Influence of Chemical Composition of CoFeB on Tunneling Magnetoresistance and Microstructure in Polycrystalline CoFeB/MgO/CoFeB Magnetic Tunnel Junctions

Abstract

We report, for the first time, the correlation between tunneling magnetoresistance (TMR) and the microstructure of polycrystalline CoFeB/MgO/CoFeB magnetic tunnel junctions with various Co/Fe ratios in the (CoFe)81B19 reference and free layers. It is found that the Co/Fe ratio in the (CoFe)81B19 reference layer strongly affects the (001) out-of-plane texture of the MgO tunnel barrier, resulting in the variation in TMR ratio. Further microstructure characterization of the magnetic tunnel junction with a higher TMR ratio and a stronger (001) out-of-plane texture in the MgO tunnel barrier reveals a grain-to-grain lattice match between the crystallized bcc CoFeB reference layer and MgO with a 45° rotational epitaxial relationship, that is, CoFeB(001)[110]∥MgO(001)[100].