DRAM Sub Word Line Drivers with Variable Driving Capability
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Solution Overview
Problem
As DRAM manufacturing processes shrink, the increasing coupling effect between word lines leads to fluctuations in threshold voltage and ground noise, weakening the dynamic refresh operation characteristic of semiconductor memory devices.
Innovation Solution
A semiconductor memory device with sub word line drivers having different driving capabilities, where first sub word line drivers with higher capability are placed between sub cell arrays and second sub word line drivers with lower capability are placed at the edges, along with word line loading matching elements to optimize word line loading and reduce noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If DRAM manufacturing processes are shrunk to increase integration density, then productivity and capacity are improved, but coupling effect between word lines increases causing threshold voltage fluctuation and ground noise
Solution Approach 1:
The memory cell array is divided into multiple sub-cell arrays, each driven by dedicated sub-word line drivers. This segmentation isolates the coupling effects within smaller regions, preventing noise propagation across the entire array while maintaining high integration density
Solution Approach 2:
Different sub-word line drivers are assigned different driving capabilities based on their local requirements. Edge sub-cell arrays receive weaker driving signals to minimize noise, while central sub-cell arrays receive stronger signals to overcome higher coupling effects, optimizing performance locally throughout the array
2Speed
If uniform strong driving capability is applied to all sub-word line drivers, then word line activation speed is improved, but dynamic refresh characteristic deteriorates due to increased noise and threshold voltage fluctuation
Solution Approach 1:
Sub-word line drivers are configured with different driving capabilities matched to their specific locations. Central sub-word line drivers have stronger capability to ensure fast activation where coupling effects are highest, while edge sub-word line drivers have weaker capability to minimize noise generation and protect dynamic refresh characteristics
Solution Approach 2:
The driving capability parameter of sub-word line drivers is varied based on position within the memory array. This parameter optimization balances activation speed and noise generation, ensuring reliable dynamic refresh operation while maintaining fast word line activation where needed
Data Source
AI summary
A semiconductor memory device may include a memory cell array, a plurality of first sub word line drivers, and a plurality of second sub word line drivers. The memory cell array may comprise a plurality of sub cell arrays, a plurality of first word lines and a plurality of second word lines, wherein a loading of each of the first word lines is greater than a loading of each of the second word lines. Each of the plurality of first sub word line drivers may be connected to drive a corresponding one of the plurality of first word lines, wherein each of the first sub word line drivers has a first driving capability. Each of the plurality of second sub word line drivers may be connected to drive a corresponding one of the plurality of second word lines, wherein each of the second sub word line drivers has a second driving capability different from the first driving capability.