LED Electrode Structure with Barrier Layer for Light Extraction
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Solution Overview
Problem
The internal light-emitting efficiency of light-emitting diodes (LEDs) is degraded due to light absorption by electrodes and light-emitting layers, and the use of expensive gold for bonding pads increases costs.
Innovation Solution
A light-emitting device with an electrode structure comprising a bonding layer, a conductive layer with higher standard oxidation potential than the bonding layer, and a mirror layer to reflect light without absorption, along with barrier layers to prevent interdiffusion and enhance adhesion and conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a mirror layer is provided under the electrode to reflect light, then light extraction efficiency is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The electrode structure is divided into multiple functional layers: a bonding layer for wire bonding, a conductive layer for electrical conduction, and a barrier layer to prevent interdiffusion. This segmentation allows each layer to perform its specific function optimally while maintaining overall light extraction efficiency.
Solution Approach 2:
The electrode uses a composite structure combining different materials with complementary properties: the bonding layer (e.g., Au) provides excellent bonding characteristics, the conductive layer (e.g., Al, Ag, Cu) provides high electrical conductivity, and the barrier layer prevents material interdiffusion. This composite approach achieves both light reflection and electrical functionality.
2Reliability
If gold is used for the bonding pad to ensure good bonding properties, then reliability is improved, but manufacturing cost increases
Solution Approach 1:
The bonding function is separated from the conductive function into distinct layers. The bonding layer uses gold or other expensive materials only where needed for wire bonding, while the conductive layer uses cheaper materials like Al, Ag, or Cu for the remaining electrical conduction path, reducing overall material cost.
Solution Approach 2:
Expensive bonding materials are applied only in the specific region where bonding is required (the bonding layer), rather than using expensive materials throughout the entire electrode structure. This localized application of high-quality materials maintains bonding reliability while reducing overall cost.
3Quantity of substance
If the electrode structure is simplified to reduce cost, then manufacturing cost decreases, but light absorption increases and efficiency deteriorates
Solution Approach 1:
The light reflection function is extracted from the traditional single-layer electrode and assigned to the conductive layer, which is positioned to reflect light back into the active region. This separation allows the electrode to maintain both electrical functionality and optical efficiency without requiring additional expensive mirror layers.
4Reliability
If barrier layers are added to prevent interdiffusion, then reliability is improved, but device complexity and manufacturing steps increase
Solution Approach 1:
A barrier layer is introduced as an intermediary between the bonding layer and conductive layer to prevent interdiffusion of metal atoms. This thin intermediary layer maintains the integrity of adjacent layers and prevents formation of high-resistance intermetallic compounds, ensuring long-term reliability.
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 enhances light-emitting efficiency by minimizing light absorption and reduces costs by using less expensive materials for the electrode structure, improving the overall reliability and performance of the light-emitting device.
Implementation Method 1
the mirror can reflect but not absorbs the light
Implementation Method 2
a first barrier layer between the bonding layer and the conductive layer
Data Source
AI summary
A light-emitting device, comprising: a substrate; a semiconductor stacking layer comprising a first type semiconductor layer on the substrate, an active layer on the first semiconductor layer, and a second semiconductor layer on the active layer; and an electrode structure on the second semiconductor layer, wherein the electrode structure comprises a bonding layer, a conductive layer, and a first barrier layer between the bonding layer and the conductive layer; wherein the conductive layer has higher standard oxidation potential than that of the bonding layer.