Multi-level Operation in Ultra-scaled MRAM

Abstract

Magnetoresistive random access memory (MRAM) prototypes demonstrate fast operation and are suitable for the last level caches. MRAM possesses high endurance, long retention, and requires less masks for fabrication than its competitor flash memory. MRAM is nonvolatile and scalable. Strong perpendicular magnetic anisotropy in most advanced single-digit nanoscale footprint devices is enhanced by elongating the magnetic layers. To facilitate the switching and to increase the interface-induced magnetic anisotropy even further, the free magnetic layers are made of several elongated pieces separated by tunnel barriers with multiple interfaces. To properly model such devices, accurate evaluation of the spin-transfer torques is required. The interfacial and bulk-torques are not independent, and the use of a spin-charge transport approach coupled to the magnetization dynamics allowing to treat the torques on equal footing in magnetic tunnel junctions with elongated layers becomes mandatory. By employing this advanced modeling approach a multi-level memory operation in an ultra-scaled MRAM cell with a composite free layer is demonstrated.