Browsing by Author "Wu, CJ"

Now showing 1 - 20 of 22

AC permeability of the flux-line liquid in the anisotropic high-T-c superconducting crystals
(1996-09-01)
Wu, CJ
;
Tseng, TY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
AC properties of the flux-line liquid in the anisotropic high-temperature superconducting crystals in a parallel field are theoretically investigated. The ac responses in the simple flux-flow regime are analyzed from associated effective ac-magnetic permeability calculated on the hydrodynamic theory basis. The responses are studied as functions of anisotropic ratio and sample dimensions. The results illustrate the influence of the platelet crystal's size on permeability in the anisotropic superconductors while in the isotropic superconductors, the relationship of responses between a square rod and cylinder is found. It indicates that the permeability of a cylinder can be essentially replaced by that of a square rod and vice versa. The geometric effect on response is also elucidated in the isotropic superconductors.
AC permeability of the flux-line liquid in the anisotropic high-T-c superconducting crystals
(1996-09-01)
Wu, CJ
;
Tseng, TY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
AC properties of the flux-line liquid in the anisotropic high-temperature superconducting crystals in a parallel field are theoretically investigated. The ac responses in the simple flux-flow regime are analyzed from associated effective ac-magnetic permeability calculated on the hydrodynamic theory basis. The responses are studied as functions of anisotropic ratio and sample dimensions. The results illustrate the influence of the platelet crystal's size on permeability in the anisotropic superconductors while in the isotropic superconductors, the relationship of responses between a square rod and cylinder is found. It indicates that the permeability of a cylinder can be essentially replaced by that of a square rod and vice versa. The geometric effect on response is also elucidated in the isotropic superconductors.
AC response of the vortex liquid in the high-T-c superconducting cylinder
(1996-04-01)
Wu, CJ
;
Tseng, TY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The ac response of the vortex liquid of a high-T-c superconducting cylinder in the parallel field configuration is examined theoretically The ac properties are analyzed from the associated complex ac permeability calculated on the basis of hydrodynamics theory. The permeability is primarily dominated by two frequency-dependent penetration lengths which are also shown to be independent of the geometries considered. in the simple flux-flow regime, the second peak in ac loss is observed to be enhanced while the first peak is depressed for the superconducting cylinder In the viscous flux liquid, the ac response is found to rely on the viscosity, ratio of shear modulus to nonlocal compressional modulus, and the geometries discussed. The results indicate some basic difference in ac permeabilities between superconducting cylinder and slab.
Device modeling of ferroelectric memory field-effect transistor (FeMFET)
(2002-10-01)
Lue, HT
;
Wu, CJ
;
Tseng, TY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
A numerical analysis of the electrical characteristics for the ferroelectric memory field-effect transistors (FeMFETs) is presented. Two important structures such as the metal-ferroelectric-insulator-semiconductor field-effect transistor (MFISFET) and metal-ferroelectric-metal-insulator-semiconductor field-effect transistor (MFMISFET) are considered. A new analytic expression for the relation of polarization versus electric field (P-E) is proposed to describe the nonsaturated hysteresis loop of the ferroelectric material. In order to provide a more accurate simulation, we incorporate the combined effects of the nonsaturated polarization of ferroelectric layers and the nonuniform distributions of electric field and charge along the channel. We also discuss the possible nonideal effects due to the fixed charges, charge injection, and short channel. The present theoretical work provides some new design rules for improving the performance of FeMFETs.
Device Modeling of ferroelectric memory field-effect transistor for the application of ferroelectric random access memory
(2003-01-01)
Lue, HT
;
Wu, CJ
;
Tseng, TY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
An improved theoretical analysis on the electrical characteristics of ferroelectric memory field-effect transistor (FeMFET) is given. First, we propose a new analytical expression for the polarization versus electric field (P-E) for the ferroelectric material. It is determined by one parameter and explicitly includes both the saturated and nonsaturated hysteresis loops. Using this expression, we then examine the operational properties for two practical devices such as the metal-ferroelectric-insulator-semiconductor field-effect transistor (MFIS-FET) and metal-ferroelectric-metal-insulator-semiconductor field-effect transistor (MFMIS-FET) as well. A double integral also has been used, in order to include the possible effects due to the nonuniform field and charge distribution along the channel of the device, to calculate the drain current of FeMFET. By using the relevant material parameters close to the (Bi, La)(4)Ti3O12 (BLT) system, accurate analyses on the capacitors and FeMFET's at various applied biases are made. We also address the issues of depolarization field and retention time about such a device.
Effective microwave surface impedance of superconducting films in the mixed state
(1997-05-01)
Wu, CJ
;
Tseng, TY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The effective microwave surface impedance of mulitilayer structures made of high-ir, superconducting films in the mixed state, lossy dielectrics, and normal metals are theoretically calculated. The linear response of the superconductor to a microwave field is analyzed within both transmission line theory and the framework of self-consistent treatment of vortex dynamics reported by Coffey and Clem [18]. The microwave properties are investigated as a function of static field and film thickness for nonresonant structures. The effect of substrate thickness on the resonant phenomenon is carefully studied as well. Numerical results reveal that the substrate resonance in the Meissner state behaves like a parallel lumped-parameter resonantor, while in the vortex state it behaves as a series lumped resonant circuit. The basic distinction suggests that care should be taken in microwave applications when using superconducting films in the vortex state.
Effective microwave surface impedance of superconducting films in the mixed state
(1997-05-01)
Wu, CJ
;
Tseng, TY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The effective microwave surface impedance of mulitilayer structures made of high-ir, superconducting films in the mixed state, lossy dielectrics, and normal metals are theoretically calculated. The linear response of the superconductor to a microwave field is analyzed within both transmission line theory and the framework of self-consistent treatment of vortex dynamics reported by Coffey and Clem [18]. The microwave properties are investigated as a function of static field and film thickness for nonresonant structures. The effect of substrate thickness on the resonant phenomenon is carefully studied as well. Numerical results reveal that the substrate resonance in the Meissner state behaves like a parallel lumped-parameter resonantor, while in the vortex state it behaves as a series lumped resonant circuit. The basic distinction suggests that care should be taken in microwave applications when using superconducting films in the vortex state.
High-frequency vortex response of anisotropic type-II superconductors
(1996-07-01)
Wu, CJ
;
Tseng, TY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The theory of the self-consistent treatment of vortex dynamics developed by Coffey and Clem is extended to the case of anisotropic type-II superconductors. The vortex response to a microwave electromagnetic field is theoretically investigated based on the associated complex rf magnetic permeability of anisotropic superconductors. Microwave dissipation due to vortex motion is studied as a function of the temperature, de magnetic field, and microwave frequency. Comparisons of numerical results between anisotropic and isotropic superconductors are also given. The influence of the thin edge of superconducting platelets on the microwave properties is specifically examined as well. The extension presented provides the possible applicability in studying the high-frequency response of real anisotropic high-temperature superconducting single-crystal platelets in the mixed state.
High-frequency vortex response of anisotropic type-II superconductors
(1996-07-01)
Wu, CJ
;
Tseng, TY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The theory of the self-consistent treatment of vortex dynamics developed by Coffey and Clem is extended to the case of anisotropic type-II superconductors. The vortex response to a microwave electromagnetic field is theoretically investigated based on the associated complex rf magnetic permeability of anisotropic superconductors. Microwave dissipation due to vortex motion is studied as a function of the temperature, de magnetic field, and microwave frequency. Comparisons of numerical results between anisotropic and isotropic superconductors are also given. The influence of the thin edge of superconducting platelets on the microwave properties is specifically examined as well. The extension presented provides the possible applicability in studying the high-frequency response of real anisotropic high-temperature superconducting single-crystal platelets in the mixed state.
Influences of deposition temperature on thermal stability and moisture resistance of chemical vapor deposited fluorinated silicon oxide by using indirect fluorinating precursor
(1996-08-26)
Chang, KM
;
Wang, SW
;
Wu, CJ
;
Yeh, TH
;
Li, CH
In this letter, fluorinated silicon oxide (FxSiOy) films were deposited in the electron cyclotron resonance (ECR) chemical vapor deposition system with SiH4, O-2, and CF4 as the reaction gases. The CF4, in contrast to SiF4 or FSi(OC2H5)(3) used in other reports, is an indirect fluorinating source. The fluorinating mechanism is similar to that of the etching of oxide by fluorocarbon plasma, therefore, the thermal stability of the incorporated fluorine must strongly depend on the deposition temperature. It is found that the thermal stability and moisture resistance are greatly improved by increasing the deposition temperature. However, the higher deposition temperature also results in a higher compressed stress and dielectric constant. Besides, to get the moisture resistance, the deposition temperature must be above 300 degrees C. On the other hand, ECR-SiO2 (without fluorination), even deposited at room temperature, is shown to have a good water resistance. Therefore, by choosing deposition temperature for FxSiOy to have enough thermal tolerance and capping with ECR-SiO2, the moisture resistor is suggested for the inter metal dielectric applications.
Influences of deposition temperature on thermal stability and moisture resistance of chemical vapor deposited fluorinated silicon oxide by using indirect fluorinating precursor
(1996-08-26)
Chang, KM
;
Wang, SW
;
Wu, CJ
;
Yeh, TH
;
Li, CH
In this letter, fluorinated silicon oxide (FxSiOy) films were deposited in the electron cyclotron resonance (ECR) chemical vapor deposition system with SiH4, O-2, and CF4 as the reaction gases. The CF4, in contrast to SiF4 or FSi(OC2H5)(3) used in other reports, is an indirect fluorinating source. The fluorinating mechanism is similar to that of the etching of oxide by fluorocarbon plasma, therefore, the thermal stability of the incorporated fluorine must strongly depend on the deposition temperature. It is found that the thermal stability and moisture resistance are greatly improved by increasing the deposition temperature. However, the higher deposition temperature also results in a higher compressed stress and dielectric constant. Besides, to get the moisture resistance, the deposition temperature must be above 300 degrees C. On the other hand, ECR-SiO2 (without fluorination), even deposited at room temperature, is shown to have a good water resistance. Therefore, by choosing deposition temperature for FxSiOy to have enough thermal tolerance and capping with ECR-SiO2, the moisture resistor is suggested for the inter metal dielectric applications.
Microwave response of superconducting platelet crystals
(1996-07-01)
Wu, CJ
;
Tseng, TY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
A theoretical study of the microwave response of isotropic and anisotropic superconductors in the Meissner state is presented, We consider a superconducting thin platelet crystal oriented in a parallel field configuration. The linear response analysis is investigated on the basis of modified two-fluid models along with the diffusion equation. The CS coherence effect for conventional superconductors and the anomalous peak in the loss for anisotropic high-T-c. cuprates are considered. The microwave properties are analyzed by the derived dimensionless magnetic permeability. The results show that thin edges have essentially nothing to do with the microwave loss in isotropic superconductors and the simple slab geometry suffices in studying their microwave properties. As for the high-T-c superconductors, the anisotropic effect itself makes the thin edges crucial in determining the microwave loss. The, calculated results qualitatively indicate some good consistence with the reported experimental data. The role of thin edges of the superconducting platelet crystal in the microwave response is therefore evidently clarified.
Microwave response of superconducting platelet crystals
(1996-07-01)
Wu, CJ
;
Tseng, TY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
A theoretical study of the microwave response of isotropic and anisotropic superconductors in the Meissner state is presented, We consider a superconducting thin platelet crystal oriented in a parallel field configuration. The linear response analysis is investigated on the basis of modified two-fluid models along with the diffusion equation. The CS coherence effect for conventional superconductors and the anomalous peak in the loss for anisotropic high-T-c. cuprates are considered. The microwave properties are analyzed by the derived dimensionless magnetic permeability. The results show that thin edges have essentially nothing to do with the microwave loss in isotropic superconductors and the simple slab geometry suffices in studying their microwave properties. As for the high-T-c superconductors, the anisotropic effect itself makes the thin edges crucial in determining the microwave loss. The, calculated results qualitatively indicate some good consistence with the reported experimental data. The role of thin edges of the superconducting platelet crystal in the microwave response is therefore evidently clarified.
Microwave surface impedances of BCS superconducting thin films
(1996-06-01)
Wu, CJ
;
Tseng, TY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The microwave propagation-dominated problem in the multilayer structure made of a BCS superconducting film and a dielectric substrate is investigated theoretically by using the modified two-fluid model and transmission tine theory, The effective microwave surface impedances are studied as functions of temperature, frequency, and film thickness, as well as substrate thickness, Special attention is paid to the substrate resonance phenomenon in the resonant structure. The influence of BCS coherence effects on surface impedance and resonant behavior is clearly demonstrated. The resonant effect in the stack structure is wed interpreted with the help of the transverse resonance technique in the microwave theory.
PCUP: Pipelined cyclic upstream protocol over hybrid fiber coax
(1997-01-01)
Lin, YD
;
Wu, CJ
;
Yin, WM
;
交大名義發表
;
資訊工程學系
In order to bring NII (National Information Infrastructure) into the home, the community cable TV networks have to be reengineered to support two-way interactive services. In this work, the authors propose PCUP (Pipelined Cyclic Upstream Protocol) as the upstream MAC (medium access control) protocol for HFC (hybrid fiber coax) community access network. PCUP is designed with the intention of pipelining the upstream channel. This is achieved by proper station positioning, which measures the station propagation offset from the headend, and transmission scheduling, which assigns each station a transmission starting time and duration in a cycle. By taking into account the propagation offsets and transmission times, transmitted cells can appear back-to-back (i.e., pipelined) at the headend. Since only the active stations are scheduled to transmit in a cycle, a membership control mechanism, which runs a contention-based tree walk algorithm, is executed periodically to allow the stations to join or leave. The authors also compare PCUP with various schemes proposed to IEEE 802.14 committee.
PCUP: Pipelined cyclic upstream protocol over hybrid fiber coax
(1997-01-01)
Lin, YD
;
Wu, CJ
;
Yin, WM
;
資訊工程學系
;
Department of Computer Science
In order to bring NII (National Information Infrastructure) into the home, the community cable TV networks have to be reengineered to support two-way interactive services. In this work, the authors propose PCUP (Pipelined Cyclic Upstream Protocol) as the upstream MAC (medium access control) protocol for HFC (hybrid fiber coax) community access network. PCUP is designed with the intention of pipelining the upstream channel. This is achieved by proper station positioning, which measures the station propagation offset from the headend, and transmission scheduling, which assigns each station a transmission starting time and duration in a cycle. By taking into account the propagation offsets and transmission times, transmitted cells can appear back-to-back (i.e., pipelined) at the headend. Since only the active stations are scheduled to transmit in a cycle, a membership control mechanism, which runs a contention-based tree walk algorithm, is executed periodically to allow the stations to join or leave. The authors also compare PCUP with various schemes proposed to IEEE 802.14 committee.
Photonic band structure for a superconductor-dielectric superlattice
(2005-11-15)
Wu, CJ
;
Chen, MS
;
Yang, TJ
;
電子物理學系
;
Department of Electrophysics
The photonic band structure in the transversal electric mode for a one-dimensional superconductor-dielectric superlattice is theoretically calculated. By using the Abeles theory for a stratified medium, we first calculate the transmittance spectrum from which all the possible bands can be directly seen. Then we calculate the real photonic band structure based oil the transcendental equation derived from the transfer matrix method and Bloch theorem. The band structure is shown to be strongly consistent with the transmittance spectrum. We finally study the three lowest band gaps as a function of penetration of superconductor, permittivity of dielectric, and angle of incidence, respectively. The optical properties in a superconductor-dielectric superlattice thus are well disclosed. (c) 2005 Elsevier B.V. All rights reserved.
Resistive response to a microwave field in high temperature superconducting crystals
(1997-03-15)
Wu, CJ
;
Tseng, TY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The microwave properties of high temperature superconducting crystals in the resistive states are theoretically investigated. The single crystals in the shapes of platelet and cylinder in parallel held configuration are considered. The microwave responses are analyzed from the associated effective r.f. magnetic permeabilities. The influence of the anisotropic resistivity on the microwave response is stressed in an anisotropic superconductor. The results indicate the importance of thin edges of the platelet crystal to the microwave properties. In the isotropic superconductor, a relationship between the responses of a square rod and a cylinder is found. The results show that the microwave properties of a cylinder can be essentially replaced by those of a square rod and vice versa. Also the geometric effect on the response is illustrated in the isotropic superconductor.
Sparse channel estimation for OFDM transmission based on representative subspace fitting
(2005)
Wu, CJ
;
Lin, DW
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
In channel estimation for OFDM transmission over sparse channels, the time-domain approach requires estimation of much fewer parameters than the frequency-domain approach, but one needs to estimate both the delay and the gain of each path. We consider the time-domain approach and propose an algorithm that finds a set of delays under a certain criterion on the approximation error. More specifically, we obtain one additional path delay at a time, with each newly added term selected to reduce by the most amount the difference between a subspace spanned by the estimated delays and that perceived at the pilot subcarriers. The proposed method can handle non-sample-spaced path delays and it allows arbitrary, irregularly spaced pilot allocations. Simulation results show some of its operational characteristics and demonstrate its superiority over simple frequency-domain interpolation methods.
Two-phase minislot scheduling algorithm for HFC QoS services provisioning
(2002-03-01)
Yin, WM
;
Wu, CJ
;
Lin, YD
;
資訊工程學系
;
Department of Computer Science
Data-Over-Cable Service Interface Specifications v1.1 (DOCSIS v1.1 ), developed for data transmissions over Hybrid Fiber Coaxial (HFC networks. defines five upstream services for supporting per-flow Quality of Services QoS). The cable modern termination system (CMTS) must periodically grant upstream transmission opportunities to the QoS flows based on their QoS parameters. However, packets may violate QoS requirements when several flows demand the same interval for transmission. This study proposes a two-phase, i.e.. the scheduling sequence determination phase and the minislot assignment phase. minislot scheduling algorithm to reduce the QoS violation rate. In the scheduling sequence determination phase, the flow whose packets are most unlikely to violate QoS is scheduled first. Then. in the minislot assignment phase, the scheduler allocates to a flow the available interval where the likelihood of packet violation is minimum. Simulation results demonstrate that our scheduling algorithm can reduce the QoS violation rate by 80-35% over that of the first-come-first-serve-random-selection algorithm. It increases the utilization by 25% as well, The two-phase minislot scheduling algorithm can work within the DOCSIS v1.1 framework.