Multi-level cell (MLC) is an efficient solution to improve the storage density of the MRAM. However, the conventional spin transfer torque-based MLC (STT-MLC) suffers from the performance bottlenecks such as high write energy and complicated two-step operation. In this work, we propose a spin Hall effect-based MLC (SHE-MLC) to overcome these bottlenecks. In the SHE-MLC structure, the write current does not pass the MTJ, which avoids the barrier breakdown and reduces the write energy. Moreover, the written data is only dependent on the direction of the write current, thus the two-step operation is not required. Simulation results demonstrate that, under the same access transistor size, e.g. 600 nm, the proposed SHE-MLC can achieve 55× faster write operation and 58× lower write energy than the conventional STT-MLC.
['Q. Shi', 'Zhaohao Wang', 'Yuqian Gao', 'Liang Chang', 'Wang Kang', 'Youguang Zhang', 'Weisheng Zhao']
A spin Hall effect-based multi-level cell for MRAM