Transparent LED with Inverted Cone Extractor
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Solution Overview
Problem
Conventional LEDs suffer from decreased efficiency due to re-absorption of reflected light by the emitting layer, as the photon energy matches the band-gap energy, leading to reduced light output power.
Innovation Solution
The LED is embedded in a shaped optical element, such as an inverted cone made of transparent materials like epoxy or glass, with side walls angled to reflect light out of the cone for extraction from multiple sides, including a phosphor layer and textured surfaces to enhance light extraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a mirror is placed on the backside of the substrate or on the lead frame to increase light output power, then light extraction from the front side is improved, but the light is re-absorbed by the emitting layer causing decreased efficiency
Solution Approach 1:
The patent extracts the light extraction function from the traditional mirror-based reflection system and implements it through multiple independent extraction paths: front surface extraction through the substrate, back surface extraction through the lead frame, and side surface extraction through the transparent encapsulant. This eliminates the need for mirrors and prevents re-absorption by distributing light extraction across multiple directions and interfaces.
Solution Approach 2:
The patent transitions from traditional single-direction (front-side) light extraction to multi-dimensional extraction by enabling light to exit through the front substrate, back lead frame, and side surfaces of the transparent encapsulant. This spatial distribution across multiple dimensions prevents light from being reflected back into the emitting layer where re-absorption would occur.
2Illumination intensity
If conventional LED structures with mirrors are used, then light extraction is attempted, but the device complexity increases due to mirror placement requirements
Solution Approach 1:
The patent removes the mirror component entirely from the LED structure and extracts the light extraction function to the fundamental interfaces and surfaces: the front substrate interface, the back lead frame interface, and the side surfaces of the transparent encapsulant. This simplification eliminates the complexity of mirror placement while maintaining effective light extraction.
Solution Approach 2:
The patent enables the LED structure to perform its own light extraction function through the inherent optical properties of its components: the transparent substrate allows front surface extraction, the transparent lead frame enables back surface extraction, and the transparent encapsulant provides side surface extraction. The structure serves its own light extraction needs without requiring additional mirror components.
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 configuration allows for multi-directional light extraction from the LED, increasing light output power by preventing re-absorption and enhancing light extraction efficiency from both the top and bottom sides.
Implementation Method 1
The inverted cone shape has side walls positioned at an angle to the inverted cone shape's base, wherein the angle is more than sin−1(n1/n2), n1 is a refractive index of air, and n2 is a refractive index of the inverted cone shape's material. The light is reflected to a top surface of the inverted cone shape by the side walls of the inverted cone shape for emission through the top surface of the inverted cone shape.
Implementation Method 2
The inverted cone shape has side walls positioned at an angle to the inverted cone shape's base, wherein the angle is more than sin−1(n1/n2), n1 is a refractive index of air, and n2 is a refractive index of the inverted cone shape's material.
Data Source
AI summary
An (Al, Ga, In)N light emitting diode (LED) in which multi-directional light can be extracted from one or more surfaces of the LED before entering a shaped optical element and subsequently being extracted to air. In particular, the (Al, Ga, In)N and transparent contact layers (such as ITO or ZnO) are embedded in or combined with a shaped optical element comprising an epoxy, glass, silicon or other material molded into an inverted cone shape, wherein most of the light entering the inverted cone shape lies within a critical angle and is extracted. In addition, the present invention stands the LED on end, i.e., rotates the position of the LED within the shaped optical element by approximately 90° as compared to a conventional LED, in order to extract light more effectively from the LED. The present invention also minimizes internal reflections within the LED by eliminating mirrors and/or mirrored surfaces, in order to minimize re-absorption of the LED's light by the emitting layer (or the active layer) of the LED. To assist in minimizing internal reflections, transparent electrodes, such as ITO or ZnO, may be used. Surface roughening by patterning or anisotropically etching (i.e., creating microcones) may also assist in light extraction, as well as minimizing internal reflections.