Advanced error-prediction LDPC with temperature compensation for highly reliable SSDs. (September 2015)

• Record Type: Journal Article
• Authors: Tokutomi, Tsukasa; Tanakamaru, Shuhei; Iwasaki, Tomoko Ogura; Takeuchi, Ken
• Is Part Of: Solid-state electronics. Volume 111(2015)
• Page Start: 129
• Page End: 140
• Publication Date: 2015-09
• Subjects: NAND Flash memory -- Solid-state drive (SSD) -- Low-density-parity-check (LDPC) -- Error-correcting code (ECC); Semiconductors -- Periodicals; Semiconducteurs -- Périodiques; 621.38152
• DOI: 10.1016/j.sse.2015.05.034
• Languages: English
• ISSNs: 0038-1101

Abstract

Highlights: The effects of AEP-LDPC are investigated in a 2×nm TLC NAND Flash memory. Compared with conventional BCH, data-retention time is extended by 12×. AEP-LDPC can correct errors with pre-determined tables made at higher temperature. It is found that one table can cover behavior over a range of temperatures. The total table size can be reduced, which makes this approach more practical. Abstract: To improve the reliability of NAND Flash memory based solid-state drives (SSDs), error-prediction LDPC (EP-LDPC) has been proposed for multi-level-cell (MLC) NAND Flash memory (Tanakamaru et al., 2012, 2013), which is effective for long retention times. However, EP-LDPC is not as effective for triple-level cell (TLC) NAND Flash memory, because TLC NAND Flash has higher error rates and is more sensitive to program-disturb error. Therefore, advanced error-prediction LDPC (AEP-LDPC) has been proposed for TLC NAND Flash memory (Tokutomi et al., 2014). AEP-LDPC can correct errors more accurately by precisely describing the error phenomena. In this paper, the effects of AEP-LDPC are investigated in a 2×nm TLC NAND Flash memory with temperature characterization. Compared with LDPC-with-BER-only, the SSD's data-retention time is increased by 3.4× and 9.5× at room-temperature (RT) and 85 °C, respectively. Similarly, the acceptable BER is increased by 1.8× and 2.3×, respectively. Moreover, AEP-LDPC can correct errors with pre-determined tables made at higher temperatures to shorten the measurement time before shipping. Furthermore, it is found that one table can cover behavior over a range of temperatures in AEP-LDPC. As a result, the total table size can be reduced to 777 kBytes, which makes this approach more practical.