Flash session 4: Flash Reliability
By Avi Klein, Senior
Principal Engineer, Memory Technology Strategy
Video | Duration: 10:24 min |
This session discusses why reliability is critical for flash
memory, the major reliability challenges - data retention,
endurance; disturb errors and bad blocks - and how they are being
overcome.
Chapter 1: Introduction
Introduces the topics to be discussed in this session. Defines
reliability as it relates to flash memory, and why reliability
matters to users of computer electronic devices, USB flash drives
and computers. Defines terms that describe the major challenges to
flash reliability: data retention, endurance, disturbs or bit flip
errors and bad blocks.
Chapter 2: Flash Operation in Brief and
Functionality
Summarizes the basics of flash operation, detailed in a session
dedicated to this topic (link to Flash Operation). Points out the
unique functionality of flash vs. other ICs, its exposure to high
electrical fields, its sensitivity to electron loss, and the
associated reliability challenges.
Chapter 3: Major Flash Reliability
Challenges
Discusses data retention, including how insulating oxide layers
prevent leakage of the stored charge, and the use of testing to
extrapolate data retention rates over time. Presents the challenges
of endurance, and the effect of repeated write/erase cycles.
Describes the nature and occurrence of write, read and erase
disturb errors. Discusses bad blocks that are both intrinsic to
flash and are created over the flash lifecycle.
Chapter 4: Overcoming Flash Reliability
Challenges
Describes error detection and error correction code (EDC/ECC), and
the difference in effectiveness of applying 4-bit vs. 6-bit ECC to
extend the flash lifecycle. Discusses the correlation between data
retention and endurance. Explains how wear-leveling operates to
distribute workload evenly over all blocks to prevent early
failure. Presents bad block management, and describes how it
operates to prevent the usage of bad blocks.
Chapter 5: Summary
Reviews the subjects discussed in the presentation, including a
definition of reliability, basic flash operation, the major
challenges to flash reliability, and how these challenges are
overcome to improve the flash reliability while extending its
lifespan.
Keywords
Flash reliability, Data retention, Endurance, Error Detection Code
(EDC), Error Correction Code (ECC), Bad blocks, Disturb errors, Bit
flip errors, Bad block management, Wear-leveling