Conductive Phosphor Layer for Vertical LED Current Spreading
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Solution Overview
Problem
Current vertical LEDs face issues with total internal reflection and light attenuation at the interface of the phosphor and transparent conductor layers, leading to reduced light conversion efficiency and color uniformity, and the process of etching the phosphor layer to expose the top electrode is wasteful and inefficient.
Innovation Solution
A conductive phosphor layer is printed over the dielectric layer of vertical LEDs, allowing for electrical contact and eliminating the need for a separate transparent conductor layer, with phosphor particles and a transparent conductor material used to control light leakage and uniformity, enabling efficient wavelength conversion without etching the phosphor layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a transparent conductor layer is deposited between the phosphor layer and LED semiconductor layers to spread current laterally, then current distribution is improved, but total internal reflection occurs at the interface causing light attenuation and reduced conversion efficiency
Solution Approach 1:
The patent combines the transparent conductor material and phosphor particles into a single integrated conductive phosphor layer, eliminating the separate transparent conductor layer and its harmful interface. This merged structure allows current spreading while avoiding total internal reflection losses at distinct layer interfaces.
Solution Approach 2:
The conductive phosphor layer uses a composite material consisting of phosphor particles suspended in a transparent conductor material. This composite provides both electrical conductivity for current spreading and optical transparency for light transmission, eliminating the need for a separate transparent conductor layer.
2Ease of operation
If the phosphor layer is etched to expose the top electrode for wire bonding, then electrode accessibility is improved, but phosphor is wasted and color uniformity is reduced
Solution Approach 1:
The conductive phosphor layer serves dual functions as both the phosphor conversion layer and the top electrode, eliminating the need to etch away phosphor material. The wire bond contacts the conductive phosphor layer directly, providing electrode accessibility without phosphor waste.
Solution Approach 2:
The conductive phosphor layer performs multiple functions simultaneously: wavelength conversion, current spreading, and electrode function. This multi-functionality eliminates the need for separate electrode structures that would require etching, preserving phosphor material and color uniformity.
3Illumination intensity
If the top metal electrode is made small or patterned to avoid blocking light, then light transmission is improved, but current spreading capability is reduced
Solution Approach 1:
The conductive phosphor layer uses a composite material that provides both optical transparency and electrical conductivity. This allows the electrode to maintain a large surface area for effective current spreading while remaining optically transparent to maximize light transmission, unlike traditional metal electrodes that must be minimized.
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 solution enhances light conversion efficiency and color uniformity by allowing precise control of light leakage and eliminating the need for etching, resulting in improved performance and reduced waste.
Implementation Method 1
the phosphor layer may be a YAG phosphor that emits yellow light when energized by a blue light, and the active layer may emit blue light. Some of the blue light leaks through the phosphor layer to combine with the yellow light to create white light
Implementation Method 2
The conductive phosphor layer is designed to allow a precise amount of the blue light to leak through so that the resulting light is white. The phosphor is designed to be optimally energized by the LED peak emission wavelength.
Implementation Method 3
An electrically conductive phosphor layer, customized for use with the LEDs, is then printed over the dielectric layer to electrically contact the top anode surface of the LEDs
Implementation Method 4
A dielectric layer is then printed over the first conductive layer so as to expose the top anode electrodes
Data Source
AI summary
In a method for forming a phosphor-converted LED, an array of vertical LEDs is printed over a conductive surface of a substrate such that a bottom electrode of the LEDs ohmically contacts the conductive surface. A dielectric layer then formed over the conductive surface. An electrically conductive phosphor layer is deposited over the dielectric layer and the LEDs to ohmically contact the top surface of the LEDs and connect the LEDs in parallel. The conductive phosphor layer is formed by phosphor particles intermixed with a transparent conductor material. One or more metal contacts over the conductive phosphor layer conduct current through the conductive phosphor layer and the LEDs to illuminate the LEDs. A portion of light generated by the LED leaks through the conductive phosphor layer, and the combination of the LED light and phosphor light creates a composite light.