Logic Cell Layout With Shared Active Region for Lower Delay
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Solution Overview
Problem
As integrated circuits continue to downscale, the increasing number of standard cells leads to larger chip areas, necessitating a more compact and efficient logic cell design to optimize space and performance.
Innovation Solution
The semiconductor structure incorporates a logic cell with a specific arrangement of transistors and isolation structures, including tie-gate transistors and dielectric-base gate structures, which reduce cell area and mitigate diffusion break stress, thereby minimizing cell delay and maintaining high saturation drain current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the number of standard cells is increased to enhance logic functionality, then the logic capability is improved, but the chip area increases
Solution Approach 1:
The patent combines multiple transistors into a shared active region with common source and drain regions. Specifically, the first and second transistors share a first source region and a first drain region, while the third and fourth transistors share a second source region and a second drain region. This merging of transistor structures reduces the overall area required for each logic cell while maintaining the necessary logic functionality through the shared components.
Solution Approach 2:
The isolation structures serve multiple functions: they electrically isolate adjacent active regions, provide mechanical support, and define the boundaries of the shared source and drain regions. The gate electrodes also serve dual purposes by controlling multiple transistors simultaneously through their positioning over the shared source/drain regions. This multi-functionality reduces the total component count and area required.
2Area of stationary object
If the active region is reduced to minimize cell area, then the area is improved, but the saturation drain current decreases
Solution Approach 1:
The patent implements local quality by creating distinct regions with different doping types within the active region. The first active region contains a first source region and a second source region with different doping types, as do the drain regions. This local differentiation allows each transistor to maintain its specific electrical characteristics and current driving capability while sharing the physical space, thereby preserving saturation drain current despite reduced overall area.
Solution Approach 2:
The patent employs a nested structure where multiple transistor channels are embedded within a single active region. The gate electrodes are positioned such that they extend over the shared source and drain regions, creating a nested arrangement where the control elements are interspersed within the active region rather than requiring separate dedicated regions for each transistor. This nesting allows multiple transistors to occupy the same physical footprint while maintaining individual current paths.
3Speed
If isolation structures are added to reduce cell delay, then the speed is improved, but the device complexity increases
Solution Approach 1:
The isolation structures are designed to perform multiple functions simultaneously: they electrically isolate adjacent active regions to prevent cross-contamination, provide mechanical support for the gate electrodes, define the geometric boundaries of the shared source and drain regions, and serve as spacers during fabrication processes. By consolidating these multiple functions into single structural elements rather than using separate components for each function, the patent reduces overall device complexity while achieving the speed improvements necessary for reduced cell delay.
Data Source
AI summary
A semiconductor structure is provided. A logic cell with a logic function includes a plurality of first transistors in an active region over a semiconductor substrate, a second transistor in the active region, a third transistor in the active region, and first and second isolation structures on opposite edges of the active region and extending along the first direction. Each first transistor includes a first gate electrode extending along the first direction. The second transistor includes a second gate electrode extending along the first direction. The third transistor includes a third gate electrode extending along the first direction. The first gate electrodes are disposed between the first and second isolation structures. The second gate electrode is disposed between the first gate electrodes and the first isolation structure. The third gate electrode is disposed between the first gate electrodes and the second isolation structure.