Additive High-Index LED Coating for Better Light Extraction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current semiconductor LEDs and pcLEDs face challenges in light extraction and control of light output distribution due to high refractive index surfaces, which often result in significant light being waveguided or absorbed, rather than outputted, especially when using subtractive techniques like etching that can be expensive, difficult to control, and lead to mechanical defects.
Innovation Solution
A structured high refractive index coating is applied additively to the light output surface of LEDs and pcLEDs, comprising particles dispersed in a high refractive index binder, which improves light extraction by being transparent to emitted wavelengths and avoiding the drawbacks of subtractive processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a high refractive index surface is used in LEDs and pcLEDs, then light extraction efficiency is improved, but a significant fraction of light is waveguided and absorbed inside the device instead of being output
Solution Approach 1:
The patent applies a porous low-refractive-index coating layer on the light output surface of LEDs and pcLEDs. This porous structure creates multiple air-material interfaces that scatter and redirect light waves, reducing total internal reflection and waveguiding effects. The porous morphology allows light to escape more efficiently while maintaining a high refractive index substrate, thereby resolving the contradiction between light extraction efficiency and internal light absorption.
Solution Approach 2:
The patent uses a composite structure consisting of a high refractive index substrate (such as sapphire, SiC, GaN, or GaP) combined with a low refractive index porous coating layer. This composite material system leverages the high optical quality of the substrate while the porous coating reduces waveguiding losses. The combination allows the device to maintain structural integrity and high refractive index benefits while minimizing internal light absorption through the porous overlay.
2Use of energy by moving object
If subtractive techniques like etching are used to roughen the light output surface, then light extraction is enhanced, but the process is expensive, difficult to control, and creates mechanical defects
Solution Approach 1:
Instead of using subtractive techniques to roughen the surface, the patent applies an additive approach by depositing a porous low-refractive-index coating layer. This inverts the conventional methodology: rather than removing material to create light-scattering features, the patent adds a layer with inherent porous structure that provides the same optical function. This additive process is less expensive, easier to control, and avoids mechanical defects associated with etching.
Solution Approach 2:
The patent replaces mechanical subtractive processes (etching, abrasion) with a chemical or physical deposition process that creates a porous coating. Instead of mechanically removing material to roughen the surface, the invention uses coating deposition techniques to create a porous structure that achieves light extraction enhancement without the drawbacks of mechanical processing. This substitution eliminates costly and difficult-to-control subtractive manufacturing steps.
3Use of energy by moving object
If subtractive techniques are used to roughen the surface, then light extraction is improved, but mechanical defects and contamination are introduced
Solution Approach 1:
The patent inverts the approach by adding a porous coating layer instead of removing material. This additive method preserves the mechanical integrity of the original high refractive index substrate while introducing light-scattering features through the porous coating structure. The inversion avoids creating mechanical defects, stress concentrations, or contamination that would compromise device reliability.
Solution Approach 2:
The porous coating layer provides light extraction enhancement through its inherent porous structure without requiring mechanical roughening of the substrate. The porous morphology creates multiple interfaces for light scattering while the coating layer itself acts as a protective overlay that prevents contamination and maintains mechanical stability. This approach introduces no mechanical defects into the substrate while achieving improved light extraction.
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 additive structured coating enhances light extraction efficiency, reduces mechanical defects, and improves light output distribution, allowing for better performance in various applications such as displays and adaptive illumination systems.
Implementation Method 1
Light extraction into air through a high refractive index surface may be enhanced by roughening the surface... The structured high refractive index coating comprises particles dispersed in a high refractive index binder
Implementation Method 2
The air-ceramic interface through which light is output by the device exhibits a large RI discontinuity resulting in a significant fraction of the light being waveguided
Data Source
AI summary
This specification discloses LEDs, pcLEDs, and arrays of LEDs or pcLEDs in which the LEDs or pcLEDs comprise a structured high refractive index coating on a light output surface that improves light extraction from the device through the light output surface. The coating is formed additively instead of by a subtractive process that removes material from the surface, and consequently can avoid the disadvantages associated with subtractive processes.