A new in-field bad block detection scheme for NAND flash chips

A NAND flash system has been adopted as storage. However, due to its distinctive operation mechanisms, it endures only the limited number of program/Erase cycles. So, bad blocks are inevitably developed during the life time of the storage system. A bad block is a block that contains faulty bits that cannot be covered by ECC. In this paper, a novel in-field bad block detection scheme is proposed. Through simple write verifications, the proposed bad block detector finds bad blocks in real-time, and ensures that written data is reliable. The detection method includes neither costly data-mirroring nor complex ECC processing, but it requires an additional detection module of which size is less than 0.15% of the controller size.