Subword Line Discharge Control for Row Hammer Mitigation
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Solution Overview
Problem
The repeated access to a particular subword line in semiconductor memory devices, known as a 'row hammer' event, leads to increased data degradation in nearby subword lines due to free electrons generated in the back-gate region, causing channel dissipation and voltage fluctuations.
Innovation Solution
The discharge of subword lines is controlled by driving the main word line to a first low potential and subsequently to a second low potential, which may be a negative voltage, and by resetting word driver line signals to manage the voltage and rate of discharge, thereby mitigating the effects of row hammer events.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If repeated access to a particular subword line is performed, then data access speed is improved, but data degradation in nearby subword lines increases due to row hammer events
Solution Approach 1:
The patent applies preliminary anti-action by detecting row hammer events before they cause significant data degradation and preemptively applying corrective actions. When a row hammer event is detected (through monitoring access patterns or error correction code failures), the system proactively performs read-disturb mitigation operations on potentially affected subword lines, even before actual data corruption occurs. This prevents the harmful effects of repeated access from propagating to neighboring lines.
Solution Approach 2:
The patent implements feedback mechanisms by continuously monitoring the state of subword lines during repeated access operations. Error correction code (ECC) status, read-disturb detection circuits, and access pattern analysis provide real-time feedback about the health of memory cells. Based on this feedback, the system dynamically adjusts its behavior, such as refreshing affected lines, reducing access frequency to vulnerable areas, or triggering corrective operations when degradation thresholds are approached.
2Productivity
If subword lines are driven to high potential frequently, then data access performance is improved, but channel dissipation and voltage fluctuations increase
Solution Approach 1:
The patent applies periodic action by implementing scheduled refresh operations and controlled discharge cycles for subword lines. Instead of continuously maintaining high potential states, the system periodically refreshes subword lines that have been accessed, and implements controlled discharge phases where subword lines are deliberately brought to low potential states. This periodic cycling prevents continuous voltage stress on the channels while maintaining data accessibility during active periods.
Solution Approach 2:
The patent utilizes parameter changes by dynamically adjusting the potential levels and discharge rates of subword lines based on operational conditions. When row hammer events are detected or voltage instability is measured, the system changes the discharge parameters (such as discharge voltage level, discharge duration, and discharge timing) to mitigate channel dissipation. This allows the system to optimize between performance and stability by adapting electrical parameters rather than maintaining fixed operating conditions.
Data Source
AI summary
Apparatuses and methods for controlling the discharge of subword lines are described. The rate of discharge and/or the voltage level discharged to may be controlled. In some embodiments, a main word line may be driven to multiple low potentials to control a discharge of a subword line. In some embodiments, a first word driver line signal and/or a second word driver line signal may be reset to control a discharge of a subword line. In some embodiments, a combination of driving the main word line and the first word driver line signal and/or the second word driver line signal resetting may be used to control a discharge of the subword line.