Energy, latency, and lifetime improvements in MLC NVM with enhanced WOM code

Abstract

Non-volatile memories (NVMs), such as phase change memory (PCM) and resistive random access memory (ReRAM), have emerged as promising memory technologies for replacements of DRAM due to their advantages, such as better scalability, zero cell leakage, and DRAM-comparable read latency. Furthermore, multiple level cell (MLC) NVMs offer high data density and memory capacity over single level cell (SLC) NVM-s. However, the adoption of MLC NVMs is limited by their high programming energy and latency as well as the low endurance. In this paper, we propose an enhanced (23}2/4 WOM code for ML-C NVMs, which exploits the asymmetric characteristic in MLC NVM cell state transitions. Unlike the conventional WOM codes that focus on eliminating the worst-case latency writes, we propose to enlarge the best-case latency writes in MLC NVM cell state transitions. After data shaping with the enhanced WOM code, proportion of the best-case latency writes is maximized. In this way, the enhanced WOM code simultaneously reduces energy and latency, and improves lifetime with no memory and logic overheads. Evaluations show exciting improvement from the proposed approach.