Nonvolatile Memory Read-Reclaim Based on Erase Leaving Times
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Solution Overview
Problem
Flash memory devices face reliability issues due to changes in threshold voltages of memory cells caused by physical characteristics and external factors, leading to data deterioration, which existing error correction methods and data management techniques struggle to address effectively.
Innovation Solution
A nonvolatile memory system operation method that includes a memory controller managing erase leaving times (ELT) of memory blocks, detecting and correcting error bits, and performing read-reclaim operations based on estimated error bits and ELT to maintain data reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional error correction methods are used, then some error bits can be corrected, but data reliability deteriorates due to threshold voltage changes from physical characteristics and external factors
Solution Approach 1:
The patent performs preliminary actions by conducting dummy read operations on unselected word lines before actual data read operations. This allows the system to detect potential error bits caused by threshold voltage changes in advance, estimate error rates, and proactively perform read-reclaim operations to relocate data from memory blocks with high error rates, thereby preventing data deterioration before it affects actual data integrity.
Solution Approach 2:
The patent implements feedback mechanisms by using error bits detected from dummy read operations to estimate error rates of unselected word lines. This feedback information is then used to dynamically determine whether to perform read-reclaim operations on specific memory blocks, creating a closed-loop system that continuously monitors and responds to threshold voltage changes and error conditions to maintain data reliability.
2Reliability
If read-reclaim operations are performed on all memory blocks, then data reliability is improved, but system overhead increases significantly
Solution Approach 1:
The patent applies local quality by performing read-reclaim operations selectively on specific memory blocks rather than uniformly across all blocks. The system identifies memory blocks with high error rates based on error bit detection from dummy reads and threshold voltage change analysis, and applies read-reclaim operations only to those localized areas where errors are detected, thereby improving data reliability where needed while minimizing unnecessary operations and overhead in healthy memory blocks.
Solution Approach 2:
The patent uses partial action by performing dummy read operations on only some unselected word lines (e.g., a predetermined number or percentage) rather than all word lines, and performing read-reclaim operations only on memory blocks that exceed error rate thresholds. This partial approach reduces system overhead compared to comprehensive operations while still effectively identifying and addressing the majority of error-prone areas.
3Measurement precision
If dummy read operations are performed on all unselected word lines, then error bit detection accuracy is improved, but operation time increases
Solution Approach 1:
The patent applies partial action by performing dummy read operations on a predetermined number or percentage of unselected word lines rather than all unselected word lines. This selective sampling approach provides sufficient statistical information to estimate error rates of the entire memory block while significantly reducing the time required compared to comprehensive reads of all word lines, thus balancing measurement precision with operation time efficiency.
Data Source
AI summary
A nonvolatile memory system includes a nonvolatile memory device and a memory controller managing the nonvolatile memory device. The operation method includes receiving a read command and a read address from an external device, reading read data stored in memory cells connected to a selected word line of a selected memory block corresponding to the read address in response to the read command, and detecting and correcting error bits of the read data. The method includes estimating the number of error bits of unselected word lines on the basis of erase leaving times of memory cells connected to the unselected word lines of the selected memory block and the detected error bits, and performing read-reclaim operation on at least one word line among the selected word line and the unselected word lines on the basis of the estimated number of error bits.