The SOT-MRAM Pioneer

MAGNETIC TUNNEL JUNCTION (MTJ)

A magnetic tunnel junction is composed of two ferromagnetic layers separated by a thin insulating (tunnel) barrier. The MTJ stores the binary memory value as the magnetization direction of one of the ferromagnetic thin films, which is called the “Free Layer”. The other ferromagnetic layer is called the “Fixed Layer”(or “Reference Layer”) for its magnetization never moves. The electric resistance of the MTJ is larger when the magnetizations of the two ferromagnetic layers are antiparallel (coding a “0”), while it is lower when the two magnetizations are parallel (coding a “1”). This effect is called tunnel magnetoresistance and is used for reading the data. Writing consists of switching the magnetization of the free layer from one direction to the other, which can be done by a magnetic field, STT or SOT.

SOT uses the same core MTJ as the existing STT and can thus be easily implemented in the same manufacturing environment as STT.