SRAM Periphery Layout With Alternating Wells for Tight Cell Pitch
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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 rule violations and increased costs when trying to implement FinFET devices with different design rules for SRAM cells and periphery circuits.
Innovation Solution
The proposed solution involves a circuit layout for SRAM periphery circuits where n-type and p-type transistors are disposed in alternating well regions, allowing for a single type of well within each column, which reduces implantation spacing costs and avoids design rule violations by ensuring each column has a single type of active region, thus enabling efficient implementation of FinFET devices within the constraints of existing design rules.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If traditional SRAM layouts are used at nanometer nodes, then device density can be increased, but cell pitch becomes insufficient to accommodate two source active regions
Solution Approach 1:
The patent transitions from a planar 2D layout to a 3D vertical structure by implementing FinFET devices with channels extending in the vertical dimension. This allows the transistor channel to be formed beneath the gate electrode in a vertical fin structure, enabling higher device density within the same footprint without requiring additional horizontal space for source active regions.
Solution Approach 2:
The patent nests multiple functional components within a compact vertical structure. The FinFET channel is nested within the isolation layer, with the gate electrode positioned above the fin structure. This nested arrangement allows complex transistor functionality to be achieved within a reduced planar footprint, resolving the cell pitch insufficiency issue.
2Reliability
If FinFET devices are implemented with different design rules for SRAM cells and periphery circuits, then device performance can be improved, but design rule violations and increased costs occur
Solution Approach 1:
The patent implements a universal design rule set that applies to both SRAM cell and periphery circuit FinFET devices. The same isolation layer formation, fin structure creation, and gate electrode positioning processes are used across different circuit regions, eliminating the need for separate design rules while maintaining high device performance through consistent vertical channel formation.
Solution Approach 2:
The patent maintains consistent FinFET structural parameters (fin height, channel width, gate length) across SRAM cells and periphery circuits, using parameter optimization within a unified design framework rather than different design rules. This approach achieves high performance through precise control of vertical dimension parameters while simplifying manufacturing.
3Manufacturing precision
If additional spacing is provided between different types of well regions, then design rule violations are avoided, but manufacturing costs increase
Solution Approach 1:
The patent merges n-well and p-well regions into a shared isolation structure, where a single isolation layer serves both well types. This consolidation eliminates the need for separate isolation regions and additional spacing between different well types, achieving design rule compliance while reducing manufacturing steps and costs.
Solution Approach 2:
The isolation layer is designed to universally support both n-well and p-well FinFET devices, performing multiple functions simultaneously: electrical isolation, mechanical support, and stress management. This universal approach eliminates the need for well-type-specific spacing requirements, reducing complexity and manufacturing cost.
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.