Single Crystalline Phosphor Bonded to LED Wafer
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Solution Overview
Problem
Conventional light emitting diodes (LEDs) face challenges in generating white light due to non-uniform color temperature and inconsistent emission characteristics, primarily because of difficulties in controlling the geometry and thickness of phosphor layers, which lead to scattering losses and total internal reflection, resulting in inefficient light conversion and reproduction.
Innovation Solution
The use of single crystalline phosphors bonded directly to LED wafers or substrates for light conversion, allowing for wafer-level fabrication and minimizing scattering and total internal reflection, while providing mechanical support and enabling the production of LEDs with consistent emission characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional phosphor coating methods (syringe or stencil) are used, then phosphor can be applied to LED, but the geometry and thickness of phosphor layer cannot be controlled uniformly
Solution Approach 1:
The phosphor layer is prepared in advance as a separate wafer with controlled thickness and geometry, then bonded to the LED wafer. This preliminary preparation allows precise control of phosphor layer properties before application, resolving the contradiction between manufacturing precision and ease of manufacture.
Solution Approach 2:
The device is divided into separate wafers (LED wafer and phosphor wafer) that are independently fabricated and then bonded together. This segmentation allows each component to be optimized separately with precise control over geometry and thickness, while simplifying the overall manufacturing process.
2Loss of energy
If phosphor layer thickness is non-uniform, then coating process is simpler, but light conversion efficiency decreases due to scattering losses and total internal reflection
Solution Approach 1:
The phosphor wafer is fabricated with controlled, uniform thickness before bonding to the LED. This preliminary control of thickness uniformity minimizes light scattering and total internal reflection losses, thereby reducing energy loss while maintaining manufacturing simplicity.
3Loss of energy
If phosphor is applied as powder with binder, then application process is easier, but light scattering increases and conversion efficiency decreases
Solution Approach 1:
The binder material is eliminated by fabricating the phosphor layer as a solid wafer structure without requiring powder-phosphor-in-binder compositions. This extraction of the binder eliminates light scattering associated with particle-binder interfaces while maintaining ease of manufacture through wafer bonding technology.
4Illumination intensity
If multiple phosphor layers or multicolor phosphors are used, then white light generation is improved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
Multiple phosphor layers or multicolor phosphors are fabricated as a single integrated phosphor wafer with spatially varying composition. This segmentation approach allows complex multicolor phosphor structures to be manufactured as one unified component, reducing device complexity while maintaining white light quality.
Solution Approach 2:
The phosphor wafer exhibits local quality variations in composition and thickness to achieve different color conversions in different regions. This allows sophisticated white light generation with multiple phosphors while maintaining relatively simple overall device structure and fabrication.
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 approach enhances light conversion efficiency, reduces scattering and total internal reflection, and allows for the consistent reproduction of LEDs with uniform color temperature by utilizing single crystalline phosphors that absorb and re-emit light effectively, improving package efficiency and thermal conduction.
Implementation Method 1
Light is emitted from the active layer and from all surfaces of the LED. Conventional LEDs cannot generate white light from their active layers. Light from a blue emitting LED has been converted to white light by surrounding the LED with a yellow phosphor
Implementation Method 2
difficult to control the phosphor layer's geometry and thickness. As a result, light emitting from the LED at different angles can pass through different amounts of conversion material, which can result in an LED with non-uniform color temperature as a function of viewing angle
Implementation Method 3
The use of single crystalline phosphors allows for wafer-level fabrication and minimizing scattering and total internal reflection
Data Source
AI summary
Methods for fabricating LED chips from a wafer and devices fabricated using the methods with one method comprising depositing LED epitaxial layers on an LED growth wafer to form a plurality of LEDs on the growth wafer. A single crystalline phosphor is bonded over at least some the plurality of LEDs so that at least some light from the covered LEDs passes through the single crystalline phosphor and is converted. The LED chips can then be singulated from the wafer to provide LED chips each having a portion of said single crystalline phosphor to convert LED light.