Offset Power Rail Layout for More Signal Routing Tracks
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Solution Overview
Problem
Conventional standard cell design with wide metal power rails limits the number of signal routing tracks due to space constraints, necessitating a more efficient power rail layout that balances electromigration, IR drop, and routing requirements.
Innovation Solution
Implementing an offset power rail design using narrow metal tracks that extend to connect all power taps without occupying the full space of standard power rails, thereby freeing up area for signal routing and optimizing power distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If wide metal power rails are used in conventional standard cell design, then electromigration and IR drop performance are improved, but the number of signal routing tracks is reduced due to space constraints
Solution Approach 1:
The power distribution network is segmented into multiple independent power rails (first power rail, second power rail, third power rail) that extend from different sides of the cell row. This segmentation allows each power rail to be narrower while collectively providing sufficient power distribution capacity, thereby freeing up routing tracks without compromising electromigration or IR drop performance.
Solution Approach 2:
Instead of using a single wide power rail occupying horizontal space, the design transitions to a multi-dimensional approach by introducing power rails from multiple sides (left, right, and potentially top/bottom). This spatial redistribution in multiple dimensions achieves the same power distribution function with reduced footprint, enabling more routing tracks.
2Productivity
If narrow metal power rails are used to free up space for signal routing, then the number of signal routing tracks is improved, but electromigration and IR drop performance may deteriorate
Solution Approach 1:
Multiple narrow power rails are merged in function to collectively perform the power distribution task. The first power rail extending from the left side, second power rail from the right side, and third power rail from another side work together to provide comprehensive power distribution, achieving the reliability of a wide rail while maintaining narrow individual widths that free up routing space.
Solution Approach 2:
Each power rail is optimized for its specific local region. The first power rail serves cells on the left side, the second power rail serves cells on the right side, and the third power rail provides additional localized power distribution. This local optimization ensures that each narrow rail is sufficiently dimensioned for its specific load, maintaining overall reliability while enabling narrow widths.
3Device complexity
If standard power rail layout is used, then power distribution is simplified, but space utilization for signal routing is reduced
Solution Approach 1:
The conventional single power rail is segmented into multiple power rails (first, second, and third power rails) extending from different sides. This segmentation reduces the footprint of individual power rails while maintaining comprehensive power distribution coverage, thereby increasing space available for signal routing without significantly increasing design complexity.
Solution Approach 2:
The multiple power rails serve universal power distribution functions across different regions of the cell row. Each power rail can independently supply power to cells in its respective region, providing multi-functional power distribution that replaces the need for a single wide rail, thus freeing up routing space while maintaining distribution simplicity through modular repetition.
Data Source
AI summary
The semiconductor device includes a first cell row, a first power rail and a second power rail. The first cell row includes a first plurality of cells. The first power rail extends from a first side of the first cell row. The first power rail connects to a first group of the first plurality of cells. The second power rail extends form a second side of the first cell row. The second power rail connects to a second group of the first plurality of cells.