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 advanced modeling techniques, we investigated the back-hopping effect in ultra-scaled STT-MRAM devices, defined as the unintended switching of the last part of the free layer, leading to an undesired 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. However, the observed back-hopping effect can also 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. Our studies on ultra-scaled STT-MRAM devices highlight the significant back-hopping effect which, when harnessed, can enable multi-bit cells with four distinct states, enhancing storage and functionality. These insights are pivotal for the design and optimization of future miniaturized spintronics devices.