Browsing by Author "Wu, JW"

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Au/Ge/Pd ohmic contacts to n-GaAs with the Mo/Ti diffusion barrier
(1996-12-01)
Chai, CY
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Huang, JA
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Lai, YL
;
Wu, JW
;
Chang, CY
The influences of the As-outdiffusion and Au-indiffusion on the performances of the Au/Ge/Pd/n-GaAs ohmic metallization systems are clarified by investigating three different types of barrier metal structures Au/Ge/Pd/GaAs, Au/Ti/Ge/Pd/GaAs, and Au/Mo/Ti/Ge/Pd/GaAs. The results indicate? that As-outdiffusion leads to higher specific contact resistivity, whereas Au-indiffusion contributes to the turnaround of the contact resistivity at even higher annealing temperature. For Au/Mo/Ti/Ge/Pd/n-GaAs samples, they exhibit the smoothest surface and the lowest specific contact resistivity with the wildest available annealing temperature,range, Moreover, Auger electron spectroscopy depth profiles show that the existing Ti oxide for the Mo/Ti bilayer can very effectively retard Au-indiffusion, reflecting the onset of the turnaround point at much higher annealing temperature.
Combined conduction and radiation heat transfer in plane-parallel packed beds with variable porosity
(1999-03-01)
Wu, JW
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Chu, HS
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機械工程學系
;
Department of Mechanical Engineering
The primary concern of this study deals with the prediction of thermal performance of packed beds with variable porosity. Combined conduction and radiation heat transfer in plane-parallel packed beds of spherical particles was investigated numerically. The effects of variable porosity, effective thermal conductivity, and thermal radiation were taken into account. The method for radiative transfer equation was based on the P-3-spherical harmonic approximation, while the finite-difference scheme was employed to solve the energy equation. Four different models of porosity distributions were tested. It was found that variable porosity and effective thermal conductivity effects on the mean total effective thermal conductivity and radiative heat flux distributions are important and should not be ignored. (C) 1999 Elsevier Science Ltd. All rights reserved.
Effects of rapid thermal annealing on Si delta-doped GaInP grown by low pressure metalorganic chemical vapor deposition
(1995-12-01)
Wang, CJ
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Feng, MS
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Chan, SH
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Wu, JW
;
Chang, CY
We have investigated the effects of rapid thermal annealing on the Si delta-doped GaInP. The spatial localization of carriers was derived and used to determine the diffusion coefficient of Si in GaInP by the capacitance-voltage measurement. We found an unusual mobility change of Si delta-doped GaInP after annealing from Hall-effect measurement. The compensation effect of Si amphoteric property could not be used to explain this behavior. From photoluminescence spectra, it is suggested that the ordered/disordered transformation is the dominate factor for mobility increase after annealing. On the contrary, the degradation of quantum confinement in delta-doped structure by dopant diffusion after annealing is responsible for the decrease of mobility. Therefore, the behavior of mobility could be considered as a competition result of these two mechanisms.
Excellent Au/Ge/Pd ohmic contacts to n-type GaAs using Mo/Ti as the diffusion barrier
(1996-04-01)
Chai, CY
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Huang, JA
;
Lai, YL
;
Wu, JW
;
Chang, CY
Au/Ge/Pd metallization system using Mo/Ti as the diffusion barrier between the Au overlayer and the Ge/Pd underlayer has been performed for the first time to achieve excellent ohmic contacts to n(+)-GaAs with the Si-doping concentration of about 2 x 10(18) cm(-3). The minimum specific contact resistivity as low as 1.2 x 10(-7) Ohm . cm(2) can be obtained after the rapid thermal annealing at 325 degrees C for 60 s, which is much lower than those of the conventional Au/Ge/Pd metallization systems. Furthermore, the available annealing temperature range for such low specific contact resistivities is also significantly extended from 325 degrees C to 400 degrees C. The improvement is attributed to the effective retardation of As-outdiffusion by the Mo/Ti barrier.
Excess low-frequency noise in ultrathin oxide n-MOSFETs arising from valence-band electron tunneling
(2005-09-01)
Wu, JW
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You, JW
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Ma, HC
;
Cheng, CC
;
Hsu, CF
Low-frequency flicker noise in analog n-MOSFETs with 15-angstrom gate oxide is investigated. A new noise generation mechanism resulting from valence-band electron tunneling is proposed. In strong inversion conditions, valence-band electron tunneling from Si substrate to polysilicon gate takes place and results in the splitting of electron and hole quasi-Fermi-levels in the channel. The excess low-frequency noise is attributed to electron and hole recombination at interface traps between the two quasi-Fermi-levels. Random telegraph signals due to the capture of channel electrons and holes is characterized in a small area device to support our model.
Heat transfer in open cell polyurethane foam insulation
(1998-11-01)
Wu, JW
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Chu, HS
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機械工程學系
;
Department of Mechanical Engineering
This paper study systematic investigates the combined conductive and non-gray radiative heat transfer of open cell polyurethane (PU) foam in the pressure range between 760 and 0.02 Torr. Direct transmission measurements are also taken using Fourier transform infrared (FTIR) spectrometer. In doing so, experimental results are obtained for the spectral extinction coefficient from 2.5 to 25 mu m. In addition, the P-3 approximation method along with the box model is employed to calculate the non-gray radiative heat flux. The diffusion approximation method is also applied to calculated the radiative conductivity. Also tested herein are three samples with different cell sizes ranging from 330 to 147 mu m. According to those results, the spectral extinction coefficient increases with a decrease of cell size, leading to a decrease of thermal conductivity. Moreover, evacuating the gases in the foam cells can reduce the thermal conductivity of the PU foam by as much as 75%. Furthermore, radiative heat transfer accounts for about 4% of total heat transfer at 760 Torr and increases to 20% at 0.02 Torr.
High power Al0.3Ga0.7As/In0.2Ga0.8As enhancement-mode PHEMT for low-voltage wireless communication systems
(2002-08-29)
Chen, SH
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Chang, L
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Chang, EY
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Wu, JW
;
Chang, CY
A 20 mm-wide enhancement-mode pseudomorphic high-electron-mobility transistor (E-PHEMT) has been developed. The device has high transconductance of 490 mS/mm, and high maximum drain current of 350 mA/mm due to the use of an Al(0.3)G(4.7)As/In0.2Ga0.8As-based structure for carrier confinement. At 1.9 GHz and 3.0 V, the E-PHEMT shows 34.1 dBm (128 mW/mm) output power with power-added efficiency (PAE) of 64.5%. At 2.4 V, the maximum saturated output power is 32.25 dBm and maximum PAE is 78.5%. The E-PHEMT demonstrates excellent power performance at 1.9 GHz and below 3 V.
High-performance An/Ti/Ge/Pd ohmic contacts on n-Type In0.5Ga0.5P
(1996-04-01)
Chai, CY
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Wu, JW
;
Guo, JD
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Huang, JA
;
Lai, YL
High-performance Au/Ti/Ge/Pd ohmic contacts on n(+)-In0.5Ga0.5P have been fabricated for the first time. Using an n(+)-In0.5Ga0.5P epitaxial layer grown by low pressure metalorganic chemical vapor deposition (LP-MOCVD) with a Si dopant concentration of about 2 x 10(18) cm(-3), the minimum specific contact resistivity is as low as 1.2 x 10(-5) Ohm . cm(2), which is much lower than that of AuGeNi contacts after rapid thermal annealing at 400 degrees C for 60 s. The thermal stability of the Au/Ti/Ge/Pd system is significantly higher than that of conventional AuGeNi due to the introduction of the Ti barrier layer. Many holes and islands are observed on the surfaces of samples annealed at high temperature. The outdiffusion of P from the decomposed In0.5Ga0.5P substrate and agglomeration of Pd and Ge are the primary causes of contact degradation.
Hot carrier degradation in LDMOS power transistors
(2004)
Cheng, CC
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Wu, JW
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Lee, CC
;
Shao, JH
;
Wang, T
The hot carrier performance of N-LDMOS and P-LDMOS transistors is evaluated. For N-LDMOS transistors, the drain current degradation is shown to be due to hot electron injection in the drift region field oxide (bird's beak edge). On the other hand, the hot carrier-damaged region of P-LDMOS transistors is within the channel region, and hot electron is also the source of degradation.
Low frequency noise degradation in ultra-thin oxide (I5A) analog n-MOSFETs resulting from valence-band tunneling
(2005)
Wu, JW
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You, JW
;
Ma, HC
;
Cheng, CC
;
Hsu, C
Abnormal increase of low frequency flicker noise in analog n-MOSFETs with gate oxide in valence band tunneling domain is investigated. In 15 angstrom oxide devices, valence-band electron tunneling from Si substrate to poly-gate occurs at a positive gate voltage and results in the splitting of electron and hole quasi Fermi-levels in the channel. The excess low frequency noise is attributed to electron and hole recombination at interface traps between the two quasi Fermilevels. The trap capture and emission times in valence band tunneling domain are extracted from random telegraph signal. The dependence of measured trap times on gate voltage is consistent with our proposed model.
Pocket implantation effect on drain current flicker noise in analog nMOSFET devices
(2004-08-01)
Wu, JW
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Cheng, CC
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Chiu, KL
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Guo, JC
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Lien, WY
The pocket implantation effect on drain current flicker noise in 0.13 mum CMOS process based high performance analog nMOSFETs is investigated. Our result shows that pocket implantation will significantly degrade device low-frequency noise primarily because of nonuniform threshold voltage distribution along the channel. An analytical flicker noise model to account for a pocket doping effect is proposed. In our model, the local threshold voltage and the width of the pocket implant region are extracted from the measured reverse short-channel effect, and the oxide trap density is extracted from a long-channel device. Good agreement between our model and the measurement result is obtained without other fitting parameters.
Thermal conductivity of polyurethane foams
(1999-06-01)
Wu, JW
;
Sung, WF
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Chu, HS
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機械工程學系
;
Department of Mechanical Engineering
The thermal conductivity of polyurethane (PU) foams at gas pressure between 760 torr and 0.014 torr is investigated theoretically and experimentally. Six different cell sizes ranging from 150 to 350 mu m of PU foam insulation are used as the samples. Experimental results are also obtained for the spectral extinction coefficient using a Fourier transform infrared spectrometer. The thermal conductivity of PU foams for different cell sizes at 760 torr varies from 33.3 to 34.5 mW/m K, and reduces to 6.82-9.15 mW/m K at a gas pressure of 0.014 torr; the effective thermal conductivity decreases when the cell size becomes smaller. At gas pressure 0.014 torr, radiative heat transfer accounts for approximately 20% of the total heat transfer through PU foams, while solid conduction accounts for the other 80%. (C) 1999 Elsevier Science Ltd. All rights reserved.
Valence-band tunneling induced low frequency noise in ultrathin oxide (15 angstrom) n-type metal-oxide-semiconductor field effect transistors
(2004-11-22)
Wu, JW
;
You, JW
;
Ma, HC
;
Cheng, CC
;
Chang, CS
Low frequency flicker noise in n-type metal-oxide-semiconductor field effect transistors (n-MOSFETs) with 15 Angstrom gate oxide is investigated. A noise generation mechanism resulting from valence band tunneling is proposed. In strong inversion condition, valence-band electron tunneling takes place and results in the splitting of electron and hole quasi-Fermi levels in the channel. The excess low frequency noise is attributed to electron and hole recombination at interface traps between the two quasi-Fermi levels. Random telegraph signal in a small area device is characterized to support our model. (C) 2004 American Institute of Physics.