₂O₆ thin film. All of the BaTa₂O₆ films in this study exhibited a low leakage current, a high breakdown field strength (3-4.5 MV/cm), and a high dielectric constant (20-30). From the temperature dependence of the leakage current, we could conclude that the dominant conduction mechanism under high electrical fields (>1 MV/cm) is ascribed to the Schottky emission while the ohmic conduction is dominant at low electrical fields (<1 MV/cm). Furthermore, the oxygen plasma treatment on the surface of as-deposited BaTa₂O₆ resulted in a lowering of the interface barrier height and thus, a reduction of the leakage current at Al under a negative bias. This can be explained by the formation of Ba-rich metallic layer by surface etching effect and by filling the oxygen vacancies in the bulk.