4-CPP Memory Structure Reducing Wordline RC
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Solution Overview
Problem
Current 2-port bitcells in modern circuitry face issues with increased metal resistance as device geometries scale, leading to higher wordline resistance-capacitance (RC) values, which slow down memory performance and result in unfavorable aspect-ratios and longer access times in system-on-chip (SoC) designs.
Innovation Solution
Implementing a 4-cell-poly-pitch (4-CPP) layout with L-shaped bitcells joined together, which widens the wordline width to reduce metal resistance and capacitance, improving the aspect-ratio and access time while maintaining low source voltage resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If 2-CPP bitcell layout is used, then area utilization is improved, but wordline resistance and capacitance increase
Solution Approach 1:
The patent transitions from traditional 2-CPP (two-cell poly pitch) layout to 4-CPP (four-cell poly pitch) layout, changing the dimensional organization of bitcells. This dimensional change allows wordlines to serve four bitcells instead of two, effectively reducing wordline RC without increasing area, as the bitcells are reorganized in a different spatial configuration
2Area of moving object
If device geometries are scaled to smaller nodes, then integration density is improved, but metal resistance increases exponentially
Solution Approach 1:
The patent merges the serving scope of wordlines by having a single wordline control four bitcells in the 4-CPP layout instead of the traditional two. This merging approach compensates for increased metal resistance at smaller nodes by reducing the total number of wordlines required, thereby reducing overall RC without sacrificing integration density
3Ease of manufacture
If 2-CPP bitcell layout is used, then manufacturing simplicity is maintained, but access time increases
Solution Approach 1:
The patent employs 4-CPP layout which reorganizes bitcells in a different dimensional arrangement, allowing shorter wordline lengths while maintaining manufacturing compatibility with standard CMOS processes. This dimensional reorganization reduces the distance signals must travel, thereby reducing access time without complicating manufacturing
4Object-affected harmful factors
If wordline length is reduced, then wordline resistance and capacitance decrease, but bitcell layout complexity increases
Solution Approach 1:
The patent segments the memory array into blocks where each wordline serves a specific group of four bitcells in the 4-CPP configuration. This segmentation allows for shorter, more manageable wordline lengths while organizing bitcells in a systematic pattern that, while different from traditional layouts, follows regular design rules and does not excessively increase manufacturing complexity
Data Source
AI summary
Various implementations described herein refer to an integrated circuit having a memory structure with a two-bitcell layout and a four cell poly pitch. The two-bitcell layout includes a first bitcell and a second bitcell with structural contours that are joined together in a coupling arrangement. The first bitcell and the second bitcell have multiple transistors that are arranged to store data during write operations and allow access of data during read operations.