[Co/NM/Pt]_n-based seedless synthetic anti-ferromagnetic layer design for preventing MgO crystallinity degradation from Pt diffusion

Since the report of sub-nm CoFeB/MgO-based perpendicular spin-transfer-torque magnetic-tunnel-junction (p-STT-MTJ) spin valves, Pt seed-based [Co/Pt] or [Co/Pd] synthetic anti-ferromagnetic (SyAF) has been used for its high thermal stability However, it faces an issue where perpendicular magnetic anisotropy (PMA) at the CoFeB/MgO interface is compromised by Pt atoms diffusing from the Pt seed/[Co/Pt] super lattice during the annealing process for back end of line (BEOL) and PMA property. To solve this problem, this study introduced a new structure [Co(0.55 nm)/Ta(0.148 nm)/Pt(1.12 nm)]₃ SyAF layer, ensuring high PMA property and crystallinity of L₁₀ without Pt seed. Additionally, by employing this new SyAF layer, a p-STT-MTJ was fabricated in a device with a diameter of 1.5 µm. Instead of using Pt seed layer, Pt atom diffusion into the MgO tunneling barrier was reduced by 40% and improved body-centered-cubic (b.c.c.) crystallinity in MgO tunneling was achieved. Finally, the TMR of Pt seedless p-STT-MTJ was improved 2.6 times compared to the Pt seed p-STT-MTJ.