Browsing by Issue Date, starting with "2007-04-30"

Now showing 1 - 20 of 59808

Low refractive index Si nanopillars on Si substrate
(2007-04-30)
Lin, Gong-Ru
;
Chang, Ya-Chung
;
Liu, En-Shao
;
Kuo, Hao-Chung
;
Lin, Huang-Shen
Low refractive index of a stalagmitelike high-aspect-ratio Si nanopillar array on Si dry etched using a self-aggregated Ni nanodot mask is demonstrated, which exhibits two minimum reflectances of 1.23 and 1.4 with corresponding refractive indices of 1.25 and 1.48 at 400 and 1200 nm, respectively. Angular dependency of the transverse electrical mode reflectance at 632.8 nm of the surface roughened Si nanopillar array is released, and the Brewster angle of 63 degrees with equivalent refractive index of 1.5 is determined. (C) 2007 American Institute of Physics.
Nonvolatile low-temperature polycrystalline silicon thin-film-transistor memory devices with oxide-nitride-oxide stacks
(2007-04-30)
Liu, Po-Tsun
;
Huang, C. S.
;
Chen, C. W.
;
光電工程學系
;
顯示科技研究所
Nonvolatile memory devices with oxide-nitride-oxide stack structures were fabricated on glass substrates using low-temperature polycrystalline silicon technology. The Fowler-Nordheim tunneling scheme is more suitable than channel hot carrier injection for the programming of the polycrystalline silicon nonvolatile memory device. A memory window of 1.5 V can be obtained at a programming voltage of 20 V. After 10(4) programming/erasing cycles, a threshold voltage shift of 1.5 V is maintained. Furthermore, the proposed memory device exhibits good retention for 50 h at 60 degrees C without a significant decline in the memory window. (C) 2007 American Institute of Physics.
Effects of strained InGaN interlayer on contact resistance between p-GaN and indium tin oxide
(2007-04-30)
Lee, Chi-Ling
;
Lee, Wei-I
;
電子物理學系
;
Department of Electrophysics
Indium tin oxide (ITO), with its transparency and strong adhesion to GaN, has been used as a replacement for Ni/Au as a contact on p-GaN. However, ITO suffers from high contact resistance on p-GaN. In this work, low contact resistance between ITO and the p-GaN layer was consistently achieved using various strained InGaN layers as the interface layers between ITO and p-GaN layer. The doping of InGaN, whether n type or p type, has a relatively weak effect on the contact resistance as long as the thickness of the InGaN layer is adequately controlled. The secondary-ion-mass spectroscopy depth profile reveals that the n-type InGaN strained contact layer was also heavily doped with Mg. Results of this study demonstrate that the piezoelectric field between InGaN and p-GaN is important in reducing the barrier height of Ohmic contact. (c) 2007 American Institute of Physics.
Quantitative phase retrieval in transmission hard x-ray microscope
(2007-04-30)
Yin, Gung-Chian
;
Chen, Fu-Rong
;
Hwu, Yeukuang
;
Shieh, Han-Ping D.
;
Liang, Keng S.
Quantitative phase retrieval with a sub-100-nm resolution is achieved from micrographs of a zone plate based transmission x-ray microscope. A plastic zone plate containing objects of sizes from micrometers down to tens of nanometers is used as a test sample to quantify the retrieved phase. Utilizing the focal serial images in the image plane, the phase information is retrieved quantitatively across the entire range of sizes by combining the transport intensity equation and self-consistent wave propagation methods in this partial coherence system. The study demonstrates a solution to overcome the deficiency encountered in the two phase retrieval approaches. (c) 2007 American Institute of Physics.
Optical characteristics of a-plane InGaN/GaN multiple quantum wells with different well widths
(2007-04-30)
Ko, T. S.
;
Lu, T. C.
;
Wang, T. C.
;
Lo, M. H.
;
Chen, J. R.
a-plane InGaN/GaN multiple quantum wells of different widths ranging from 3 to 12 nm were grown on r-plane sapphire by metal organic chemical vapor deposition for investigation. The peak emission intensity of the photoluminescence (PL) reveals a decreasing trend as the well width increases from 3 to 12 nm. Low temperature (9 K) time-resolved PL study shows that the sample with 3-nm-thick wells has a better optical property with a fast exciton decay time of 0.57 ns. The results of cathodoluminescence and micro-PL scanning images for samples of different well widths further verify the more uniform and stronger luminescence intensity distribution observed for the samples of thinner quantum wells, indicating that the important growth parameters for a-plane InGaN/GaN multiple quantum wells could be dominated by the In fluctuation and crystal quality during the epitaxial growth. (c) 2007 American Institute of Physics.
A non-additive model for evaluating airline service quality
(2007-05-01)
Liou, James J. H.
;
Tzeng, Gwo-Hshiung
;
科技管理研究所
;
Institute of Management of Technology
This study develops a non-additive model for evaluating and improving the service quality of airlines and compares its results with the conventional additive method. Service quality is a composite of various attributes and many in a system have inter-dependent characteristics that may not be correctly evaluated using conventional additive measures. A fuzzy integral is thus proposed. Factor analysis is initially used to extract some independent common-factors and fuzzy integral used to integrate the performance ratings of inter-dependent attributes in each common-factor. For the analytic hierarchy process a pair-wise comparative approach is adopted to determine the relative weights linking each independent common-factor. Finally, Grey relation analysis and simple additive weight method are used to find airline service quality. A study of international airlines is conducted for verification. Safety and reliability emerge as the critical factors of service quality. (C) 2007 Elsevier Ltd. All rights reserved.
Patterned self-assembly of magnetic biomolecules on semiconductor substrates
(2007-05-01)
Sun, Kien Wen
;
Chang, Chia-Ching
;
生物科技學系
;
應用化學系
;
應用化學系分子科學碩博班
The paper reports on the methods of preparing and patterning magnetic metallothionein (Mn,Cd-MT-2) molecules on semiconductor surfaces. The molecules are placed into nanopores prepared on silicon (0 0 1) substrates. We observe the self-assembled growth of those MT molecules on the patterned Si surface. Dense arrays of molecular rods are demonstrated on templates with small pores and pitch sizes. Then the structures of the self-assembled protein are studied by atomic force microscopy (AFM) and magnetic force microscopy (MFM). Our measurements indicate that molecular self-assembly has a magnetic dipole moment which interacts with the applied magnetic field. (c) 2007 Elsevier Ltd. All rights reserved.
Evaluating intertwined effects in e-learning programs: A novel hybrid MCDM model based on factor analysis and DEMATEL
(2007-05-01)
Gwo-Hshiung Tzeng
;
Cheng-Hsin Chiang
;
Chung-Wei Li
;
科技管理研究所
;
Institute of Management of Technology
Internet evolution has affected all industrial and commercial activity and accelerated e-learning growth. Due to cost, time, or flexibility for designer courses and learners, e-learning has been adopted by corporations as an alternative training method. E-learning effectiveness evaluation is vital, and evaluation criteria are diverse. A large effort has been made regarding e-learning effectiveness evaluation; however, a generalized quantitative evaluation model, which considers both the interaffected relation between criteria and the fuzziness of subjective perception concurrently, is lacking. In this paper, the proposed new novel hybrid MCDM model addresses the independent relations of evaluation criteria with the aid of factor analysis and the dependent relations of evaluation criteria with the aid of DEM-ATEL. The AHP and the fuzzy integral methods are used for synthetic utility in accordance with subjective perception environment. Empirical experimental results show the proposed model is capable of producing effective evaluation of e-learning programs with adequate criteria that tit with respondent's perception patterns, especially when the evaluation criteria are numerous and intertwined. (C) 2006 Elsevier Ltd. All rights reserved.
10-GHz highly symmetrical sub-harmonic Gilbert mixer using GaInP/GaAs HBT technology
(2007-05-01)
Wu, Tzung-Han
;
Meng, Chinchun
;
電信工程研究所
;
Institute of Communications Engineering
A 10-GHz sub-harmonic Gilbert mixer is demonstrated using GaInP/GaAs hetero-junction bipolar transistor technology. The local oscillator (LO) signal time-delay path in the sub-harmonic LO stage is compensated using the fully symmetrical stacked-LO doubler; therefore, the balance of the sub-harmonic LO stage, the radio frequency to intermediate frequency isolation, and IIP2 are improved. The demonstrated 10-GHz sub-harmonic mixer achieves 10 dB conversion gain, IP1dB of -12 dBm, IIP3 of 2 dBm and IIP2 of 33 dBm.
Optical characterization of Zn0.97Mn0.03Se/ZnSe0.92Te0.08 type II multiple-quantum-well structures
(2007-05-01)
Lin, D. Y.
;
Shiu, J. J.
;
Wu, J. D.
;
Yang, C. S.
;
Chou, W. C.
The optical characterization of type II Zn0.97Mn0.03Se/ZnSe0.92Te0.08 multiple-quantum-well structures have been studied using photoluminescence (PL), temperature-dependent PL, polarized PL, power-dependent PL, and photoreflectance (PR) in this study. The PL data reveal that the band alignment of the ZnMnSe/ZnSeTe system is type II. Comparing with the theoretical calculation based on the Schrodinger equation, the valence band offset is estimated to be 0.6 eV. From the power-dependent PL spectra, it is observed that the peak position of PL spectra shows a blueshift under different excitation power. The blueshift can be interpreted in terms of the band-bending effect due to spatially photoexcited carriers in a type II alignment. The thermal activation energy (E-A) for quenching the PL intensity was determined from temperature-dependent PL spectra. The thermal activation energy was found to decrease as the thickness of ZnMnSe and ZnSeTe layers decreased. The polarized PL spectra exhibit a large in-plane polarization with the polarization degree up to 50%. The polarization does not depend on the excitation intensity as well as temperature. The large polarization is an inherent orientation of the interface chemical bonds. The higher transition features observed in PR spectra show a blueshift with the similar trend observed in the PL spectra as decreasing the thickness of ZnSeTe layer. This result provides a consistent evidence for the assumption that square-like well shapes were built in the ZnSeTe layers. (C) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Properties of vortex propagation in a niobium film with spacing-graded density of pinning sites
(2007-05-01)
Horng, Lance
;
Wu, T. C.
;
Wu, J. C.
;
Cao, R.
;
Yang, T. J.
The vortex propagation has been investigated in Nb superconductors with one dimension spacing-graded density of submicrometer-scaled holes in this research. A rectification effect can be discerned because the applied ac is transformed into a net dc voltage. These results demonstrate that the rectification is mainly characterized by the asymmetric pinning landscape and the rectified voltage depends considerably on temperature and the amplitude of applied ac. The dc voltage increases steeply up to the maximum value and then decreases to zero dc voltage with the increase of ac. The shape of peaks in the dc voltage signal become steeper and move to higher applied ac regime with the decrease of temperature.
Nonplanar modeling and experimental validation of a spindle-disk system equipped with an automatic balancer system in optical disk drives
(2007-05-01)
Chao, Paul C. -P.
;
Sung, Cheng-Kuo
;
Wu, Szu-Tuo
;
Huang, Jeng-Sheng
;
電控工程研究所
Non-planar dynamic modeling and experimental validation of a spindle-disk system equipped with an automatic ball-type balancer system (ABS) in optical disc drives are performed in this study. Recent studies about planar dynamic modeling and analysis have shown the capability of the ABS in spindle-disk assembly via counteracting the inherent imbalance. To extend the analysis to be practical, non-planar dynamic modeling are conducted in this study to re-affirm the pre-claimed capability of the ABS system, along with experiments being designed and conducted to validate the theoretical findings. Euler angles are first utilized to formulate potential and kinetic energies, which is followed by the application of Lagrange's equation to derive governing equations of motion. Numerical simulations are next carried out to explore dynamic characteristics of the system. It is found that the levels of residual runout (radial vibration), as compared to those without the ABS, are significantly reduced, while the tilting angle of the rotating assembly can be kept small with the ABS installed below the inherent imbalance of the spindle-disk system. Experimental study is also conducted, and successfully validates the aforementioned theoretical findings. It is suggested that the users of the ABS need to cautiously operate the spindle motor out of the speeds close to the resonances associated with various degrees of freedom. In this way, the ABS could hold the expected capability of reducing vibration in all important directions, most importantly in radial directions.
Sub-THz photonic-transmitters based on separated-transport-recombination photodiodes and a micromachined slot antenna
(2007-05-01)
Li, Yu-Tai
;
Shi, J.-W.
;
Pan, Ci-Ling
;
Chiu, C.-H.
;
Liu, W.-S.
We demonstrate a novel photonic transmitter, which is composed of a low-temperature-grown GaAs (LTG-GaAs)-based separated-transport-recombination photodiode and a micromachined slot antenna. Under femtosecond optical pulse illumination, this device radiates strong electrical pulses (4.5-mW peak power) without the use of a Si-lens. It can be observed in the Fourier transform infrared spectrometer spectrum of radiated pulses that a significant resonance, with a peak power of approximately 300 mu W, occurs at 500 GHz, which corresponds to the designed resonant frequency of the slot antenna. The saturation problem related to the output terahertz power that occurs with the traditional LTG-GaAs-based photonic-transmitters when operated under high external applied electrical fields (> 50 kV/cm) has been eliminated by the use of our device.
Effect of top electrode material on resistive switching properties of ZrO2 film memory devices
(2007-05-01)
Lin, Chih-Yang
;
Wu, Chen-Yu
;
Wu, Chung-Yi
;
Lee, Tzyh-Cheang
;
Yang, Fu-Liang
The influence of top electrode material on the resistive switching properties of ZrO2 -based memory film using Pt as a bottom electrode was investigated in this letter. In comparison with Pt/ZrO2/Pt and Al/ZrO2/Pt devices, the Ti/ZrO2/Pt device exhibits different resistive switching current-voltage (I-V) curve, which can be traced and reproduced by a dc voltage more than 1000 times only showing a little decrease of resistance ratio between high and low resistance states. Furthermore, the broad dispersions of resistive switching characteristics in the Pt/ZrO2/Pt and Al/ZrO2/Pt devices are generally observed during successive resistive switching, but those dispersions are suppressed by the device using Ti as a top electrode. The reliability results, such as cycling endurance and continuous readout test, are also presented. The write-read-erase-read operations can be over 104 cycles without degradation. No data loss is found upon successive readout after performing various endurance cycles.
Light-output enhancement of nano-roughened GaN laser lift-off light-emitting diodes formed by ICP dry etching
(2007-05-01)
Kao, Chih-Chiang
;
Kuo, H. C.
;
Yeh, K. F.
;
Chu, J. T.
;
Peng, W. L.
In this paper, we report the fabrication and characteristics of nano-roughened GaN laser lift-off (LLO) light-emitting diodes (LEDs) with different scale surface roughness. The surface roughness of devices was controlled by inductively coupled plasma reactive inn etching. Using this fabrication method to form nanoscaled roughness, the electrical property was almost not degraded. Furthermore, the light-output power and wall-plug efficiency of LLO LED could be both significantly enhanced about two times using this simple method.
On the architecture design and performance evaluation of a configurable Blueweb network
(2007-05-01)
Yu, Chih-Min
;
Huang, Chia-Chi
;
電信工程研究所
;
Institute of Communications Engineering
Blueweb is a self-organizing Bluetooth-based multihop network equipped with a scatternet formation algorithm and a modified source routing protocol. In this paper, we first review the basic Blueweb network. Then we focus on a heuristic automatic configuration algorithm which can be used to partition a large-scale Blueweb network. This algorithm contains three main functional blocks including route master selection, node assignment, and subnet number decision. The route master selection block selects new route masters at a low computation cost. The node assignment block assigns nodes to each newly configured subnet in order to minimize the average route query cost. The subnet number decision block determines the optimal number of subnet which achieves the largest system performance improvement ratio at minimum operation cost. With these three functional blocks, optimal network configuration for Blueweb routing protocol can be determined. Computer simulations show that a configured Blueweb achieves higher network capacity than an unconfigured Blueweb.
Characterizing nonlinear rate-dependent behaviors of graphite/epoxy composites using a micromechanical approach
(2007-05-01)
Tsai, Jia-Lin
;
Chen, Kuei-Han
;
機械工程學系
;
Department of Mechanical Engineering
This research aims to characterize the nonlinear rate-dependent behaviors of graphite/epoxy composites using micromechanical analysis. In this analysis, graphite fibers are considered as elastic solids, while the surrounding epoxy matrix exhibiting rate sensitivities are described using the three-parameter viscoplasticity model. By using Aboudi's generalized method of cells (GMC), the incremental form of the constitutive relations of the composites are expressed in terms of the constituent properties as well as the geometry parameters of the representative volume element. After a numerical iteration, the corresponding stress and strain relations of composites at different strain rates are generated. In order to verify the model predictions, off-axis graphite/epoxy composite specimens are tested at strain rates from 10(-4) to 550/s. For strain rates less than 1/s, the experiments are conducted using a hydraulic MTS machine, while high-strain-rate tests were carried out using a split Hopkinson pressure bar. Experimental results indicate that the stress and strain curves are quite sensitive to the strain rate; moreover, when the strain rates increase, the material stiffens. A comparison of model predictions with experimental results indicates that the rate-dependent behaviors of composites can be characterized effectively with the GMC model in conjunction with the viscoplastic properties of epoxy.
Unitizations of double-ring structure and Erbium-doped waveguide amplifier for stable and tunable fiber laser
(2007-05-01)
Chou, S.-Y.
;
Yeh, C.-H.
;
Chi, S.
;
光電工程學系
;
Department of Photonics
We propose and demonstrate experimentally a single longitudinal-mode (SLM) fiber double-ring laser using an Erbium-doped waveguide amplifier (EDWA), polarization controller (PC), and a fiber Fabry-Perot tunable filter (FFP-TF) into the ring cavity. In addition the output power side mode suppression ratio (SMSR), and the stabilities of power and wavelength of the laser also are investigated.
Effect of different gold nanoparticle sizes to build an electrical detection DNA between nanogap electrodes
(2007-05-01)
Chang, Tien-Li
;
Lee, Ya-Wei
;
Chen, Chun-Chi
;
Ko, Fu-Hsiang
;
材料科學與工程學系奈米科技碩博班
An experimental study for identifying DNA strands immobilized in the different particle sizes of gold nanoparticle (AuNP) between nanogap electrodes is presented. The nanogap-based electrics chip demonstrates a significant electrical property with a target DNA (DNA) concentration of 10 pM in the different particle sizes of AuNP to be analyzed in order to make the assay useful for an integrated lab-on-a-chip application system. The biochips with nanogap electrodes are fabricated by e-beam lithography (EBL). Different from traditional detection methods including polymerase chain reaction (PCR) based on assays which are expensive and time consuming for DNA strands research. By the method of electrical characterization, a change in measured current through the different particle sizes of AuNP can pave the way for further use in sensitive biomolecule detection study. (c) 2007 Published by Elsevier B.V.
Corner stress singularities in an FGM thin plate
(2007-05-01)
Huang, C. S.
;
Chang, M. J.
;
土木工程學系
;
Department of Civil Engineering
Describing the behaviors of stress singularities correctly is essential for obtaining accurate numerical solutions of complicated problems with stress singularities. This analysis derives asymptotic solutions for functionally graded material (FGM) thin plates with geometrically induced stress singularities. The classical thin plate theory is used to establish the equilibrium equations for FGM thin plates. It is assumed that the Young's modulus varies along the thickness and Poisson's ratio is constant. The eigenfunction expansion method is employed to the equilibrium equations in terms of displacement components for an asymptotic analysis in the vicinity of a sharp corner. The characteristic equations for determining the stress singularity order at the corner vertex and the corresponding corner functions are explicitly given for different combinations of boundary conditions along the radial edges forming the sharp corner. The non-homogeneous elasticity properties are present only in the characteristic equations corresponding to boundary conditions involving simple support. Finally, the effects of material non-homogeneity following a power law on the stress singularity orders are thoroughly examined by showing the minimum real values of the roots of the characteristic equations varying with the material properties and vertex angle. (c) 2006 Elsevier Ltd. All rights reserved.