Tuning the oxygen ratio in perpendicular magnetic tunnel junctions with MgAl₂O₄ barriers

MgO is the barrier of choice for modern magnetic tunnel junctions (MTJs). However, the lattice parameter of MgO cannot be tuned to match with other ferromagnetic materials which limits the practical application of MTJ devices. Therefore, the exploration of other barriers with the tunable lattice parameter is important to design the energy efficient MTJs. Here we present our study on perpendicular MTJs with MgAl₂O₄ barrier. A unique three steps deposition process has been employed to enhance the O₂ concentration in the barrier, without over-oxidizing the bottom CoFeB electrode. As a result, the TMR ratio greater than 60 % is achieved for the first time in perpendicular MTJs with MgAl₂O₄-barrier. An interfacial perpendicular magnetic anisotropy energy density of 2.25 mJ/m² is obtained for the samples annealed at 400°C. The V_half, bias voltage at which the tunneling magnetoresistance drops to half of the zero-bias value, is found to be about 1V, which is substantially higher than that of MgO-based junctions.