Effect of Anti-Diffusion Oxide Layer on Enhanced Thermal Stability of Magnetic Tunnel Junctions

Magnetic tunnel junctions (MTJs) with one proper oxidized FeOx layer placed between the Al oxide barrier and the top CoFe pinned layer show large tunnelling-magnetoresistance (TMR) signals as high as 39% after anneal at 380°C. The increased TMR signal may originate from the as-deposited Fe/FeO_x (non-magnetic) layers changing to Fe+magnetic FeOy layer (some Fe₃O₄ and mostly other kind of magnetic Fe oxide) after high temperature anneal. The maximum TMR value (TMR_max) and the corresponding temperature T_s where the TMR_max occurs upon annealing are closely associated with the oxidation time of the AlO_x and FeO_x layers, too long oxidation for the Fe layers is detrimental for the TMR value. In addition to the enhanced AlO_x barrier quality upon anneal, the improved thermal stability is also attributed to the Mn diffusion retardation by the presence of the FeO_x layer which acts as an antidiffusion layer. For MTJs without the interposed FeO_x layer, the TMR signal reduction at 300°C originates from the MnIr/CoFe partially decoupling and CoFe/AlO_x interface polarization loss due to the significant Mn diffusion.