Effect of nitrogen plasma treatment at the Al2O3/Fe interface in magnetic tunnel junction

We investigated the effects of nitrogen plasma treatment on top surface of Fe pinned layer for short times (tex=0, 10, 30, and 60 s) in magnetic tunnel junctions and annealing of the junctions. The nitrogen-treated junctions show much reduced magnetoresistance (MR) ratio and significantly lower resistance-area (RA) products compared with the untreated junction, i.e., MR≅3%, RA≅30 kΩ μm2 for tex=10 s and MR≅10%, RA≅60 kΩ μm2 for tex=0 s. The untreated junction showed enhanced MR ratio up to about 17% and higher RA (≅70 kΩ μm2) upon thermal annealing at Ta=230 deg. C, as expected. For the nitrogen-treated junctions, while the MR ratio also increases up to about 16% upon annealing at Ta=230 deg. C, which is almost the same value as the one of the optimal reference junction, the RA values of the annealed junctions still keep as low as their initial values. We believe that the redistribution of nitrogen during the annealing process is responsible for the change of properties of nitrogen-treated junction. The bias dependence of MR and the estimation of effective barrier height and thickness are studied and found to be consistent with the observed changes in nitrogen-treated junctions