A multi-level cell for ultra-scaled STT-MRAM realized by back-hopping

Abstract

The development of advanced magnetic tunnel junctions with a footprint in the single-digit nanometer range can be achieved using structures with an elongated and composite ferromagnetic free layer. Using the spin drift-diffusion model, we investigated the back-hopping effect in ultra-scaled STT-MRAM devices. Unwanted switching of the last layer of the structure has been identified as a possible cause of the back-hopping effect, which leads to a writing error in the magnetization state of the free layer. To understand the switching of the free layer, the torque acting on both parts of the composite free layer must be studied in detail. A reduction in the size of MRAM components to increase the memory density may lead to back-hopping. Moreover, the observed back-hopping effect can be exploited for the realization of multi-level cells. For this purpose, we have carefully investigated the switching behavior of a device with several tunnel barrier interfaces and a few nanometers in diameter, in particular the impact of changes in the material parameters.