Micro LED Coating Structure for Transfer Yield and Light Extraction
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Solution Overview
Problem
Existing methods for transferring micro light-emitting elements to substrates face challenges in achieving high transfer yield and light extraction efficiency due to low surface roughness, which leads to adhesion issues and reduced light output.
Innovation Solution
The micro light-emitting elements are designed with a first conductivity type semiconductor layer having an uneven pattern and a transparent coating layer with a lower surface roughness, enhancing adhesion and light extraction by using materials like polyimide, spin-on-glass, or silicon nitride with controlled refractive index and surface roughness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the lower surface of the micro light-emitting element has a low surface roughness (several nm or less), then the adhesion to the substrate is strong and transfer yield is high, but the light extraction efficiency is reduced due to total reflection
Solution Approach 1:
The patent applies different surface roughness characteristics to different surfaces of the micro light-emitting element. The lower surface (contacting the substrate) has low surface roughness (several nm or less) to ensure strong adhesion and high transfer yield, while the upper surface (light emission surface) has high surface roughness (tens of nm to several μm) to enhance light extraction efficiency by reducing total reflection. This local differentiation of surface properties resolves the contradiction between adhesion and light extraction.
2Loss of energy
If the lower surface has high surface roughness, then the light extraction efficiency is improved, but the adhesion to the substrate decreases and transfer yield is reduced
Solution Approach 1:
The patent implements local quality by assigning different surface roughness values to different functional surfaces. The lower surface maintains low roughness (several nm or less) for optimal adhesion and transfer yield, while the upper surface has high roughness (tens of nm to several μm) for improved light extraction. This spatial differentiation allows each surface to optimize its specific function without compromising the other.
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 design improves both transfer yield and light extraction efficiency by increasing adhesion to the substrate while minimizing total reflection, maintaining high light output.
Implementation Method 1
a transparent coating layer including a first surface covering the lower surface of the first conductivity type semiconductor layer, and a second surface facing the first surface and having a second surface roughness that is less than the first surface roughness
Implementation Method 2
if an incident angle of light emitted from an active layer of the micro light-emitting element on the lower surface of the micro light-emitting element deviates from a critical incidence angle, the light may not be output to the outside due to a total reflection on the lower surfaces of the micro light-emitting elements
Implementation Method 3
a lower surface on which an uneven pattern is formed, the lower surface of the first conductivity type semiconductor layer having a first surface roughness
Data Source
AI summary
A micro light-emitting element includes a first conductivity type semiconductor layer including a lower surface on which an uneven pattern is formed, an active layer provided on the first conductivity type semiconductor layer, a second conductivity type semiconductor layer provided on the active layer, at least one electrode provided on the second conductivity type semiconductor layer, and a transparent coating layer including a first surface covering the lower surface of the first conductivity type semiconductor layer, and a second surface facing the first surface and having a second surface roughness that is less than a first surface roughness of the lower surface of the first conductivity type semiconductor layer.