DRAM Row Hammer Protection via Sub-bank Segmentation
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Solution Overview
Problem
Existing DRAM memory technologies face challenges in effectively managing the row hammer effect, particularly in fine-geometry DRAMs where the critical hammer value is low, leading to complex and resource-intensive algorithms that struggle to prevent bit inversions in adjacent rows beyond immediate neighbors.
Innovation Solution
A method that divides the DRAM memory bank into sub-banks and employs a prevention logic to execute a preventive refresh sequence, incrementing activation counters and triggering refreshes before critical hammer values are reached, using a data structure like a tree to manage and prioritize sub-banks needing refreshes, ensuring all rows within a sub-bank are refreshed before they exceed the critical value.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a table-based algorithm is used to prevent row hammer effect, then protection against hammer is achieved, but the number of table entries must be 8 times greater for fine-geometry DRAMs with low critical hammer values
Solution Approach 1:
The patent divides the DRAM bank into multiple sub-banks, each with its own smaller activation counter. This segmentation allows the system to track row activations in finer granularity without requiring a single large table, thus reducing the overall complexity while maintaining protection against row hammer effects in fine-geometry DRAMs
2Reliability
If a table-based algorithm with many entries is used, then low critical hammer values are addressed, but the time to go through table entries increases refresh operation time
Solution Approach 1:
By segmenting the bank into sub-banks with smaller counters, the patent reduces the time required to monitor and refresh rows. Each sub-counter requires less time to process, allowing the system to address low critical hammer values without excessive refresh delays
Solution Approach 2:
The patent performs preliminary refresh operations on sub-banks before the critical hammer value is reached. By monitoring activation counts in sub-banks and refreshing proactively, the system prevents row hammer effects without requiring lengthy table traversals during critical moments
3Device complexity
If protection is limited to immediate adjacent rows (scope 1), then the algorithm remains simple, but victim rows beyond immediate neighbors are not protected
Solution Approach 1:
The patent uses sub-bank segmentation to extend protection scope. By organizing rows into sub-banks and monitoring activation patterns within each sub-bank, the system can identify and protect victim rows at greater distances from aggressor rows without requiring complex cross-sub-bank coordination logic
Solution Approach 2:
The sub-bank structure acts as an intermediary between individual rows. It provides a hierarchical level that enables the system to track and protect rows beyond immediate neighbors while maintaining manageable complexity through the intermediate sub-bank abstraction layer
Data Source
AI summary
A method of protecting a DRAM memory device from the row hammer effect, the memory device comprising a plurality of banks composed of memory rows, may be implemented by at least one logic prevention device configured to respectively associate contiguous sections of rows of a bank with sub-banks. The prevention logic is also configured to execute a preventive refresh cycle of the sub-banks that is entirely executed before the number of rows activated in a sub-bank exceed a critical hammer value. A DRAM memory device, a buffer circuit or a controller of such a memory may comprise the logic for preventing the row hammer effect.