1+1>2: variation-aware lifetime enhancement for embedded 3D NAND flash systems

Abstract

Three-dimensional (3D) NAND flash has been developed to boost the storage capacity by stacking memory cells vertically. One critical characteristic of 3D NAND flash is its large endurance variation. With this characteristic, the lifetime will be determined by the unit with the worst endurance. However, few works can exploit the variations with acceptable overhead for lifetime improvement. In this paper, a variation-aware lifetime improvement framework is proposed. The basic idea is motivated by an observation that there is an elegant matching between unit endurance and wearing variations when wear leveling and implicit compression are applied together. To achieve the matching goal, the framework is designed from three-type-unit levels, including cell, line, and block, respectively. Series of evaluations are conducted, and the evaluation results show that the lifetime improvement is encouraging, better than that of the combination with the state-of-the-art schemes.