Browsing by Author "Chou, C. P."

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A novel scrape-applied method for the manufacture of the membrane-electrode assembly of the fuel-cell system
(2009-12-01)
Wu, S. D.
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Chou, C. P.
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Peng, R. G.
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Lee, C. H.
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Wang, Y. Z.
This study investigates the transfer of the scrape-applied method from the electrodes of a lithium battery to the membrane-electrode assembly of fuel cells, including Proton Exchange Membrane Fuel Cells and Direct Methanol Fuel Cell. Three methods are commonly used to manufacture lithium battery electrodes: the roller-applied method, the spraying-applied method, and the scrape-applied method. This study develops novel scrape-applied equipment for lithium battery electrodes. This method is novel and suitable for producing fuel cell, better than other traditional methods. In this study, the stability of coating process was tested by measuring the weight and thickness of a dry electrode. The stability and reproducibility of electrode fabrication were examined by systematic data analysis. Finally, the study used a specially designed single cell composed of 16 conductive segments, which are insulated locally. The current passing through each segment was measured using Hall Effect sensors connected to the segment compartments. Based on the measured distribution of the local current in a segmented single cell, the influence of flooding and stoichiometry variation of feed gas was discussed in terms of electrochemical reaction rate. The experimental results serve as an important basis for future research in this field, which hold potential benefits to the academia and the industry.
Antireflection subwavelength structures analyzed by using the finite difference time domain method
(2009)
Ting, Chia-Jen
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Chen, Chi-Feng
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Chou, C. P.
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機械工程學系
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Department of Mechanical Engineering
Antireflection subwavelength structures (ASSs) are analyzed by using the finite difference time domain (FDTD) method in the visible light spectrum. Low reflectance can be obtained by both the conical and pyramidal shapes over a broadband range. Comparing the reflectance of different structure shapes and aspect ratios by the FDTD method, it shows that the antireflection efficiencies of the pyramidal structures are better than that of the conical structures when the aspect ratio is up to 0.8. It is found that, for the conical structure surface, the average transmittance increases gradually with the aspect ratio and the average transmittance is about 99.6% with the aspect ratio of 2.0. However, for the pyramidal structure with the aspect ratio ranging from 1.0 to 2.0, the average transmittance is up to 99.7%. (C) 2008 Elsevier GmbH. All rights reserved.
Characterization of Hot Cracking Due to Welding of High-Strength Aluminum Alloys
(2012)
Chang, C. C.
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Chen, C. L.
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Wen, J. Y.
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Cheng, C. M.
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Chou, C. P.
The "Spot-Varestraint Test'' was applied to assess the sensitivity of three aluminum alloys-A2024-T351, A2219-T87, and A7050-T6 to hot cracking from welding. The results indicate that the number of cracks increases with increasing augmented strain. This phenomenon occurs in both the fusion and the heat-affected zones. The number of thermal cycles also has a significant influence on the heat-affected zone; the number of hot cracks increases, especially in the heat-affected zone of the metal weld, with increasing number of thermal cycles. The compositions of these three alloys show that A2024 and A7050 have similar tendencies to be subject to hot cracking, greater than A2219. With increasing number of thermal cycles, the hot cracks show the same tendency, A2024 > A7050 > 2219.
Effect of adding Sc and Zr on grain refinement and ductility of AZ31 magnesium alloy
(2008-02-01)
Wang, S. C.
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Chou, C. P.
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機械工程學系
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Department of Mechanical Engineering
Grain size in the microstructure dominates the ductility of Mg-Al-Zn magnesium alloy. The strengthening and grain refinement of aluminum alloys by Sc have been extensively studied recently. As is well known, Zr refines grains in magnesium alloys. This work presents a novel approach for enhancing the grain refinement of magnesium alloy by adding Sc and Zr. Rolling and equal channel angular extrusion (ECAE) are performed to refine the grains. Experimental results indicate that adding 0.03-0.06 wt% of Sc and 0.05-0.15 wt% of Zr reduced the mean grain size of AZ31 to 2.47 mu m. The ductility of AZ31-0.15Zr-0.06Sc modified alloy can be increased to 324% at 300 degrees C. Results of this study demonstrate that both Sc and Zr are important in controlling grain size and ductility. (C) 2007 Elsevier B.V. All rights reserved.
Effect of Laser Welding on Properties of Dissimilar Joint of Al-Mg-Si and Al-Mn Aluminum Alloys
(2010-03-01)
Chang, C. C.
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Chou, C. P.
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Hsu, S. N.
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Hsiung, G. Y.
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Chen, J. R.
This study discusses the welding properties for the components of an aluminum-alloy ultra-high vacuum chamber and beam position monitor (BPM). The welding parameters include the modes of laser output (pulsed wave and continuous wave), welding speed, shield gas flow, welding bead structure, and focusing distance. The results showed that the welding defect rate of the pulsed wave type was larger than that of the continuous wave type. The crack in the welding bead reduced with decreasing welding speed. The fusion penetration of the welding bead was higher when the focusing distance was long enough to deepen into the welding material. Weld morphology during the experimental process revealed the proper flow of shield gas. The adaptability design of the welding bead structure in the preceding processes had more effect on overall welding structure and morphology.
Effects of sputtering pressure and Al buffer layer thickness on properties of AZO films grown by rf magnetron sputtering
(2010-08-20)
Tseng, C. H.
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Wang, W. H.
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Chang, H. C.
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Chou, C. P.
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Hsu, C. Y.
Transparent and conductive Al-doped (2 wt.%) zinc oxide (AZO) films were deposited on inexpensive soda-lime glass substrates by using rf magnetron sputtering at room temperature. This study analyzed the effects of argon sputtering pressure, which varied in the range from 0.46 to 2.0 Pa, on the morphological, electrical and optical properties of AZO films. The only (0 0 2) diffraction peak of the film were observed at 20 similar to 34.45 degrees, exhibiting that the AZO films had hexagonal ZnO wurtzite structure, and a preferred orientation with the c-axis perpendicular to the substrate. By applying a very thin aluminum buffer layer with the thickness of 2 nm, findings show that the electrical resistivity was 9.46 x 10(-4) Omega-cm, and the average optical transmittance in the visible part of the spectra was approximately 81%. Furthermore, as for 10 nm thick buffer layer, the electrical resistivity was lower, but the transmittance was decreased. (C) 2010 Elsevier Ltd. All rights reserved.
Evaluation research of polishing methods for large area diamond films produced by chemical vapor deposition
(2007-02-01)
Tsai, H. Y.
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Ting, C. J.
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Chou, C. P.
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機械工程學系
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Department of Mechanical Engineering
The current study compared several polishing techniques of chemical vapor deposition (CVD) diamond films. Although research on various diamond polishing techniques has been carried for years, some issues still need to be examined in order to facilitate application on large areas in a cost-efficient manner. In the present work, microwave plasma enhanced chemical vapor deposition (CVD) was used to obtain diamond films with full width half magnitude (FWHM) less than 10 wavenummbers at 1332 cm(-1) Raman peak. The diamond films were processed through mechanical polishing, chemical-assisted mechanical polishing, thermo-chemical polishing, excimer laser ablation, and catalytic reaction assisted grinding. A profilometer, an atomic force microscope, and a scanning electron microscope have been used to evaluate the surface morphology of diamond Films before and after polishing. The results obtained by using the above mentioned techniques were analyzed and compared. (c) 2006 Elsevier B.V. All rights reserved.
Experimental study of a silver layer on an antireflection subwavelength-structured surface
(2008-07-01)
Ting, Chia-Jen
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Chen, Chi-Feng
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Chou, C. P.
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機械工程學系
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Department of Mechanical Engineering
The optical characteristics of a silver layer deposited on an antireflection subwavelength-structured surface are investigated. The experimental results of the reflectance and the transmittance of several different thicknesses of silver layer on the subwavelength-structured surface are carried out. A subwavelength structure with the spatial period and diameter of about 230 nm and height of about 150 nm on polyethylene terphthalate film is fabricated by microreplication process. It is shown that such an element with the suitable silver layer deposited on an antireflection subwavelength-structured surface has high transmittance and low glare in the visible spectral range and high reflectance in the infrared range. Obviously, the optical film with silver layer can not only obtain the high performance of heat insulation but also give an application in automobile and house windows.
Fabrication of an antireflective polymer optical film with subwavelength structures using a roll-to-roll micro-replication process
(2008-07-01)
Ting, Chia-Jen
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Chang, Fuh-Yu
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Chen, Chi-Feng
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Chou, C. P.
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機械工程學系
An antireflective optical film with subwavelength structures replicated by use of a roll-to-roll micro-replication process (RMRP) is investigated. Firstly, a single layer of a nanostructure on a polymer film is designed for an antireflection purpose by the finite difference time domain method in the visible light spectrum. Structures of a conical cylinder array, with spatial period of 400 nm, diameter of 200 nm and height of 350 nm, are numerically obtained. Then, such structures are fabricated by RMRP combining originated structure fabrication realized by deep ultra-violet lithography and dry etching, Ni mold electroplating and replication by using the roll-to-roll process imprinting into the flexible polyethylene terephthalate substrate. A nanostructure roller mold bonded with Ni molds has been successfully fabricated and coated with the self-assembly monolayer process for the purpose of fabricating an anti-adhesion film and improving the lifetime of the Ni molds. The duplicated nanostructure films show a good optical quality of antireflection (AR <= 2.45% in a 400-700 nm spectral range) and are in good agreement with the theoretical predictions. The experimental results show that the developed process is a promising and cost-effective method for the continuous duplication of flexible devices with nano-scaled feature sizes used in nanophotonics by RMRP.
Finite difference time domain analysis of 3-D sub-wavelength structured arrays
(2007-01-01)
Ting, C. J.
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Tsai, H. Y.
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Hsu, C. J.
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Chou, C. P.
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機械工程學系
GROWTH OF AZO FILMS ON BUFFER LAYERS BY RF MAGNETRON SPUTTERING
(2010-12-20)
Chen, C. W.
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Tseng, C. H.
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Hsu, C. Y.
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Chou, C. P.
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Hou, K. H.
Al(2)O(3)-doped zinc oxide (in AZO, the Al(2)O(3) contents are approximately 2 wt.%) films have been grown by radio frequency (RF) magnetron sputtering at room temperature under varied sputtering pressures ranging from 3.5-15 mTorr. The electrical resistivity of AZO films is about 2.22 x 10(-3) Omega cm (sheet resistance similar to 89 Omega/square for a thickness similar to 250 nm), and the visible range transmittance is a bout 80% at the argon sputtering pressure of 15 mTorr and a RF power of 100 W. This study analyzes the structural, morphological, electrical and optical properties of AZO thin films grown on soda-lime glass substrate with 2, 5, and 10 nm thick Al buffer layers (and SiO(2) buffer). For the films deposited on the 2 nm thick Al buffer layer, we obtained ac-axis-oriented AZO/Al thin film on glass with the XRD full-width at half maximum (FWHM) of 0.31 and root mean square (RMS) surface roughness of about 3.22 nm. The lowest resistivity of 9.46 x 10(-4) Omega cm (sheet resistance similar to 37.87 Omega/square for a thickness similar to 250 nm) and a high transmittance (80%) were obtained by applying a 2 nm thick Al buffer layer. In contrast, the resistivity was slightly increased by applying the SiO(2) buffer layer.
High density and low leakage current in TiO(2) MIM capacitors processed at 300 degrees C
(2008-08-01)
Cheng, C. H.
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Lin, S. H.
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Jhou, K. Y.
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Chen, W. J.
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Chou, C. P.
We report Ir/TiO(2)/TaN metal-insulator-metal capacitors processed at only 300 degrees C, which show a capacitance density of 28 fF/mu m(2) and a leakage current of 3 x 10(-8) (25 degrees C) or 6 x 10(-7) (125 degrees C) A/cm(2) at -1 V. This performance is due to the combined effects of 300 degrees C nanocrystallized high-kappa, TiO(2), a high conduction band offset, and high work-function upper electrode. These devices show potential for integration in future very-large-scale-integration technologies.
High Performance Ir/TiPrO/TaN MIM Capacitors for Analog ICs Application
(2008)
Huang, C. C.
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Cheng, C. H.
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Chin, Albert
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Chou, C. P.
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電子工程學系及電子研究所
In this paper, we demonstrate high quality material TiPrO and high density Ti(x)Pr(1-x)O (x similar to 0.67) metal-insulator-metal (MIM) capacitors using high work function (similar to 5.3 eV) Ir top electrode. Very low leakage current of 7x10(-9) A/cm(2) at -1 V and high 16 fF/mu m(2) capacitance density are achieved for 400 degrees C anneal TiPrO, which also meets the ITRS goals (at year 2018) of 10 fF/mu m(2) density and J/(C.V) <7 fA/(pF.V). Furthermore, the improved high 20 fF/mu m(2) capacitance density TiPrO MIM is obtained at higher annealing temperature, where low leakage current 1.2x10(-7) A/cm(2) is measured at -1 V. These good performances indicate TiPrO MIM is suitable for analog/RF ICs Applications.
High-Performance MIM Capacitors Using a High-kappa TiZrO Dielectric
(2008)
Cheng, C. H.
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Pan, H. C.
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Lin, S. H.
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Hsu, H. H.
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Hsiao, C. N.
We have fabricated high-kappa Ni/TiZrO/TaN metal-insulator-metal (MIM) capacitors. A low leakage current of 3.3x10(-8) A/cm(2) at -1 V was obtained for a 18 fF/mu m(2) capacitance density. For a 5.5 fF/mu m(2) capacitance density device, a small voltage coefficient of capacitance alpha of 105 ppm/V(2) and temperature coefficient of capacitance of 156 ppm/degrees C were measured. (c) 2008 The Electrochemical Society. [DOI: 10.1149/1.2993977] All rights reserved.
High-temperature leakage improvement in metal-insulator-metal capacitors by work-function tuning
(2007-03-01)
Chiang, K. C.
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Cheng, C. H.
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Pan, H. C.
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Hsiao, N.
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Chou, C. P.
Using low-cost and high work-function Ni, a low leakage current of 5 x 10(-6) A/cm(2) at 125 degrees C is obtained in a high 25-fF/mu m(2)-density SrTiO3 metal-insulator-metal (MIM) capacitor processed at 400 degrees C. This is approximately two orders of magnitude better than the same device using a TaN electrode, with added advantages of improved voltage and temperature coefficients of capacitance. This work-function tuning method also has merit for achieving both low thermal leakage and high overall k value beyond previous laminate structure.
Hot Cracking in AZ31 and AZ61 Magnesium Alloy
(2011-07-01)
Huang, C. J.
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Cheng, C. M.
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Chou, C. P.
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Chen, F. H.
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機械工程學系
This paper examined the impact of the number of thermal cycles and augmented strain on hot cracking in AZ31 and AZ61 magnesium alloy. Statistical analyses were performed. Following observation using a scanning electron microscope (SEM), an energy dispersive spectrometer (EDS) was used for component analysis. Results showed that Al content in magnesium alloy has an effect on hot cracking susceptibility. In addition, the nonequilibrium solidification process produced segregation in Al content, causing higher liquid Mg-alloy rich Al content at grain boundaries, and resulting into liquefied grain boundaries of partially melted zone (PMZ). In summary, under multiple thermal cycles AZ61 produced serious liquation cracking. AZ61 has higher (6 wt%) Al content and produced much liquefied Mg(17)Al(12) at grain boundaries under multiple thermal cycles. The liquefied Mg(17)Al(12) were pulled apart and hot cracks formed at weld metal HAZ due to the augmented strain. Since AZ31 had half the Al content of AZ61, its hot-cracking susceptibility was lower than AZ61. In addition, AZ61 showed longer total crack length (TCL) in one thermal cycle compared to that in three thermal cycles. This phenomenon was possibly due to high-temperature gasification of Al during the welding process, which resulted in lower overall Al content. Consequently, shorter hot cracks exhibited in three thermal cycles. It was found the Al content of AZ31 and AZ61 can be used to assess the hot-cracking susceptibility.
Improved high-temperature leakage in high-density MIM capacitors by using a TiLaO dielectric and an Ir electrode
(2007-12-01)
Cheng, C. H.
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Pan, H. C.
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Yang, H. J.
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Hsiao, C. N.
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Chou, C. P.
We have fabricated high-kappa. TaN/Ir/TiLaO/TaN metal-insulator-metal capacitors. A low leakage current of 6.6 x 10(-7) A/cm(2) was obtained at 125 degrees C for 24-fF/mu m(2) density capacitors. The excellent device performance is due to the combined effects of the high-kappa TiLaO dielectric, a high work-function Ir electrode, and large conduction band offset.
Improved Lower Electrode Oxidation of High-kappa TiCeO Metal-Insulator-Metal Capacitors by Using a Novel Plasma Treatment
(2008)
Cheng, C. H.
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Hsu, H. H.
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Deng, C. K.
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Chin, Albert
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Chou, C. P.
We have fabricated high-kappa Ir/TiCeO/TaN metal-insulator-metal (MIM) capacitors using a dual plasma treatment on bottom electrode. The novel plasma treatment suppresses the growth of bottom interfacial layer to reduce the degradation of capacitor performance under 400 degrees C PDA. A low leakage current of 1.7x10(-7) A/cm(2) at -1 V and capacitance density of similar to 18 fF/mu m(2) at 1 MHz were obtained for 21 nm thick TiCeO MIM devices; moreover, a 37 nn thick TiCeO film has a capacitance density of 11 fF/mu m(2), which gives a kappa value of 45. Consequently, the excellent device performance is due to the combined effects of the dual plasma treatment, high-kappa TiCeO dielectric and a high work-function Ir metal.
Improvement of the performance of TiHfO MIM capacitors by using a dual plasma treatment of the lower electrode
(2008-10-01)
Cheng, C. H.
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Pan, H. C.
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Huang, C. C.
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Chou, C. P.
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Hsiao, C. N.
We show that a conventional nitrogen plasma treatment is insufficient to suppress the formation of an interfacial layer at the bottom electrode of TiHfO metal-insulator-metal (MIM) capacitors. However, the capacitance density and leakage current of TaN/TiHfO/TaN MIM capacitors monotonically improve by exposing the lower TaN electrode to an additional oxygen plasma treatment. By performing dual oxygen and nitrogen plasma treatments on the lower electrode, the leakage current was 4.8 x 10(-6) A/cm(2) (at -1 V) at a 28 fF/mu m(2) capacitance density.
Influence of oxygen flow rate on photocatalytic TiO2 films deposited by rf magnetron sputtering
(2012-02-01)
Chiou, A. H.
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Kuo, C. G.
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Huang, C. H.
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Wu, W. F.
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Chou, C. P.
Titanium dioxide (TiO2) thin films having anatase (1 0 1) crystal structure were prepared on non-alkali glass substrates by rf (13.56 MHz) magnetron sputtering using a TiO2 ceramic target under various oxygen partial pressures. At a fixed substrate temperature of 400 A degrees C and total gas pressure of 1 Pa after 3 h deposition. Effects of oxygen partial pressure on the structural, surface morphology, and photocatalytic activities of the TiO2 thin films were investigated. We performed both photoinduced decomposition of methylene blue (MB) and photoinduced hydrophilicity under UV light illumination. The XRD patterns exhibited a broad-hump shape indicating the amorphous structure of TiO2 thin films. The results showed that when the [O-2/(Ar + O-2)] flow rate increased to 50%, the photoinduced decomposition of MB and photoinduced hydrophilicity were enhanced. The water contact angle after 9 min UV illumination was approximately 4.5A degrees, and the methylene blue (MB) solution decomposition from 12 down to 3.34 mu mol/L for 240 min UV irradiation.