Memory Controller Reclaim Strategy for Flash Read Disturbance
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Solution Overview
Problem
The existing memory systems face challenges in extending the lifetime and improving performance of flash memory devices due to read disturbances, which cause cell deterioration and data loss, especially in non-volatile memory devices like charge trap flash (CTF) memory cells.
Innovation Solution
A memory controller with a reclaim controller is introduced to perform read operations and count read counts, initiating a reclaim operation by moving data from a selected memory block to another when the read count exceeds a threshold, thereby reducing read disturbances and extending the memory device's lifespan.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If read operations are performed frequently on flash memory, then data access performance is improved, but read disturbance causes cell deterioration and data loss
Solution Approach 1:
The patent performs reclaim operations proactively based on read count thresholds before actual data loss occurs. The controller monitors read counts for each memory block and initiates data relocation when the read count exceeds a predetermined threshold, preventing read disturbance from causing cell deterioration and data loss
Solution Approach 2:
The patent implements a feedback mechanism by continuously monitoring read counts for each memory block and using this information to dynamically control reclaim operations. The controller adjusts when to perform data relocation based on the accumulated read count feedback, creating a closed-loop system that balances performance and reliability
2Reliability
If reclaim operations are performed frequently, then read disturbance is reduced and memory lifetime is extended, but system performance and productivity decrease
Solution Approach 1:
The patent dynamically adjusts the read count threshold parameter based on wear level information. As the memory device wears, the threshold is adjusted to optimize the balance between extending memory lifetime and maintaining system performance. This parameter adaptation allows the system to perform reclaim operations at optimal intervals rather than using a fixed threshold
Solution Approach 2:
The patent performs reclaim operations selectively based on read count thresholds rather than continuously or uniformly across all memory blocks. By targeting only those blocks that exceed the threshold, the system performs partial reclaim actions that are sufficient to prevent read disturbance damage without the excessive performance penalty of universal reclaim operations
Data Source
AI summary
A method of controlling the operation of a memory controller includes, in a read operation of a non-volatile memory device, the memory controller counting a selected read count of a selected string in a selected memory block and/or counting a non-selected read count of a non-selected string in the selected memory block. The memory controller performs a reclaim operation of the selected memory block when the selected read count and/or the non-selected read count exceeds a read threshold. To move data of the selected memory block to another memory block by the reclaim operation, the memory controller may copy the data of the selected memory block to another block by using a changed page address.