Flip Chip LED with Distributed Bragg Reflector
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Solution Overview
Problem
Flip chip type light emitting diodes using metal reflective layers suffer from significant light loss due to low reflectivity and decreased reflectivity over time, necessitating a solution to enhance light extraction efficiency and stability.
Innovation Solution
The use of a distributed Bragg reflector with a structured current spreader design, including inclined side surfaces and a transparent electrode, to improve reflectivity and prevent breakage, while maintaining electrical stability and reducing light loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a metal reflective layer is used to achieve both light reflection and electrical connection, then electrical connection is improved, but light reflectivity is insufficient causing significant light loss
Solution Approach 1:
The invention divides the functional layers into separate components: a dedicated reflective layer (distributed Bragg reflector) for light reflection and separate electrode structures (transparent electrode and current spreader) for electrical connection. This segmentation allows each layer to optimize its specific function without compromise, solving the contradiction between electrical connection and light reflectivity.
Solution Approach 2:
The distributed Bragg reflector serves multiple functions: it provides high light reflectivity for the light-emitting region while also serving as an electrical connection path through the current spreader structure. This multi-functionality resolves the contradiction by making one component system responsible for both optical and electrical functions.
2Illumination intensity
If a metal reflective layer is used to provide reflection characteristic, then light reflection is achieved, but reflectivity decreases over extended periods
Solution Approach 1:
The reflective layer is constructed as a composite structure using alternating layers of high refractive index and low refractive index materials (distributed Bragg reflector). This composite material approach provides superior optical reflection properties and enhanced long-term stability compared to single-layer metal reflective layers, addressing both light reflection and durability requirements.
3Strength
If the lateral distance between the first current spreader and the mesa is increased to reduce stress, then breakage prevention is improved, but electrical connection efficiency may be affected
Solution Approach 1:
The current spreader is designed with an extended structure that spreads current in multiple directions and planes. The elongated shape with controlled lateral distance creates a stress-distributing geometry that prevents breakage while maintaining effective electrical connection through its extended configuration.
Solution Approach 2:
The current spreader features non-uniform geometry with different lateral distances at different locations. The region closer to the mesa has optimized dimensions for electrical connection, while regions farther away provide stress relief and breakage prevention, creating local quality variations that satisfy both requirements simultaneously.
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 achieves higher reflectivity and improved electrical stability by using a distributed Bragg reflector with a structured current spreader, effectively reducing light loss and enhancing the luminous efficacy of the light emitting diode chip.
Implementation Method 1
an insulation layer covering the first conductivity type semiconductor layer, the mesa, the transparent electrode, the first current spreader and the second current spreader, having openings exposing portions of the first current spreader and the second current spreader, and including a distributed Bragg reflector
Implementation Method 2
a transparent electrode being in ohmic contact with the second conductivity type semiconductor layer
Implementation Method 3
a first current spreader disposed on the first conductivity type semiconductor layer near the mesa, and being in ohmic contact with the first conductivity type semiconductor layer
Data Source
AI summary
A light emitting diode chip includes: a first conductivity type semiconductor layer; a mesa disposed on a partial region of the first conductivity type semiconductor layer, and including an active layer and a second conductivity type semiconductor layer; a transparent electrode being in ohmic contact with the second conductivity type semiconductor layer; a first current spreader being in ohmic contact with the first conductivity type semiconductor layer; a second current spreader electrically connected to the transparent electrode; an insulation layer covering the mesa, the first current spreader and the second current spreader, and including a distributed Bragg reflector. A lateral distance between the first current spreader and the mesa is larger than a thickness of the insulation layer, and a first side surface of the first current spreader close to the mesa is longer than the second side surface thereof.