Patterned LED Substrate With Mesh Electrode and Stress Relief
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Solution Overview
Problem
Conventional flip chip light emitting diodes face limitations in current spreading performance and light extraction efficiency due to high resistance in linear extensions and significant light loss from reflective electrodes, as well as stress issues from thermal expansion differences between reflective and barrier metal layers.
Innovation Solution
A light emitting diode structure with mesa-etched areas and a reflective electrode that includes a stress relieving layer between the reflective and barrier metal layers, along with a current spreading layer that covers the mesas and semiconductor layers, enhancing current spreading and light reflection while relieving thermal stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a reflective electrode is formed on the P-type semiconductor layer, then light extraction efficiency is improved, but light loss occurs due to pads and extensions
Solution Approach 1:
The reflective electrode pattern transitions from linear extensions to a two-dimensional mesh structure, increasing the reflective surface area from one-dimensional lines to two-dimensional interconnected regions, thereby improving light extraction efficiency while reducing light loss through optimized spatial distribution
Solution Approach 2:
The mesh pattern creates localized reflective regions strategically positioned to reflect light from specific emission zones, with varying mesh densities in different areas to optimize light extraction where needed while minimizing light loss in other regions
2Reliability
If linear extensions are used for current spreading, then current spreading is achieved, but resistance is high limiting performance
Solution Approach 1:
The continuous linear extension is segmented into a mesh pattern of interconnected conductive paths, creating multiple parallel current flow routes that reduce overall resistance while maintaining effective current spreading across the semiconductor layer
Solution Approach 2:
The current spreading structure transitions from one-dimensional linear extensions to a two-dimensional mesh network, providing multiple dimensional pathways for current flow and significantly reducing electrical resistance through increased path options
3Illumination intensity
If a reflective metal layer is formed above semiconductor layers, then light reflection is improved, but stress occurs due to thermal expansion difference
Solution Approach 1:
A stress relieving layer is introduced as an intermediary between the reflective metal layer and the barrier metal layer, absorbing and distributing thermal stress generated by coefficient of thermal expansion differences, thereby preventing separation while maintaining light reflection functionality
Solution Approach 2:
The electrode structure becomes a composite multi-layer system combining reflective metal, stress relieving material, and barrier metal, where each layer contributes specific properties (reflection, stress management, diffusion prevention) to resolve the contradiction between light reflection and thermal stress
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
Improves current spreading performance and light extraction efficiency while simplifying the manufacturing process and reducing stress from thermal expansion differences, leading to a more effective and cost-efficient flip chip light emitting diode design.
Implementation Method 1
the stress relieving layer has a coefficient of thermal expansion between the coefficient of thermal expansion of the reflective metal layer and the coefficient of thermal expansion of the barrier metal layer
Implementation Method 2
The reflective electrode reflects light generated in the active layer to enhance light extraction efficiency
Data Source
Figure 1~4
Figure 5~6(b)
Figure 7(a)~7(b)
AI summary
A patterned substrate (19) for a light emitting diode includes a substrate (15) having recessed depressions (17) and an anti-reflective layer (16) disposed between the depressions (17).