SOI FET RF Switches with Shaped Diffusion Regions
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Solution Overview
Problem
Field-effect transistor (FET)-based RF switches, particularly silicon-on-insulator (SOI) switches, face challenges in achieving low Rds-on per area while maintaining high isolation and reliability, especially under high RF power or voltage conditions, due to their rectangular finger configurations which result in high Rds-on values.
Innovation Solution
The design incorporates non-rectangular shaped diffusion regions, such as diamond, hexagonal, and octagonal shapes, arranged in a staggered configuration with elongate and parallelogram shapes, to reduce the product of Rds-on and area, along with a gate layer and conductors that connect these regions, forming a series of transistors for voltage division and improved isolation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If rectangular finger configurations are used in SOI switches, then the device structure is simple and easy to manufacture, but the Rds-on per area product is high
Solution Approach 1:
The patent applies asymmetry by changing the diffusion region shape from traditional rectangular to non-rectangular shapes (diamond, hexagonal, octagonal). This asymmetric geometry optimization reduces the Rds-on per area product by approximately 26% compared to rectangular configurations, directly addressing the contradiction between manufacturing simplicity and performance
2Reliability
If multiple SOI switches are arranged in series to handle high voltage, then breakdown concerns are mitigated and reliability is improved, but the voltage division reduces the RF signal efficiency
Solution Approach 1:
The patent changes the geometric parameters of the diffusion regions (shape, area, arrangement) to optimize the Rds-on characteristics. By modifying the shape parameter from rectangular to non-rectangular forms and adjusting the area and positioning of diffusion regions, the invention achieves lower Rds-on values that reduce the impact of voltage division in series configurations, thereby improving RF signal efficiency while maintaining reliability
Data Source
AI summary
Disclosed are devices and methods related to radio-frequency (RF) switches having silicon-on-insulator (SOI) field-effect transistors (FETs). In some embodiments, an RF switch can include an FET with shaped source, drain, and gate selected to yield a reduced per-area value of resistance in linear operating region (Rds-on). In some implementations, a plurality of such FETs can be connected in series to allow use of SOI technology in high power RF switching applications while maintaining a relatively small die size.