Stress polarity dependence of breakdown characteristics in magnetic tunnel junctions

Time-dependent dielectric breakdown (TDDB) measurements under constant voltage stress with positive and negative bias polarities are carried out for magnetic tunnel junctions (MTJs) with different oxidation status (under-, optimal, and overoxidation). We found that there is significant polarity dependence in the TDDB and speculated that the polarity dependence is due to both intrinsic and extrinsic origins. Optimally oxidized MTJs with positive bias on the top electrode show shorter times to breakdown (t(BD)'s) and lower barrier height than with negative bias, indicating that asymmetric band structure, in part, causes the polarity dependence. On the other hand, under- and overoxidized MTJs show much shorter t(BD)'s than optimally oxidized one and show a higher 1/f noise power density for positive bias than for negative bias, indicating that the polarity dependence is also, in part, due to the interface states, which acts like precursors for the dielectric breakdown. (C) 2006 American Institute of Physics.