Endurance of magnetic tunnel junctions under dynamic voltage stress

Abstract

MgAl2O4 (MAO)-based magnetic tunnel junctions (MTJs) with an MAO thickness of similar to 1.25 nm are fabricated and their cycling characteristics under dynamic voltage stress are evaluated. The speed of breakdown strongly depended on the pulse polarities used, bipolar, positive (+) unipolar, and negative (-) unipolar. The bipolar condition yielded more rapid breakdown under cycling. Between the two unipolar conditions, positive bias yielded more rapid breakdown than negative bias; the difference between these is understood to arise from the conditions of the interface between the MAO and ferromagnetic layers. Among apparently normal MTJ cells showing little resistance drift, 20% were degraded during a long cycling test in the bipolar stress condition. Thus, the use of bipolar voltage stress is essential to screen for potentially defective MTJs, and the asymmetric condition at the interface is minimised by process control for application of the simple unipolar bias condition.