Switching methods in magnetic random access memory for low power applications

摘要

Effect of saturation magnetization (M-s) of the free layer (FL) on the switching current is analyzed for spin transfer torque (STT) magnetic random access memory (MRAM). For in-plane FL, critical switching current (I-c0) decreases as Ms decreases. However, reduction in Ms also results in a low thermal stability factor (Delta), which must be compensated through increasing shape anisotropy, thus limiting scalability. For perpendicular FL, I-c0 reduction by using low-M-s materials is actually at the expense of data retention. To save energy consumed by STT current, two electric field (EF) controlled switching methods are proposed. Our simulation results show that elliptical FL can be switched by an EF pulse with a suitable width. However, it is difficult to implement this type of switching in real MRAM devices due to the distribution of the required switching pulse widths. A reliable switching method is to use an Oersted field guided switching. Our simulation and experimental results show that the bi-directional magnetization switching could be realized by an EF with an external field as low as +/- 5 Oe if the offset field could be removed.