Browsing by Author "Wang, Chien-Ping"

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Assessment of ESD Robustness in High Power Light-Emitting Diodes
(2010)
Yang, Shih-Chun
;
Lin, Pang
;
Fu, Han-Kuei
;
Wang, Chien-Ping
;
Chen, Tzung-Te
The capability of high-power nitride-based light-emitting diodes (HPLED) to withstand electrostatic discharge (ESD) is very important key index due to the horizontal structure of the insulating property of the sapphire substrate. However, it is difficult to real-time monitor the damage caused by the ESD stress because it occurred in a very short period. Current-voltage (I-V) curves and electroluminescence (EL) spectrum were applied to study the change during the series ESD stress. Time-resolved optical beam induced current (TR-OBIC) was used to analyze the characteristics of the delay time between normal region and the defect point caused by ESD stress. Transmission electron microscopy (TEM) was used to compare to the difference in the distribution of damage region and investigate the failure modes. During the series ESD stresses, V-shaped pits suffered from the high electrical field and the distance from multi-quantum well (MQW). The bottom of V-shaped defect would be one of index to assess the ESD endurance of LED chips.
Failure and degradation mechanisms of high-power white light emitting diodes
(2010-07-01)
Yang, Shih-Chun
;
Lin, Pang
;
Wang, Chien-Ping
;
Huang, Sheng Bang
;
Chen, Chiu-Ling
The investigation explores the factors that influence the long-term performance of high-power 1 W white light emitting diodes (LEDs). LEDs underwent an aging test in which they were exposed to various temperatures and electrical currents, to identify both their degradation mechanisms and the limitations of the LED chip and package materials. The degradation rates of luminous flux increased with electrical and thermal stresses. High electric stress induced surface and bulk defects in the LED chip during short-term aging, which rapidly increased the leakage current. Yellowing and cracking of the encapsulating lens were also important in package degradation at 0.7 A/85 degrees C and 0.7 A/55 degrees C. This degradation reduced the light extraction efficiency to an extent that is strongly related to junction temperature and the period of aging. junction temperatures were measured at various stresses to determine the thermal contribution and the degradation mechanisms. The results provided a complete understanding of the degradation mechanisms of both chip and package, which is useful in designing highly reliable and long-lifetime LEDs. Crown Copyright (C) 2010 Published by Elsevier Ltd. All rights reserved.
Sapphire surface patterning using femtosecond laser micromachining
(2012-11-01)
Chang, Cho-Wei
;
Chen, Chien-Yu
;
Chang, Tien-Li
;
Ting, Chia-Jen
;
Wang, Chien-Ping
This study presents an alternative method for micron-resolution patterning of a sapphire surface utilizing the characteristic of an ultra-short pulse (10(-15) s) from ytterbium (Yb) femtosecond laser (FS-laser) irradiation. Conventional processes often involve several steps, such as wet chemical or dry etching, for surface structuring of sapphire. In this study, two-dimensional array patterns on the sapphire surface with an area of 5x5 mm(2) and a depth of 1.2 +/- 0.1 mu m can be directly and easily fabricated by a single step of the FS-laser process, which involves 350-fs laser pulses with a wavelength of 517 nm at a repetition rate of 100 kHz. The measured ablation depths on the sapphire surface display that the proposed process can be under well-controlled conditions. Based on the design changes for being quickly implemented in the micromachining process, a FS laser can be a promising and competitive tool for patterning sapphire with an acceptable quality for industrial usage.
Study of Metals by Femtosecond Laser Processing for Electro-Optics Applications
(2012)
Chang, Cho-Wei
;
Chang, Tien-Li
;
Tsai, Ting-Kai
;
Ting, Chia-Jen
;
Wang, Chien-Ping
Femtosecond laser (FS-laser) microstructuring of metals has become a promising tool because of its non-contact nature, which allows the micromachining and direct processing of materials with a minimized volume of heat-affected zone for electro-optics applications such as light emitting diodes (LED) and solar photovoltaic (PV) lighting. This study presents ultra-short pulse (10(-15) sec) FS-laser processing. Through integrating the laser source, optical system and dynamic control modules, the materials of metals with micro-scale or nano-scale structures can be fabricated. In traditional processing such as semiconductor processing, development, exposure and etching necessitate expensive equipment and time-consuming tasks. With FS-laser processing, high-precision patterns are obtained, which will be a great benefit to keeping costs down. In this study, the wavelengths of FS-laser ablation are employed using visible and infrared light. To make a breakthrough in electro-optics processes, the CIGS thin-film of solar cells in metal process can be easily produced by the FS-laser. The ablation speed of the FS-laser for thin film layer CIGS solar cells can reach 2000 mm/s which is faster than the current Nd:YAG laser machine (similar to 1000 mm/s). On the other hand, the minimum size of metal lines can be controlled to a value that is lower than 40 mu m. Furthermore, green energy can be effectively developed for the future.
Transient evolution of carbon monoxide poisoning effect of PBI membrane fuel cells
(2007-07-10)
Wang, Chien-Ping
;
Chu, Hsin-Sen
;
Yan, Yi-Yie
;
Hsueh, Kan-Lin
;
機械工程學系
High temperature poly benzimidazole membrane fuel cells are the focus of attention due to high CO tolerance and overcoming water managements. This paper develops a transient. one-dimensional mathematical model to predict CO tolerance, and validates it with experiments. Experimental results are measured at different temperatures. Fuel cell performance degradations with time are also measured under various fuel compositions. Transient evolutions of current density, H-2 coverage, CO coverage, and ionic potential are shown during the CO poisoning process. The theoretical results show that hydrogen coverage decreases with time, reducing hydrogen oxidation reactions and dropping ionic potential loss. The effects of temperature. CO contents. and H-2 dilutions on fuel cell performance and the time to reach steady t(ss) are all investigated. Predictions of fuel cell current density degradation also show good agreement with experimental results. (c) 2007 Elsevier B.V. All rights reserved.
Two-phase modeling of a PEMFC with CO poisoning effect using dilute hydrogen feed
(2006)
Wang, Chien-Ping
;
Chu, Hsin-Sen
;
機械工程學系
;
Department of Mechanical Engineering
A one-dimensional, two-phase mathematical model was developed to analyze the poisoning effect of anode CO kinetics on the performance of a PEM fuel cell. Both vapor and liquid water transport are examined inside the cell. The theoretical results indicate that a higher CO concentration results in large CO coverage across the anode catalyst layer. The slowing of the chemical reactions at both the anode and the cathode reduce the liquid water saturation level in the catalytic layers. At high CO concentration and dilute hydrogen feed, the effect of the electro-osmotic drag is small and less liquid water is generated at the cathode catalyst layer, causing the liquid water distribution to have a small slope across the membrane. The distribution of liquid water depends more strongly on the CO concentration than on dilution of hydrogen in the MEA of the fuel cell. A large dropping rate of the current density is observed in the range between 10-50 ppm CO. Increasing the amount of pure hydrogen drastically increases the current density for a wide range of CO contents, promoting the tolerance for CO of the fuel cell.