Browsing by Issue Date, starting with "2000-10-03"

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The effects of growth temperature on the microstructure and electrical barrier height in PtSi/p-Si(100) Schottky barrier detector
(2000-10-03)
Horng, GJ
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Chang, CY
;
Ho, C
;
Lee, CY
;
Huang, TY
The effects of growth temperature on the microstructure and electrical barrier height of the PtSi Schottky barrier detector (SBD) have been investigated. PtSi films, 4 nm in thickness were deposited at various temperatures ranging from 350 to 550 degreesC. The electron diffraction patterns showed that PtSi film formed at 350 degreesC depicts an intermingling of both (1 (1) over bar1) and (1 (2) over bar1) orientations. However, only (1 (2) over bar1) orientation was shown when the PtSi films were formed above 450 degreesC. Moreover, SBD formed at 350 degreesC was found to depict an electrical barrier that is approximately 0.02 eV higher than those formed above 450 degreesC. Although the microstructure and the electrical barrier height of the PtSi film do not change when the formation temperature was further increased from 450 to 550 degreesC. Nevertheless, the higher formation temperature resulted in a larger grain size, indicating that grain size alone does not affect the barrier height of the resultant SBD. (C) 2000 Elsevier Science S.A. All rights reserved.
Least-squares finite element approximations to the Timoshenko beam problem
(2000-10-06)
Jou, J
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Yang, SY
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應用數學系
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Department of Applied Mathematics
In this paper a least-squares finite element method for the Timoshenko beam problem is proposed and analyzed. The method is shown to be convergent and stable without requiring extra smoothness of the exact solutions. For sufficiently regular exact solutions, the method achieves optimal order of convergence in the H-1-norm for all the unknowns (displacement, rotation, shear, moment), uniformly in the small parameter which is generally proportional to the ratio of thickness to length. Thus the locking phenomenon disappears as the parameter tends to zero, A sharp a posteriori error estimator which is exact in the energy norm and equivalent in the H-1-norm is also briefly discussed. (C) 2000 Published by Elsevier Science Inc. All rights reserved. AMS classification: 65N15; 65N30.
Donor states in a multi-layered quantum dot
(2000-10-09)
Hsieh, CY
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Chuu, DS
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電子物理學系
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Department of Electrophysics
The ground and excited state energies of a hydrogenic impurity located at the centre of a multi-layered quantum dot (MLQD) are calculated in the framework of the effective-mass approximation. The MLQD consists of a spherical core (e.g. GaAs) and a coated spherical shell (e.g. Ga1-xAlxAs). The whole dot is then embedded inside a bulk material (e.g. Ga1-xAlyAs). We solve the Schrodinger equation exactly. The eigenfunctions of the impurity are expressed in terms of Whittaker function and Coulomb wavefunction. The state energies are expressed in terms of the shell thickness, core radius, total dot radius and the potential heights. Our calculation shows that, as the dot radius approaches infinity, the state energies of an impurity located at the centre of a multi-layered or a single-layered QD approach -1/n(2) Ry, where n is the principal quantum number, Ry = mue(4)/2 epsilon (2)h(2), mu and epsilon are the electronic effective mass and the dielectric constant of GaAs material. Thus it behaves like a three-dimensional free hydrogen atom. For very small dot radius, however, the state energy of the hydrogenic impurity of a MLQD behaves very differently from that of a single-layered QD. For a multi-layered QD with finite shell and bulk potential barrier heights, the state energies of the impurity are found to be dependent on the difference of the shell potential (V-2) and the bulk potential (V-3).
A 1.2-V operation power pseudomorphic high electron mobility transistor for personal handy phone handset application
(2000-10-15)
Chang, EY
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Lee, DH
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Chen, SH
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材料科學與工程學系
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Department of Materials Science and Engineering
A 1.2 V GaAs power pseudomorphic high electron mobility transistors (PHEMT's) for personal handy phone system (PHS) handset application was developed. The power PHEMT has a dual delta doped AlGaAs/InGaAs/GaAs based structure with compact device layout. The 6.72 mm device exhibits maximum power added efficiency (PAE) of 43.62% at 1.2V drain bias with an output power of 22.18 dBm. Under 1.9 GHz pi /4-shifted quadrature phase shift keying (QPSK) modulated PHS signal, the device shows an adjacent channel leakage power (P-adj) Of -56.86 dBc at 600 kHz apart from the center frequency and a linear efficiency of 41.31%. This is the first report on the 1.2-V operation power PHEMT for PHS handset application so far.
Inflationary universe in higher derivative induced gravity
(2000-10-15)
Kao, WF
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物理研究所
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Institute of Physics
In an induced-gravity model, the stability condition of an inflationary slow-rollover solution is shown to be phi (0)partial derivative (phi0) V(phi (0)) = 4 V(phi (0)). The presence of higher derivative terms will, however, act against the stability of this expanding solution unless further constraints on the field parameters are imposed. We find that these models will acquire a nonvanishing cosmological constant at the end of inflation. Some models are analyzed for their implication to the early universe.
Circulations and eddies over the South China Sea derived from TOPEX/Poseidon altimetry
(2000-10-15)
Hwang, C
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Chen, SA
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土木工程學系
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Department of Civil Engineering
TOPEX/Poseidon (T/P) altimeter data were used to derive time-varying circulation and eddies over the South China Sea (SCS) for 1993-1999. Large variabilities of sea surface heights and dense distribution of eddies were found to occur along a band across the SCS basin. A crossover method is introduced to compute pointwise velocity components. The TiP-derived circulations and eddies are consistent with the drifter results from the World Ocean Circulation Experiment data center. (1) Because of monsoons, the SCS circulation is largely cyclonic in winter, is largely anticyclonic in summer, and is modulated interannually by El Nino - Southern Oscillation. (2) Both cold- and warm-core eddies were found in the waters east of Vietnam, west of Luzon, and west of the Luzon Strait, but their times of occurrence and the way they evolved vary interannually. (3) The reversal of the alongshore currents east of Vietnam was in complete accordance with wind stress. The locations and kinematic properties of eddies over SCS were estimated by the least squares method. The averaged vorticities of the cold- and warm-core eddies are 1.684x10(-6) and -1.738x10(-6) rad s(-1), respectively, and the shearing and stretching deformations are one thousandth of the vorticities. The angular velocity of eddy decreases with increasing radius. Coherence analysis suggests that the interannual and seasonal variations of circulation are largely due to wind stress, and the semi-annual variation is largely due to wind stress curl. The angular velocities of eddies over the central SCS basin are coherent with the magnitudes and signs of wind stress curl. The seasonal steric anomaly was also computed, and its spatial pattern and scale are quite different from those of circulation and eddy.
Kaluza-Klein induced gravity inflation
(2000-10-15)
Kao, WF
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物理研究所
;
Institute of Physics
A D-dimensional induced gravity theory is studied carefully in a 4 + (D-4) dimensional Friedmann-Robertson-Walker space-time. We try to extract information about the symmetry-breaking potential in search of an inflationary solution with a nonexpanding internal space. We find that the induced gravity model imposes strong constraints on the form of the symmetry-breaking potential in order to generate an acceptable inflationary universe. These constraints are analyzed carefully in this paper.
Structural evolution and optical properties of TiO2 thin films prepared by thermal oxidation of sputtered Ti films
(2000-10-15)
Ting, CC
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Chen, SY
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Liu, DM
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材料科學與工程學系
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Department of Materials Science and Engineering
A dense rutile TiO2 thin film was synthesized by the thermal oxidation of a sputtered titanium metal film in ambient air. The effects on optical properties of TiO2 films of the crystal structure and microstructural evolution at various oxidation temperatures were investigated. The Ti films transformed into single-phase rutile TiO2 at temperatures greater than or equal to 550 degrees C without going through an anatase-to-rutile transformation. Instead, an additional crystalline Ti2O phase was detected at 550 degrees C only. An increase in the oxidation temperatures ranging between 700 and 900 degrees C led to an increase in both the refractive index and absorption coefficient, but a decrease in the band gap energy (E-g). According to the coherent potential approximation model, the band gap evolution of the oxidized films was primarily attributed to the electronic disorder due to oxygen deficiency at a higher oxidation temperature rather than the presence of an amorphous component in the prepared films. (C) 2000 American Institute of Physics. [S0021-8979(00)07920-2].
Characterization of excimer-laser-annealed polycrystalline silicon films grown by ultrahigh-vacuum chemical vapor deposition
(2000-10-16)
Chen, YC
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Wu, YCS
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Tung, IC
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Chao, CW
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Feng, MS
Polycrystalline silicon (poly-Si) films grown by ultrahigh-vacuum chemical vapor deposition (UHVCVD) system and then annealed by excimer laser at room temperature have been investigated for the applications in polycrystalline silicon thin-film transistors (poly-Si TFTs). The results showed that the grain size of the laser-annealed poly-Si film decreased with laser energy density when a lower laser energy density below 157.7 mJ/cm(2) was used. At about the threshold laser energy density (similar to 134.5 mJ/cm(2)), the finest grain structure could be obtained due to the partial melting in the top layer of the film. When the energy density of the excimer laser was larger than the threshold energy density, the large grain growth was initiated. The largest grain structure could be obtained at similar to 184 mJ/cm(2), while its surface roughness was better than that of the nonannealed UHVCVD poly-Si films. The surface roughening was suggested to arise from the specific melt-regrowth process but not the rapid release of hydrogen or capillary wave mechanism derived from laser-annealed amorphous silicon. By use of the laser-annealed UHVCVD poly-Si films as the active layer, the fabricated poly-Si TFT exhibited a field-effect mobility of 138 cm(2)/V s, a subthreshold swing of 0.8 V/dec, a threshold voltage of 3.5 V, and an on/off current ratio of similar to 10(6). (C) 2000 American Institute of Physics. [S0003- 6951(00)03842-0].
Synthesis and epoxy curing of Mannich bases derived from bisphenol A and poly(oxyalkylene)diamine
(2000-10-17)
Lin, JJ
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Lin, SF
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Kuo, TT
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Chang, FC
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Tseng, FP
A family of Mannich bases were prepared from the reaction of 2,2-bis-(4-hydroxyphenyl)propane (bisphenol A or BPA), formaldehyde, and poly(oxyalkylene)diamines at 1 : 1 : 1 or 1 : 2 : 2 molar ratio. By varying the molar ratio of bisphenol A to amine and the chemical structures of poly(oxyalkylene)diamines, a series of products with multiple functionalities of primary/secondary amines, phenols, and poly(oxyalkylene) were prepared. The curing profiles of these products toward the diglycidyl ether of bisphenol A (DGEBA) were examined by a differential scanning calorimeter (DSC). The physical properties of these cured materials were correlated with the chemical structures of the Mannich bases. Compared with the poly(oxyalkylene)diamines, the built-in phenol moiety in Mannich bases accelerated the curing rate. Both amine and phenol functionalities could be reactive sites toward diglycidyl ethers in a step-wise fashion under catalytic (triphenylphosphine) and different temperature conditions. Furthermore, the cured polymers demonstrated improved properties including tensile and flexural strength in comparison with those cured by the corresponding poly(oxyalkylene)diamines. (C) 2000 John Wiley & Sons, Inc.
哈佛大學與MIT通識教育之研究(II)
(2000-10-28)
黃坤錦
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交通大學教育學程中心
Electronic structure and optical properties of rhombohedral CsGeI3 crystal
(2000-10-30)
Tang, LC
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Chang, CS
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Huang, JY
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光電工程學系
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Department of Photonics
We analyse the electronic structure of the perovskite crystal CsGeI3 by means of first-principles calculations and compare our findings to experimental results. Our calculation indicates that CsGeI3 has a direct-transition gap of 0.74 eV at (k) over right arrow = (pi /a)(111). The top of the valence bands was found to mainly comprise the 5p orbitals of iodine, while the bottom of the conduction bands is dominated by the 4p orbital of germanium. Photoluminescence (PL) measurements on a single crystal of CsGeI3 indicate two peaks, one at 0.82 mum (1.51 eV) and the other at 1.15 mum (1.08 eV). The shorter-wavelength PL peak is assigned as arising from an interband transition at (k) over right arrow = (pi /a)(111) and the longer-wavelength PL is presumably ascribable as originating from a transition involving an energy level within the fundamental band gap. Fourier-transformed infrared spectroscopy reveals that the transparent range of CsGeI3 could extend from similar to2 mum to >12 mum The short-wavelength cut-off is mainly limited by the energy band gap, while the long-wavelength limit possibly originates from lattice phonon absorption. Raman spectra of the crystal exhibit two major peaks at 105 cm(-1) and 151 cm(-1) and the corresponding overtones at 220 cm(-1) and 293 cm(-1).
Isoelectronic As doping effects on the optical characteristics of GaN films grown by metalorganic chemical-vapor deposition
(2000-10-30)
Huang, HY
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Lin, WC
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Lee, WH
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Shu, CK
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Liao, KC
We have studied the As doping effects on the optical characteristics of GaN films by time-integrated photoluminescence and time-resolved photoluminescence. When As is incorporated into the film, the localized defect levels and donor-acceptor pair transition become less resolved. The recombination lifetime of neutral-donor-bound exciton (I-2) transition in undoped GaN increases with temperature as T-1.5. However, the I-2 recombination lifetime in As-doped GaN first decreases exponentially from 98 to 41 ps between 12 and 75 K, then increases gradually to 72 ps at 250 K. Such a difference is related to the isoelectronic As impurities in GaN, which generate nearby shallow levels that dominate the recombination process. (C) 2000 American Institute of Physics. [S0003-6951(00)01941-0].
Sequential construction of a circular consecutive-2 system
(2000-10-31)
Hwang, FK
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Pai, CK
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應用數學系
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Department of Applied Mathematics
Derman, Lieberman and Ross solved the problem of sequentially assigning n components with different reliabilities to a consecutive-2 linear system to maximize the system reliability. Furthermore, they show that the optimal assignment is invariant, i.e., it depends only on the ranking of the component reliabilities, but not their values. We study the same problem for the consecutive-2 circular system and prove that an invariant optimal assignment does not exist. But we reduce the number of candidates of an optimal assignment from n! to [n/2] - 2. We also find the first-order invariant optimal assignment. (C) 2000 Elsevier Science B.V. All rights reserved.
The Optimized Threshold Decision of pseudo noise code acquisition in spread spectrum communication
(2000-11-01)
Wu, ML
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Wen, KA
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Chen, CS
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電子工程學系及電子研究所
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Department of Electronics Engineering and Institute of Electronics
In this paper, the authors derived the distributions of the probability of detection and of false alarm in function of the decision threshold. An Optimized Threshold Decision (OTD) algorithm was proposed to decide the optimal threshold for reaching the best system performance in a given known channel noise. By applying this OTD algorithm, the multiple access capacity can thus be maximized.
Characterization of additive systems for damascene Cu electroplating by the superfilling profile monitor
(2000-11-01)
Chiu, SY
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Shieh, JM
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Chang, SC
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Lin, KC
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Dai, BT
Gap-filling dynamics of several different species of additives for copper electrodeposition was investigated by monitoring the cross section of a partially filled copper profile on the scanning electron microscopy photo. The filling ration Deltay/Deltax between "bottom-up" with "sidewall shift" was found to be proportional to the filing power of additives. The adsorption-diffusion model combined with cathode polarization and cyclic voltammetric stripping measurements was employed to explain the attribution of additives in superfilling phenomena. The superfilling dynamics was achieved under behavior of additives providing selective inhibition gradient within the damascene feature. By means of those analyses, we have optimized the appropriate amount of additives and achieved the superfilling performance for 0.15 mum vias with aspect ratio 6 by an acid-copper electrolyte with polyethylene glycol, Cl-, and 2-mercaptopyridine (2-MP). Due to the additive of 2-MP, chelate formed which enhanced adsorption ability on Cu-0 surface, and the concentration gradient between side-wall shift and bottom-up in the damascene became high enough to attend superfilling electroplating. (C) 2000 American Vacuum Society. [S0734-211X(00)13506-1].
The effect of copper on gate oxide integrity
(2000-11-01)
Lin, YH
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Wu, YH
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Chin, A
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Pan, FM
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電子工程學系及電子研究所
We have studied the effect of copper contamination after the front-end metal-oxide-semiconductor capacitor fabrication on gate oxide integrity. The significant effect of Cu contamination on the pretunneling current, in combination with insensitive dependence of the Fowler-Nordheim tunneling current, oxide charge density, and breakdown field on the Cu concentration, suggests that the current leakage mechanism may be due to neutral traps generated by Cu inside oxide. In addition to pretunneling oxide leakage, a small amount of Cu contamination increases the interface trap density that may degrade the device performance. (C) 2000 The Electrochemical Society. S0013-4651(00)03-073-1. All rights reserved.
User adaptive handwriting recognition by self-growing probabilistic decision-based neural networks
(2000-11-01)
Fu, HC
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Chang, HY
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Xu, YY
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Pao, HT
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資訊工程學系
It is generally agreed that, for a given handwriting recognition task, a user dependent system usually outperforms a user independent system, as long as a sufficient amount of training data is available. When the amount of user training data is limited, however, such a performance gain is not guaranteed. One way to improve the performance is to make use of existing knowledge, contained in a rich multiuser data base, so that a minimum amount of training data is sufficient to initialize a model for the new user, We mainly address the user adaption issues for a handwriting recognition system, Based on self-growing probabilistic decision-based neural networks (SPDNNs), user adaptation of the parameters of SPDNN is formulated as incremental reinforced and antireinforced learning procedures, which are easily integrated into the batched training procedures of the SPDNN, In this study, me developed 1) an SPDNN based handwriting recognition system; 2) a two-stage recognition structure; and 3) a three-phase training methodology for a) a global coarse classifier (stage 1); b) a user independent hand written character recognizer (stage 2); and c) a user adaptation module on a personal computer. With training and testing on a 600-word commonly used Chinese character set, the recognition results indicate that the user adaptation module significantly improved the recognition accuracy The average recognition rate increased from 44.2% to 82.4% in five adapting cycles, and the performance could finally increase up to 90.2% in ten adapting cycles.
Thermal uniformity of 12-in silicon wafer during rapid thermal processing by inverse heat transfer method
(2000-11-01)
Lin, S
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Chu, HS
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機械工程學系
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Department of Mechanical Engineering
Through an inverse heat transfer method, this paper presents a finite difference formulation for determination of incident heat fluxes to achieve thermal uniformity in a 12-in silicon wafer during rapid thermal processing. A one-dimensional thermal model and temperature-dependent thermal properties of a silicon wafer are adopted in this study. Our results show that the thermal nonuniformity ran be reduced considerably if the incident heat fluxes on the wafer are dynamically controlled according to the inverse-method results, An effect of successive temperature measurement errors on thermal uniformity is discussed. The resulting maximum temperature differences are only 0.618, 0.776, 0.981, and 0.326 degreesC for 4-, 6-, 8- and 12-in wafers, respectively, The required edge heating compensation ratio for thermal uniformity in 4-, 6-, 8- and 12-in silicon wafers is also evaluated.
Analysis of the dielectric characteristics for polycrystalline Ba0.65Sr0.35TiO3 (I)-frequency dependence in the paraelectric state
(2000-11-01)
Liou, JW
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Chiou, BS
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電子工程學系及電子研究所
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Department of Electronics Engineering and Institute of Electronics
The frequency and d.c. field dependences of dielectric properties of Ba0.65Sr0.35TiO3 (BST) with various grain sizes (0.87 mum to 5.43 mum) have been studied in the paraelectric state. The frequency response is analyzed by two approximated power laws obtained on the basis of the Cole-Cole expression. The distribution of relaxation times in BST is broader for specimens with finer grains. The d.c. field is found to affect the static permittivity epsilon (0) rather than the distribution of relaxation times. The effect of the d.c. field on the dielectric permittivity is suppressed for samples with smaller grains and transition broadening is presumed to cause this suppression. It is concluded that both the temperature dependence and the frequency response of the dielectric characteristics of Ba0.65Sr0.35TiO3 are suppressed by the transition broadening. (C) 2000 Kluwer Academic Publishers.