Adaptive Memory Refresh Period Control for Row Hammer Protection
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Solution Overview
Problem
As memory devices become denser, adjacent memory cells are affected by voltage distribution during intense access to a row, leading to data changes in adjacent rows, known as row hammer, which existing refresh methods fail to adequately address.
Innovation Solution
A memory device with a refresh controller that adjusts the refresh period based on access counts and row addresses, identifying intensive access patterns to modify the refresh strategy for affected rows, reducing unnecessary refresh operations and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If regular refresh operations are performed on all rows, then data integrity is maintained, but power consumption increases and unnecessary refresh operations occur
Solution Approach 1:
The patent applies local quality by transitioning from uniform refresh across all rows to selective refresh based on individual row characteristics. The refresh controller monitors access counts for each row and identifies victim rows that require refresh, while skipping rows that do not need it. This localized approach ensures data integrity is maintained only where necessary, significantly reducing unnecessary refresh operations and associated power consumption.
Solution Approach 2:
The patent implements dynamics by making the refresh strategy adaptive rather than static. The refresh controller continuously monitors access patterns and dynamically adjusts which rows receive refresh operations based on real-time access count data. This dynamic adaptation allows the system to respond to changing access patterns and optimize power consumption while maintaining reliability.
2Reliability
If refresh operations are performed on victim rows, then bit flips in adjacent cells are prevented, but device complexity increases due to access count monitoring
Solution Approach 1:
The patent applies self-service by enabling the refresh controller to autonomously monitor access counts and identify victim rows without external intervention. The refresh controller independently tracks access patterns, compares access counts against thresholds, and determines which rows require refresh. This self-service capability prevents bit flips while managing complexity within the control logic rather than requiring additional hardware components.
Solution Approach 2:
The patent implements feedback by using access count information to guide refresh operations. The refresh controller continuously monitors access counts for each row and uses this feedback to determine which rows are victim rows requiring refresh. This feedback mechanism ensures reliable prevention of bit flips by basing refresh decisions on actual access patterns rather than predetermined schedules.
3Reliability
If access count threshold is set low, then more rows are refreshed preventing bit flips, but more false positives occur causing unnecessary refresh
Solution Approach 1:
The patent applies parameter changes by using different access count thresholds for different rows based on their individual characteristics and access patterns. Rather than using a single threshold for all rows, the system can adjust thresholds dynamically to optimize the balance between comprehensive bit flip prevention and avoiding false positives. This parameter adjustment maintains reliability while preserving refresh operation efficiency.
4Measurement precision
If access count is monitored for all rows, then accurate victim row identification is achieved, but loss of time occurs due to extensive monitoring
Solution Approach 1:
The patent applies taking out by extracting only the necessary monitoring information for victim row identification. Rather than comprehensively analyzing all access patterns for all rows, the system focuses monitoring resources on identifying rows that meet the victim row criteria. This selective extraction maintains accurate victim row identification while minimizing the time lost to monitoring activities.
Data Source
AI summary
A memory device according to an embodiment includes a memory cell array including a plurality of memory cells disposed in a plurality of rows, a register configured to store row addresses corresponding to the plurality of rows and access counts for the plurality of rows, and a refresh controller configured to determine a refresh address based on the stored row addresses and a refresh command being received, and change a refresh period for a target row based on the refresh address being associated with a previously performed refresh for the target row and the access count for a row corresponding to the target row being reached a threshold value.