Charge trapping-detrapping mechanism of barrier breakdown in MgO magnetic tunnel junctions

Endurance of MgO-based magnetic tunnel junctions has been studied using a time-dependent dielectric breakdown method. Series of successive electrical pulses were applied until electrical breakdown of the tunnel barrier. We show that two electrical breakdown regimes exist depending on the time interval Delta t between pulses compared to a characteristic escape time of trapped electrons tau(0) similar to 100 ns. For Delta t < tau(0), breakdown is caused by a high average charge trapped in the barrier. For Delta t > tau(0), breakdown is ascribed to large temporal modulation of trapped charges causing alternating stress in the barrier oxide. Between these two regimes, the tunnel junctions reach a very high endurance. (C) 2011 American Institute of Physics. [doi:10.1063/1.3615654]