Adaptive ECC Techniques for Reliability and Yield Enhancement of Phase Change Memory

The yield and reliability issues are important challenges for the emerging phase change memory (PCM). Hard repair techniques based on fault replacement and error correction codes are usually used to cure these dilemmas. However, the probability of occurring permanent faults is low and soft errors are not a main threat for PCM, equipping ECC for each data word will waste a lot of storage space. Therefore, an adaptive ECC technique is proposed to solve this drawback. The main idea is to equip ECC for memory words when they are detected faulty. A separated ECC DRAM is used for storing the check bits. According to experimental results, the degradation of repair rate is almost negligible. However, the hardware overhead is at least 70% lower than the original ECC technique.