Control of Switching Current Asymmetry by Magnetostatic Field in MgO-Based Magnetic Tunnel Junctions

The inherent switching current asymmetry (beta) pertaining to ordinary magnetic tunnel junctions (MTJs) significantly reduces the write margin of spin-transfer-torque magnetoresistive random access memory (STT-MRAM). In this letter, we report how beta can be controlled by the effective magnetostatic field (
H

_e
) that develops along the easy axis of the MTJs. As
H

_e
is varied by 24% of the effective uniaxial anisotropy field, beta measured at 100 ns is reduced from 1.51 to 1.04. The results suggest that tuning the magnetostatic offset field (
H

_off
) arising from the dipolar coupling between adjacent ferromagnetic layers can control beta and improve the write margin of STT-MRAM.