Shaped Data Decoding for Flash Memory Wear Balance
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Solution Overview
Problem
Conventional flash memory systems face reduced data retention and increased failure rates due to wear of oxide isolation layers, especially in NAND-based flash memory, where shaped data with imbalanced bit error rates can lead to unbalanced bit error rates between logical pages, compromising MLC error rates and SLC endurance.
Innovation Solution
Improved decoding methods for shaped data that utilize statistics to generate correction values for soft metrics, enabling more accurate initial reliability estimates and enhanced error correction capabilities, thereby improving data retention and reducing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If data is shaped to increase the proportion of 1-s (erase state) in flash memory, then the useful life of flash memory is extended and wear is reduced, but unbalanced bit error rates between logical pages occur in MLC partitions
Solution Approach 1:
The patent applies parameter changes by adjusting the distribution of bit values in shaped data to achieve a more balanced distribution across logical pages. Specifically, the system modifies the shaping process to control the proportion of 1-s and 0-s in different logical pages, thereby balancing bit error rates while maintaining the overall benefit of extended flash memory life through reduced wear on erase cycles.
2Reliability
If conventional decoding methods are used for shaped data, then decoding simplicity is maintained, but error correction capability is insufficient and data retention is reduced
Solution Approach 1:
The patent implements preliminary action by performing data shaping before storage that anticipates and compensates for future bit error rate imbalances. The shaping process is designed in advance to create a more uniform distribution of 1-s and 0-s across logical pages, which preemptively reduces bit error rates during read operations, thereby improving data retention without requiring complex decoding mechanisms.
3Productivity
If SLC cache is used for fast programming, then programming speed is improved, but the SLC partition becomes susceptible to wearing and limits system useful life
Solution Approach 1:
The patent applies local quality by treating different logical pages within the SLC cache differently through controlled data shaping. By adjusting the bit distribution locally in each logical page to achieve more balanced 1-s and 0-s proportions, the system reduces wear on specific pages that would otherwise be heavily used, thereby extending the overall endurance of the SLC partition while maintaining fast programming capabilities.
Data Source
AI summary
Systems and methods of encoding and decoding shaped data include determining a bit representation corresponding to a bit in a representation of a codeword that is read from a non-volatile memory of a data storage device. A soft metric corresponding to the bit representation is determined at least partially based on an amount of shaping of data.