UV LED Chip Phosphor-on-Chip Color Stability
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Solution Overview
Problem
Conventional white light-emitting diode (LED) devices face issues with low durability, unstable quantum efficiency, and high cost due to large deviations in color temperature when driven by high current density, particularly in UV-phosphor systems and multi-chip configurations.
Innovation Solution
A wavelength-converting LED device with an LED chip emitting primary light of wavelength shorter than 430 nm, driven by current density greater than 200 mA/cm², utilizing a phosphor-on-chip process involving a Ba2SiO4:Eu phosphor encapsulated in resin, which improves efficiency and maintains consistent color temperature across chips from the same wafer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a blue LED with wavelength between 450-470 nm is used together with YAG:Ce phosphor to produce white light, then the color temperature is high (6000K-8000K) comparable to sunlight, but the quantum efficiency decreases rapidly when driven by high current density and color temperature deviation is large
Solution Approach 1:
The patent changes the wavelength parameter of the LED from conventional 450-470 nm blue light to 405 nm UV light, and changes the phosphor material from YAG:Ce to BaMgAl10O17:Eu (BAM:Eu) phosphor. This parameter change enables the system to maintain stable quantum efficiency even at high current densities while achieving consistent color temperature across different chips.
2Manufacturing precision
If there is a large deviation of color temperatures of LEDs in a wafer, then additional chip sorting process after dicing is necessary to provide stable color temperature, but this increases the cost and reduces productivity
Solution Approach 1:
The patent extracts and eliminates the chip sorting process by developing a phosphor-on-chip integration method that ensures uniform phosphor distribution and consistent optical properties across all chips in a wafer. This extraction of the sorting step directly improves productivity while maintaining color temperature consistency.
3Illumination intensity
If a lamp contains at least three LED chips (red, green, and blue chips) encapsulated in a single epoxy package, then white light can be produced, but the device becomes complicated and the cost increases
Solution Approach 1:
The patent merges the functions of multiple LED chips (red, green, blue) into a single UV LED chip that excites a phosphor layer to produce white light. This consolidation reduces device complexity by eliminating the need for multiple chips, multiple electrical leads, and complex control circuits while maintaining white light output capability.
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 solution enhances light efficiency, reduces color temperature deviations, and eliminates the need for additional chip sorting, resulting in cost savings and improved productivity while maintaining high color rendering index.
Implementation Method 1
Conversion of the primary light of the LED to a longer wavelength is commonly referred to as 'down-conversion' of the primary light
Implementation Method 2
a wavelength-converting material above the LED chip for absorbing the primary light to excite a secondary light
Data Source
AI summary
A light-emitting device includes an LED chip emitting a primary light, and a phosphor deposited on the LED chip for absorbing the primary light to excite a secondary light, wherein the wavelength of the primary light is shorter than 430 nm and the LED chip is driven by current density greater than 200 mA/cm2. The wavelength-converting light-emitting device has a high light efficiency and a stable color temperature, wherein LED chip is diced from a wafer made by means of a phosphor-on-chip process.