Postbreakdown Conduction in Ultrathin La2 O3 Gate Dielectrics

The evolution of the conduction characteristics of ultrathin lanthanum oxide (La₂O₃) gate dielectrics that are subjected to constant and ramped electrical stresses was investigated. The samples were obtained by the electron-beam evaporation technique and annealed in situ in ultrahigh vacuum conditions to minimize the formation of an interfacial oxide layer. We have shown that the total current flowing through the device consists of two parallel contributions, where one is associated with direct and Fowler-Nordheim tunneling and the other one is associated with multiple breakdown (BD) path conduction. This latter component is sensitive to the applied stress and evolves from soft BD to diodelike conduction as the degradation proceeds. We analyzed the experimental data in terms of two well-known models for post-BD conduction. The importance of considering series and parallel resistances within these formulations is shown.