Browsing by Author "Fu, CM"

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Decomposing K-n UP into triangles
(2004-07-06)
Fu, CM
;
Fu, HL
;
Rodger, CA
;
應用數學系
;
Department of Applied Mathematics
In this paper, we extend the work on minimum coverings of K-n with triangles. We prove that when P is any forest on n vertices the multigraph G = K-n boolean OR P can be decomposed into triangles if and only if three trivial necessary conditions are satisfied: (i) each vertex in G has even degree, (ii) each vertex in P has odd degree, and (iii) the number of edges in G is a multiple of 3. This result is of particular interest because the corresponding packing problem where the leave is any forest is yet to be solved. We also consider some other families of packings, and provide a variation on a proof by Colbourn and Rosa which settled the packing problem when P is any 2-regular graph on at most n vertices. (C) 2004 Elsevier B.V. All rights reserved.
Effects of oxygen content on the penetration depth in YBCO thin films
(1996)
Hsieh, MC
;
Tseng, TY
;
Fu, CM
;
Wu, KH
;
Juang, JY
By varying oxygen content of the microstrip line resonator of YBa2Cu3O7-x, the effective penetration depth was studied. Based on the two-fluid model, we fit the data of the resonant frequency by means of the inductance formula. It allows us to determine the zero-temperature penetration depth of the fully oxygenated,(O approximate to 7) and oxygen deficient (O = 6.8) states in the same strip to be 483.2 nm and 789.8 nm, respectively. The ratio of the superconducting carrier densities with different oxygen contents is then derived and found to be consistent with the result of Hall measurement. A correlation between oxygen contents and charge carriers of the samples will be obtained in our work as accurately as possible.
Effects of oxygen content on the penetration depth of pulsed laser deposited YBCO thin films
(1996-04-01)
Hsieh, MC
;
Tseng, TY
;
Wei, SM
;
Fu, CM
;
Wu, KH
By systematically varying the oxygen content of microstrip line resonators made of pulsed laser deposited YBa2Cu3O7-x films, the effect of oxygen deficiency on the effective penetration depth were studied. By using the two-fluid model, the zero-temperature penetration depths for the fully oxygenated (i.e. O=7) and oxygen deficient (O=6.8) states in the same strip are found to be 483.2 nm and 789.8 nm, respectively. The large values obtained are attributed to the granular nature of the YBCO films used. The correlation between the penetration depths and superconducting carrier densities as functions of the oxygen content are also discussed.
Polycrystalline beta-SiC film growth on Si by ECR-CVD at 178-500 degrees C
(1996)
Cheng, KL
;
Liu, CC
;
Fu, CM
;
Cheng, HC
;
Lee, C
Preparation and electronic properties of YBa2Cu3Ox films with controlled oxygen stoichiometries
(1998-08-01)
Wu, KH
;
Hsieh, MC
;
Chen, SP
;
Chao, SC
;
Juang, JY
We describe a novel technique capable of controlling the oxygen content of YBa2Cu3Ox (YBCO) films in a precise and reversible manner. The temperature dependence of resistivity and the distinct two-plateau behavior in critical temperature T-CO versus oxygen content plot of these films are consistent with those observed in the bulk and single crystals of YBCO. The O 1s and Cu 2p absorption spectra of these films were measured by polarization-dependent X-ray absorption spectroscopy (XAS). The intensity variations of the pre-edge peaks as a function of oxygen content are discussed. We also used these films to systematically study the electron-phonon coupling strength and the position of Fermi level by using a femtosecond pump-probe technique. A clear sign-reversal of the transient reflectivity, which was consistently explained by the thermomodulation model, was observed. Both of these optical measurements support the idea that the electronic structure of YBCO cuprates is based on the charge transfer model with hybridization between the Cu and O sites.
Suppression of fluorine impurity in blanket chemical vapor deposited tungsten film for via fills with a novel two-step deposition technique
(1997-04-01)
Chang, KM
;
Yeh, TH
;
Lain, KD
;
Fu, CM
;
電子工程學系及電子研究所
Blanket chemical vapor deposited tungsten (CVD-W) offers the potential to fabricate reliable contacts for submicron multilevel metallization. In via filling application, various aluminum fluorides were formed by the reduction of WF6 with aluminum underlayer. These compounds will stay at CVD-W/Al interface and act as insulating layers which cause electrical degradation. In addition, impurities like fluorine or oxygen induce the formation of beta-W lattices as well as high film resistivity. In this work, a two-step chemical vapor deposition of tungsten was developed to suppress the fluorine impurities in tungsten films and at CVD-W/Al interface for blanket CVD-W application. The first step involves a gas phase nucleation with high SiH4/WF6 flow ratio (i.e., 2.5) to deposit a thin tungsten film as the glue layer. It was found that the probability of the WF6 reduction with underlying aluminum was suppressed because the WF6 was completely consumed by SiH4 before arriving onto aluminum surface. Meanwhile, this gas phase nucleated tungsten exhibits blanket deposition capability and an amorphous structure. The second step includes typical CVD-W process (i.e., SiH4/WF6 flow ratio <1) to grow thick tungsten film. Secondary Ion Mass Spectroscopy (SIMS) measurements indicate that the fluorine impurities in tungsten aim and at CVD-W/Al interface are drastically reduced. Also, the gas phase nucleated tungsten can be reproducibly deposited without attacking the aluminum underlayer. Moreover, a lower tungsten resistivity, lower via resistance and longer electromigration lifetime are achieved in the Al/W/Al Kelvin structures produced by two-step deposition technique than those of the typical CVD-W films deposited directly on aluminum.
Suppression of fluorine impurity in blanket chemical vapor deposited tungsten film for via fills with a novel two-step deposition technique
(1997-04-01)
Chang, KM
;
Yeh, TH
;
Lain, KD
;
Fu, CM
;
電子工程學系及電子研究所
Blanket chemical vapor deposited tungsten (CVD-W) offers the potential to fabricate reliable contacts for submicron multilevel metallization. In via filling application, various aluminum fluorides were formed by the reduction of WF6 with aluminum underlayer. These compounds will stay at CVD-W/Al interface and act as insulating layers which cause electrical degradation. In addition, impurities like fluorine or oxygen induce the formation of beta-W lattices as well as high film resistivity. In this work, a two-step chemical vapor deposition of tungsten was developed to suppress the fluorine impurities in tungsten films and at CVD-W/Al interface for blanket CVD-W application. The first step involves a gas phase nucleation with high SiH4/WF6 flow ratio (i.e., 2.5) to deposit a thin tungsten film as the glue layer. It was found that the probability of the WF6 reduction with underlying aluminum was suppressed because the WF6 was completely consumed by SiH4 before arriving onto aluminum surface. Meanwhile, this gas phase nucleated tungsten exhibits blanket deposition capability and an amorphous structure. The second step includes typical CVD-W process (i.e., SiH4/WF6 flow ratio <1) to grow thick tungsten film. Secondary Ion Mass Spectroscopy (SIMS) measurements indicate that the fluorine impurities in tungsten aim and at CVD-W/Al interface are drastically reduced. Also, the gas phase nucleated tungsten can be reproducibly deposited without attacking the aluminum underlayer. Moreover, a lower tungsten resistivity, lower via resistance and longer electromigration lifetime are achieved in the Al/W/Al Kelvin structures produced by two-step deposition technique than those of the typical CVD-W films deposited directly on aluminum.
The characteristics of chemical vapor deposited amorphous-like tungsten film as a gate electrode
(1998-09-01)
Chang, KM
;
Deng, IC
;
Shih, CW
;
Lain, KD
;
Fu, CM
Tungsten films are often advantageously formed by the chemical vapor deposition system which using WF6 gas through SiH4 or H-2 reduction. The fluorine species will diffuse into poly-Si/SiO2/[Si] multilayers by a driving force which is the reaction of WF6 and poly-Si gate. When too many fluorine atoms diffused into the gate oxide, the fluorine atoms will cause more strain in the gate oxide and the electrical characteristics of device will shift. An amorphous-like tungsten layer was deposited at a flow rate ratio of 2.5 of SiH4/WF6. The driving force in the amorphous-like tungsten film deposition is far less than that in selective tungsten film deposition; therefore, the concentration of fluorine atoms in the amorphous-like tungsten film is much less than in the selective tungsten film. We proved that only few fluorine atoms were incorporated in amorphous-like tungsten film which has good characteristics in the application of gate electrode.
The minimum size of critical sets in latin squares
(1997-08-15)
Fu, CM
;
Fu, HL
;
Rodger, CA
;
應用數學系
;
Department of Applied Mathematics
A critical set C of order n is a partial latin square of order n which is uniquely completable to a latin square, and omitting any entry of the partial latin square destroys this property. The size s(C) of a critical set C is the number of filled cells in the partial latin square. The size of a minimum critical set of order n is s(n). It is likely that s(n) is approximately 1/4n(2), though to date the best-known lower bound is that s(n)greater than or equal to n+1. In this paper, we obtain some conditions on C which force s(C)greater than or equal to[(n-1)/2](2). For n > 20, this is used to show that in generals(n)greater than or equal to[(7n-3)/6], thus improving the best-known result. (C) 1997 Elsevier Science B.V.
The minimum size of critical sets in latin squares
(1997-08-15)
Fu, CM
;
Fu, HL
;
Rodger, CA
;
應用數學系
;
Department of Applied Mathematics
A critical set C of order n is a partial latin square of order n which is uniquely completable to a latin square, and omitting any entry of the partial latin square destroys this property. The size s(C) of a critical set C is the number of filled cells in the partial latin square. The size of a minimum critical set of order n is s(n). It is likely that s(n) is approximately 1/4n(2), though to date the best-known lower bound is that s(n)greater than or equal to n+1. In this paper, we obtain some conditions on C which force s(C)greater than or equal to[(n-1)/2](2). For n > 20, this is used to show that in generals(n)greater than or equal to[(7n-3)/6], thus improving the best-known result. (C) 1997 Elsevier Science B.V.
Thermal stability of amorphous-like WNx/W bilayered diffusion barrier for chemical vapor deposited-tungsten/p(+)-Si contact system
(1999-03-01)
Chang, KM
;
Deng, IC
;
Yeh, TH
;
Lain, KD
;
Fu, CM
The barrier characteristics of tungsten nitride/tungsten (WNx/W) bilayer formed by an in situ nitridation on a thin chemical vapor deposited amorphous-like tungsten (CVD a-W) film in CVD-W/Si contact system have been investigated. The thickness of WNx layer after a 5 min of N-2 plasma exposure at 300 degrees C approximated 50 nm and the atomic ratio of W to N in WNx layer was 2 : 1. In the CVD-W/a-WNx/a-W/Si multilayered sample, no discernible tungsten silicide was detected by X-ray diffractometer (XRD) at W/Si interface after annealing at 750 degrees C. Meanwhile, with the Rutherford backscattering spectroscopy (RBS) analysis and the measurement of p(+)n junction leakage current, the CVD-W/a-WNx/a-W/Si multilayer maintained the integrity of interface and the CVD-W/a-WNx/a-W/p(+)n diode kept the reverse leakage current density less than 9 x 10(-9) A/cm(2) while the post annealing was carried out at 700 degrees C for 30 min. As the experimental results, the effectiveness of amorphous-like WNx/W bilayered diffusion barrier is attributed to stuff grain boundary with N atoms as well as to eliminate the rapid diffusion paths by using CVD a-W material.