Browsing by Issue Date, starting with "2000-06-15"

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Reaction kinetics and mechanism of BaPbO3 formation
(2000-06-15)
Chang, MC
;
Wu, JM
;
Cheng, SY
;
Chen, SY
;
材料科學與工程學系
The influence of starting materials on the formation of BaPbO3 is studied. The reaction kinetics of perovskite BaPbO3 phase formation depends greatly on the phase of lead oxide raw materials. Kinetics of BaPbO3 formation is analyzed by the Johnson-Mehl-Avrami model. The experimental results reveals that the reaction of BaCO3-PbO2 raw materials has a reaction order of n = 5/2, and the reaction is controlled by diffusion. On the other hand, in the case of BaCO3-PbO system, the reaction order n is equal to 1. The formation is controlled by the interface reaction. In the final stage of both systems, the reaction orders are the same of about 0.5. The phases left in the final stage are BaPbO3 and BaCO3. (C) 2000 Elsevier Science S.A. All rights reserved.
Improvement of polysilicon oxide integrity using NF3-annealing
(2000-06-15)
Yang, WL
;
Shieh, MS
;
Chen, YM
;
Chao, TS
;
Liu, DG
We report a method to improve the polysilicon oxide integrity by using NF3-annealing. Incorporating with stronger Si-N and Si-F bonds at the polysilicon/polyoxide interface, significant improvements are found in terms of roughness, breakdown strength, charge-to-breakdown, and stress-induced-leakage-current.
Microscopic morphology and energy surface landscape in a supercooled soft-sphere system
(2000-06-15)
Ma, WJ
;
Wu, TM
;
物理研究所
;
Institute of Physics
We carry out a systematic study on the microscopic morphology and its relationship with the signatures of the traces swept over the potential energy surface in a soft-sphere fluid system interacting via a truncated Lennard-Jones potential. The state of the model system is tuned by changing its temperature obtained in a molecular dynamics simulation, ranging from the equilibrium fluid phase to the deeply quenched supercooled states. The density and the range of interaction are chosen so that the instantaneously barely isolated centers are present. We analyze the microscopic structural origin of the features in the instantaneous-normal-mode (INM) spectrum and search for evidence of state transformation. It is found that the presence of drastic changes in the INM spectra upon entering the deep supercooled regime is accompanied by the reduction in the spatial connectivity. We develop a method to characterize the spatial configuration ration in an attempt to address the origin of the temperature-dependent changes in the spectra. (C) 2000 Elsevier Science B.V. All rights reserved.
Photoluminescence and electron paramagnetic resonance studies of defect centers in porous silicon
(2000-06-15)
Lue, HT
;
Huang, BY
;
Lue, JT
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Photoluminescence (PL) and electron spin resonance (ESR) spectrometers were exploited to study the Pb defect centers in porous silicon (PS) under various heat treatments. The breaking of Si-H-x and Si-O-H bonds in PS by thermal annealing changes the emission wavelength and increases the recombination centers resulting in degrading the PL intensity. Four kinds of dangling bonds on interfaces of silicon (1 1 1), (1,-1,-1), (-1,1,-1), and (-1,-1,1) faces and SiO2 with C-3V symmetry were identified. The skeleton structure of PS collapsed under thermal annealing. Annealing in hydrogen gas, which is controvertible to the pervasive anticipation, cannot passivate the dangling bonds introduced at high temperatures. (C) 2000 Elsevier Science S.A. All rights reserved.
Carrier-carrier scattering in GaAs/AlxGa1-xAs quantum wells
(2000-06-15)
Sun, KW
;
Song, TS
;
Sun, CK
;
Wang, JC
;
Kane, MG
We have studied carrier dynamics in highly nonequilibrium two-dimensional (2D) carrier distributions generated with femtosecond laser pulses in p-doped GaAs/Al0.32Ga0.68As quantum wells at photoexcited carrier densities between 10(9) and 10(11) cm(-2). The initially nonthermal carrier distribution is quickly broadened due to inelastic carrier-carrier scattering, with the broadening rate increasing as carrier density is increased. Measurements of the unrelaxed peak height in the hot electron-neutral acceptor luminescence spectra are compared with calculations of the carrier distribution using integration of the 2D dynamically screened Boltzmann equation. Our results indicate that carrier-carrier scattering becomes as significant a scattering mechanism as LO-phonon emission at density of about 10(10) cm(-2).
Temperature dependence of rate coefficients of reactions of NO2 with CH3S and C2H5S
(2000-06-15)
Chang, PF
;
Wang, TT
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Wang, NS
;
Hwang, YL
;
Lee, YP
Rate coefficients of reactions (1) CH3S + NO2 and (2) C2H5S + NO2 were determined using laser photolysis and laser-induced fluorescence, CH3S and C2H5S radicals were generated on photolysis of CH3SSCH3 and C2H5SSC2H5, respectively, with a KrF excimer laser at 248 nm. Their concentrations were monitored via fluorescence excited by emission from a dye laser at 371.4 nm (for CH3S) or 410.3 nm (for C2H5S) pumped with a pulsed XeCl excimer laser at 308 nm. Our measurements show that k(1) (297 K) = (1.01 +/- 0.15) x 10(-10) cm(3) molccule(-1) s(-1) is similar to a value reported by Balla ct al. and approximately 50% greater than other previously reported values; listed errors represent 95% confidence limits. Reaction 1 has a negative activation energy: k(1) = (4.3 +/- 1.3) x 10(-11) exp[(240 +/- 100)/T] cm(3) molecule(-1) s(-1) for T = 222-420 K. Reaction 2 has a rate coefficient similar to reaction 1 at room temperature: k(2)(296 K) = (1.05 +/- 0.16) x 10(-10) cm(3) molecule(-1) s(-1) but has a small positive activation energy with k(2) = (2.4 +/- 0.7) x 10(-10) exp[(-210 +/- 80)/T] cm(3) molecule(-1) s(-1) for T = 223-402 K. The temperature dependence of k(2) is determined for the first time. Reactions of NO2 with HS, CH3S, and C2H5S are compared.
Phosphorus vacancy as a deep level in AlInP layers
(2000-06-15)
Sung, WJ
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Wu, YR
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Lee, SC
;
Wen, TC
;
Li, TJ
Deep levels in AlInP layers, grown by metal-organic chemical vapor deposition (MOCVD) with various V/III mole ratios, have been carefully investigated by deep-level transient spectroscopy (DLTS). A deep level originating from phosphorus vacancy was observed with the activation energy of 0.65 eV. Examining this phosphorus-vacancy-related deep level provided a relatively simple means of understanding the phosphorus vacancy in AlInP, thus allowing us to determine an appropriate V/III mole ratio for growing AlInP.
CMOS compatible thermoelectric infrared sensors
(2000-06-22)
Shown, CS
;
Chi, S
;
光電工程學系
;
Department of Photonics
A new structure for CMOS compatible thermoelectric infrared sensors is proposed. By using micro-link structures to connect several floating membranes, the largest floating membrane area yet obtained and large output voltages have been realised. The characteristics of the sensors have been measured, and are compared with those of existing devices.
Computing the noncentral beta distribution with S-system
(2000-06-28)
Chen, ZY
;
Chou, YC
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管理科學系
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Department of Management Science
Based on the recasting techniques of Rust and Volt (1990, J. Amer. Statist. Assoc. 85, 572-578), an S-system form of the noncentral beta distribution is extended from that of the noncentral F distribution and the other one is newly derived. The computing methods of this distribution have received much attention during the last decade. Its cumulative probabilities, densities, quantiles and related distributional values can be calculated in one S-system form. We demonstrate the new computational results using the S-system numerical solver ESSYNS. Consistent results are obtained from these two S-system forms under various situations. In addition, we compare the performance with an ad hoc computing method by evaluating the cumulative probabilities and densities jointly. The S-system formulation provides significant numerical advantages over its original form. Further properties are also discussed (C) 2000 Elsevier Science B.V. All rights reserved.
Direction of arrival estimation based on phase differences using neural fuzzy network
(2000-07-01)
Shieh, CS
;
Lin, CT
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電控工程研究所
;
Institute of Electrical and Control Engineering
A new high-resolution direction of arrival (DOA) estimation technique using a neural fuzzy network based on phase difference (PD) is proposed in this paper. The conventional DOA estimation method such as MUSIC and MLE, are computationally intensive and difficult to implement in real time. To attach these problems, neural networks have become popular for DOA estimation in recent years. However, the normal neural networks such as multilayer perceptron (MLP) and radial basis function network (RBFN) usually produce the extra problems of low convergence speed and/or large network size (i.e., the number of network parameters is large). Also, the way to decide the network structure is heuristic. To overcome these defects and take use of neural learning ability, a powerful self-constructing neural fuzzy inference network (SONFIN) is used to develop a new DOA estimation algorithm in this paper. By feeding the PD's of received radar-array signals, the trained SONFIN can give high-resolution DOA estimation. The proposed scheme is thus called PD-SONFIN, This new algorithm avoids the need of empirically determining the network size and parameters in normal neural networks due to the powerful on-line structure and parameter learning ability of SONFIN, The PD-SONFIN can always find itself an economical network size in fast learning process. Our simulation results show that the performance of the new algorithm is superior to the RBFN in terms of convergence accuracy, estimation accuracy, sensitivity to noise, and network size.
Prediction-based lower triangular transform
(2000-07-01)
Phoong, SM
;
Lin, YP
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電控工程研究所
;
Institute of Electrical and Control Engineering
In this paper, a new nonunitary transform called the prediction-based lower triangular transform (PLT) is introduced for signal compression. The new transform has the same decorrelation property as the Kahurnen-Loeve transform (KLT), but its implementational cost is less than one half of KLT, Compared with the KLT, the design cost of an M x M PLT is much lower and is only of the order of O(M-2). Moreover, the PLT can be factorized into simple building blocks, Using two different factorizations, we introduce two minimum noise structures that have roughly the same complexity as the direct implementation of PLT. These minimum noise structures have the following properties: 1) Its noise gain is unity even though the transform is nonunitary; 2) perfect reconstruction is structurally guaranteed; 3) it can be used for both. lossy/lossless compression. We will show that the coding gain of PLT implemented using the minimum noise structure is the same as that of KLT. Furthermore, universal transform coders using PLT are derived. For AR(1) process, the M x M PLT has a closed form and needs only (M - 1) multiplications and additions.
Plasma-induced charging damage in ultrathin (3-nm) gate oxides
(2000-07-01)
Chen, CC
;
Lin, HC
;
Chang, CY
;
Liang, MS
;
Chien, CH
Plasma-induced damage in various 3-nm-thick gate oxides (i.e., pure oxides and N2O-nitrided oxides) was investigated by subjecting both nMOS and pMOS antenna devices to a photoresist ashing step after metal pad definition. Both charge-to-break-down and gate leakage current measurements indicated that large leakage current occurs at the wafer center as well as the wafer edge for pMOS devices, while only at the wafer center for nMOS devices. These interesting observations could be explained by the strong polarity dependence of ultra-thin oxides in charge-to breakdown measurements of nMOS devices. In addition, pMOS devices were found to be more susceptible to charging damage, which can be attributed to the intrinsic polarity dependence in tunneling current between n- and p-MOSFET,s. More importantly, our experimental results demonstrated that stress-induced leakage current (SILC) caused by plasma damage can be significantly suppressed in N2O-nitrided oxides, compared to pure oxides, especially for pMOS devices. Finally, nitrided oxides were also found to be more robust when subjected to high temperature stressing. Therefore, nitrided oxides appear to be very promising for reducing plasma charging damage in future ULSI technologies employing ultrathin gate oxides.
Nature of the 45 degrees vortex lattice reorientation in tetragonal superconductors
(2000-07-01)
Knigavko, A
;
Kogan, VG
;
Rosenstein, B
;
Yang, TJ
;
電子物理學系
The transformation of the vortex lattice in a tetragonal superconductor which consists of the 45 degrees reorientation relative to the crystal axes is studied using the nonlocal London model. It is shown that the reorientation occurs as two successive second order (continuous) phase transitions. The transition magnetic fields are calculated for a range of parameters relevant for borocarbide superconductors in which the reorientation has been observed.
Identification, purification, and characterization of a thermophilic imidase from pig liver
(2000-07-01)
Su, TM
;
Yang, YS
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生物科技學系
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Department of Biological Science and Technology
This study investigates thermophilic imidase activity of the liver. We demonstrate that imidase catalyzes the hydrolysis of imides at a temperature substantially higher than that of its native environment. Then, a thermophilic imidase is purified to homogeneity from pig liver, and its thermoproperties are studied. About 2500-fold of purification and 15% yield of imidase activity are obtained after ammonium sulfate precipitation, octyl, DEAE, chelation, and gel filtration chromatography, While avoiding heat treatment for the protein purification, this study also indicates that only one enzyme is responsible for the imidase activity. This homogenous enzyme prefers to catalyze hydrolysis of imides at above 60 degrees C rather than at the body temperature of a pig. Although stable at below 50 degrees C, imidase quickly loses its activity at above 65 degrees C. Thus, the temperature effect on imidase activity is limited mainly by its thermostability, Substrate specificity of imidase is also temperature dependent. Our results demonstrate that the hydrolysis of physiological substrates is the most temperature dependent and that of hydantoins is the least temperature dependent. When increasing the reaction temperature from 25 to 60 degrees C, specific activities increase 50- and 60-fold for dihydrouracil and dihydrothymine, respectively. The temperature effect on the K-m and V-max of imidase is substrate dependent. (C) 2000 Academic Press.
Improvement in wafer temperature uniformity and flow pattern in a lamp heated rapid thermal processor
(2000-07-01)
Yin, CP
;
Hsiao, CC
;
Lin, TF
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機械工程學系
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Department of Mechanical Engineering
An experimental lamp heated, rapid thermal processor (RTP) for an 8-in single silicon wafer was designed and established to investigate the thermal and flow characteristics in the processing chamber by transient temperature measurement and flow visualization. Experiments were carried out to explore the effects of placing a highly conducting copper plate right below the wafer on the uniformity of the wafer temperature and effects of the showerhead on the resulting flow distribution in the processing chamber. The measured data indicated that adding the copper plate can effectively reduce the nonuniformity of the wafer temperature. Besides, using a showerhead with finer holes in it results in a better flow distribution in the processor. (C) 2000 Elsevier Science B.V. All rights reserved.
High temperature formed SiGeP-MOSFET's with good device characteristics
(2000-07-01)
Wu, YH
;
Chin, A
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電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
We have used a simple process to fabricate Si0.3Ge0.7/Si p-MOSFET's. The Si0.3Ge0.7 is formed using deposited Ge followed by 950 degrees C rapid thermal annealing and solid phase epitaxy that is process compatible with existing VLSI. Hole mobility of 250 cm(2)/Vs is obtained from Si0.3Ge0.7 p-MOSFET that is similar to two times higher than Si control devices and results in a consequent substantially higher current drive. The 228 Angstrom Si0.3Ge0.7 thermal oxide grown at 1000 degrees C has a high breakdown field of 15 MV/cm, low interface trap density (D-it) of 1.5 x 10(11) eV(-1) cm(-2), and low oxide charge of 7.2 x 10(10) cm(-2). The source-drain junction leakage after implantation and 950 degrees C RTA is also comparable with Si counterpart.
An analysis for measurement of thermal diffusivity components of anisotropic platelike samples by AC calorimetric method
(2000-07-01)
Sheu, LJ
;
Lin, JD
;
機械工程學系
;
Department of Mechanical Engineering
This work examines the effects of anisotropy and transparency on measurements of thermal diffusivity components with an ac calorimetric method associated with laser heating. Analytical results indicate that the region where the two-dimensional effect occurs increases with the decrease of the ratio of cross-plane to in-plane thermal diffusivity. The region also increases with the optical thickness of the sample. The linear relations, as indicated by a decay constant from which the cross-plane thermal diffusivity is deduced, are not obtained for media of both optically moderate and thin thickness, while at sufficiently large optical thickness, anisotropy and two-dimensional effects are found insignificant.
An automatic controller extractor for HDL descriptions at the RTL
(2000-07-01)
Liu, CNJ
;
Jou, JY
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電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Extracting controlling finite-state machines can significantly reduce state space and thereby speed functional verification. The controller extraction algorithm uses an approach that frees it from restrictions on HDL code writing style.
Synthesis of dextran-(5-FU)-galactosamine conjugate through a tripeptide spacer group and its in vitro properties
(2000-07-01)
Guu, JA
;
Juang, TM
;
Hsiue, GH
;
Chiu, HC
;
應用化學系
In this study, conjugation of 5-fluorouracil (5-FU) and galactosamine with dextran via Glycyl-L-Leucyl-Glycine (Gly-Leu-Gly) tripeptidyl spacer was performed first by activation of dextran with p-nitrophenyl chloroformate, followed by aminolysis of Glycyl-L-Leucyl-Glycyl-5flurouracil (Gly-Leu-Gly-5-FU) and galactosamine with activated dextrans. Preparation of Gly-Leu-Gly-5-FU was carried out by sequential reactions of peptide synthesis in solution phases and coupling with 5-FU in the presence of diethylphosphoric cyanide. The release of 5-FU from the conjugates upon the exposure of polymeric prodrugs to papain implied that the attachment of 5-FU with the tripeptidyl spacer, Gly-Leu-Gly, was capable of being liberated by cathepsin B in lysosomes of targeted cells. The observation that the cytoxicity in vitro from the incubation of dextran-5-FU conjugate containing galactosamine residues with Hep-3B cells is higher than that in the void of galactosamine indicated the occurrence of specific binding of the targeting moieties with its receptors on cell membrane, leading to an enhanced cellular uptake of the conjugate via receptor-mediated endocytosis.
Digital multisignature schemes for authenticating delegates in mobile code systems
(2000-07-01)
Shieh, SP
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Lin, CT
;
Yang, WB
;
Sun, HM
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資訊工程學系
In this paper, we motivate the need for efficient multisignature schemes in delegated mobile services. With the schemes, delegates can be identified and delegated accesses can be controlled. First, we give a new digital signature scheme with message recovery. Based on the digital signature scheme, two digital multisignature schemes are proposed: the parallel multisignature scheme and the serial multisignature scheme. The parallel multisignature scheme allows each user to sign the same message separately and independently, and then combines all individual signatures into a multisignature, The serial multisignature scheme allows a group of users to sign the message serially, and does not need to predetermine the signing order. Both multisignature schemes tan withstand the attacks that aim to forge the signatures or to get the private kegs of the signers.