6 - Spin-orbit torque magnetoresistive random-access memory (SOT-MRAM)

Abstract

Magnetoresistive random-access memory (MRAM) is becoming more and more attractive in industry because of its promising prospects for replacing or extending various well-developed memory technologies. It can fulfill not only the speed requirements of cache memory and dynamic random-access memory (DRAM) with additional nonvolatility but also the capacity demand of hard-disk drive (HDD) and solid-state drive (SSD). So far, much effort has been devoted to spin-transfer torque-based MRAM (STT-MRAM) in which the write and read operations share the same current path flowing through the tunnel barrier of magnetic tunnel junction (MTJ) which serves as the bit storage and readout element. Presently, this physical limit still leads to considerable write error rates, access time above ~10ns, aging of tunnel barriers, and suboptimal power consumption in MRAM. In this chapter, another MRAM technology, spin-orbit torque-based MRAM (SOT-MRAM) that can have significantly improved performance on these metrics by using decoupled read and write paths or by using novel materials with giant SOT effect, is reviewed. We first give an overview of the discovery of SOT and then focus on SOT-induced magnetization switching. The removal of applied external magnetic field during SOT switching and optimization of SOT materials are further discussed. Finally, the future trends of SOT-MRAM are discussed.