Sub-word line driver soft-landing for row hammer mitigation
Solution Overview
Problem
Existing DRAM memory devices face challenges in mitigating row hammer stress, which leads to charge leakage and data integrity issues due to rapid voltage changes in word lines, particularly in distant portions of the memory cell array, where high capacitance and resistance hinder quick signal switching and are exacerbated by complex metal connections and non-adjustable voltage levels in sub-word line drivers.
Innovation Solution
The implementation of a memory system with optimized sub-word line driver circuits that include diode-configured transistors, reducing the number of transistors and metal connections, and introducing adjustable intermediate voltage levels during transitions to mitigate row hammer stress by pausing at a soft-landing state before entering the pre-charge or idle state, thereby reducing voltage induction and enhancing data retention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the global word line driver drives word lines through long signal paths with high capacitance and resistance, then the memory cell array can be addressed, but the signal switching speed deteriorates in distant portions of the array
Solution Approach 1:
The patent divides the memory cell array into multiple smaller arrays, each served by its own sub-word line driver. This segmentation reduces the signal path length from the driver to distant memory cells, improving signal switching speed while maintaining the ability to address the entire memory capacity through coordinated operation of multiple drivers.
2Adaptability or versatility
If sub-word line drivers use complex metal connections to provide multiple voltage levels, then voltage control flexibility improves, but the device complexity increases
Solution Approach 1:
The patent introduces a voltage selector circuit as an intermediary component that receives a single word line driver output voltage and selectively generates multiple voltage levels (including soft-landing voltages) based on control signals. This approach provides voltage control flexibility without requiring complex metal connections, as the voltage selection is achieved through simple transistor switching controlled by the voltage selector.
3Speed
If the word line voltage transitions rapidly from active to pre-charge state, then the operational speed improves, but row hammer stress increases causing charge leakage
Solution Approach 1:
The patent implements a soft-landing state as a preliminary intermediate voltage level that the word line passes through during the transition from active to pre-charge state. By briefly holding the voltage at this intermediate level before completing the transition, the patent reduces the stress on adjacent memory rows and prevents charge leakage, while maintaining overall operational speed through rapid completion of the full transition cycle.
4Area of stationary object
If the sub-word line driver layout area is reduced for optimization, then the manufacturing cost decreases, but the parasitic capacitance increases affecting performance
Solution Approach 1:
The patent combines multiple functions into the sub-word line driver circuit, including the voltage selection logic and soft-landing control, thereby reducing the need for separate components and metal connections. This merging of functions reduces the overall layout area while carefully managing parasitic capacitance through efficient circuit design and transistor sizing.
Data Source
AI summary
A memory device includes a plurality of sub-word line drivers with, each sub-word line driver configured to receive a main word line signal and configured to drive a respective local word line to at least one of an active state, a soft-landing state, an off state based on the main word line signal and a phase signal. The memory device also includes a plurality of phase drivers with each phase driver configured to generate the respective phase signal. The memory device can further include a processing device configured to drive the respective local word line to the soft-landing state prior to entering the off state when transitioning from the active state to the off state so as to provide row hammer stress mitigation between adjacent local word lines corresponding to the plurality of sub-word line drivers. Each sub-word line driver includes a diode-connected transistor.