Memory Controller Read Refresh for Flash Reliability
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Solution Overview
Problem
Flash memory devices face data reliability issues due to wear-out and read disturbance, which affect the threshold voltage distributions and overall performance over time, necessitating effective management of read operations to maintain data integrity.
Innovation Solution
A memory controller method that counts read operations for page-groups and performs a copy-back operation from an impaired memory block to a healthier block when the read count exceeds a reference threshold, using a read refresh control module to maintain data reliability by transferring data from blocks with diminished reliability to those with higher reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If read operations are performed frequently on flash memory cells, then data accessibility is improved, but read disturbance causes threshold voltage shifts and data reliability deteriorates
Solution Approach 1:
The patent performs copy-back operations proactively when read count reaches a threshold, before actual data corruption occurs. The controller monitors read counts and transfers data from heavily read blocks to spare blocks in advance, preventing read disturbance from causing threshold voltage shifts and data reliability issues
Solution Approach 2:
The patent identifies blocks that have suffered read disturbance and copies their data to healthy spare blocks. The impaired blocks are then discarded for future write operations, while the recovered data is stored in blocks with better reliability, effectively separating read-disturbed data from vulnerable storage locations
2Reliability
If copy-back operations are performed frequently to maintain data reliability, then data reliability is improved, but write operations increase and device lifespan is reduced
Solution Approach 1:
The patent applies different management strategies to different blocks based on their read count characteristics. Blocks with high read counts are identified for copy-back operations, while blocks with low read counts are left undisturbed. This localized approach ensures copy-back operations are performed only where necessary, minimizing unnecessary write operations and extending device lifespan
Solution Approach 2:
The patent dynamically adjusts the copy-back threshold parameter based on device wear state and usage patterns. As the device ages or usage patterns change, the threshold for triggering copy-back operations can be modified to optimize between data reliability and write operation minimization, thereby extending device lifespan while maintaining adequate data protection
3Reliability
If read count monitoring and copy-back operations are implemented, then data reliability is improved, but controller complexity increases
Solution Approach 1:
The controller autonomously monitors read counts and performs copy-back operations without requiring external intervention or complex host-side management. The read count counters and copy-back logic are integrated into the controller, allowing it to self-manage data reliability issues caused by read disturbance, thereby simplifying the overall system architecture despite the added internal functionality
Data Source
AI summary
A method of operating a memory controller includes; counting a number of read operations directed to a page-group of data stored in a block and generating a first read count number, then comparing the first read count number with a first reference count threshold among a first set of reference count thresholds associated with the page-group, and upon determining that the first read count number exceeds the first reference count threshold, performing a copy-back operation of the page-group data from the block to another block.