Reset elimination and dispersion encoding for alleviating write disturbance of phase-change memory

Abstract

Phase-change memory (PCM) is an emerging mechanism to resolve the scalability problems of dynamic random access memory (DRAM). However, with its scaling down below 20nm, PCM suffers from a write-disturbance (WD) problem in which cells lose their ‘0 (ReSET)’ state. WD occurs with the high thermal disturbance of the ReSET current when a cell changes from ‘1 (SET)’ to ‘0 (ReSET)’ and an adjacent cell is in ‘0 (ReSET)’ state. Therefore, reducing the contiguous ‘0 (ReSET)’ pattern can alleviate WD. We propose ReSET elimination and dispersion (RED) encoding for alleviating the WD in PCM. RED alleviates WD by reducing WD patterns regardless of direction, and minimizes error-correcting costs. RED reduces WD patterns by increasing the number of ‘1 (SET)’ utilizing data locality in the memory line. Additionally, RED scatters the consecutive zeros through a new data mapping policy. Our experimental results demonstrate that RED reduces the bit overhead for error correction from 21.2% to 9% by reducing WD up to 55.5% more than prior work on average.