A novel SPRAM (SPin-transfer torque RAM) with a synthetic ferrimagnetic free layer for higher immunity to read disturbance and reducing write-current dispersion

A novel SPRAM (spin-transfer torque RAM) consisting of MgO-barrier-based magnetic tunnel junctions (MTJs) with a synthetic ferrimagnetic (SyF) structure in a free layer was demonstrated for both higher immunity to read disturbance and a sufficient margin between the read and write currents. Since magnetization of the free layer becomes stable against thermal fluctuation with increasing thermal-stability factor E/k
_B
T, the SyF free layer of the MTJs realized a magnetic information retention of over 10 years due to its high E/k
_B
T of 67. Furthermore, it was found that the SyF free layer has an advantage of reducing dispersion of write-current density J
_c
, which is necessary for securing an adequate margin between the read and write currents.