Four-Poly-Pitch SRAM Cell Layout for Lower Word Line Loading
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Solution Overview
Problem
Conventional SRAM cell designs face high word line loading and require expensive interconnect layers due to their 2CPP structure, which affects routing resources and fabrication costs.
Innovation Solution
Implementing a 4CPP design with four rows of gate structures reduces word line loading and eliminates the need for interconnect layers by using VD, VG, and MO layers for internal node connections, allowing for more efficient routing and cost-effective fabrication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional 2CPP SRAM cell design is used, then the routing structure is simple, but the word line loading is high and interconnect layers are required
Solution Approach 1:
The patent transitions from a 2CPP (two contact per pitch) to a 4CPP (four contact per pitch) structure, effectively adding a dimensional aspect to the routing architecture. This allows internal node connections to be made within the same layer using VD, VG, and MO layers, eliminating the need for additional interconnect layers and reducing word line loading while maintaining routing simplicity
2Device complexity
If a 2CPP structure is used, then fewer routing layers are needed, but expensive interconnect layers are required
Solution Approach 1:
The 4CPP structure utilizes vertical depth (VD), gate (VG), and metal overlay (MO) layers to create three-dimensional routing paths within the planar layout. This eliminates the need for expensive additional interconnect layers while providing sufficient routing capacity, thereby reducing fabrication costs without compromising routing functionality
3Reliability
If a 4CPP design is implemented, then word line loading is reduced and routing space increases, but the device structure becomes more complex
Solution Approach 1:
The patent merges multiple functions into the 4CPP structure: the VD, VG, and MO layers serve both as structural elements and as routing pathways for internal node connections. By combining routing functionality with the existing gate structure, the design reduces word line loading and increases routing space without proportionally increasing overall device complexity
Data Source
AI summary
A memory cell includes first through fifth gate structures that each extend along a first lateral direction, a first active structure extending along a second lateral direction and overlaid by respective first portions of the first to fourth gate structures, a second active structure extending along the second lateral direction and overlaid by respective second portions of the first to fourth gate structures, and a third active structure extending along the second lateral direction and overlaid by respective third portions of the third and fifth gate structures. In some embodiments, the first and second gate structures are aligned with each other, with the fourth and fifth gate structures aligned with a first segment and a second segment of the third gate structure, respectively. In some embodiments, the second lateral direction perpendicular to the first lateral direction.