Optical Coupling Layer for MiniLED Light Extraction
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Solution Overview
Problem
Phosphor-converted light emitting diodes (pcLEDs) face efficiency limitations due to reflections at the interface between the semiconductor LED and the wavelength converting structure, leading to reduced light coupling and overall efficiency, especially in miniLED and microLED arrays where high refractive index contrast and scattering issues are prevalent.
Innovation Solution
The implementation of optical coupling structures on the light output surface of semiconductor miniLED or microLED arrays, comprising light scattering particles embedded in or coated with a thin layer of material with a refractive index matching or close to that of the LED, to facilitate light coupling into the wavelength converting structure, thereby enhancing extraction efficiency and package efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional LED structure with direct phosphor coating is used, then the manufacturing process is simple, but light extraction efficiency is reduced due to reflections and scattering at the interface
Solution Approach 1:
The patent introduces an optical coupling layer as an intermediary between the LED and phosphor materials. This layer has a refractive index intermediate between the high-index LED material and low-index phosphor materials, reducing reflection losses at the interface while maintaining manufacturing simplicity through conformal deposition processes
Solution Approach 2:
The patent optimizes the refractive index parameter of the optical coupling layer to match intermediate values between LED and phosphor materials. By adjusting this physical parameter, the system achieves improved light extraction efficiency without fundamentally changing the manufacturing process architecture
2Loss of energy
If the refractive index contrast between LED and wavelength converting structure is high, then light coupling is improved, but scattering losses increase and reduce overall efficiency
Solution Approach 1:
The optical coupling layer serves as a mediator that bridges the high refractive index LED material and low refractive index phosphor materials. This intermediate layer reduces the abrupt refractive index contrast, thereby minimizing scattering losses while maintaining effective light coupling between the LED and wavelength converting structure
3Loss of energy
If patterned sapphire substrates are used to improve light extraction, then extraction efficiency increases, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent replaces the mechanical/structural approach of patterned sapphire substrates with an optical approach using a conformal optical coupling layer. This substitution eliminates the need for complex substrate patterning while achieving improved light extraction through refractive index matching, thereby reducing device complexity
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, achieving a higher flux gain compared to conventional methods, while also simplifying manufacturing by avoiding the need for patterned sapphire substrates, particularly beneficial for miniLED and microLED architectures.
Implementation Method 1
a layer of transparent material in physical contact with the corresponding light output surface and having an index of refraction matching or approximately matching an index of refraction of the corresponding light output surface
Implementation Method 2
The optical coupling structures comprise light scattering particles and/or air voids embedded in or coated with a thin layer of a material
Data Source
AI summary
An optical coupling structures are disposed on light output surfaces of semiconductor LEDs 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 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 LEDs.