Micro LED Rear-Side 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 limitations in ohmic contact, reflectivity, and total reflection effects, particularly in flip-chip LED structures, which hinder the improvement of light extraction efficiency.
Innovation Solution
The proposed solution involves a micro LED structure with a bottom conductive layer, a light emitting layer, a top conductive structure, a bottom dielectric layer, and a conductive side arm, where the ohmic contact layer is thin and transparent, and the composite reflective layer enhances reflectivity, allowing for increased light extraction efficiency.
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 inverts the conventional electrode placement by positioning the transparent conductive electrode on the bottom of the LED structure rather than on top. This allows light to exit through the top surface without being blocked by the electrode, while the bottom electrode provides ohmic contact from the rear side
Solution Approach 2:
The patent moves the electrode interaction to a different spatial dimension by implementing rear-side contact. Instead of the electrode being in the light path (top dimension), it is positioned on the bottom surface, separating the electrical contact function from the optical emission path
2Illumination intensity
If a thin metal electrode is used to maintain light transmittance, then the light can pass through, but the current diffusion becomes non-uniform causing local overheating
Solution Approach 1:
By placing the electrode on the bottom side, the patent eliminates the trade-off between thickness and transmittance. The electrode can be sufficiently thick for good ohmic contact without blocking light, since it is positioned behind the light emission path
Solution Approach 2:
The patent introduces a transparent dielectric layer as an intermediary between the bottom electrode and the light emitting region. This allows the electrode to be thick for good contact while the dielectric layer ensures uniform current distribution and light can pass through without significant absorption
3Loss of energy
If a back reflective structure is added to improve reflectivity, then light extraction efficiency increases, but the contact area between metal electrode and semiconductor material decreases causing ohmic contact resistance to increase
Solution Approach 1:
The patent segments the functional areas by placing the reflective structure in one region and the ohmic contact in another region on the bottom surface. This allows both functions to be optimized independently without compromising each other
Solution Approach 2:
The patent applies different properties to different locations: the bottom surface has both a reflective structure in one area and a metal electrode contact in another area. Each location is optimized for its specific function - reflectivity where needed and electrical contact where needed
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 light extraction efficiencies of at least 20%, significantly improving upon conventional systems by optimizing ohmic contact and reflectivity, thereby enhancing the overall light extraction efficiency of micro LEDs.
Implementation Method 1
a bottom dielectric layer positioned between the bottom conductive layer and the light emitting layer
Implementation Method 2
Under a forward bias, the P-N junction emits visual light or infrared light
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.