Browsing by Issue Date, starting with "1999-05-01"

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Promotion of phase transformation and single-phase formation in silver-doped Tl-Ba-Ca-Cu-O superconducting thin films
(1999-05-01)
Koo, HS
;
Tseng, TY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Phase transformation and physical characteristics of the spray-pyrolyzed Tl-Ba-Ca-Cu-O superconducting films with 3 mol% silver dopant have been studied using electrical resistivity, x-ray diffraction, and scanning electron microscopy. The major phase formed in the resultant film, annealed at a temperature of 885 degrees C for 3 min, was found to be the nearly single-phase, high-T-c, Tl2Ba2Ca2Cu3Oy (Tl-2223), The multiple phase of Tl2Ba2Ca2Cu3Oy and TlBa2Ca2Cu3Oy (Tl-1223) appeared at annealing temperatures lower and higher than 885 degrees C. It was also observed that Ag dopant effectively reduces normal resistivity at 300 K and enhances the phase transformation of single-rrl-layer Tl-1223 to double-Tl-layer Tl-2223 phases and further helps to form the nearly single-phase Tl-2223 within a short duration. Critical transition temperature (T-c,T-zero) and current density (J(c), 77 K, 0 Tesla) of the best resultant film were shown to be 123 K and 5.7 X 10(4) A/cm(2), respectively.
Adsorption behavior of iron-cyanide onto gamma-Al2O3 interface: A coagulation approach
(1999-05-01)
Cheng, WP
;
Huang, CP
;
Pan, JRS
;
環境工程研究所
;
Institute of Environmental Engineering
Ferrocyanide and ferricyanide ions have strong coagulation ability in a natural water system due to their high valences. Studies with aluminum oxide turbid waters showed significant differences in coagulation between simple ions (Cl-, SO42-, Fe(CN)(6)Fe3-(CN)(6)(4-)) and other species (H2PO4-) that interact chemically with the oxide surface. The evidence suggested that the adsorption of ferrocyanide and ferricyanide on aluminum oxide surface is an outer-sphere reaction. The linear relationship between the logarithm of the significant coagulation concentration and Schultz-Hardy ratios indicated that the coagulation obeyed the DLVO rule. Therefore, it is concluded that the coagulation of aluminum oxide by ferrocyanide and ferricyanide is essentially caused by compression of the electric double layer rather than by charge neutralization. (C) 1999 Academic Press.
The CVD growth of Cu films using H-2 as carrier gas
(1999-05-01)
Lin, PJ
;
Chen, MC
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Copper chemical vapor deposition from Cu(hexafluoroacetylacetonate)trimethyl-vinylsilane (Cu(hfac)TMVS) was studied using a low pressure chemical vapor deposition system of a cold wall vertical reactor. The Cu films deposited using H-2 as a carrier gas revealed no impurities in the films within the detection limits of Auger electron spectroscopy and x-ray photoelectron spectroscopy. Using hydrogen as a carrier gas, the hydrogen not only acts as a reducing agent, but also reacts with the residual fragment of precursor. As a result, using H-2 as a carrier gas for Cu(hfac)TMVS resulted in Cu films of lower resistivity, denser microstructure and faster deposition rate than using Ar or N-2 as the carrier gas. Moreover, we found that N-2 plasma treatment on the substrate surface prior to Cu deposition increased the deposition rate of Cu films.
Face selection in addition and elimination in sterically unbiased systems
(1999-05-01)
Kaselj, M
;
Chung, WS
;
le Noble, WJ
;
應用化學系
;
Department of Applied Chemistry
Evaporation of water film in an enclosure filled with a porous medium
(1999-05-01)
Fu, WS
;
Ke, WW
;
機械工程學系
;
Department of Mechanical Engineering
A double diffusive natural convection in an enclosure filled with a porous medium is investigated numerically. To enhance the heat transfer rate of a heat wall, the heat wall is wetted with a thin water film, then sensible and latent heat transfer occur simultaneously. The Darcy-Brinkman-Forchheimer model is used and the factors of heat flux, porosity and diameter of bead are taken into consideration. The SIMPLEC method with iterative processes is adopted to solve the governing equations. The results show that the effect of evaporation on the heat transfer rate is apparent, and the latent heat transfer plays an important role in the high Darcy-Rayleigh number situations. The averaged Nusselt number <(Nu)over bar> is approximately 2.5 when Ra*<4. In the range of 4
Thermally driven polysilicon actuators for lateral displacement
(1999-05-01)
Wu, MF
;
Lin, CH
;
Hsu, WS
;
機械工程學系
;
Department of Mechanical Engineering
A novel one-mask; polysilicon actuator driven by thermal expansion is developed, modeled and tested. The structures are heated by electric current due to resistive dissipation. Thermal strain is magnified by two mechanical mechanisms-lever and parallelogram. The device is tested in air and has a lateral 8 mu m-displacement by applying a low voltage (below 3.5 V). The critical current to reach melting point is about 67 mA with the input voltage less than 5 V. The simulation results by analytical and FEM schemes are compared with experimental data. The maximum output forces is measured with a built-in cantilever beam and is calculated to be about 3.3 mu N.
Design and implementation of an FPGA-based control IC for AC-voltage regulation
(1999-05-01)
Jung, SL
;
Chang, MY
;
Jyang, JY
;
Yeh, LC
;
Tzou, YY
This paper presents a field-programmable gate array (FPGA)-based control integrated circuit (TC) for controlling the pulsewidth modulation (PWM) inverters used in power-conditioning systems for ac-voltage regulation, We also propose a multiple-loop control scheme for this PWM inverter control IC to achieve sinusoidal voltage regulation under large load variations. The control scheme is simple in architecture and thus facilitates realization of the proposed digital controller for the PWM inverter using the FPGA-based circuit design approach. Bit-length effect of the digital PWM inverter controller has also been examined in this paper. The designed PWM inverter control IC has been realized using a single FPGA XC4005 from Xilinx, Inc., which can be used as a coprocessor with a general-purpose microprocessor in application of ac-voltage regulation. Owing to the high-speed nature of FPGA, the sampling frequency of the constructed IC can be raised up to the range that cannot be reached using a conventional digital controller based merely on microcontrollers or a digital signal processor (DSP), Experimental results show the designed PWM inverter control IC using the proposed control scheme can achieve good voltage regulation against large load variations.
A new graph invariant for graph isomorphism: Probability propagation matrix
(1999-05-01)
King, GH
;
Tzeng, WG
;
資訊工程學系
;
Department of Computer Science
The graph isomorphism problem is to determine whether two given graphs are isomorphic or not. In this paper, we present a new graph invariant, called the probability propagation matrix. By means of this graph invariant, we present a heuristic algorithm for the problem. The algorithm is easy to implement and highly parallelizable.
Ba(Ti0.8Sn0.2)O-3 thin films prepared by radio-frequency magnetron sputtering for dynamic random access memory applications
(1999-05-01)
Kuo, YF
;
Tseng, TY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Polycrystalline thin films of Ba(Ti0.8Sn0.2)O-3 100 nm thick were deposited on Pt/TiO2/SiO2/Si(100) substrates by radio-frequency magnetron sputtering at various substrate temperatures. The films crystallized with high (111) diffraction intensity at a substrate temperature of 650 degrees C, had good crystalline quality, and exhibited a large dielectric constant. The dielectric constant and leakage current of the films increased with an increase of the intensity ratio of (111)/(110) peaks. This study also established a correlation between the dielectric constant, leakage current, and crystallinity of the films. (C) 1999 The Electrochemical Society. S1099-0062(98)11-098-2. All rights reserved.
Electrical characterization of Al2O3 on Si from thermally oxidized AlAs and Al
(1999-05-01)
Liao, CC
;
Chin, A
;
Tsai, C
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The scaling limit for VLSI gate oxide (SiO2) is 15-20 Angstrom that is determined by the large direct-tunneling leakage current. Further scaling to improve device performance can be obtained using a higher dielectric constant material. We have studied the Al2O3 to use as an alternative gate dielectric. To ensure good quality, Al2O3 is thermally oxidized from MBE-grown AlAs or Al on Si-substrates. Experimental results indicate that the leakage current from oxidized AlAs is larger than that from directly oxidized Al, which may be due to the weak As2O3 inside Al2O3. The leakage current of a 53 Angstrom Al2O3 is already lower than that of SiO2 with an equivalent oxide thickness of 21 Angstrom. (C) 1999 Published by Elsevier Science B.V. All rights reserved.
Adaptive self-quantization in wavelet-based fractal image compression
(1999-05-01)
Wu, BF
;
Hu, YQ
;
Hsu, HH
;
電控工程研究所
;
Institute of Electrical and Control Engineering
Finding a model to quantize the scale factors in wavelet-based fractal image compression is a complicated issue. To avoid error, it is helpful to model the distribution of the scale factors and quantize them before the computation process by iterated function systems. Traditionally, a fixed model with uniform distribution was frequently adopted. This is not sophisticated enough, however, to quantize these scale factors from errors since, in general, the factors are not uniformly distributed. We propose an adaptive algorithm with self-quantization to overcome this drawback. Except for the functions of adaptation and self-quantification, the approach has the optimal property that the fundamental objective is to reduce the quantization errors.
Improved electrical characteristics of CoSi2 using HF-vapor pretreatment
(1999-05-01)
Wu, YH
;
Chen, WJ
;
Chang, SL
;
Chin, A
;
Gwo, S
We have developed a simple process to form epitaxial CoSi2 for shallow junction. Prior to metal deposition, the patterned wafers were treated with HF-vapor passivation. As observed by scanning tunneling microscopy (STM), this HF, treatment drastically improves the native oxide-induced sur face roughness. The epitaxial behavior was confirmed by cross-sectional transmission electron microscopy (TEM), Decreased sheet resistance and leakage current, and improved thermal stability are displayed by the HF treated samples, which is consistent with STM and TEM results.
A novel 3-D scattering model of 1.8-GHz radio propagation in microcellular urban environment
(1999-05-01)
Tarng, JH
;
Ju, KM
;
電信工程研究所
;
Institute of Communications Engineering
This work presents a novel three-dimensional (3-D) scattering model to predict the path loss of a microcellular radio channel in an urban environment. The analytical scattering model combined with a patched-wall model predicts the median path loss more accurately than the conventional analytical ray-tracing model in the cases studied, Comparing the path loss with the measured one at 1.8 GHz demonstrates the effectiveness of the scattering model. The scattering model includes three major propagation modes: 1) a direct-path wave; 2) a ground-reflected wave; and 3) the scattered field from the walls aligned along a street. The proposed model with a polarization scattering matrix associated with the patched-wall model aptly describes the third mode, which is usually neglected or oversimplified.
A variable partition duplex scheme with enlarged reservation duration on packet reservation multiple access protocol
(1999-05-01)
Chang, C
;
Chang, CJ
;
電信工程研究所
;
Institute of Communications Engineering
A variable partition duplex scheme on packet reservation multiple access protocol (VPD-PRMA) is analyzed in this paper. We assume a four-state speech model for a conversational pair and successfully obtain performance measures by approximate Markovian analysis. Analytical results show that they quite fit simulation results; and VPD-PRMA can get higher statistical multiplexing gain than fixed partition duplex (FPD)-PRMA, due to the trunking effect. We further investigate the effect of design parameters of permission probability and enlarged reservation duration on system performance by computer simulation. Simulation results shows that it exists appropriate values for these two design parameters so that the packet dropping probability can be minimized. The adjustment of permission probability can greatly improve the performance of uplink traffic with slight deterioration of the performance of downlink traffic; the provision of enlarged reservation duration scheme can enhance the system performance.
Smooth vision-based autonomous land vehicle navigation in indoor environments by person following using sequential pattern recognition
(1999-05-01)
Ku, CH
;
Tsai, WH
;
資訊工程學系
;
Department of Computer Science
A new approach to autonomous land vehicle (ALV) navigation by the person following is proposed. This approach is based on sequential pattern recognition and computer vision techniques, and maintenance of smoothness for indoor navigation is the main goal. The ALV is guided automatically to follow a person who walks in front of the vehicle. The vehicle can be used as an autonomous handcart, go-cart, buffet car, golf cart, weeder, etc. in various applications. Sequential pattern recognition is used to design a classifier for making decisions about whether the person in front of the vehicle is walking straight or is too right or too left of the vehicle. Multiple images in a sequence are used as input to the system. Computer vision techniques are used to detect and locate the person in front of the vehicle. By sequential pattern recognition, the relation between the location of the person and that of the vehicle is categorized into three classes. Corresponding adjustments of the direction of the vehicle are computed to achieve smooth navigation. The approach is implemented on a real ALV, and successful and smooth navigation sessions confirm the feasibility of the approach. (C) 1999 John Wiley & Sons, Inc.
Preparation and characterization of garnet phosphor nanoparticles derived from oxalate coprecipitation
(1999-05-01)
Chen, TM
;
Chen, SC
;
Yu, CJ
;
應用化學系
;
Department of Applied Chemistry
Terbium-activated Y3Al5O12 (YAG:Tb) phosphor nanoparticles with homogeneous grain size and crystallinity have been prepared at 1000 degrees C by heat treatment of a metal oxalate precursor derived from an alkaline coprecipitation route, The diffraction profile of as-prepared YAG:Tb nanoparticles can be indexed as a garnet structure and exhibits peak broadening phenonmenon, as revealed by X-ray diffraction (XRD) data. Grains of YAG:Tb nanoparticles appear to be irregularly spherical or elliptical and their sizes range from 60 to 70 nm, as indicated by morphological studies from bright-field transmission electron microscopy (TEM) imaging. Furthermore, the photoluminescence (PL) spectra of the (Y2.9Tb0.1)Al5O12 phase were investigated to determine the energy level of electron transition related to luminescence processes and the possible blue shift in the excitation or emission PL spectra, (C) 1999 Academic Press.
Regular and chaotic dynamics of a rotational machine with a centrifugal governor
(1999-05-01)
Ge, ZM
;
Yang, HS
;
Chen, HH
;
Chen, HK
;
機械工程學系
The dynamic behavior of a rotational machine with centrifugal governor which is subjected to two different forms of external disturbance is studied in this paper. The Lyapunov direct method is applied to obtain conditions of stability of the equilibrium points of the system. A codimension one bifurcation analysis for the autonomous system is carried out near the degenerate point. It is found that a Hopf bifurcation occurs in the system. The incremental harmonic balance (IHB) method combined with the multi-variable Floquet theory has been effectively applied to obtain the steady state responses of the three-dimensional nonautonomous system. Phase portraits, power spectra, Poincare maps, and Lyapunov exponents are presented to observe periodic, quasi-periodic and chaotic motions. (C) 1999 Elsevier Science Ltd. All rights reserved.
Effects of Erlang call holding times on PCS call completion
(1999-05-01)
Lin, YB
;
Chlamtac, I
;
資訊工程學系
;
Department of Computer Science
This paper studies personal communications services (PCS's) channel allocation assuming the Erlang call holding time distribution (a generalization of the exponential distribution) to investigate the effect of the variance of the call holding times on the call completion probability. Our analysis indicates that the call completion probability decreases as the variance of the call holding times decreases, This effect becomes more pronounced as the variance of the cell residence times decreases.
Improved electrical characteristics of CoSi2 using HF-vapor pretreatment
(1999-05-01)
Wu, YH
;
Chen, WJ
;
Chang, SL
;
Chin, A
;
Gwo, S
We have developed a simple process to form epitaxial CoSi2 for shallow junction. Prior to metal deposition, the patterned wafers were treated with HF-vapor passivation. As observed by scanning tunneling microscopy (STM), this HF, treatment drastically improves the native oxide-induced sur face roughness. The epitaxial behavior was confirmed by cross-sectional transmission electron microscopy (TEM), Decreased sheet resistance and leakage current, and improved thermal stability are displayed by the HF treated samples, which is consistent with STM and TEM results.
Enhancement of integrity of polysilicon oxide by using a combination of N2O nitridation and CMP process
(1999-05-01)
Lei, TF
;
Chen, JH
;
Wang, MF
;
Chao, TS
;
電子工程學系及電子研究所
This work prepares and demonstrates, for the first time, a high-quality polysilicon oxide, by combining N2O nitridation and Chemical Mechanical Polishing (CMP) process. Our results demonstrate that capacitors with this process have an improved Q(bd) (charge-to-breakdown) due to the planar surface and more concentrated nitrogen at the interface of polysilicon oxide.