Micro LED Mixing Cup for Light Extraction
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Solution Overview
Problem
Micro LED display systems face significant optical losses due to light being trapped and absorbed by surrounding films and layers, leading to reduced light extraction efficiency and external quantum efficiency.
Innovation Solution
The implementation of LED mixing cup structures, including a diffuser layer with scattering particles and an angular filter, which replaces or is formed over the sidewall passivation layer, helps control light propagation and prevent total internal reflection, allowing more light to be extracted by redirecting it into an escape cone.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If light is emitted from micro LEDs into surrounding films, then the light can propagate through the display system, but significant optical loss occurs due to total internal reflection and absorption by materials in the backplane
Solution Approach 1:
A mixing cup structure filled with index-matching material is introduced as an intermediary between the micro LED and surrounding films. This mixing cup has refractive index n=1.5, which matches the sidewall passivation layer, eliminating abrupt index transitions that cause total internal reflection. The mixing cup acts as a mediator to guide light extraction while reducing optical losses at interfaces.
Solution Approach 2:
The refractive index parameter is strategically changed at different locations: the mixing cup structure provides n=1.5 to match the sidewall passivation layer, while the overcoat layer has n=1.3. This parameter variation creates controlled index transitions that reduce total internal reflection and improve light extraction efficiency without causing excessive reflection at interfaces.
2Illumination intensity
If the sidewall passivation layer and overcoat layer have high refractive indices, then light can be effectively guided, but total internal reflection increases and traps light within the layers
Solution Approach 1:
The mixing cup structure serves as an intermediary layer between the high-index sidewall passivation layer (n=1.5) and the lower-index overcoat layer (n=1.3). This intermediate structure with controlled refractive index reduces the abruptness of the index transition, thereby minimizing total internal reflection while maintaining effective light guidance through the display system.
Solution Approach 2:
Different refractive index regions are created locally: the mixing cup (n=1.5) matches the sidewall passivation layer locally to reduce reflection at that interface, while the overcoat layer (n=1.3) provides a different local index for light extraction. This local quality variation optimizes both light guidance and reduces harmful total internal reflection at specific interfaces.
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 configuration increases light extraction efficiency, induces a Lambertian profile, enhances on-axis light emission, and simplifies color matching for various observation angles, improving the overall performance of micro LED displays.
Implementation Method 1
a diffuser layer with scattering particles and an angular filter, which replaces or is formed over the sidewall passivation layer, helps control light propagation and prevent total internal reflection, allowing more light to be extracted by redirecting it into an escape cone
Data Source
AI summary
A light emitting structure including mixing cups are described. In an embodiment, a light emitting structure includes a light emitting diode (LED) bonded to a substrate, a diffuser layer adjacent the LED, an angular filter directly over the diffuser layer and the LED, and an overcoat layer directly over the angular filter and the LED.