| Summary: | 碩士 === 國立清華大學 === 動力機械工程學系 === 101 === Due to the effect of global warming, light emitting diodes (LEDs) have become more and more popular in recent years with its advantages like low pollution, low power consumption, long operation lifetime and so on. However, the reliability test standard, IES LM-80-08, which is utilized mostly by LED industry costs too much time and prolonged the time-to-market. This situation can be regarded as an obstacle to the LED Research and development.
There are several types of stress may affect the LED degradation such as temperature stress, current stress, and optical stress. In this study, an accelerated aging test on high power LEDs at different high temperature stress without input current is proposed. A Gallium Nitride (GaN) based 1-W LEDs from the same series are chosen as test samples. The samples consist of white LEDs, blue LEDs and decapsulated blue LEDs. The difference between white LEDs, and blue LEDs is that white LEDs have phosphor but blue LEDs do not. The degradation of light output was detected during aging. According to the difference of samples, each degradation mechanisms can be separated.
The accelerated aging test started from an in-depth knowledge of the device structure, and aimed at (i) extrapolating the degradation model that can provide an accurate lifetime estimation, (ii) investigating acceleration factors (AF) of temperature stress in the aging test for degradation, (iii) proposing an available method to shorten the reliability test standards, IES LM-80-08 and TM-21-11, which cost 6,000 hours at least. The results of accelerated aging test show that a high enough temperature stress can effectively shorten the unstable period of LED chip. And the estimated lifetimes calculated from the AF of temperature stress in this study conform the span of lifetimes calculated from the IES LM-80-08 and TM-21-11. Therefore, it is recommended that the temperature stress of existing LED test standard can be set harsher. It would reduce testing time and shorten time-to-market and promote the current light-emitting diode industry.
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