Scaling properties of perpendicular MTJ with dual-CoFeB/MgO interfaces and step-etch structure

We had built and studied the size scaling effect of perpendicular magnetic tunnel junctions (p-MTJs) with dual MgO/CoFeB interface and step-etch structure. Although the spin-torque-transfer (STT) switching current reduces with MTJ area, the current density increases. Our micromagnetic simulations verify that this is an intrinsic property of STT switching. The switching mode shifts gradually from coherent switching in small junctions to incoherent in large junctions. The energy density of coherent switching is higher and demands higher spin current density. At same current density, smaller size takes longer time to switch. Fortunately, the write efficiency (Δ/Isw) is higher for smaller MTJ.