Designing, Processing and Properties of Advanced Engineering Materials

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Authors: Dong Ho Park, Yeon Gil Jung, Ung Yu Paik, Jeong Wook Kim, Jin Young Yu
Abstract: Herein, we report the effects of external electrode and heat treatment on stress anisotropy and residual stress on margins of MLCCs in each direction perpendicular and parallel to internal electrode at length plane. The residual stresses estimated using an indentation method are compared in regions with and without the external electrode as a function of heat treatment. The stress anisotropy is not affected by both heat treatment and external electrode, showing residual compressive stresses in all directions. However, at the boundary, the crack length in the perpendicular direction is longer than that in the parallel direction.
Authors: S.G. Kim, Seung Boo Jung, Ji Hun Oh, H.J. Kim, Yong Hyeon Shin
Abstract: Polycrystalline ZnO thin films were for the first time deposited on SiO2/Si (100) substrate using 2-step deposition; atomic layer deposition (ALD) and RF magnetron sputtering, for Film Bulk Acoustic Resonator (FBAR) applications. The film deposition performed in this study was composed of following two procedures; the 1st deposition was using ALD method and 2nd deposition was using RF magnetron sputtering. The ZnO buffer layer ALD films were deposited using alternating diethylzinc (DEZn)/H2O exposures and ultrahigh purity argon gas for purging. Exposure time of 1 sec and purge time of 23 sec yielded an ALD cycle time. Two-step deposited ZnO films revealed stronger c-axis preferred-orientation than one-step deposited. Therefore, this method could be applied to the FBAR applications, since FBAR devices require high quality of thin films.
Authors: Hyun Kwon Shin, Sang Goo Lee, Myeong Kyu Lee
Abstract: We have preformed holographic recording in congruent LiNbO3 doped with Tb and Fe with a continuous-wave green laser at λ = 532 nm. This material exhibited a fast coloration upon exposure to ultraviolet (UV) light. The recording sensitivity was improved from about 0.02 cm/J to over 0.08 cm/J after UV pre-exposure, due to the increased visible absorption. Holograms recorded from the colored state could be quickly erased by UV illumination and a sequence of recording by green and erasure by UV could be continuously repeated without any noticeable degradation in maximum diffraction efficiency or sensitivity. The overall performances of this crystal relevant to holographic storage are here presented, in comparison to those obtained with near-stoichiometric LiNbO3:Tb,Fe.
Authors: S.M. Lee, J.W. Shur, T.I. Shin, W.S. Yang, G.Y. Kim, S.W. Baek, D.H. Yoon
Abstract: [MnO2(1.0mol%) : Tb4O7(0.5mo%)] doped stoichiometric LiNbO3 (Mn:Tb:SLN) single crystals of 0.5~1.0 mm in diameter and 30~35 mm in length were grown by micro pulling down(µ-PD) method. We investigated the photoluminescence (PL) properties of Mn:Tb:SLN single crystal. The OH- absorption band of the single crystals observed infrared the absorption spectra by using an FT-IR spectrophotometer at room temperature. Homogeneous distributions of Mn and Tb concentration were confirmed by the EPMA and observed defects by optical microscopy.
Authors: Byung Soo So, Sung Moon Kim, Young Sin Pyo, Young Hwan Kim, Jin-Ha Hwang
Abstract: Amorphous indium tin oxide (ITO) thin films were grown on plastic substrates, PES (polyethersulfone) using low temperature DC magnetron sputtering. Various post-annealing techniques are attempted to optimize conductivity, transmittance, and roughness: i) conventional thermal annealing, ii) excimer laser annealing, and iii) UV irradiation. The electrical/optical properties were measured using Hall-measurement, DC 4-point resistance measurement, and UV spectrometry along with micro-structural characterization. Optimized UV treatment exhibits enhanced conductivity and smooth surface, compared to those of conventional thermal annealing and excimer laser annealing.
Authors: Hyun Wook Ryu, Yong Joo Park, Hyo Sup Noh, Jin Seong Park
Abstract: SnO2 thin films were prepared on SiO2/Si substrate by RF-Magentron Sputtering method, varying the deposition time and Ar-to-O2 flow ratio. The post-annealing was conducted at 500 oC and 700 oC in Ar and O2 atmosphere, respectively. Film characteristics were very sensitive to the gas flow ratio during the deposition and the conditions of post-annealing. The Film thickness decreased with decreasing of Ar flow ratio at a constant amount (50 sccm) of total gas flow. Especially, the film deposited under Ar-O2 mixture gas (Ar-to-O2 ratio of 50%) showed clearly aggregated morphology of small particles (cauliflower) in a wide range of area. In the annealed films, these cauliflowers separated some small grains, decreasing the film thickness.
Authors: Gwang Pyo Choi, Yong Joo Park, Whyo Sup Noh, Jin Seong Park
Abstract: Tin oxide thin films were deposited at 375 °C on α-alumina substrate by metal-organic chemical vapor deposition (MOCVD) process. A number of hillocks on the film were formed after air annealing at 500 °C for 30 min and few things in N2 annealing. The oxygen content and the binding energy after air annealing came to close the stoichiometric SnO2. The cauliflower hillocks of the film seem to be formed by the continuous migration of crystallites from a cauliflower grain on the substrate to release the stress due to the increase of oxygen content and volume.
Authors: Dong Hyun Yoo, Moo Whan Shin
Abstract: One of obstacles hindering a realization of large area size twisted nematic liquid crystal display (TN-LCD) flat panel (for example, 1100 x 1250 mm) is a slow response time. The slow response time is due to the inverse proportionality of turn on time with the frame frequency and pixel number (number of gate lines) in the twisted nematic liquid crystal system. It is known that the slow response time in the active matrix system of LCD be solved by reducing the sheet resistance of color filter electrodes. In this paper, we report on the processing details of the deposition of transparent ITO films using a DC sputtering system. The thickness of ITO layer was set for high transmittance and good conductivity and the films were characterized with respect to the transmittance and sheet resistance. The deposited ITO films show a good uniformity across the whole area and the average thickness of the ITO is about 1350 Å under the DC power of 10.7 kW. The transmittance is increased from 72.5 to about 93 % as the oxygen content is increased to 2.5 sccm for the samples without annealing. It was found that the transmittance is significantly improved by the annealing process at 220 oC for 40 min. up to 94 %. The sheet resistance is decreased with the DC power and exhibits below 22  / after the samples were annealed.
Authors: J.H. Hong, Jae Min Myoung
Abstract: The chemical and electrical characteristics of HfO2 dielectric layers grown on the p-type Si substrate by the metalorganic molecular beam epitaxy (MOMBE) technique were investigated. The XPS spectra showed that the Hf 4f and O 1s peaks shifted to the higher level of binding energy due to the charge 1transfer effect. Electrical properties were analyzed by C-V and I-V measurements. The distortion of C-V curve at depletion region is attributed to the effect of deep trap levels’ existence. Saturation capacitance and leakage current density were in the range of 207 ~ 249 pF and 0.52 ~ 0.58 A/cm2 respectively, and the flat band voltage shift to the higher voltage appeared as the oxygen flow rate increased.
Authors: Cheng Zhu Lu, Jung Yohn Cho, Ho Jung Chang, Sang Woo Joo, Yong Sheng Wang
Abstract: We synthesized ZnO nanocrystal colloids adopting sol-gel method using zinc acetate dehydrate as precursor, and prepared ZnO films on glass substrates by a spin-coating technique. The effect of annealing temperature on the structure, optical and electrical properties has been studied. The crystallinity and morphologies were improved by the annealing. All film samples show high transmittance of above 80% in the wavelength ranging from 400nm to 1000nm. A minimum resistivity of 5.5x10-3 􀀀 cm was obtained for the film annealed at 500oC. The crystallinity, oxygen vacancies, and nanocrystalline boundaries seems likely to be crucial factors for these properties

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