Stepped Micro-Lens Structure for Micro-LED Light Collimation
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Solution Overview
Problem
Micro-LEDs face challenges in achieving high light extraction and collimation efficiencies due to total internal reflection and surface plasmon resonance, particularly in small dimensions, where precise fabrication of smooth micro-lenses is difficult using existing techniques.
Innovation Solution
The use of stepped micro-lenses with discrete thickness levels, fabricated using a self-aligned process involving etch mask layers and spacer deposition, to collimate light emitted by micro-LEDs, which can be made in semiconductor epitaxial layers or other dielectric materials, improving light extraction and collimation performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional smooth micro-lenses are fabricated using existing techniques, then light extraction and collimation can be achieved, but manufacturing precision deteriorates in small dimensions due to total internal reflection and surface plasmon resonance
Solution Approach 1:
The micro-lens is segmented into multiple discrete thickness levels (e.g., 4 or more levels) rather than being a smooth continuous surface. This segmentation allows the lens to be fabricated using standard photolithography and etching processes with discrete steps, achieving comparable or better collimation performance while overcoming the manufacturing precision limitations in small dimensions (pitch ≤ 5 μm).
Solution Approach 2:
The invention transitions from a two-dimensional smooth surface approximation to a three-dimensional stepped structure with discrete thickness levels. This dimensional approach allows precise control of light extraction and collimation by varying the thickness at different radial zones, achieving high performance without requiring ultra-precise smooth surface fabrication.
2Productivity
If micro-LED pitch is reduced to increase packing density, then display resolution improves, but light extraction efficiency deteriorates due to increased total internal reflection
Solution Approach 1:
The stepped micro-lens structure provides locally optimized thickness at different radial positions, with each thickness level tailored to extract light efficiently from the small active region. This local quality variation compensates for the reduced light extraction efficiency caused by smaller micro-LED pitch and dimensions.
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 stepped micro-lenses achieve comparable or better collimation performance than conventional convex lenses and can be more precisely manufactured, enhancing the light extraction and collimation efficiencies of micro-LEDs, particularly in small dimensions.
Implementation Method 1
an array of micro-lenses aligned with the array of micro-LEDs and configured to collimate the visible light emitted by the array of micro-LEDs, where each micro-lens of the array of micro-lenses may have a plurality of discrete thickness levels
Implementation Method 2
Light emitting diodes (LEDs) convert electrical energy into optical energy
Data Source
AI summary
A light source includes a backplane including electrical circuits fabricated thereon, an array of micro-light emitting diodes (micro-LEDs) bonded to the backplane and configured to emit visible light, and an array of micro-lenses aligned with the array of micro-LEDs and configured to collimate the visible light emitted by the array of micro-LEDs. Each micro-lens of the array of micro-lenses has a plurality of discrete thickness levels. A pitch of the array of micro-lenses is equal to or less than about 5 μm, such as about 2 μm. The pitch of the array of micro-lenses can be the same as or different from the pitch of the array of micro-LEDs.