Exploiting Resistance Drift Characteristics to Improve Reliability of LDPC-Assisted Phase-Change Memory

Abstract

Phase-change memory (PCM) as emerging non-volatile memory has attracted more attention and considered as the promising replacement of the main memory. PCM has shown good scalability and high storage density, but data storage reliability has become a challenge and concern. When data are written into PCM cells by a phase transition between amorphous and crystalline, the resistance of each state drifts as the increase of storage time due to structural relaxation. As a result, raw bit error rates (RBER) become higher and higher, severely degrading the data storage reliability (i.e., an important problem in PCM). In this paper, we first find that high error percentage exists between the full amorphous and amorphous states in multilevel cell (MLC) PCM via a preliminary experiment, which is the main factor leading to high RBER. Then, we analyze why this phenomenon exists in PCM from the view of the resistance drift. Finally, by exploiting the resistance drift characteristics, we propose drift compensation and drift-aware LDPC decoding schemes to improve reliability of PCM. Simulation results show that the proposed schemes can significantly reduce the RBER and LDPC decoding iterations.