Transparent Dielectric Layer for LED Light Extraction
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Solution Overview
Problem
Existing light emitting devices with flip-chip mounted LEDs suffer from metal reflection absorption loss due to light being reflected onto metal surfaces on the mounting board, leading to reduced light extraction efficiency.
Innovation Solution
A light emitting device design featuring a transparent conductive contact electrode with a transparent dielectric layer of lower refractive index and a pad electrode connected to it, where the transparent dielectric layer is formed between the contact electrode and the pad electrode, and the pad electrode is bonded to the contact electrode in a smaller area, reducing metal reflection absorption loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a metal pad electrode is used for flip-chip mounting to secure electrical connection, then electrical connection reliability is improved, but light extraction efficiency deteriorates due to metal reflection absorption loss
Solution Approach 1:
The patent introduces a transparent dielectric layer as an intermediary substance between the metal pad electrode and the light emitting element. This dielectric layer with lower refractive index than the contact electrode serves as an optical mediator that reduces reflection and absorption of light by the metal surface, while still allowing electrical connection through the metal pad electrode underneath
Solution Approach 2:
The patent applies local quality by creating a bonding plane region on the contact electrode where the transparent dielectric layer is formed, making this specific area optically transparent while maintaining metal conductivity in other areas. The bonding plane has a smaller area than the pad electrode top surface, concentrating the optical improvement where light extraction is most critical
2Reliability
If the pad electrode size is increased to secure electrical connection in flip-chip mounting, then electrical connection reliability is improved, but light loss increases due to larger metal reflection area
Solution Approach 1:
The patent makes the contact electrode locally optically transparent by forming a transparent dielectric layer on the bonding plane area, while maintaining the metal pad electrode structure for electrical connection. This allows the pad electrode to have sufficient size for reliable electrical bonding while minimizing light reflection loss in the critical light extraction regions
3Loss of energy
If a transparent dielectric layer with lower refractive index is formed on the contact electrode, then light extraction efficiency is improved, but electrical conductivity may be reduced
Solution Approach 1:
The patent applies local quality by forming the transparent dielectric layer only on the bonding plane region of the contact electrode, not uniformly across the entire electrode. This localized approach maintains optical transparency where light extraction occurs while preserving metal conductivity in areas needed for electrical connection
Solution Approach 2:
The patent segments the contact electrode surface into different functional regions: the bonding plane area covered by transparent dielectric layer for light extraction, and the pad electrode area that maintains metal conductivity for electrical connection. This segmentation allows simultaneous optimization of both optical and electrical properties
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 design enhances light extraction efficiency by minimizing reflection losses and maintaining electrical bonding, while the glass sealing provides stability and reliability, allowing for high-brightness and long-term performance.
Implementation Method 1
a transparent dielectric layer formed on a surface of the contact electrode and comprising a refractive index lower than the contact electrode
Implementation Method 2
light emitted toward the mounting board is inputted to a metal surface of a wiring layer etc. formed on the light emitting element or the mounting board and metal reflection absorption loss is generated when light is reflected thereon
Data Source
AI summary
A light emitting device includes a light emitting element, an element mounting board including a wiring layer on an element mounting surface thereof, and a sealing portion that seals the light emitting element. The light emitting element includes a contact electrode including a transparent conductive film, a transparent dielectric layer formed on a surface of the contact electrode and including a refractive index lower than the contact electrode, and a pad electrode electrically connected to the contact electrode. The light emitting element is flip-chip mounted on the wiring layer. A part of the transparent dielectric layer is formed between the contact electrode and the pad electrode.