LED Electrode Resistance and Light Extraction
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Solution Overview
Problem
Large LED light emitting elements face issues with increased drive voltage and reliability due to high current densities and uneven current distribution, leading to heat degradation and light extraction efficiency problems when using wide electrodes, and existing solutions fail to adequately address these issues.
Innovation Solution
A light emitting element with electrodes having electrical resistance of 1Ω or less in the farthest distance, formed on a transparent substrate with a tapered surface, using highly reflective metals and a DBR structure to improve current diffusion and light extraction efficiency, and die bonding to a current supply body for uniform current distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the size of the element is increased to increase drive current, then the luminosity is improved, but the drive voltage rises due to increased current diffusion distance
Solution Approach 1:
The patent segments the electrode structure into multiple layers (reflective electrode layer, intermediate layer, transparent electrode layer) to reduce overall resistance while maintaining large element size. This layered segmentation allows current to be conducted more efficiently through parallel paths, reducing voltage drop without limiting the element's luminosity output
2Power
If the size of the element is increased to increase drive current, then the luminosity is improved, but the voltage drop increases due to larger current diffusion distance
Solution Approach 1:
The patent employs composite electrode structures combining materials with different properties: highly reflective metals (Ag, Al) for the reflective layer to reduce resistance, transparent conductive oxides (ITO, IZO) for the transparent electrode layer to maintain electrical conductivity while allowing light transmission. This composite approach minimizes energy loss as heat while preserving high drive current capability
3Reliability
If wide electrodes are used to diffuse current, then the current distribution is improved, but the light extraction efficiency is degraded
Solution Approach 1:
The patent applies local quality by making the electrode structure transparent or semi-transparent in regions where light extraction is critical. The transparent electrode layer allows light to pass through while still providing current diffusion, creating different optical properties in different parts of the electrode structure to simultaneously achieve both current uniformity and high light extraction efficiency
4Reliability
If wiring-like electrodes are used for current diffusion, then the current distribution is improved, but the wiring resistance causes increased drive voltage
Solution Approach 1:
The patent extracts the high-resistance wiring structure and replaces it with a low-resistance reflective electrode layer that extends across the entire element surface. This extraction of the problematic wiring resistance while maintaining the current diffusion function through the reflective and transparent electrode layers reduces drive voltage while preserving current distribution uniformity
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 reduces drive voltage, enhances reliability by minimizing current concentration and electro migration, and improves light extraction efficiency by ensuring uniform current density distribution and high reflectance, making it suitable for large current applications.
Implementation Method 1
a first electrode which is reflective with respect to the wavelength and formed on a surface of the semiconductor layer... a second electrode which is reflective with respect to the wavelength and formed on the second surface
Data Source
AI summary
A light emitting element which emits light of a wavelength, includes a substrate which is transparent to the wavelength of emitted light and includes a first surface and a second surface; a semiconductor layer stacked on the first surface; a first electrode which is reflective to the wavelength of emitted light and formed on a surface of the semiconductor layer, wherein electrical resistance of the first electrode in a farthest distance is equal to or smaller than 1Ω; and a second electrode which is reflective to the wavelength of emitted light and formed on the second surface, wherein electrical resistance of the second electrode in a farthest distance is equal to or smaller than 1Ω.