Micro-lens Overcoat for Electroluminescent Display Light Extraction
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Solution Overview
Problem
The light extraction efficiency of electroluminescent display devices is degraded due to a significant portion of emitted light being trapped inside the device, primarily due to surface plasmon components and optical waveguide modes, leading to reduced external luminous efficiency.
Innovation Solution
The implementation of a micro-lens structure within the overcoat layer, which includes recessed and protruding portions, helps to redirect trapped light at angles less than the total reflection critical angle, allowing it to escape the device, and a wall structure in the non-emission area aids in forming a thicker overcoat layer in the emission area to prevent damage to the color filter pattern during processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a conventional electroluminescent display device structure is used, then the device is simple to manufacture, but light extraction efficiency is degraded due to trapped light
Solution Approach 1:
The patent introduces a micro-lens structure with curved surfaces into the overcoat layer. The lens includes a first curved surface facing the emitting layer and a second curved surface facing the external environment. This curvature refracts trapped light rays, changing their propagation angles to escape the total internal reflection condition, thereby improving light extraction efficiency without adding complex functional components.
Solution Approach 2:
The patent adds a third dimension by creating a protruding portion that extends from the overcoat layer toward the emitting layer. This vertical protrusion creates a localized region where light can be refracted at different angles, providing an additional dimensional pathway for light extraction that complements the planar device structure.
2Loss of energy
If the overcoat layer is made thicker to improve light extraction, then light can escape more easily, but the color filter pattern may be damaged during processing
Solution Approach 1:
The patent divides the overcoat layer into distinct functional regions: a first region containing the micro-lens structure with curved surfaces for light extraction, and a second region forming a wall structure that provides mechanical support. This segmentation allows the light-extraction function to be concentrated in specific areas while other areas maintain structural integrity to protect underlying layers.
Solution Approach 2:
The patent applies different structural characteristics to different locations within the overcoat layer. The micro-lens structure with specific curvature radii is positioned locally over the emission area to optimize light extraction, while the wall structure extends vertically in non-emission areas to provide mechanical support and protection during processing.
3Illumination intensity
If a micro-lens structure is added to improve light extraction, then external luminous efficiency increases, but the device structure becomes more complex
Solution Approach 1:
The overcoat layer is designed to perform multiple functions simultaneously: it provides electrical insulation, mechanical protection, and light extraction enhancement through the integrated micro-lens structure. The wall portion of the overcoat layer also serves as a protective barrier during manufacturing processes. This multi-functionality reduces the need for separate components, thereby limiting the increase in overall 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 configuration enhances light extraction efficiency by allowing more light to escape, improving external luminous efficiency and preventing image quality degradation from color filter pattern damage during the micro-lens formation process.
Implementation Method 1
redirect trapped light at angles less than the total reflection critical angle
Implementation Method 2
micro-lens structure within the overcoat layer, which includes recessed and protruding portions, helps to redirect trapped light
Data Source
AI summary
An electroluminescent display device can include a substrate including a first emission area and a first non-emission area; a first color filter pattern on the substrate and in the first emission area; a first wall disposed in the first non-emission area and surrounding the first color filter pattern; an overcoat layer on the first wall and the first color filter pattern and including a first micro-lens structure having a non-flat surface in the first emission area; and a light emitting diode on the overcoat layer and in the first emission area.