Influence of thermopolar processing on the electrophysical properties of anodic tantalum oxide

We have studied the physical mechanisms which lead to failure of Ta-Ta2O5-Al thin film capacitors during prolonged exposure to an electric field and elevated temperature. Using a thermally stimulated depolarization technique we have determined the energy spectrum of the point defect levels in the band gap of the oxide in the original structure and in that subjected to fields at high temperature. The changes observed demonstrate an increase in the shallow trap and donor concentration at the interface between the oxide and the external electrode. The transition layer which develops reduces the barrier at the Al-Ta2O5 interface, leading to increased injection and, as a result, to increased conductivity. It is shown that the stability of the structure depends on the deposition technique used for the metallic layers: an electrothermal technique yields a more stable structure than a magnetron.