White Light Emitting Device Emission Layer Thickness Gradient
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Solution Overview
Problem
Self-emission display devices face challenges in maintaining uniform color emission across different grayscale levels and current densities, leading to color abnormalities due to differences in efficiency and non-uniformity among emission layers.
Innovation Solution
A white light emitting device and light emitting display device are designed with a structure that includes a first stack emitting blue light and a second stack with sequentially stacked emission layers emitting longer wavelengths, where the thickness of the emission layers is gradually reduced, allowing for improved color representation and reduced color abnormalities by minimizing the thickness of the third emission layer to mitigate thermal stress and edge region issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If multiple emission layers are stacked to achieve high efficiency and various colors, then color representation is improved, but color uniformity deteriorates due to efficiency differences and non-uniform emission at different current densities
Solution Approach 1:
The patent applies local quality by making each emission layer have different thickness to compensate for their different emission efficiencies. The first emission layer (longest wavelength) has the greatest thickness, the second emission layer has intermediate thickness, and the third emission layer (shortest wavelength) has the smallest thickness. This non-uniform thickness distribution compensates for the efficiency differences among layers, achieving uniform color emission across all layers while maintaining high color representation quality.
2Ease of manufacture
If emission layers are made with uniform thickness, then manufacturing is simplified, but color abnormality occurs at low current density and edge regions
Solution Approach 1:
The patent implements local quality by specifying different thicknesses for different emission layers based on their wavelength characteristics. The first emission layer emits light of longest wavelength and has greatest thickness, the second emission layer has intermediate thickness, and the third emission layer emits shortest wavelength and has smallest thickness. This localized thickness variation prevents color abnormality at low current densities and edge regions while remaining manufacturable through controlled deposition processes.
3Reliability
If the third emission layer thickness is reduced to mitigate thermal stress and edge region issues, then reliability is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent applies parameter changes by establishing specific thickness relationships among the emission layers. The first emission layer has greatest thickness, the second has intermediate thickness, and the third has smallest thickness. This parameter optimization reduces thermal stress and prevents edge region color abnormalities. The patent provides specific thickness ranges and ratios that balance reliability improvement with manufacturability, avoiding excessive precision requirements while achieving the desired thermal and optical performance.
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
The solution effectively prevents color differences between regions and eliminates color characteristic variations between low and high grayscale levels, enhancing color representation and reducing color abnormalities, especially at low current densities, by optimizing the thickness ratio of emission layers.
Implementation Method 1
first to third emission layers stacked one on another, which emit lights, and wavelengths of the lights are gradually shortened in a direction moving away from the first stack
Data Source
AI summary
A white light emitting device and the light emitting display device including the same have an improved structure capable of preventing a color difference between regions and eliminating a difference in color characteristics between a low grayscale level and a high grayscale level.