Stacked Light-Emitting Display Electrodes With Bragg Reflectors
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Solution Overview
Problem
Existing display devices face challenges in efficiently emitting light from stacked light emitting elements and ensuring the reliability of bonding electrodes.
Innovation Solution
The display device incorporates a structure with light emitting elements stacked on a lower substrate, featuring bonding electrodes with distributed Bragg reflectors made of transparent conductive layers of different refractive indices, where one layer has a higher pore concentration, enhancing light emission and electrode reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If light emitting elements are stacked to improve luminous efficiency, then luminous efficiency is improved, but light emission efficiency deteriorates due to light trapping
Solution Approach 1:
A distributed Bragg reflector is introduced as an intermediary component between stacked light emitting elements. This reflector comprises alternating high refractive index layers (e.g., ITO, ZnO, IZO) and low refractive index layers (e.g., SiO2, TiO2, Nb2O5) that work together to reflect trapped light back toward the light emitting elements, converting previously lost light energy into useful emission and thereby improving overall light emission efficiency while maintaining high luminous efficiency
Solution Approach 2:
The distributed Bragg reflector utilizes controlled variations in refractive index parameters through alternating layers of different materials. By carefully selecting and stacking materials with different refractive indices (high index layers like ITO/ZnO/IZO alternating with low index layers like SiO2/TiO2/Nb2O5), the system optimizes light reflection at specific wavelengths, enabling efficient light extraction from stacked elements without compromising luminous efficiency
2Ease of manufacture
If bonding electrodes are used to connect light emitting elements, then electrical connection is achieved, but reliability deteriorates due to bonding defects
Solution Approach 1:
The bonding electrode is constructed as a composite structure comprising multiple material layers: a copper base layer providing electrical conductivity, an intermediate layer (such as ITO, ZnO, or IZO) providing both electrical conductivity and adhesion, and an upper metal layer (such as Mo, W, or Al) providing mechanical strength and reliability. This composite structure eliminates bonding defects by distributing functional requirements across different materials, thereby achieving both ease of manufacture and high reliability
3Device complexity
If pixel regions are enlarged to accommodate stacked structures, then device complexity is reduced, but area increases
Solution Approach 1:
The patent transitions from a planar arrangement of light emitting elements to a three-dimensional stacked configuration. By stacking light emitting elements vertically and using distributed Bragg reflectors to manage light propagation in the vertical dimension, the design reduces horizontal space requirements. This dimensional transition allows smaller pixel regions to accommodate the same number of light emitting elements, thereby increasing pixel density without excessive enlargement of individual pixel areas
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 improves light emission efficiency and enhances the reliability of the bonding electrodes, allowing for more efficient utilization of pixel regions and improved luminous efficiency.
Implementation Method 1
a first distributed Bragg reflector including at least one pair of a first transparent conductive layer and a second transparent conductive layer having different refractive indices that are alternately stacked
Implementation Method 2
first transparent conductive layer and a second transparent conductive layer having different refractive indices
Implementation Method 3
the second transparent conductive layer may have a higher concentration of pores compared to pores of the first transparent conductive layer
Data Source
AI summary
A display device according to an embodiment includes a lower substrate, a first bonding electrode disposed on the lower substrate, a first light emitting element disposed on the first bonding electrode, a second bonding electrode disposed on the first light emitting element, and a second light emitting element disposed on the second bonding electrode, the second bonding electrode includes a first distributed Bragg reflector including at least one pair of a first transparent conductive layer and a second transparent conductive layer having different refractive indices that are alternately stacked.