Regensburg 2002 – wissenschaftliches Programm
DF 7.5: Vortrag
Donnerstag, 14. März 2002, 11:10–11:30, 11
Transient states in the breakdown of thin oxide films in metal / insulator / metal junctions — •Detlef Diesing1 and Achim Walter Hassel2 — 1Heinrich-Heine-Universität Düsseldorf — 2Max Planck Institut für Eisenforschung, Düsseldorf
The breakdown of oxide films is an intensively investigated field. Procedures as collisional ionization processes followed by the avalanche breakdown, thermal breakdown due to local heating effects are well known. By the use of fast voltage pulses (rise time < 300 ns) and a high resolution (t=1µ s) current transient recorder the breakdown process of thin oxide films (2 nm < d < 10 nm) in Al/Al2O3/Au and Ta/Ta2O5/Au junctions has been investigated. When field strengths higher than the breakdown field strength are applied in a voltage pulse, the current transient shows after a time of capacitive chargaing (1 µ s < t < 20 µ s )time domains of constant tunnelling current(20 µ s < t < 100 µ s ). Then a sudden current increase appears and the tunnel current stabilizes on a higher value (30-110 % higher). This period of constant current lasts several 100 µ s . Further current increases happen by chance before the final breakdown starts at times t > 10 ms. We assign the step like current increases before the breakdown to an enhanced electron tunnelling through transiently distorted tunnel barriers. These precursor states always appear before the breakdown of the oxide film. Model calculations taking into account migration of Al3+ or Ta2+ ions through the oxide causing a distortion of the tunnel barrier support our assignment.