Annealing temperature window for tunneling magnetoresistance and spin torque switching in CoFeB/MgO/CoFeB perpendicular magnetic tunnel junctions

Annealing temperature (T_a) and free layer thickness dependencies of magnetic properties and spin-transfer torque switching were investigated in CoFeB-MgO based magnetic tunnel junctions with perpendicular magnetic anisotropy (PMA). Annealing process was found to be critical to buildup PMA. As T _a increases, switching field of free layer and reference layer is enhanced first then drops, corresponding to the improvement and collapse of PMA in both layers. However, it should be noted that PMA of free layer and the tunneling magnetoresistive (TMR) are maximized at different T_a zones. Spin transfer torque study pointed out that switching current density (J _c) depends on the combined effects from PMA, spin polarization, and saturation magnetization, which all depend on T_a values. Thickness dependence study revealed that J_c relies on the competing results of the thickness and PMA. The lowest critical switching current density achieved is 2.1 MA/cm², accompanied with a TMR around 52 at room temperature.