Browsing by Issue Date, starting with "1999-03-01"

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Distance graphs and T-coloring
(1999-03-01)
Chang, GJ
;
Liu, DDF
;
Zhu, XD
;
應用數學系
;
Department of Applied Mathematics
We discuss relationships among T-colorings of graphs and chromatic numbers, fractional chromatic numbers, and circular chromatic numbers of distance graphs. We first prove that for any finite integral set T that contains 0, the asymptotic T-coloring ratio R(T) is equal to the fractional chromatic number of the distance graph G(Z, D), where D = T-{0}. This fact is then used to study the distance graphs with distance sets of the form D-m,D- k = {1, 2, ..., m}- {k}. The chromatic numbers and the fractional chromatic numbers of G(Z, D-m,D- k) are determined for all values of m and k. Furthermore, circular chromatic numbers of G(Z, D-m,D- k) fur some special values of m and k are obtained. (C) 1999 Academic Press.
Anisotropic impurity scattering effects on T-c and H-c2 in YBa2Cu3Ox
(1999-03-01)
Lin, JY
;
Chen, SJ
;
Chen, SY
;
Chang, CF
;
Yang, HD
We have studied the impurity effects on the superconducting transition temperature T-c and the upper critical field H-c2 in electron irradiated YBa2Cu3Oy with in-plane oxygen defects and YBa2(Cu1-xZnx)(3)O-y. It is found that the effects of the same type of defects or impurities on T-c are the same regardless of the oxygen contents of the samples. Furthermore, T-c decreases slower in irradiated YBa2Cu3Oy than in YBa2(Cu1-xZnx)(3)O-y. This may be well explained by the model that the scattering due to in-plane oxygen defects is more anisotropic than that due to Zn impurities. The different behavior of the reduced slopes (dH(c2)/dT)(Tc)/(dH(c2)/dT)(Tc0) these two types of samples can also be understood in this context. [S0163-1829(99)08309-5].
On k-ary spanning trees of tournaments
(1999-03-01)
Lu, XY
;
Wang, DW
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Chang, GJ
;
Lin, IJ
;
Wong, CK
It is well known that every tournament contains a Hamiltonian path, which can be restated as that every tournament contains a unary spanning tree. The purpose of this article is to study the general problem of whether a tournament contains a k-ary spanning tree. In particular, we prove that, for any fixed positive integer k, there exists a minimum number h(k) such that every tournament of order at least h(k) contains a k-ary spanning tree. The existence of a Hamiltonian path for any tournament is the same as h(1) = 1. We then show that h(2) = 4 and h(3) = 8. The values of h(k) remain unknown for k greater than or equal to 4. (C) 1999 John Wiley & Sons. Inc. J Graph Theory 30: 167-176, 1999.
Finite element analysis and optimization on springback reduction
(1999-03-01)
Chou, IN
;
Hung, CH
;
機械工程學系
;
Department of Mechanical Engineering
Several springback reduction techniques used in the U-channel bending processes were analyzed with the finite element method, which included are bottoming, pinching die, spanking and movement techniques. The relationship between the amount of springback and the forming parameters in each technique was first established through finite element simulations, and then the optimization analysis was coupled with the finite element analysis to find the optimum forming parameters for each springback reduction technique. (C) 1998 Elsevier Science Ltd. All rights reserved.
Electrical properties of rapid thermal-enhanced low pressure chemical vapor deposited Ta2O5 thin films
(1999-03-01)
Lee, CJ
;
Huang, LT
;
Ezhilvalavan, S
;
Tseng, TY
;
電子工程學系及電子研究所
Electrical properties of rapid thermal-enhanced low pressure chemical vapor deposited Ta2O5 thin films subjected to an in situ two-step postannealing process were studied. Films treated by rapid thermal annealing in O-2 at 550 degrees C for 90 s followed by plasma O-2 at 550 degrees C for 30 s exhibit a leakage current density of 7.91 x 10(-9) A/cm(2) at an applied electric field of 100 kV/cm and a dielectric constant of similar to 38. The decrease in leakage current density of the annealed Ta2O5 films in comparison to the as-deposited films is attributed mainly to the effective reduction of carbon impurities and oxygen vacancies by the two-step postannealing process. (C) 1999 The Electrochemical Society. S1099-0062(98)08-064-X. All rights reserved.
Fractal extraction from a mixed fBm signal using discrete wavelet transforms
(1999-03-01)
Wu, BF
;
Su, YL
;
電控工程研究所
;
Institute of Electrical and Control Engineering
Since stationarity, ergodicity and self-similarity for the discrete wavelet transform of fractional Brownian motion (fBm) processes have been shown in previous works, these characteristics could be applied to extract the parameters of two fBm signals from a mixed fBm signal using time-average correlation functions. The goal of this paper is to distinguish the two identical power fBm signals from the mixed signal. In this case, we suppose that the mixed signal is available, but information on the parameters of the two fBm signals is not provided. A method is proposed to find the parameters of these two fBm signals. The smaller parameter can be detected from the fractal dimension of the mixed fBm signal. The parameter of the other fBm is estimated by processing the wavelet coefficients of the mixed fBm signal. Finally, the simulation results showed that this approach works well in increasing the difference between the parameters of the two fBms.
Preparation and properties of tantalum pentoxide (Ta2O5) thin films for ultra large scale integrated circuits (ULSIs) application - A review
(1999-03-01)
Ezhilvalavan, S
;
Tseng, TY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Tantalum pentoxide (Ta2O5) thin films have rapidly evolved into an important field of research/development for both basic and applied science with the promise of creating a new generation of advanced micro devices for electronics applications. This paper provides a broad review of the current status and future trends of Ta2O5 thin films as a high ly promising storage dielectric material for high-density dynamic random access memory applications. Various methods of thin film material processing are briefly reviewed. The physical, electrical and dielectric characteristics of Ta2O5 thin films with specific examples from recent literature and the associated conduction mechanisms are summarized and discussed. Some suggestions to improve the electrical properties of the films are finally included. (C) 1998 Kluwer Academic Publishers.
Nano-carbon nitride synthesis from a bio-molecular target for ion beam sputtering at low temperature
(1999-03-01)
Wu, JJ
;
Lu, TR
;
Wu, CT
;
Wang, TY
;
Chen, LC
Nano-crystalline carbon nitride has been successfully synthesized at a temperature below 100 degrees C from an adenine(C5N5H5) target sputtered by an Ar ion beam. Because adenine possesses a ring structure similar to the hypothetical beta-C3N4 phase, the use of this bio-molecular compound as the target is believed to reduce the energy barrier of carbon-nitride growth. The effect of Ar ion-sputtering voltage on the film growth and the effect of extra-N-atom incorporation on the carbon-nitride film growth are examined in this study. Only a carbon film is formed with an ion energy of 500 V. For the ion-beam energy above 750 V, carbon nitride films are deposited, and there is some hydrogen incorporation in the films. The N/C composition ratio in the films could reach 1:1 and is independent on the ion beam voltage. The nitrogen is bonded with carbon within the films, as determined by the IR and XPS measurements. However, the films deposited at a higher ion voltage could possess some original functional groups of adenine. A strong and broad peak at a d-spacing of 0.32 nm, comparable to the calculated d-spacing of the beta-C3N4(110), is observed in the XRD spectra of the carbon nitride films. The TEM results indicated that the film contained nano-crystalline grains. Several d values are also in good agreement with those of adenine and the calculated values of beta-C3N4. The C/N ratios of the films are still kept at almost 1:1 with N atoms added during deposition. The XRD spectra and IR spectra of these films are all similar to the film deposited without nitrogen source. (C) 1999 Elsevier Science S.A. All rights reserved.
Transition of carrier distribution from a strained to relaxed state in InGaAs/GaAs quantum well
(1999-03-01)
Wang, PY
;
Chen, JF
;
Wang, JS
;
Chen, NC
;
Chen, YS
This work investigates the transition of carrier distribution from the strained to the relaxed state in In0.2Ga0.8As/GaAs quantum well by measuring capacitance voltage and analyzing x-ray diffraction. According to those results, there is carrier confinement in the In0.2Ga0.8As quantum well with well thickness less than the critical thickness. Increasing the well thickness beyond the critical thickness leads to a significant carrier depletion around the quantum well. Double-crystal x-ray rocking curves reveal that when InGaAs well thickness increases beyond the critical thickness, the interference pattern disappears and relaxation begins to occur from near the bottom InGaAs/GaAs interface while the top interface still remains strained. Results obtained from the critical thickness determined from x-ray diffraction correspond to the transition of carrier distribution, illustrating that the capacitance-voltage measurement is a rather effective means of determining the critical thickness. (C) 1999 American Institute of Physics. [S0021-8979(99)01505-4].
Properties and thermal stability of chemically vapor deposited W-rich WSix thin films
(1999-03-01)
Wang, MT
;
Lin, YC
;
Chuang, MS
;
Chun, MC
;
Chen, LJ
The tungsten-rich (Si/W atomic ratio less than 2.0) chemical vapor deposition (CVD)-WSix layer was found to be an efficient diffusion barrier against Cu diffusion. In this study, the properties and thermal stability of the W-rich WSix films chemically vapor deposited at various deposition temperatures, pressures, and SiH4/WF6 reactant gas flow ratios were investigated. With SiH4/WF6 flow rates of 6/2 seem and a total gas pressure of 12 mTorr, the activation energy of the CVD process was determined to be 3.0 kcal/mole, and the film deposited at 250 degrees C has a Si/W atomic ratio of unity. The WSix, films have a low residual stress, low electrical resistivity, and excellent step coverage. For the WSix layers deposited on Si substrates, the residual stress varies from 7 to 9 X 10(8) dynes/cm(2) depending on the deposition temperature. The resistivity of the WSI, films varies from 200 to 340 mu Omega cm; higher deposition temperatures and SiH4/WF6 flow ratios resulted in higher film resistivities. The as-deposited amorphous WSix layer is thermally stable up to 600 degrees C; however, crystallization of the deposited film takes place at 650 degrees C and WSix was transformed into WSi2 phase when the WSix/Si structure was thermally annealed at temperatures above 650 degrees C. (C) 1999 American Vacuum Society. [S0734-211X(99)03602-1].
A distributed fault-tolerant design for multiple-server VOD systems
(1999-03-01)
Shyu, IJ
;
Shieh, SP
;
資訊工程學系
;
Department of Computer Science
Fault tolerance is an important design criterion for reliable and robust video-on-demand systems. Conventional fault-tolerant designs use either a primary backup or an active replication method to provide system fault tolerance. However, these approaches suffer from low utilization of the backup or replication system. In this paper we propose two playback-recovery schemes for distributed video-on-demand systems called the forward playback-recovery scheme and the backward playback-recovery scheme. Unlike conventional fault-tolerant designs, our schemes use existing playback resources to recover faulty playbacks without allocating new resources, significantly reducing recovery overhead. To use the schemes effectively, we developed a distributed algorithm for determining the order and gap information between the playbacks on the distributed video-on-demand servers so that overhead for recovering from a server failure can be minimized. This algorithm achieves N - 1 fault-tolerant resiliency for N-server video-on-demand systems. In addition, three server-recovery policies are also presented to guide surviving servers in applying the proper scheme to recover faulty playbacks, thus reducing overall recovery costs. Simulation results show that the proposed recovery schemes are effective and useful in designing fault-tolerant multiple-server video-on-demand systems.
The market acceptance of electric motorcycles in Taiwan experience through a stated preference analysis
(1999-03-01)
Chiu, YC
;
Tzeng, GH
;
運輸與物流管理系註：原交通所+運管所
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Department of Transportation and Logistics Management
The environmental and energy concerns of using motorcycles in urban areas have fostered the rapid development development of electric motorcycles (EMs) in Taiwan in recent years. EMs' zero-emission, low noise level and high energy efficiency features provide the promising potential to alleviate the severe environmental pollution problem caused by the existing gasoline motorcycles. This study summarizes the recent development of the EM. More specifically, this study aims to analyze the potential demand for EMs based on an interview survey using stated preference modeling approaches. Study results show that female motorists are the potential target market for EMs. Developmental and energy-use issues of EMs are also discussed in this study. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.
Electron paramagnetic resonance and luminescence study of sol-gel derived YAG : Cr powder
(1999-03-01)
Lo, JR
;
Ezhilvalavan, S
;
Tseng, TY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Electron paramagnetic resonance (EPR) and luminescence studies were carried out for the sol-gel-derived YAG:Cr powders subjected to three kinds of heat treatment processes. The results show that powders processed using the two-step heat treatment process with the addition of 20 wt% LiCl and by direct heat treatment at 1500 degrees C exhibit good luminescence properties. The emission spectrum for the powders obtained by the two-step process shows the R-line at 688 nm, whereas the powders directly heat treated at 1500 degrees C display an additional R-line of Al2O3 : Cr at 694 nm: EPR measurements show that the presence or absence of absorption peaks depends on the Cr3+ environment in-the host lattice resulting from the different methods of heat treatment of the powder. The EPR spectra of YAG:Cr3+ phosphors were interpreted to indicate both Cr3+ single ion and Cr3+-Cr3+ pair (with spin three) transitions.
Magnetic domain pinning in lithographically patterned amorphous magnetic layer
(1999-03-01)
Wu, JC
;
Huang, YW
;
Chen, BM
;
Wu, TH
;
Shieh, HPD
Artificial pinning sites have been fabricated for the magnetic domain pinning in perpendicular anisotropy magneto-optical (MO) thin film media. The pinning sites were radial hole array made by patterning a layer of radial gold grid on the silicon nitride (SiN) coated silicon (Si) substrate using a standard electron beam lithography. Various magnetization and demagnetization procedures were performed to investigate the magnetic domain pinning behavior. A polar Kerr microscope was used in situ to monitor the magnetic wall motion and a magnetic force microscope was employed to scan the magnetic domain structures. Magnetic domains were found to be pinned inside the hole array and resembled to the geometric shape of the holes. The coercivity in the patterned MO layer is much higher than in thr unpatterned MO layer. Moreover, the coercivity in the larger pinning sites area is higher than in the smaller pinning sites area.
Formation of silicided shallow p(+) n junctions by BF2+ implantation into thin amorphous-Si or Ni/amorphous-Si films on Si substrates and subsequent Ni silicidation
(1999-03-01)
Juang, MH
;
Hu, MC
;
Yang, CJ
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The process scheme that forms NiSi-silicided shallow p(+)n junctions by BF2+ implantation into thin amorphous-Si (a-Si) or Ni/a-Si films on Si substrates and subsequent Ni silicidation has been studied. As for the scheme using a-Si as an implantation barrier, an NiSi-silicided junction with a leakage of about 0.7 nA/cm(2) at - 5 V is obtained by the sample Ni silicided at 700 degrees C for 30 min. The implantation energy and the crystallinity of the deposited Si films after annealing would greatly affect the junctions formed at various temperatures, attributable to different, implantation effects and boron depth profile. However, the junctions formed by rapid thermal processing or high implant energy are considerably degraded at 800 degrees C, attributable to anomalous Ni penetration into the Si substrate with the further silicidation of NiSi into NiSi2. On the other hand, the specimens with Ni/a-Si as an implantation barrier sustain few defects, thus significantly suppressing the junction degradation at 800 degrees C. However the formed junctions are worse than those by the former scheme, mainly due to lower dopant drive-in efficiency. (C) 1999 American Vacuum Society. [S0734-211X(99)03902-5].
Thermal stability of amorphous-like WNx/W bilayered diffusion barrier for chemical vapor deposited-tungsten/p(+)-Si contact system
(1999-03-01)
Chang, KM
;
Deng, IC
;
Yeh, TH
;
Lain, KD
;
Fu, CM
The barrier characteristics of tungsten nitride/tungsten (WNx/W) bilayer formed by an in situ nitridation on a thin chemical vapor deposited amorphous-like tungsten (CVD a-W) film in CVD-W/Si contact system have been investigated. The thickness of WNx layer after a 5 min of N-2 plasma exposure at 300 degrees C approximated 50 nm and the atomic ratio of W to N in WNx layer was 2 : 1. In the CVD-W/a-WNx/a-W/Si multilayered sample, no discernible tungsten silicide was detected by X-ray diffractometer (XRD) at W/Si interface after annealing at 750 degrees C. Meanwhile, with the Rutherford backscattering spectroscopy (RBS) analysis and the measurement of p(+)n junction leakage current, the CVD-W/a-WNx/a-W/Si multilayer maintained the integrity of interface and the CVD-W/a-WNx/a-W/p(+)n diode kept the reverse leakage current density less than 9 x 10(-9) A/cm(2) while the post annealing was carried out at 700 degrees C for 30 min. As the experimental results, the effectiveness of amorphous-like WNx/W bilayered diffusion barrier is attributed to stuff grain boundary with N atoms as well as to eliminate the rapid diffusion paths by using CVD a-W material.
Distributed-program reliability analysis: Complexity and efficient algorithms
(1999-03-01)
Lin, MS
;
Chang, MS
;
Chen, DJ
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資訊工程學系
;
Department of Computer Science
This paper investigates the problem of distributed-program reliability in various classes of distributed computing systems. This problem is computationally intractable for arbitrary distributed computing systems, even when it is restricted to the class of star distributed computing systems. One solvable case for star distributed computing systems is identified, in which data files are distributed with respective to a consecutive property; a polynomial-time algorithm is developed for this case. A linear-time algorithm is developed to test whether or not an arbitrary star distributed computing system has this consecutive file distribution property. Efficient algorithms may still be sought for computing lower & upper bounds on the distributed program reliability for arbitrary distributed computing systems.
Algorithmic aspects of linear k-arboricity
(1999-03-01)
Chang, GJ
;
應用數學系
;
Department of Applied Mathematics
For a fixed positive integer k, the linear k-arboricity la(k)(G) of a graph G is the minimum number l such that the edge set E(G) can be partitioned into l disjoint sets, each induces a subgraph whose components are paths of lengths at most k. This paper examines linear k-arboricity from an algorithmic point of view. In particular, we present a linear-time algorithm for determining whether a tree T has la(2)(T) less than or equal to m. We also give a characterization for a tree T with maximum degree 2m having la(2)(T) = m.
Oxide thickness dependence of plasma charging damage
(1999-03-01)
Lin, HC
;
Chen, CC
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Wang, MF
;
Hsien, SK
;
Chien, CH
Charging damage induced in oxides with thickness ranging from 8.7 to 2.5 nm is investigated. Results of charge-to-breakdown (Q(bd)) measurements performed on control devices indicate that the polarity dependence increases with decreasing oxide thickness at both room and elevated temperature (180 degrees C) conditions. As the oxide thickness is thinned down below 3nm, the Q(bd) becomes very sensitive to the stressing current density and temperature. Experimental results show that severe antenna effect would occur during plasma ashing treatment in devices with gate oxides as thin as 2.6 nm. It is concluded that high stressing current level, negative plasma charging, and high process temperature are key factors responsible for the damage. (C) 1999 Elsevier Science Ltd. All rights reserved.
Effect of deposited particles and particle charge on the penetration of small sampling cyclones
(1999-03-01)
Tsai, CJ
;
Shiau, HG
;
Lin, KC
;
Shih, TS
;
環境工程研究所
Effects of particle mass deposited in the cyclone and particle electrostatic charge on the particle penetration of the commonly used 10mm nylon cyclone have been experimentally investigated in this study. The solid particle penetration of the cyclone has been found to decrease with an increase in particle mass deposited in the cyclone. This effect is most significant for particles near the cutoff aerodynamic diameter and when the deposited particle mass is low. The penetration of the cyclone has also been found to be influenced by particle electrostatic charge. This effect is also significant for particles near the cutoff aerodynamic diameter and when the number of elementary units of charge is greater than several thousands. To overcome these problems, a new cyclone made of conductive aluminum and with inner diameter nearly twice that of the 10 mm nylon cyclone has been designed and tested. Experimental results indicate that effects of both deposited particle mass as well as electrostatic charge on the penetration are reduced substantially in this cyclone. (C) 1999 Elsevier Science Ltd. All rights reserved.