발간논문

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The electromigration characteristics of A1 films deposited onto low dielectric polyimide and CVD-Si02 have been investigated. The polyimides used in this study were DuPont PI-2734 and Toray BG 2480. 500 ㎚ Al-0.5%Cu- l%Si thin films were deposited onto polyimides and LPCVD-SiO₂ by DC magnetron sputtering. Al lines were tested at constant voltage, at a temperature of 225℃ and a current density of 1.85 MA/㎠. The electromigration reliability of Al lines onto polyimides was worse than that onto SiO₂. Joule heating was the main cause of the degradation of electromigration reliability in the Al lines deposited onto polyimides. Since the thermal conductivity of polyimide is about one order lower than that of SiO₂, joule heating was more significant in Al/polyimide during electromigration test and the temperature increase of A1 lines on polyimide decreased the electromigration life.

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CdI₂ and CdCl₂ doped n-type 90% Bi₂Te₃ 10% Bi₂Se₃ single crystals were grown by the vertical zone melting method, and the thermoelectric properties along the ingot were analyzed. The sharp increase of the Seebeck coefficient and electrical resistivity at the last-to-freeze region were considered as a result of the evaporation of I and Cl from the molten zone. The maximum Figure-of-Merit of the CdI₂ and CdCl₂ doped n-type 90% Bi₂Te₃ 10% Bi₂Se₃ single crystals were 2.7×10^(-3)/K and 2.8×10^(-3)/K, respectively. The higher Figure-of-Merit for the CdCl₂ doped specimens was mainly due to the lower (κ-κ_(el)). The optimum doping amount of CdI₂ and CdCl₂ for n-type 90% Bi₂Te₃-10% Bi₂Se₃ single crystals, grown by the vertical zone melting method, were 0.075-0.10 wt% and 0.04-0.05 wt%, respectively.

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Thermoelectric properties of (Pb_(0.7)Sn_(0.3))Te alloy, fabricated by mechanical alloying and hot pressing, were investigated with addition of Na₂Te up to 1.5 at% as acceptor dopant. A transition from p-type to n-type occurred at 425℃ for the undoped (Pb_(0.7)Sn_(0.3))Te. With doping Na₂ Te more than 0.1 at%, however, the hot-pressed (Pb_(0.7)Sn_(0.3))Te exhibited ptype conduction up to 450℃. Electrical resistivity of the hot-pressed (Pb_(0.7)Sn_(0.3)) Te increased by reduction treatment of the powders in hydrogen atmosphere before hot pressing, which was due to the fact that oxide layer on the powder surface was removed by reduction treatment. Figure-of-merit of the hot-pressed (Pb_(0.7)Sn_(0.3))Te was optimized to be 0.83×10^(-3)/K at 200℃ with doping 0.5 at% Na₂Te.

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The solubility of silver in molten CaO-B₂O₃ slag at high temperature was measured to understand the dissolution behaviors of silver into the slags as a fundamental study on the measure of basicity. The B₂O₃ bearing fluxes, which have wide range of liquid at the temperature of interest would be shown the effects of flux composition on the solubility of silver as an indicator of basicity through the whole range of liquid. The solubility of silver in slag has a minimum value as a function of flux composition. and it is suggested that a silver behaves as an amphoteric substance, i.e, it shows a different stability in slag of the different basicity. The solubility of silver decreases with increasing temperature. It was also decreased with the content of basic oxide in the acidic region, and vice versa in the basic region. From the view point of the Ag solubility as a measure of basicity, the relationship between depolimerization of borate network and basicity was discussed by introducing the relative basicity. The relationship between the solubility of silver and nitride capacity as well as theoretical optical basicity was also discussed.

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To study mechanism of the slag coating on lining of LD converters, uncoated and coated high carbon MgO bricks have been recovered and made into polished and thin sections for optical and electron optics investigations. Slag coating practice is first to drain about two-thirds of the slag after tapping, and add dolomite then rock the furnace for about 3 minutes. Formation of the dense MgO layer was found to be the major mechanism of slag attack resistance in the slag coat on high carbon MgO brick. Dissolution of dolomite made coats of high melting temperatures and protected the bricks, so that the use of burnt dolomite is preferred. In addition, gaseous reaction products of MgO+C resulted in reduction of iron oxide in the slag with MgO enriched, which decreased the corrosion potential of the slag. Fused MgO grains showed better resistance to slag attack than sintered MgO grains, thus remaining protruded which served as an anchor for the slag coating. The use of slag splashing technologies that, provide selective distribution of the slag coating on the highly worn region in the furnace lining such as trunnion areas will increase the BOF lining life.

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An attempt was made to determine the charging characteristics of oxide particles suspended in a liquid Hg at room temperature. The pure liquid Hg and the liquid Hg containing oxide particles were respectively chosen as a reference electrode and a sample electrode for the potential measurement. Experimental results show that oxides carry the positive charge by providing electrons to the liquid Hg regardless of the nature of oxides i.e. n-type ZnO, Al₂O₃ or p-type NiO. It is also interesting to note that the potential was slightly increased with increasing the purity of Al₂O₃ and also was increased with increasing amount of Al₂O₃ added to the liquid Hg. The highest potential obtained was 4.5 μN for 5g of Al₂O₃.

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For the economic manufacturing of Mg₂Ni hydrogen absorbing materials, Mg and Ni chips were mechanically alloyed under 20 bar`s hydrogen atmosphere. The homogeneous Mg₂NiH_x was formed after 48hr M.A (Mechanical Alloying). The hydrogen content of Mg₂NiH_x reaches 1.75wt.% and the dehydriding reaction starts at around 210℃ The specific magnetization value is reduced from 13.7 emu/g to 0.13 emu/g with respect to mechanical alloying time. The homogeneous Mg₂NiH_x composites were obtained after 96 hr M.A. They are composed of the crystalline matrix phase and the disordered interface phase which seems to be the reason of the elevated dehydriding kinetics and decreased magnetic intensity.

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Generally, the density of films deposited by evaporation techniques are lower than sputtering, due to the lower kinetic energy of the evaporated atoms (or ions). The authors report an enhancement of the kinetic energy by increasing the chamber pressure with an inert gas (e.g., Ar). The validity of the idea has been proved with permalloy(NiN_(80)Fe_(20))/Cu multilayer films, of which the quality was characterized using synchrotron X-ray and atomic force microscopy.

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