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

The spin transfer switching current distribution within a cell was studied inmagnetic tunnel junction based structures having alumina barriers withresistance-area product (RA) of 10 to 30 Ohm-um2 and tunnelingmagneto-resistance (TMR) of ~20%. These were patterned into currentperpendicular to plane configured nano-pillars having elliptical cross-sectionsof area ~0.02 um2. The width of the critical current distribution(sigma/average of distribution), measured using 30 ms current pulse width, wasfound to be 7.5% and 3.5% for cells with thermal factor (KuV/kBT) of 40 and 65respectively. The distribution width did not change significantly for pulsewidths between 1 s and 4 ms. An analytical expression for probability densityfunction, p(I/Ico) was derived considering the thermally activated spintransfer model, which supports the experimental observation that the thermalfactor is the most significant parameter in determining the within cellcritical current distribution width.Comment: 12 pages, 4 figure