Browsing by Issue Date, starting with "2007-01-25"

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Investigation of InGaN/GaN light emitting diodes with nano-roughened surface by excimer laser etching method
(2007-01-25)
Huang, Hung-Wen
;
Kao, Chih-Chiang
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Chu, Jung-Tang
;
Wang, Wei-Chih
;
Lu, Tien-Chang
The InGaN/GaN light emitting diodes (LEDs) with a nano-roughened top p-GaN surface fabricated by using Ni nano-masks and laser etching methods were demonstrated and analyzed. The experiment results observed the maximum light output power of the InGaN/GaN LED with a nano-roughened top p-GaN surface etched with the laser energy of 300 mJ/cm(2) was 1.55 times higher than that of a conventional LED, and the wall-plug efficiency was enhanced 68% at 20 mA. The series resistance of InGaN/GaN LED was reduced by 32% by the increase in the contact area of the nano-roughened surface. (c) 2006 Elsevier B.V. All rights reserved.
東埔之梅 ,漁人
(2007-01-27)
管管
Enhanced photoresponse of a metal-oxide-semiconductor photodetector with silicon nanocrystals embedded in the oxide layer
(2007-01-29)
Shieh, Jia-Min
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Lai, Yi-Fan
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Ni, Wei-Xin
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Kuo, Hao-Chung
;
Fang, Chih-Yao
The authors report a two-terminal metal-oxide-semiconductor photodetector for which light is absorbed in a capping layer of silicon nanocrystals embedded in a mesoporous silica matrix on p-type silicon substrates. Operated at reverse bias, enhanced photoresponse from 300 to 700 nm was observed. The highest optoelectronic conversion efficiency is as high as 200%. The enhancements were explained by a transistorlike mechanism, in which the inversion layer acts as the emitter and trapped positive charges in the mesoporous dielectric layer assist carrier injection from the inversion layer to the contact, such that the primary photocurrent could be amplified. (c) 2007 American Institute of Physics.
Evanescent-field optical amplifiers and lasers
(2007-01-30)
Chen
;
Nan-Kuang
;
Chi
;
Sien
;
Tseng
An optical amplifier and a laser generator based on the fiber side-polished technology, having a high pumping efficiency, a low noise figure and a small footprint are provided in this application. The optical amplifier and the laser, which have a very long effective interaction length in conjunction with highly doped Erbium glass attached to its surface and an addition of a slanted fiber grating inscribed in the guiding core at the polished region can spatially separate the signal and pump power to simultaneously improve the pumping efficiency and optimize the penetrated depth of the signal evanescent-field. The spontaneous emission is kept from being amplified and therefore a high quality amplified signal is produced.
SODOCK: Swarm optimization for highly flexible protein-ligand docking
(2007-01-30)
Chen, Hung-Ming
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Liu, Bo-Fu
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Huang, Hui-Ling
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Hwang, Shiow-Fen
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Ho, Shinn-Ying
Protein-ligand docking can be formulated as a parameter optimization problem associated with an accurate scoring function, which aims to identify the translation, orientation, and conformation of a docked ligand with the lowest energy. The parameter optimization problem for highly flexible ligands with many rotatable bonds is more difficult than that for less flexible ligands using genetic algorithm (GA)-based approaches, due to the large numbers of parameters and high correlations among these parameters. This investigation presents a novel optimization algorithm SODOCK based on particle swarm optimization (PSO) for solving flexible protein-ligand docking problems. To improve efficiency and robustness of PSO, an efficient local search strategy is incorporated into SODOCK. The implementation of SODOCK adopts the environment and energy function of AutoDock 3.05. Computer simulation results reveal that SODOCK is superior to the Lamarckian genetic algorithm (LGA) of AutoDock. in terms of convergence performance, robustness, and obtained energy, especially for highly flexible ligands. The results also reveal that PSO is more suitable than the conventional GA in dealing with flexible docking problems with high correlations among parameters. This investigation also compared SODOCK with four state-of-the-art docking methods, namely GOLD 1.2, DOCK 4.0, FlexX 1.8, and LGA of AutoDock 3.05. SODOCK obtained the smallest RMSD in 19 of 37 cases. The average 2.29 angstrom of the 37 RMSD values of SODOCK was better than those of other docking programs, which were all above 3.0 angstrom. (C) 2006 Wiley Periodicals, Inc.
Two-dimensional densely packed DNA nanostructure derived from DNA complexation with a low-generation poly(amidoamine) dendrimer
(2007-01-30)
Su, Chun-Jen
;
Liu, Yi-Chun
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Chen, Hsin-Lung
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Li, Yen-Cheng
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Lin, Hsien-Kuang
One of the keys for using deoxyribonucleic acid (DNA) as a nanomaterial relies on how the individual DNA chain can be aligned and how a multitude of DNA chains can be packed into ordered nanostructures. Here we present a simple method for constructing a 2-D densely packed DNA nanostructure using the electrostatic complex of DNA with a poly(amidoamine) (PAMAM) dendrimer of generation two. Ordered DNA arrays are formed by drop-casting an aqueous solution containing positively overcharged complexes onto mica followed by a prolonged incubation. During the incubation, the complexes tend to adsorb onto the negatively charged mica surface through electrostatic attraction. The rodlike complexes organize to form ordered arrays to increase the surface density of the adsorbed complexes and hence the attractive free energy of adsorption. The densely packed nanostructure obtained here is distinguished from the previously reported spheroid or toroid structure derived from DNA complexations with the higher-generation dendrimers.
Protein complexity, gene duplicability and gene dispensability in the yeast genome
(2007-01-31)
Lin, Yeong-Shin
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Hwang, Jenn-Kang
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Li, Wen-Hsiung
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生物科技學系
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Department of Biological Science and Technology
Using functional genomic and protein structural data we studied the effects of protein complexity (here defined as the number of subunit types in a protein) on gene dispensability and gene duplicability. We found that in terms of gene duplicability the major distinction in protein complexity is between hetero-complexes, each of which includes at least two different types of subunits (polypeptides), and homo-complexes, which include monomers and complexes that consist of only subunits of one polypeptide type. However, gene dispensability decreases only gradually as the number of subunit types in a protein complex increases. These observations suggest that the dosage balance hypothesis can explain well gene duplicability of complex proteins, but cannot completely explain the difference in dispensabilities between hetero-complex subunits. It is likely that knocking out a gene coding for a hetero-complex subunit would disrupt the function of the whole complex, so that the deletion effect on fitness would increase with protein complexity. We also found that multi-domain polypeptide genes are less dispensable but more duplicable than single-domain polypeptide genes. Duplicate genes derived from the whole genuine duplication event in yeast are more dispensable (except for ribosomal protein genes) than other duplicate genes. Further, we found that subunits of the same protein complex tend to have similar expression levels and similar effects of gene deletion on fitness. Finally, we estimated that in yeast the contribution of duplicate genes to genetic robustness against null mutation is similar to 9%, smaller than previously estimated. In yeast, protein complexity may serve as a better indicator of gene dispensability than do duplicate genes. (c) 2006 Elsevier B.V All rights reserved.
Covalently bonded polyhedral oligomeric silsesquioxane/polyimide nanocomposites and process for synthesizing the same
(2007-02-01)
Wei, Kuang-Hwa
;
Leu, Chyi-Ming
Polyhedral oligomeric silsesquioxane/polyimide nanocomposites with certain mechanical properties and low dielectric constant is synthesized by covalently tethering functionalized polyhedral oligomeric silsesquioxane molecules to polyimide. These nanocomposites appear to be self-assembled systems. A process for synthesizing said polyhedral oligomeric silsesquioxane/polyimide nanocomposites also is provided, comprising a step of forming porous type polyhedral oligomeric silsesquioxane, and a subsequent step of reacting with dianhydride or directly reacting with synthesized polyimide.
Three-dimensional thermoelectrical simulation in flip-chip solder joints with thick underbump metallizations during accelerated electromigration testing
(2007-02-01)
Liang, S. W.
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Chang, Y. W.
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Chen, Chih
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材料科學與工程學系
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Department of Materials Science and Engineering
In flip-chip solder joints, thick Cu and Ni films have been used as under bump metallization (UBM) for Pb-free solders. In addition, electromigration has become a crucial reliability concern for fine-pitch flip-chip solder joints. In this paper, the three-dimensional (3-D) finite element method was employed to simulate the current-density and temperature distributions for the eutectic SnPb solder joints with 5-mu m Cu, 10-mu m Cu, 25-mu m Cu, and 25-mu m Ni UBMs. It was found that the thicker the UBM is the lower the maximum current density inside the solder. The maximum current density is 4.37 x 10(4) A/cm(2), 1.69 x 10(4) A/cm(2), 7.54 x 10(3) A/cm(2), and 1.34 x 10(4) A/cm(2), respectively, when the solder joints with the above four UBMs are stressed by 0.567 A. The solder joints with thick UBMs can effectively relieve the current crowding effect inside the solder. In addition, the joint with the thicker Cu UBM has a lower Joule heating effect in the solder. The joint with the 25-mu m Ni UBM has the highest Joule heating effect among the four models.
Evaluation research of polishing methods for large area diamond films produced by chemical vapor deposition
(2007-02-01)
Tsai, H. Y.
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Ting, C. J.
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Chou, C. P.
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機械工程學系
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Department of Mechanical Engineering
The current study compared several polishing techniques of chemical vapor deposition (CVD) diamond films. Although research on various diamond polishing techniques has been carried for years, some issues still need to be examined in order to facilitate application on large areas in a cost-efficient manner. In the present work, microwave plasma enhanced chemical vapor deposition (CVD) was used to obtain diamond films with full width half magnitude (FWHM) less than 10 wavenummbers at 1332 cm(-1) Raman peak. The diamond films were processed through mechanical polishing, chemical-assisted mechanical polishing, thermo-chemical polishing, excimer laser ablation, and catalytic reaction assisted grinding. A profilometer, an atomic force microscope, and a scanning electron microscope have been used to evaluate the surface morphology of diamond Films before and after polishing. The results obtained by using the above mentioned techniques were analyzed and compared. (c) 2006 Elsevier B.V. All rights reserved.
Laboratory astrophysics in Taiwan
(2007-02-01)
Lin, G. -L.
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Liu, T. -C.
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Huang, M. A.
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Hwang, W-Y. P.
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Chen, C. -C.
We report the development of laboratory astrophysics program in Taiwan. We begin with outlining Taiwan's participation in the FLASH collaboration for measuring the fluorescence yield using SLAC 28.5 GeV electron beam. We then report the domestic effort of studying cosmic ray shower properties using NSRRC 1.5 GeV electron beam.
Optimum power-saving method for power MOSFET width of DC-DC converters
(2007-02-01)
Chen, K.-H.
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Chien, C.-C.
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Hsu, C.-H.
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Huang, L.-R.
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電控工程研究所
An optimum power metal-oxide-semiconductor field effect transistor (MOSFET) width technique is proposed for enhancing the efficiency characteristics of switching DC-DC converters. By implementing a one-cycle buck DC-DC converter, it is demonstrated that the dynamic power MOSFET width controlling technique has a much improved power reduction whether the load current is light or heavy. The maximum efficiency of the buck converter is similar to 92% with a 3% efficiency improvement for the heavy load condition. The efficiency is further improved by similar to 16% for the light load condition as a result of the power reduction from the large power MOSFET transistors. Also proposed is a new error-correction loop circuit to enable a better load regulation than that of previous designs. Compared with the adaptive gate driver voltage technique, the optimum power MOSFET width can achieve a significant improvement in power saving. It is also superior to the low-voltage-swing MOSFET gate drive technique for switching DC-DC converters.
Effect of oxygen concentration on characteristics of NiOx-based resistance random access memory
(2007-02-01)
Lee, Ming-Daou
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Ho, Chia-Hua
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Lo, Chi-Kuen
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Peng, Tai-Yen
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Yao, Yeong-Der
The resistance bistability and the switching effect has been systematically studied in nickel oxide films with variable oxygen concentrations. Both the switching bias voltage and the resistance ratio of RESET to SET were found to be strongly concentration dependent. Meanwhile, the electrical characteristics can be exactly examined by an Schottky emission. By means of mathematical fitting, the resistance bistability seems to be related to the alternating of dielectric constant and the barrier height. Furthermore, the room temperature cycle endurance with a distinguishable operation window was found to exceed 800. This indicates that the nickel oxide has the potential to be a promising material on resistance random access memory.
Fast and versatile algorithm for nearest neighbor search based on a lower bound tree
(2007-02-01)
Chen, Yong-Sheng
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Hung, Yi-Ping
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Yen, Ting-Fang
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Fuh, Chiou-Shann
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資訊工程學系
In this paper, we present a fast and versatile algorithm which can rapidly perform a variety of nearest neighbor searches. Efficiency improvement is achieved by utilizing the distance lower bound to avoid the calculation of the distance itself if the lower bound is already larger than the global minimum distance. At the preprocessing stage, the proposed algorithm constructs a lower bound tree (LB-tree) by agglorneratively clustering all the sample points to be searched. Given a query point, the lower bound of its distance to each sample point can be calculated by using the internal node of the LB-tree. To reduce the amount of lower bounds actually calculated, the winner-update search strategy is used for traversing the tree. For further efficiency improvement, data transformation can be applied to the sample and the query points. In addition to finding the nearest neighbor, the proposed algorithm can also (i) provide the k-nearest neighbors progressively; (ii) find the nearest neighbors within a specified distance threshold; and (iii) identify neighbors whose distances to the query are sufficiently close to the minimum distance of the nearest neighbor. Our experiments have shown that the proposed algorithm can save substantial computation, particularly when the distance of the query point to its nearest neighbor is relatively small compared with its distance to most other samples (which is the case for many object recognition problems). (c) 2005 Pattern Recognition Society. Published by Elsevier Ltd. All rights reserved.
A novel dilute antimony channel In0.2Ga0.8AsSb/GaAs HEMT
(2007-02-01)
Su, Ke-Hua
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Hsu, Wei-Chou
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Lee, Ching-Sung
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Wu, Tsung-Yeh
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Wu, Yue-Han
This letter reports, for the first time, a high-electron mobility. transistor (HEMT) using A dilute antimony In0.2Ga0.8AsSb channel, which is grown by a molecular-beam epitaxy system. The interfacial quality within the InGaAsSb/GaAs quantum well of the HEMT device was effectively improved by introducing the surfactantlike Sb atoms during the growth of the InGaAs layer. The improved heterostructural quality and electron transport properties have also been verified by various surface characterization techniques. In comparison, the proposed HEMT with (without) the incorporation of Sb atoms has demonstrated the maximum extrinsic transconductance g(m,max) of 227 (180) mS/mm, a drain saturation current density I-DSS of 218 (170) mA/mm, a gate-voltage swing of 1.215 (1.15) V, a cutoff frequency f(T) of 25 (20.6) GHz, and the maximum oscillation frequency f(max) of 28.3 (25.6) GHz at 300 K with gate dimensions of 1.2 x 200 mu m(2).
LQG controller for active vibration absorber in optical disk drive
(2007-02-01)
Chang, C. S.
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Liu, T. S.
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機械工程學系
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Department of Mechanical Engineering
Unbalanced disks in rotation will lead to the main vibration of an optical disk drive. Passive vibration absorbers are usually used in current optical disk drives to suppress vibration. Generally, optical disk drives have to make a disk spin at multiple speeds by different read/write conditions. However, the passive vibration absorber only suppresses vibration at a specific rotating speed and may excite vibration at other speeds. This paper uses a linear quadratic Gaussian (LQG) controller for active vibration absorbers to reduce diskdrive vibration at multiple rotating speeds. The absorber with LQG control is validated based on simulation and experimental results.
Effect of gate sinking on the device performance, of the InGaP/AlGaAs/InGaAs enhancement-mode PHEMT
(2007-02-01)
Chu, L. H.
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Chang, E. Y.
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Chang, L.
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Wu, Y. H.
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Chen, S. H.
An enhancement-mode InGaP/AlGaAs/InGaAs pseudomorphic high-electron mobility transistor using platinum (Pt) as the Schottky contact metal was investigated for the first time. Following the Pt/Ti/Pt/Au gate metal deposition, the devices were thermally annealed at 325 degrees C for gate sinking. After the annealing, the device showed a positive threshold voltage (V-th) shift from 0.17 to 0.41 V and a very low drain leakage current from 1.56 to 0.16 mu A/mm. These improvements are attributed to the Schottky barrier height increase and the decrease of the gate-to-channel distance as Pt sinks into the InGaP Schottky layer during gate-sinking process. The shift in the V-th was very uniform across a 4-in wafer and was reproducible from wafer to wafer. The device also showed excellent RF power performance after the gate-sinking process.
The direct integral of some weighted Bergman spaces
(2007-02-01)
Chuah, Meng-Kiat
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應用數學系
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Department of Applied Mathematics
Let G be the abelian Lie group R(n) x R(k)/Z(k), acting on the complex space X = R(n+k) x iG. Let F be a strictly convex function on R(n+k). Let H be the Bergman space of holomorphic functions on X which are square-integrable with respect to the weight e(-F). The G-action on X leads to a unitary G-representation on the Hilbert space H. We study the irreducible representations which occur in H by means of their direct integral. This problem is motivated by geometric quantization, which associates unitary representations with invariant Kahler forms. As an application, we construct a model in the sense that every irreducible G-representation occurs exactly once in H.
Effect of plasma treatment on the microstructure and electrical properties of MIM capacitors with PECVD silicon oxide and silicon nitride
(2007-02-01)
Ho, Chia-Cheng
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Chiou, Bi-Shiou
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電子工程學系及電子研究所
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Innovative Packaging Research Center
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Department of Electronics Engineering and Institute of Electronics
Metal-insulator-metal (MIM) capacitors with plasma enhanced chemical vapor deposited (PECVD) nitride exhibit trap-induced dispersive behavior and electrical hysteresis, which lead to degradation in capacitor linearity at low frequencies. The dominant defect was suggested to be silicon dangling bonds originated from nitrogen deficiency. Previous methods to eliminate the dispersive behavior and electrical hysteresis include use of oxide-nitride-oxide (ONO) stacks and/or plasma pre-treatment of silicon substrate before nitride deposition [Van Huylenbroeck S, Decoutere S, Venegas R, Jenei S, Winderickx G (2002) IEEE Electron Device Lett 23:191; Lau WS (1990) Jpn J Appl Phys 29:L690]. In this study, the plasma post-treatment method was employed; MIM capacitors with PECVD oxide and nitride were treated with N2O and SiH4/NH3 plasma, respectively, after deposition of the dielectric layer. No apparent change in film microstructure is observed after plasma treatment. Plasma post-treatment is effective in eliminating the electrical hysteresis shift of the nitride capacitors. Fourier transform infrared (FTIR) absorption spectra suggest an increase of the Si-H bond after SiH4/NH3 plasma bombardment of the nitride films. Auger depth profiling indicates a slight increase of nitrogen to silicon ratio after plasma treatment. The increase of the Si-H bonds as well as the raise of nitrogen to silicon ratio are two possible causes for the elimination of the hysteresis shift of the plasma-treated nitride capacitors. The time dependent dielectric breakdown testing indicates a decrease in both the leakage current and the lifetime of the MIM capacitors treated with plasma. Possible dielectric degradation mechanism is explored.
Optimization of the lens holder and yoke for a near-field optical pickup actuator to enhance frequency response
(2007-02-01)
Peng, Ming-Tsan
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Huang, Hai-Jo
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Wu, Chun-Te
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Lee, Kwen-Jin
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Yang, Lei-Ming
A four-wire voice-coil actuator is designed and optimized for use in a near-field optical drive. The first objective was to design a lens holder which could accommodate a large-size lens module while possessing a strong mechanical structure. The second objective was to optimize the yoke so that the magnetic field would be uniform within the stroke range of the voice coils. These improvements eventually helped to improve the bandwidth of the frequency response of the actuator.