• Journal of the Institute of Electronics Engineers of Korea SD
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• v.39 no.5
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• pp.1-7
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• 2002

Deep sub-micron bulk CMOS circuits require gate electrode materials such as metal silicide and titanium silicide for gate oxides. Many authors have conducted research to improve the quality of the sub-micron gate oxide. However, few have reported on the electrical quality and reliability of an ultra-thin gate. In this paper, we will recommend a novel shallow trench isolation structure and a two-step TiS $i_2$ formation process to improve the corner metal oxide semiconductor field-effect transistor (MOSFET) for sub-0.1${\mu}{\textrm}{m}$ VLSI devices. Differently from using normal LOCOS technology, deep sub-micron CMOS devices using the novel shallow trench isolation (STI) technology have unique "inverse narrow-channel effects" when the channel width of the device is scaled down. The titanium silicide process has problems because fluorine contamination caused by the gate sidewall etching inhibits the silicide reaction and accelerates agglomeration. To resolve these Problems, we developed a novel two-step deposited silicide process. The key point of this process is the deposition and subsequent removal of titanium before the titanium silicide process. It was found by using focused ion beam transmission electron microscopy that the STI structure improved the narrow channel effect and reduced the junction leakage current and threshold voltage at the edge of the channel. In terms of transistor characteristics, we also obtained a low gate voltage variation and a low trap density, saturation current, some more to be large transconductance at the channel for sub-0.1${\mu}{\textrm}{m}$ VLSI devices.

• Journal of the Korean Society for Precision Engineering
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• v.31 no.12
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• pp.1101-1106
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• 2014

Hybrid manufacturing technology has been advanced to overcome limitations due to traditional fabrication methods. To fabricate a micro/nano-scale structure, various manufacturing technologies such as lithography and etching were attempted. Since these manufacturing processes are limited by their materials, temperature and features, it is necessary to develop a new three-dimensional (3D) printing method. A novel nano-scale 3D printing system was developed consisting of the Nano-Particle Deposition System (NPDS) and the Focused Ion Beam (FIB) to overcome these limitations. By repeating deposition and machining processes, it was possible to fabricate micro/nano-scale 3D structures with various metals and ceramics. Since each process works in different chambers, a transfer process is required. In this research, nanoscale 3D printing system was briefly explained and an alignment algorithm for nano-scale 3D printing system was developed. Implementing the algorithm leads to an accepted error margin of 0.5% by compensating error in rotational, horizontal, and vertical axes.

• Progress in Superconductivity
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• v.7 no.1
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• pp.6-10
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• 2005

We have studied feasibility of single-layer second-order $high-T_c$ SQUID gradiometers in magnetocardiography. We have measured human cardiomagnetic signals using a short-baseline (5.8 mm) single-layer second-order YBCO gradiometer in partially shielded environments. The gradiometer has an overall size of $17.6\;mm{\times}6\;mm$ and contains three parallel-connected pickup coils which are directly coupled to a step-edge junction SQUID. The gradiometer showed an unshielded gradient noise of $0.84\;pT/cm^2/Hz^{1/2}$ at 1 Hz, which corresponds to an equivalent field noise of $280\;fT/Hz^{1/2}$. The balancing factor was $10^3$. Based on the same design rules as the short-baseline devices, we have studied fabrication of 30 mm-long baseline gradiometers. The devices had an overall size of $70.2\;mm{\times}10.6\;mm$ with each pickup coil of $10\;mm{\times}10\;mm$ in outer size. As Josephson elements we made two types of submicron bridges, which are variable thickness bridge (VTB) and constant thickness bridge (CTB), from $3\;{\mu}m-wide$ and 300 nm-thick YBCO lines with a thin layer of Au on top by using a focused ion beam (FIB) patterning method. VTB was 300 nm wide, 200 nm thick, 30 nm long with Au removed and CTB 100 nm wide and 30 nm long. In temperature-dependent critical currents, $I_c(T)$, VTB showed an nonmetallic barrier-type behavior and CTB an SNS behavior. We believe that those characteristics are ascribed to naturally formed grain boundaries crossing the bridges.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.12
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• pp.1171-1176
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• 2012

The selective patterning of a carbon nanotube (CNT) forest on a Si substrate has been performed using a femtosecond laser. The high shock wave generated by the femtosecond laser effectively removed the CNTs without damage to the Si substrate. This process has many advantages because it is performed without chemicals and can be easily applied to large-area patterning. The CNTs grown by plasma-enhanced chemical vapor deposition (PECVD) have a catalyst cap at the end of the nanotube owing to the tip-growth mode mechanism. For the application of an electron emission and biosensor probe, the catalyst cap is usually removed chemically, which damages the surface of the CNT wall. Precise control of the femtosecond laser power and focal position could solve this problem. Furthermore, selective CNT cutting using a femtosecond laser is also possible without any phase change in the CNTs, which is usually observed in the focused ion beam irradiation of CNTs.

• Journal of Powder Materials
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• v.21 no.3
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• pp.207-214
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• 2014

In this study, nano-scale copper powders were reduction treated in a hydrogen atmosphere at the relatively high temperature of $350^{\circ}C$ in order to eliminate surface oxide layers, which are the main obstacles for fabricating a nano/ultrafine grained bulk parts from the nano-scale powders. The changes in composition and microstructure before and after the hydrogen reduction treatment were evaluated by analyzing X-ray diffraction (XRD) line profile patterns using the convolutional multiple whole profile (CMWP) procedure. In order to confirm the result from the XRD line profile analysis, transmitted electron microscope observations were performed on the specimen of the hydrogen reduction treated powders fabricated using a focused ion beam process. A quasi-statically compacted specimen from the nano-scale powders was produced and Vickers micro-hardness was measured to verify the potential of the powders as the basis for a bulk nano/ultrafine grained material. Although the bonding between particles and the growth in size of the particles occurred, crystallites retained their nano-scale size evaluated using the XRD results. The hardness results demonstrate the usefulness of the powders for a nano/ultrafine grained material, once a good consolidation of powders is achieved.

• Applied Chemistry for Engineering
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• v.25 no.6
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• pp.577-580
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• 2014

Indium hydroxy sulfide ($In(OH)_xS_y$) as a cadmium (Cd)-free buffer layer for $CuInGaSe_2$ (CIGS) solar cells was prepared by the chemical bath deposition (CBD) and the reaction time was optimized. The band gap energy and transmittance data alongside the thickness results from the direct observation with focused ion beam system (FIB) could be a powerful tool for optimizing the conditions. In addition, X-ray diffractometer (XRD), X-ray photoelectron microscopy (XPS), and scanning electron microscope (SEM) were also employed for the layer characterization. The results indicated that the optimum reaction time for $In(OH)_xS_y$ buffer layer deposition by CBD was 20 min at $70^{\circ}C$ under the conditions employed. At the optimum conditions, the buffer layer thickness was near 57 nm and the band gap energy was 2.7 eV. In addition, it was found that there was no XPS peak shift in between the buffer layers deposited on molybdenum (Mo)/glass and that on CIGS layer.

• 한국정보디스플레이학회:학술대회논문집
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• 2000.01a
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• pp.117-118
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• 2000

The secondary electron emission coefficient ${\gamma}$ of MgO single crystals according to the gas mixture ratio of Xe to Ne have been investigated by ${\gamma}-focused$ ion beam system. It is found that the MgO single crystals of (111) crystallinity has the highest ${\gamma}$ from 0.09(0.03) up to 0.16(0.04), while from 0.07(0.02) to 0.15(0.03) for (200) and from 0.06(0.01) to 0.13(0.02) for (220) crystallinity for operating Ne (Xe) ions ranging from 50eV to 200eV throughout this experiment. And it is found that the ${\gamma}$ ranged from 0.03 up to 0.06 for Ne-Xe mixtures are much smaller than those of 0.09 up to 0.16 for pure Ne ions under accelerating voltage ranged from 50V to 200V.

• Proceedings of the Materials Research Society of Korea Conference
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• 2012.05a
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• pp.55.2-55.2
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• 2012

Intensive theoretical and experimental studies have been carried out at Korean Institute of Science and Technology (KIST) on controlling the bio absorbing rate of the Mg alloys with high mechanical strength through tailoring of electrochemical potential. Key technology for retarding the corrosion of the Mg alloys is to equalize the corrosion potentials of the constituent phases in the alloys, which prevented the formation of Galvanic circuit between the constituent phases resulting in remarkable reduction of corrosion rate. By thermodynamic consideration, the possible phases of a given alloy system were identified and their work functions, which are related to their corrosion potentials, were calculated by the first principle calculation. The designed alloys, of which the constituent phases have similar work function, were fabricated by clean melting and extrusion system. The newly developed Mg alloys named as KISTUI-MG showed much lower corrosion rate as well as higher strength than previously developed Mg alloys. Biocompatibility and feasibility of the Mg alloys as orthopedic implant materials were evaluated by in vitro cell viability test, in vitro degradation test of mechanical strength during bio-corrosion, in vivo implantation and continuous observation of the implant during in vivo absorbing procedures. Moreover, the cells attached on the Mg alloys was observed using cryo-FIB (focused ion beam) system without the distortion of cell morphology and its organ through the removal of drying steps essential for the preparation of normal SEM/TEM samples. Our Mg alloys showed excellent biocompatibility satisfying the regulations required for biomedical application without evident hydrogen evolution when it implanted into the muscle, inter spine disk, as well as condyle bone of rat and well contact interface with bone tissue when it was implanted into rat condyle.

• Nuclear Engineering and Technology
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• v.46 no.2
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• pp.147-158
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• 2014

In order to investigate how the microstructure of fuel/matrix-interaction (FMI) layers change during irradiation, different U-7Mo dispersion fuel plates have been irradiated to high fission density and then characterized using scanning electron microscopy (SEM). Specifially, samples from irradiated U-7Mo dispersion fuel elements with pure Al, Al-2Si and AA4043 (~4.5 wt.%Si) matrices were SEM characterized using polished samples and samples that were prepared with a focused ion beam (FIB). Features not observable for the polished samples could be captured in SEM images taken of the FIB samples. For the Al matrix sample, a relatively large FMI layer develops, with enrichment of Xe at the FMI layer/Al matrix interface and evidence of debonding. Overall, a significant penetration of Si from the FMI layer into the U-7Mo fuel was observed for samples with Si in the Al matrix, which resulted in a change of the size (larger) and shape (round) of the fission gas bubbles. Additionally, solid fission product phases were observed to nucleate and grow within these bubbles. These changes in the localized regions of the microstructure of the U-7Mo may contribute to changes observed in the macroscopic swelling of fuel plates with Al-Si matrices.

• Korean Journal of Metals and Materials
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• v.48 no.6
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• pp.533-542
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• 2010

The specific motivation for joining an Al alloy and Zn-coated steel arises from the need to save fuel consumption by weight reduction and to enhance the durability of vehicle structures in the automobile industry. In this study, the lap joining A6K31 Al alloy (top) and SGARC340 Zn-coated steel (bottom) sheets with a thickness of 1.0 mm and 0.8 mm, respectively, was carried out using the friction stir weld (FSW) technique. The probe of a tool did not contact the surface of the lower Zn-coated steel sheet. The friction stir welding was carried out at rotation speeds of 1500 rpm and travel speeds of 80~200 mm/min. The effects of tool geometry and welding speed on the mechanical properties and the structure of a joint were investigated. The tensile properties for the joints welded with a larger tool were better than those for the joints done with a smaller tool. A good correlation between the tensile load and area of the welded region were observed. The bond strength using a larger tool (M4 and M3) decreased with an increase in welding speed. Most fractures occurred along the interface between the Zn-coated steel and the Al alloy. However, in certain conditions with a lower welding speed, fractures occurred at the A6K31 Al alloy.