FinFET Dummy Gate Decoupling Capacitor for Voltage Rail Stability
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Solution Overview
Problem
FinFETs exhibit larger gate capacitance compared to planar FETs, leading to rail voltage droop when gates switch, which decreases switching speed and affects overall semiconductor chip timing.
Innovation Solution
Incorporating a dummy fin structure with a dummy gate coupled to a different voltage rail, forming a decoupling capacitor with the fin to mitigate voltage droop by using stored charge to maintain rail voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If finFET structure is used to improve transistor performance, then switching speed is improved, but gate capacitance increases causing voltage rail droop
Solution Approach 1:
A dummy gate structure is introduced as an intermediary element between the power supply and the finFET gate. This dummy gate forms a parasitic capacitor that acts as a local energy reservoir, mediating the power delivery to the actual gate and preventing voltage droop during switching operations.
Solution Approach 2:
The parasitic capacitance formed by the dummy gate, which would normally be considered a harmful effect or waste structure, is converted into a beneficial decoupling capacitor. This structure intentionally exploits the parasitic effect to stabilize voltage rails and improve power supply integrity.
2Reliability
If decoupling capacitance is added to stabilize voltage rails, then voltage droop is reduced, but device complexity increases
Solution Approach 1:
The decoupling capacitor function is merged with the existing dummy gate structure. Instead of adding a separate capacitor component, the solution combines the capacitive function with the gate structure itself, thereby stabilizing voltage rails without increasing overall device complexity.
Solution Approach 2:
The dummy gate structure serves multiple functions: it acts as both a structural element for the finFET and simultaneously provides decoupling capacitance for voltage stabilization. This multi-functionality eliminates the need for additional dedicated decoupling components.
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 decoupling capacitance reduces or prevents voltage rail drooping, allowing finFETs to operate at faster frequencies by acting as a local power source to stabilize voltage rails.
Implementation Method 1
the interaction between a fin in the finFET and a dummy gate... forming a decoupling capacitor with the fin to mitigate voltage droop by using stored charge to maintain rail voltages
Data Source
AI summary
Embodiments herein describe dummy gates disposed over a portion of a fin in finFETs. That is, instead of separating the dummy gates from the finFET structure, the fins may be extended and covered, at least partially, by the dummy gates. An insulative material is disposed between the dummy gate and the fin in order to form a decoupling capacitor. In one embodiment, the dummy gate overlaps a portion of the fin that is held at a voltage rail. Moreover, the dummy gate may be coupled to a different (e.g., opposite) voltage rail than rail coupled to the fin. For example, if the fin is coupled to VHIGH then the dummy gate is coupled to VLOW, or vice versa. Thus, the capacitor formed using the fin and the dummy gate provides a decoupling capacitance between the power sources generating the voltage rails (i.e., VHIGH and VLOW).