발간논문

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This study examined the role of excess free volume on the corrosion resistance of an amorphous alloy. Corrosion behaviors were monitored on the amorphous alloys, of which amount of free volume was controlled via the isothermal annealing below the glass transition temperature, using immersion tests and potentiodynamic polarization tests in HCl aqueous solutions. It was found that the corrosion resistance of the amorphous alloy is improved by reducing the amount of excess free volume. The possible reason explaining the experimental result was discussed from the viewpoint of the internal energy associated with the annihilation of excess free volume.

keyword : amorphous alloys, corrosion resistance, free volume, structural relaxation

Surface-void defects observed on the galvannealed(GA) steel sheets in Interstitial-free high-strengthened steels containing Si and Mn have been investigated using the combination of the FIB(Focused Ion Beam) and FE-TEM(Field Emission-Transmission Electron Microscope) techniques. The scanning ion micrographs of cross-section microstructure of defects showed that these defects were identified as craters which were formed on the projecting part of the substrate surface. Also, those craters were formed on the Si or Mn-Si oxides film through the whole interface between galvannealed coating and steel substrate. Interface enrichments and oxidations of the active alloying elements such as Si and Mn during reduction annealing process for galvanizing were found to interrupt Zn and Fe interdiffusion during galvannealing process. During galvannealing, Zn and Fe interdiffusion is preferentially started on the clean substrate surface which have no oxide layer on. And then, during galvannealing, crater is developed with consumption of molten zinc on the oxide layer.

keyword : hot-dip galvannealed steel(GA), crater, selective oxidation, Si oxide, Mn oxide

Generally CCM (cold crucible melting) is not suitable for melting glass. However, in this study we described the quantitative relationship between the basic property of glass and power balance, the power absorption in the melt, the losses in the coil and the cold crucible, for melting glass in CCM. The dependence of power balance on the applied frequency and the electric conductivity has been found. Above 300 kHz, the glass (B) contained alkali ion which has the low resistance 3.0 Ω·cm at 900℃ and 1.36 Ω·cm at 1,100℃ was melted easily and 60% of the overall power was absorbed in the melt and 30% and 10% of the overall power was lost in the cold crucible and coil respectively. Under the same condition, the glass (A) contained non-alkali ion was not melted easily and 50% of the overall power was absorbed in the melt and 40% and 10% of the overall power was lost in the cold crucible and coil respectively. In conclusion, the small absorbed power of the overall power in melt prevented a successful melting as for glass A, and the successful melting depends on the relative size of the absorbed power in melt irrespective of the melting volume. Hence, as typical for direct induction heating method(CCM), the successful melting strongly depended on the chosen working frequency based on electric conductivity of glass, power balance and the control of the critical power which was absorbed in melt.

keyword : CCM, cold crucible melter, electric conductivity, power balance

A composition consisting of 10 nm-Ni/1 nm-Pd/(30 nm or 70 nm-poly)Si was thermally annealed using rapid thermal for 40 seconds at 300~1100℃ to improve the thermal stability of conventional nickel monosilicide. The annealed bilayer structure developed into Ni(Pd)Six, and the resulting changes in sheet resistance, microstructure, phase, chemical composition, and surface roughness were investigated. The silicide, which formed on single crystal silicon, could defer the transformation of NiSi2, and was stable at temperatures up to 1100℃. It remained unchanged on polysilicon substrate compared with the sheet resistance of conventional nickel silicide. The silicides annealed at 700℃, formed on single crystal silicon and 30 nm polysilicon substrates exhibited 30 nm-thick uniform silicide layers. However, silicide annealed at 1,000℃ showed preferred and agglomerated phase. The high resistance was due to the agglomerated and mixed microstructures. Through X-ray diffraction analysis, the silicide formed on single crystal silicon and 30 nm polysilicon substrate, showed NiSi phase on the entire temperature range and mixed phases of NiSi and NiSi2 on 70 nm polysilicon substrate. Through scanning probe microscope (SPM) analysis, we confirmed that the surface roughness increased abruptly until 36 nm on 30 nm polysilicon substrate while not changed on single crystal and 70 nm polysilicon substrates. The Pd-inserted nickel monosilicide could maintain low resistance in a wide temperature range and is considered suitable for nano-thick silicide processing.

keyword : Ni silicide, Pd-inserted Ni silicide, salicide, nano-thick, thermal stability

Many researches related to the reliability of Pb-free solder joints with PCB (printed circuit board) surface finish under thermal or vibration stresses are in progress, because the electronics is operating in hash environment. Therefore, it is necessary to assess Pb-free solder joints life with PCB surface finish under thermal and mechanical stresses. We have investigated 4-points bending fatigue lifetime of Pb-free solder joints with OSP (organic solderability preservative) and ENIG (electroless nickel and immersion gold) surface finish. To predict the bending fatigue life of Sn-3.0Ag-0.5Cu solder joints, we use the test coupons mounted 192 BGA (ball grid array) package to be added the thermal stress by conducting thermal shock test, 500, 1,000, 1,500 and 2,000 cycles, respectively. An 4-point bending test is performed in force controlling mode. It is considered that as a failure when the resistance of daisy-chain circuit of test coupons reaches more than 1,000 Ω. Finally, we obtained the solder joints fatigue life with OSP and ENIG surface finish using by Weibull probability distribution.

keyword : Pb-free solder joint, fatigue Life, OSP surface finish, ENIG surface finish, thermal shock test, 4-point bending fatigue test

Thermal evaporated 10 nm-Ni50Co50/(70 nm-poly)Si films were deposited to examine the energy saving properties of silicides formed by rapid thermal annealing at temperature ranging from 500 to 1,100℃ for 40 seconds. Thermal evaporated 10 nm-Ni/(70 nm-poly)Si films were also deposited as a reference using the same method for depositing the 10 nm-Ni50Co50/(70 nm-poly)Si films. A four-point probe was used to examine the sheet resistance. Transmission electron microscopy (TEM) and X-ray diffraction XRD were used to determine cross sectional microstructure and phase changes, respectively. UV-VIS-NIR and FT-IR (Fourier transform infrared spectroscopy) were used to examine the near-infrared (NIR) and middle-infrared (MIR) absorbance. TEM analysis confirmed that the uniform nickel-cobalt composite silicide layers approximately 21 to 55 nm in thickness had formed on the single and polycrystalline silicon substrates as well as on the 25 to 100 nm thick nickel silicide layers. In particular, nickel-cobalt composite silicides showed a low sheet resistance, even after rapid annealing at 1,100℃. Nickel-cobalt composite silicide and nickel silicide films on the single silicon substrates showed similar absorbance in the near-IR region, while those on the polycrystalline silicon substrates showed excellent absorbance until the 1,750 nm region. Silicides on polycrystalline substrates showed high absorbance in the middle IR region. Nickel-cobalt composite silicides on the poly-Si substrates annealed at 1,000℃ superior IR absorption on both NIR and MIR region. These results suggest that the newly proposed Ni50Co50 composite silicides may be suitable for applications of IR absorption coatings.

keyword : Nickel-cobalt composite silicide, nikel silicide, infrared rays, absorbance, silicide

Black interlayer was introduced into between ITO and Bus electrodes to enhance a bright room contrast ratio of a plasma display panel. To measure the electrical resistance of the black interlayer, we designed two test patterns, type I and type II, of which type II pattern was successful. Using type II test pattern, the electrical resistance of the black interlayer was measured to be 300Ω for 2 μm thickness case and infinitely high for 4, 6 μm thickness. This result shows that electrical resistance of the black interlayer in the ITO/black interlayer/Bus electrodes structure is a critical parameter which determines the electrical characteristics of the PDP.

keyword : plasma display panel, electrical resistance, black interlayer, ITO, bus

Process of the hydroxyapatite (HA) formation on bioactive titanium metal prepared by NaOH treatment in a modified-simulated body fluid (mSBF) containing bovine serum albumin (BSA) was investigated by high resolution transmission electron microscope attached with energy dispersive X-ray spectrometer (EDX). The amorphous titanate, which was formed on titanium surface by NaOH treatment, combined with the calcium ions in the liquid to form an amorphous calcium titanite. With increasing of soaking time in the liquid, an amorphous calcium titanite combined with the phosphate ions to form an amorphous calcium phosphate with low Ca/P atomic ratio, and it grows as aggregates of plate (or needle)-like substance on titanium surface. The crystalline apatite layers, which are needle-shaped with the c axis parallel to the long axis, are formed in an amorphous calcium phosphate with further increase in soaking time. The formation of needle-shaped apatite layers can be explained by electrostatic effects and difference of concentration between calcium, phosphate, and albumin ions.

keyword : Hydroxyapatite, HA, modified-simulated body fluid, mSBF, bovine serum albumin, BSA, high resolution electron microscopy, HREM