Write and Read Frequency-Based Word-Line Batch $V_{\mathrm{TH}}$ Modulation for 2-D and 3-D-TLC NAND Flash Memories
Yoshiaki Deguchi, Shun Suzuki, Ken Takeuchi · IEEE Journal of Solid-State Circuits · 2018
As a comprehensive solution based on the data access frequency, this paper proposes word-line batch VTHmodulation (WBVM) to improve the reliability of 2-D and 3-D-triple-level-cell (TLC) nand flash memories. Proposed WBVM modulates the threshold voltage (VTH) distribution and decreases errors of frequently written/erased “write-hot data,” infrequently written or read “writeand read-cold data,” and frequently read “read-hot data.” For write-hot data, the proposed WBVM VTHscore modulation suppresses the degradation of the tunnel oxide, which is caused by programming higher VTHstate. On the other hand, for writeand read-cold and read-hot data, the proposed WBVM bit error rate (BER) score modulation reduces errors during data retention and read cycles. Moreover, for archive memory, the proposed BER score nLC-modulation achieves the higher reliability by expanding the read margin of the least reliable VTHstate. As a result, the proposed WBVM realizes the comprehensive reliability enhancement for write-hot, write and read-cold, and read-hot data of 2-D and 3-D-TLC nand flash. WBVM extends the acceptable write/erase cycles, the acceptable data-retention time, and the acceptable read cycles by up to 1.8×, 45×, and 4.7×, respectively.