Micro-LED Pixel with DBR Reflector and Convex Lens
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Solution Overview
Problem
Micro-LEDs face challenges in achieving efficient light emission and color purity due to pump light leakage and low conversion efficiency of color converting materials, as well as limited light collection efficiency by projection lenses, which results in reduced color saturation and low optical efficiency.
Innovation Solution
A pixel design incorporating a light-emitting diode layer, a container layer with a convex lens and reflector assembly that includes a first reflector to reflect pump light and transmit converted light, allowing multiple passes through the color converting material and increasing light extraction efficiency by collimating the emitted light beam.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If colour converting material is used to convert pump light to converted light, then colour display capability is improved, but pump light leakage reduces colour purity
Solution Approach 1:
A distributed Bragg reflector (DBR) is introduced as an intermediary optical element between the colour converting material and the external environment. The DBR selectively reflects pump light wavelengths while transmitting converted light wavelengths, acting as a wavelength-dependent mediator that separates the two light types and prevents pump light leakage, thereby maintaining high colour purity while preserving colour display capability.
2Manufacturing precision
If optical filters are used to reflect pump light back to micro-LED, then colour purity is improved, but device complexity increases
Solution Approach 1:
The distributed Bragg reflector (DBR) is designed to perform multiple functions simultaneously: it reflects pump light to improve colour purity, transmits converted light to maintain display capability, and can be integrated directly onto the micro-LED structure. This multi-functionality reduces the need for separate optical filters and complex assembly steps, thereby improving colour purity without proportionally increasing device complexity.
3Manufacturing precision
If black matrix photoresist is used to block pump light, then pump light leakage is reduced, but conversion efficiency is considerably reduced
Solution Approach 1:
The solution applies different optical properties to different spatial locations: the distributed Bragg reflector is positioned specifically at the boundaries or strategic locations where pump light leakage occurs, while the central region maintains high transmission for converted light. This localized application of pump light reflection prevents broad absorption of converted light that would occur with a black matrix, thereby blocking pump light leakage while preserving high conversion efficiency.
4Illumination intensity
If micro-LED emits light in Lambertian distribution, then light emission is achieved, but light collection efficiency by projection lens is low
Solution Approach 1:
A convex lens is positioned over the micro-LED to collect and collimate emitted light. The curved surface of the convex lens refracts light rays from the Lambertian-emitting micro-LED, redirecting them into a more directional beam that falls within the acceptance angle of the projection lens. This curvature-based optical element transforms the omnidirectional emission pattern into a focused beam, significantly improving light collection efficiency while maintaining the micro-LED's inherent light emission capability.
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 enhances color saturation and optical efficiency by recycling pump light for re-conversion and improving light collection, resulting in a higher proportion of emitted light being within the acceptance angle of the lens, thereby increasing the overall light extraction efficiency.
Implementation Method 1
a first reflector to reflect pump light and transmit converted light
Implementation Method 2
the colour converting material may absorb some converted light, reducing efficiency
Implementation Method 3
a container layer with a convex lens and reflector assembly that includes a first reflector to reflect pump light and transmit converted light, allowing multiple passes through the color converting material and increasing light extraction efficiency by collimating the emitted light beam
Data Source
AI summary
A pixel comprising a first sub-pixel. The first sub-pixel comprises an LED layer comprising a light-emitting material configured to emit pump light having a pump wavelength. A container layer has a container surface comprising a first container aperture that defines a first container volume extending through the container layer. A first colour converting layer provided in the first container volume is configured to receive pump light from the LED layer and emit first converted light of a first converted wavelength. A first lens is provided on the container layer over the first container aperture, having an outer side that comprises a first convex surface. A first reflector conforming to the first convex surface comprises a first reflector configured to reflect light at the pump wavelength and transmit light at the first converted wavelength; and a second reflector configured to reflect light at both the pump wavelength and the first converted wavelength.