Browsing by Author "CHEN, CH"

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A NEW APPROACH TO MODELING THE SUBSTRATE CURRENT OF PRESTRESSED AND POST-STRESSED MOSFETS
(1995-06-01)
YANG, JJ
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SHAOSHIUN, S
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CHOU, PC
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CHEN, CH
;
LIN, MS
In this paper, we propose a closed form expression of a new and accurate analytical substrate current model for both pre-stressed and post-stressed MOSFET's, It was derived based on the concept of effective electric field, which gives a more reasonable impact ionization rate in the lucky-electron model, This effective electric field, composed by two experimentally determined parameters, ran be regarded as a result of nonlocal heating effects within de,ices, This model shows a significant improvement to the conventional local field model. One salient feature of the present model is that it allows us to characterize the time evolution of the substrate current of stressed MOSFET's for the first time. Experimental verification for a wide variety of MOSFET's with effective channel lengths down to 0.3 mu m shows that the new model is very accurate and is feasible for any kind of MOS device with different drain structures, The present model can be applied to explore the hot carrier effect in designing submicrometer MOS devices with emphasis on the design optimization of a device drain engineering issue, In addition, the present model is well suited for device reliability analysis and circuit level simulations.
A NUMERICAL STUDY OF FLAME SPREAD AND BLOWOFF OVER A THERMALLY-THIN SOLID FUEL IN AN OPPOSED AIR-FLOW
(1990)
CHEN, CH
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交大名義發表
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機械工程學系
;
National Chiao Tung University
;
Department of Mechanical Engineering
A PARTIAL VARIATIONAL ANALYSIS OF PLANAR DIELECTRIC ANTENNAS
(1991-06-01)
CHUNG, SJ
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CHEN, CH
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電信工程研究所
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Institute of Communications Engineering
The reflection and radiation characteristics of a planar dielectric antenna with arbitrary geometrical configuration are analyzed numerically. A variational equation is first established based on the partial variational principle (PVP), and then solved by the finite element method coupled with the frontal solution technique. The radiation and boundary conditions are incorporated by combining the modal expansion method and the Green's function approach for exterior field representation. The reflection coefficients, the radiation patterns, and the directive and power gains of several antennas with linearized structures are studied and compared.
A THEORY FOR DOWNWARD FLAME SPREAD OVER A THERMALLY THIN FUEL
(1991)
DUH, RC
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CHEN, CH
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交大名義發表
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機械工程學系
;
National Chiao Tung University
DIFFUSION FLAME STABILIZATION AND EXTINCTION UNDER NATURALLY CONVECTIVE FLOWS
(1991-02-01)
CHEN, CH
;
HOU, WH
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交大名義發表
;
機械工程學系
;
National Chiao Tung University
The stabilization and extinction phenomena for a two-dimensional diffusion flame around the leading edge of an upright solid fuel under naturally convective environments are studied theoretically. The governing system consists of two-dimensional Navier-Stokes' momentum (including a body force term), energy, species, and continuity equations, together with a finite-rate chemical kinetics described by a second-order Arrhenius-type rate equation. The burning rate of fuel is expressed by an Arrhenius-type pyrolysis law. The nondimensional model is solved numerically. Two parametric studies, based on changing gravity level and ambient oxygen index, respectively, are investigated. Under the variation of gravity, both Damkohler number and preexponential factor for fuel pyrolysis are changed. Two quenching limits are identified separately at a very low and a high gravity level. The envelope flame exists when gravity is less than 1.95 g. As gravity is increased, there appears a transition to open-tip flame, stabilized on the side of fuel plate. A similar trend is found when ambient oxygen index is decreased from the higher value of the lower one but only with a quenching limit that is blowoff. The detailed flame structures for envelope and open-tip flames are illustrated graphically.
FLAME SPREAD OVER A THERMALLY-THIN SOLID FUEL IN ZERO GRAVITY
(1993)
DUH, FC
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CHEN, CH
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交大名義發表
;
機械工程學系
;
National Chiao Tung University
An analysis of flame spreading over a thin solid fuel in zero-gravity environment is presented. The mathematical model includes two-dimensional Navier-SLokes' momentum, energy and species equations with a one-step overall chemical reaction. The fuel consumption rate is described by a second-order Arrhenius kinetics. The energy balance along the solid fuel consists of the conduction, convection and radiation. The surface radiative loss is found to be the dominant factor for flame extinction in the low oxygen mass fraction regime. The computed flame spread rate and standoff distance are in agreement with the experimental measurements by Olson [2]. The flame spread rate, the flame size and the solid pyrolysis length become greater as the oxygen mass fraction increases, but the standoff distance shows an opposite trend. The flame structures are illustrated graphically showing the interaction between the flow and thermal fields and the multidimensional feature in the flame front.
FLAME STABILIZATION AND BLOWOFF OVER A POROUS CYLINDER
(1990)
CHEN, CH
;
WENG, FB
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交大名義發表
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機械工程學系
;
National Chiao Tung University
FLAME STABILIZATION AND BLOWOFF OVER A SINGLE DROPLET
(1995-01-01)
HUANG, LW
;
CHEN, CH
;
交大名義發表
;
機械工程學系
;
National Chiao Tung University
The burning behavior of a liquid fuel droplet under forced convection has been investigated numerically. The normalized governing system makes up the complete Navier-Stokes momentum, energy, species, and continuity equations in r-z coordinates with a one-step overall chemical reaction and finite-rate global kinetics. The evaporation process obeys the Clausius-Clapeyron law. The effects of incoming velocity (muBAR(infinity)) and droplet diameter (dBAR) are investigated separately. The envelope flame exists when free stream velocity is low. When uBAR(infinity) increases gradually, a critical velocity can be reached, at which the flame suddenly converts into a wake flame. No side falme is found. The envelope flames are retained throughout the decrement of the droplet diameter under the low-speed flow regime. The d2 law is found to still hold in such an environment.
GAS-PHASE RADIATIVE EFFECTS ON DOWNWARD FLAME SPREAD IN LOW GRAVITY
(1994)
CHEN, CH
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CHENG, MC
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交大名義發表
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機械工程學系
;
National Chiao Tung University
A theoretical analysis is developed to study the effect of radiative heat transfer on downward flame spread over a thin fuel in low gravity. The combustion model, which is an extension of that in Duh and Chen (1991), approximates gas-phase radiation using a two-flux method applied in the cross-stream direction. Numerical results show that there is a quenching limit in the low-gravity region which is inaccessible if radiation is neglected. The main controlling factor in low gravity (g < 0.05) is the conduction to radiation parameter (N(infinity)) where the flame spread rate increases with an increase in N(infinity). Also, the Damkohler number alone is found to be insufficient to characterize the flame spread behavior. On the other hand, in higher gravity the Damkohler number becomes dominant. Parametric studies are carried out by changing the gravity level and the ambient oxygen concentration subject to gas-phase radiation. Finally, a flammability map is constructed that combines the two effects.
HEAT-TRANSFER FOR INCOMPRESSIBLE AND COMPRESSIBLE FLUID-FLOWS OVER A HEATED CYLINDER
(1990-10-01)
CHEN, CH
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WENG, FB
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交大名義發表
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機械工程學系
;
National Chiao Tung University
MULTIOBJECTIVE DECISION-MAKING FOR TRAFFIC ASSIGNMENT
(1993-05-01)
TZENG, GH
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CHEN, CH
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運輸與物流管理系註：原交通所+運管所
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Department of Transportation and Logistics Management
In traditional traffic-assignment problems, only a single objective is considered. Although people's living quality improves and transportation needs increase, the environmental quality is destroyed with rapid economic and traffic growth. The concept of traffic assignment, an important procedure for transportation planning, should take all needs into consideration. Based on the viewpoints of all constituencies, this paper attempts to determine optimal flow patterns using three objectives-total travel time for road users, air pollution for nonusers (such as community residents), and travel distance for government-to formulate an effective multiobjective model for traffic assignment. By using multiobjective decision making and nonlinear programming techniques, a series of noninferior solutions is generated. By combining an eigenvector weighting method with pairwise comparison, we obtain a compromise solution for the flow pattern. An application case for the Taipei network system is also presented and discussed. The results show that if other nontraffic related factors are taken into account, the multiobjective traffic-assignment approach is more reasonable and suitable than conventional approaches.
NEW OBSERVATION AND THE MODELING OF GATE AND DRAIN CURRENTS IN OFF-STATE P-MOSFETS
(1994-05-01)
CHEN, MJ
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CHAO, KC
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CHEN, CH
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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 work reports new observations concerning the gate and drain currents measured at off-state conditions in buried-type p-channel LDD MOSFET devices. Detailed investigation of the observed phenomena reveals that 1) the drain current can be separated into two distinct components: band-to-band tunneling in the gate-to-drain overlap region and collection of holes generated via impact ionization by electrons inside the oxide; and 2) the gate current can be separated into two distinct components: the hot electron injection into the oxide and the Fowler-Nordheim electron tunneling through the oxide. At low negative drain voltage, the dominant component of the drain current is the hole generation inside the oxide. At high negative drain voltage, the drain current is essentially due to band-to-band tunneling, and it is correlated with the hot-electron injection-induced gate current.
SINGLE DROPLET COMBUSTION IN A GRAVITATIONAL ENVIRONMENT
(1994-07-01)
HUANG, LW
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CHEN, CH
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交大名義發表
;
機械工程學系
;
National Chiao Tung University
A theoretical analysis is developed to study the combustion characteristics of a fuel droplet in a gravitational field. The normalized governing system consists of the complete conservation equations in r-z coordinates and includes finite-rate global kinetics. The Clausius-Clapeyron law is applied at the liquid-vapor interface to describe the evaporation process. A modified body-fitted grid generation technique is used to handle irregular boundaries. The effects of changing the droplet diameter (dBAR) and the gravity level (gBAR) are investigated. Under the variation of droplet diameter, flame structures, including isotherms, flame shape, velocity vector field, and mass burning rate are studied in detail. The predicted results exhibit good agreement with experimental data. When the gravity level increases, the computed results show that the flame shape is sensitive to variation in gravity. A simple correlation, mBAR = m0BAR [1 + const. (alpha/gBAR)0.52], is found. Within the elevated gravity domain of experiment, the computed data agree well with measurements obtained by Okajima and Kumagai [10].
TURBULENT BOUNDARY-LAYER DIFFUSION FLAME - EFFECTS OF PROBABILITY DENSITY-FUNCTION
(1991-03-01)
CHEN, CH
;
LAN, CY
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SHAN, DY
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機械工程學系
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Department of Mechanical Engineering
A turbulent diffusion flame adjacent to a solid fuel in a parallel airflow is studied analytically. The flow is assumed to be of boundary-layer type where the mean properties of flowfield are predicted by a low-Reynolds-number K-epsilon two-equation model. The chemical reaction is approximated as one-step and infinite-fast. The mean mass-fraction distribution in the boundary layer is described by probability density function (p.d.f.). Four kinds of p.d.f.s are used and they are beta, clipped Gaussian, double delta, and ten-point delta p.d.f.s respectively. The general features of each flame structure by applying corresponding p.d.f.s are quite similar. An overlap exists between fuel and oxidizer mean mass-fraction distributions. The maximal flame temperature is below the value of adiabatic one and its profile is rounded. The velocity, mixture fraction and its fluctuation, and total enthalpy are found to be almost invariant with the form of p.d.f.s. The mass fraction and temperature profiles appear nearly identical by the uses of beta and clipped Gaussian p.d.f.s. In application of double delta p.d.f., discontinuity shows up in these profiles. The modified ten-point delta p.d.f. has the maximum flame temperature due to its smallest overlap of YBAR(F) and YBAR(O) among these p.d.f.s.