Browsing by Author "Lee, CT"

Now showing 1 - 18 of 18

5 mm high-power-density dual-delta-doped power HEMT's for 3 V L-band applications
(1996-05-01)
Lai, YL
;
Chang, EY
;
Chang, CY
;
Chen, TK
;
Liu, TH
A high-power-density dual-delta-doped AlGaAs/InGaAs/GaAs high electron mobility transistor (HEMT) for personal communication applications has been developed. A 5.0 mm gate-width device operating at a drain bias of 3.0 V gave an output power over 1 W, The 1 mu m gate-length HEMT exhibited a current density of 425 mA/mm at V-gs = 0.5 V, The maximum transconductance of the device was 270 mS/mm, The effective knee voltage was as low as 0.3 V, At the class AB operation, the HEMT demonstrated an output power density of 200 mW/mm, 64% power-added efficiency and 18.2 dB linear gain at 900 MHz, This is the highest power density of a dual-delta-doped AlGaAs/InGaAs/GaAs HEMT reported to date for low voltage (3 V) wireless applications.
5 mm high-power-density dual-delta-doped power HEMT's for 3 V L-band applications
(1996-05-01)
Lai, YL
;
Chang, EY
;
Chang, CY
;
Chen, TK
;
Liu, TH
A high-power-density dual-delta-doped AlGaAs/InGaAs/GaAs high electron mobility transistor (HEMT) for personal communication applications has been developed. A 5.0 mm gate-width device operating at a drain bias of 3.0 V gave an output power over 1 W, The 1 mu m gate-length HEMT exhibited a current density of 425 mA/mm at V-gs = 0.5 V, The maximum transconductance of the device was 270 mS/mm, The effective knee voltage was as low as 0.3 V, At the class AB operation, the HEMT demonstrated an output power density of 200 mW/mm, 64% power-added efficiency and 18.2 dB linear gain at 900 MHz, This is the highest power density of a dual-delta-doped AlGaAs/InGaAs/GaAs HEMT reported to date for low voltage (3 V) wireless applications.
A bilayer Ti/Ag ohmic contact for highly doped n-type GaN films
(1996-01-08)
Guo, JD
;
Lin, CI
;
Feng, MS
;
Pan, FM
;
Chi, GC
Ohmic contacts with low resistance are fabricated on n-type GaN films using Ti/Ag bilayer metallization. The GaN films are grown by low pressure metalorganic chemical vapor deposition (LP-MOCVD) with Si as the dopant. Ohmic characteristics are studied for films with carrier concentration range from 1.5 x 10(17) to 1.7 x 10(19) cm(-3). The lowest value for the specific contact resistivity of 6.5 x 10(-5) Ohm cm(2) is obtained without annealing. The barrier height of Ti on GaN is calculated to be 0.067 eV. (C) 1996 American Institute of Physics.
A gold-free fully copper-metallized InP heterojunction bipolar transistor using non-alloyed ohmic contact and platinum diffusion barrier
(2005)
Chang, SW
;
Chang, EY
;
Lee, CS
;
Chen, KS
;
Tseng, CW
A gold-free, fully Cu-metallized InP heterojunction bipolar transistor using non-alloyed Ti/Pt/Cu and Pt/Ti/Pt/Cu ohmic contacts and platinum diffusion barrier has been successfully fabricated. The InGaAs/Ti/Pt/Cu ohmic structure was stable after annealing up to 350 degrees C as judged from the Auger depth profiles. A current-accelerated stress test was conducted on the device with a current density J(C) = 80kA/cm(2) for 24h, and the current gain showed no degradation after the current stress. The devices were also thermally annealed at 200 degrees C for 3 h and showed almost no change in the electrical parameters after the heat treatment. The results show that the Au-free, fully Cu-metallized InP heterojunction bipolar transistor (HBT) can be realized using non-alloyed ohmic contacts and Pt diffusion barrier.
Accelerated ageing behavior of compatible IPNs based on epoxy and methacrylated epoxy resins
(1998)
Lin, MS
;
Wang, MW
;
Lee, CT
;
Shao, SY
;
應用化學系
Methacrylated diglycidyl ether of bisphenol A (MADGEBA) was synthesized from the reaction of the diglycidyl ether of bisphenol A (DGEBA) and methacrylic acid. The MADGEBA was blended with DGEBA in weight ratios of 100/0, 50/50 and 0/100, and cured simultaneously with dicumyl peroxide (DICUP) and hexahydrophthalic anhydride (HHPA) to obtain interpenetrating polymer networks (IPNs). The three samples were irradiated with ultraviolet in a Q-UVA weatherometer for various periods to study their ageing behavior. Experimental results indicate that the methacryloyl moiety thus incorporated confers significant stabilization against photodegradation. (C) 1998 Elsevier Science Limited. All rights reserved.
Catalytic decomposition of hydrogen peroxide and 4-chlorophenol in the presence of modified activated carbons
(2003-06-01)
Huang, HH
;
Lu, MC
;
Chen, JN
;
Lee, CT
;
環境工程研究所
The objective of this research was to examine the heterogeneous catalytic decomposition of H2O2 and 4-chlorophenol (4-CP) in the presence of activated carbons modified with chemical pretreatments. The decomposition of H2O2 was suppressed significantly by-the change of surface properties including the decreased pH(pzc) modified with oxidizing agent and the reduced active sites occupied by the adsorption of 4-CP. The apparent reaction rate of H2O2 decomposition was dominated by the intrinsic reaction rates on the surface of activated carbon rather than the mass transfer rate of H2O2 to the solid surface. By the detection of chloride ion in suspension, the reduction of 4-CP was not only attributed to the advanced adsorption but also the degradation of 4-CP. The catalytic activity toward 4-CP for the activated carbon followed the inverse sequence of the activity toward H2O2, suggesting that acidic surface functional group could retard the H2O2 loss and reduce the effect of surface scavenging resulting in the increase of the 4-CP degradation efficiency. Few effective radicals were expected to react with 4-CP for the strong effect of surface scavenging, which could explain why the degradation rate of 4-CP observed in this study was so slow and the dechlorination efficiency was independent of the 4-CP concentration in aqueous phase. Results show that the combination of H2O2 and granular activated carbon (GAC) did increase the total removal of 4-CP than that by single GAC adsorption. (C) 2003 Elsevier Science Ltd. All rights reserved.
Constructing quantitative models from qualitative mutant phenotypes: preferences in selecting sensory organ precursors
(2006-06-01)
Hsu, CP
;
Lee, PH
;
Chang, CW
;
Lee, CT
;
應用化學系分子科學碩博班
Motivation: To study biology from the systems level, mathematical models that describe the time-evolution of the system offer useful insights. Quantitative information is required for constructing such models, but such information is rarely provided. Results: We propose a scheme-based on random searches over a parameter space, according to criteria set by qualitative experimental observations-for inferring quantitative parameters from qualitative experimental results. We used five mutant constraints to construct genetic network models for sensory organ precursor formation in Drosophila development. Most of the models were capable of generating expression patterns for the gene Enhancer of split that were compatible with experimental observations for wild type and two Notch mutants. We further examined factors differentiating the neural fate among cells in a proneural cluster, and found two opposite driving forces that bias the choice between middle cells and the peripheral cells. Therefore, it is possible to build numerical models from mutant screening and to study mechanisms behind the complicated network.
Curing behaviour of compatible interpenetrating polymer networks based on epoxy and methacrylated epoxy
(1997-12-01)
Wang, MW
;
Lee, CT
;
Lin, MS
;
應用化學系
;
Department of Applied Chemistry
Compatible interpenetrating polymer networks (IPNs) based on diglycidyl ether of bisphenol A (DGEBA) and methacrylated diglycidyl ether of bisphenol A (MADGEBA) in weight ratios of 100/0, 75/25, 50/50, 25/75 and 0/100 were blended and cured simultaneously by using dicumyl peroxide (DICUP) and hexahydrophthalic anhydride (HHPA) as curing agents. Fourier transform infrared spectroscopy (FTIR) was employed to investigate the intermolecular interactions and functional group changes. Viscosity increases during crosslinking were examined with a Brookfield viscometer. Curing exothermic peaks were studied with differential scanning calorimetry (DSC). The gel fractions of various IPN compositions were measured with a Soxhlet extractor. Samples thus prepared were checked for their compatibility by measuring glass transitions with DSC and damping peaks with rheometric dynamic spectroscopy (RDS). Experimental results revealed that good compatibility between components induced a network interlock, which subsequently resulted in incomplete cure of the IPN materials.
Differences in PM10 concentrations measured by beta-gauge monitor and hi-vol sampler
(2001-11-01)
Chang, CT
;
Tsai, CJ
;
Lee, CT
;
Chang, SY
;
Cheng, MT
In this paper. differences between the 24-h average PM10 concentrations of Wedding beta -gauge monitor and Andersen or Wedding hi-vol sampler were studied. When the deliquescent point is not exceeded, PM10 concentrations of the beta -gauge are close to those of the manual samplers. The ratio of beta -gauge PM10 to Andersen PM10 and Wedding PM10 is 1.08 +/-0.06 and 1.09 +/-0.12, respectively. However, when the deliquescent point is exceeded, water absorption by the inorganics of aerosols leads to higher PM10 concentrations of the beta -gauge compared to those of the manual sampler. The ratio of beta -gauge PM10 to Andersen PM10 and Wedding PM10 is 1.21 +/-0.22 and 1.27 +/-0.15, respectively. However., due to evaporation of water from the aerosols collected on the filter tape of the beta -gauge, differences in PM10 concentrations are much less than theoretically calculated. (C) 2001 Elsevier Science Ltd. All rights reserved.
High-efficiency and low-distortion directly-ion-implanted GaAs power MESFET's for digital personal handy-phone applications
(1997-09-01)
Lai, YL
;
Chang, EY
;
Chang, CY
;
Tai, MC
;
Liu, TH
We report a high-efficiency and low-distortion GaAs power MESFET using direct ion implantation technology for the digital wireless personal handy-phone system (PHS). When qualified by 1.9-GHz pi/4-shifted quadrature phase shift keying (QPSK) modulated PBS standard signals, the 2.2-V-operation device with a gate width (W-g) of 2 mm exhibited a power-added efficiency (PAE) of 57.2% and an adjacent channel leakage power (P-adj) of -58 dBc at an output power of 21.3 dBm. The MESFET with the optimized direct ion implantation conditions and fabrication process achieved the highest PAE for PHS applications, The low-cost MMIC-oriented direct ion implantation technology has demonstrated the state-of-the-art results for new-generation PHS handsets for the first time.
Influence of surface modification on catalytic activity of activated carbon toward decomposition of hydrogen peroxide and 2-chlorophenol
(2003)
Huang, HH
;
Lu, MC
;
Chen, JN
;
Lee, CT
;
環境工程研究所
The objective of this research was to investigate the influence of the activated carbons modified by chemical treatment on the surface catalyzed loss of H2O2 and 2-CP. The characteristics of the modified activated carbons were examined by several techniques including nitrogen adsorption, SEM, and EDS. The H2O2 decomposition rate would be suppressed significantly either by the change of surface properties modified with chemical treatment or the reduction of active sites occupied with the adsorption of 2-CP. In addition, the H2O2 decomposition rate with activated carbons within a specific time can be described by a second-order kinetic expression with respect to the concentration of GAC and H2O2 in the absence or presence of 2-CP. The catalytic activities of the three activated carbons toward 2-CP reduction followed the inverse sequence of those toward H-2-O-2 loss, implying that acidic surface functional group could retard the H2O2 loss and reduce the effect of surface scavenging resulting in increasing the reduction efficiency of 2-CP. By the detection of chloride ions in reaction mixture, it can be demonstrated that the reduction of 2-CP was not only attributed to the advanced adsorption but also the oxidation of the 2-CP with effective radicals. The real oxidation efficiency of 2-CP for the activated carbon modified with hot nitric acid was observed between 0.04 and 0.01 (mol/mol), offering a comparable efficiency to that of the other oxidation system using metal oxide as catalyst.
Optimization of the growth of the InGaP etch-stop layer by MOVPE for InGaP/GaAs HBT device application
(2006-03-15)
Hsieh, YC
;
Chang, EY
;
Yeh, SS
;
Chang, CW
;
Luo, GL
InGaP has high etching selectivity to GaAs. It can be used as the etch-stop layer to easily fabricate the InGaP/GaAs heterojunction bipolar transistors (HBTs). This process will also increase the uniformity and manufacturability of the HBT devices. However, the InGaP etch-stop layer will increase the energy barrier height that electrons have to overcome flowing from the collector to the subcollector, which will decrease the DC current gain of the device (T. Kobayashi, K. Taira, F. Nakamua, H. Kawai, J. Appl. Phys. 65 (1989) 4898). Therefore, the InGaP etch-stop layer has to be thin enough not to affect the device performance. But the spontaneous formation of the InxGa1-xAsyP1-y intermixing layer between GaAs/InGaP during the metal organic vapour-phase epitaxy (MOVPE) growth will affect the InGaP layer thickness needed as an effective etch-stop layer. In this paper, very thin InGaP layer was achieved with the suppression of InxGa1-xAsyP1-y formation by the optimization of the growth temperature and the gas switching sequence time. An effective 20 angstrom InGaP etch-stop layer was grown at 575 degrees C with interruption time of 3 s. Both STEM and PL data proved that the intermixing InxGa1-xAsyP1-y layer was eliminated and from the selective etching experiment, this 20 angstrom InGaP layer can stand 45 s etching by the H3PO4:H2O2:H2O = 1:1:20 solution. (c) 2005 Elsevier B.V. All rights reserved.
Photostabilization of PET via photo-fries' rearrangement.
(2001-04-01)
Lin, MS
;
Lee, CT
;
應用化學系
;
Department of Applied Chemistry
Poly(phenyl acrylate) and Poly(p-methylphenyl acrylate) as photo-stabilizers II. Protection of PET against photo-oxidation
(2004-03-01)
Lee, CT
;
Wu, CH
;
Lin, MS
;
應用化學系
;
Department of Applied Chemistry
Poly(phenyl acrylate) (PPA) and poly(p-methylphenyl acrylate) (PMPA) were used as inherent photo-stabilizers for PET. PPA/ PET and PMPA/PET in weight ratios of 0/100, 5/95, 10/90, 20/80 and 100/0 were blended. These blends were then cast into films and drawn into fibres and were irradiated with an accelerated weathering tester (QUV). Functional group changes in the films during irradation were monitored with FTIR and the absorbance changes for different samples were compared with one another. Tensile strength of fibres after 42 days of irradiation were tested. Experimental results revealed that when 5% of PPA or PMPA was incorporated into PET, good stabilization of the film and fibres were observed, with PMPA exhibiting more photo-stabilization capability and better retention of tensile strength after 42 days of accelerated aging. (C) 2003 Elsevier Ltd. All rights reserved.
Simulation study of carbon nanotube field emission display with under-gate and planar-gate structures
(2004-05-01)
Lan, YC
;
Lee, CT
;
Hu, Y
;
Chen, SH
;
Lee, CC
Recently, two new CNTs-based triode structures, i.e., under-gate and planar-gate structures, for field emission display were proposed and exhibited good characteristics. In this paper, we will investigate how the current density distributed on anode plate and how the display's resolution affected by the bias conditions of the emitter and the gate electrode via computer simulation. Our simulation results exhibit that the gate voltage has a strong effect on display's resolution. For the planar triode structure, the good resolution is achieved when the gate voltage is adjusted to converge the electron beams on an anode plate. For the under-gate structure, the display has a good resolution provided that the gate voltage is not too large to pull the electrons striking on other pixels. In general, the under-gate structure has a wider gate-biased operating condition, but the planar triode structure has a higher light efficiency under the same resolution. Due to the lack of field effect in the y-direction, the spot size of the current density on anode plate looks like strips instead of points. And the resolution of the display will be affected by this factor. (C) 2004 American Vacuum Society.
Structured design of standard-compatible error-resilient video coding, with application to H.263
(2000)
Lin, DW
;
Chen, YL
;
Lee, CT
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Many methods for video transmission error control have been proposed recently, especially in relation to transmission over bursty-error channels. However, a thorough, structural taxonomical framework for analysis and design of such methods seems lacking. Such a framework helps clarity in thought and aids in inspiring new error control methods or combinations thereof. We present a framework for classification of the various transmission error control techniques. We then consider error control for H.263. Several techniques are presented from the viewpoint of the proposed analysis framework and they illustrate how different techniques can be integrated coherently to achieve enhanced error resilience in the overall system. In particular, we employ slotted multiplexing at the multiplex level to reduce synchronization errors in variable-length coded data and to randomize the locations of the remaining error-corrupted image areas. At the source level, we introduce two standard-compatible schemes, called length-based intra refresh and motion vector pairing, respectively, which further limit spatial-temporal error propagation.
The influence of surface ruptures on building damage in the 1999 Chi-Chi earthquake: a case study in Fengyuan City
(2004-01-01)
Dong, JJ
;
Wang, CD
;
Lee, CT
;
Liao, JJ
;
Pan, YW
In addition to the main surface rupture along the Chelungpu fault associated with the 1999 Chi-Chi, Taiwan earthquake, numerous secondary or branch ruptures on hangingwall were also observed. These secondary surface ruptures are parallel or sub-parallel to the main rupture within a distance of a few meters to 1-2 km. The rupture length of these secondary ruptures varies from a few tens of meters up to 5 km. The surface deformation resulted in serious damages of buildings. The present work studied the features of surface deformation on the hangingwall around the Chung-Cheng Park, Fengyuan, Taichung. Three distinct surface ruptures, minor ruptures and tension cracks were observed in this area. The observed distribution and types of building damage on the hangingwall are demonstrated. Due to the difference in geological condition and complex pattern of surface deformation, the resulted building damages on the hangingwall vary. A series of site investigation including field survey, drilling, seismic prospecting, P-S logging tests and laboratory tests were carried out in the interested area. A geological structure model was proposed on the basis of the results of site investigation. Numerical simulation was carried out to model the surface deformation as well as subsurface potential damage zone of an active fault. It reasonably explains the observed pattern of surface deformation and indicates that the surface deformation zone during a catastrophic earthquake is predictable. (C) 2003 Elsevier Science B.V. All rights reserved.
Toughened interpenetrating polymer network materials based on unsaturated polyester and epoxy
(1999-04-25)
Lin, MS
;
Liu, CC
;
Lee, CT
;
應用化學系
;
Department of Applied Chemistry
Simultaneous interpenetrating polymer networks (IPNs) based on epoxy (diglycidyl ether of bisphenol A) and unsaturated polyester (UP) were prepared by using m-xylenediamine and benzoyl peroxide as curing agents. A single glass transition temperature for each IPN was observed with differential scanning calorimetry, which suggests good compatibility of epoxy and UP. This compatibility was further confirmed by the single damping peak of the rheometric dynamic spectroscopy. Curing behaviors were studied with dynamic differential scanning calorimetry, and the curing rates were measured with a Brookfield RTV viscometer. It was noted that an interlock between the two growing networks did exist and led to a retarded viscosity increase. However, the hydroxyl end groups in UP catalyzed the curing reaction of epoxy; in some IPNs where the hydroxyl concentration was high enough, such catalytic effect predominated the network interlock effect, leading to fast viscosity increases. In addition, the entanglement of the two interlocked networks played an important role in cracking energy absorption and reflected in a toughness improvement. (C) 1999 John Wiley & Sons, Inc.