Switching Current Dispersion in Magnetic Memory Bits Due to Inhomogeneity of Perpendicular Anisotropy

The switching current density in a bit of spin transfer torque magnetic random access memory (STT-MRAM) has to be <;1 MA/cm² for realistic application. The STT-MRAM using CoFeB magnetic tunnel junctions (MTJs) with perpendicular anisotropy are possible to match this target. In this paper, the switching properties in this system are investigated by a micromagnetic model. To simulate the perpendicular and in-plane hysteresis loops correctly, inhomogeneity of the perpendicular interfacial anisotropy constant K is introduced to the free layer of the MTJ. The calculated resistance versus applied current density curves of the bits are highly asymmetric, which agrees with experiment. The critical switching currents have dispersion due to the inhomogeneity of K. In addition, the simulation confirms the nucleation-type reversal process, and the reversal time decreases with increasing applied current.