Multi-Gate RF Switch Layout for Lower Parasitic Coupling
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Solution Overview
Problem
Conventional multi-gate RF switches suffer from direct input to output metal parasitics, long metal fingers handling large currents, additional coupling from internal drain-to-source routing, and lack of body bias, which degrades their figure of merit (FOM) especially at high frequencies.
Innovation Solution
The RF switch layout incorporates a dual-gate design with polysilicon gate routing, body biasing, and reduced drain/source metal resistance by omitting metal at the end of fingers and using silicide for current distribution, along with internal drain/source DC biasing to minimize parasitic capacitance and coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional multi-gate RF switch design is used, then the switch can handle large currents, but metal routing resistance and parasitic capacitance increase degrading FOM at high frequencies
Solution Approach 1:
The patent extracts and removes metal routing from the finger regions, replacing it with silicide-based current distribution paths. This eliminates the parasitic inductance and resistance associated with long metal fingers while maintaining current handling capability through the silicide layer and optimized source/drain connections.
Solution Approach 2:
The patent introduces silicide as an intermediary material between the metal routing and the active region. This silicide layer serves as a low-resistance current distribution path that replaces the traditional metal finger structure, reducing parasitic effects while maintaining electrical connectivity.
2Power
If long metal fingers are used to handle large currents, then current handling capability is improved, but parasitic inductance and resistance increase
Solution Approach 1:
The patent replaces the mechanical metal finger structure with a silicide-based current distribution system. This substitution eliminates the physical constraints of long metal fingers while maintaining current handling through the highly conductive silicide layer and optimized source/drain region geometry.
Solution Approach 2:
The patent transitions from a two-dimensional metal finger layout to a three-dimensional current distribution approach using silicide layers and vertically-oriented source/drain connections. This dimensional change allows current to flow through multiple paths and reduces the effective length of current paths, minimizing parasitic effects.
3Adaptability or versatility
If internal drain-to-source routing is included, then device functionality is improved, but additional coupling and parasitic capacitance are introduced
Solution Approach 1:
The patent extracts and removes the internal drain-to-source metal routing that causes parasitic coupling. Instead, it uses the silicide layer and direct source/drain connections to provide necessary electrical paths without introducing additional parasitic capacitance between drain and source regions.
4Device complexity
If body biasing is omitted, then device complexity is reduced, but control over threshold voltage and performance tuning is lost
Solution Approach 1:
The patent integrates body biasing functionality into the existing device structure by incorporating body contacts and biasing circuits that work alongside the dual-gate configuration. This allows the device to maintain its simplified dual-gate structure while gaining the additional performance tuning capability through body voltage control.
Data Source
AI summary
Apparatus and methods for multi-gate radio frequency (RF) switches are disclosed herein. The RF switches use various layout design techniques to improve figure of merit (FOM). Examples of such techniques include using only two field-effect transistors (FETs) in series to maintain shorter fingers for lower metal resistance, placing a body contact on only one side of the RF switch layout, implementing metallization with reduced coupling from input to output, and/or providing air gaps to improve high frequency performance.