Segmented Shunt Power Rail Mitigates Electron Migration
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Solution Overview
Problem
The reduction in widths of metal power rails and shunt power rails in integrated circuits due to continuous scaling leads to an increasing risk of electron migration, which can cause physical breakage, and increasing the width of shunt power rails results in place and route resource loss.
Innovation Solution
A cell circuit design that includes conductive shunts with shorter line lengths in a third conductive layer, electrically coupled to power rails and conductive lines, achieving a 'short line effect' that mitigates electron migration while minimizing resource loss by using separate shunts instead of continuous shunts and optimizing their lengths and configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the width of shunt power rails is increased to reduce electron migration risk, then reliability improves, but area occupied by shunt power rails increases leading to place and route resource loss
Solution Approach 1:
The shunt power rail is divided into multiple discrete shunt segments rather than using a continuous shunt structure. Each segment has a limited length, creating gaps between segments. This segmentation reduces the total area occupied by shunt power rails while maintaining electron migration resistance through the distributed segment structure.
Solution Approach 2:
The patent introduces a temporal dimension to the shunt power rail design by using alternating patterns of shunt segments and gaps along the rail. This dimensional approach allows the shunt to provide protection against electron migration without requiring continuous wide coverage, thereby reducing overall area occupation while maintaining reliability.
2Productivity
If continuous scaling is pursued to reduce standard cell height, then productivity improves, but the width of metal power rails and shunt power rails decreases leading to increased electron migration risk
Solution Approach 1:
By segmenting the shunt power rail into discrete sections with gaps between them, the design maintains effective electron migration protection even as overall rail dimensions are reduced through scaling. The segmented structure compensates for reduced width by creating multiple protection points along the power rail path.
Solution Approach 2:
The patent changes the structural parameters of the shunt power rail from continuous to segmented, and optimizes the length and spacing of individual segments. This parameter transformation allows the shunt to maintain protective function at smaller scaled dimensions, enabling continued scaling while preserving reliability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design effectively reduces the risk of electron migration, allowing for higher direct current capacity without increasing the width of shunt power rails, thus preventing physical breakage and maintaining efficient resource utilization.
Implementation Method 1
When a stress gradient builds up during copper migration, a reflective force is generated that opposes an electron migration force. In order to achieve the short line effect, the conductive shunt in the third conductive layer has a shorter line length than the first power rail in the first conductive layer.
Data Source
AI summary
A cell circuit includes a first power rail, having a first line length, in a first layer. The first power rail is configured to receive a first voltage for the cell circuit. The cell circuit includes multiple lines in a second layer and a shunt in a third layer. The shunt is electrically coupled to the first power rail and a first set of lines of the multiple lines. The shunt has a second line length shorter than the first line length. The cell circuit includes another shunt in t the third layer. The other shunt is also parallel to the first power rail. The other shunt is electrically coupled to the first power rail and a second set of lines of the multiple lines. The other shunt has a third line length shorter than the first line length.