Pulse stress testing for ultra-thin MgO barrier magnetic tunnel junctions

Pulse stress tests on magnetic tunnel junctions (MTJs) with a MgO barrier (~5.5 Aring) were conducted. Both the E (McPherson and Mogul, 1998) and 1/E (Chen and Holland, 1985; Schuegraf and Hu, 1994) models can describe the intrinsic breakdown behavior of this ultrathin barrier within the range of voltages studied. While constant voltage stress (CVS) and ramped voltage pulse stress (RVPS) testing yield different experimental failure times for the same failure voltage, accounting for the buildup of degradation from each pulse in the RVPS testing yields the same fundamental degradation rate for the two techniques. The barrier parameter change (before hard breakdown) is related to trap generation and trapped electrons. The variation in the barrier parameters after constant stress testing was also studied by fitting I-V data using Simmons' model (1963). A decrease in the effective barrier thickness and an increase in the effective barrier height were found after constant current/voltage stress. Annealing MTJs with minor damage for 2 hours at 120degC restored the stressed barrier to its initial state.