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Complex-stress accelerated lifetime test for high-power light-emitting diodes
Byungjin Ma,Jemin Kim IET 2012 Electronics letters Vol.48 No.8
<P>To reduce testing time and enhance the accuracy of the lifetime estimation of light emitting diode (LED) packages, a new complex-stress accelerated lifetime test (ALT) is proposed, which is based on the combination of thermal stress and optical stress. An in situ monitoring of electrical, optical and thermal characteristics took place during the ALT. The transient response of voltage change in the LED chips was used to measure the thermal properties such as junction temperature and thermal resistance to consider the thermal stress. The relative optical power and luminous flux, monitored during the ALT, were used as the optical stress and a measure of lifetime prediction. Compared to a conventional temperature-stress ALT model, the proposed ALT model describes an actual optical degradation and thus enables accurate estimation of the lifetime of LED packages.</P>
835-nm GaAs/AlGaAs High-Power Laser Diode for Up-Conversion Fiber Lasers
Byungjin Ma,Changyun Lee,Donghun Kang,Junseok Kang,Seongju Bae,Yuseung Kim 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.50 No.3
High-power and high-efficiency 835-nm GaAs/AlGaAs single-quantum-well pumping laser diodes (LDs) for visible up-conversion fiber laser applications were fabricated. To achieve the highly efficient pump laser diode, a 1.0-$\mu$m-thick separate confinement heterostructure layer was inserted; namely, a large optical cavity (LOC) structure was adopted. This LOC structure minimizes the overlap between the optical modal fields and the highly doped cladding layers, which reduces the optical internal loss and increases the slope efficiency of the pumping LDs. LD arrays of 10 emitters with a 1,000-$\mu$m total emitter width were fabricated to evaluate the high-power LD characteristics and to check the feasibility of the up-conversion fiber lasers. A LD array with a small total emitter size of 1,000 $\mu$m operated at over 20 W with a very high 20-mW/$\mu$m optical power density. The threshold current and the slope efficiency of the LD array were about 4.1 A and 1.17 W/A, respectively. We present a visible up-conversion fiber laser pumped by using our developed high-power, high-efficiency 835-nm LD array.
Proposal of New Measurement Method for Internal Quantum Efficiency of Light-Emitting Diodes
Ma, Byungjin,Lee, Kwanhoon IOP Publishing 2013 Japanese journal of applied physics Vol.52 No.8
<P>A new evaluation method for effective internal optical power (IOP) and internal quantum efficiency (IQE) of light-emitting diodes (LEDs) is demonstrated. This method is based on the optical and thermal properties of LEDs. By using this proposed method, the effective IOP and the IQE of LEDs could be directly extracted from the measurements of external optical power (EOP) and junction temperature of LEDs. This method needs no assumption of the injection efficiency of carriers in the LEDs and no measurement-condition limitation of low current-injection level. (C) 2013 The Japan Society of Applied Physics</P>
Thermal Properties and Lifetime Comparison of Various Ceramic-Package Light-Emitting Diodes
Byungjin Ma,Yungjun Ahn,김제민,최성순,Kwanhoon Lee 대한금속·재료학회 2013 ELECTRONIC MATERIALS LETTERS Vol.9 No.4
We developed two thermal structures with heat-conducting paths at the bottom side of low temperature cofired ceramic (LTCC) LED packages and compared their thermal properties and reliability. Using a computational fluidic dynamics (CFD) simulation, we were able to anticipate the improvement of the thermal properties. In addition, we experimentally confirmed the expected thermal properties using a method based on thermal transient responses. The measured thermal resistances of the small-via structure and the thermalslug structure were about 50% and 40% of the value of a normal structure with no via or slug, respectively. Lifetime tests of each LED package over 4,000 hours were carried out to compare the lifetimes of the LTCC LED packages and to investigate the relationships between the thermal properties and the lifetimes of the LTCC LED packages. We were able to estimate a lifetime of over 32,000 hours for the LTCC LED packages with thermal paths while the lifetime of the normal LTCC LED packages was estimated to be about 18,200hours. Also, we verified the strong relationship between the thermal property and the lifetime in LTCC LED packages.
Reliability Estimation of High-Brightness Ceramic Package LED
Byungjin Ma,Jemin Kim,Kwanhun Lee,Byoungsuk Song 대한전자공학회 2010 ICEIC:International Conference on Electronics, Inf Vol.1 No.1
We achieved the junction to air thermal resistance as low as 13 [K/W] and the enhanced lifetime (MTTF) estimated over 50,000 hours using a thermal-via structure in LTCC-based LED packages. Exponential decay of brightness in the LED packages was assumed and Arrehenius model as a life-stress model was used to analyze the lifetime of the LED packages.
Comparison of Effect of Epoxy and Silicone Adhesive on the Lifetime of Plastic LED Package
김제민,Byungjin Ma,이관훈 대한금속·재료학회 2013 ELECTRONIC MATERIALS LETTERS Vol.9 No.4
To compare the reliability of plastic LED packages based on different types of bonding adhesive, we designed two plastic LED package models using epoxy or silicone as bonding adhesive with normal refractive index (NRI) silicone, or high refractive index (HRI) silicone, as encapsulant. In addition, thermal acceleration tests were performed for 1,000 hours under three different temperatures, and optical characteristics were measured every 250 hours. Exponential decay of luminous flux of the plastic LED package was assumed and extrapolation was used to analyze the time-to-failure (TTF) of the plastic LED packages. From TTF data, statistical analysis was performed and reliability parameters such as acceleration factor (AF) and B10 lifetime at 40°C were estimated according to types of bonding adhesive and silicone encapsulant in plastic LED packages, with 90% confidence.
Performance and reliability of SC-type optical fixed attenuators for optical network system
Jemin Kim,Byungjin Ma,Kwanhun Lee 대한전자공학회 2008 ICEIC:International Conference on Electronics, Inf Vol.1 No.1
The void and delamination on the surface of the SC-type optical fixed attenuators under damp heat condition were detected and analyzed. We improved them by modifying cleaning process, housing structures and materials of parts. Then the performance and reliability of old and new models were checked. The results of several environmental tests such as damp heat and mechanical test showed that the improved model had the advantages of production cost and environmental characteristics analyzed by using statistical method such as T-test.