Micro LED Reflective Contact Structure for Higher Light Extraction
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Solution Overview
Problem
Conventional micro light emitting diode (LED) systems face challenges in achieving high light extraction efficiency due to issues such as total reflection, low ohmic contact resistance, and limited reflective area, which hinder the improvement of light extraction efficiency.
Innovation Solution
The proposed micro LED structure includes a bottom conductive layer, a light emitting layer, a top conductive structure, a bottom dielectric layer, and a conductive side arm, with a thin ohmic contact layer that is transparent and narrow, enhancing light extraction efficiency by increasing the reflective area and reducing shielding effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thick metal electrode is used to achieve good ohmic contact, then the ohmic contact resistance is reduced, but the light transmittance of the electrode decreases due to shielding
Solution Approach 1:
The patent transitions from a planar electrode structure to a three-dimensional mesh structure, where the electrode is configured as intersecting conductive lines forming openings. This dimensional change allows light to pass through the openings while maintaining electrical conductivity through the mesh pattern, simultaneously achieving low contact resistance and high light transmittance.
Solution Approach 2:
The electrode structure employs different local configurations: the mesh pattern provides high transmittance in the center area where light emission occurs, while the conductive lines maintain low resistance where electrical contact is needed. The local structure adapts to the functional requirements of different regions.
2Illumination intensity
If a thin metal electrode is used to maintain light transmittance, then the light shielding effect is reduced, but the current diffusion becomes non-uniform causing local overheating
Solution Approach 1:
By creating a mesh structure with conductive lines extending in multiple directions, the electrode provides distributed current pathways in three dimensions. This ensures uniform current diffusion across the LED chip surface while maintaining sufficient light transmission through the mesh openings, preventing localized overheating.
Solution Approach 2:
The continuous electrode layer is segmented into a mesh pattern with discrete conductive lines and openings. This segmentation allows light to pass through the openings while the distributed conductive lines provide multiple current pathways, ensuring uniform current distribution without requiring a solid continuous layer that would block light.
3Loss of energy
If a back reflective structure is added to improve light extraction, then the reflectivity is increased, but the contact area between metal electrode and semiconductor material is decreased causing ohmic contact resistance to increase
Solution Approach 1:
The patent combines the reflective function and the electrical contact function into a single integrated mesh electrode structure. The same conductive mesh that provides electrical contact also serves as the reflective layer, eliminating the need for separate back contact and reflective structure. This merging maintains full contact area with the semiconductor while providing both electrical and optical functions.
Solution Approach 2:
The mesh electrode structure performs multiple functions simultaneously: it provides electrical contact, reflects light, and allows current diffusion. The universal design eliminates the trade-off between contact area and reflectivity by integrating all functions into one structure that maintains full contact with the semiconductor surface.
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 configuration achieves a high light extraction efficiency of at least 20%, with some embodiments reaching efficiencies of up to 60%, by optimizing the reflective area and minimizing ohmic contact resistance, thereby overcoming the limitations of conventional LED systems.
Implementation Method 1
a bottom dielectric layer arranged between the bottom conductive layer and the light emitting layer
Implementation Method 2
a thin ohmic contact layer that is transparent and narrow, enhancing light extraction efficiency by increasing the reflective area and reducing shielding effects
Implementation Method 3
a light emitting layer on the bottom conductive layer
Data Source
AI summary
A micro light emitting diode (LED) having a high light extraction efficiency includes a bottom conductive layer, a light emitting layer on the bottom conductive layer, and a top conductive structure on the light emitting layer. The micro LED additionally includes a conductive side arm electrically connecting the sidewall of the light emitting layer with the bottom conductive layer, and a reflective bottom dielectric layer arranged under the light emitting layer and above the bottom conductive layer. In some embodiments, the micro LED further includes an ohmic contact between the top conductive structure and the light emitting layer that has a small area and is transparent, thereby increasing the light emergent area and improving the light extraction efficiency.