• Journal of Welding and Joining
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• 제24권2호
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• pp.71-78
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• 2006

It has been reported that good quality weld beads are not easily obtained during the $CO_2$ CW laser welding of primer coated plate. However, by introducing a small gap clearance in the lap position, the zinc vapor can escape through it and sound weld beads can be acquired. Therefore, this study examines for keyhole behavior by observing the laser-induced plasma and investigates the relation between keyhole behavior and formation of weld defect. Laser-induced plasma has accompanied with the vaporizing pressure of zinc ejecting from keyhole to surface of primer coated plate. This dynamic behavior of plasma was very unstable and this instability was closely related to the unstable motion of keyhole during laser welding. As a result of observing the composition of porosity, much of Zn element was found from inner surface of porosity. But Zn was not found from the dimple structure fractured at the weld metal. By analyzing of vaporizing element in laser welding, a component ratio of Zn was decreased by introducing a small gap clearance. Therefore we can prove that the major cause of porosity is the vaporization of primer in lap position. Mechanism of porosity-formation is that the primer vaporized from the lap position accelerates dynamic behavior of the key hole and the bubble separated from the key hole is trapped in the solidification boundary and romaines as porosity.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.316-321
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• 2003

The spatter and porosity could be occurred during $CO_2$ CW laser welding of Primer-coated Steel for Shipbuilding. This study has suggested an alternative idea by examining of weld-defect formation mechanism. The primer-coated plate has caused the spatter, humping bead and porosity and these are main part of the welding defect, attributed to the powerful vaporizing pressure of primer attached on the base metal. The zinc of primer has a boiling point that is the lower temperature than melting point of steel. Zinc va}X)f will build up at the interface between the two sheets and this tends to deteriorate the quality of the weld by ejecting weld material from lap position or leaving porosity. Therefore introducing a small gap clearance in the lap position, the zinc vapor could escape through it and sound weld beads can be acquired. In conclusion, we suggested the occurred and prevented mechanism of weld defects with searching the factor.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2010년도 제39회 하계학술대회 초록집
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• pp.207-207
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• 2010

Both ZnO and GaN have excellent physical properties in optoelectronic devices such as blue light emitting diode (LED), blue laser diode (LD), and ultra-violet (UV) detector. The ZnO/GaN heterostructure, which has a potential to achieve the cost efficient LED technology, has been fabricated by using radio frequency (RF) sputtering, pyrolysis, metal organic chemical vapor deposition (MOCVD), direct current (DC) arc plasmatron, and pulsed laser deposition (PLD) methods. Among them, the PLD system has a benefit to control the composition ratio of the grown film from the mixture target. A 500-nm-thick ZnO film was grown by PLD technique on c-plane GaN/sapphire substrates. The post annealing process was executed at some varied temperature between from $300^{\circ}C$ to $900^{\circ}C$. The morphology and crystal structural properties obtained by using atomic force microscope (AFM) and x-ray diffraction (XRD) showed that the crystal quality of ZnO thin films can be improved as increasing the annealing temperature. We will discuss the post-treatment effect on film quality (uniformity and reliability) of ZnO/GaN heterostructures.

• 한국초전도ㆍ저온공학회논문지
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• 제14권4호
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• pp.5-11
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• 2012

In this review article, we focus on various co-evaporation technologies developed for the fabrication of high performance $REBa_2Cu_3O_{7-{\delta}}$ (RE: Y and Rare earth elements, REBCO) superconducting films. Compared with other manufacturing technologies for REBCO films such as sputtering, pulsed laser deposition (PLD), metal-organic deposition (MOD), and metal organic chemical vapor deposition (MOCVD), the co-evaporation method has a strong advantage of higher deposition rate because metal sources can be used as precursor materials. After the first attempt to produce REBCO films by the co-evaporation method in 1987, various co-evaporation technologies for high performance REBCO films have been developed during last several decades. The key points of each co-evaporation technology are reviewed in this article, which enables us to have a good insight into a new high throughput process, called as a Reactive Co-Evaporation by Deposition and Reaction (RCE-DR).

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제42회 동계 정기 학술대회 초록집
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• pp.391-392
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• 2012

In these days, the desire for the precise and tiny displays in mobile application has been increased strongly. Currently, laser displays ranging from large-size laser TV to mobile projectors, are commercially available or due to appear on the market [1]. In order to achieve a mobile projectors, the semiconductor laser diodes should be used as a laser source due to their size and weight. In this presentation, the continuous etch characteristics of Pd and AlGaN/GaN superlattice for the fabrication of blue laser diodes were investigated by using inductively coupled $CHF_3$ and $Cl_2$ -based plasma. The GaN laser diode samples were grown on the sapphire (0001) substrate using a metal organic chemical vapor deposition system. A Si-doped GaN layer was grown on the substrate, followed by growth of LD structures, including the active layers of InGaN/GaN quantum well and barriers layer, as shown in other literature [2], and the palladium was used as a p-type ohmic contact metal. The etch rate of AlGaN/GaN superlattice (2.5/2.5 nm for 100 periods) and n-GaN by using $Cl_2$ (90%)/Ar (10%) and $Cl_2$ (50%)/$CHF_3$ (50%) plasma chemistry, respectively. While when the $Cl_2$/Ar plasma were used, the etch rate of AlGaN/GaN superlattice shows a similar etch rate as that of n-GaN, the $Cl_2/CHF_3$ plasma shows decreased etch rate, compared with that of $Cl_2$/Ar plasma, especially for AlGaN/GaN superlattice. Furthermore, it was also found that the Pd which is deposited on top of the superlattice couldn't be etched with $Cl_2$/Ar plasma. It was indicating that the etching step should be separated into 2 steps for the Pd etching and the superlattice etching, respectively. The etched surface of stacked Pd/superlattice as a result of 2-step etching process including Pd etching ($Cl_2/CHF_3$) and SLs ($Cl_2$/Ar) etching, respectively. EDX results shows that the etched surface is a GaN waveguide free from the Al, indicating the SLs were fully removed by etching. Furthermore, the optical and electrical properties will be also investigated in this presentation. In summary, Pd/AlGaN/GaN SLs were successfully etched exploiting noble 2-step etching processes.

• 전자공학회논문지A
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• 제30A권10호
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• pp.27-32
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• 1993

Separate-confinement hetero-structure (SCH) broad area Laser Diodes (LD's) were fabricated from $Al_{0.07}$Ga$_{0.93}$/. As single-quantum-well (SQW) grown by metal organic chemical vapor deposition (MOCVD). Under pulsed operation, we obtained maximum output powers of about 0.8watt/facet and 1.83watt/facet from LD's with 60$\mu$m and 160$\mu$m channel width, respectively, without facet coatings. The differential quantum efficiency of the 60$\mu$m wide LD was about 21.7%/facet and its threshold current density was about 1k [A/cm$^{2}$]. The differential quantum efficiency of the 160$\mu$m wide LD was about 25.6%/facet and its threshold current density was about 1k[A/cm$^{2}$]. The minimum threshold current density of 60$\mu$m wide LD's was 620[A/cm$^{2}$] when the cavity length was 603$\mu$m and the minimum threshold current density of 160$\mu$m wide Ld's was 675[A/cm$^{2}$] when the cavity length was 752$\mu$m. The internal quantum efficienty and the internal loss of both LD's were 92.3% and 18.1cm$^{1}$, respectively.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.319-319
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• 2013

Even though the fabrication methods of metal oxide based thin film capacitor have been well established such as RF sputtering, Sol-gel, metal organic chemical vapor deposition (MOCVD), ion beam assisted deposition (IBAD) and pulsed laser deposition (PLD), an applicable capacitor of printed circuit board (PCB) has not realized yet by these methods. Barium Strontium Titanate (BST) and other high-k ceramic oxides are important materials used in integrated passive devices, multi-chip modules (MCM), high-density interconnect, and chip-scale packaging. Thin film multi-layer technology is strongly demanded for having high capacitance (120 nF/$mm^2$). In this study, we suggest novel multi-layer thin film capacitor design and fabrication technology utilized by plasma assisted deposition and photolithography processes. Ba0.6Sr0.4TiO3 (BST) was used for the dielectric material since it has high dielectric constant and low dielectric loss. 5-layered BST and Pt thin films with multi-layer sandwich structures were formed on Pt/Ti/$SiO_2$/Si substrate by RF-magnetron sputtering and DC-sputtering. Pt electrodes and BST layers were patterned to reveal internal electrodes by photolithography. SiO2 passivation layer was deposited by plasma-enhanced chemical vapor deposition (PE-CVD). The passivation layer plays an important role to prevent short connection between the electrodes. It was patterned to create holes for the connection between internal electrodes and external electrodes by reactive-ion etching (RIE). External contact pads were formed by Pt electrodes. The microstructure and dielectric characteristics of the capacitors were investigated by scanning electron microscopy (SEM) and impedance analyzer, respectively. In conclusion, the 0402 sized thin film multi-layer capacitors have been demonstrated, which have capacitance of 10 nF. They are expected to be used for decoupling purpose and have been fabricated with high yield.

• 대한전자공학회논문지SD
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• 제40권9호
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• pp.666-672
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• 2003

본 논문에서는 광의 결합 메커니즘이 다른 ITG(integrated-twin-guide) 와 BT(butt coupled) 구조를 가지는 두 종류의 파장 가변 DBR-LD의 제작공정과 성능에 대해서 기술하였다. 두 종류의 DBR-LD는 PBH(planar buried heterostructure) 구조론 가지며, MOVPE 성장으로 제작하였다. 제작된 DBR-LD 광출력 특성을 측정한 결과 BT-DBR-LD가 ITG-DBR-LD보다 임계전류 변화폭, 광출력 변화 폭, 기울기 효율에서 2배 이상의 우수한 특성을 나타내었다. 그리고, 준 연속 파장 가변 특성은 BT-DBR-LD가 7.2nm, ITG-DBR-LD가 7.4nm 이며, SMSR이 35dB 이상으로 우수하게 나타났다. 이와 같이 BT DBR-LD가 특성이 우수한 것은 BT 구조가 ITG 구조보다 높은 결합 효율을 나타내기 때문이다.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2003년도 추계학술발표강연 및 논문개요집
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• pp.93-93
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• 2003

Tungsten and tungsten heavy alloys have widespread application as radiation shielding devices and heavy duty electrical contacts. High density and good room temperature mechanical properties have generated interest in evaluating tungsten and tungsten alloys as kinetic energy penetrators against armor. Nowdays ultra fine-grained tungsten powders are in great interest because higly dense structures can be obtained at low temperature, pressure and lower sintering time. Several physical md chemical methods are available for the synthesis of nanometric metal Powders: ball milling, laser abalation, vapor condensation, chemical precipitation, metallic wire explosion i.e. However production rates of the above mentioned methods are low and further efforts are needed to find out large-scale synthesis methods. From this point of view solid state combustion method ( known as SHS) represents undoubted interest.

• Applied Science and Convergence Technology
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• 제23권6호
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• pp.371-375
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• 2014

Diffusion coefficient of Fe in polycrystalline host ZnSe as a mid-IR gain medium has been measured in the annealing temperature ranges of 850 to $950^{\circ}C$. The synthesis of the samples was carried out in quartz ampoule in which the Fe thin film deposited by physical vapor evaporation method on the ZnSe. One can realize that the diffusion coefficient strongly depends on the surface active surfactants through the cleaning process and the substrate temperature during the thin film deposition leading to $2.04{\times}10^{-9}cm^2/s$ for $Fe^{2+}:ZnSe$. The Annealing temperature dependence of the Fe ions diffusion in ZnSe was used to evaluate the activation energy, $E_a$=1.39 eV for diffusion and the pre-exponential factor $D_0$ of $13.5cm^2/s$.