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 10-30 × μ m2 and a tunneling magnetoresistance of ∼20%. These were patterned into current perpendicular to plane configured nanopillars having elliptical cross sections of area ∼0.02 μ m2. The width of the critical current distribution (sigmaaverage of distribution), measured using 30-ms current pulse width, was found to be 7. 5% and 3.5% for cells with thermal factor (Ku V kB T) 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 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. © 2005 American Institute of Physics.