Perpendicular magnetic tunnel junctions with synthetic antiferromagnetic pinned layers based on [Co/Pd] multilayers

摘要

We fabricated MgO-based perpendicular magnetic tunnel junctions (p-MTJ) with Ta/CoFeB magnetic electrodes. Synthetic antiferromagnetic (SAF) pinned layers with perpendicular magnetic anisotropy (PMA) were included into the p-MTJs by using two Co/Pd multilayers (MLs) separated by a thin Ru spacer layer. The MTJs stack has the structure bottom contact/free layer CoFeB (1.0)/ MgO (1)/pinned layer CoFeB (1.0)/Ta spacer layer/SAF/Ru cap layer/top contact (the units in parenthesis are in nanometers). The SAF was optimized by changing the repetition period n in one of the Co/Pd multilayers and the Ru thickness in order to obtain PMA with antiferromagnetic (AFM) coupling. The Ru spacer values were 0.7, 0.75, 0.8, 0.85, and 0.9 nm. The magnetic studies show that all magnetic films, including the Ta/CoFeB layers, are perpendicularly magnetized. The two Co/Pd MLs are AFM coupled for n ＞ 2. Controlling the Ru thickness, the interlayer exchange coupling strength J_(iec) can be tailored. J_(iec) vs. Ru thickness exhibits a simple exponential decay. The electrical properties of the full p-MTJ with SAF show a low resistance-area (RA) product of 44.7 Ω μm~2 and a tunnel magnetoresistance (TMR) ratio of 10.2%.