SRAM Cell Criss-Cross Transistor Layout for Compact Design
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Solution Overview
Problem
Conventional three-dimensional Complementary-FET (CFET) architecture for SRAM memory cells faces challenges in routing connections between transistors, leading to complex metal routing, increased risk of electrical shorts, and inefficient use of space, making it unsuitable for smaller feature sizes and future technology nodes.
Innovation Solution
A criss-cross design for SRAM memory cells where storage transistors on different layers are oriented perpendicular to each other, allowing for nearly vertical connections and reduced risk of electrical shorts, resulting in a more compact and efficient layout with up to 50% area reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional three-dimensional CFET architecture is used with transistors arranged on the same level, then routing connections becomes complex and risk of electrical shorts increases, but transitioning to perpendicular orientation on different layers requires additional manufacturing complexity
Solution Approach 1:
The patent transitions from planar transistor arrangement to three-dimensional stacked architecture, placing transistors on different layers with perpendicular orientations. This dimensional change enables nearly vertical connections that reduce routing complexity and electrical short risk while maintaining manufacturability through standard semiconductor fabrication processes.
Solution Approach 2:
The patent employs asymmetric orientation of transistors on different layers, with storage transistors perpendicular to access transistors. This asymmetric arrangement optimizes connection paths and reduces interference between adjacent transistors, improving reliability without significantly increasing manufacturing complexity.
2Area of stationary object
If conventional side-by-side transistor arrangement is used, then routing is simpler, but area utilization is inefficient and cell size is larger
Solution Approach 1:
By stacking transistors vertically on different layers rather than arranging them side-by-side in a single plane, the patent achieves up to 50% area reduction. The three-dimensional configuration allows more efficient space utilization while the vertical connection paths simplify routing compared to lateral connections in planar designs.
3Area of stationary object
If transistors are oriented in the same direction on different layers, then alignment is easier, but connection routing becomes more complex and area efficiency decreases
Solution Approach 1:
The patent uses perpendicular orientation of transistors on different layers, creating an asymmetric criss-cross pattern. This orientation reduces the area required for connection routing while the alignment is maintained through standard semiconductor fabrication techniques that can accommodate perpendicular transistor orientations on stacked layers.
Data Source
AI summary
A six transistor SRAM memory cell design is discussed. An SRAM memory cell includes criss-crossed transistors in cross-coupled inverters to achieve a more compact form factor and simplify fabrication.