GaN LED Light Extraction via Patterned Substrate Lift-Off
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Solution Overview
Problem
GaN-based LEDs fabricated on sapphire substrates face issues with heat dissipation, reduced light extraction efficiency due to total internal reflection, and complex chip separation processes, leading to decreased luminance and yield.
Innovation Solution
A method involving pattern formation on the substrate surface, followed by a lift-off process to create a light emitting structure with embedded patterns, enhancing light extraction efficiency by preventing total internal reflection and simplifying chip separation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If sapphire substrate is used for LED fabrication, then mechanical strength and chemical stability are improved, but thermal conductivity deteriorates causing heat accumulation
Solution Approach 1:
The patent extracts the light-emitting active layer from the sapphire substrate using a lift-off process, separating the functional LED structure from the problematic substrate that causes heat accumulation and facet mismatch, while retaining the benefits of sapphire during the growth phase
Solution Approach 2:
The patent introduces a patterned metal layer as an intermediary between the sapphire substrate and the active layer, serving as both a growth template and a heat dissipation pathway, mediating between the substrate's mechanical stability and the active layer's thermal management needs
2Ease of manufacture
If planar substrate surface is used, then fabrication process is simplified, but light extraction efficiency deteriorates due to total internal reflection
Solution Approach 1:
The patent applies curved pattern structures (circles, ellipses, or irregular curves) to the substrate surface instead of flat planes, creating varying surface normals that redirect light at different angles to escape total internal reflection while maintaining manufacturability through standard photolithography patterning
Solution Approach 2:
The patent modifies only the local surface quality at the substrate level where patterns are formed, while keeping the bulk substrate material and overall device structure simple, achieving enhanced light extraction without complicating the entire fabrication process
3Device complexity
If electrodes are formed in the same direction on LED surface, then process steps are reduced, but light emitting area is reduced due to electrode coverage
Solution Approach 1:
The patent moves one electrode formation to the substrate level before the lift-off process, forming electrode patterns in the plane of the substrate rather than on top of the active layer, thereby separating electrode placement from light emission space and enabling both electrodes to be formed with minimal process steps while preserving maximum light emitting area
4Stability of the object's composition
If sapphire substrate is used for wafer processing, then initial growth is stable, but yield rate deteriorates due to facet mismatch during lapping and polishing
Solution Approach 1:
The patent extracts the active layer from the sapphire substrate through lift-off before the lapping and polishing steps, eliminating the facet mismatch problem between sapphire and GaN that occurs during mechanical processing, while still utilizing sapphire's growth stability during the epitaxial growth phase
Solution Approach 2:
The patent performs the lift-off operation as a preliminary action before wafer-level mechanical processing, preparing the structure in advance to avoid subsequent facet mismatch issues during lapping and polishing, thereby protecting the yield rate while maintaining growth stability benefits
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 method improves light extraction efficiency and reduces manufacturing complexity by embedding patterns on the substrate surface, allowing for better light emission and easier chip separation, thereby enhancing the quality and yield of LEDs.
Implementation Method 1
if the light emitted from an active layer 153 of the nitride compound LED of the prior art travels toward a transparent electrode 155 at an angle larger than the critical angle, it is totally reflected and confined within the device
Implementation Method 2
light traveling between two media each having a different refractive index experiences reflection and transmission at an interface
Data Source
AI summary
A method for manufacturing the LEDs is disclosed, whereby the light extraction efficiency of the device can be enhanced by forming patterns on a top surface of a substrate, a light emitting structure is formed on the top surface of the substrate formed with the patterns, the substrate is removed from the light emitting structure, and patterns corresponding to those formed on top surface of the substrate are formed on the surface of the light emitting structure.