DRAM Sensor Cells for Rowhammer Disturbance Detection
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Solution Overview
Problem
Dynamic Random-Access Memory (DRAM) devices are vulnerable to disturbance errors induced by rowhammer attacks, which existing mitigation methods such as throttling access or increasing refresh rates fail to effectively prevent, causing performance and power consumption issues.
Innovation Solution
Incorporating sensor cells within the DRAM array to detect electromagnetic disturbances, allowing for controlled refresh cycles and prioritization of rows exposed to disturbances, thereby preventing bit flips before they occur.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If rowhammer attacks are mitigated by throttling access or increasing refresh rate, then DRAM reliability is improved, but performance and power consumption deteriorate
Solution Approach 1:
The patent segments the DRAM array into regular memory cells and dedicated sensor cells. Each row contains both types of cells, allowing independent monitoring of electromagnetic disturbances without affecting the entire array's operation. This segmentation enables targeted refresh operations only for rows experiencing disturbances, rather than throttling access or refreshing all rows, thus maintaining performance while improving reliability.
Solution Approach 2:
Sensor cells act as intermediary elements between the memory cells and the refresh control mechanism. These sensor cells detect electromagnetic disturbances and provide information to the row refresh circuit, which then decides whether to perform a refresh operation. This intermediary detection mechanism allows the system to respond selectively to actual threats rather than applying blanket performance-reducing measures.
2Reliability
If rowhammer attacks are mitigated by increasing refresh rate, then DRAM reliability is improved, but power consumption increases
Solution Approach 1:
Instead of applying excessive refresh operations to all rows (which would increase power consumption), the patent uses sensor cells to detect disturbances and triggers refresh operations only for the specific rows that need them. This partial action approach maintains reliability for affected rows while avoiding unnecessary power consumption in unaffected rows.
Solution Approach 2:
The sensor cells continuously monitor for electromagnetic disturbances and provide feedback to the row refresh circuit. This feedback mechanism allows the system to dynamically adjust refresh operations based on actual disturbance conditions, refreshing only when necessary. This eliminates the need for continuously high refresh rates, thereby reducing power consumption while maintaining reliability.
3Reliability
If sensor cells are added to detect electromagnetic disturbances, then rowhammer attack prevention is improved, but device complexity increases
Solution Approach 1:
The sensor cells are designed with the same basic structure as regular memory cells (transistor-capacitor pairs), using identical or similar materials and fabrication processes. This homogeneity allows the sensor cells to be integrated into the existing DRAM array without requiring fundamentally different components, thereby limiting the increase in device complexity while still providing the needed detection capability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Effectively prevents rowhammer attacks by promptly refreshing affected rows, thereby stopping electromagnetic disturbances from causing errors in memory cells, enhancing DRAM reliability and performance.
Implementation Method 1
detecting whether a particular row of the memory cells has been exposed to more than a predetermined cumulative amount of electromagnetic disturbance
Implementation Method 2
a sensor amplifier including a first input connected to the sensor cell at a point located between the first non-gate terminal of the sensor cell transistor and an input terminal of the sensor cell capacitor
Implementation Method 3
the capacitor of the memory cell can either be charged or discharged (not charged) to represent one of the possible binary values 0 and 1. However, the electric charge on the capacitors slowly drops. In order to prevent data loss as a result of the capacitor losing charge over time, DRAM requires a memory refresh circuit that periodically reads and then immediately rewrites the data in the capacitors
Data Source
AI summary
A dynamic random-access memory array includes a plurality of memory cells and sensor cells physical arranged in a row. The sensor cells include a transistor and a capacitor having an input terminal connected to a first non-gate terminal of the transistor. A wordline is connected to transistor gates of both the memory cells and sensor cells in the row. A sensor amplifier has inputs connected to the sensor cell, a high voltage reference line, and a low voltage reference line, and an output in communication with a row refresh circuit. If the sensor amplifier detects that the sensor cell voltage falls outside of the range of the high and low voltage reference lines, then a trigger signal is output to request that the row refresh circuit perform a priority row refresh of the memory cells and the sensor cell in the row.