Boundary Word Line Read Disturb Mitigation in MLC Memory
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Solution Overview
Problem
Nonvolatile memory systems experience high error rates due to read disturb errors, particularly in Multi Level Cell (MLC) blocks where data is susceptible to interference from nearby read operations, especially at word line boundaries and physical edges, leading to potential data loss if not corrected in time.
Innovation Solution
Identifying high-risk word lines in MLC blocks and selectively copying data to Single Level Cell (SLC) blocks to mitigate read disturb errors, using a combination of identifying circuits to detect proximity to boundaries and read operation counts, and maintaining a copy outside the original block for faster and error-free data retrieval.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If data is stored in MLC blocks with multiple word lines, then storage capacity is improved, but read disturb errors increase at boundary word lines
Solution Approach 1:
The patent extracts high-risk data from boundary word lines in MLC blocks and relocates it to safe word lines within the same block. This separation removes the disturbing data from the harmful electromagnetic field environment at block boundaries, eliminating read disturb errors while preserving storage capacity.
Solution Approach 2:
The patent introduces boundary word lines as intermediary storage locations that absorb read disturb errors. By positioning these high-risk word lines at block boundaries and using them as buffer zones, the system protects critical data from corruption while maintaining overall storage efficiency.
2Reliability
If data is copied from MLC block to SLC block to avoid read disturb errors, then data reliability is improved, but device complexity increases
Solution Approach 1:
The patent merges the error protection function into the existing MLC block structure by utilizing safe word lines within the same block. This integration eliminates the need for separate SLC block copies, reducing device complexity while maintaining data reliability through intra-block data relocation.
Solution Approach 2:
The patent enables MLC blocks to self-protect against read disturb errors by using internal safe word lines as refuge locations. The memory system serves its own protection needs without requiring external SLC blocks, achieving self-sufficient error mitigation that reduces overall system complexity.
3Productivity
If read operations are performed frequently on boundary word lines, then data accessibility is improved, but read disturb errors accumulate
Solution Approach 1:
The patent performs preliminary data relocation by proactively moving data from boundary word lines to safe word lines before read disturb errors can accumulate. This preventive action maintains data accessibility while eliminating the risk of error accumulation from frequent read operations.
Solution Approach 2:
The patent converts the harmful effect of frequent reads on boundary word lines into a benefit by using the same boundary location as a safe refuge. Data is moved to these boundary word lines after they have absorbed initial read disturbance, transforming the previously harmful location into a protected storage zone that benefits from the dissipated electromagnetic energy.
Data Source
AI summary
One or more word lines in a Multi Level Cell (MLC) block are identified as being at high risk of read disturb errors and data is selectively copied from such high risk word lines to a location outside the MLC block where the copy is maintained. Subsequent read requests for the data may be directed to the copy of the data outside the MLC block.