Perpendicular magnetic anisotropy in Co X Pd 100−X alloys for magnetic tunnel junctions

Abstract CoFeB/MgO-based perpendicular magnetic tunnel junctions (p-MTJ’s) with high anisotropy and low damping are critical for spin-torque transfer random access memory (STT-RAM). Most schemes of making the pinned CoFeB fully perpendicular require ferrimagnets with high damping constants, a high temperature-grown L1 0 alloy, or an overly complex multilayered synthetic antiferromagnet (SyAF). We report a compositional study of perpendicular Co x Pd alloy-pinned Co 20 Fe 60 B 20 /MgO based MTJ stacks, grown at moderate temperatures in a planetary deposition system. The perpendicular anisotropy of the Co x Pd alloy films can be tuned based on the layer thickness and composition. The films were characterized by alternating gradient magnetometry (AGM), energy-dispersive X-rays (EDX), and X-ray diffraction (XRD). Current-in-plane tunneling (CIPT) measurements have also been performed on the compositionally varied Co x Pd MTJ stacks. The Co x Pd alloy becomes fully perpendicular at approximately x = 30% (atomic fraction) Co. Full-film MTJ stacks of Si/SiO 2 /MgO (13)/Co X Pd 100−x (50)/Ta (0.3)/CoFeB (1)/MgO (1.6)/CoFeB (1)/Ta (5)/Ru (10), with the numbers enclosed in parentheses being the layer thicknesses in nm, were sputtered onto thermally oxidized silicon substrates and in-situ lamp annealed at 400 °C for 5 min. CIPT measurements indicate that the highest TMR is observed for the CoPd composition with the highest perpendicular magnetic anisotropy.