NAND Flash Data Page Management for Voltage Disturbance Mitigation
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Solution Overview
Problem
NAND flash memory devices experience frequent errors in data pages closest to the source select line (SSL) and drain select line (DSL due to voltage disturbances and stress, leading to reduced data retention and programming efficiency.
Innovation Solution
Differentiate the data pages near the SSL and DSL by using techniques such as downgrading NAND memory cell usage, employing different error correcting codes, data compression, weighted wear leveling, and varying data page utilization scheduling, and configuring multi-level NAND memory cells as single-level cells for specific pages after a predetermined number of cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If data is stored in data pages closest to SSL and DSL, then storage capacity is utilized, but error frequency increases due to voltage disturbances and stress
Solution Approach 1:
The patent applies local quality by differentiating management strategies for different data page regions. Data pages closest to SSL and DSL (first and second sets) are managed differently from remaining data pages (third set). Specifically, the first and second sets use SLC mode with stronger ECC protection, while the third set uses MLC mode, optimizing reliability for pages exposed to harmful voltage disturbances and stress near the select lines
Solution Approach 2:
The patent changes operational parameters based on location. Multi-level NAND memory cells are configured as single-level cells for data pages in the first and second sets (near SSL and DSL) after a predetermined number of programming and erase cycles, while remaining pages continue using multi-level configuration. This parameter change adapts the memory cells to withstand the harsher electrical conditions near the select lines
2Reliability
If multi-level NAND memory cells are used for all data pages, then storage density is maximized, but data retention deteriorates in pages near SSL and DSL
Solution Approach 1:
The patent segments the plurality of data pages into three distinct sets: a first set closest to SSL, a second set closest to DSL, and a third set of remaining pages. This segmentation allows differentiated configuration management where the first and second sets use SLC mode with enhanced protection, while the third set uses MLC mode, balancing data retention with manageable complexity
Solution Approach 2:
The patent implements dynamic configuration of memory cells based on operational cycles and location. Multi-level NAND memory cells are dynamically switched between SLC and MLC modes depending on the number of programming and erase cycles performed and their proximity to SSL/DSL. This dynamic adaptation optimizes data retention while managing the complexity of configuration through automated cycle-based transitions
3Reliability
If uniform wear leveling is applied across all data pages, then simplicity is maintained, but wear distribution becomes uneven due to differential stress near SSL and DSL
Solution Approach 1:
The patent applies local quality to wear leveling by implementing weighted wear leveling that accounts for location-specific stress. Data pages in the first and second sets (near SSL and DSL) are assigned different wear weights compared to the third set, reflecting the differential stress and error susceptibility. This localized approach ensures more accurate wear distribution while managing algorithmic complexity through position-based weighting factors
Data Source
AI summary
Embodiments of the present disclosure provide methods and apparatus for providing a NAND flash memory arrangement that comprises a source select line (SSL), a drain select line (DSL) and a plurality of NAND memory cells arranged to provide a plurality of data pages. The method further includes defining a first set of data pages in close proximity to the SSL, defining a second set of data pages in close proximity to the DSL, and differentiating the first set of data pages and the second set of data pages from at least the remaining data pages.