Highly stable perpendicular magnetic anisotropies of CoFeB/MgO frames employing W buffer and capping layers

Abstract

Typical CoFeB/MgO frames ensuring interface perpendicular magnetic anisotropy (PMA) features are one of the most reliable building blocks to meet the demand of PMA-based memory devices. However, employing the CoFeB/MgO frame with a Ta buffer layer has been restricted by the rapid PMA degradation that occurs during annealing at temperatures greater than 300°C and the need of an ultrathin CoFeB layer of approximately 1.3nm. Thus, the ability to enhance thermally strong PMA characteristics is still a key step toward extending their use. Here, we examine the effect of W layers on PMA features through both W buffer/CoFeB/MgO and MgO/CeFeB/W capping frames at various annealing temperatures. Highly stable PMA was achieved up to 450°C at a specific W thickness, along with the presence of the dominant PMA properties at a relatively thick CoFeB greater than 1.3nm and the achievement of a high Keff of approximately 5Merg/cc.