Device/Circuit/Architecture Co-Design of Reliable STT-MRAM

Spin transfer torque magnetic random access memory (STT-MRAM), using magnetic tunnel junctions (MTJ) has garnered significant attention in the research community due to its immense potential for on-chip, high-density and non-volatile memory. However, process variations may significantly impact the achievable yield in STT-MRAM. To this end, several yield enhancement techniques that improve STT-MRAM failures at the bit-cell, and at the architecture level of design abstraction have been proposed in the literature. However, these techniques may lead to a suboptimal design because they do not consider the impact of design choices at every level of design abstraction. In this paper, we propose a unified device-circuit-architecture co-design framework to optimize and enhance the yield of STT-MRAM. We studied the interaction between device parameters (viz. energy barrier height) and bit-cell level parameters ( viz. transistor width), together with different Error Correcting Codes (ECC) to optimize the robustness and energy efficiency of STT-MRAM cache. The advantages of our proposed approach to STT-MRAM design are explored at the 32nm technology node. We show that for a target yield of 500 Defects Per Million (DPM) for an example array with 64-bit word length, our proposed approach with realistic parameters can save up to 15% and 13% in cell area and total power consumption, respectively, in comparison with a design that does not use any array level yield enhancement technique.