An adaptive ECC scheme for dynamic protection of NAND Flash memories

Liu Yuan, Huaida Liu, Pingui Jia, Yiping Yang

Abstract: Error correcting code (ECC) is an essential method in protection of NAND Flash memories. Complexity of it is increasing rapidly with the increment of error correction capability. Traditionally, the software implementation of ECC which has less cost and high flexibility is nearly ignored due to its inefficiency. This situation can be changed by design of faster software-based ECC scheme. We have found that the reliability is constantly changing with Program/Erase cycles and retention time during the lifetime of memories. However, regular ECC methods fail to take into account the variable kinds of reliability and result in a great waste of computations. In order to achieve better software implementation, an adaptive ECC scheme is proposed to provide various amount of protection. By assigning appropriate ECC, an adaptive ECC with Hamming and more efficient BCH codes is designed to provide corresponding protection. Proposed ECC scheme is suitable for diverse devices and applications. The coding time can be obviously decreased, making it possible to replace hardware methods with software methods.