Semiconductor Passivation for RF Linearity
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Solution Overview
Problem
High resistivity Silicon substrates used in RF devices exhibit non-linear characteristics due to surface conduction layers, leading to harmonic distortion in RF signals, which existing methods attempt to mitigate through conductive shielding, increasing complexity and signal loss.
Innovation Solution
A potentially trap-rich layer, such as a polycrystalline Silicon layer, is used over passivation regions of semiconductor substrates to immobilize surface conduction layers, preventing capacitance and inductance changes at RF frequencies, thereby reducing harmonic distortion without the need for conductive shielding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conductive shielding layer is incorporated between the surface of the Silicon substrate and other layers handling RF signals, then the non-linear characteristics and harmonic distortion are reduced, but the device complexity and signal loss increase
Solution Approach 1:
The patent removes the harmful surface conduction layer through oxidation processes, creating a passivated surface that eliminates the source of non-linear characteristics. This extraction approach eliminates the need for additional shielding layers, resolving the contradiction between harmonic distortion reduction and device complexity
Solution Approach 2:
The patent introduces an intermediate oxide layer between the Silicon substrate and the RF signal path. This oxide layer acts as a mediator that passivates the surface, preventing the formation of surface conduction layers while maintaining signal integrity without requiring conductive shielding
2Reliability
If a conductive shielding layer is incorporated to reduce non-linear characteristics, then harmonic distortion is reduced, but signal loss increases
Solution Approach 1:
By extracting and removing the harmful surface conduction layer through oxidation, the patent eliminates the source of non-linear characteristics without introducing additional layers that would cause signal loss, thus resolving the contradiction between harmonic distortion reduction and signal loss
Solution Approach 2:
The oxidation process allows the substrate surface to self-passivate, creating a protective oxide layer that inherently prevents surface conduction layer formation. This self-service mechanism eliminates the need for external shielding structures that would otherwise cause signal loss
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
The use of a trap-rich layer effectively immobilizes surface conduction layers, significantly reducing or eliminating harmonic distortion in RF signals, while maintaining standard CMOS process techniques and avoiding signal loss.
Implementation Method 1
The potentially trap-rich layer may have a high density of traps that trap carriers from the surface conduction layer
Implementation Method 2
incorporating a passivation layer, such as an oxide layer or a potentially trap-rich layer, into a semiconductor substrate
Data Source
AI summary
The present invention relates to using a potentially trap-rich layer, such as a polycrystalline Silicon layer, over a passivation region of a semiconductor substrate or a Silicon-on-insulator (SOI) device layer to substantially immobilize a surface conduction layer at the surface of the semiconductor substrate or SOI device layer at radio frequency (RF) frequencies. The potentially trap-rich layer may have a high density of traps that trap carriers from the surface conduction layer. The average release time from the traps may be longer than the period of any present RF signals, thereby effectively immobilizing the surface conduction layer, which may substantially prevent capacitance and inductance changes due to the RF signals. Therefore, harmonic distortion of the RF signals may be significantly reduced or eliminated. The semiconductor substrate may be a Silicon substrate, a Gallium Arsenide substrate, or another substrate.