Flash Memory Block Retirement Policy for Read Error Management
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Solution Overview
Problem
Flash memory devices experience data errors due to factors like data retention, cross-temperature issues, and read disturb errors, which can be exacerbated in mobile and automotive applications with varying operating temperatures, affecting memory cell reliability and storage integrity.
Innovation Solution
A memory block retirement policy is implemented, where read errors are tested to determine if they are temporary or permanent, with data from error-prone blocks being copied to a new block and the original block either returned to service or permanently retired based on iterative testing and error thresholds, using a memory controller to manage erasing, programming, and reading processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If flash memory blocks are used for storage, then storage capacity is provided, but read errors occur due to data retention issues, cross-temperature effects, and read disturb errors
Solution Approach 1:
The flash memory array is divided into multiple blocks, each with its own error tracking and management. When read errors are detected in a specific block, only that block is isolated and retired, while other blocks continue to operate normally. This segmentation allows the system to maintain overall storage capacity while addressing reliability issues in affected areas.
Solution Approach 2:
Blocks exhibiting permanent read errors are extracted from the active storage pool and permanently retired. The system identifies problematic blocks through iterative testing and removes them from service, transferring their data to healthy blocks. This extraction process maintains data integrity by removing sources of errors while preserving the functionality of remaining blocks.
2Reliability
If memory blocks experiencing read errors are permanently retired, then data integrity is maintained, but available storage capacity decreases
Solution Approach 1:
The system dynamically determines the fate of error-prone blocks through iterative reading and error analysis. Rather than immediately retiring blocks, the system performs multiple read cycles to distinguish between temporary and permanent errors. Blocks showing transient errors may be returned to service, while only blocks with persistent errors are retired. This dynamic approach optimizes the balance between data integrity and available capacity.
Solution Approach 2:
The system implements continuous feedback through iterative reading of memory blocks to monitor error patterns. By repeatedly reading blocks and analyzing error characteristics, the system builds a feedback loop that identifies permanent failures versus temporary issues. This feedback mechanism ensures that only truly defective blocks are permanently retired, maximizing the utilization of available storage capacity while maintaining data integrity.
3Reliability
If iterative testing is performed to distinguish temporary and permanent errors, then accurate block retirement decisions are made, but processing time increases
Solution Approach 1:
The system performs a limited number of iterative read cycles rather than exhaustive testing. By conducting a predetermined number of read operations (e.g., three iterations), the system achieves sufficient accuracy to distinguish between temporary and permanent errors without undertaking overly time-consuming analysis. This partial action approach balances reliability with processing time by using enough iterations to make accurate decisions while avoiding excessive testing overhead.
Data Source
AI summary
Devices and techniques for a flash memory block retirement policy are disclosed herein. In an example embodiment, a first memory block is provisionally removed from service in response to encountering read errors in the first memory block. Memory pages of the first memory block are tested in a second mode comprising reading memory pages at different read voltages. A raw bit error rate (RBER) or a read window budget (RWB) is determined for memory pages at the different read voltages and the provisionally removed first memory block is returned to service or retired based on the determined RBER or the RWB.