• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.12
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• pp.1805-1810
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• 2010

We present a simple, cost-effective, and fast fabrication process for three-dimensional (3D) microstructures; this process is based on multi-step electrochemical etching of metal foils which facilitates the mass production of 3D microstructures. Compared to electroplating, this process maintains uniform and well-controlled material properties of the microstructure. In the experimental study, we perform single-step electrochemical etching of aluminum foils for the fabrication of 2D cantilever arrays. In the single-step etching, the depth etch rate and bias etch rate are measured as $1.50{\pm}0.10 {\mu}m/min$ and $0.77{\pm}0.03 {\mu}m/min$, respectively. Using the results of single-step etching, we perform two-step electrochemical etching for 3D microstructures with probe tips on cantilevers. The errors in height and lateral fabrication in the case of the fabricated structures are $15.5{\pm}5.8% $ and $3.3{\pm}0.9%$, respectively; the surface roughness is $37.4{\pm}9.6nm$.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.363-363
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• 2014

Ruthenium (Ru) has attractive material properties due to its promising characteristics such as a low resistivity ($7.1{\mu}{\Omega}{\cdot}cm$ in the bulk), a high work function of 4.7 eV, and feasibility for the dry etch process. These properties make Ru films appropriate for various applications in the state-of-art semiconductor device technologies. Thus, it has been widely investigated as an electrode for capacitor in the dynamic random access memory (DRAM), a metal gate for metal-oxide semiconductor field effect transistor (MOSFET), and a seed layer for Cu metallization. Due to the continuous shrinkage of microelectronic devices, better deposition processes for Ru thin films are critically required with excellent step coverages in high aspect ratio (AR) structures. In these respects, atomic layer deposition (ALD) is a viable solution for preparing Ru thin films because it enables atomic-scale control of the film thickness with excellent conformality. A recent investigation reported that the nucleation of ALD-Ru film was enhanced considerably by using a zero-valent metallorganic precursor, compared to the utilization of precursors with higher metal valences. In this study, we will present our research results on the synthesis and characterization of novel ruthenium complexes. The ruthenium compounds were easy synthesized by the reaction of ruthenium halide with appropriate organic ligands in protic solvent, and characterized by NMR, elemental analysis and thermogravimetric analysis. The molecular structures of the complexes were studied by single crystal diffraction. ALD of Ru film was demonstrated using the new Ru metallorganic precursor and O2 as the Ru source and reactant, respectively, at the deposition temperatures of $300-350^{\circ}C$. Self-limited reaction behavior was observed as increasing Ru precursor and O2 pulse time, suggesting that newly developed Ru precursor is applicable for ALD process. Detailed discussions on the chemical and structural properties of Ru thin films as well as its growth behavior using new Ru precursor will be also presented.

• Restorative Dentistry and Endodontics
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• v.18 no.1
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• pp.1-26
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• 1993

The purpose of this study was to investigate the effect of acid etching on the surface appearance and fracture toughness of five glass ionomer cements. Five kinds of commercially available glass ionomer cements including chemical curing filling type, chemical curing lining type, chemical curing metal reinforced type, light curing tilling type and light curing lining type were used for this study. The specimens for SEM study were fabricated by treating each glass ionomer cement with either visible light curing or self curing after being inserted into a rubber mold (diameter 4mm, depth 1mm). Some of the specimens were etched with 37% phosphoric acid for 0, 15, 30, 60, go seconds, at 5 minutes, 1 hour and 1 day after mixing of powder and liquid. Unetched ones comprised the control group and the others were the experimental groups. The surface texture was examined by using scanning electron microscope at 20 kV. (S-2300, Hitachi Co., Japan). The specimens for fracture toughness were fabricated by curing of each glass ionomer cement previously inserted into a metal mold for the single edge notch specimen according to the ASTME399. They were subjected to a three-point bend test after etching for 0, 30, 60, and 90 seconds at 5 minutes-, 1 hour-and 1 day-lapse after the fabrication of the specimens. The plane strain fracture toughness ($K_{IC}$) was determined by three-point bend test which was conducted with cross-head speed of 0.5 mm/min using Instron universal testing machine (Model No. 1122) following seven days storage of the etched specimens under $37^{\circ}C$, 100% humidity condition. Following conclusions were drawn. 1. In unetched control group, crack was present, but the surface was generally smooth. 2. Deterioration of the surface appearance such as serious dissolving of gel matrix and loss of glass particles occured as the etching time was increased beyond 15 s following Immediate etching of chemical curing type of glass ionomer cements. 3. Etching after 1 h, and 1 d reduced surface damage, 15 s, and 30s etch gave rough surface appearance without loss of glass particle of chemical curing type of glass ionomer cements. 4. Light curing type glass ionomer cement was etched by acid, but there was no difference in surface appearances according to various waiting periods. 5. It was found that the value of plane stram fracture toughness of glass ionomer cements was highest in the light curing filling type as $1.79\;MNm^{-1.5}$ followed by the light curing lining type, chemical curing metal reinforced type, chemical curing filling type and chemical curing lining type. 6. The value of plane stram fracture toughness of the chemical curing lining type glass ionomer cement etched after 5 minutes was lower than those of the cement etched after 1 hour or day or unetched (P < 0.05). 7. Light curing glass ionomer cement showed Irregular fractured surface and chemical curing cement showed smooth fractured surface.

• ETRI Journal
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• v.24 no.4
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• pp.290-298
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• 2002

We present, for the first time, a prototype active-matrix field emission display (AMFED) in which an amorphous silicon thin-film transistor (a-Si TFT) and a molybdenum-tip field emitter array (Mo-tip FEA) were monolithically integrated on a glass substrate for a novel active-matrix cathode (AMC) plate. The fabricated AMFED showed good display images with a low-voltage scan and data signals irrespective of a high voltage for field emissions. We introduced a light shield layer of metal into our AMC to reduce the photo leakage and back channel currents of the a-Si TFT. We designed the light shield to act as a focusing grid to focus emitted electron beams from the AMC onto the corresponding anode pixel. The thin film depositions in the a-Si TFTs were performed at a high temperature of above 360°C to guarantee the vacuum packaging of the AMC and anode plates. We also developed a novel wet etching process for $n^+-doped$ a-Si etching with high etch selectivity to intrinsic a-Si and used it in the fabrication of an inverted stagger TFT with a very thin active layer. The developed a-Si TFTs performed well enough to be used as control devices for AMCs. The gate bias of the a-Si TFTs well controlled the field emission currents of the AMC plates. The AMFED with these AMC plates showed low-voltage matrix addressing, good stability and reliability of field emission, and good light emissions from the anode plate with phosphors.

• Korean Journal of Crystallography
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• v.5 no.2
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• pp.67-77
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• 1994

From the Y3-3xNd3xAl5O12single crystals grown by the Czochralski technique, various types of defects were detected and 1) the reason of opical in homogeneous phases, 2) the mechanism of formation of the iridum metal inclusions accompanying bubbles, and 3) the mechanism of formation of the core and facet were analysed After preparing the wafers of the <111> growth parallel, defscts were observed by the polarising microscope using a photoelasic effect and then some images of stress-birefringence were compared to their etch Pits patterns.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.150-150
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• 2008

본 연구에서는 Wet chemistry damage가 Nanopatterned p-ohmic electrode에 미치는 영향을 연구하였다. Nanopattern은 Metal clustering을 이용하여, P-GaN와 Ohmic형성에 유리한 Pd을 50$\AA$ 적층한 후 Rapid Thermal Annealing방법으로 $850^{\circ}C$, $N_2$분위기에서 3min열처리를 하여 Pd Clustering mask 를 제작하였다. Wet etching은 $85^{\circ}C$, $H_3PO_4$조건에서 시간에 따라 Sample을 Dipping하는 방법으로 시행하였다 Ohmic test를 위해서 Circular - Transmission line Model 방법을 이용하였으며, Atomic Force Microscopy과 Parameter Analyzer로 Nanopatterned GaN surface위에 형성된 Ni/ Au Contact에서의 전기적 분석과, 표면구조분석을 시행하였다. AFM결과 Wet처리시간에 따라서 Etching형상 및 Etch rate이 영향을 받는 것이 확인되었고, Ohmic test에서 Wet chemistry처리에 의한 Tunneling parameter와 Schottky Barrier Height가 크게 증/감함을 관찰하였다. 이러한 결과들은 Wet처리에 의해서 발생된 Defect가 GaN의 표면과 하부에서 발생되며, Deep acceptor trap 및 transfer거동과 밀접한 관련이 있음을 확인 할 수 있었다. 보다 자세한 Transport 및 Wet chemical처리영향에 관한 형성 Mechanism은 후에 I-V-T, I-V, C-V, AFM결과 들을 활용하여 발표할 예정이다.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.27 no.6
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• pp.303-308
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• 2017

The $FeCl_3$ waste solution used to etch various metals contains valuable metal such as nickel. In this study, we recovered as high purity nickel carbonate crystalline powders from nickel-containing etching waste solution after regeneration of iron chloride. Firstly we eliminated about of the iron impurities under the condition of pH 4 using 5 % NaOH aqueous solution and then removed the remaining impurities such as Ca, Mn and Zn etc. by using solvent extractant D2EHPA (Di-(2-ethylhexyl) phosphoric acid). Thereafter, nickel carbonate powder having a purity of 99.9 % or more was obtained through reaction with sodium carbonate in a nickel chloride solution.

• Journal of Welding and Joining
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• v.31 no.5
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• pp.47-53
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• 2013

We have investigated the traits of clad metals in hot-rolled clad steel plates, including the sensitization and mechanical properties of STS 316 steel plate and carbon steel (A516), under various specific circumstances regarding post heat treatment, multilayered welds, and thick or repeated welds for repair. For evaluations, sectioned weldments and external surfaces were investigated to reveal the degree of sensitization by micro vickers hardness, tensile, and etching tests the results were compared with those of EPR tests. The clad steel plates were butt-welded using FCAW and SAW with the time of heat treatment as the variable, a that was conducted at $625^{\circ}C$, for 80, 160, 320, 640, and 1280 min. Then, the change in corrosion resistance was evaluated in these specimens. With carbon steel (A516), as the heat treatment time increased, the annealing effect caused the tensile strength to decrease. The micro-hardness gradually increased and decreased after 640 min. The elongation and contraction of the area also increased gradually. The oxalic acid etch test and EPR test on STS316 and the clad metal showed STEP structure and no sensitization. From the test results on multi-layered and repair welds, it could be concluded that there is no effect on the corrosion resistance of clad metals. The purpose of this study was to suggest some considerations for developing on-site techniques to evaluate the sensitization of stainless steels.

• Korean Journal of Materials Research
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• v.10 no.6
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• pp.450-455
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• 2000

For further scaling down of the silicon devices, the application of low dielectric constant materials instead of silicon oxide has been considered to reduce power consumption, crosstalk, and interconnection delay. In this paper, the effect of $O_2/SF_6$ plasma chemistry on the etching characteristics of polyimide-one of the promising low-k interlayer dielectrics-has been studied. The etch rate of polyimide decreases with the addition of $SF_6$ gas due to formation of nonvolatile fluorine compounds inhibiting reaction between oxygen and hydrocarbon polymer, while applying substrate bias enhances etching process through physical attack. However, addition of small amount of $SF_6$ is desirable for etching topography. $SiO_2$ hard mask for polyimide etching is effective under $O_2$plasma etching(selectivity~30), while $O_2/SF_6$ chemistry degrades etching selectivity down to 4. Based on the above results, $1-2\mu\textrm{m}$ L&S PI2610 patterns were successfully etched.

• Korean Journal of Materials Research
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• v.28 no.5
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• pp.268-272
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• 2018

An $Al_2O_3/AlN$ bilayer deposited on GaN by atomic layer deposition (ALD) is employed to prepare $Al_2O_3/AlN/GaN$ metal-insulator-semiconductor (MIS) diodes, and their interfacial properties are investigated using X-ray photoelectron spectroscopy (XPS) with sputter etch treatment and current-voltage (I-V) measurements. XPS analyses reveal that the native oxides on the GaN surface are reduced significantly during the early ALD stage, indicating that AlN deposition effectively clelans up the GaN surface. In addition, the suppression of Al-OH bonds is observed through the ALD process. This result may be related to the improved device performance because Al-OH bonds act as interface defects. Finally, temperature dependent I-V analyses show that the barrier height increases and the ideality factor decreases with an increase in temperature, which is associated with the barrier inhomogeneity. A Modified Richardson plot produces the Richardson constant of $A^{**}$ as $30.45Acm^{-2}K^{-2}$, which is similar to the theoretical value of $26.4Acm^{-2}K^{-2}$ for n-GaN. This indicates that the barrier inhomogeneity appropriately explains the forward current transport across the $Au/Al_2O_3/AlN/GaN$ interface.