Browsing by Issue Date, starting with "1998-04-06"

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Sr0.8Bi2.5Ta1.2Nb0.9O9+x ferroelectric thin films prepared by two-target off-axis radio frequency magnetron sputtering
(1998-04-06)
Tsai, HM
;
Lin, P
;
Tseng, TY
;
材料科學與工程學系
;
電子工程學系及電子研究所
Ferroelectric Sr0.8Bi2.5Ta1.2Nb0.9O9+x thin films on a Pt/SiO2/Si substrate were prepared by using two-target off-axis radio frequency magnetron sputtering, and their structural and electrical properties were investigated. The films crystallized with high (115) diffraction intensity at a substrate temperature of 600 degrees C, and showed columnar microstructure. The 600 degrees C sputtered films with a thickness of 440 nm exhibited remanent polarization (2P(r)) of 52 mu C/cm(2) and coercive field (2E(c)) 28 kV/cm at an applied voltage of 1.5 V. The leakage current density was about 6 X 10(-6) A/cm(2) at an electric field of 50 kV/cm. The films demonstrated fatigue free characteristics up to 1.0 X 10(10) switching cycles under a 3 V bipolar 1 MHz square wave. (C) 1998 American Institute of Physics. [S0003-6951(98)04014-5].
A study of the total chromatic number of equibipartite graphs
(1998-04-06)
Chen, BL
;
Cheng, CK
;
Fu, HL
;
Huang, KC
;
應用數學系
The total chromatic number chi(t)(G) of a graph G is the least number of colors needed to color the vertices and edges of G so that no adjacent vertices or edges receive the same color, no incident edges receive the same color as either of the vertices it is incident with. In this paper, we obtain some results of the total chromatic number of the equibiparrite graphs of order 2n with maximum degree n - 1. As a part of our results, we disprove the biconformability conjecture. (C) 1998 Published by Elsevier Science B.V. All rights reserved.
High resolution and energy filtering TEM study of interfacial structure and reaction in advanced materials processing
(1998-04-10)
Chang, HL
;
Chang, L
;
Chen, FR
;
Kai, JJ
;
Tzou, E
High resolution TEM becomes more powerful when coupled with a Gatan imaging filler (GIF). It gives both structural and compositional information simultaneously with subnanometer and nanometer resolution. respectively. By means of these combined techniques, the failure mechanism of diffusion barrier layers in IC devices, having the structure of Al-1%Si-0.5%CuiTiNITi/Si substrate, was investigated. In non-oxygen stuffed samples thermally stressed at 550 degrees C for 1 h serious Al spikes below contacts were observed where metal layer Ti also reacted with Si substrate to form C49-TiSi2 and was consumed completely. TiN and Al become unstable due to high temperature thermal stress and reacted into TiAl3 and AlN. Decomposition of TiN degraded the function of the barrier layer, and so a diffusion path at the weakest point of the contact corner was opened for metal Al alloy to diffuse through the barrier layer and to form a spike below the TiN layer. We also showed that the oxygen-stuffing processes after each TiN/Ti deposition enhances the barrier capability against Al/Si diffusion in thermal stress. It was found that Ti and TiN were oxidized to form titanium oxide which reacted with the Al alloy. As a result, Al2O3 and TiAl3 were found above the TiN layer. Therefore, it is concluded that oxidation during oxygen-stuffing processes provides a means to inhibit diffusion in thermal stress processes, and maintains integrity of the stack structure. (C) 1998 Acta Metallurgica Inc.
A consistent finite element formulation for linear buckling analysis of spatial beams
(1998-04-14)
Hsiao, KM
;
Yang, RT
;
Lin, WY
;
機械工程學系
;
Department of Mechanical Engineering
A consistent co-rotational finite element formulation and numerical procedure for the linear buckling analysis of three-dimensional elastic Euler beam is presented. A mechanism for generating configuration dependent conservative moment is proposed and the corresponding load stiffness matrix is derived. It is assumed that the prebuckling displacements and rotations of the structure and the corresponding deformations of the elements are linearly proportional to the external loading. The prebuckling rotations of the structure are fixed axis rotations or small rotations, and the effect of the prebuckling displacement on transformation matrix for the coordinates transformation can be ignored. All coupling among bending, twisting and stretching deformations for beam element is considered by consistent linearization of the fully geometrically nonlinear beam theory. An inverse power method for the solution of the generalized eigenvalue problem is used to find the buckling load and buckling mode. Numerical examples are presented to demonstrate the accuracy and efficiency of the proposed method. (C) 1998 Elsevier Science S.A.
pi plasmons in carbon nanotube bundles
(1998-04-15)
Lin, MF
;
Chuu, DS
;
電子物理學系
;
Department of Electrophysics
The pi-electronic collective excitations (pi plasmons) in carbon nanotube bundles are studied within the linear-response approximation. The intertube Coulomb interactions significantly affect the electronic excitations, so that the pi plasmons in nanotube bundles are quite different from those in a single nanotube. The pi plasmons strongly depend on the direction and magnitude of the transferred momentum. They clearly exhibit the anisotropic behavior. Moreover, the pi plasmon frequencies are lower for bundles made up of larger nanotubes.
Two-dimensional arsenic precipitation in superlattice structures of alternately undoped and heavily Be-doped GaAs grown by low-temperature molecular beam epitaxy
(1998-04-20)
Su, ZA
;
Huang, JH
;
Hsieh, LZ
;
Lee, WI
;
電子物理學系
The precipitation of arsenic in superlattice structures of alternately undoped and [Be]=2.4 x 10(19) cm(-3) doped GaAs grown at low temperatures has been studied using transmission electron microscopy. Novel precipitate microstructures were observed in annealed samples, including preferential accumulation of precipitates toward each interface of Be-doped GaAs and the following grown undoped GaAs. Specifically, after 800 degrees C annealing, the precipitates are totally confined in Be-doped regions, forming mio-dimensional dot arrays near the aforementioned interfaces. Data are also presented to show that the heavily Be-doped GaAs has a smaller lattice constant than the undoped GaAs. A strain-induced mechanism was proposed to account for the segregation of As clusters. (C) 1998 American Institute of Physics.
Optical unwinding and reentrance phenomena in chiral smectic-C liquid crystals
(1998-04-20)
Chen, SH
;
Chen, CY
;
光電工程學系
;
Department of Photonics
We optically measure the molecular reorientation induced by an argon laser in homeotropically aligned chiral smectic-C films. Optical unwinding of the helix is observed and the critical unwinding intensity is determined. We have also developed a theory which not only explains the observed effect but also predicts a novel reentrance phenomenon of the unwinding state. (C) 1998 American Institute of Physics.
On the Miura and Backlund transformations associated with the supersymmetric Gelfand-Dickey bracket
(1998-04-20)
Shaw, JC
;
Tu, MH
;
應用數學系
;
物理研究所
;
Department of Applied Mathematics
The supersymmetric version of the Miura and Backlund transformations associated with the supersymmetric Gelfand-Dickey bracket are investigated from the point of view of the Kupershmidt-Wilson theorem.
Design and analysis of electrically calibrated tympanic thermometers
(1998-05-01)
Ou-Yang, M
;
Shie, JS
;
Tsao, C
;
光電工程學系
;
Department of Photonics
A new tympanic thermometer is analyzed and tested experimentally. An electrically calibrated pyroelectric detector of special configuration is employed to determine a person's body temperature. An energy-storage, power-supply-isolated capacitor is used as the electrical heating reference. The new thermometer design has an accuracy within +/-0.1 degrees C with a 90% confidence and is immune to ambient temperature, detector aging, and parameter variations. An equivalent-circuit model is established in the analysis to account for the heat exchanges among the tympanum, the surroundings, and the detector as well as for the electrothermal behavior of the detector. The model provides effective simulation of the thermometer with PSPICE. Critical parameters governing the accuracy and the Limitation of the tympanic thermometer are also pointed out by the simulation. (C) 1998 Optical Society of America.
Well supply voltage effect on escape current of guard rings in epitaxial CMOS technology
(1998-05-01)
Huang, CY
;
Chen, MJ
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
An n-well guard ring dual collector structure formed on an epitaxial substrate has been characterized and simulated. The measured I-V characteristics have exhibited that a reduction of well supply voltage from 5.0 to 1.0 V causes an increase in the escape current into the outer well by a factor of about 14, while the base and inner guard ring collector currents are hardly changed. This will influence neighboring latchup susceptibility substantially. This experimental observation can provide a new evidence of the published theory responsible for the escape current: the injected minority carriers flow through a quasi-neutral layer between the upper collecting plate and the bottom high/low junction reflecting plate. Based on this theory actual epitaxial layer thickness can be extracted with low guard ring voltages as well. Published by Elsevier Science Ltd. All rights reserved.
A dual CP slot antenna using a modified Wilkinson power divider configuration
(1998-05-01)
Tseng, WJ
;
Chung, SJ
;
電信工程研究所
;
Institute of Communications Engineering
A dual circularly polarized (CP) slot antenna based on a proposed equal-split Wilkinson power divider is presented, An offset-fed slot antenna, which was analyzed using the method of moments together with a mixed potential integral equation, was used to replace the lumped resistor in the divider. A dual CP slot antenna operating at S-band was designed and demonstrated experimentally. The antenna possessed a return loss bandwidth of 39.3%, an isolation bandwidth of 10% for VSWR <2, and 3-dB axial ratio bandwidth of 28%.
Inverse Vening Meinesz formula and deflection-geoid formula: applications to the predictions of gravity and geoid over the South China Sea
(1998-05-01)
Hwang, C
;
土木工程學系
;
Department of Civil Engineering
Using the spherical harmonic representations of the earth's disturbing potential and its functionals, we derive the inverse Vening Meinesz formula, which converts deflection of the vertical to gravity anomaly using the gradient of the H function. The deflection-geoid formula is also derived that converts deflection to geoidal undulation using the gradient of the C function. The two formulae are implemented by the 1D FFT and the 2D FFT methods. The innermost zone effect is derived. The inverse Vening Meinesz formula is employed to compute gravity anomalies and geoidal undulations over the South China Sea using deflections from Seasat, Geosat, ERS-1 and TOPEX//POSEIDON satellite altimetry. The 1D FFT yields the best result of 9.9-mgal rms difference with the shipborne gravity anomalies. Using the simulated deflections from EGM96, the deflection-geoid formula yields a 4-cm rms difference with the EGM96-generated geoid. The predicted gravity anomalies and geoidal undulations can be used to study the tectonic structure and the ocean circulations of the South China Sea.
The role of partial miscibility on the properties of ternary blends of liquid crystalline copolyesters and polyetherimide
(1998-05-01)
Wei, KH
;
Tyan, HL
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Binary blends of liquid crystalline copoly(oxybenzoate-p-ethylene terephthalate) at molar ratio 60/40, POB-PET, and polyetherimide (PEI) were investigated with differential scanning calorimetry and polarised optical microscopy. It was found that POB-PET and PEI were partially miscible when PEI was the major component. Adding a small amount (5 phr) of POB-PET to the originally immiscible blends of liquid crystalline copoly(oxybenzoate-naphthalate) (73/27), Vectra, and PEI resulted in better interfacial adhesions between Vectra and PEI as evidenced by the morphological observations with scanning electron microscopy. The enhancement in the interfacial adhesions caused an increase in the ultimate tensile strength and the impact strength of these ternary blends of Vectra, POB-PET and PEI as compared to that of the corresponding binary blends of Vectra and PEI in an injection molding process. (C) 1998 Elsevier Science Ltd. All rights reserved.
An RNN-based prosodic information synthesizer for Mandarin text-to-speech
(1998-05-01)
Chen, SH
;
Hwang, SH
;
Wang, YR
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
A new RNN-based prosodic information synthesizer for Mandarin Chinese text-to-speech (TTS) is proposed in this paper. Its four-layer recurrent neural network (RNN) generates prosodic information such as syllable pitch contours, syllable energy levels, syllable initial and final durations, as well as inter-syllable pause durations. The input layer and first hidden layer operate with a word-synchronized clock to represent current-word phonologic states within the prosodic structure of text to be synthesized. The second hidden layer and output layer operate on a syllable-synchronized clock and use outputs from the preceding layers, along with additional syllable-level inputs fed directly to the second hidden layer, to generate desired prosodic parameters. The RNN was trained on a large set of actual utterances accompanied by associated texts, and can automatically learn many human-prosody phonologic rules, including the well-known Sandhi Tone 3 F0-change rule. Experimental results show that all synthesized prosodic parameter sequences matched quite well with their original counterparts, and a pitch-synchronous-overlap-add-based (PSOLA-based) Mandarin TTS system was also used for testing of our approach. While subjective tests are difficult to perform and remain to be done in the future, we have carried out informal listening tests by a significant number of native Chinese speakers and the results confirmed that all synthesized speech sounded quite natural.
Analysis and application of a two-port aperture-coupled microstrip antenna
(1998-05-01)
Tseng, WJ
;
Chung, SJ
;
電信工程研究所
;
Institute of Communications Engineering
A two-port aperture-coupled microstrip antenna was analyzed using the method of moments together with a mixed potential integral equation (MPIE), The antenna contains two microstrip-line ports (i.e., a feeding port and a coupling port), The field coming from one microstrip line on the circuit layer is fed into the patch through an aperture on the ground plane, Part of the field is then coupled back to a second microstrip line through another aperture on the same ground. The influences of the stub lengths, along with the positions and sizes of the apertures, on the coupling power and the resonant frequency were investigated. As an application, a feedback antenna oscillator was designed using the present structure where the antenna served not only as a radiator, but also as a feedback resonator. The oscillation was stable and with a clean spectrum at the frequency of 9.79 GHz, which was only 0.2% different from the design one. An effective isotropic radiated power (EIRP) of 39 mW was achieved. The measured cross-polarized fields were at least 15 dB lower than the copolarized ones.
Magnetic force microscopy study of domain walls on a thin cobalt film
(1998-05-01)
Lin, HN
;
Chiou, YH
;
Chen, BM
;
Shieh, HPD
;
Chang, CR
Two types of 180 degrees domain walls on a 115 nm cobalt film are observed by magnetic force microscopy. The surface Neel wall on top of an asymmetric Bloch wall is found inhomogeneous. with the width estimated to be around 200 nm. The width of the rhomb-structured cross-tie wall, on the other hand, is approximately 400 nm. The coexistence of these two types of domain walls indicates that their wall energies are comparable at the film thickness. (C) 1998 American institute of Physics.
管管作品三首
(1998-05-01)
管管
Growth of MgWO4 phosphor by RF magnetron sputtering
(1998-05-01)
Chu, JP
;
Hsieh, IJ
;
Chen, JT
;
Feng, MS
;
材料科學與工程學系
Magnesium tungstate (MgWO4) thin film phosphors prepared by radio frequency (RF) magnetron sputter deposition were characterized. alpha- and beta-MgWO4 were determined as the major phases in the films studied. Since the deposition rates of film were influenced by RF power. working pressure as well as oxygen content, these processing parameters played an important role in affecting the phase present in the as-deposited films. It is found that the formation of alpha-MgWO4 phase was favorable for the films grown at low deposition rates (<40 Angstrom min(-1)) whereas beta-MgWO4 was a dominant phase at high deposition rates. Substrate temperatures showed no detectable effects on the deposition rates and thus the beta-MgWO4 was the only phase present for the substrate temperature range examined. A phase formation mechanism due to the deposition rate difference is described. Post-deposition annealing significantly improved the cathodoluminescence (CL) properties of films, with annealing temperatures at 750 degrees C or above being the most effective. CL property improvement appeared to he attributed to the enhancement of crystallinity and the transformation to the stable beta-MgWO4 phase during the annealing. Annealing-induced film delamination and blisters. however, resulted in deterioration of low voltage CL properties. (C) 1998 Elsevier Science S.A. All lights reserved.
Electron-phonon scattering times in crystalline disordered titanium alloys between 3 and 15 K
(1998-05-01)
Wu, CY
;
Jian, WB
;
Lin, JJ
;
物理研究所
;
Institute of Physics
We have successfully fabricated bulk crystalline disordered titanium alloys (Ti1-xSnx, T1-xGex, and Ti0.97-xSn0.03Scx) with nominal concentration x of the order of a few at. %. The impurity atoms are gradually introduced into a titanium host to tune the degree of disorder, resulting in residual resistivities rho(0) varying from approximate to 40 to 160 mu Omega cm (corresponding to values of k(F)l approximate to 5-20, with k(F) being the Fermi wave number and l being the electron elastic mean free path). With this wide range of experimentally accessible rho(0), we are able to perform systematic studies of the disorder rho(0), or electron elastic mean free path l, behavior of the electron-phonon scattering time tau(ph). We have measured the magnetoresistivities of these alloys between 3 and 15 K, and compared our results with weak-localization theoretical predictions to extract tau(ph)(T,l) Unexpectedly, we obtain a rather diversified temperature dependence and disorder dependence of tau(ph) as follows. (a) In Ti1-xSnx alloys with rho(0) greater than or similar to 100 mu Omega cm we find 1/tau(ph)similar to T-2/l. (b) In Ti1-xSnx alloys with rho(0) less than or similar to 70 mu Omega cm we find 1/tau(ph)similar to T-3/l. (c) In Ti1-xGex alloys with 50 less than or similar to p(0) less than or similar to 130 mu Omega cm we find 1/tau(ph)similar to T-3 in some alloys and 1/tau(ph)similar to T-4 in others, while at a given temperature 1/tau(ph) is essentially independent of disorder. (d) In Ti0.97-xSn0.03Scx alloys with 55 less than or similar to rho(0) less than or similar to 75 mu Omega cm we obtain 1/tau(ph)similar to T-2. These experimental observations altogether imply that electron-phonon interactions in the presence of strong impurity scattering are very sensitive to the local material environment (the microscopic quality) of a particular sample system, which might be variously modulated with the doping of different kinds of impurity atoms. Our results are compared with existing theoretical predictions for electron-phonon scattering in disordered conductors.
管管作品三首
(1998-05-01)
管管