Embedded Reflector Micro-LED Cavity for Sub-5 μm Brightness
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Solution Overview
Problem
Current micro-LEDs face challenges in scaling down to sub-5 μm sizes due to sidewall defects, which harm efficiency, and lack sufficient brightness to meet the needs of augmented reality (AR) and virtual reality (VR) displays, limiting pixel resolution and 'useable light' in existing headsets.
Innovation Solution
The development of a micro light emitting diode array using an embedded reflector design, specifically a resonant-cavity light emitting diode (RC-LED) architecture, which features a three-dimensional III-N semiconductor structure with embedded reflectors and laterally grown LED layers, enabling high-resolution, high-brightness, and directionally focused light emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If micro-LED size is scaled down to sub-5 μm, then resolution is improved, but sidewall defects increase causing efficiency to deteriorate
Solution Approach 1:
The patent transitions from planar micro-LED structures to three-dimensional vertically-cavity-emitting LED (VCSEL) structures. By growing epitaxial layers in the vertical dimension and creating cavity structures with top and bottom reflectors, the design achieves sub-5 μm lateral dimensions with controlled sidewalls through vertical growth rather than lateral scaling, thus maintaining efficiency while achieving high resolution
Solution Approach 2:
The patent changes the growth parameters and structural configuration by using selective area epitaxial growth to create three-dimensional III-N structures with controlled morphology. The cavity depth, reflector positions, and layer thicknesses are precisely controlled during growth to optimize both resolution and efficiency, transforming the traditional planar geometry into a vertical cavity structure
2Ease of manufacture
If conventional micro-LEDs are used, then manufacturing is simpler, but brightness is insufficient for AR displays
Solution Approach 1:
The patent employs vertical cavity emission geometry where light is emitted perpendicular to the substrate through a resonant cavity structure. This vertical configuration with top and bottom DBR reflectors creates optical resonance that enhances light extraction efficiency and brightness, while the epitaxial growth process remains compatible with existing semiconductor manufacturing techniques
Solution Approach 2:
The patent optimizes optical parameters by designing cavity lengths and reflector configurations that resonate at specific wavelengths, enhancing light extraction. The epitaxial growth parameters are controlled to achieve precise layer thicknesses and compositions that maximize electroluminescence efficiency and brightness output
3Illumination intensity
If laser-based systems are used, then brightness is improved, but safety hazards and resolution limitations increase
Solution Approach 1:
The patent uses conventional LED materials and epitaxial growth processes that are well-established and safe, replacing laser sources with LED-based resonant cavity emitters. This approach provides sufficient brightness for AR displays without the safety hazards of laser radiation, using proven semiconductor manufacturing techniques
Solution Approach 2:
The patent changes the emission characteristics by using spontaneous emission from LED quantum wells rather than stimulated emission from lasers. The resonant cavity enhances the LED output to achieve brightness levels suitable for AR displays while maintaining the safety advantages of non-coherent LED light sources
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 approach allows for micron-sized sub-pixel light emitters that can be densely spaced, providing high-resolution, high-brightness displays with reduced safety concerns and improved light coupling, overcoming the etendue constraint while maintaining efficiency and resolution, suitable for next-generation AR/VR headsets.
Implementation Method 1
A resonant cavity light emitting diode (RC-LED) design using an array of micro-LEDs with embedded reflectors... minimizing etendue through cavity effects
Implementation Method 2
Current delivered by the electrical contacts causes non-coherent, spontaneous light emissions through one of the top reflectors or bottom reflectors
Implementation Method 3
Bottom reflectors are patterned as an array of closed shapes on a top plane of the base layer... One or more top reflectors are grown or deposited on the III-N LED layers and located over the bottom reflectors
Implementation Method 4
A three-dimensional III-N structure is epitaxially grown around the array of closed shapes and extends above the bottom reflectors. The three-dimensional III-N structure is a contiguous crystalline structure that extend across the array
Data Source
AI summary
A light emitting diode (LED) array includes bottom reflectors patterned as an array of closed shapes on a top plane of a base layer for III-N growth. A three-dimensional III-N structure is epitaxially grown around the array of closed shapes and extending above the bottom reflectors. The three-dimensional III-N structures is a contiguous crystalline structure extending across the array. A laterally grown III-N layer is formed in contact with both the reflectors and the three-dimensional III-N structures, and III-N LED layers are grown on the laterally grown layer. One or more top reflectors are grown or deposited on the III-N LED layers and located over the bottom reflectors.