Suppression of Switching-Field Variation by Surface Oxidation Depending on the Shape of the CoFeB Free Layer

We investigated the suppression of the variation of switching field H
_sw
by reducing magnetization M in submicron-sized magnetic tunnel junctions (MTJs) by oxidizing the surface of the CoFeB layer. Examination confirmed a reduction in the M of oxidized CoFeB film. The results also confirmed that oxidization enlarges anisotropy field H
_k
of CoFeB films. We applied this film to the free layer of submicron-sized MTJs of various aspect ratios. The results revealed that H
_sw
variation depending on the aspect ratio is reduced more with oxidation than without. We confirmed that H
_sw
variation in submicron-sized MTJs originating in the CoFeB free layer's shape decreased due to the oxidation, which reduced the switching field distribution (SFD) for the MTJs