LED Wavelength Correction via Sequential Phosphor Coating
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Solution Overview
Problem
Conventional white LEDs face challenges in achieving color uniformity due to wavelength variations across semiconductor wafers, which affect the emission spectrum and require careful control of phosphor properties and layer thickness, leading to perceptible color differences that can reduce customer satisfaction.
Innovation Solution
A method involving sequential coating of semiconductor devices with a base wavelength conversion material and tuning wavelength conversion materials, including phosphors, to correct for wavelength variations and ensure color uniformity, particularly applicable to warm white light emission, where base and tuning phosphors are applied to achieve specific color points.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single phosphor coating is applied to semiconductor devices with wavelength variations, then the manufacturing process is simple, but the color uniformity deteriorates
Solution Approach 1:
The phosphor coating process is segmented into multiple sequential steps: first applying a base phosphor coating, then applying additional phosphor materials in targeted areas. This segmentation allows different regions of the semiconductor device to receive different phosphor compositions, correcting wavelength variations while maintaining manufacturing feasibility through automated sequential deposition
Solution Approach 2:
The patent applies different phosphor materials and concentrations to different locations on the semiconductor device based on measured wavelength variations. Devices with blue-shifted wavelengths receive yellow phosphor coatings, while devices with red-shifted wavelengths receive different phosphor compositions, achieving local optimization of color uniformity across the wafer
2Manufacturing precision
If phosphor properties and layer thickness are carefully controlled to achieve uniform color, then color consistency improves, but the device complexity and process control requirements increase
Solution Approach 1:
The patent systematically varies phosphor parameters including material composition, particle size distribution, concentration, and layer thickness to compensate for wavelength variations. By changing these parameters in a controlled manner across different device locations, the invention achieves color uniformity without requiring overly complex multi-layer phosphor structures
Solution Approach 2:
The patent replaces complex mechanical control of single-layer phosphor thickness with a simpler sequential coating approach using multiple phosphor materials. Instead of precisely controlling the thickness of one phosphor layer to account for all variations, the system uses multiple phosphor coatings with different optical properties, reducing the complexity of thickness control requirements
3Manufacturing precision
If wavelength variations across the wafer are corrected using individualized phosphor applications, then color uniformity improves, but the manufacturing time and process steps increase
Solution Approach 1:
The patent measures the emission wavelength of each semiconductor device before phosphor application and uses this information to determine the optimal phosphor coating strategy. This preliminary characterization allows the system to pre-plan the phosphor deposition pattern, avoiding iterative adjustments and reducing total process time
Solution Approach 2:
The patent combines multiple phosphor deposition steps into a single sequential coating process that can be performed in one continuous manufacturing run. By merging the application of different phosphor materials into a unified process flow with automated transition between materials, the system achieves wavelength correction without requiring multiple separate processing cycles
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 enables the production of LEDs with improved color consistency and reduced color variation, enhancing customer acceptance by achieving targeted chromaticity and luminous flux across the wafer, allowing for more efficient binning and packaging processes.
Implementation Method 1
Light from a blue emitting LED has been converted to white light by surrounding the LED with a yellow phosphor... The surrounding phosphor material converts the wavelength of some of the LED's blue light, changing its color.
Implementation Method 2
Tuning wavelength conversion material is disposed on the plurality of semiconductor devices, the tuning wavelength material comprising at least one tuning phosphor.
Data Source
AI summary
Methods for fabricating semiconductor devices such as LED chips with emission wavelength correction and devices fabricated using these methods. Different embodiments include sequential coating methods that provide two or more coatings or layers of conversion material over LEDs, which can be done at the wafer level. The methods are particularly applicable to fabricating LED chips that emit a warm white light, which typically requires covering LEDs with one or more wavelength conversion materials such as phosphors. In one embodiment, a base wavelength conversion material is applied to the semiconductor devices. A portion of the base conversion material is removed. At least two different tuning wavelength conversion materials are also applied to the semiconductor devices, either before or after the application of the base conversion material.