Reduce Refresh Operations on 3-D TLC nand Flash System via Wordline (WL) Interference

As the storage density of 3-D NAND flash memory increases, reliability issues become a bottleneck. Among all reliability issues, decreased retention time is the dominant one. To extend the retention time, data refresh is a straightforward approach. However, refresh operations introduce redundant operations, which hurt the performance of the 3-D NAND flash system. With the observation that retention time can be extended by wordline (WL) interference, this letter first proposes to extend retention time with WL interference practically, and then presents a refresh scheme, which refreshes only one-third of pages in a block and postpones the refresh on the remaining two-thirds of pages with WI. The evaluation results show that the refresh operations are reduced by 40.7% at most. Compared with previous work, the read and write response times are decreased by 31.2% and 43.5%, respectively, with a 7-day refresh period.