Triangular Polysilicon Gate Extensions for RF Switch Power Handling
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Solution Overview
Problem
SOI CMOS transistors used in RF switches face a trade-off between reducing on-resistance and off-capacitance, which decreases breakdown voltage, making it difficult to maintain high power handling capabilities while minimizing RON×COFF values.
Innovation Solution
Incorporating triangular polysilicon extension regions at the ends of polysilicon gate fingers in SOI CMOS transistors allows for reduced gate lengths while maintaining or increasing breakdown voltages, thereby reducing on-resistance and off-capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If gate length is reduced to decrease on-resistance and off-capacitance, then RON×COFF value is improved, but breakdown voltage decreases
Solution Approach 1:
The invention introduces triangular extension regions that protrude from the gate finger ends in a direction perpendicular to the gate length, effectively adding a dimensional component to the gate structure. This allows the gate to provide both the short channel effects (reduced RON and COFF) and the extended field control (maintained breakdown voltage) simultaneously, resolving the contradiction between reducing gate length and maintaining breakdown voltage.
Solution Approach 2:
The triangular extension regions are strategically placed only at the gate finger ends where the electric field concentration occurs during breakdown. This localized structure provides enhanced field control precisely where needed, while the main gate channel remains short to minimize RON and COFF. The local quality modification allows different regions of the gate to serve different functions.
2Power
If gate length is reduced to minimize RON×COFF values, then power handling capability is improved, but voltage withstanding capability deteriorates
Solution Approach 1:
By adding triangular extensions perpendicular to the gate length direction, the invention creates a three-dimensional gate structure that simultaneously achieves short channel dimensions (for low RON×COFF and high power handling) and extended field control regions (for high voltage withstanding). The extensions provide additional field control without increasing the effective channel length that determines RON and COFF.
Solution Approach 2:
The triangular extension regions are formed as part of the gate structure fabrication process, preliminarily establishing the enhanced field control geometry before device operation. This preliminary structural preparation ensures that the breakdown voltage is maintained from the outset, allowing the device to operate at higher powers without compromising voltage withstanding capability.
Data Source
AI summary
A radio frequency (RF) switch includes a plurality of series-connected silicon-on-insulator (SOI) CMOS transistors, including a plurality of parallel source/drain regions, a plurality of channel regions located between the plurality of source/drain regions, and a polysilicon gate structure located over the plurality of channel regions. The polysilicon gate structure includes a plurality of polysilicon gate fingers, wherein each polysilicon gate finger extends over a corresponding one of the channel regions. The polysilicon gate structure also includes a polysilicon base region that connects first ends of the polysilicon gate fingers. The polysilicon gate structure also includes triangular polysilicon extension regions coupled to the polysilicon gate fingers. The triangular extension regions can be located at the first ends of the polysilicon gate fingers (abutting the polysilicon base region), or at second (opposing ends) of the polysilicon gate fingers.