Micro LED Sidewall Reflector Structure for Uniform Light Extraction
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Solution Overview
Problem
Vertically stacked micro light-emitting diodes face challenges such as non-uniform light patterns and uneven brightness due to anisotropic dry etching, which affects the epitaxial quality and conductivity, and the use of transparent electrodes leads to light-blocking issues and reduced light extraction efficiency.
Innovation Solution
A micro light-emitting element with a metal reflecting layer covering the sidewalls of the intrinsic semiconductor, increasing conductive area without blocking the light-emitting surface, and a patterned light-guiding structure integrated into the intrinsic semiconductor, eliminating the need for separate dry etching and ensuring uniformity in light-guiding effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If dry etching is used to form light-guiding patterns, then light-guiding patterns can be formed on the top surface, but the applied energy cannot be kept uniform leading to top shape inconsistencies and thickness variations
Solution Approach 1:
The patent transitions from forming light-guiding patterns on the top surface (2D plane) to forming them on the side surface (vertical dimension) of the micro light-emitting element. This dimensional change allows the patterns to be created through lateral etching rather than top-down etching, avoiding the energy uniformity issues associated with dry etching of thin layers while maintaining effective light guidance functionality.
2Reliability
If transparent electrode (ITO) is used on N-side light-emitting surface, then conduction is achieved, but work function difference requires metal electrode which loses light-emitting area
Solution Approach 1:
The patent moves the metal reflecting layer from the top surface to the side surface of the micro light-emitting element. This allows the metal layer to provide electrical conduction and light reflection functionality without occupying the top light-emitting area, effectively resolving the conflict between needing metal for good ohmic contact and maintaining maximum light-emitting surface area.
Solution Approach 2:
The side surface metal reflecting layer serves multiple functions simultaneously: it provides electrical conduction (replacing the need for separate metal electrode), acts as a light reflector to enhance light extraction, and maintains the integrity of the top light-emitting surface. This multi-functionality eliminates the trade-off between conduction quality and light-emitting area.
3Ease of manufacture
If wet etching is used for patterning, then patterns are formed, but undercut structure is created making transparent electrode deposition difficult
Solution Approach 1:
The patent forms light-guiding patterns on the vertical side surface rather than the horizontal top surface. This dimensional change eliminates the undercut structure problem because the patterns are created laterally without the overhang issues that plague top-surface patterning. The side surface patterns provide stable geometric profiles that facilitate subsequent electrode deposition processes.
4Reliability
If ITO thickness is increased to compensate for open circuit risk, then conduction reliability improves, but light extraction efficiency decreases due to incomplete transparency
Solution Approach 1:
The patent relocates the metal reflecting layer to the side surface, which eliminates the need for thick ITO layers altogether. The side surface metal layer provides excellent conduction reliability through direct metal-semiconductor contact while the top surface remains fully transparent for optimal light extraction. This spatial separation resolves the inverse relationship between ITO thickness and light extraction efficiency.
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 solution enhances light extraction efficiency, reduces the risk of open circuits, and achieves consistent light patterns by increasing the conductive area and maintaining uniformity in the micro light-emitting elements.
Implementation Method 1
a metal reflecting layer that laterally covers the sidewalls of the intrinsic semiconductor and a portion of the second-type semiconductor adjacent to the intrinsic semiconductor
Data Source
AI summary
A micro light-emitting element is provided. The micro light-emitting element includes a first-type semiconductor having a bottom surface and a light-emitting layer disposed on the first-type semiconductor. The micro light-emitting element also includes a second-type semiconductor disposed on the light-emitting layer and an intrinsic semiconductor disposed on the second-type semiconductor and made of the same material as the second-type semiconductor. The intrinsic semiconductor has a top surface relative to the bottom surface. The sidewalls of the first-type semiconductor, the light-emitting layer, the second-type semiconductor, and the intrinsic semiconductor form a continuous side surface, and the side surface connects the bottom surface to the top surface. The micro light-emitting element further includes a metal reflecting layer disposed on the side surface and laterally covering the sidewalls of the intrinsic semiconductor and the portion of the second-type semiconductor that is adjacent to the intrinsic semiconductor.