Multi-Port SRAM Active Region Width Layout for Compact Cells
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Solution Overview
Problem
Multi-port SRAM cells face challenges in cell size reduction while maintaining key performance indicators such as voltage dynamic data retention (VDDR), maximum operating voltage (Vmax), minimum operating voltage (Vmin), alpha ratio, and beta ratio, particularly due to the limited area usage and current drive capability of p-type transistors.
Innovation Solution
Implementing a gate-all-around (GAA) transistor manufacturing process that includes a dielectric dummy layer to replace sacrificial layers, enhancing channel integrity and current drive capability, and allowing variable active region widths for p-type transistors, particularly in multi-gate devices like FinFETs and GAA transistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multi-port SRAM cell structure is used to increase bandwidth, then parallel operation capability is improved, but cell size becomes large due to insufficient area usage
Solution Approach 1:
The patent merges the active regions of p-type transistors by making them co-planar and adjacent, allowing shared source/drain regions and common gate structures. This integration enables multiple transistors to occupy less total area while maintaining parallel operation capability for increased bandwidth.
Solution Approach 2:
The patent utilizes three-dimensional vertical stacking of transistors and interconnect layers to achieve parallel operations without proportionally increasing planar area. By extending operations into the vertical dimension, the cell achieves high bandwidth while controlling overall cell footprint.
2Area of stationary object
If active region width is reduced to decrease cell size, then area usage is improved, but current drive capability of p-type transistors deteriorates
Solution Approach 1:
The patent implements different active region widths for different transistor types within the same cell. P-type transistors have optimized (wider) active regions to maintain current drive capability, while n-type transistors have narrower active regions to save area. This localized optimization resolves the contradiction between cell size and current drive capability.
Solution Approach 2:
The patent changes the active region width parameter selectively based on transistor type and operational requirements. By allowing variable width parameters rather than uniform sizing, the design achieves both compact cell size and sufficient current drive capability where needed.
3Ease of manufacture
If uniform active region width is used for all transistors, then manufacturing simplicity is maintained, but area usage efficiency deteriorates
Solution Approach 1:
The patent applies different active region widths to different transistor types (wider for p-type, narrower for n-type) to optimize area usage. This localized differentiation improves area efficiency while remaining compatible with standard CMOS manufacturing processes through selective doping and patterning techniques.
Data Source
AI summary
A memory cell includes first and second active regions and first, second, third, and fourth gate structures. The first, second, third, and fourth gate structures are configured to engage the first active region in forming first, second, third, and fourth transistors of a write-port of the memory cell, respectively. The second and third gate structures are configured to further engage the second active region in forming fifth and sixth transistors of the write-port of the memory cell. The memory cell also includes a fifth gate structure configured to engage the second active region in forming a seventh transistor of a read-port of the memory cell. The second active region has a first segment providing a channel region for the seventh transistor and a second segment providing channel regions for the fifth and sixth transistors. The first and second segments have different widths.