Resin Layer Refractive Index Matching for Display Light Extraction
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Solution Overview
Problem
The efficiency of light extraction in display devices is reduced due to interface reflection caused by the difference in refractive indices between various layers, particularly when a sealing film with a large refractive index, such as SiN, is used.
Innovation Solution
A display device configuration where the refractive index differences between the silicon nitride sealing film and the resin layers are minimized, with the first resin layer having a refractive index close to the silicon nitride film and the second resin layer having a refractive index close to the glass substrate, reducing interface reflection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a sealing film with large refractive index (such as SiN) is used, then shielding effectiveness and durability are improved, but interface reflection increases and light extraction efficiency decreases
Solution Approach 1:
The patent introduces an intermediate resin layer between the high-refractive-index silicon nitride sealing film and the adhesive layer. This intermediate layer has a refractive index that gradually transitions from the sealing film side to the adhesive side, acting as an optical mediator that reduces the abrupt refractive index difference. The resin layer's refractive index is specifically controlled to be within 0.3 of the silicon nitride film's refractive index, thereby minimizing interface reflection while preserving the sealing film's protective function.
Solution Approach 2:
The patent applies parameter changes by precisely controlling the refractive index of the resin layer to fall within a specific range (difference less than 0.3 from the silicon nitride film). This parameter optimization reduces the refractive index mismatch at interfaces, thereby reducing reflection losses. The patent also specifies thickness parameters for the resin layer (50-200 nm) to further optimize the optical performance while maintaining the sealing structure's integrity.
2Adaptability or versatility
If multiple layers with different materials are stacked, then functional requirements are met, but refractive index differences cause increased interface reflection
Solution Approach 1:
The patent applies local quality by giving different regions of the resin layer different optical properties. The resin layer is designed with a refractive index that is locally optimized at each interface: closer to the silicon nitride film's refractive index at the sealing film interface, and closer to the adhesive's refractive index at the adhesive interface. This localized optimization of refractive index reduces reflection at each specific interface while maintaining the overall multi-layer functional structure.
Solution Approach 2:
The patent uses composite material structure by combining the silicon nitride sealing film with a resin layer of specifically controlled refractive index properties. This composite structure integrates the protective function of the silicon nitride film with the optical matching function of the resin layer, creating a multi-functional composite that simultaneously provides sealing, protection, and optimized light transmission.
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 significantly reduces interface reflection, enhancing light use efficiency and transmittance by matching the refractive indices of the layers, thereby improving the overall performance of the display device.
Implementation Method 1
Since a plurality of layers to be stacked have different refractive indices when formed of different materials, there is a problem in that efficiency of light extraction (transmittance or light use efficiency) is reduced due to interface reflection
Data Source
AI summary
A display device includes: a light-emitting element including a light-emitting layer, an anode, and a cathode, the anode and the cathode interposing the light-emitting layer therebetween; a sealing layer covering the light-emitting element, at least an uppermost layer of the sealing layer being composed of a silicon nitride film; a first resin layer stacked on and in contact with the silicon nitride film; and a second resin layer stacked on and in contact with the first resin layer. A difference between refractive indices of the silicon nitride film and the first resin layer is less than 0.3. A difference between refractive indices of the first resin layer and the second resin layer is less than 0.3.