System-level read disturb suppression techniques of TLC NAND flash memories for Read-Hot/Cold data mixed applications

• Published in: Solid-state electronics Vol. 147; pp. 63 - 77
• Main Authors: Watanabe, Hikaru, Deguchi, Yoshiaki, Kobayashi, Atsuro, Matsui, Chihiro, Takeuchi, Ken
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.09.2018
• Subjects: Bit-error rate (BER); Error-correcting code (ECC); NAND flash memory; Read-disturb error; Solid-state drive (SSD); Triple-level cell (TLC); NAND flash memory; Solid-state drive (SSD); Read-disturb error; Bit-error rate (BER); Triple-level cell (TLC); Error-correcting code (ECC)
• ISSN: 0038-1101; 1879-2405
• DOI: 10.1016/j.sse.2018.05.004

•Four techniques are proposed for data center application solid-state drives (SSDs).•This paper proposes the versatile control techniques for 1Xnm triple level cell (TLC) NAND flash.•By combining all of these techniques, the reliability of TLC NAND flash is enhanced for both read-hot and cold data. In this paper, versatile triple-level cell (TLC) NAND flash memory control with four proposed techniques, Read-Hot/Cold Migration, Read Voltage Control (RVC), Edge Word-Line Protection (EWLP), and Worst Page Detection (WPD), is proposed for data center application solid-state drives (SSDs). To apply the optimal reliability enhancement techniques for stored data, first proposal of Read-Hot/Cold Migration separates read-hot/cold data into each region. Then, second proposal, Read Voltage Control applies the optimal read reference voltages (VREF) for each read-hot/cold region to improve the overall reliability of TLC NAND flash. Third proposal, Edge Word-Line Protection reduces the bit error rate (BER) of the edge word-lines (WLs), which have the worst reliability in read-hot data as reported in this paper. Finally, Worst Page Detection is proposed to predict the worst page BER in a block precisely to prevent judging entire block as bad and optimizes the refresh interval of read-hot block. By combining all of these techniques, the reliability of TLC NAND flash is enhanced for both read-hot and cold data.