Row Hammer Refresh Mechanism for DRAM Timing Optimization

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Solution Overview

Problem

Semiconductor memory devices face data degradation due to row hammer effects, where charge is lost in word lines from repeated activation/deactivation, especially in smaller devices with closer word lines, necessitating efficient refresh mechanisms to compensate for this loss.

Innovation Solution

Implementing a row hammer refresh (RHR) mechanism that steals non-consecutive clock cycles for refresh operations, ensuring that consecutive RHR operations do not share sense amplifier gaps, thereby reducing precharge time and improving efficiency by separating the timing of RHR and scheduled refresh operations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If conventional refresh operations are used, then memory cells are refreshed, but precharge time is excessive and refresh efficiency is reduced

Engineering Contradiction:

Improverefresh operation efficiencyVSAvoidprecharge time

Core Design Contradiction:

ProductivityVSLoss of time

Solution Approach 1:

The patent segments the refresh operation into distinct phases: active phase, precharge phase, and recovery phase. By identifying and separating the sense amplifier gap (recovery phase) from the active refresh operation, the patent enables overlapping of subsequent refresh operations during the recovery phase, thereby reducing total precharge time and improving refresh efficiency.

Inventive Principle:

Principle #1Segmentation

2Reliability

If RHR operations are performed consecutively, then row hammer refresh is achieved, but sense amplifier gaps overlap causing increased precharge time

Engineering Contradiction:

Improverow hammer protectionVSAvoidprecharge time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent implements a mechanism that monitors and tracks sense amplifier gap timing in advance. By predicting when sense amplifier gaps will occur and overlapping them proactively with subsequent RHR operations, the patent reduces precharge time while maintaining reliable row hammer protection.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent employs periodic monitoring of sense amplifier gaps at predetermined intervals during refresh operations. This periodic detection enables systematic overlapping of RHR operations with sense amplifier gaps, reducing precharge time while ensuring row hammer protection is maintained through regular refresh cycles.

Inventive Principle:

Principle #19Periodic action

3Volume of moving object

If word lines are closely spaced to reduce device size, then device scaling is achieved, but row hammer effects increase causing greater charge loss

Engineering Contradiction:

Improvedevice sizeVSAvoidrow hammer effects

Core Design Contradiction:

Volume of moving objectVSObject-affected harmful factors

Solution Approach 1:

The patent applies preliminary anti-action by proactively refreshing adjacent word lines (victim rows) before charge loss from row hammer effects becomes critical. The system detects aggressive row access patterns and pre-refreshes neighboring word lines, counteracting the harmful capacitive coupling effects that arise from closely spaced word lines in scaled devices.

Inventive Principle:

Principle #9Preliminary anti-action

Data Source

PatentUS10818336B2Apparatus with a row hit rate/refresh management mechanism

Publication Date: 2020.10.27 MICRON TECHNOLOGY INC

AI summary

The apparatus includes a row hammer refresh (RHR) circuit configured to steal a first refresh cycle to implement a first RHR segment; and steal a second refresh cycle after one or more operating cycles, the second refresh cycle to implement a second RHR segment.