Memory Controller Data Grouping for Read Disturb Mitigation
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Solution Overview
Problem
The miniaturization of memory cells in nonvolatile semiconductor memory systems, such as SSDs, leads to deteriorated data reliability due to increased interference noise and read disturb stress, which affects the accuracy of data retrieval and storage.
Innovation Solution
A memory system with a controller that monitors and manages read frequencies across blocks and pages, moving data with similar read frequencies to the same block to reduce refresh operations and mitigate read disturb stress, while employing specific write methods to enhance data reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If memory cell size is miniaturized to increase storage capacity, then storage density is improved, but data reliability deteriorates due to increased interference noise and read disturb stress
Solution Approach 1:
The memory system is divided into multiple blocks, and within each block, multiple sub-blocks are created by dividing word lines. This segmentation allows independent management of different memory regions, enabling selective refresh operations on sub-blocks that require it while leaving others untouched, thus maintaining reliability in miniaturized cells without unnecessary operations on the entire block.
Solution Approach 2:
The system dynamically determines refresh needs based on actual read frequencies of different sub-blocks. The controller monitors read operations and identifies sub-blocks with high read frequencies that are susceptible to read disturb stress, then selectively applies refresh operations only to those sub-blocks, adapting the refresh strategy to current usage patterns rather than applying static uniform refresh to all blocks.
2Reliability
If refresh operations are performed frequently to maintain data reliability, then data reliability is improved, but system performance deteriorates due to increased operation frequency
Solution Approach 1:
Instead of performing refresh operations on entire blocks or all memory cells, the system applies partial refresh actions only to specific sub-blocks that exhibit high read frequencies and are therefore most susceptible to read disturb stress. This partial action approach provides sufficient reliability protection for vulnerable regions while avoiding unnecessary refresh operations in other regions, thereby maintaining system performance.
Solution Approach 2:
The refresh strategy is localized to specific sub-blocks based on their individual read frequency characteristics. Each sub-block receives refresh treatment proportional to its actual need, with high-read sub-blocks receiving refresh operations and low-read sub-blocks leaving them untouched. This local quality approach ensures reliability where needed while preserving overall system performance.
3Reliability
If uniform refresh operations are applied to all blocks, then data reliability is maintained, but operation efficiency deteriorates due to unnecessary refresh operations
Solution Approach 1:
The system transitions from static uniform refresh to dynamic selective refresh by continuously monitoring read frequencies of different sub-blocks. The controller adapts the refresh strategy in real-time, identifying sub-blocks with high read frequencies that require refresh protection and applying refresh operations only to those sub-blocks, thereby eliminating unnecessary refresh operations on low-read sub-blocks and improving operation efficiency.
Solution Approach 2:
The memory system implements self-service by autonomously monitoring its own read patterns and identifying which sub-blocks require refresh protection. The controller automatically determines refresh needs based on observed read frequencies and executes selective refresh operations without external intervention, optimizing the balance between reliability and efficiency based on actual usage patterns.
Data Source
AI summary
According to one embodiment, a memory system includes a memory and a controller electrically connected to the memory. The memory includes blocks. Each of the blocks includes one or more sub-blocks. Each of the one or more sub-blocks includes nonvolatile memory cells. The controller is configured to obtain read frequency of at least one of the sub-blocks, and move data stored in the at least one of the sub-blocks so that data having substantially the same read frequency are written into one block.