Browsing by Author "Lee, C. H."

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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.
Aberrations measurement of fiber-end microlens by free-space microoptical Ronchi interferometer
(2006-07-01)
Tien, C. H.
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Hung, C. H.
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Lee, C. H.
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光電工程學系
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顯示科技研究所
We developed a microoptical Ronchi interferometer system in which a V-groove, an out-of-plane grating, a beam splitter, and a 45 degrees upward reflector integrated on a single silicon chip were used to measure the wavefront aberration caused by a microlens on the fiber front end. By the use of the microelectromechanical systems configuration, the fringe patterns caused by the different spherical aberration and defocus balances of the 0.34-numerical-aperture microlens can be captured and analyzed accordingly. As demonstrated by the experimental results, the proposed setup is capable of carrying out a simple wavefront variation measurement in the microscopic scale.
Al(2)O(3)/Ga(2)O(3)(Gd(2)O(3)) passivation on In(0.20)Ga(0.80)As/GaAs-structural intactness with high-temperature annealing
(2010-04-07)
Lee, Y. J.
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Lee, C. H.
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Tung, L. T.
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Chiang, T. H.
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Lai, T. Y.
Molecular beam epitaxy grown Al(2)O(3)/Ga(2)O(3)(Gd(2)O(3))/In(0.20)Ga(0.80)As/GaAs has been rapidly thermal annealed to 850 degrees C in N(2). The hetero-structure remained intact, with the In(0.20)Ga(0.80)As/GaAs interface being free of misfit dislocation and In(0.20)Ga(0.80)As strained, as observed by high-resolution transmission electron microscopy and high-resolution x-ray diffraction using synchrotron radiation. Excellent capacitance-voltage characteristics as well as low electrical leakages were obtained. These structural and electrical results demonstrate that employing Ga(2)O(3)(Gd(2)O(3)) as a dielectric with an in situ Al(2)O(3) capping layer efficiently protects strained InGaAs layers from relaxing and volatilizing during rapid thermal annealing to 850 degrees C, important for fabricating inversion-channel InGaAs metal-oxide-semiconductor field-effect-transistors, a candidate for beyond the 16 nm node complementary MOS technology.
Al2O3/Ga2O3(Gd2O3) passivation on In0.20Ga0.80As/GaAs-structural intactness with high-temperature annealing
(2010-04-07)
Lee, Y. J.
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Lee, C. H.
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Tung, L. T.
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Chiang, T. H.
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Lai, T. Y.
Molecular beam epitaxy grown Al2O3/Ga2O3(Gd2O3)/In0.20Ga0.80As/GaAs has been rapidly thermal annealed to 850 degrees C in N-2. The hetero-structure remained intact, with the In0.20Ga0.80As/GaAs interface being free of misfit dislocation and In0.20Ga0.80As strained, as observed by high-resolution transmission electron microscopy and high-resolution x-ray diffraction using synchrotron radiation. Excellent capacitance-voltage characteristics as well as low electrical leakages were obtained. These structural and electrical results demonstrate that employing Ga2O3(Gd2O3) as a dielectric with an in situ Al2O3 capping layer efficiently protects strained InGaAs layers from relaxing and volatilizing during rapid thermal annealing to 850 degrees C, important for fabricating inversion-channel InGaAs metal-oxide-semiconductor field-effect-transistors, a candidate for beyond the 16 nm node complementary MOS technology.
Antiferroelectric antiferromagnetic type-I multiferroic Cu9O2(SeO3)(4)Cl-6
(2019-12-11)
Wu, H. C.
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Denisova, K. N.
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Menzel, D.
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Kakarla, D. Chandrasekhar
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Maximova, O. V.
We report that Cu9O2(SeO3)(4)Cl-6 is a new multiferroic compound. Comprehensive studies of this compound have been carried out on single crystals as well as polycrystalline samples. Magnetic susceptibility chi and specific heat C with H parallel to c axis both reveal an anomaly at T-N = 37 K associated with the long-range antiferromagnetic order. However, no signature of this phase transition is seen with the H parallel to b axis, providing evidence of the anisotropic nature of its magnetic properties. The results of chi measurements are consistent with the temperature evolution of the intensity of magnetic reflections from the neutron diffraction experiments. The magnetic structure derived from neutron scattering measurements shows that half of the Cu(5) ions carry no moments. Furthermore, an anomaly in the dielectric constant near T-N and observable magnetoelectric coupling below T-N are found. At high temperatures, a dielectric peak at T-E = 267 K is identified with no measurable spontaneous polarization below T-E, thereby suggesting an antiferroelectric order. A steplike anomaly seen in chi(T) at T-E hints the weak spin-lattice coupling. Concomitantly, high-resolution temperature-dependent synchrotron x-ray diffraction experiments elucidate a local structural distortion at T-E.
Cell Endurance Prediction from a Large-area SONOS Capacitor
(2009)
Lee, C. H.
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Tu, W. H.
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Gu, S. H.
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Wu, C. W.
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Lin, S. W.
Endurance considerations induced by the degadation of top and bottom oxides are proposed for a SONOS memory. First, a correlation is found between the widespread C-V curves induced by interface generation and cycling numbers (cyc. #). Unlike V-FB (accumulation region), V-T (inversion region) shows a much severe shift. Inter-face state (N-it) is identified as a key factor even when a 2nm bottom oxide is used. Moreover, charge to breakdown (Q(BD)) for an ONO capacitor under positive and negative constant current stress (CCS) is investigated. Our study reveals that QBD of such stacks strongly depends on the top oxide thickness. A field enhancement induced by charges in a trapping nitride layer is the root cause. Based on Weibull statistics, the risk of dielectric breakdown for both blocking layers is then evaluated.
Growth and structural characteristics of GaN/AlN/nanothick gamma-Al(2)O(3)/Si (111)
(2008-05-01)
Lee, W. C.
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Lee, Y. J.
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Tung, L. T.
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Wu, S. Y.
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Lee, C. H.
The authors report on the growth of GaN by nitrogen plasma-assisted molecular beam epitaxy (MBE) on a 2 in. Si (111) substrates with a nanothick (similar to 4.8 nm thick) gamma-Al(2)O(3) as a template/buffer. A thin layer of MBE-AlN similar to 40 nm thick was inserted prior to the growth of GaN. High-resolution transmission electron microscopy (HR-TEM) and high-resolution x-ray diffraction studies indicated that both of the nanothick gamma-Al(2)O(3) and AlN are a single crystal. Reflection high-energy electron diffraction, high-resolution x-ray scattering using synchrotron radiation, and cross-sectional HR-TEM measurements indicated an orientation relationship of GaN(0002)parallel to AlN(0002)parallel to gamma-Al(2)O(3)(111)parallel to Si(111) and GaN[10-10]parallel to AlN[10-10]parallel to gamma-Al(2)O(3)[2-1-1]parallel to Si[2-1-1]. A dislocation density of 5x(10(8)-10(9))/cm(2) in the GaN similar to 0.5 mu m thick was determined using cross-sectional TEM images under weak-beam dark-field conditions. (C) 2008 American Vacuum Society.
Nonpolar light emitting diode made by m-plane n-ZnO/p-GaN heterostructure
(2011-12-01)
Chen, C. W.
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Hung, S. C.
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Lee, C. H.
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Tun, C. J.
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Kuo, C. H.
Nonpolar (100) m-plane n-ZnO/p-GaN light-emitting-diodes (LEDs) were grown by chemical vapor deposition on p-GaN templates which was grown by metalorganic chemical vapor deposition on LiAlO(2)(100) substrate. Direct current (DC) electroluminescence (EL) measurements yielded a peak at 458nm. The EL peak position was independent of drive current and a full width of half maximum (FWHM) of 21.8 nm was realized at 20mA. The current-voltage characteristics of these diodes showed a forward voltage (V(f)) of 6V with a series resistance of 2.2 x 10(5) Omega. (C) 2011 Optical Society of America
Observation of charge-transfer-driven antiferroelectricity in 3d-pyrochlore multiferroic Cu2OCl2
(2019-03-01)
Wu, H. C.
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Yuan, J. K.
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Chandrasekhar, K. D.
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Lee, C. H.
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Li, W. H.
Very recently, multiferroic behavior close to the boiling temperature of liquid nitrogen was reported in oxohalide-based Cu2OCl2. In this study, we have established yet another novel mechanism for the origin of charge ordering in multiferroic Cu2OCl2. The direct current (DC) magnetization, specific heat, and neutron diffraction measurements confirm the antiferromagnetic (AFM) ordering (T-N) of Cu2OCl2 near 70 K. The collinear AFM spin structure in Cu(2)OCl(2)was obtained from neutron powder diffraction experiments based on the fitting to the combination of two irreducible representations-Gamma(1)circle plus Gamma(2). Electrical properties, such as dielectric constant, pyroelectric current, and polarization-electric field hysteresis-loop measurements, together suggest a long-range antiferroelectric ordering near T-E approximate to 75 K. The charge transfer from Cl to O along the c-axis was found to induce antiferroelectricity near TE and is supported from ab initio calculations. This finding largely reduces the possibility of well-known Dzyaloshinskii -Moriya interaction in the observed multiferroic behaviors and provides insight into the various origins of high-T-c multiferroics. (C) 2018 Elsevier Ltd. All rights reserved.
Overall Operation Considerations for a SONOS-based Memory
(2009)
Lee, C. H.
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Tu, W. H.
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Chong, L. H.
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Gu, S. H.
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Chen, K. F.
Erase characteristics of a SONOS-based structure are emulated not only for n(+)-poly and p(+)-poly gates but also for TaN-gate+Al2O3 combination. By incorporating our previous studies, performances including program, erase, and read disturb can be reviewed for both SONOS and TANOS devices. Unsurprisingly, it is hard to satisfy all requirements by using a SONOS device. In a TANOS device, an optimal bottom oxide thickness can be specified with the consideration of the three factors simultaneously. Moreover, it is found that conventional extrapolation methodology is inadequate to predict the lifetime of a TANOS device and tends to under-estimate the tolerable read bias.