SOI MOSFET Charge Sink Structure for RF Linearity
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Solution Overview
Problem
SOI MOSFETs operating in an accumulated charge regime experience non-linear responses and increased harmonic distortion and intermodulation distortion, which adversely affect their performance and linearity, particularly in RF switching circuits.
Innovation Solution
The implementation of an accumulated charge sink (ACS) with a high impedance connection to the MOSFET body, which controls and removes the accumulated charge, thereby reducing non-linearity and improving the drain-to-source breakdown voltage (BVDSS) characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If SOI MOSFETs operate in an accumulated charge regime, then device operation is enabled, but non-linear responses and harmonic distortion increase
Solution Approach 1:
The patent extracts the harmful accumulated charge from the MOSFET body by introducing an accumulated charge sink (ACS) structure. The ACS is connected to the body through a high-impedance path and provides a dedicated pathway for accumulated charge to be removed, thereby eliminating the source of non-linearity and distortion while preserving normal device operation.
Solution Approach 2:
The patent introduces an intermediary element - the accumulated charge sink (ACS) with high-impedance connection - that mediates between the MOSFET body and the charge removal mechanism. This intermediary structure allows selective removal of accumulated charge without disrupting the normal operation of the MOSFET, resolving the contradiction between operation and distortion reduction.
2Reliability
If accumulated charge is present in the MOSFET body, then device conduction is maintained, but linearity deteriorates
Solution Approach 1:
The patent extracts accumulated charge from the MOSFET body using an ACS structure connected through a high-impedance path. This selective extraction removes the charge causing linearity degradation while preserving the conduction characteristics necessary for device operation.
Solution Approach 2:
The patent changes the impedance parameter of the body connection by introducing a high-impedance path to the ACS. This parameter change enables selective charge removal at specific operating conditions without affecting the overall conduction behavior, thereby improving linearity while maintaining device function.
3Manufacturing precision
If an accumulated charge sink is added to control charge, then linearity improves, but device complexity increases
Solution Approach 1:
The patent segments the MOSFET structure by adding a separate ACS region and a dedicated high-impedance connection path. This segmentation allows independent control of charge accumulation without affecting the main conduction path, improving linearity while keeping the added complexity localized and manageable.
Solution Approach 2:
The ACS structure serves multiple functions: it removes accumulated charge to improve linearity, maintains device conduction through high-impedance coupling, and can be integrated into existing MOSFET fabrication processes. This multi-functionality justifies the added structural complexity by delivering multiple benefits from a single addition.
Data Source
AI summary
A method and apparatus for use in improving linearity sensitivity of MOSFET devices having an accumulated charge sink (ACS) are disclosed. The method and apparatus are adapted to address degradation in second- and third-order intermodulation harmonic distortion at a desired range of operating voltage in devices employing an accumulated charge sink.