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Blocks of 3D-NAND flash memory are programmed in order of WL. In real usage of 3D-NAND flash memory, a block contains both programmed WLs and not programmed WLs because the programmed data do not always fill the block. In the block, the last data are programmed at 'last-programmed WL' where the upper WL is not programmed. The last programmed data are supposed to have high reliability owing to shorter data-retention time. However, when upper WL is not programmed, BER of last-programmed WL largely increases because upper WL has less electrons and causes lateral charge migration. To suppress the errors at last-programmed word-line, this paper proposes Last-programmed Word-line Protection (LWLP). Proposed LWLP suppresses BER by 37% at last-programmed WL and extends data-retention time by more than 4 times.

Read-disturb Modeled Artificial Neural Network Coupled LDPC ECC (RDNN-LDPC) is proposed to correct errors of read-hot data for 3D-TLC NAND flash. Conventional ANN-LDPC is optimized to correct errors of read-cold data. However, ANN-LDPC does not correct errors of read-hot data. To correct errors of read-hot data, this paper analyzes how input parameter and model change. As a result, measured results of proposed RDNN-LDPC extend acceptable read cycle of 3D-TLC NAND flash by 10-times.