3D Word Line Configuration for DRAM Voltage Drop Reduction
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Solution Overview
Problem
The reduction in size of DRAM memory cells leads to increased resistance in word lines, causing voltage drops and operational issues due to decreased cross-sectional area, resulting in disturbances between memory cells and word lines.
Innovation Solution
A memory device with a mesa structure and a word line configuration featuring two linear sections and an interconnecting portion that penetrates through the mesa, minimizing voltage differences between linear sections and reducing word line resistance, while maintaining a small memory cell size by using a method of fabricating deep and shallow isolations and depressions to form conductive layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If memory cell size is reduced to increase memory storage, then memory storage capacity is improved, but word line resistance increases causing voltage drops and operational issues
Solution Approach 1:
The word line is configured to extend in three dimensions: horizontally along the top surface and vertically through the trench to reach the channel base region. This 3D configuration allows the word line to maintain sufficient length for low resistance while staying within the compact memory cell footprint, resolving the contradiction between small cell size and low word line resistance.
Solution Approach 2:
The word line is nested within the trench structure, with the conductive material filling the trench space. This nesting approach utilizes the vertical dimension of the trench to accommodate the word line path, enabling the word line to extend deeper into the structure and reduce resistance without increasing the planar cell area.
2Area of moving object
If word line cross-sectional area is reduced to fit smaller memory cells, then memory cell size is improved, but word line resistance increases causing voltage drops
Solution Approach 1:
The word line transitions from a 2D planar configuration to a 3D configuration by extending vertically through the trench. This dimensional change allows the word line to achieve sufficient conductive path length and effective cross-sectional area for low resistance, while the memory cell maintains its compact planar dimensions.
Solution Approach 2:
The word line is formed using a conductive material that fills the trench structure, creating a composite configuration where the conductive material is integrated with the trench walls. This composite structure increases the effective conductive cross-section and reduces resistance without increasing the memory cell footprint.
3Manufacturing precision
If deep trenches are used to form isolations, then manufacturing precision is improved, but fabrication complexity increases due to multiple etching and filling steps
Solution Approach 1:
The isolation structure is segmented into two levels: deep trenches extending to the substrate for primary isolation, and shallow trenches for secondary isolation. This segmentation allows each trench type to be optimized for its specific function and formed using targeted etching and filling steps, improving precision while managing fabrication complexity through systematic process decomposition.
Solution Approach 2:
Different regions of the structure receive different treatment: deep trenches are formed in specific areas for strong isolation, while shallow trenches are formed in other areas for additional isolation or word line formation. This local differentiation optimizes the isolation effectiveness in each region while allowing the fabrication process to be tailored to local requirements.
Data Source
AI summary
A memory device includes a mesa structure and a word line. The mesa structure, having two opposite side surfaces, includes at least one pair of source/drain regions and at least one channel base region corresponding to the pair of source/drain regions formed therein. The word line includes two linear sections and at least one interconnecting portion. Each linear section extends on the respective side surface of the mesa structure, adjacent to the channel base region. The at least one interconnecting portion penetrates through the mesa structure, connecting the two linear sections.