ITO Waveguide Contacts for Silicon Photonic Modulators

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

High-speed optical modulators face significant optical loss due to the large difference in refractive indices between semiconductor materials and surrounding oxide layers, leading to absorption issues with metal contacts and defects in poly-Si waveguides, which compromise modulation efficiency and increase resistance.

Innovation Solution

The use of a conductive contact material with an optical refractive index close to that of the surrounding oxide layer, such as Indium Tin Oxide (ITO) or carbon nanotubes, is applied on top of the waveguide rib to isolate the optical mode from metal electrodes, minimizing optical loss while maintaining excellent electrical connectivity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If metal contacts are used on top of the waveguide rib, then electrical connectivity is improved, but optical loss increases due to absorption

Engineering Contradiction:

Improveelectrical connectivityVSAvoidoptical loss

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The patent introduces an intermediary material layer (such as ITO or carbon nanotubes) between the metal electrode and the waveguide rib. This intermediate layer has optical properties that reduce absorption while maintaining electrical conductivity, thereby mediating between the conflicting requirements of electrical connectivity and optical transmission.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent employs composite material structures combining metal electrodes with transparent conductive materials (like ITO) or carbon nanotubes. This composite approach leverages the high electrical conductivity of metals while incorporating the optical transparency of the other materials, reducing overall optical absorption in the contact structure.

Inventive Principle:

Principle #40Composite materials

2Ease of manufacture

If poly-Si waveguide rib is used, then manufacturing is simplified, but optical loss increases due to defects

Engineering Contradiction:

Improvewaveguide fabricationVSAvoidoptical loss

Core Design Contradiction:

Ease of manufactureVSLoss of energy

Solution Approach 1:

The patent applies different material qualities to different regions: the waveguide rib maintains poly-Si for ease of manufacturing, while the contact region uses materials with superior optical properties (like ITO or carbon nanotubes). This local differentiation allows simplified manufacturing where needed while minimizing optical loss in critical regions.

Inventive Principle:

Principle #3Local quality

3Volume of moving object

If waveguide width is reduced for compactness, then device size is improved, but optical mode isolation becomes difficult

Engineering Contradiction:

Improvedevice sizeVSAvoidoptical mode isolation

Core Design Contradiction:

Volume of moving objectVSReliability

Solution Approach 1:

The intermediate material layer serves as an optical isolator between the metal electrode and the compressed waveguide structure. Even at reduced widths, this intermediary layer prevents unwanted optical mode coupling and maintains isolation, enabling compact designs without sacrificing optical performance.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 reduces optical loss and device resistance, enhancing modulation efficiency and allowing for smaller waveguide widths, thereby improving the performance of high-speed optical modulators.

Implementation Method 1

the abovementioned enormous optical absorption coefficient of metal contacts

Methodology Applied

Scientific EffectOptical absorption: Absorption (EM radiation)

Implementation Method 2

the large difference in optical refractive indices between Si/poly-Si and the surrounding oxide layer

Methodology Applied

Scientific EffectRefraction: Refraction

Implementation Method 3

maintaining excellent electrical connectivity and low optical loss

Methodology Applied

Scientific EffectElectrical conduction: Conduction (electrical)

Data Source

PatentUS8014636B2Electrical contacts on top of waveguide structures for efficient optical modulation in silicon photonic devices

Publication Date: 2011.09.06 ORACLE AMERICAN INC

AI summary

A phase modulation waveguide structure includes one of a semiconductor and a semiconductor-on-insulator substrate, a doped semiconductor layer formed over the one of a semiconductor and a semiconductor-on-insulator substrate, the doped semiconductor portion including a waveguide rib protruding from a surface thereof not in contact with the one of a semiconductor and a semiconductor-on-insulator substrate, and an electrical contact on top of the waveguide rib. The electrical contact is formed of a material with an optical refractive index close to that of a surrounding oxide layer that surrounds the waveguide rib and the electrical contact and lower than the optical refractive index of the doped semiconductor layer. During propagation of an optical mode within the waveguide structure, the electrical contact isolates the optical mode between the doped semiconductor layer and a metal electrode contact on top of the electrical contact.