Atomic-scale spectroscopic imaging of CoFeB/Mg–B–O/CoFeB magnetic tunnel junctions

Atomic-scale electron spectroscopic imaging on sputtered magnetic tunnel junctions (MTJs) with a thin, <2 nm, MgO layer and B-alloyed electrodes reveals B diffusion into the MgO, resulting in a Mg–B–O tunnel barrier. This ∼2 nm thick interfacial layer forms due to oxidation of CoFeB during radio frequency sputtering of MgO and subsequent B diffusion into MgO during annealing. We measure a room-temperature tunneling magnetoresistance (TMR) of ∼200% in IrMn/CoFeB/Mg–B–O/CoFeB MTJs after annealing, demonstrating that thin Mg–B–O barriers can produce relatively high TMR.