MTJ-based hybrid storage cells for 'normally-off and instant-on' computing

Besides increasing a computing throughput, multi-core processor architectures bring increased capacity of SRAM-based cache memory. As a result, cache memory now occupies large proportion of recent processor chips, becoming a major source of the leakage power consumption. The power gating technique applied on a SRAM cache is not efficient since it is paid by data loss. In this paper, we present two hybrid memory cells that combine a conventional volatile CMOS part with Magnetic Tunnel Junctions (MTJs) able to store a data bit in a non-volatile way. Being inherently non-volatile, these hybrid cells enable instantaneous power off and thus complete reduction of the leakage power. Moreover, given that the data bit can be stored in local MTJs and not in distant storage memories, these cells also offer instantaneous and efficient data retrieval. To demonstrate their functionality, the cells are designed using 28 nm FD-SOI technology for the CMOS part and 45 nm round spin transfer torque MTJs (STT-MTJs) with perpendicular magnetization anisotropy. We report the measured performances of the cells in terms of required silicon area, robustness, read/write speed and energy consumption.