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

摘要

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 (V-REF) 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.