CoFeB/MgO/CoFeB magnetic tunnel junctions prepared by layer-by-layer growth of naturally oxidized MgO

We fabricated CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs) by naturally oxidizing dc-sputtered Mg and investigated the formation process of MgO(001) by reflective high-energy diffraction. The 0.26 nm thick Mg layer on amorphous CoFe(B) had an amorphous structure in the as-deposited state and a monolayer (ML) of textured MgO(001) formed by natural oxidation. By repeating the deposition/oxidation of 0.26 nm thick Mg layers, a highly textured MgO(001) barrier layer was prepared. Surprisingly, (001)-oriented crystallization was confirmed even for 2 ML thick MgO. The MTJs prepared by layer-by-layer growth of naturally oxidized MgO exhibited high MR ratios (up to 200%) and low resistance-area products suited for device applications.