Adaptive Moving Read Reference Table for NAND Memory
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Solution Overview
Problem
Fixed MRR tables with a limited number of entries in a fixed order often fail to account for all possible moving read reference values, leading to premature labeling of memory cells as unreadable and repeated use of irrelevant entries, resulting in inefficiencies in error correction in non-volatile memory systems.
Innovation Solution
An adaptive MRR table is generated with priority-based entries that are ordered based on assigned priorities, taking into account program/erase cycle counts, historical parameters, and cell characteristics such as program disturb and intrinsic charge loss, to dynamically recover from read errors in non-volatile memory systems like NAND memory.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed MRR table with limited entries in fixed order is used, then the device complexity is reduced and ease of operation is improved, but the reliability of error correction deteriorates and productivity decreases due to repeated re-reads
Solution Approach 1:
The patent implements dynamic MRR table generation where the table is adaptively created based on actual read error patterns and memory cell characteristics. The table entries and their order are dynamically adjusted based on historical error data, program/erase cycle counts, and cell-specific parameters, transforming the static fixed table into a dynamic adaptive structure that improves reliability while maintaining reasonable complexity
Solution Approach 2:
The system incorporates feedback mechanisms by monitoring read error patterns and using this information to generate and update the MRR table. The table generation process uses feedback from actual memory operations, error correction outcomes, and memory cell state changes to optimize the sequence of read reference voltage adjustments, thereby improving error correction reliability
2Ease of operation
If a fixed MRR table with limited entries is used, then the ease of operation is improved, but the productivity decreases due to increased number of re-read attempts
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing optimal read reference voltage adjustments in the MRR table based on anticipated error patterns. The table is generated in advance with entry sequences optimized for common error types, allowing the system to quickly attempt corrections without real-time calculation overhead, thus improving read recovery efficiency while maintaining ease of operation
Solution Approach 2:
The system changes parameters by adaptively adjusting the MRR table contents based on memory cell characteristics, program/erase cycle counts, and observed error patterns. The read reference voltage values and their sequence are modified as parameters to match actual memory conditions, improving the effectiveness of error correction attempts and reducing the number of re-reads required
3Device complexity
If a fixed order MRR table is used, then the device complexity is reduced, but the reliability deteriorates due to premature labeling of memory cells as unreadable
Solution Approach 1:
The patent applies local quality by customizing the MRR table for specific memory cells based on their individual characteristics such as program/erase cycle counts, error patterns, and threshold voltage distributions. Each memory cell or block can have a tailored MRR table generated from its local error characteristics, improving the accuracy of readability assessment while keeping the overall system complexity manageable through automated generation
4Ease of operation
If repeated use of irrelevant MRR table entries occurs, then the ease of operation is maintained, but the productivity decreases due to wasted correction attempts
Solution Approach 1:
The system uses feedback from the outcomes of MRR table entry attempts to optimize future operations. When certain entries are repeatedly tried without success, the system learns from this feedback and adjusts the MRR table generation to reduce or eliminate repeated use of ineffective entries, thereby improving error correction efficiency while maintaining automatic operation
Solution Approach 2:
The patent changes the MRR table parameters dynamically based on observed performance. The frequency and sequence of entry usage are adjusted as parameters based on actual error correction outcomes, preventing wasteful repeated attempts at irrelevant entries and improving overall correction efficiency while keeping the automatic operation simple
Data Source
AI summary
Examples are disclosed for generating or providing a moving read reference (MRR) table for recovering from a read error of one or more memory cells of a non-volatile memory included in a storage device. Priorities may be adaptively assigned to entries included in the MRR table and the entries may be ordered for use based on the assigned priorities. Other examples are described and claimed.