Effect of Ta getter on the quality of MgO tunnel barrier in the polycrystalline CoFeB∕MgO∕CoFeB magnetic tunnel junction

X-ray photoelectron spectroscopy and high-resolution Rutherford backscattering reveal that Ta getter presputtering enhances the stoichiometry and lowers the interstitial defect density of MgO barrier. This results in higher magnetoresistance ratio, 205%, of magnetic tunnel junction, compared to 46% for no Ta getter, at 1.2nm MgO thickness. Fitting yields the corresponding barrier height of the MgO of 3.0eV, which is higher compared to 2.3eV for without Ta getter. However, the tunnel junction prepared with Ta getter shows lower resistance-area product by an order of magnitude. Microstructure of MgO barrier and oxidation of bottom electrode can be attributed to the contradictory results.