Micro-LED Mesa Structure for Light Collimation
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Solution Overview
Problem
Micro-LED devices with mesa structures face limitations in achieving improved collimation of light output, as existing technologies prioritize high extraction efficiency over collimation, leading to reduced light collimation and increased half-angle of emitted beams.
Innovation Solution
The implementation of a micro-LED design featuring a low aspect ratio near-parabolic mesa structure combined with a polished reflective surface of low roughness, which internally reflects parasitic rays to enhance collimation, while maintaining satisfactory extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a high aspect ratio mesa structure is used to enhance extraction efficiency, then light extraction is improved, but light collimation deteriorates and half-angle increases
Solution Approach 1:
The patent changes the aspect ratio parameter of the mesa structure from conventional high values to low values (less than 0.5), and modifies the surface roughness parameter of the reflective surface to less than 500 nm. These parameter changes resolve the contradiction by achieving better collimation while maintaining acceptable extraction efficiency through the combined effect of low aspect ratio and polished reflective surfaces.
Solution Approach 2:
Instead of using a high aspect ratio mesa structure as conventionally done to maximize extraction efficiency, the patent inverts the approach by using a low aspect ratio mesa structure. This inversion, combined with a polished reflective surface, redirects parasitic rays through internal reflection to improve collimation while maintaining extraction efficiency.
2Loss of energy
If a rough or shaped reflective surface is used to enhance extraction efficiency, then light extraction is improved, but light collimation deteriorates
Solution Approach 1:
The patent changes the surface roughness parameter of the reflective surface to a low value (less than 500 nm), contrary to conventional approaches that use rough surfaces. This parameter change, combined with the low aspect ratio mesa structure, enables internal reflection of parasitic rays to improve collimation while maintaining extraction efficiency.
Solution Approach 2:
Instead of using a rough reflective surface as conventionally done to enhance extraction efficiency, the patent inverts the approach by using a polished (smooth) reflective surface. This inversion, combined with the low aspect ratio mesa structure, achieves better collimation through internal reflection of parasitic rays.
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 design significantly improves light collimation by reducing the half-angle of emitted beams, offering improved performance for applications requiring directional light output, such as electro-optical systems and displays.
Implementation Method 1
the μLED further comprises a reflective surface located in a region from the light emitting source to the primary emission surface, wherein the reflective surface has a roughness, Ra, less than 500 nm... the combination of these features allows parasitic rays emitted from the emission source to be internally reflected, thereby reducing the half angle (and increasing the collimation) of the μLED
Data Source
AI summary
A Light emitting diode (LED) includes a mesa structure, a light emitting source within the mesa structure, and a primary emission surface on a side of the LED opposed to a top of the mesa structure. The light emitting source is configured to emit light anisotropically in a first direction perpendicular to a second direction of emission of the light from the LED at the primary emission surface.