Low Harmonic RF Switch in SOI Substrate
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Solution Overview
Problem
Silicon-on-insulator (SOI) substrates introduce harmonics into radio-frequency (RF) switches, leading to undesirable device characteristics such as signal distortions due to non-linear coupling, which existing techniques like trench formation and inert ion implantation are ineffective in isolating active devices like RF switches.
Innovation Solution
The method involves forming trenches in the buried oxide layer around active devices and isotropically etching the silicon substrate underneath to create air cavities, disrupting the substrate-insulator interface and reducing coupling, using techniques like STS deep silicon etching to achieve lateral undercuts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If trenches are formed in the BOX layer and inert ion implantation is performed, then substrate coupling is reduced for passive structures, but the technique is ineffective for isolating active devices like RF switches because the implant does not diffuse laterally under the FET
Solution Approach 1:
The patent extracts the harmful substrate coupling effect by removing the silicon substrate material itself through isotropic etching to form air cavities, rather than attempting to block electrical coupling through ion implantation. This physical removal of the substrate directly beneath active devices eliminates the inversion layer coupling mechanism that plagues conventional approaches.
Solution Approach 2:
The patent transitions from two-dimensional planar isolation (trenches in the BOX layer) to three-dimensional isolation by forming air cavities that extend vertically into the substrate and laterally beneath the active devices. This dimensional extension allows the isolation structure to reach under the FET gates and drain regions, providing effective coupling reduction where conventional planar techniques fail.
2Object-affected harmful factors
If the silicon substrate is removed to reduce substrate coupling, then signal distortion is minimized, but structural support may be compromised
Solution Approach 1:
The patent segments the substrate removal process by forming discrete air cavities at specific locations beneath active devices rather than removing the entire substrate. This selective segmentation maintains structural integrity in regions where substrate support is needed while eliminating coupling effects only where harmful, beneath the active device regions.
Solution Approach 2:
The patent applies local quality by creating air cavities with specific dimensions and positions tailored to the underlying active device geometry. The cavities are formed only where needed beneath FETs and RF switches, leaving the surrounding substrate intact to provide mechanical support, thus achieving local coupling reduction without global structural compromise.
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
This approach effectively reduces signal distortion by minimizing substrate coupling, improving the performance of RF switches by eliminating harmonic issues and maintaining structural integrity.
Implementation Method 1
forming at least one cavity in a substrate under the insulator layer and extending laterally from the at least one trench to underneath the device
Data Source
AI summary
A low harmonic radio-frequency (RF) switch in a silicon-on-insulator (SOI) substrate and methods of manufacture. A method includes forming at least one trench through an insulator layer. The at least one trench is adjacent a device formed in an active region on the insulator layer. The method also includes forming at least one cavity in a substrate under the insulator layer and extending laterally from the at least one trench to underneath the device.