Abstract
The degradation behaviors of high power GaN-based vertical blue LEDs on Si substrates were measured using in-situ accelerated life test. The results show that the dominant failure mechanism would be different during the operation. Besides that, the corresponding associated failure mechanisms were investigated systematically by using different analysis technologies, such as Scan Electron Microscopy, Reflectivity spectroscopy, Transient Thermal Analysis, Raman Spectra, etc. It is shown that initially, the failure modes were mainly originated from the semiconductor die and interconnect, while afterwards, the following serious deterioration of the radiant fluxes was attributed to the package. The interface material and quality, such as die attach and frame, play an important role in determining the thermal performance and reliability. In addition, the heating effect during the operation will also release the compressive strain in the chip. These findings will help to improve the reliability of GaN-based LEDs, especially for the LEDs with vertical structure.
Highlights
GaN-based LEDs with vertical structure have been widely used in many kinds of applications, such as general illumination, automotive headlamp, etc., because of the advantages to improve the heat dissipation[1] and release the current crowding.[2]
It is shown that initially, the failure modes were mainly originated from the semiconductor die and interconnect, while afterwards, the following serious deterioration of the radiant fluxes was attributed to the package
The failure mechanism have been found to be mostly related to the defect generation/propagation, dopant diffusion, and electro-migration;[9,10] The interconnects associated failure mechanisms were mostly due to the bond wire fracture, wire ball bond fatigue, and electrostatic discharge;[11,12,13] While for the packages, carbonization of encapsulant, delamination, encapsulant yellowing, and phosphor thermal quenching from the package have been observed.[14,15,16]
Summary
GaN-based LEDs with vertical structure have been widely used in many kinds of applications, such as general illumination, automotive headlamp, etc., because of the advantages to improve the heat dissipation[1] and release the current crowding.[2]. Accelerated tests of LEDs have been often studied under different stress conditions, including electrical overstress, temperature, moisture and electrostatic discharge, to evaluate the LED reliability.[3,4,5,6,7] The failures of LEDs can be originated from the different parts of device structure, such as semiconductor die, interconnects and package.[8] For the semiconductor die, the failure mechanism have been found to be mostly related to the defect generation/propagation, dopant diffusion, and electro-migration;[9,10] The interconnects associated failure mechanisms were mostly due to the bond wire fracture, wire ball bond fatigue, and electrostatic discharge;[11,12,13] While for the packages, carbonization of encapsulant, delamination, encapsulant yellowing, and phosphor thermal quenching from the package have been observed.[14,15,16].
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