Effects of Ta and Pt/Ta seed layer on the thermal stability of CoFeB/MgO perpendicular magnetic anisotropy film

Abstract

The effects of Pt/Ta seed layer on the thermal stability of perpendicular magnetic anisotropy (PMA) compared to a single Ta seed layer was investigated in detail. The results showed that the PMA property is still stable in Pt/Ta/CoFeB/MgO sample above 300 °C annealing temperature. However, it deteriorates in Ta single seed layer when the annealing temperature increase up to 270 °C. Through microstructure analysis, the reason was attributed to the different elements diffusion tendency in the whole structure. It was found that the crystallization of seed layer Pt supplies an efficient diffusion paths for Ta. It decreases the ratio of Ta (about 15%) at CoFeB/MgO interface, and ensure more Fe-O bonding to improve PMA and its temperature stability. However, the Ta single seed layer is amorphous. It may diffuse to the CoFeB easily and decrease the hybridization between Fe/Co 3d and O 2p orbits. These observations confirm that the Pt/Ta seed layer provides a promising avenue to enhance the thermal stability of PMA effect, and meets the requirement of field-free spin-orbit torque (SOT) switching based on their opposite spin Hall angels.