Composite High Reflectivity Layer for LED Light Extraction
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Solution Overview
Problem
Conventional light emitting diodes (LEDs) face limitations in light extraction efficiency due to total internal reflection (TIR) caused by the high refractive index difference between semiconductor materials and their surroundings, leading to optical losses and reduced brightness, despite the use of reflective surfaces and coatings like silver, which have less than 100% reflectivity and are ineffective across multiple angles and wavelengths.
Innovation Solution
A composite high reflectivity layer is introduced in or on LED packages and chips, comprising multiple layers with varying indices of refraction and thicknesses, along with a reflective layer, to enhance light reflection and reduce TIR, while also allowing for conductive vias for electrical signal passage, thereby improving light emission efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single reflective layer (e.g., silver) is used to reflect light, then the structure is simple, but the reflectivity is less than 100% and ineffective across multiple angles and wavelengths
Solution Approach 1:
The patent applies composite materials by combining multiple layers with different optical properties (DBR layers with alternating high and low refractive indices, metal reflective layer, and dielectric layers) to create a composite reflective structure that achieves superior reflectivity across multiple angles and wavelengths compared to single-material reflectors
Solution Approach 2:
The reflective structure is segmented into multiple functional layers: DBR layers for wavelength-selective reflection, metal layer for broadband reflection, and dielectric layers for optical matching. Each segment performs a specific function that collectively solves the limitation of single-layer reflectors
2Loss of energy
If surface texturing is applied to increase light escape probability, then light extraction efficiency improves, but the device complexity increases
Solution Approach 1:
The patent addresses light extraction by adding vertical layering (another dimension) through multiple reflective and dielectric layers, rather than only modifying the surface topology. This dimensional approach provides angle-independent reflection without the manufacturing complexity of surface texturing
3Ease of operation
If metal reflective layers are used to direct light, then light direction control improves, but optical losses occur due to less than 100% reflectivity
Solution Approach 1:
The patent combines metal reflective layers with DBR layers and dielectric materials to create a composite structure that maintains the light-directioning capability of metals while compensating for their less-than-perfect reflectivity through the additive effect of multiple layers with complementary reflection characteristics
4Loss of energy
If a composite layer with multiple layers of varying indices of refraction is used, then reflectivity across broader angles and wavelengths improves, but the device complexity increases
Solution Approach 1:
The patent systematically varies optical parameters (refractive index, layer thickness, material composition) across multiple layers to optimize reflectivity performance. By changing these parameters in a controlled sequence, the structure achieves broadband and wide-angle reflection while maintaining manufacturability through standardized fabrication processes
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 composite layer achieves higher reflectivity across a broader range of angles and wavelengths, minimizing optical losses and increasing the overall brightness of LEDs by ensuring that more light is directed towards useful emission, exceeding the efficiency of standard metal contacts and DBRs.
Implementation Method 1
The composite layer achieves higher reflectivity across a broader range of angles and wavelengths, minimizing optical losses
Implementation Method 2
For conventional LEDs with a single out-coupling surface, the external quantum efficiency can be limited by total internal reflection (TIR) of light from the LED's emission region
Implementation Method 3
one of said plurality of layers has an index of refraction lower than the encapsulant
Data Source
AI summary
A high efficiency light emitting diode with a composite high reflectivity layer integral to said LED or package to improve emission efficiency. One embodiment of a light emitting diode (LED) chip comprises a LED and a composite high reflectivity layer integral to the LED to reflect light emitted from the active region. One embodiment of a LED package comprises a LED mounted on a substrate with an encapsulant over said LED and a composite high reflectivity layer arranged to reflect emitted light. The composite layer comprises a plurality of layers such that at least one of said plurality of layers has an index of refraction lower than the encapsulant and a reflective layer on a side of said plurality of layers opposite the LED. In some embodiments, conductive vias are included through the composite layer to allow an electrical signal to pass through the layer to the LED.