Effect of Diffused B During Annealing on the Electronic Structure of the MgO Barrier in CoFeB/MgO/CoFeB Magnetic Tunnel Junctions

We investigate the chemical state and electronic structure of boron in the MgO layer in CoFeB/MgO/CoFeB magnetic tunnel junctions by synchrotron radiation X-ray photoelectron spectroscopy and first-principles calculations. In the top CoFeB, we observe three boron 1s peaks corresponding to oxidic, intermediate, and metallic boron. As the annealed films were etched, the B2O3 starts to appear together with the Mg 2p peak, indicating that boron atoms diffuse into the MgO barrier. Our calculations show that B impurities in the MgO barrier do not create any midgap states but reduce the MgO barrier height with the increase of boron concentration. (c) 2012 The Japan Society of Applied Physics