Accelerated Life Test of High Brightness
Light Emitting Diodes
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陳詠升
Outline
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INTRODUCTION
EXPERIMENTAL SETUP
RESULTS AND DISCUSSION
CONCLUSION
REFERENCES
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INTRODUCTION
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• In the last fewyears, great efforts have been spent
in the improvements of materials and structure in
terms of process and reliability. Novel
technologies for low defect densities in active
region allow a better efficiency, and an efficacy of
110 lm/W at 350 mA has been demonstrated .
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• The high junction temperature reached during
operation limits the lifetime of devices, and better
performing heat sinks are needed in order to
operate at high current level.
EXPERIMENTAL SETUP
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Temperature increase for devices operated at 400 mA without heat sink at ambient
temperature of about 35 ◦C. The temperature was collected from voltage transient and
thermal coefficient.
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Light output decay for different aging temperatures (180 ◦C–230 ◦C) during first 50 h.
The time constant of quasi-exponential kinetic decreased with higher temperatures.
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Arrhenius plot of the MTTF70% during temperature aging for LEDs of sets A and B.
The line represents the linear fitting of data from set A.
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Light output of LEDs from set A during thermal and electrical aging.X-axis was plotted in log
scale in order to identify the exponential decay of 220 ◦C aged devices. Devices have been
characterized in the same conditions for different stress test. The kinetics were well correlated
for the first 10 h of stress.
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CIE 1964 chromatic coordinates during thermal aging were reported
on the chromatic diagram: LEDs from set A exhibited stronger blue shift.
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Forward voltage measured at 400 mA for LEDs of set A submitted to
different stress conditions.
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Optical images of surface and cross section of LEDs submitted to (a) 100 h at 200 ◦C
and (b) 100 h at 400 mA.
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Electroluminescence images of untreated and aged device of set A biased at (a) low
current and (b) high current levels; the (c) schematic diagram was also reported.
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(Above) Cumulative and (below) differential structure function of device of set A
submitted to electrical aging at 400 mA.
CONCLUSION
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• The optical decay could be ascribed to a lowering
of blue chip emission and a degradation of yellow
conversion efficiency.
• The modifications of thermal properties of the
materials (die attach, epoxy) could induce the
thermal resistance increase detected for aged
devices.
• The use of silicone materials rather than epoxy
plastic for package will improve the lumen
maintenance of such devices.
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REFERENCES
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• S. Ishizaki, H. Kimura, and M. Sugimoto, “Lifetime estimation of high
power white LEDs,” J. Light Vis. Environ., vol. 31, no. 1, pp. 11–
18,Apr. 2007.
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• P. N. Grillot, M. R. Krames, H. Zhao, and S. H. Teoh, “Sixty thousand
hour light output reliability of AlGaInP light emitting diodes,” IEEE
Trans. Device Mater. Rel., vol. 6, no. 4, pp. 564–574, Dec. 2006.
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