Browsing by Author "Chu, TC"

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Application of VSC reliable design to spacecraft attitude tracking
(2005)
Liang, YW
;
Xu, SD
;
Chu, TC
;
Cheng, CC
;
Liaw, DC
This study investigates variable structure reliable control issues of nonlinear systems and its applications to spacecraft attitude tracking problems. The proposed passive reliable control laws must know in advance which group of actuators is allowed to fail. These reliable controllers need not the solution of Hamilton-Jacobi (HJ) equation or inequality that are essentials in optimal approaches such as LQR and Hoo reliable designs. As a matter of fact, this approach is able to relax the computational load in computing the solution of HJ equation. The proposed reliable designs are also applied to spacecraft attitude tracking problems to explain their effectiveness and benefits. Finally, simulation results and comparisons between LQR and Variable Structure Control (VSC) reliable designs are presented to illustrate the merits of the proposed scheme. Although the proposed design is a passive one, it may provide a guideline for active design when a Fault Detection and Diagnosis (FDD) scheme is available.
Characterization and lithographic parameters extraction for the modified resists
(1999)
Ko, FH
;
Lu, JK
;
Chu, TC
;
Huang, TY
;
Yang, CC
The modification of the i-line resist structure after spiking with various amount of poly(4-vinylphenol) polymer is characterized by the spectra of ultraviolet visible (UV-VIS) and gel permeation chromatography (GPC). The chemical structure of photoactive compound is found to be unchanged after modification, while slight change in the polymer chain is observed. The resist layer coated onto the wafer is characterized by various methods including n&k analyzer, Nanospec, Fourier transform infrared red (FTIR), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC) to fully evaluate the film properties in terms of porosity, thickness, vibrational spectrum, and thermal stability. Our thermal analysis results show that the resists are mainly decomposed in three stages. The photoactive compound (PAC) is found to decompose during the first stage, while the polymer decomposes during the latter stages. The resist exposure parameters, namely, A, B and C at 365 mn are determined by the absorbance measurement. The extracted parameters are further used in the resist profile simulation by PROLITH/2. It is shown that the spiking of poly(4-vinylphenol) polymer into the resist can improve the resolution and linearity for dense lines. In addition, the swing effects can be reduced by up to 35 and 31 % for dense and isolated lines after resist modification, respectively.
Characterization of imprinting polymeric temperature variation with fluorescent Rhodamine B molecule
(2006-04-01)
Ko, FH
;
Weng, LY
;
Ko, CJ
;
Chu, TC
;
材料科學與工程學系奈米科技碩博班
The method to measure the imprint temperature variation of resist film with fluorescence probe technique was established. The maximal Rhodamine B concentration was 8 X 10(-4) M to achieve higher sensitivity and avoid precipitation problem. The temperature effect was a critical parameter on the temperature sensing, while imprinting pressure was not. The fluorescence intensity of Rhodamine B linearly decayed with time at various temperatures due to the formation of lactone-containing molecule during thermal stressing. The usual imprint time of less than 20 min was not affected by the signal decay effect due to limited percentage of signal variation during 100200 degrees C. The technique based on fluorescence probe method was successfully applied to measure the resist temperature variation of the imprint on the resist film of 6-in. wafer. (c) 2006 Elsevier B.V. All rights reserved.
Evaluation of cleaning efficiency with a radioactive tracer and development of a microwave digestion method for semiconductor processes
(2000-02-29)
Lu, JK
;
Ko, FH
;
Chu, TC
;
Sun, YC
;
Wang, MY
A radioactive tracer technique was applied to investigate the effectiveness of various wet cleaning recipes in removing metallic impurities such as sodium, iron and cesium. The effects of solution temperatures and substrate types were studied. The mechanisms of the electrochemical segregation of metallic impurities between the substrate and cleaning solution were examined. The enthalpy of oxide formation and the effect of adsorption were the two reasons for the presence of surface metal impurities in the cleaning solutions. Our results indicated that SC2 and DHF can effectively remove the metallic impurities at 47 and 82 degrees C, while SPM and BOE are only effective at 82 degrees C. The gravimetric method was successfully implemented to evaluate the open-focused microwave digestion efficiency for anti-reflective coating and photoresist (PR) samples. By following the established microwave digestion method and inductively coupled plasma mass spectrometric determination, the detection limits (DLs) obtained for multi-elements were in the ng ml(-1) and sub-ng ml(-1) levels. Except for calcium, the spike recoveries of the metals were in the range 82-121% for the lithographic samples. The analytical results were found to be in reasonably good agreement with literature values, and the lithographic sample throughput can achieve up to 3.5 samples per hour for the analysis of 13 elements. (C) 2000 Elsevier Science B.V. All rights reserved.
Fabrication of sub-60-nm contact holes in silicon dioxide layers
(2004-06-01)
Ko, FH
;
You, HC
;
Chu, TC
;
Lei, TF
;
Hsu, CC
We have developed a fabrication technique, comprising electron-beam writing, chemical shrinking, and silicon dioxide etching, for the fabrication of sub-60-nm contact holes. The dimensions of the contact holes after the electron-beam writing, chemical shrinkage, and plasma etching steps were 140, 93, and 53 nm, respectively. We carefully evaluated the critical process parameters, such as mixing-bake temperature, mixing-bake time, plasma etch selectivity, and the profile shapes. A higher mixing-bake temperature led to an overhang of the contact hole in the resist; the optimal mixing-bake conditions occur when heating at 110 degreesC for 70 s. A fluorinated mixture of gases (CHF3/CF4 = 1:1) was used to etch the nano-scale contact holes in the silicon dioxide layer. The formation of side-wall polymers during the plasma etch phase contributed further to the contact hole shrinkage in addition to resist chemical shrinkage. The ratio of the hole's perimeter to its area affects the shrinkage dimensions of the etch process, especially for smaller contact holes. The pattern reduction due to side-wall polymer deposition in etch process has the inverse relationship with the diameter of contact hole. (C) 2004 Elsevier B.V. All rights reserved.
Numerical simulation of flow pattern formation in a bottom heated cylindrical fluid layer
(1996-10-01)
Li, YH
;
Chu, TC
;
Lin, TF
;
機械工程學系
;
Department of Mechanical Engineering
The temporal formation of the buoyancy-driven flow structures in a bottom heated, shadow, cylindrical fluid layer was numerically studied. The unsteady three-dimensional Navier-Stokes and energy equations were discretized by the power law scheme and solved by the fully implicit Marker-and-Cell method. Computations were carried out for the pressurized argon (Pr = 0.69) and wafer (Pr = 6.1) layers for various Rayleigh numbers and heating rates of the layer. ln the pressurized argon layer at a slightly supercritical Rayleigh number with Ra-f = 1.05Ra(c), a steady straight roll pattern was formed when the heating rate was very slow (a = 0.001) after a long transient stage. When the heating rate was raised to a = 0.01, a very different structure like U-rolls was formed at steady state. In the water layer with Ra-f = 1.05Ra(c), a straight roll pattern was again formed, hut at a = 0.01. At Ra-f = 1.13Ra(c), curved rolls with the three foci at the sidewall were formed for a = 0.01. A pattern in the form of U-rolls appears at a = 0.01. Regular concentric circular rods prevail at a = 1.0. When the Rayleigh number is further raised to 1.23Ra(c), the resulting steady flow is dominated by incomplete circular rolls with open ends near theta = 0 degrees.
Numerical simulation of flow pattern formation in a bottom heated cylindrical fluid layer
(1996-10-01)
Li, YH
;
Chu, TC
;
Lin, TF
;
機械工程學系
;
Department of Mechanical Engineering
The temporal formation of the buoyancy-driven flow structures in a bottom heated, shadow, cylindrical fluid layer was numerically studied. The unsteady three-dimensional Navier-Stokes and energy equations were discretized by the power law scheme and solved by the fully implicit Marker-and-Cell method. Computations were carried out for the pressurized argon (Pr = 0.69) and wafer (Pr = 6.1) layers for various Rayleigh numbers and heating rates of the layer. ln the pressurized argon layer at a slightly supercritical Rayleigh number with Ra-f = 1.05Ra(c), a steady straight roll pattern was formed when the heating rate was very slow (a = 0.001) after a long transient stage. When the heating rate was raised to a = 0.01, a very different structure like U-rolls was formed at steady state. In the water layer with Ra-f = 1.05Ra(c), a straight roll pattern was again formed, hut at a = 0.01. At Ra-f = 1.13Ra(c), curved rolls with the three foci at the sidewall were formed for a = 0.01. A pattern in the form of U-rolls appears at a = 0.01. Regular concentric circular rods prevail at a = 1.0. When the Rayleigh number is further raised to 1.23Ra(c), the resulting steady flow is dominated by incomplete circular rolls with open ends near theta = 0 degrees.
Probing the microwave degradation mechanism of phenol-containing polymeric compounds by sample pretreatment and GC-MS analysis
(2004-11-22)
Chang, YC
;
Ko, FH
;
Ko, CJ
;
Chu, TC
;
材料科學與工程學系奈米科技碩博班
We have detected the volatile organic species obtained after microwave digestion of poly(hydroxystyrene) with nitric acid in closed vessels at various reaction temperatures by using headspace solid-phase microextraction (HS-SPME) and gas chromatography/mass spectrometry (GC-MS). We probed the digestion reaction by measuring the response of the detectable species - we detected a total of 20 volatile organic compounds - with respect to the temperature over the range from room temperature to 80 degreesC. These compounds can be classified into alkane, alkanol, and aromatic species. The alkane species decreased monotonically, whereas the alkanol and aromatic compounds first increased and then decreased, as the digestion temperature increased. We have established the degradation mechanisms, which involve bond scission, recombination, adduct formation, and ring opening, on the basis of product analyses and bond length simulations. (C) 2004 Elsevier B.V. All rights reserved.
Purification of multi-walled carbon nanotubes through microwave heating of nitric acid in a closed vessel
(2005)
Ko, FH
;
Lee, CY
;
Ko, CJ
;
Chu, TC
;
材料科學與工程學系奈米科技碩博班
We demonstrate that microwave-assisted heating in 5mL of nitric acid eliminates impurities, such as amorphous carbon, carbon nanoparticles, and metals, from multi-walled carbon nanotubes (MWNTs). Heating the closed reaction vessel under microwave irradiation at 160degreesC for 30min is a very effective means of purifying the MWNTs. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images confirm that these reaction conditions are beneficial for removing the impurities and ensuring that the MWNTs remain intact. In contrast, a purification temperature of 180degreesC provides too strongly oxidizing conditions that destroy the MWNTs. The ratio of the G and D bands in the Raman spectra also confirms that a temperature of 160degreesC. is optimal. The defect peak that we observed in the differential thermogravimetry (DTG) analysis of the raw material was not present after microwave purification. The presence of metal impurities in the MWNTs can be reduced significantly when using this method. (C) 2004 Elsevier Ltd. All rights reserved.
Reliable control of nonlinear systems via variable structure scheme
(2003)
Liang, YW
;
Chu, TC
;
Liaw, DC
;
Cheng, CC
;
電控工程研究所
This study proposes a class of reliable Variable Structure Control (VSC) laws, which are shown to be able to tolerate the outage of actuators within a prespecified subset of actuators. The gain margins of guaranteeing system stability are estimated, which depend on control parameters and are larger than those obtained by LQR reliable design (Veillette, 1995 and Liang et. al., 2000). In addition, this approach does not need to solve the Hamilton-Jacobi equation or inequality, which is known difficult to solve and is an essential part in the reliable LQR and H-infinity designs. As a matter of fact, this approach can also relax the computational load for solving the Hamilton-Jacobi inequality.
Reliable output tracking control for a class of nonlinear systems
(2004-09-01)
Liang, YW
;
Xu, SD
;
Chu, TC
;
Cheng, CC
;
電控工程研究所
This study investigates nonlinear reliable output tracking control issues. Both passive and active reliable control laws are proposed using Variable Structure Control technique. These reliable laws need not the solution of Hamilton-Jacobi (HJ) equation or inequality, which are essential for optimal approaches such as LQR and H-infinity reliable designs. As a matter of fact, this approach is able to relax the computational burden for solving the HJ equation. The proposed reliable designs are also applied to a bank-to-turn missile system to illustrate their benefits.
Robust attitude control for spacecraft
(2002)
Liang, YW
;
Chu, TC
;
Cheng, CC
;
電控工程研究所
;
Institute of Electrical and Control Engineering
This paper, deals with the spacecraft attitude tracking problems in the presence of model uncertainties and external disturbances. A modified VSC design scheme is proposed by the use of Variable Structure Control (VSC) design technique. These modified VSC laws are continuous, which are shown able to alleviate chattering drawback inherited from sign-type VSC controllers and enhance the uniformly ultimate boundedness performance suffered by saturation-type ones to asymptotic stability level. Numerical simulations are also given to demonstrate the benefits of the proposed VSC scheme.