Browsing by Author "Chang, H. C."

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A 45nm dual-port SRAM with write and read capability enhancement at low voltage
(2007)
Wang, D. P.
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Lia, H. J.
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Yamauchi, H.
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Chen, Y. H.
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Lin, Y. L.
This paper presents circuit techniques to improve write and read capability for dual-port SRAM design fabricated in a 45nm low-power process. The write capability is enhanced by negative write biasing without any reduction in the cell current for the other port. The result shows 12% better improvement with just 1.9% area overhead. This technique has been verified successfully on 65nm and 45nm SRAM chip and improved 120mV lower at 95% yield of minimum operation voltage than a conventional one. The read capability is enhanced by cell current boosting and word line voltage lowering schemes. The SNM is also enhanced significantly. The target is to work below 0.8V with the worst process corner variation.
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.
Potential energy surfaces for the lowest excited states of the nitrogen-vacancy point defects in diamonds: A quantum chemical study
(2008-09-10)
Zyubin, A. S.
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Mebel, A. M.
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Chang, H. C.
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Lin, S. H.
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應用化學系
Quantum chemical calculations of geometry relaxation in lowest excited states of neutral (NV(O)) and negatively charged (NV) nitrogen-vacancy point defects in diamond have been performed employing the CASSCF method with a finite NC(19)H(28) model cluster. Vibrations activated by the electronic transitions are determined by comparing calculated atomic displacements in the excited states with normal mode vectors, and the activated frequencies are evaluated as similar to 600 cm (1). The barrier for N migration through the vacancy in NV is estimated at the TD-B3LYP level and no significant decrease of this barrier (similar to 5 eV in the ground state) is found due to electronic excitations. (c) 2008 Elsevier B. V. All rights reserved.
Quantum Chemical Modeling of Photoabsorption Properties of Two- and Three-Nitrogen Vacancy Point Defects in Diamond
(2009-06-18)
Zyubin, A. S.
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Mebel, A. M.
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Hayashi, M.
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Chang, H. C.
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Lin, S. H.
Quantum chemical calculations of the geometric and electronic structures and vertical transition energies for several low-lying excited states of the neutral and negatively charged vacancy-related point defects in diamond containing two and three nitrogen atoms (N(2)V(0), N(2)V(-), and N(3)V(0)) have been performed employing various theoretical methods (time-dependent density functional theory, equation-of-motion coupled cluster, and multireference perturbation theory) and different basis sets and using C(21)H(28), C(35)H(36), and C(51)H(52) finite model clusters. In the;round states, the vacancy-related atoms are found to be shifted away from the vacancy center by similar to 0.1 angstrom, whereas the positions of atoms from the second layer around them vacancy remain nearly unchanged, indicating a local character of geometry relaxation due to defects. The lowest excited states are formed with participation of the stretched (N(2)V) or broken (N(3)V) C-C bond and nonbonding combinations of nitrogen lone pairs as donors, with the C-C antibonding molecular orbital (MO) in N(2)V(0), broken C-C bond in N(3)V(0), and diffuse vacancy-related MOs serving as acceptors. Normally, the first excited states have a valence character, but the diffuse states are rather close in energy, especially for N(3)V(0) (2(2)A(1) and 1(2)E excited states). The first optically active excitation in the N(2)V(0) defect with the calculated energy of similar to 2.6 eV (in close agreement with the experiment) is formed by the electronic transition from the stretched C-C bond to the antibonding C-C MO, with an additional contribution from the combination of nitrogen lone pairs. For the negatively charged N(2)V(-) system, the lowest excitation to the 1(2)A(1) state is predicted to occur from the singly occupied antibonding b(1) MO to the empty diffuse a(1) orbital, but the CASPT2 calculated excitation energy, similar to 0.9 eV, underestimates the experimental zero phonon line observed at 1.26 eV. The lowest excited states of N(3)V(0), 2(2)A(1), and 1(2)E correspond to transitions from the singly occupied MO (SOMO) to the diffuse lowest vacant orbital and from the nonbonding combination of nitrogen lone pairs to SOMO, respectively, and have similar energies of about 3.1-3.3 eV, in agreement with the experimental photoabsorption band maximum at similar to 3 eV.
Quantum Chemical Modeling of Photoadsorption Properties of the Nitrogen-Vacancy Pint Defect in Diamond
(2009-01-15)
Zyubin, A. S.
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Mebel, A. M.
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Hayashi, M.
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Chang, H. C.
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Lin, S. H.
Quantum chemical Calculations of geometric and electronic structure and vertical transition energies for several low-lying excited states of the neutral and negatively charged nitrogen-vacancy point defect in diamond (NV(0) and NV(-)) have been performed employing various theoretical methods and basis Sets and using finite model NC(n)H(m) clusters. Unpaired electrons in the ground doublet state of NV(0) and triplet state of NV(-) are found to be localized mainly on three carbon atoms around the vacancy and the electronic density on the nitrogen and rest of C atoms is only weakly disturbed. The lowest excited states involve different electronic distributions on molecular orbitals localized close to the vacancy and their wave functions exhibit a strong multireference character with significant contributions from diffuse functions. CASSCF calculations underestimate excitation energies for the anionic defect and overestimate those for the neutral system. The inclusion of dynamic electronic correlation at the CASPT2 level leads to a reasonable agreement (within 0.25 eV) of the calculated transition energy to the lowest excited state with experiment for both systems. Several excited states for NV(-) are found in the energy range of 2-3 eV, but only for the 1(3)E and 5(3)E states the excitation probabilities from the ground state are significant, with tile first absorption band calculated at similar to 1.9 eV and the second lying 0.8-1 eV higher in energy than the first one. For NV(0) we predict the following order of electronic states: 1(2)E (0.0), 1(2)A(2) (similar to 2.4 eV), 2(2)E (2.7-2.8 eV), 1(2)A(1), 3(2)E (similar to 3.2 eV and higher). (C) 2008 Wiley Periodicals, Inc. J Comput Chem 30: 119-131, 2009
Quantum Chemical Modeling of Photoadsorption Properties of the Nitrogen-Vacancy Pint Defect in Diamond
(2009-01-15)
Zyubin, A. S.
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Mebel, A. M.
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Hayashi, M.
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Chang, H. C.
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Lin, S. H.
Quantum chemical Calculations of geometric and electronic structure and vertical transition energies for several low-lying excited states of the neutral and negatively charged nitrogen-vacancy point defect in diamond (NV0 and NV-) have been performed employing various theoretical methods and basis Sets and using finite model NCnHm clusters. Unpaired electrons in the ground doublet state of NV0 and triplet state of NV- are found to be localized mainly on three carbon atoms around the vacancy and the electronic density on the nitrogen and rest of C atoms is only weakly disturbed. The lowest excited states involve different electronic distributions on molecular orbitals localized close to the vacancy and their wave functions exhibit a strong multireference character with significant contributions from diffuse functions. CASSCF calculations underestimate excitation energies for the anionic defect and overestimate those for the neutral system. The inclusion of dynamic electronic correlation at the CASPT2 level leads to a reasonable agreement (within 0.25 eV) of the calculated transition energy to the lowest excited state with experiment for both systems. Several excited states for NV- are found in the energy range of 2-3 eV, but only for the 1(3)E and 5(3)E states the excitation probabilities from the ground state are significant, with tile first absorption band calculated at similar to 1.9 eV and the second lying 0.8-1 eV higher in energy than the first one. For NV0 we predict the following order of electronic states: 1(2)E (0.0), 1(2)A(2) (similar to 2.4 eV), 2(2)E (2.7-2.8 eV), 1(2)A(1), 3(2)E (similar to 3.2 eV and higher). (C) 2008 Wiley Periodicals, Inc. J Comput Chem 30: 119-131, 2009
Structural and optoelectronic properties of Al-doped zinc oxide films deposited on flexible substrates by radio frequency magnetron sputtering
(2011-09-01)
Tseng, C. H.
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Huang, C. H.
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Chang, H. C.
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Chen, D. Y.
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Chou, C. P.
Al-doped zinc oxide (AZO) thin films were deposited onto flexible polyethylene terephthalate substrates, using the radio frequency (RF) magnetron sputtering process, with an AZO ceramic target (The Al(2)O(3) content was about 2 wt.%). The effects of the argon sputtering pressure (in the range from 0.66 to 2.0 Pa), thickness of the Al buffer layer (thickness of 2, 5, and 10 nm) and annealing in a vacuum (6.6 x 10(-4) Pa), for 30 min at 120 degrees C, on the morphology and optoelectronic performances of AZO films were investigated. The resistivity was 9.22 x 10(-3) Omega cm, carrier concentration was 4.64 x 10(21) cm(-3), Hall mobility was 2.68 cm(2)/V s and visible range transmittance was about 80%, at an argon sputtering pressure of 2.0 Pa and an RF power of 100 W. Using an Al buffer decreases the resistivity and optical transmittance of the AZO films. The crystalline and microstructure characteristics of the AZO films are improved by annealing. (C) 2011 Elsevier BM. All rights reserved.
The Photocatalytic Activity and Compact Layer Characteristics of TiO2 Films Prepared Using Radio Frequency Magnetron Sputtering
(2014)
Chang, H. C.
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Huang, H. H.
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Wu, C. Y.
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Hsu, R. Q.
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Hsu, C. Y.
TiO2 compact layers are used in dye-sensitized solar cells (DSSCs) to prevent charge recombination between the electrolyte and the transparent conductive substrate (indium tin oxide, ITO; fluorine-doped tin oxide, FTO). Thin TiO2 compact layers are deposited onto ITO/glass by means of radio frequency (rf) magnetron sputtering, using deposition parameters that ensure greater photocatalytic activity and increased DSSC conversion efficiency. The photoinduced decomposition of methylene blue (MB) and the photoinduced hydrophilicity of the TiO2 thin films are also investigated. The photocatalytic performance characteristics for the deposition of TiO2 films are improved by using the Grey-Taguchi method. The average transmittance in the visible region exceeds 85% for all samples. The XRD patterns of the TiO2 films, for sol-gel with spin coating of porous TiO2 /TiO2 compact/ITO/glass, show a good crystalline structure. In contrast, without the TiO2 compact layer (only porous TiO2), the peak intensity of the anatase (101) plane in the XRD patterns for the TiO2 film has a lower value, which demonstrates inferior crystalline quality. With a TiO2 compact layer to prevent charge recombination, a higher short-circuit current density is obtained. The DSSC with the FTO/glass and Pt counter electrode demonstrates the energy conversion efficiency increased.