Improving the reliability of MLC NAND flash memories through adaptive data refresh and error control coding

Chengen Yang, Hsing Min Chen, Trevor N. Mudge, Chaitali Chakrabarti

Research output: Contribution to journalArticle

7 Scopus citations

Abstract

NAND Flash memory has become the most widely used non-volatile memory technology. We focus on multi-level cell (MLC) NAND Flash memories because they have high storage density. Unfortunately MLC NAND Flash memory also has reliability problems due to narrower threshold voltage gap between logical states. Errors in these memories can be classified into data retention (DR) errors and program interference (PI) errors. DR errors are dominant if the data storage time is longer than 1 day and these errors can be reduced by refreshing the data. PI errors are dominant if the data storage time is less than 1 day and these errors can be handled by error control coding (ECC). In this paper we propose a combination of data refresh policies and low cost ECC schemes that are cognizant of application characteristics to address the errors in MLC NAND Flash memories. First, we use Gray code based encoding to reduce the error rates in the four subpages (MSB-even, LSB-even, MSB-odd, LSB-odd) of a 2-bit MLC NAND Flash memory. Next, we apply data refresh techniques where the refresh interval is a function of the program/erase (P/E) frequency of the application. We show that an appropriate choice of refresh interval and BCH based ECC scheme can minimize memory energy while satisfying the reliability constraint.

Original languageEnglish (US)
Pages (from-to)225-234
Number of pages10
JournalJournal of Signal Processing Systems
Volume76
Issue number3
DOIs
StatePublished - Sep 2014

Keywords

  • Data refresh
  • Data retention error
  • ECC
  • MLC NAND Flash
  • Program interferences error

ASJC Scopus subject areas

  • Control and Systems Engineering
  • Theoretical Computer Science
  • Signal Processing
  • Information Systems
  • Modeling and Simulation
  • Hardware and Architecture

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