Tunnel Magnetoresistance Effect in $\hbox {CoFeB/MgAlO}_{\rm x}/\hbox {CoFeB}$ Magnetic Tunnel Junctions

Magnetic tunnel junctions (MTJs) with the core structure of CoFeB/MgAlO_x/CoFeB were fabricated using magnetron sputtering technique. The MgAlO_x tunnel barrier was obtained by plasma oxidation of an Mg/Al bilayer in an Ar+O₂ atmosphere. Series of MTJs were fabricated with different Mg layer thicknesses (t_Mg), and Al layer thickness was fixed at 1.3 nm. The annealing effect on the tunneling magnetoresistance (TMR) ratio was investigated, and TMR ratio of 65% at room temperature (RT) was shown when it was annealed at 375 °C with the t_Mg=0.5 nm. The temperature dependence of conductance can be fit by the magnon-assisted tunneling model by adding spin independent tunneling contribution for the samples investigated here, and the spin independent conductance GSI varies with t_Mg, possibly due to less oxidation for thicker Mg layer.