Browsing by Issue Date, starting with "2002-06-15"

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Silicon nanostructures fabricated by scanning probe oxidation and tetra-methyl ammonium hydroxide etching
(2002-06-15)
Chien, FSS
;
Hsieh, WF
;
Gwo, S
;
Vladar, AE
;
Dagata, JA
Fabrication of silicon nanostructures is a key technique for the development of monolithically integrated optoelectronic circuits. We demonstrated that the process of scanning probe microscope (SPM) oxidation and anisotropic tetra-methyl ammonium hydroxide (TMAH) etching is a low-cost and reliable method to produce smooth and uniform silicon nanostructures on a variety of silicon substrates. Etched structures with a pitch of 100 nm, positive- and negative-contrast structures, and features height greater than 100 nm have been produced on bare silicon, and Si3N4-coated and silicon-on-insulator wafers. Evolution of hexagonal pits on two-dimensional grid structures were shown to depend on the pattern spacing and orientation with respect to Si(110) crystal directions. We successfully combined SPM oxidation with traditional optical lithography in a mixed, multilevel patterning method for realizing micrometer-and nanometer-scale feature sizes, as required for photonic device designs. The combination of SPM oxidation and TMAH etching is a promising approach to rapid prototyping of functional nano-photonic devices. (C) 2002 American Institute of Physics.
Non-Fourier heat conduction with radiation in an absorbing, emitting, and isotropically scattering medium
(2002-06-15)
Chu, HS
;
Lin, SP
;
Lin, CH
;
機械工程學系
;
Department of Mechanical Engineering
This article numerically analyses the combined conductive and radiative heat transfer in an absorbing, emitting, and isotropically scattering medium. The non-Fourier heat conduction equation, which includes the time lag between heat flux and the temperature gradient, is used to model the conductive heat transfer in the medium. It predicts that a temperature disturbance will propagate as a wave at finite speed. The radiative heat transfer is solved using the P-3 approximation method. In addition, the MacCormack's explicit predictor-corrector scheme is used to solve the non-Fourier problem. The effects of radiation including single scattering albedo, conduction-to-radiation parameter, and optical thickness of the medium on the transient and steady state temperature distributions are investigated in detail. Analysis results indicate that the internal radiation in the medium significantly influences the wave nature. The thermal wave nature in the combined non-Fourier heat conduction with radiation is more obvious for large values of conduction-to-radiation parameter, small values of optical thickness and higher scattering medium. The results from non-Fourier-effect equation are also compared to those obtained from the Fourier equation. Non-Fourier effect becomes insignificant as either time increases or the effect of radiation increases. (C) 2002 Elsevier Science Ltd. All rights reserved.
Electron-hole capture suppression and ultraviolet emission in conjugated polymers under high electric fields
(2002-06-15)
Chen, ES
;
Yeh, SH
;
Meng, HF
;
物理研究所
;
Institute of Physics
The probability for the Coulomb capture of an electron-hole pair to form an exciton in conjugated polymers is found to be significantly suppressed under high electric field, which is usually required for electroluminescence due to the low mobility. The Coulomb capture is a continuous descent of electronic energy through cascade emission of phonons, and the high field prevents this descent by heating up the carriers. On the other hand, ultraviolet emission through direct interband transition is found to be much less affected by the field, and becomes the dominant radiative decay channel for field beyond 10(8) V/m. Combined with impact ionization, our model provides a complete quantitative explanation of the peculiar high-field behaviors of the visible emission, ultraviolet emission, and current observed in conjugated polymer both before and after the avalanche breakdown.
Film structure and ferroelectric properties of vanadium-doped Sr0.8Bi2.3Ta2O9 thin films
(2002-06-15)
Chen, SY
;
Lan, BC
;
Taso, CS
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Vanadium-doped strontium bismuth tantalate Sr0.8Bi2.3(Ta2-xVx)O-9 (SBTV) (x = 0-0.8) have been prepared on Pt/Ti/SiO2/Si substrates using a metalorganic decomposition method. Well-crystallized and dense SBTV films can be obtained at an annealing temperature as lower as 650-700 degreesC that can be attributed to the enhanced densification due to the addition of vanadium. With partial substitution of tantalum by vanadium up to x = 0.15, a larger remanent polarization (2P(r)) of 30.5 muC/cm(2) can be obtained for the Sr0.8Bi2.3Ta1.85V0.15O9 film at 800 degreesC that is attributed to the larger grain size and increased "rattling space." Furthermore, the vanadium substitution for tantalum ion can effectively reduce the leakage current density as lower as 5 x 10(-8) A/cm(2) at an applied electric field of 100 kV/cm because of the reduced mobility of charge carriers. However, the incorporation of vanadium does not cause appreciable negative effect on the fatigue endurance of Sr-deficient Sr0.8Bi2.3Ta2O9 films until more than 20 mol % (x = 0.2) vanadium was added. (C) 2002 American Institute of Physics.
A fuzzy clustering-based approach to automatic freeway incident detection and characterization
(2002-06-16)
Sheu, HB
;
運輸與物流管理系註：原交通所+運管所
;
Department of Transportation and Logistics Management
Automatic incident detection and characterization is urgently required in the development of advanced technologies used for reducing non-recurrent traffic congestion on freeways. This paper presents a new method which is constructed primarily on the basis of the fuzzy clustering theories to identify automatically freeway incidents. The proposed approach is capable of distinguishing the time-varying patterns of incident-induced traffic states from the patterns of incident-free traffic states, and characterizing incidents with respect to the onset and end time steps of incidents, incident location, the temporal and spatial change patterns of incident-related traffic variables in response to the impacts of incidents on freeway traffic flows in real time. Lane traffic count and density are the two major types of input data, which can be readily collected from point detectors. Based on the spatial and temporal relationships of the collected raw traffic data, several time-varying state variables are defined, and then evaluated quantitatively and qualitatively to determine the decision variables used for real-time incident characterization. Utilizing the specified decision variables, the proposed fuzzy clustering-based algorithm executes recurrently three major procedures: (1) identification of traffic flow conditions, (2) recognition of incident occurrence, and (3) incident characterization. In this study, data used for model tests are generated from the CORSIM traffic simulator. Our preliminary test results indicate that the proposed approach is promising, and, in expectation, can be integrated with any published real-time incident detection technologies. Importantly, this study may contribute significantly to the applications of fuzzy clustering techniques, and stimulate more related research. (C) 2002 Elsevier Science B.V. All rights reserved.
A study of subbands in AlGaN/GaN high-electron-mobility transistor structures using low-temperature photoluminescence spectroscopy
(2002-06-17)
Fang, CY
;
Lin, CF
;
Chang, EY
;
Feng, MS
;
材料科學與工程學系
Al0.15Ga0.85N/GaN high-electron-mobility transistor (HEMT) structures with various delta-doping concentrations and spacer thicknesses grown on sapphire by metalorganic chemical-vapor deposition are investigated. The Hall mobility is as high as 1333 cm(2)/V s at room temperature and 6330 cm(2)/V s at 77 K. Two-dimensional electron gas (2DEG) phenomena, which have not been clearly resolved in the literature, are observed by photoluminescence (PL) spectra at low temperature in this study. The PL spectra peaks of the interband transitions from 2DEG subbands to the valence band are in the range from 3.486 to 3.312 eV. The effects of the strain caused by different Al fractions of the top layer, and that of the spacer thickness on the 2DEG phenomena are discussed. Redshifts due to temperature variations for various HEMT structures are observed in 2DEG subbands and in the band-edge emission, which is believed to be evidence of interband transitions from 2DEG subbands to valence bands. (C) 2002 American Institute of Physics.
Forming silicon carbon nitride crystals and silicon carbon nitride nanotubes by microwave plasma-enhanced chemical vapor deposition
(2002-06-17)
Chang, HL
;
Hsu, CM
;
Kuo, CT
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Catalyst-assisted silicon carbon nitride (SiCN) nanotubes and SiCN crystals are prepared. The SiCN nanotubes and SiCN crystals are formed by gaseous sources of CH4/N-2/H-2 and CH4/N-2, respectively, and using solid Si columns arranged symmetrically around the specimen as additional Si sources. The formation of the tubular structure is related to the ambient of process that includes H-2 gas, which is considered to delay the action of the so-called catalyst poisons and keep the tube end open during growth. Analysis shows that the SiCN crystals exhibit tetragonal or hexagonal shapes with sizes of about several microns, and multibonding structures. In contrast, the SiCN tubes are randomly orientated with various diameters, and graphitelike structure. The growth mechanisms of SiCN crystals and SiCN nanotubes are discussed. (C) 2002 American Institute of Physics.
Reliability of laser-activated low-temperature polycrystalline silicon thin-film transistors
(2002-06-24)
Peng, DZ
;
Chang, TC
;
Zan, HW
;
Huang, TY
;
Chang, CY
In this letter, the characteristics and reliability of laser-activated polycrystalline silicon thin-film transistors (poly-Si TFTs) have been investigated by stressing the devices under V-ds=12 V and V-gs=15 V. In comparison with traditional furnace-activated poly-Si TFTs, the leakage current is relatively large for laser-activated poly-Si TFTs. Further, while the degradation rates of threshold voltage and subthreshold swing are comparable to those of traditional furnace-activated TFTs, the post-stress leakage and on/off current ratio for laser-activated poly-Si TFTs degrade much faster than those of furnace-activated counterparts. The laser activation modifies the grain structure between the drain and the channel region, and causes grain discontinuity extending from the drain to the channel region. As a result, an inferior reliability with extra trap state density and larger leakage current was observed in the laser-activated poly-Si TFTs. (C) 2002 American Institute of Physics.
A multiprocess performance analysis chart based on the incapability index C-pp: an application to the chip resistors
(2002-07-01)
Pearn, WL
;
Ko, CH
;
Wang, KH
;
工業工程與管理學系
;
Department of Industrial Engineering and Management
Statistical process control charts, such as the (X) over bar, R, S-2, S, and MR charts, have been widely used in the manufacturing industry for controlling/monitoring process performance, which are essential tools for any quality improvement activities. Those charts are easy to understand, which effectively communicate critical process information without using words and formula. In this paper, we introduce a new control chart, called the C-pp multiple process performance analysis chart (MPPAC), using the incapability index C-pp. The C-pp MPPAC displays multiple processes with the departure, and process variability relative to the specification tolerances, on one single chart. We demonstrate the use of the C-pp MPPAC by presenting a case study on some resistor component manufacturing processes, to evaluate the factory performance. (C) 2002 Elsevier Science Ltd. All rights reserved.
A simple remote user authentication scheme
(2002-07-01)
Hwang, MS
;
Lee, CC
;
Tang, YL
;
資訊工程學系
;
Department of Computer Science
In this article, we propose a simple remote user authentication scheme using smart cards. This scheme has the following features. First, it does not require any password or verification tables. Second, it can withstand the message replay attack. Third, any legal users can arbitrarily choose and change their own passwords at will. And finally, the password of a user is not revealed to the server. In addition, the computational costs of this scheme are less than those of any previously proposed schemes. (C) 2002 Elsevier Science Ltd. All rights reserved.
Solutions of semilinear elliptic equations with asymptotic linear nonlinearity
(2002-07-01)
Hsu, CH
;
Shih, YW
;
應用數學系
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Department of Applied Mathematics
Structure effects on electron-optical phonon interaction in GaAs/AlxGa1-xAs quantum wells
(2002-07-01)
Lee, HC
;
Sun, KW
;
Lee, CP
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Based on the dielectric continuum model, we have studied the electron-optical phonon scattering rates in GaAs/AlxGa1-xAs quantum wells with different structure parameters. It was found that the scattering rate of the symmetric interface phonon mode has a stronger dependence on the Al composition in the barriers than that of the confined mode. The effective phonon energy emitted by hot electrons in GaAs/AlxGa1-xAs quantum wells with various Al compositions was estimated and the calculated value agrees with the experimental results qualitatively. For the dependence on the well width, scattering rates of the S+ mode drop considerably as the well width is increased. The dependence of the electron-optical phonon interaction on structure parameters can be clearly explained by the H and G factors defined in the article. (C) 2002 American Institute of Physics.
Formation of self-assembled ZnTe quantum dots on ZnSe buffer layer grown on GaAs substrate by molecular beam epitaxy
(2002-07-01)
Kuo, MC
;
Yang, CS
;
Tseng, PY
;
Lee, J
;
Shen, JL
Self-assembled ZnTe quantum dot structures were grown by molecular beam epitaxy on GaAs substrates with a 200 nm ZnSe buffer layer. Surface morphology was studied by atomic force microscopy. A three-dimensional Volmer-Weber growth mode was identified. Two types of dots were observed. Strong photoluminescence observed at 1.9-2.2 eV was attributed to emission from the large type II ZnTe quantum dots. Emission from the smaller ZnTe quantum dots was observed at an energy of around 2.26 eV. The density of the larger and smaller dots was approximately 10(8)/cm(2) and 10(9)/cm(2), respectively. (C) 2002 Elsevier Science B.V. All rights reserved.
A new process-variation-immunity method for extracting capacitance coupling coefficients in flash memory cells
(2002-07-01)
Cho, CYS
;
Chen, MJ
;
Lin, JH
;
Chen, CF
;
電子工程學系及電子研究所
Overestimation of capacitance coupling coefficients in flash memory cells is encountered in the subthreshold slope method. By means of a two-parameters subthreshold current model I-D = I-o exp[q(V-GB - nV(SB))/nkT], a mathematical formulation of the subthreshold swing ratio in the subthreshold slope method is constructed to isolate the measurement errors caused by process variations from the errors traditionally caused by bulk capacitance coupling. To minimize the effect of process variations, a new method is developed based on the model. In this method, the control gate voltage shift due to weak body effect is measured in flash memory cells in subthreshold, while the corresponding slope factor n is adequately deduced from threshold voltage versus source-to-substrate bias measurement in dummy devices. The corrected capacitance coupling coefficients show large improvements compared to the design values, and the updated errors are found to be close to that caused solely by bulk capacitance coupling. The method is also fast since only a small source-to-substrate bias of 0.1 V is needed for implementation of weak body effect, and thereby it can be used as an in-line monitor of capacitance coupling coefficients.
Method for determining the optical axis and (n(e), n(o)) of a birefringent crystal
(2002-07-01)
Su, DC
;
Hsu, CC
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光電工程學系
;
Department of Photonics
There is a phase difference between s and p polarizations when a circularly polarized heterodyne light beam is reflected from a birefringent crystal. It can be measured accurately with a common-path heterodyne interferometric technique. We have derived an equation that describes the relationship between the phase differences and n(e) n(o), and alpha. Two groups of solutions for (n(e), n(o)) can be obtained from this equation by the phase measurements performed at three incident angles under moderate conditions. Each group consists of three pairs of solutions for (n(e), n(o)). Finally, by justifying with physical conditions, we obtained the correct solution for (n(e), n(o)). Azimuth angle alpha of the birefringent crystal optical axis can also be determined. And the feasibility of this method is demonstrated. (C) 2002 Optical Society of America.
Reduction of etching plasma damage on low dielectric constant fluorinated amorphous carbon films by multiple H-2 plasma treatment
(2002-07-01)
Shieh, JM
;
Tsai, KC
;
Dai, BT
;
Wu, YC
;
Wu, YH
Two-step hydrogen plasma treatment on low dielectric constant (low-k) fluorinated amorphous carbon films (a-C:F) was conducted to improve their thermal stability and reduce the damage caused by the patterning processes. First, hydrogen plasma treatment repairs imperfect bonds of as-deposited a-C:F films, stabilizing their chemical structures and increasing their resistance against elevated thermal stresses. After this passivation process, an additional hydrogen plasma treatment was applied to a-C:F films that had been etched using a mixture of N-2+O-2+CHF3, enabling sub-130 nm damascene trenches to be patterned and repairing the chemical structures destroyed by the etching plasma. (C) 2002 American Vacuum Society.
Synthesis of alkyl-branched main chain copolyimides and their effect on the pretilt angles of liquid crystal alignment
(2002-07-01)
Lee, WC
;
Chen, JT
;
Hsu, CS
;
Wu, ST
;
應用化學系
Three series of copolyimides containing long alkyl branches were synthesized using the two-step method via poly(amic acid) precursors and chemical imidization. Most of the copolyimides prepared are soluble in polar organic solvents. Good liquid crystal alignment was achieved by buffing the copolyimide films spin-coated onto indium tin oxide glass substrates. The measured liquid crystal pretilt angles range from 0.16degrees to 15.54degrees. The Titan simulation program was used to calculate the dipole of each dianhydride structure and correlate with the observed pretilt angles. Main chain copolyimides with a long alkyl side chain, small dipole, and linear, symmetric and rigid core structures are favourable for generating large pretilt angles.
Charge pumping profiling technique for the evaluation of plasma-charging-enhanced hot-carrier effect in short-N-channel metal-oxide-semiconductor field-effect transistors
(2002-07-01)
Chen, SJ
;
Chung, SSS
;
Lin, HC
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Plasma etching of poly-silicon in a metal-oxide-semiconductor field-effect transistor (MOSFET) during the gate definition process induces edge damage at the gate-drain overlap edge. This edge damage will be further enhanced by the antenna effect and cause a more serious hot-carrier (HC) effect, particularly in short-channel devices. We call this phenomenon the plasma-charging-enhanced HC effect. In this paper, this plasma-charging-enhanced HC effect is evaluated by the charge pumping (CP) profiling technique, in which the enhanced damage at the gate-drain overlap gate oxide region can be identified. A three-phase plasma damage mechanism is then proposed to explain the observed effect. According to experimental results, it was shown that the interface traps generated at the gate-drain overlap edge are mainly attributed to the plasma-charging-enhanced HC effect. These interface traps (Nit) become the dominant mechanism of the drain current (ID) degradation, which increases with a reducing channel length (L). Again, the enhanced HC-effect-induced-degradation will dominate the device reliability under long-term operations.
Sensation seeking and internet dependence of Taiwanese high school adolescents
(2002-07-01)
Lin, SSJ
;
Tsai, CC
;
師資培育中心
;
Center of Teacher Education
The present study examined excessive Internet use of Taiwanese adolescents and a psychological aspect of users. sensation seeking, thus to differentiate motivation of Internet dependents and non-dependents. Seven hundred and fifty three Taiwanese high school student, were selected using cluster sampling and 88 of them were categorized as Internet dependent users. Results indicated that Internet dependents spent more time on-line than non-dependents. While Internet dependents perceived significantly more negative Internet influences on daily routines, school performance. and parental relation than non-dependents, both Internet dependents and non-dependents viewed Internet use as enhancing peer relations. Making friends through the Internet has become a popular activity among adolescents, Potentially leading to its excessive use. Internet dependents scored significantly higher on overall sensation seeking and disinhibition than Internet non-dependents. Ho ever. both groups did not differ in the life experience seeking subscale and thrill and adventure seeking subscale. This finding contradicts that of Lavin, Marvin. McLarney, Nola. and Scott [CyberPsychol. Behav. 2 (2000) 425], Possible reasons for this discrepancy and for the relation between Internet dependence and disinhibition in Taiwanese adolescents are also discussed. (C) 2002 Elsevier Science Ltd. All rights reserved.
Subgrouping small states based on socioeconomic characteristics
(2002-07-01)
Liou, FM
;
Ding, CG
;
交大名義發表
;
National Chiao Tung University
Developing small states are often discussed as a whole because of shared vulnerabilities, but could instead be treated according to their different socioeconomic characteristics. This paper investigates those differences and subgroups them through the use of statistical methods. Seven common factors were first extracted from 25 key socioeconomic indicators. Cluster analysis based on factor scores was then used to obtain distinct clusters of small states. Nine well-delineated clusters were thus obtained, each of which containing small states with similar characteristics, Managerial implications for international aid based on the findings are then proposed. (C) 2002 Elsevier Science Ltd. All rights reserved.