DRAM Sub-bank Segmentation for Row Hammer Prevention
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Solution Overview
Problem
Existing DRAM memory technologies face challenges in effectively managing the row hammer effect, particularly with fine-geometry DRAMs, where the critical hammer value is low, and existing solutions are either too complex or inadequate in preventing row hammer phenomena with scopes greater than 1, affecting non-adjacent rows and requiring inefficient refresh operations.
Innovation Solution
A method that divides the DRAM memory bank into sub-banks with activation thresholds, incrementing a counter for each row activation, and executing preventive refreshes to prevent row hammer effects by identifying and refreshing sub-banks before they reach a critical hammer value, allowing for efficient and timely prevention of row hammer effects across multiple rows.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a table-based algorithm is used to prevent row hammer effect, then protection against row hammer is improved, but the complexity and time required to process low critical hammer values (e.g., 4800) increases significantly
Solution Approach 1:
The patent divides the memory bank into multiple sub-banks, each with its own activation counter and protection logic. This segmentation allows each sub-bank to be monitored independently with smaller, more manageable counters, reducing the overall complexity compared to a single large table that would be needed to track all rows individually.
Solution Approach 2:
The patent implements preventive refresh operations by monitoring activation counts and triggering refreshes before the critical hammer value is reached. This preliminary action prevents row hammer effects from occurring in the first place, rather than detecting and correcting them after damage has occurred, which would require more complex error correction mechanisms.
2Quantity of substance
If fine-geometry manufacturing is used to increase memory density, then memory capacity is improved, but the critical hammer value decreases making row hammer protection more difficult
Solution Approach 1:
The patent implements dynamic monitoring and adaptive refresh strategies where the activation counters and refresh thresholds are adjusted based on actual usage patterns. This allows the system to optimize protection for low critical hammer values by dynamically allocating refresh resources to sub-banks that are approaching their thresholds, rather than using static protection schemes.
Solution Approach 2:
The patent changes the monitoring parameters by using activation counters that track the number of times each sub-bank is accessed, and by adjusting refresh thresholds based on the critical hammer values specific to fine-geometry DRAMs. This parameter-based approach allows the system to adapt to the lower critical hammer values inherent in fine-geometry manufacturing.
3Reliability
If existing protection algorithms are applied to fine-geometry DRAMs, then some row hammer protection is achieved, but the solution is too slow to process the required number of table entries in time
Solution Approach 1:
By segmenting the memory bank into sub-banks with independent counters, the patent reduces the number of entries that need to be processed simultaneously. Each sub-bank's counter can be updated and checked in parallel, significantly improving processing speed compared to sequentially processing a large table of all rows.
Solution Approach 2:
The patent implements self-service protection where each sub-bank autonomously tracks its own activation count and triggers its own refresh operations when thresholds are approached. This distributed self-monitoring eliminates the need for a centralized, slow processing system that would need to coordinate refresh operations across the entire memory bank.
4Reliability
If block-based refresh redirection is used, then row hammer protection is provided, but the logic cannot perform preventive refresh in other blocks during block refresh period
Solution Approach 1:
The patent segments the memory bank into multiple sub-banks that can be monitored and refreshed independently. This allows parallel refresh operations across different sub-banks, maintaining productivity while providing comprehensive protection. When one sub-bank requires refresh, other sub-banks can continue to be accessed or refreshed simultaneously.
Solution Approach 2:
The patent performs preliminary refresh operations on sub-banks that are approaching their activation thresholds, before row hammer effects can occur. This proactive approach allows the system to schedule and execute refresh operations in advance, reducing the need for urgent, disruptive refresh interruptions and maintaining better overall productivity.
Data Source
AI summary
A method of protecting a DRAM memory device from the row hammer effect includes the memory device comprising a plurality of banks composed of memory rows, the method being implemented by at least one logic prevention device configured to respectively associate contiguous sections of rows of a bank with sub-banks and to execute, on each activation of a row of a sub-bank (b) of the memory, an increment step of a required number of preventive refreshments (REFRESH_ACC; REFRESH_ACC/PARAM_D) of the sub-bank (b) using an activation threshold (PARAM_D) of the sub-bank (b). The prevention logic is also configured to execute a preventive refresh sequence of the sub-banks according to their required number of preventive refreshes. A DRAM memory device, a buffer circuit or a controller of such a memory may comprise the logic for preventing the row hammer effect.