Papers by Author: Sang Hoon Hyun

Abstract: Conductive pastes have drawn significant interest due to their advantageous physical properties as well as their potential in electronic material industries. Conductive pastes consist of conductive fillers, organic binders, solvents and additives. Metal powders, such as Au, Ag, Ni, Cu, etc. are used for conductive filler. Filler dispersion is a very important and yet a difficult process in conductive paste manufacturing. Meanwhile, there are some metal powders such as copper, nickel etc that are used for pastes which have serious surface corrosion problems. This problem leads to change of the color and decrease in conductivity and affect storage stability of conductive pastes. To overcome these problems, we adopted two kinds of surface modification method. One is a method involving coating of silane coupling agent to conductive metal powders to overcome the corrosion stability and the other is a method involving addition of a dispersing agent to increase the degree of dispersion of metal powders. A coupling agent and dispersing agent are used to reduce the interfacial energy between filler and organic binder to enhance dispersion and its stability. By using silane coupling agent and dispersion agent, we can ensure both the corrosion stability and long term storage stability, and enhance the high performance electrical and mechanical properties of EMI shielding silicone sealant.

Abstract: Yttria stabilized zirconia (YSZ) films with the thickness of up to 12 μm were prepared on alumina and NiO-YSZ substrates by electron beam physical vapor deposition (EB-PVD). The films showed nano-scaled columnar structures depending on the substrate temperature. Electrical conductivity of the YSZ films on alumina was also investigated at the temperature between 700 and 1000oC in oxidizing atmosphere. High activation energy of the conductivity (>1.03eV) indicated that the conduction via grain boundary controlled the ionic conduction in the films prepared by EB-PVD. La0.6Sr0.4CoO3-δ as a cathode was applied on the YSZ/NiO-YSZ in order to evaluate the performance of the YSZ electrolyte.

Abstract: This paper presents the work on the development of ceramic coating processing. Nano-structured zirconia coating has been developed with functions; substrate temperature and oxygen gas change in chamber by electron beam physical vapor deposition (EB-PVD). The microstructure of the coating layer has been characterized with FE-SEM, and SEM. The crystalline phase of the coating layer has been also characterized with XRD. The zirconia coating by EB-PVD had not monoclinic zirconia phase as shown in XRD pattern and Raman spectra and the thickness of coating were quite homogeneous. The fracture microstructure of the coating layer for a thickness of ~15 μm showed columnar or non-columnar structure and had nano-structure with nano scaled grain as shown in micrograph by FE-SEM.

Abstract: In the surface machining of brittle materials, there exists a transition from brittle to ductile modes when the depth of cut is reduced below a critical size using ultrafine abrasive grains. Vitrified grinding wheels containing ultrafine abrasives in the sub-micrometer to nanometer range were fabricated by mechanochemically milling nanoabrasive particles and subsequent viscous sintering of abrasive-binder composites. The grinding characteristics of the nanoabrasive grinding wheels were evaluated for the fine grinding of silicon wafers in terms of a variety of variables. Preliminary wafer grinding results are presented on material removal rate and surface quality of silicon wafers.

Abstract: Nano-crystalline CeO2 was synthesized by the mechanical milling and subsequent heat-treatment from the mixture of Ce(OH)4 as precursor, and NaCl as diluent. The diluent provided diffusion barrier during milling and heat-treatment, which was easily dissolved out by deionized water. The size of crystallite and the strain variance of CeO2 were depended on the temperature and heat-treatment time: increased with the temperature (400~700oC) and time (1~24 hours) increasing, and saturated near at 20nm in size owing to the densification of diluent. The synthesized nano-crystalline CeO2 powder was applied as an abrasive in CMP (Chemical Mechanical Planarization) slurry. When blanket-type SiO2 and Si3N4 wafers were polished with the slurries, the removal rates (RR) of SiO2 and Si3N4 wafers and selectivities (RRSiO2/RRSi3N4) were influenced by synthetic condition of abrasive, the suspension stability and the pHs of slurries.