Browsing by Issue Date, starting with "2000-10-30"

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Electronic structure and optical properties of rhombohedral CsGeI3 crystal
(2000-10-30)
Tang, LC
;
Chang, CS
;
Huang, JY
;
光電工程學系
;
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
;
Lin, WC
;
Lee, WH
;
Shu, CK
;
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
;
Pai, CK
;
應用數學系
;
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
;
Wen, KA
;
Chen, CS
;
電子工程學系及電子研究所
;
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
;
Shieh, JM
;
Chang, SC
;
Lin, KC
;
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
;
Wu, YH
;
Chin, A
;
Pan, FM
;
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
;
Chang, HY
;
Xu, YY
;
Pao, HT
;
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
;
Chu, HS
;
機械工程學系
;
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
;
Chiou, BS
;
電子工程學系及電子研究所
;
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.
Noncoherent detectors for PN code acquisition in the presence of data modulation
(2000-11-01)
Wu, RC
;
Su, YT
;
Lin, WC
;
電信工程研究所
;
Institute of Communications Engineering
Noncoherent detectors for use in acquiring data-modulated direct-sequence spread-spectrum (DS/SS) signals are considered in this paper. Taking data modulation and timing uncertainty into account and using the generalized maximum likelihood (GML) or maximum likelihood (ML) detection approaches, we derive optimal detectors in the sense of Bayes or Neyman-Pearson and propose various suboptimal detectors. A simple systematic means for their realization is suggested and the numerical performance of these detectors is presented. We also compare their performance with that of the noncoherent combining (NC1) detector that had been proposed to serve the same need. Numerical results show that even the proposed suboptimal detectors can outperform the NC1 detector in most cases of interest.
Pump-to-mode size ratio dependence of thermal loading in diode-end-pumped solid-state lasers
(2000-11-01)
Chen, YF
;
電子物理學系
;
Department of Electrophysics
The fractional thermal loading in a diode-end-pumped solid-state laser is deduced from experimental measurement of the critical pump power. The results show that fractional thermal loading critically depends on the pump-to-mode size ratio. This dependence is attributed to the effect of the pump-to-mode size ratio on the population inversion and to the effect of energy-transfer upconversion. Rigorous modeling calculations have been performed to yield a comprehensive understanding of the thermal loading in diode-end-pumped solid-state lasers. (C) 2000 Optical Society of America [S0740-3224(00)01011-0].
Absence of the paramagnetic contribution in the low-temperature specific heat of La1.9Sr0.1Cu0.98Zn0.02O4
(2000-11-01)
Lin, JY
;
Chang, CF
;
Yang, HD
;
物理研究所
;
Institute of Physics
The absence of the paramagnetic contribution in the low-temperature specific heat (C) of Zn-doped cuprates has attracted much attention recently. The phenomenon was usually explained as possible screening in the superconducting state. We have measured C of La1.9Sr0.1Cu0.98Zn0.02O4 which is not superconducting. Intriguingly, The upper limit of the magnetic contribution is found to be two orders of magnitude smaller than the expected value with no screening effect. This result puts the above explanation in a serious jeopardy.
Enhancement in field emission of silicon microtips by bias-assisted carburization
(2000-11-01)
Kichambare, PD
;
Tarntair, FG
;
Chen, LC
;
Chen, KH
;
Cheng, HC
Ultrathin carbon layers with thicknesses below 50 Angstrom have been deposited on silicon microtip arrays by bias-assisted carburization (BAC) using microwave plasma chemical vapor deposition. The tip radius of these silicon tips is reduced below 55 nm under low deposition temperature. The field emission characterization has been performed in a high-vacuum environment. An enhancement in the field emission is observed of about 3 orders of magnitude in BAC silicon microtips over untreated silicon microtips. With an applied voltage of 1100 V, emission currents of 80 and 120 muA have been achieved for the films grown (at de bias of -200 V for 40 min) with 15% and 25% CH4/H-2 gas ratio, respectively. An emission current of 40 muA has been achieved for the film grown (at de bias of -300 V for 30 min) with 3.5% CH4/H-2 ratio. The BAC silicon emitter has good emission stability at a constant voltage of 1100 V. These investigations indicate that further improvement of this technology will lead to simple and inexpensive field emission display devices. (C) 2000 American Vacuum Society. [S0734-211X(00)10706-1].
Experimental observation of the slowdown of optical beams by a volume-index grating in a photorefractive LiNbO3 crystal
(2000-11-01)
Lin, SH
;
Hsu, KY
;
Yeh, P
;
電子物理學系
;
光電工程學系
We investigate the group velocity of light in a one-dimensional volume-index grating inside a photorefractive LiNbO3 crystal. The slowdown of the group electromagnetic propagation is observed experimentally by tuning of the wave number of the optical beam close to the outside edge of the forbidden bandgap. We obtain a large group index of up to 7.5 in a 3.5-cm crystal sample. The group index is compared with the result of a theoretical derivation. The results are presented and discussed. (C) 2000 Optical Society of America OCIS codes: 050.7330, 260.2030, 190.5530, 160.3730.
Dynamic GOST
(2000-11-01)
Yeh, YS
;
Lin, CH
;
Wang, CC
;
資訊科學與工程研究所
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Institute of Computer Science and Engineering
GOST is a block algorithm which was adopted as a standard by the former Soviet Union. Because it keeps a lot of secret information, including S-boxes, the algorithm is secure and easy to understand. In this article, we propose a variant of COST, called dynamic COST, in which permutations are applied. With the permutation information securely kept: the new version of COST is more secure and better to withstand differential and linear attacks.
Superconductivity of alpha-TiAl alloys
(2000-11-01)
Liu, SM
;
Jing, XN
;
Lu, L
;
Li, SL
;
Lin, JJ
The superconducting transition temperature Tc of alpha TiAl alloys has been measured up to 10 atomic percentage of Al. T-c monotonously increases with a tendency to saturation for high Al content.
Analysis of the dielectric characteristics for polycrystalline Ba(0.65)Sr(0.35)TiO(3) (I)-frequency dependence in the paraelectric state
(2000-11-01)
Liou, JW
;
Chiou, BS
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The frequency and d.c. field dependences of dielectric properties of Ba(0.65)Sr(0.35)TiO(3) (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 Ba(0.65)Sr(0.35)TiO(3) are suppressed by the transition broadening. (C) 2000 Kluwer Academic Publishers.
High-resolution double self-pumped phase conjugations with plus c-face incident configuration in a BaTiO3 crystal
(2000-11-01)
Chen, TC
;
Chang, CC
;
Tang, LC
;
Yau, HF
;
光電工程學系
The geometry of creating two stable self-pumped phase-conjugate outputs in one photorefractive BaTiO3 crystal is demonstrated. This novel geometry provides two phase-conjugate images with a resolution as high as 4 mum (or 114 1p/mm). The reflectivity versus the angle of the incident beam is also investigated.
Improvement of post-chemical mechanical planarization characteristics on organic low k methylsilsesquioxane as intermetal dielectric
(2000-11-01)
Liu, PT
;
Chang, TC
;
Huang, MC
;
Yang, YL
;
Mor, YS
This work has investigated the electrical and material characteristics of post-chemical mechanical planarization (CMP) methylsilsesquioxane (MSQ). Experimental results have shown that the dielectric properties of low k MSQ deteriorate after the CMP process. However, by applying H-2-plasma post-treatment, the degraded characteristics can be restored to a similar state as that of a pre-CMP MSQ film. Material and electrical analyses were performed to elucidate the detailed mechanisms of H-2-plasma treatment on post-CMP MSQ. H-2-plasma treatment provides active hydro en radicals to passivate the dangling bonds exposed in the MSQ after the CMP process. The hydrogen-rich passivation layer is hydrophobic and effectively prevents further moisture uptake. Therefore, a degradation-free CMP process can be achieved employing H-2-plasma treatment. (C) 2000 The Electrochemical Society. S0013-4651(00)04-098-2. All rights reserved.
Network address translators: Effects on security protocols and applications in the TCP/IP stack
(2000-11-01)
Shieh, SP
;
Ho, FS
;
Huang, YL
;
Luo, JN
;
資訊工程學系