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

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 10-30 Omega mu m(2) and a tunneling magnetoresistance of similar to 20%. These were patterned into current perpendicular to plane configured nanopillars having elliptical cross sections of area similar to 0.02 mu m2. 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 1 s and 4 ms. An analytical expression for probability density function, p(I/I-c0) 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. (c) 2005 American Institute of Physics.