Papers by Author: Tae Sung Oh

Abstract: The codeposition behavior of submicron sized diamond with nickel from nickel electrolytes has been investigated. Electroplating of diamond dispersed nickel composites was carried out on a rotating disk electrode (RDE). The effects of current type and current density on the electrodeposited Ni-diamond composite coating were investigated. The effects of pH and surfactants on the composite coating were also investigated. The hardness of coating was measured with varying electroplating conditions. As diamond was incorporated into the coating, the hardness of coating as well as the wear resistance was improved. The surface morphologies of the Ni-diamond composite coatings were observed using FESEM.

Abstract: In Ni-SiC composite coating, the SiC content is dependent on the surface properties of SiC particles. As sulfuric acid has a strong dehydration force, addition of sulfuric acid in the Ni sulfamate bath changed the surface properties of SiC particles, affecting the codeposition behavior of SiC particles. Also the additives such as SDS affect the electrodeposition behavior of the Ni-SiC composite coating. In this study, effects of the HSO4 ‾ and the current density on the electrodeposition behavior of the Ni-SiC composite coating have been investigated. The Ni-SiC composite coatings were electrodeposited at current densities of 50~200mA/cm2. The surface and cross-sectional morphologies of the Ni-SiC composite coatings were observed using SEM, and their mechanical properties were characterized with micro-Vikers hardness.

Abstract: For flip-chip process of RF system-on-packages(SOP), double bump bonding processes were investigated. Sn-Ag and Sn solder joints were formed by the reflowed double bumping process, and Sn/In/Sn bump joints were fabricated by the non-reflowed double bump bonding process. The height-to-size ratios of 0.78 and 0.65 were obtained for the reflowed double bumping and the non-reflowed bumping, respectively. Average contact resistance of the reflowed Sn-Ag and Sn solder joints was about 13m/ which was much lower than 24~33m/ of the non-reflowed Sn/In/Sn bump joints. The reflowed solder double bumping method is more suitable for flip-chip process of RF-SOP than the non-reflowed double bump bonding.

Abstract: Electrodeposition behavior and thermoelectric properties of the p-type (Bi,Sb)2Te3 films were investigated for thermoelectric energy conversion and nanowire applications. Composition and thermoelectric properties of the electrodeposited (Bi,Sb)2Te3 films were strongly dependent on the electrodeposition current density. The (Bi,Sb)2Te3 films electrodeposited in a 30mM solution of the 5mM Bi-15mM Sb-10mM Te concentration at current densities of 0.3~0.5 mA/cm2 exhibited the power factors of 2~3.4 ×10-4 W/K2-m, which were equivalent to the values reported for the sputter-deposited (Bi,Sb)2Te3 films.

Abstract: The p-type (Bi0.2Sb0.8)2Te3/(Pb0.7Sn0.3)Te functional gradient material (FGM) was fabricated by hot-pressing the mechanically alloyed (Bi0.2Sb0.8)2Te3 and the 0.5 at% Na2Te-doped (Pb0.7Sn0.3)Te powders. Also, the n-type Bi2(Te0.9Se0.1)3/PbTe FGM was processed by hot-pressing the mechanically alloyed Bi2(Te0.9Se0.1)3 and the 0.3 wt% Bi-doped PbTe powders. With △T larger than 300°C, the p-type (Bi0.2Sb0.8)2Te3/(Pb0.7Sn0.3)Te FGM exhibited larger thermoelectric output power than those of the (Bi0.2Sb0.8)2Te3 and the 0.5 at% Na2Te-doped (Pb0.7Sn0.3)Te alloys. For the n-type Bi2(Te0.9Se0.1)3/PbTe FGM, the thermoelectric output power superior to those of the Bi2(Te0.9Se0.1)3 and the 0.3 wt% Bi-doped PbTe was predicted at △T larger than 300°C.

Abstract: Ferroelectric characteristics of the 400 nm-thick Sr_xBi_2.4Ta₂O₉(0.7≤x≤1.3) thin films processed by metalorganic decomposition were investigated, and electrical properties of the Pt/Sr_0.85Bi_2.4Ta₂O₉/TiO₂/Si structure prepared using TiO₂ buffer layer were characterized. The Sr-deficient Sr_xBi_2.4Ta₂O₉ films exhibited well-developed ferroelectric hysteresis curves compared to those of the Sr-excess films. The Sr0.85Bi2.4Ta2O9 film exhibited optimum ferroelectric properties, such as high remanent polarization and low leakage current density, among Sr_xBi_2.4Ta₂O₉ films. A memory window of the Pt/SrxBi2.4Ta2O9/TiO2/Si structure was dependent upon the coercive field of the Sr_xBi_2.4Ta₂O₉ film, and the Pt/Sr_xBi_2.4Ta₂O₉/TiO₂/Si exhibited a maximum memory window of 1.3 V at the sweeping voltage of ±5 V.

Abstract: Reactions between 48Sn-52In solder and under bump metallurgies(UBM) such as 100nmTi/8µm Cu and 300nm Al/400nm Ni(V)/400nm Cu have been investigated, and the shear strength of 48Sn-52In solder bumps on each UBM has been evaluated. While intermetallic compounds with two different morphologies were continuously thickened on Ti/Cu with repeating the reflow process, the intermetallics on Al/Ni(V)/Cu spalled into the solder with increasing the number of reflow times. The solder bumps on Ti/Cu exhibited higher shear strength than those on Al/Ni(V)/Cu.

Abstract: Electroplating behavior of Bi ₂Te ₃ and thermoelectric properties of the electroplated Bi ₂Te ₃ films were investigated for nanowire application. Composition, microstructure, and thermoelectric properties of the electroplated Bi-Te films were strongly dependent upon composition of the electroplating solutions and plating current density. While the power factor of the Bi ₂Te ₃ film plated at a current density of 1×10^-4 A/cm² was 1.75×10^-4 W/K²-m, the film formed at 5×10^-4 A/cm² exhibited the value of 3.5×10^-4 W/K²-m. Substantial pore filling was achieved with electrodeposition of Bi ₂Te ₃ for the alumina template with 200 nm pores.