Resistivity-Engineered PIC Substrate for RF Common-Mode Suppression

Solution Overview

Problem

Photonic integrated circuits (PICs) face challenges in suppressing radio-frequency (RF) common-mode signals, which induce significant RF crosstalk and degrade performance due to weak confinement and resonance issues, while also experiencing undesirable absorption loss for desirable RF signals.

Innovation Solution

A resistivity-engineered semiconductor substrate with a high resistivity top portion and low resistivity bottom portion is used to suppress common-mode signals through RF absorption, while minimizing absorption loss for non-common mode RF signals by strategically varying the resistivity levels to manage electric field penetration.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a low resistivity substrate is used to suppress common-mode signals through RF absorption, then common-mode suppression is improved, but RF absorption loss for desirable RF signals increases

Engineering Contradiction:

Improvecommon-mode suppressionVSAvoidRF absorption loss

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The substrate is divided into two distinct regions with different resistivity values: a first region with high resistivity (50-500 ohm·cm) beneath the conductor to minimize RF absorption loss for differential mode signals, and a second region with low resistivity (1-10 ohm·cm) at the periphery to suppress common-mode signals through RF absorption. This spatial differentiation of substrate properties allows simultaneous optimization of both signal transmission and common-mode suppression.

Inventive Principle:

Principle #3Local quality

2Reliability

If the substrate resistivity is uniformly low to suppress common-mode signals, then common-mode suppression is improved, but electric field penetration increases causing more RF loss

Engineering Contradiction:

Improvecommon-mode suppressionVSAvoidelectric field penetration loss

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The substrate is divided into two distinct regions with different resistivity values: a first region with high resistivity (50-500 ohm·cm) beneath the conductor to minimize RF absorption loss for differential mode signals, and a second region with low resistivity (1-10 ohm·cm) at the periphery to suppress common-mode signals through RF absorption. This spatial differentiation of substrate properties allows simultaneous optimization of both signal transmission and common-mode suppression.

Inventive Principle:

Principle #3Local quality

3Loss of energy

If the substrate resistivity is uniformly high to reduce RF absorption loss, then RF transmission efficiency is improved, but common-mode signal suppression deteriorates

Engineering Contradiction:

ImproveRF absorption lossVSAvoidcommon-mode suppression

Core Design Contradiction:

Loss of energyVSReliability

Solution Approach 1:

The substrate is divided into two distinct regions with different resistivity values: a first region with high resistivity (50-500 ohm·cm) beneath the conductor to minimize RF absorption loss for differential mode signals, and a second region with low resistivity (1-10 ohm·cm) at the periphery to suppress common-mode signals through RF absorption. This spatial differentiation of substrate properties allows simultaneous optimization of both signal transmission and common-mode suppression.

Inventive Principle:

Principle #3Local quality

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 resistivity-engineered substrate effectively suppresses common-mode signals while reducing RF absorption loss for differential mode signals, improving the overall RF transmission characteristics and performance of PICs by localizing electric field penetration and minimizing substrate absorption effects.

Implementation Method 1

a bottom portion of the semiconductor substrate has a low resistivity to suppress common mode via RF absorption

Methodology Applied

Scientific EffectRF absorption: Absorption (EM radiation)

Implementation Method 2

common mode signals are suppressed through RF absorption in the low resistivity bottom portion

Methodology Applied

Scientific EffectResistive heating: Joule Heating

Data Source

PatentUS12081268B2Resistivity engineered substrate for RF common-mode suppression

Publication Date: 2024.09.03 ACACIA TECH INC

AI summary

Aspects of the present disclosure are directed to a photonic integrated circuit (PIC) having a resistivity-engineered substrate to suppress radio-frequency (RF) common-mode signals. In some embodiments, a semiconductor substrate is provided that comprises two portions having different levels of resistivity to provide both suppression of common mode signals, and reduction of RF absorption loss for non-common mode RF signals. In such embodiments, a bottom portion of the semiconductor substrate has a low resistivity to suppress common mode via RF absorption, while a top portion of the semiconductor substrate that is adjacent to conductors in the IC has a high resistivity to reduce RF loss.