Domain Wall Memory-Layout, Circuit and Synergistic Systems

Abstract

Domain wall memory (DWM) is gaining significant attention for embedded cache application due to low standby power, excellent retention, and ability to store multiple bits per cell. Additionally, it provides fast access time, good endurance, and good retention. However, it suffers from poor write latency, shift latency, shift power, and write power. DWM is sequential in nature and latency of read/write operations depends on the offset of the bit from the read/write head. This paper investigates the circuit design challenges such as bitcell layout, head positioning, utilization factor of the nanowire, shift power, shift latency, and provides solutions to deal with these issues. A synergistic system is proposed by combining circuit techniques such as merged read/write heads (for compact layout), flipped-bitcell and shift gating (for shift power optimization), wordline strapping (for access latency), shift circuit design with two micro-architectural techniques: 1) segmented cache and 2) workload-aware dynamic shift and write current boosting to realize energy-efficient and robust DWM cache. Simulations show 3-33% performance and 1.2-14.4X power consumption improvement for cache segregation and 2.5-31% performance and 1.3-14.9X power enhancement for dynamic current boosting over a wide range of PARSEC benchmarks.