Evaluation of barrier uniformity in magnetic tunnel junctions prepared using natural oxidation of thin Mg layers

We fabricated submicron magnetic tunnel junctions (MTJs) using natural oxidation of thin Mg layers deposited by dc sputtering. The MTJs exhibited magnetoresistance (MR) ratios of up to about 150% with a low resistance-area product (RpA) of 8 Ω μm2, which are comparable to those for radio-frequency-sputtered MgO barriers. The submicron MTJs had highly variable MR and RpA values due to a high pinhole density (20 μm−2) in the barriers, whereas current-in-plane-tunneling (CIPT) measurements on the same MTJ films revealed highly reproducible MR and RpA values. This indicates that reproducible CIPT measurements do not necessarily give accurate results of MR and RpA at high pinhole densities.