Optical Coupling Structures for MiniLED Phosphor Interface Losses
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Solution Overview
Problem
Existing miniLED and microLED arrays face challenges with poor light extraction efficiency due to high refractive index contrast at the semiconductor-light converting structure interface, leading to significant light reflection and absorption, particularly in phosphor-converted LEDs.
Innovation Solution
The implementation of optical coupling structures comprising light scattering particles embedded in a thin layer of high refractive index material, matched to the semiconductor LED output surface, to facilitate light coupling into the wavelength converting structure, thereby reducing reflections and enhancing extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a phosphor layer is disposed directly on the LED to convert wavelength, then wavelength conversion is achieved, but light reflection and absorption increase due to high refractive index contrast at the interface
Solution Approach 1:
An optical coupling layer is introduced as an intermediary between the LED and the phosphor layer. This coupling layer has a refractive index that is intermediate between the high-index semiconductor LED material and the lower-index phosphor layer, thereby reducing the refractive index contrast at the interface and minimizing light reflection and absorption losses while maintaining effective wavelength conversion.
Solution Approach 2:
The refractive index parameter of the interface between LED and phosphor layer is modified by inserting an optical coupling layer with a specific refractive index value. This parameter change optimizes the optical impedance matching, reducing Fresnel reflections and improving light extraction efficiency into the phosphor layer.
2Volume of moving object
If miniLED or microLED arrays are used to reduce device size, then compactness is achieved, but light extraction efficiency deteriorates due to increased refractive index contrast effects
Solution Approach 1:
The optical coupling layer serves as a mediator that addresses the light extraction efficiency problem in miniLED and microLED arrays. By reducing the refractive index contrast at the LED-phosphor interface, it minimizes reflection losses that are particularly problematic in small-scale devices where light extraction is already challenging, thereby improving overall device performance without increasing size.
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 significantly improves light extraction and package efficiency by minimizing reflections and scattering losses, particularly suitable for miniLED and microLED arrays, achieving flux gains of up to 21% compared to conventional methods.
Implementation Method 1
optical coupling structures comprising light scattering particles and/or air voids embedded in or coated with a thin layer of a material that has an index of refraction close to or matching the index of refraction of the material forming the light output surface of the semiconductor LED
Implementation Method 2
optical coupling structures comprising light scattering particles and/or air voids embedded in or coated with a thin layer of a material
Data Source
Figure 1~2B
Figure 2C
Figure 2D
AI summary
Optical coupling structures (505 = {505A; 505B}) are disposed on light output surfaces (102D) of semiconductor LEDs (102) of a miniLED or microLED array to facilitate coupling of light emitted by the semiconductor LEDs through the light output surfaces. The optical coupling structures comprise light scattering particles (505A) and/or air voids (705) embedded in or coated with a thin layer (505B) of a material that has an index of refraction close to or matching the index of refraction of the material forming the light output surface of the semiconductor LEDs.