Highly enhanced perpendicular magnetic anisotropic features in a CoFeB/MgO free layer via WN diffusion barrier

Abstract

Ferromagnet/oxide interfaces that ensure perpendicular magnetic anisotropy (PMA) features are critical for developing spintronic technologies such as perpendicular magnetic tunnel junctions, which are the most reliable building blocks for spin transfer torque switching or spin-orbit-torque switching. As such, metal/CoFeB/MgO frames containing various transition metals have been a central component to achieve large PMA and higher annealing stability. However, metal/CoFeB/MgO frames can experience thermally activated boron and transition metal diffusion behavior during annealing at temperatures greater than 300 degrees C, which deteriorates PMA. In this work, we introduce the simple incorporation of tungsten nitride (WN) at the interface of Ta/CoFeB as a generic alternative approach to obtain an enhanced PMA in Ta/CoFeB/MgO frames without thermal degradation. Precise control of the thickness and composition of WN was required to ensure stable PMA even after a 425 degrees C annealing process, along with the achievement of a high effective magnetic anisotropy energy density of almost 10 Merg/cc.