Memory Controller Read Reclaim for Data Integrity
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Solution Overview
Problem
Existing non-volatile memory systems face challenges in efficiently managing data storage and retrieval, particularly in multi-bit memory devices where error correction and data integrity are compromised due to shifting threshold voltage distributions, leading to uncorrectable errors and data loss.
Innovation Solution
A memory system with a memory controller that performs a read reclaim operation by transferring valid data from high-error memory blocks in a second memory area to lower-error memory blocks in a first memory area, ensuring data integrity and preventing open word lines, thereby maintaining data accuracy and system reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If data is stored in high-density memory blocks (second memory area), then storage capacity is improved, but error rate increases due to threshold voltage distribution shifts
Solution Approach 1:
The memory system is segmented into two distinct memory areas: a first memory area with memory blocks storing n-bit data per cell (lower density, higher reliability) and a second memory area with memory blocks storing m-bit data per cell (higher density, higher error rate). This segmentation allows the system to separately manage high-capacity storage and high-reliability data migration, resolving the contradiction between storage capacity and error rate.
Solution Approach 2:
The system changes the parameter of bits-per-cell (from n-bit to m-bit) to create different memory areas with different characteristics. By varying this parameter, the system can allocate data to appropriate memory areas based on reliability requirements, thereby managing the trade-off between storage capacity and error rate.
2Reliability
If read reclaim operation transfers all valid data from target memory block, then data integrity is improved, but operation time increases
Solution Approach 1:
The read reclaim operation automatically identifies target memory blocks requiring data migration and executes the transfer of valid data to the first memory area without external intervention. The memory controller autonomously manages the entire process, including tracking operation status and determining completion when all valid data is transferred, thereby maintaining data integrity while minimizing manual overhead.
Solution Approach 2:
The system implements feedback mechanisms to track the status of read reclaim operations. The memory controller monitors whether all valid data has been successfully transferred from the target memory block and uses this feedback to determine when the operation is complete, ensuring data integrity while optimizing operation timing.
Data Source
AI summary
A memory system includes a nonvolatile memory device including a first memory area formed of memory blocks which store n-bit data per cell and a second memory area formed of memory blocks which store m-bit data per cell, where n and m are different integers, and a memory controller configured to control the nonvolatile memory device. The memory controller is configured to execute a read operation, and to execute a read reclaim operation in which valid data of a target memory block of the second memory area is transferred to one or more memory blocks of the first memory area, the target memory block selected during the read operation. The read reclaim operation is processed as complete when all the valid data of the target memory block is transferred to the one or more memory blocks of the first memory area.