Micro LED Optical Cavity Structure Without Mesa Edge Damage
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Solution Overview
Problem
The manufacturing process of micro LED devices, particularly the etching process for forming a pseudo parabolic MESA, results in damage to the semiconductor material, leading to reduced Internal Quantum Efficiency (IQE) and Light Extraction Efficiency (LEE).
Innovation Solution
A method of forming optical devices involves creating spacers on the sidewalls of a sacrificial mesa, depositing a reflective metallic layer, removing the sacrificial mesa to form a pocket, and installing a die into this pocket. The spacers are made of optically transparent materials with angled external faces, enhancing light extraction by directing photons towards the light emitting surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a pseudo parabolic MESA is formed using RIE or ICP etching to improve light extraction efficiency, then photons are directed to the emitting surface, but the edge of the MESA becomes damaged causing reduced internal quantum efficiency
Solution Approach 1:
The device is segmented into distinct functional regions: a sacrificial mesa structure for defining the cavity, spacers forming the optical cavity walls, and a separate die containing the light-emitting MQWs. This segmentation allows the mesa to be removed after serving its structural purpose, eliminating the source of edge damage while preserving the optical cavity geometry.
Solution Approach 2:
The sacrificial mesa is completely removed after the spacers are formed, extracting the harmful element (the damaged mesa edge) from the final device structure. This leaves only the beneficial spacers that define the optical cavity without the harmful etched edges that cause surface recombination.
Solution Approach 3:
The spacers act as an intermediary structure that transfers the function of light extraction enhancement from the damaged mesa to a undamaged structure. The spacers provide the pseudo-parabolic geometry needed for light extraction without suffering from the edge damage that plagues etched mesas.
2Area of moving object
If the micro LED size is reduced to enable smaller display pixels, then display resolution is improved, but the perimeter-to-area ratio increases causing more surface leakage and reduced efficiency
Solution Approach 1:
The spacers provide localized optical enhancement at the cavity boundaries where light extraction is most needed. By concentrating the light extraction enhancement function at the sidewalls through the pseudo-parabolic spacer geometry, small LEDs can maintain high efficiency despite their reduced size and increased perimeter-to-area ratio.
Solution Approach 2:
The solution moves from a planar light extraction approach to a three-dimensional optical cavity defined by the spacers. The pseudo-parabolic sidewalls create an additional spatial dimension for light management, directing photons toward the emitting surface and compensating for the increased surface recombination losses in smaller devices.
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 method significantly improves the light extraction efficiency and internal quantum efficiency of micro LED devices, leading to enhanced brightness and efficiency figures, while also allowing for the replacement of defective dies.
Implementation Method 1
depositing a reflective metallic layer so as to form a mirror layer on the external face of the spacers
Implementation Method 2
The spacers are made of optically transparent materials with angled external faces, enhancing light extraction by directing photons towards the light emitting surface
Data Source
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AI summary
A method of forming an optical device, the method comprising the steps of forming spacers on the substantially vertical sidewalls of a sacrificial mesa, the spacers being formed from a first electrically insulating, optically transparent material, and having an internal face contacting the mesa, and a second opposing external face; depositing a reflective, electrically conducting material so as to form a mirror layer on the external face of the spacers; removing the sacrificial mesa so as to form a pocket between the internal faces of the spacers; installing a die having substantially vertical sidewalls into the pocket between the internal faces of the spacers.