Electrical properties of Cu/a-BaTiO3/Cu capacitors studied in dc and ac regimes

Electrical properties of Cu/a-BaTiO3/Cu capacitors have been investigated in both dc and ac regimes as a function of temperature. A clear correlation is found between the temperature dependence of dc leakage currents and the temperature variation of the dielectric relaxation, showing that these measurement techniques are probing the same defects. Using either of these two techniques, we were able to detect at least three types of electrical active defects. Oxygen vacancy diffusion takes place at high temperature with an activation energy of around 1 eV. The diffusion of copper creates ionic defects in the a-BaTiO3 layer, which introduces two other contributions to the conduction process. The first is related to the motion of ionic species (ionic conduction, thermally activated with an activation energy of 0.3 eV). In addition, it has been argued that the presence of copper ions introduces a discrete set of shallow traps within the bandgap, resulting in a n-type conductivity (electronic conduction). The traps depth and their effective density are 0.45 eV and 4×1016 cm−3, respectively.