Adaptive Read-Retry Offset for Word Line Groups
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Solution Overview
Problem
Existing memory sub-systems face challenges in maintaining data integrity due to degradation of non-volatile memory cells over time, leading to shifts in threshold voltage distributions and increased raw bit error rates, which affect read performance and quality of service (QoS).
Innovation Solution
An adaptive read-retry offset based on word line groups is applied, allowing for independent voltage offset signals with varying voltages, periodicities, and frequencies to be applied to different word line groups based on their specific quality characteristics, such as program-erase cycles, read disturb metrics, and cross-temperature metrics, to correct voltage shifts and improve data retrieval accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single voltage offset is applied to all word line groups, then device complexity is reduced, but read performance and data integrity deteriorate due to varying quality characteristics across different word line groups
Solution Approach 1:
The patent segments the memory device's word line groups into multiple independent groups, each with its own voltage offset control. The controller separately determines and applies voltage offsets to different word line groups based on their individual quality characteristics (program-erase cycles, read disturb metrics, cross-temperature metrics), rather than applying a unified offset to all groups. This segmentation enables targeted compensation for degradation in each group, improving data integrity while maintaining manageable complexity through modular control.
Solution Approach 2:
The patent implements local quality control by assigning different voltage offset values to different word line groups based on their specific quality characteristics. Each word line group receives a customized voltage offset tailored to its degradation level and operational history, rather than a uniform offset. This local differentiation allows the system to address quality variations across the memory device, improving overall reliability without requiring excessive complexity in the control mechanism.
2Reliability
If voltage offset signals are applied frequently to correct threshold voltage shifts, then data integrity is improved, but read latency increases due to additional retry operations
Solution Approach 1:
The patent applies voltage offsets to word line groups proactively based on their quality characteristics and degradation metrics before read errors occur. The controller monitors program-erase cycle counts, read disturb metrics, and cross-temperature metrics to predict which word line groups are prone to threshold voltage shifts, and pre-applies appropriate voltage offsets. This preliminary action prevents the need for multiple retry operations during actual read operations, reducing read latency while maintaining data integrity.
Solution Approach 2:
The patent implements a feedback mechanism where the controller continuously monitors quality characteristics of word line groups (program-erase cycles, read disturb metrics, cross-temperature metrics) and adjusts voltage offsets accordingly. This feedback loop enables the system to optimize the frequency and magnitude of voltage offset applications, applying offsets only when and where needed based on actual degradation patterns. This reduces unnecessary retry operations and associated latency while ensuring data integrity is maintained in degraded regions.
3Ease of operation
If uniform read operations are used across all word line groups, then operation simplicity is maintained, but quality of service deteriorates due to varying degradation levels
Solution Approach 1:
The patent introduces dynamic voltage offset adjustment for different word line groups while maintaining a uniform read operation interface. The controller dynamically determines and applies appropriate voltage offsets to specific word line groups based on their quality characteristics (program-erase cycles, read disturb metrics, cross-temperature metrics), but this dynamic control is transparent to the host system which continues to use standard read operations. This dynamic adaptation improves quality of service by optimizing reads for degraded regions without complicating the operational interface.
Data Source
AI summary
A method includes determining, for a set of memory cells of a word line group, a parameter corresponding to a quality of the set of memory cells of the word line group and determining, for the set of memory cells, a range of voltage offset values corresponding to the parameter. The method can further include determining a voltage offset to be applied to the set of memory cells of the word line group based on the parameter or the range of voltage offset values, or both and applying a signal corresponding to the determined voltage offset to the set of memory cells of the word line group.