Browsing by Issue Date, starting with "1997-08-15"

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Growth process of Ge on Si(100)-(2x1) in atomic-layer epitaxy from Ge2H6
(1997-08-15)
Huang, KH
;
Ku, TS
;
Lin, DS
;
物理研究所
;
Institute of Physics
This study investigates the growth process of Ge on Si(100) during atomic-layer epitaxy (ALE) utilizing digermane. The surface ordering, morphology, and stoichiometry of the digermane saturated Si(100) surface at temperatures between 300 and 900 K, as well as the grown films are examined both by scanning tunneling microscopy (STM) and high-resolution core-level photoemission spectroscopy employing synchrotron radiation. An exposure of more than 15 L (1 L=10(-6) T s) of digermane on the Si(100)-(2x1) surface at room-temperature results in a saturated and disordered surface. When the digermane saturated surface is heated to 725 K for 60 s, diluted Ge dimer chains are created and surrounded by SiH species. Further annealing to 810 K completely desorbs hydrogen from the surface, leaving large two-dimensional islands covering similar to 41% of its area. The surface recovers its smooth 2x1 structure, but is interspersed with poorly ordered short dimer vacancy lines at 900 K with no observable contrast on the atomic terraces, indicating displacive adsorption of Ge on the terraces. Significant differences of the surface diffusion phenomena between the gas-phase and solid-phase molecular-beam epitaxy (MBE) are observed. Multilayer Si deposition is performed by ALE, i.e., cyclic digermane adsorption at near room temperature, followed by thermal annealing at 900 K. STM images reveal the formation of 2 x n structures and increasing roughening of the surface as the growth cycle increases, similar to what occurs during MBE. Issues related to the atomic origins of surface core-level shifts and the chemical composition of the surface layer resulting from the formation of mixed Ge-Si or Ge-Ge during the submonolayer adsorption of Ge on Si(100) are also discussed.
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.
Impurity screening in carbon nanotubes
(1997-08-15)
Lin, MF
;
Chuu, DS
;
電子物理學系
;
Department of Electrophysics
Nanotube geometry determines electronic structure and thus impurity screening. A metallic carbon nanotube could effectively screen a charged impurity, while a semiconducting carbon nanotube could not. The ability to screen a long-range Coulomb field is mainly determined by whether there are: Free carriers in the subbands nearest the Fermi level. The detailed screening propel-ties are sensitive to the impurity position, and the tubular structure (such as radius and chiral angle). Strong, short-wavelength Friedel oscillations at long distances are found to exist only in metallic armchair nanotubes. They are relatively obvious for a smaller armchair nanotube, and could survive at room temperature.
Hyper-Rayleigh scattering of thiophene-incorporated polyene chromophores with pi-configuration locking
(1997-08-15)
Hsu, CC
;
Shu, CF
;
Huang, TH
;
Wang, CH
;
Lin, JL
The hyper-Rayleigh scattering (HRS) technique is used to determine and compare the first hyperpolarizabilities (beta) of thiophene-incorporated polyene chromophores with and without a configuration locked trans-triene bridge, To ensure the purity of the HRS signal, special attention is paid to its dependence on the fundamental intensity and the spectral content of the scattered radiation including the two-photon absorption induced fluorescence. From the HRS results, it is found that the configuration-locked trans-triene bridge enhances the beta values of the chromophores studied, The beta-enhancement is more pronounced when the electron acceptor CHC(CN)(2) in the chromophores is replaced with C-2(CN)(3). (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.
蒼坡村是一株宋朝的木芙蓉
(1997-08-16)
管管
Field and temperature effects on oxide charge detrapping in a metal-oxide-semiconductor field effect transistor by measuring a subthreshold current transient
(1997-08-25)
Chiang, LP
;
Zous, NK
;
Wang, TH
;
Chang, TE
;
Shen, KY
A technique to characterize oxide charge detrapping in a Fowler-Nordheim stressed n-metal-oxide-semiconductor field effect transistor is proposed. This technique consist of two alternating phases, an oxide charge detrapping phase and a subthreshold current measurement phase. An analytical model relating a subthreshold current transient to oxide charge density and detrapping time constants was derived. By varying the gate bias in the detrapping phase and the ambient temperature, the field and temperature dependences of oxide charge detrapping can be obtained from the subthreshold current transients measured. (C) 1997 American Institute of Physics.
Characterization of yttria-stabilized zirconia thin films grown by planar magnetron sputtering
(1997-08-28)
Tsai, WC
;
Tseng, TY
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Yttria-stabilized zirconia (YSZ) thin films were grown on Si by rf magnetron sputtering. Sputtering gun was positioned at various angles to the substrate normal to change the amount of plasma bombardment on the as-deposited films. YSZ films grown by off-axis sputtering (90 degrees) are readily (200)-preferred orientated but the preferred orientation of the film is deteriorated when the growth angle is decreased and, consequently, plasma bombardment is increased due to the decreasing growth angles. The off-axis grown YSZ films exhibit atomically smooth interfaces, which are not observed for those films grown by on-axis sputtering. The variation of oxide charge with the growth angle is studied with the Al/YSZ/Si structure. The plasma bombardment plays an important role on the crystallinity and, therefore, the defect type of the films and is also considered to be responsible for the Si outdiffusion occurring in an on-axis grown film. (C) 1997 Elsevier Science S.A.
Computation of unstable liquid metal convection in a vertical closed cylinder heated from the side and cooled from above
(1997-08-29)
Li, YH
;
Lin, KC
;
Lin, TF
;
機械工程學系
;
Department of Mechanical Engineering
Three-dimensional unsteady numerical computation was carried out to investigate buoyancy-driven unstable convection processes in a side-wad-heated and top-wad-cooled vertical closed cylinder containing liquid metal. The time-dependent basic flow equations were directly solved by the implicit Marker-and-Cell (MAC) scheme with the power law approximation to treat the convection-diffusion couplings. Results were obtained for liquid metal (Pr = 0.02) in a cylinder of finite aspect ratio (Gamma = 2) for various Rayleigh numbers. The predicted results indicate that the flow is relatively unstable except at low buoyancy. Specifically, of Ra = 2000 the flow evolves to a steady state but is highly asymmetric. As Ra = 3000 and 4000, the flow Becomes time periodic after the transient has died out with increasing asymmetry. At a still higher buoyancy the oscillation amplitude and flow asymmetry get larger, and a second fundamental frequency appears. The flow is quasi-periodic. Qualitatively, the flow structure is characterized by a main recirculation ill the major portion of the cylinder along with two uprising smaller cells near the side wall in the bottom half of the cylinder and another two counter rotating cells in the top half of the cylinder Finally, the critical Rayleigh number for the transition from a steady to a time periodic state was evaluated.
Computation of unstable liquid metal convection in a vertical closed cylinder heated from the side and cooled from above
(1997-08-29)
Li, YH
;
Lin, KC
;
Lin, TF
;
機械工程學系
;
Department of Mechanical Engineering
Three-dimensional unsteady numerical computation was carried out to investigate buoyancy-driven unstable convection processes in a side-wad-heated and top-wad-cooled vertical closed cylinder containing liquid metal. The time-dependent basic flow equations were directly solved by the implicit Marker-and-Cell (MAC) scheme with the power law approximation to treat the convection-diffusion couplings. Results were obtained for liquid metal (Pr = 0.02) in a cylinder of finite aspect ratio (Gamma = 2) for various Rayleigh numbers. The predicted results indicate that the flow is relatively unstable except at low buoyancy. Specifically, of Ra = 2000 the flow evolves to a steady state but is highly asymmetric. As Ra = 3000 and 4000, the flow Becomes time periodic after the transient has died out with increasing asymmetry. At a still higher buoyancy the oscillation amplitude and flow asymmetry get larger, and a second fundamental frequency appears. The flow is quasi-periodic. Qualitatively, the flow structure is characterized by a main recirculation ill the major portion of the cylinder along with two uprising smaller cells near the side wall in the bottom half of the cylinder and another two counter rotating cells in the top half of the cylinder Finally, the critical Rayleigh number for the transition from a steady to a time periodic state was evaluated.
Analysis and synthesis of geometric models using tree structured relations
(1997-09-01)
Tsai, PL
;
Fu, CC
;
Chieng, WH
;
機械工程學系
;
Department of Mechanical Engineering
In this study, we propose a methodology capable of analysing and synthesizing relational geometric design models, based on a mapping between geometric nodes (points) on the model and the physical dimensions of the solid model. The relations that include translation and rotation between the geometric nodes are stored in a toe structure. Based on this methodology, an implementation is developed that allows a designer to freely synthesize and analyse geometric relations among admissible physical dimensions of the object. Meanwhile the management of the underlying parameterized relational geometric data automatically occurs. (C) 1997 Elsevier Science Ltd.
The oxidation mechanism of low-pressure dry oxidation of nitrides for memory devices
(1997-09-01)
Liu, HW
;
Su, HP
;
Lai, WK
;
Cheng, HC
;
電子工程學系及電子研究所
To be utilized in the high density dynamic random access memory devices, low-pressure dry oxidation of the very thin nitrides has been performed to successfully obtain the ultrathin capacitors' dielectrics with the effective oxide thickness (t(ox,eff)) of 30 - 60 Angstrom. For the electrical properties, the low-pressure dry oxidized (LPDO) nitrides express thinner effective oxide thickness, lower leakage current, and higher reliability than do the atmospheric pressure dry oxidized (APDO) nitrides. After analyzing the diluted HF etching profiles, Auger electron spectrum and Fourier transform infrared spectrum data, an oxide/nitride/oxide (O/N/O) structure is realized for the LPDO samples with respect to the nitride/oxide structure for the APDO ones. This ultrathin O/N/O structure is believed to be the main cause of improving the electrical characteristics. Finally, a low-pressure enhanced oxidation model is also proposed to explain the unusual oxidation phenomenon on the top of the nitride films. The mechanisms of APDO and atmospheric pressure wet oxidation of nitride films are also compared.
Thin oxides with in situ native oxide removal
(1997-09-01)
Chin, A
;
Chen, WJ
;
Chang, T
;
Kao, RH
;
Lin, BC
We have studied the inversion layer mobility of n-MOSFET's with thin-gate oxide of 20 to 70 Angstrom. Direct relationship of electron mobility to oxide/channel interface roughness was obtained from measured mobility of MOSFET's and high-resolution TEM. By using a low-pressure oxidation process with native oxide removed in situ prior to oxidation, atomically smooth interface of oxide/channel was observed by high-resolution TEM for oxide thicknesses of 11 and 38 Angstrom. The roughness increased to one to two monolayers of Si in a 55-Angstrom oxide. Significant mobility improvement was obtained from these oxides with smoother interface than that from conventional furnace oxidation. Mobility reduction with decreasing oxide thickness was observed in the 20- and 35-Angstrom oxide, with the same atomically smooth oxide/channel interface. This may be due to the remote Coulomb scattering from gate electrode or the gate field variation from poly-gate/oxide interface roughness.
Polynomial approximation coding for progressive image transmission
(1997-09-01)
Lu, CY
;
Chen, AY
;
Wen, KA
;
交大名義發表
;
National Chiao Tung University
This paper presents a progressive image transmission scheme in which polynomial approximation coding is effectively applied to encoding residual images at each stage. This polynomial approximation coding is derived from a regressive model based on the relation between a set of data and their positions. Because the close relation is embedded in a certain polynomial function, the highly efficient compression can be implemented and the decimation and interpolation are also easily realized at the receiving side. Simulations and experimental results are discussed in the later part of this paper. (C) 1997 Academic Press.
Polynomial approximation coding for progressive image transmission
(1997-09-01)
Lu, CY
;
Chen, AY
;
Wen, KA
;
交大名義發表
;
National Chiao Tung University
This paper presents a progressive image transmission scheme in which polynomial approximation coding is effectively applied to encoding residual images at each stage. This polynomial approximation coding is derived from a regressive model based on the relation between a set of data and their positions. Because the close relation is embedded in a certain polynomial function, the highly efficient compression can be implemented and the decimation and interpolation are also easily realized at the receiving side. Simulations and experimental results are discussed in the later part of this paper. (C) 1997 Academic Press.
An efficient conflict-resolution approach to support read/write operations in a video server
(1997-09-01)
Lee, CI
;
Chang, YI
;
Yang, WP
;
資訊工程學系
;
Department of Computer Science
In this paper, we propose an efficient conflict-resolution approach based on the multi-disk architecture for the insertion/deletion operations on continuous media that are split up into blocks and placed in various locations on the disk, without reorganizing the whole data. When a new subobject is inserted after subobject i, it will be assigned with an identification number (i+1) and be inserted into a disk in which the retrieval of the new subobject does not conflict with the retrieval of any other subobject, where a conflict means a pair of two consecutive subobjects that are stored in the same disk have to be retrieved simultaneously However, a new conflict on the same disk may occur since all the identification numbers of subobjects after subobject i are increased by one. Only when such a new conflict occurs, one movement operation is required, so does the case of a deletion operation. Moreover, to reduce those additional movement cost, a deferring approach is proposed at the cost of an additional buffer. In this approach, n data insertions are deferred and stored in a buffer. Then, the system starts to insert those data after an optimal insertion sequence is determined. Based on this approach, two strategies are proposed: the conflict-resolved-first-deferring strategy (the CRFD strategy) and the conflict-resolved-last-deferring strategy (the CRLD strategy). From our performance analysis, we will prove that the CRLD strategy with an insertion sequence according to the ascending order of identification numbers is an optimal strategy based on the proposed deferring approach.
Design of a rule-based continuous process controller using modified IDEF0 methodology
(1997-09-01)
Chen, SG
;
Wu, MZ
;
Li, RK
;
工業工程與管理學系
;
Department of Industrial Engineering and Management
This article proposes a new method to design a rule-based Continuous Process (CP) controller. This approach adopts Modified IDEF0 (MI) diagrams as a graphical representation of production rules. Initially, the material flows or functional requirements for the CP are specified by synthesizing the MI diagram primitives. The control flows for the CP are then created by a number of transformation rules. The MI diagrams are therefore transformed to the Final MI (FMI) diagrams which can be directly transformed to production rules. The fact that production rules are created by systematical transformation eliminates any redundant, contradictory, or unnecessary rules. The simulation approach can verify the consistency of the designed CP controller. Thus, a feasible rule-based CP controller can be systematically developed. An illustrative gas transmission system is examined with three manufacturing policies, i.e. Proportional plus Integral plus Derivative (PID) control, Neural control and Fuzzy control. The results indicate that all of these policies are feasible in applying the proposed method. This method not only provides graphical representations to construct well-organized production rules, but also includes a systematical transformation of the control flows for a CP controller.
Full-wave segmentation analysis of arbitrarily shaped planar circuit
(1997-09-01)
Liu, SP
;
Tzuang, CKC
;
電信工程研究所
;
Institute of Communications Engineering
This paper presents a novel full-wave segmentation method for analyzing a complex and large microwave planar circuit which is divided into several smaller segments with corresponding multiport network parameters, They are obtained by a full-wave space-domain integral-equation technique in connection to a proposed excitation model based on the equivalence principle, The integral equation is solved numerically by Galerkin's procedure resulting in the generalized scattering-matrix (GSM) descriptions of all the subcircuit segments. The combination of these GSM's yields an overall network characterization of the composite circuit, Rigorous convergence studies and extensive validity checks confirm the reliability and accuracy of the proposed method, The novel technique immediately demonstrates its obvious application for quantitative characterization of higher order modes associated with a microwave-circuit discontinuity problem, Finally, very good agreement is obtained in a comparative study of an arbitrary planar structure analyzed by our full-wave method with and without segmentation, respectively.
Monitoring trapped charge generation for gate oxide under stress
(1997-09-01)
Lin, YH
;
Lee, CL
;
Lei, TF
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
A measurement method to extract the respective quantities and centroids of positive and negative trapped charges, i.e., Q(p) and Q(n), generated by the negative current stress for gate oxides is proposed and demonstrated, The method is based on neutralization of Q(p) by a low positive current stress to differentiate the effects of Q(p) and Q(n). From the extracted quantities and centroids of Q(p) and Q(n) of negatively stressed oxides, it was found that Q(p) and Q(n) are generated near the oxide/substrate interface and Q(p) is initially much larger than Q(n). After the continuous stressing, Q(p) saturates and moves closer to the interface, but Q(n) keeps increasing and moves away from the interface, especially for those oxides after the post-poly anneal (PPA) treatment, Q(n) is very unstable and easily neutralized, either by a small stress of opposite polarity or the same polarity, For the latter, Q(n) is mainly dependent on the level of the final stressing field.
Monitoring trapped charge generation for gate oxide under stress
(1997-09-01)
Lin, YH
;
Lee, CL
;
Lei, TF
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
A measurement method to extract the respective quantities and centroids of positive and negative trapped charges, i.e., Q(p) and Q(n), generated by the negative current stress for gate oxides is proposed and demonstrated, The method is based on neutralization of Q(p) by a low positive current stress to differentiate the effects of Q(p) and Q(n). From the extracted quantities and centroids of Q(p) and Q(n) of negatively stressed oxides, it was found that Q(p) and Q(n) are generated near the oxide/substrate interface and Q(p) is initially much larger than Q(n). After the continuous stressing, Q(p) saturates and moves closer to the interface, but Q(n) keeps increasing and moves away from the interface, especially for those oxides after the post-poly anneal (PPA) treatment, Q(n) is very unstable and easily neutralized, either by a small stress of opposite polarity or the same polarity, For the latter, Q(n) is mainly dependent on the level of the final stressing field.