Critical current distribution in spin-transfer-switched magnetic tunnel junctions

Abstract

The spin transfer switching current distribution within a cell was studied in magnetic-tunnel-junction-based structures having alumina barriers with a resistance-area product (RA) of 10–30Ωμm2 and a tunneling magnetoresistance of ∼20%. These were patterned into current perpendicular to plane configured nanopillars having elliptical cross sections of area ∼0.02μm2. The width of the critical current distribution (sigma∕average of distribution), measured using 30-ms current pulse width, was found to be 7.5% and 3.5% for cells with thermal factor (KuV∕kBT) of 40 and 65, respectively. The distribution width did not change significantly for pulse widths between 1s and 4ms. An analytical expression for probability density function, p(I∕Ic0) was derived considering the thermally activated spin transfer model, which supports the experimental observation that the thermal factor is the most significant parameter in determining the within-cell critical current distribution width.