Inorganic Encapsulation Layer Stack for Viewing-Angle Color Control
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Solution Overview
Problem
Display devices with thin film encapsulation layers experience changes in visibility as the viewing angle changes, leading to color shifts, particularly in top emission type displays where the intended white appearance is altered due to the structure of the encapsulation layer.
Innovation Solution
A multi-layer encapsulation structure comprising a capping layer, first and second sub-inorganic encapsulation layers, and an organic encapsulation layer, with specific refractive index and thickness ratios, is used to minimize color shifts by carefully controlling the refractive indices and thicknesses of each layer, including silicon, nitrogen, and oxygen content, to maintain visibility consistency across different viewing angles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thin film encapsulation layer is used to protect light-emitting elements, then protection from outside air or moisture is improved, but color shifts and visibility changes occur at different viewing angles
Solution Approach 1:
The encapsulation layer is divided into multiple sub-layers (first sub-inorganic encapsulation layer, second sub-inorganic encapsulation layer, organic encapsulation layer) with different refractive indices. This segmentation allows each layer to contribute differently to light transmission, reducing overall color shifts while maintaining protection functionality.
Solution Approach 2:
Different regions of the encapsulation structure are assigned different refractive indices through the use of materials with specific optical properties. The first sub-inorganic layer has a lower refractive index (1.6-1.8) compared to the second sub-inorganic layer (1.8-2.0), creating localized optical characteristics that compensate for viewing angle-dependent color shifts.
2Power
If the refractive index of the encapsulation layer is increased to improve light extraction, then light emission efficiency is improved, but color shifts become more pronounced at larger viewing angles
Solution Approach 1:
The solution moves from a single-dimensional refractive index parameter to a multi-dimensional approach by introducing multiple layers with different refractive indices. This creates a gradient structure that manages light extraction efficiency while compensating for viewing angle effects through the cumulative optical path through each layer.
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 proposed multi-layer encapsulation structure effectively reduces color shifts and maintains the intended white appearance even at larger viewing angles, enhancing the display's color consistency and user experience.
Implementation Method 1
A refractive index of the capping layer is larger than a refractive index of the first sub-inorganic encapsulation layer. A refractive index of the second sub-inorganic encapsulation layer is larger than the refractive index of the first sub-inorganic encapsulation layer.
Data Source
AI summary
A display device includes a substrate; a light-emitting element on the substrate; a capping layer on the light-emitting element; a first inorganic encapsulation layer on the capping layer; an organic encapsulation layer on the first inorganic encapsulation layer; and a second inorganic encapsulation layer on the organic encapsulation layer. The first inorganic encapsulation layer includes a first sub-inorganic encapsulation layer between the capping layer and the organic encapsulation layer, and a second sub-inorganic encapsulation layer between the first sub-inorganic encapsulation layer and the organic encapsulation layer.