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Emerging trend for LED wafer level packaging
S. W. Ricky LEE, Rong ZHANG, K. CHEN, Jeffery C. C. LO
Front Optoelec. 2012, 5 (2): 119-126.
https://doi.org/10.1007/s12200-012-0259-9
Currently most light emitting diode (LED) components are made with individual chip packaging technology. The main manufacturing processes follow conventional chip-based IC packaging. In the past several years, there has been an uprising trend in the IC industry to migrate from chip-based packaging to wafer level packaging (WLP). Therefore, there is a need for LEDs to catch up. This paper introduces advanced LED WLP technologies. The contents cover key enabling processes such as preparation of silicon sub-mount wafer, implementation of interconnection, deposition of phosphor, wafer level encapsulation, and their integration. The emphasis is placed on how to achieve high throughput, low cost manufacturing through WLP.
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Optical constants study of YAG:Ce phosphor layer blended with SiO2 particles by Mie theory for white light-emitting diode package
Run HU, Xiaobing LUO, Huai ZHENG, Sheng LIU
Front Optoelec. 2012, 5 (2): 138-146.
https://doi.org/10.1007/s12200-012-0255-0
Optical constants, including scattering coefficient, absorption coefficient, asymmetry parameter and reduced scattering coefficient, of cerium-doped yttrium aluminium garnets (YAG:Ce) phosphor blended with SiO2 particle for white light-emitting diode (LED) packages were calculated based on Mie theory in this study. Calculation processes were presented in detail. Variations of the optical constants with the changes of phosphor weight fraction, dopant weight fraction, phosphor particle radius and SiO2 particle radius, were shown and analyzed separately. It was found that the asymmetry parameter is the intrinsic characteristic of the particles, and the increase of the phosphor weight fraction (or concentration) will lead to the increase of the optical constants. It was also discovered that the increase of the dopant weight fraction will enhance the scattering coefficient, but result in the decreases of the reduced scattering coefficient and the absorption coefficient.
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Self-adaptive phosphor coating technology for white LED packaging
Haibo RAO, Kun DING, Jirong SONG, Likun XIE, Wei WANG, Xianlong WAN, Linsong ZHOU, Junyuan LIAO
Front Optoelec. 2012, 5 (2): 147-152.
https://doi.org/10.1007/s12200-012-0236-3
Phosphor-converted light-emitting diodes (pc-LEDs), which employ blue LEDs with yellow phosphors to generate white light illumination, is a widely used solid-state lighting source. In order to conduct a phosphor layer coating with high quality on LED chip, a self-adaptive coating technology is introduced in this paper. A slurry coating technique combined with self-exposure method is applied and developed to demonstrate the benefits of self-adaptive coating layer. For self-exposure, the slurry coating is exposed to the blue emission of LED itself other than to ultraviolet (UV) light outside to make photoresist crosslinking. Results of measurement indicate that white LEDs with self-adaptive coating have shown self-adaptability to the angular distribution of intensity of blue light and performed higher spatial color uniformity than those with conventional coating and other conformal coating.
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Vertical-external-cavity surface-emitting lasers and quantum dot lasers
Guangcun SHAN, Xinghai ZHAO, Mingjun HU, Chan-Hung SHEK, Wei HUANG
Front Optoelec. 2012, 5 (2): 157-170.
https://doi.org/10.1007/s12200-012-0237-2
The use of cavity to manipulate photon emission of quantum dots (QDs) has been opening unprecedented opportunities for realizing quantum functional nanophotonic devices and quantum information devices. In particular, in the field of semiconductor lasers, QDs were introduced as a superior alternative to quantum wells (QWs) to suppress the temperature dependence of the threshold current in vertical-external-cavity surface-emitting lasers (VECSELs). In this work, a review of properties and development of semiconductor VECSEL devices and QD laser devices is given. Based on the features of VECSEL devices, the main emphasis is put on the recent development of technological approach on semiconductor QD VECSELs. Then, from the viewpoint of both single QD nanolaser and cavity quantum electrodynamics (QED), a single-QD-cavity system resulting from the strong coupling of QD cavity is presented. In this review, we will cover both fundamental aspects and technological approaches of QD VECSEL devices. Lastly, the presented review here has provided deep insight into useful guideline for the development of QD VECSEL technology, future quantum functional nanophotonic devices and monolithic photonic integrated circuits (MPhICs).
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Development and prospect of near-field optical measurements and characterizations
Jia WANG, Qingyan WANG, Mingqian ZHANG
Front Optoelec. 2012, 5 (2): 171-181.
https://doi.org/10.1007/s12200-012-0257-y
Scanning near-field optical microscopy (SNOM) is an ideal experimental measuring system in nano-optical measurements and characterizations. Besides microscopy with resolution beyond the diffraction limit, spectroscope with nanometer resolution and other instruments with novel performances have been indispensable for researches in nano-optics and nanophotonics. This paper reviews the developing history of near-field optical (NFO) measuring method and foresees its prospects in future. The development of NFO measurements has gone through four stages, including optical imaging with super resolution, near-field spectroscopy, measurements of nano-optical parameters, and detections of near-field interactions. For every stage, research objectives, technological properties and application fields are discussed.
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A simple experimental scheme for M-QAM optical signals generation
Lei LEI, Yu YU, Fei LOU, Zheng ZHANG, Lei XIANG, Xinliang ZHANG
Front Optoelec. 2012, 5 (2): 200-207.
https://doi.org/10.1007/s12200-012-0263-0
A simple scheme to generate optical quadrature amplitude modulation (QAM) signals is proposed based on different types of delay interferometers (DIs). The simulated results show that 16QAM, 64QAM and 256 QAM optical signals can be generated by 2×2, 3×3 and 4×4 DI, respectively, and the outputs of the proposed scheme are similar to those of the conventional schemes. The operation principle is discussed and the transmission properties of the square 16QAM as well as 64QAM signals are analyzed and compared with common approach.
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Preparation of titanium dioxide-double-walled carbon nanotubes and its application in flexible dye-sensitized solar cells
Cunxi CHENG, Jihuai WU, Yaoming XIAO, Yuan CHEN, Haijun YU, Ziying TANG, Jianming LIN, Miaoliang HUANG
Front Optoelec. 2012, 5 (2): 224-230.
https://doi.org/10.1007/s12200-012-0198-5
Titanium dioxide-double-walled carbon nanotubes (TiO2-DWCNTs) with DWCNTs/TiO2 of 20 wt.% is prepared by a conventional sol-gel method. Doping the TiO2-DWCNTs in TiO2 photoanode, a flexible dye-sensitized solar cell (DSSC) is fabricated. The sample is characterized by scanning electron microscopy, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) absorption, ultraviolet-visible spectroscopy (UV-vis) absorption spectra,electrochemical impedance spectroscopy (EIS) technique and photovoltaic measurement. It is found that adding a certain amount of TiO2-DWCNTs can efficiently decrease the resistance of charge transport, improve dye adsorption. Under an optimal condition, a flexible DSSC contained with 0.50 wt.% TiO2-DWCNTs achieves a light-to-electric energy conversion efficiency of 3.89% under a simulate solar light irradiation of 100 mW·cm-2.
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18 articles
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