SRAM Periphery Layout for Bitcell-Pitch FinFET Integration
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Solution Overview
Problem
As semiconductor technology advances to nanometer nodes, traditional SRAM layouts face challenges in accommodating two source active regions due to insufficient cell pitch, leading to design and fabrication issues that affect device density, performance, power consumption, and cost.
Innovation Solution
The proposed solution involves a novel layout for SRAM cells using FinFET transistors with specific configurations and gate electrode arrangements, allowing for efficient placement of transistors within the limited pitch, enabling higher current driving capacity and smaller bitcell sizes while maintaining design rule compliance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional SRAM layouts are used at nanometer nodes, then design and fabrication are simpler, but cell pitch is insufficient to place two source active regions
Solution Approach 1:
The patent transitions from a planar 2D layout to a 3D vertical architecture by stacking transistors and active regions in multiple layers. Source active regions are positioned at different vertical levels (e.g., first source region at lower level, second source region at upper level), allowing both to fit within the limited pitch while maintaining proper electrical isolation and connectivity.
Solution Approach 2:
The SRAM cell is divided into multiple functional blocks distributed across different vertical layers. Transistors are segmented into separate stacks, with source regions, drain regions, and channel regions positioned at different heights. This segmentation allows independent optimization of each region's placement and reduces interference between adjacent components.
2Quantity of substance
If cell size is reduced to increase density, then device density improves, but it becomes difficult to accommodate all necessary transistor components
Solution Approach 1:
Multiple transistor components are nested within a compact vertical structure. Channels are formed between source and drain regions in a stacked arrangement, with gates wrapping around or positioned adjacent to the channel stack. This nesting allows six or more transistors to be packed into a small footprint by utilizing the vertical dimension for component placement.
Solution Approach 2:
The patent exploits the vertical dimension to increase component capacity without expanding the planar footprint. By stacking source regions, drain regions, and channels vertically, the design accommodates more transistors per cell while reducing the lateral cell pitch, thereby increasing overall device density.
3Quantity of substance
If pitch is reduced for higher density, then device density increases, but design rule compliance becomes more difficult
Solution Approach 1:
The patent reduces lateral pitch constraints by moving component placement to the vertical dimension. Design rules that traditionally limited minimum spacing between source regions in the planar direction are circumvented by positioning source regions at different vertical levels, allowing tighter lateral packing while maintaining required separation through vertical isolation.
Solution Approach 2:
The cell structure is segmented into vertically separated regions that can be independently designed and manufactured. Each segment (source region, drain region, channel, gate) is positioned at a specific vertical level, allowing standard manufacturing processes to address each segment separately while achieving overall compliance with design rules at reduced pitch.
Data Source
AI summary
A static random access memory (SRAM) periphery circuit includes a first n-type transistor and a second n-type transistor that are disposed in a first well region of first conductivity type, the first well region occupies a first distance in a row direction equal to a bitcell-pitch of an SRAM array. The SRAM periphery circuit includes a first p-type transistor and a second p-type transistor that are disposed in a second well region of second conductivity type. The second well region occupies a second distance in the row direction equal to the bitcell-pitch of the SRAM array. The second well region is disposed adjacent to the first well region in the row direction.