Broadband Mirror With Patterned Dielectric Interfaces
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Solution Overview
Problem
Existing broadband mirrors, such as distributed Bragg reflectors and metal mirrors, suffer from wavelength-dependency and angle-dependent reflectivity, leading to inefficient light reflection and potential reliability issues at high temperatures, especially in light-emitting diodes (LEDs).
Innovation Solution
A broadband mirror is created using a dielectric layer stack with patterned and non-patterned surfaces between low-index and high-index layers, which increases reflectivity across a wide range of wavelengths and angles of incidence, reducing the need for a reflective backing and enhancing light outcoupling through scattering effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a distributed Bragg reflector (DBR) is used to achieve high reflectivity, then reflectivity within a specific wavelength band is improved, but the mirror becomes wavelength-dependent and cannot reflect light outside this band
Solution Approach 1:
The patent changes the physical state and optical properties of dielectric layers by introducing patterned surfaces with varying roughness scales. This transforms the flat, uniform interfaces into multi-scale patterned structures that manipulate light scattering across different wavelengths, enabling broadband reflection without wavelength dependency
Solution Approach 2:
The patent creates a composite dielectric layer structure combining multiple materials with different refractive indices (e.g., SiO2, Si3N4, TiO2) in alternating layers. Each layer has specific optical properties, and their combination with patterned interfaces produces synergistic effects that achieve broadband high reflectivity across visible and near-infrared spectra
2Illumination intensity
If a metal reflective backing is used to ensure high reflectivity, then light reflection is improved, but the metal absorbs some light and causes reliability problems at high temperatures
Solution Approach 1:
The patent extracts and eliminates the metal reflective backing layer from the LED structure, replacing it entirely with a dielectric mirror stack. This removal eliminates the harmful effects of metal light absorption and thermal degradation while maintaining or improving reflectivity performance through the dielectric layer design
Solution Approach 2:
The patent replaces the durable but problematic metal backing with a stack of dielectric layers that, while potentially less inherently durable, provide superior optical performance and thermal stability. The dielectric structure achieves the necessary reflectivity without the thermal reliability issues of metals, making it suitable for high-temperature LED operation
3Illumination intensity
If a DBR is used to achieve high reflectivity, then reflectivity is improved, but the reflectivity response depends on the angle of incidence and is limited to a narrow angular range
Solution Approach 1:
The patent introduces patterned surfaces with controlled roughness parameters into the dielectric layers, changing the interface geometry from flat to multi-scale patterned. This modification scatters incident light in multiple directions, reducing the sensitivity to angle of incidence and expanding the effective angular range for high reflectivity
4Loss of energy
If a reflective backing is used in LED, then light reflection is improved, but it absorbs some light and generates heat that causes reliability problems
Solution Approach 1:
The patent removes the metal reflective backing that causes light absorption and heat generation, replacing it with a dielectric mirror structure that reflects light more efficiently with minimal absorption, thereby reducing heat generation and improving thermal reliability
Solution Approach 2:
The patent converts the previously harmful light absorption and heat generation by metal backing into beneficial effects by using dielectric materials with low absorption coefficients. The dielectric mirror structure transforms the energy that would have been absorbed into reflected light, improving overall system efficiency and reducing thermal stress
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 solution significantly improves light reflection and output in LEDs by using a dielectric layer stack with patterned interfaces, achieving higher reflectivity with fewer layers compared to traditional mirrors, and is independent of wavelength, thus enhancing the efficiency and reliability of LEDs.
Implementation Method 1
The patterned interface causes scattering in the light-emitting layer. This is a beneficial effect since scattering is favourable to light outcoupling from the device.
Implementation Method 2
a broadband mirror comprises an outer surface layer and a dielectric layer stack—an alternating arrangement of low-index layers and high-index layers—applied underneath the outer surface layer
Data Source
AI summary
The invention describes a broadband mirror comprising an outer surface layer; and a dielectric layer stack arranged underneath the outer surface layer; characterized in that the dielectric layer stack comprises at least one patterned surface at an interface between adjacent dielectric layers of the dielectric layer stack. The invention further describes a light-emitting diode. The invention also describes a method of manufacturing a broadband mirror, which method comprises the steps of providing an outer surface layer and applying a plurality of dielectric layers to build a dielectric layer stack underneath the outer surface layer, characterized by the step of patterning the surface of at least one dielectric layer before applying a subsequent dielectric layer to the patterned surface.