Micro-Structured Display Stack for Higher Light Extraction
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Solution Overview
Problem
Existing micro LED display devices face challenges in achieving high light output efficiency due to limitations in light extraction and transmission through the substrate and adhesive layers.
Innovation Solution
The display device incorporates a first and second substrate, an adhesive layer, at least one light-emitting unit, and an intermediate layer. The light-emitting unit features micro structures on its surface, and the intermediate layer has a refractive index greater than 1 but less than that of the adhesive layer, optimizing light extraction and transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a conventional adhesive layer with high refractive index is used between substrates, then strong adhesion is achieved, but light extraction efficiency deteriorates due to total internal reflection at the interface
Solution Approach 1:
An intermediate layer with refractive index between 1.3 and 1.7 is introduced between the adhesive layer (refractive index >1.7) and the light-emitting element. This intermediate layer acts as a refractive index bridge, reducing the abrupt refractive index difference at the interface and minimizing total internal reflection, thereby improving light extraction efficiency while maintaining adhesion through the underlying adhesive layer
Solution Approach 2:
The refractive index of the intermediate layer is specifically controlled to be between 1.3 and 1.7, which is higher than air (1.0) but lower than the adhesive layer (>1.7). This parameter optimization creates a gradual refractive index transition, reducing optical impedance mismatch and improving light coupling from the light-emitting element through the adhesive layer to the substrate
2Loss of energy
If micro structures are added to the light-emitting element surface to improve light extraction, then light output efficiency is enhanced, but device complexity increases
Solution Approach 1:
The light-emitting element surface is segmented into multiple micro structures (such as micropillars, microwells, or microcones) with specific geometries. This segmentation creates multiple light extraction pathways and interfaces, scattering and redirecting light waves to escape the high-refractive-index medium more effectively, thereby improving light output efficiency through increased extraction area and reduced total internal reflection
Solution Approach 2:
The micro structures are designed with curved surfaces (such as hemispherical tops or tapered sides) rather than sharp edges. These curved geometries facilitate gradual light wave transition and reduce abrupt refraction, improving light extraction efficiency while the specific shape parameters are optimized to balance optical performance with manufacturing feasibility
3Strength
If the refractive index of the adhesive layer is increased to improve bonding, then adhesion is strengthened, but light transmission is reduced due to increased total internal reflection
Solution Approach 1:
The intermediate layer serves as an optical mediator between the high-refractive-index adhesive layer and the light-emitting element. By providing a intermediate refractive index value (1.3-1.7), it reduces the optical impedance mismatch, allowing the adhesive layer to maintain its high refractive index for strong bonding while the intermediate layer ensures efficient light transmission by minimizing interfacial reflection
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 the extraction efficiency of light emitted from the light-emitting elements, leading to improved overall light output efficiency of the display device, particularly when the included angle of the micro structures is between 15 degrees and 40 degrees.
Implementation Method 1
The refractive index of the intermediate layer is greater than 1 and less than the refractive index of the adhesive layer
Implementation Method 2
limitations in light extraction and transmission through the substrate and adhesive layers
Implementation Method 3
a surface of the light-emitting element facing toward the adhesive layer is configured with a plurality of micro structures
Data Source
AI summary
A display device includes a first substrate, a second substrate, an adhesive layer, at least one light-emitting unit, and an intermediate layer. The second substrate is disposed opposite to the first substrate. The adhesive layer is disposed between the first substrate and the second substrate. The light-emitting unit is disposed between the adhesive layer and the first substrate, and the light-emitting unit includes at least one light-emitting element. The surface of the light-emitting element facing toward the adhesive layer is configured with a plurality of micro structures. The intermediate layer is disposed between the adhesive layer and the micro structures. The refractive index of the intermediate layer is greater than 1 and less than the refractive index of the adhesive layer.