GaN HEMT Transparent Electrodes for Optical Phased Arrays
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Solution Overview
Problem
Conventional transparent electrodes in liquid crystal devices, such as indium oxide, suffer from high optical absorption and birefringence, which affect the performance of optical phased arrays and other applications by increasing optical absorption and altering the polarization of steered optical beams, and are costly and limited in substrate size.
Innovation Solution
The use of gallium nitride high electron mobility transistor (GaN HEMT) structures with an aluminum nitride interlayer on inexpensive, large-area silicon substrates, which are then transferred to optically transparent and non-birefringent substrates, providing improved conductivity and reduced optical losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If highly doped indium oxide is used as transparent conductor to achieve satisfactory conductivity, then electrical resistance is reduced, but optical absorption increases
Solution Approach 1:
The patent changes the material parameters by transitioning from highly doped indium oxide to gallium nitride with high electron mobility. This parameter change allows achieving the same conductivity with fewer carriers, thereby reducing free carrier absorption and optical losses in the infrared spectrum
Solution Approach 2:
The patent employs a composite structure consisting of gallium nitride layer combined with aluminum nitride interlayer on silicon substrate. This composite material system provides both high conductivity through the GaN layer and low optical absorption, resolving the contradiction between electrical performance and optical transparency
2Ease of manufacture
If sapphire substrates are used for transparent electrodes, then substrate availability is improved, but birefringence alters polarization of steered optical beams
Solution Approach 1:
The patent extracts the electrode functional layer (gallium nitride) from the sapphire substrate and transfers it to a new substrate platform. This separation allows the electrode material to be optimized for electrical performance while the substrate is selected specifically for low birefringence properties, eliminating the polarization alteration issue
Solution Approach 2:
The patent introduces an aluminum nitride interlayer as an intermediary between the gallium nitride electrode and the silicon substrate. This intermediary layer facilitates the transfer process and enables the use of silicon substrates which have superior optical properties with minimal birefringence, thereby preserving optical beam polarization
3Object-generated harmful factors
If cubic spinel substrates are used to avoid birefringence, then polarization is maintained, but cost increases and substrate diameter is limited
Solution Approach 1:
The patent replaces expensive cubic spinel substrates with inexpensive silicon substrates. The silicon substrates can be obtained in large diameters at lower cost, enabling mass production while maintaining the required optical properties through the transferred gallium nitride electrode structure
Solution Approach 2:
The aluminum nitride interlayer serves as a mediator that enables the use of silicon substrates instead of expensive spinel substrates. This intermediary facilitates the transfer of the GaN electrode to silicon, achieving both cost reduction and large substrate area availability while maintaining low birefringence properties
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 results in lower optical absorption and minimized polarization changes, enabling more efficient and cost-effective production of transparent electrodes with improved conductivity and reduced substrate costs, allowing for larger-scale fabrication of optical phased array elements.
Implementation Method 1
gallium nitride high electron mobility transistor (GaN HEMT) structures with an aluminum nitride interlayer... providing improved conductivity and reduced optical losses
Implementation Method 2
The use of an aluminum nitride (AlN) interlayer results in the HEMT having increased conductivity from improved mobility since alloy scattering at the AlGaN/GaN interface is reduced by the insertion of the AlN interlayer
Implementation Method 3
an alternative substrate material having low optical absorption and minimal or no birefringence is desired... having little or no birefringence
Data Source
AI summary
Described herein is a liquid crystal (LC) device having Gallium Nitride HEMT electrodes. The Gallium Nitride HEMT electrodes can be grown on a variety of substrates, including but not limited to sapphire, silicon carbide, silicon, fused silica (using a calcium flouride buffer layer), and spinel. Also described is a structure provided from GaN HEMT grown on large area silicon substrates and transferred to another substrate with appropriate properties for OPA devices. Such substrates include, but are not limited to sapphire, silicon carbide, silicon, fused silica (using a calcium fluoride buffer layer), and spinel. The GaN HEMT structure includes an AlN interlayer for improving the mobility of the structure.