Effect of Ta getter on the quality of MgO tunnel barrier in the polycrystalline CoFeB/MgO/CoFeB magnetic tunnel junction
ABSTRACT 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 1.2 nm MgO thickness. Fitting yields the corresponding barrier height of the MgO of 3.0 eV , which is higher compared to 2.3 eV 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.
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ABSTRACT: In the first part of this paper, we report a systematic study on the structural evolution under rapid thermal annealing and the corresponding transport properties in magnetic tunnel junctions (MTJs) with a crystalline MgO barrier. The results clearly indicate that high tunneling magnetic resistance can be achieved by annealing MTJs at a very short time, and it is directly related to the formation of (001) crystalline structures. In the second part, we report the spin dynamics in tunneling structure through direct electrical detection. A surprisingly large voltage generation in F/I/N and F/I/F junctions was observed, which is contradictory to the prediction from the standard spin-pumping theory. We proposed a theoretical formalism to study spin-pumping effects in ferromagnetic multilayer structures. The formalism can yield a remarkably clean physical picture of the spin and charge pumping in tunneling structures. The calculated values are consistent with experimental results.IEEE Transactions on Magnetics 11/2009; · 1.36 Impact Factor