Virtual Block Media Scanning for Uneven Read Disturb Stress
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Solution Overview
Problem
Memory cells in physical blocks experience uneven read disturb stress and charge loss due to disparate read operations, leading to inconsistent read performance and increased error rates.
Innovation Solution
Implement a selective media scan on virtual blocks composed of fractional good blocks, where the controller selects wordlines based on the highest read counter value to mitigate errors by treating the block's health based on the least reliable block, accommodating a worst-case scenario.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If media scan is performed on all blocks uniformly, then reliability monitoring is comprehensive, but read performance degradation increases due to excessive read operations on already stressed blocks
Solution Approach 1:
The patent applies local quality by differentiating treatment based on block health status. Healthy blocks undergo regular media scans for reliability monitoring, while stressed blocks skip scans to avoid additional read disturb. The controller tracks read counts per block and selectively applies scan operations only where needed, optimizing both reliability monitoring and stress reduction.
Solution Approach 2:
The patent implements dynamics by making the media scan schedule adaptive rather than static. The controller dynamically adjusts scan frequency based on real-time block health metrics (read counts, error rates), transitioning blocks between scanned and non-scanned states as their condition changes. This dynamic approach balances comprehensive monitoring with stress reduction.
2Quantity of substance
If virtual blocks are created to combine multiple physical blocks, then data storage capacity increases, but read performance consistency deteriorates due to uneven stress distribution
Solution Approach 1:
The patent applies segmentation by dividing virtual blocks into constituent physical blocks and tracking each physical block's health status independently. The controller maintains separate read count metrics for each physical block within a virtual block, enabling granular monitoring. This segmentation allows the system to identify which physical blocks are stressed and exclude them from media scans, maintaining read performance consistency despite the virtual block's aggregated capacity.
Data Source
AI summary
A method for performing a media scan operation on a virtual block in a memory device is described herein. The method includes incrementing a first count value of a first read counter via a controller in response to a first read operation performed on a first fractional good block of the virtual block. The method also includes incrementing a second count value of a second read counter via the controller in response to a second read operation performed on a second fractional good block of the virtual block. The method also includes selecting one of the first and second fractional good blocks for the media scan operation via the controller based on a difference between the first and second count values. The method further includes performing the media scan operation on a wordline of the selected one of the first and second fractional good blocks via the controller.