Flash Memory Block Usability Management via Cell Type Detection
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Solution Overview
Problem
Flash memory cells degrade over time, making them unusable due to changes in erasure and program threshold voltages, especially in multi-level cells, leading to data loss and reduced storage capacity, which existing error detection and correction methods struggle to manage effectively.
Innovation Solution
A method to determine the type of cells in a block upon error detection and selectively change cell type and bad block indicators to manage the block's usability, allowing for a copy back operation and adjusting storage capacity indicators to mitigate degradation, thereby preventing complete unusability and maintaining storage capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If error detection and correction methods are used to manage flash memory blocks, then data integrity is improved, but cell degradation still leads to complete unusability and storage capacity loss
Solution Approach 1:
The flash memory block is segmented into multiple sub-blocks, allowing the system to identify and isolate degraded cells within specific sub-blocks while keeping other sub-blocks functional. This segmentation enables partial usage of degraded blocks rather than complete abandonment, thereby preserving storage capacity while maintaining data integrity through targeted error management.
Solution Approach 2:
The patent applies local quality by treating different sub-blocks within a flash memory block differently based on their degradation status. Instead of uniformly marking the entire block as bad, the system selectively identifies degraded regions and applies error correction or isolation measures only to affected areas, allowing healthy portions to continue functioning and thus preventing complete storage capacity loss.
2Quantity of substance
If multi-level cells are used to increase storage capacity, then storage density is improved, but cell degradation occurs more rapidly leading to earlier unusability
Solution Approach 1:
The system performs preliminary monitoring and detection of cell degradation trends in multi-level cells before they become completely unusable. By detecting threshold voltage shifts and degradation patterns early, the system can proactively relocate data, refresh affected cells, or isolate degraded sub-blocks, thereby extending the operational lifespan of multi-level cells while maintaining their high storage density advantage.
Solution Approach 2:
The patent implements feedback mechanisms that continuously monitor the health status of multi-level cells, tracking threshold voltage changes and error rates. This feedback information is used to dynamically adjust error correction thresholds, trigger data relocation operations, or mark sub-blocks for isolation, creating a closed-loop system that extends cell lifespan while preserving the high storage capacity of multi-level architecture.
3Reliability
If bad block flags are set to mark unusable blocks, then data integrity is maintained, but storage capacity is reduced due to complete block abandonment
Solution Approach 1:
Instead of marking entire blocks as bad when degradation is detected, the patent segments the block into sub-blocks and applies bad block flags only to the specific degraded sub-blocks. This granular approach allows the remaining healthy sub-blocks within the same physical block to continue being used, significantly increasing the amount of usable storage capacity while maintaining data integrity through selective isolation of only the necessary degraded portions.
Data Source
AI summary
One embodiment of the method includes determining a type of cells in a block of the flash memory if an error is detected in at least a portion of the block, and selectively changing one of a cell type indicator and a bad block indicator associated with the block based on the determined type of cells in the block. The cell type indicator indicates a type of the cells in the associated block, and the bad block indicator indicates whether the associated block is a usable block.