Micro-LED Micro-Lens Structure for Higher Light Extraction
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Solution Overview
Problem
Micro-LEDs with reduced physical dimensions face challenges in improving their internal and external quantum efficiencies, particularly in extracting light within a small emission cone, leading to low light extraction efficiency and external quantum efficiency in display systems.
Innovation Solution
The implementation of a micro-LED device with a semiconductor mesa structure having inwardly tilted sidewalls and a spacer layer with a micro-lens on top, where the spacer layer's thickness is optimized to position the focal point of the micro-lens at the front surface of the mesa, enhancing light extraction and collimation efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If micro-LED physical dimensions are reduced to increase packing density, then display resolution is improved, but light extraction efficiency deteriorates
Solution Approach 1:
The patent applies curvature by forming a micro-lens on the spacer layer above the micro-LED. This lens structure has a curved surface that focuses and extracts light more efficiently from the small-area micro-LED, converting the problematic small emission area into an advantage by concentrating light extraction through the curved lens geometry.
Solution Approach 2:
The patent introduces a spacer layer as an intermediary component between the micro-LED and the micro-lens. This spacer layer with optimized thickness (greater than or equal to 2 times the semiconductor material thickness) positions the micro-lens focal point at the front surface of the semiconductor mesa, acting as a mediator that enables efficient light extraction without direct contact between the lens and the LED structure.
2Productivity
If micro-LED size is reduced for higher packing density, then device integration is improved, but light extraction within small emission cone deteriorates
Solution Approach 1:
The micro-lens with its curved surface is specifically designed to work with small-area micro-LEDs. The curvature of the lens focuses the light from the small emission area into a concentrated beam, improving light extraction efficiency within the small emission cone while maintaining the small size necessary for high packing density.
Solution Approach 2:
The patent optimizes the spacer layer thickness parameter to be greater than or equal to 2 times the thickness of the semiconductor materials. This parameter change positions the focal point of the micro-lens precisely at the front surface of the semiconductor mesa, maximizing light extraction efficiency for small-sized micro-LEDs.
3Ease of manufacture
If conventional LED structure is used, then manufacturing is simpler, but light extraction efficiency and external quantum efficiency are low
Solution Approach 1:
The patent segments the LED structure into distinct functional layers: the semiconductor mesa structure, the spacer layer, and the micro-lens layer. This segmentation allows each component to be optimized for its specific function while maintaining overall manufacturability through established semiconductor fabrication processes.
Solution Approach 2:
The micro-lens with its curved surface is formed on the spacer layer using standard fabrication techniques such as reflow processing. This curvature is essential for achieving high light extraction efficiency and external quantum efficiency, as it focuses and extracts light effectively from the underlying micro-LED structure.
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 significantly increases the collected light extraction efficiency and the ratio of collected to total light extraction efficiency, improving the display system's performance by better coupling light into the waveguide and towards the user's eye.
Implementation Method 1
a micro-lens on the spacer layer and configured to extract and collimate the light emitted by the micro-LED
Data Source
AI summary
Disclosed herein are techniques for micro-light emitting diodes (micro-LEDs). According to certain embodiments, a micro-LED device includes a micro-LED comprising a semiconductor mesa structure configured to emit light, a spacer layer on the micro-LED, and a micro-lens on the spacer layer and configured to extract and collimate the light emitted by the micro-LED, where a thickness of the spacer layer is selected such that a focal point of the micro-lens is at a front surface of the semiconductor mesa structure.