Memory Sub-System Refresh Using Dual Word Line Access Thresholds
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Solution Overview
Problem
Existing memory sub-systems face inefficiencies due to over-refreshing, which consumes system resources and reduces performance and device life expectancy, as they refresh entire blocks of memory cells based on the poorest performing word line, even when other word lines have improved characterization data.
Innovation Solution
Implementing a dual-threshold approach where a first memory access count threshold refreshes the first word line and a second, higher threshold refreshes the second word line, allowing for individual word line refreshes without simultaneous block refreshes, thereby reducing over-refreshing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If entire blocks of memory cells are refreshed based on the poorest performing word line, then reliability of memory data is improved, but system resources are consumed excessively and performance is reduced
Solution Approach 1:
The patent segments the memory block into individual word lines and implements separate refresh operations for each word line based on its specific access count threshold. Instead of refreshing the entire block uniformly, each word line is refreshed independently when its access count reaches its threshold, allowing selective refresh of only those word lines that need it.
Solution Approach 2:
The patent applies local quality by assigning different refresh thresholds to different word lines based on their individual access patterns and performance characteristics. Word lines with higher access counts have lower thresholds, while word lines with lower access counts have higher thresholds, creating a localized, differentiated refresh strategy that optimizes both reliability and performance.
2Stability of the object's composition
If entire blocks of memory cells are refreshed based on the poorest performing word line, then data retention is improved, but device life expectancy is reduced
Solution Approach 1:
The patent divides the memory block into individual word lines and implements separate refresh operations for each word line based on its specific access count threshold. This segmentation prevents unnecessary refresh operations on word lines that do not require them, thereby extending device life while maintaining data retention for word lines that actually need refreshing.
Solution Approach 2:
The patent applies partial action by refreshing only the necessary portion of the memory block (specific word lines that have reached their access thresholds) rather than performing excessive full-block refreshes. This reduces wear on the memory device while maintaining adequate data retention for the word lines that require it.
3Loss of energy
If individual word line refreshes are implemented with different thresholds, then system resource consumption is reduced, but device complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-determining and storing access count thresholds for each word line based on their historical access patterns and performance characteristics. These thresholds are established in advance and used to guide refresh decisions, eliminating the need for complex real-time analysis during operation and reducing both energy consumption and operational complexity.
Data Source
AI summary
A method includes determining a first memory access count threshold for a first word line of a block of memory cells and determining a second memory access count threshold for a second word line of the block of memory cells. The second memory access count threshold can be greater than the first memory access count threshold. The method can further include incrementing a memory block access count corresponding to the block of memory cells that includes the first word line and the second word line in response to receiving a memory access command and refreshing the first word line when the memory block access count corresponding to the block of memory cells is equal to the first memory access count threshold.