• Applied Chemistry for Engineering
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• v.32 no.3
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• pp.268-276
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• 2021

As wireless communication devices become more common, interests in how to control the electromagnetic waves generated from the devices are increasing. One of the most commonly used electromagnetic wave control materials is magnetic one, but due to the features that make the product heavy and thick when applied to the product, it is difficult to use them in curved electronic devices. Therefore, a polymer flexible meta electronic device has been presented to sort out the problem, which is thin and can have various curvatures. However, it requires an additional evaluation of curvature reliability. In this study, we developed a method to predict electromagnetic wave control characteristics through the resistance/length of the conductive ink line patterns of polymer flexible meta electronic devices, which is inversely proportional to the electromagnetic wave control characteristics. As the radius of curvature decreased, the resistance/length increased, and there was little variations with the duration times of curvature. We also found that both permanent and recoverable changes along with the removal of curvature were occurred when the curvature was applied, and that the cause of these changes was newly created vertical cracks in the conductive ink line pattern due to the tensile stress applied by applying curvature.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.187-187
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• 2012

In this report, the plasmonic nanopores of less than 5 nm diameter were fabricated on the apex of the pyramidal cavity array. The metallic pyramidal pit cavity can also utilized as the plasmonic bioreactor, and the fabricated Au or Al metallic nanopore can provide the controllable translocation speed down using the plasmonic optical force. Initially, the SiO2 nanopore on the pyramidal pit cavity were fabricated using conventional microfabrication techniques. Then, the metallic thin film was sputter-deposited, followed by surface modification of the nanometer thick membrane using FESEM, TEM and EPMA. The huge electron intensity of FESEM with ~microsecond scan speed can provide the rapid solid phase surface transformation. However, the moderate electron beam intensity from the normal TEM without high speed scanning can only provide the liquid phase surface modification. After metal deposition, the 100 nm diameter aperture using FIB beam drilling was obtained in order to obtain the uniform nano-aperture. Then, the nanometer size aperture was reduced down to ~50 nm using electron beam surface modification using high speed scanning FESEM. The followed EPMA electron beam exposure without high speed scanning presents the reduction of the nanosize aperture down to 10 nm. During these processes, the widening or the shrinking of the nanometer pore was observed depending upon the electron beam intensity. Finally, using 200 keV TEM, the diameter of the nanopore was successively down from 10 nm down to 1.5 nm.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.218-218
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• 2012

Recently, hexagonal manganites have attracted much attention because of the coexistence of ferroelectricity and antiferromagnetic (AFM) order. The crystal structure of hexagonal manganites consists of $MnO_5$ polyhedra in which $Mn^{3+}$ ion is surrounded by three oxygen atoms in plane and two apical oxygen ions. The Mn ions within Mn-O plane form a triangular lattice and couple the spins through the AFM superexchange interaction. Due to incomplete AFM coupling between neighboring Mn ions in the triangular lattice, the system forms a geometrically-frustrated magnetic state. Among hexagonal manganites, $YMnO_3$, in particular, is the best known experimentally since the f states are empty. In addition, for applications, $YMnO_3$ thin films have been known as promising candidates for non-volatile ferroelectric random access memories. However, $YMnO_3$ has low magnetic order temperature (~70 K) and A-type AFM structure, which hinders its applications. We have synthesized $YMn1_{-x}Cr_xO_3$ (x = 0, 0.05 and 0.1) samples by the conventional solid-state reaction. The powders of stoichiometric proportions were mixed, and calcined at $900^{\circ}C$ for $YMn1_{-x}Cr_xO_3$ for 24 h. The obtained powders were ground, and pressed into 5-mm-thick disks of 1/2-inch diameter. The disks were directly put into the oven, and heated up to $1,300^{\circ}C$ and sintered in air for 24 h. The phase of samples was checked at room temperature by powder x-ray diffraction using a Rigaku Miniflex diffractometer with Cu $K{\alpha}$ radiation. All the magnetization measurements were carried out with a superconducting quantum-interference-device magnetometer. Our experiments point out that the Cr-doped samples show the characteristics of a spin-glass state at low temperatures.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.99-99
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• 2009

Two different micro-flows during the evaporation of ink droplets were achieved by engineering both surface tension gradient and compositional gradient across the ink droplet: (1) Coffee-ring generating flow resulting from the outward flow inside the ink droplet & (2) Marangoni flow leading to the circulation flow inside the ink droplet. The surface tension gradient and the compositional gradient in the ink droplets were tailored by mixing two different solvents with difference surface tension and boiling point. In order to create the coffee-ring generating flow (outward flow), a single-solvent system using N,N-dimethylformamide with nano-sized spherical alumina particles was formulated, Marangoni flow (circulation flow) was created in the ink droplets by combining N,N-dimethylformamide and fotmamide with the spherical alumina powders as a co-solvent ink system. We have investigated the effect of these two different flows on the formation of ceramic films by inkjet printing method, The packing density of the ceramic films printed with two different ink systems (single- and co-solvent systems) and their surface roughness were characterized. The dielectric properties of these inkjet-printed ceramic films such as dielectric constant and dissipation factor were also studied in order to evaluate the feasibility of their application to the electronic ceramic package substrate.

• Proceedings of the IEEK Conference
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• 2005.11a
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• pp.603-606
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• 2005

In this paper, the formation and thermal stability of Ni-silicide using Ni-Pd alloys is studied for ultra shallow S/D junction of nano-scale CMOSFETs. There are no different effects when Ni-Pd is used in single structure and TiN capping structure. But, in case of Cobalt interlayer structure, it was found that Pure Ni had lower sheet resistance than Ni-Pd, because of a thick silicide. Also, Ni-Pd has merits that surface of silicide and interface between silicide and silicon have a good morphology characteristics. As a result, Ni-Pd is an optimal candidate for shallow S/D junction when cobalt is used for thermal stability.

• Journal of the Korean Electrochemical Society
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• v.20 no.2
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• pp.41-48
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• 2017

Herein, we have fabricated an ultrathin aluminum oxide ($Al_2O_3$) coated PP separator by using a RF sputter deposition process. Approximately 20 nm thickness coating layer on the bare PP separator was formed at the power of 55 W for 2 minutes without thermal damage. Whereas only permeability of the coated separator was degraded slightly, other properties such as thermal stability, uptake amount of liquid electrolyte, and ionic conductivity were improved comparing to the bare PP separator. As a result, an only 20-nm-thick $Al_2O_3$ coating layer could improve the rate capability compared with a bare PP separator under a high current density.

• Transactions of the Korean hydrogen and new energy society
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• v.17 no.1
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• pp.69-74
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• 2006

Thick film $H_2$ sensors were fabricated using $SnO_2$ loaded with $Ag_2O$ and $PtO_x$. The composition that gave the highest sensitivity for $H_2$ was in the weight% ratio of $SnO_2 : PtO_x : Ag_2O$ as 93 : 1 : 6. The nano-crystalline powders of $SnO_2$ synthesized by sol-gel method were screen printed with $Ag_2O$ and $PtO_x$ on alumina substrates. The fabricated sensors were tested against gases like $H_2$, $CH_4$, $C_3H_8$, $C_2H_5OH$ and $SO_2$. The composite material was found sensitive against $H_2$ at the working temperature $130^{\circ}C$, with minor interference of other gases. The $H_2$ gas as low as 100 ppm can be detected by the present fabricated sensors. It was found that the sensors based on $SnO_2-Ag_2O-PtO_x$ system exhibited the high performance, high selectivity and very short response time to $H_2$ at ppm level. These characteristics make the sensor to be a promising candidate for detecting low concentrations of $H_2$.

• 한국신재생에너지학회:학술대회논문집
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• 2009.06a
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• pp.138-138
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• 2009

Recently, thin-film solar cells of Cu(In,Ga)$Se_2$(CIGS) have reached a high level of performance, which has resulted in a 19.9%-efficient device. These conventional devices were typically fabricated using chemical bath deposited CdS buffer layer between the CIGS absorber layer and ZnO window layer. However, the short wavelength response of CIGS solar cell is limited by narrow CdS band gap of about 2.42 eV. Taking into consideration the environmental aspect, the toxic Cd element should be replaced by a different material. It is why during last decades many efforts have been provided to achieve high efficiency Cd-free CIGS solar cells. In order to alternate CdS buffer layer, ZnS buffer layer is grown by using chemical bath deposition(CBD) technique. The thickness and chemical composition of ZnS buffer layer can be conveniently by varying the CBD processing parameters. The processing parameters were optimized to match band gap of ZnS films to the solar spectrum and exclude the creation of morphology defects. Optimized ZnS buffer layer showed higher optical transmittance than conventional thick-CdS buffer layer at the short wavelength below ~520 nm. Then, chemically deposited ZnS buffer layer was applied to CIGS solar cell as a alternative for the standard CdS/CIGS device configuration. This CIGS solar cells were characterized by current-voltage and quantum efficiency measurement.

• Journal of Sensor Science and Technology
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• v.15 no.5
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• pp.309-316
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• 2006

The $SnO_{2}$ thin film sensors were fabricated by a thermal oxidation method. $SnO_{2}$ thin film sensors were treated in $N_{2}$ atmosphere. The sensors with $O_{2}$ treatment after $N_{2}$ treatment showed 70 % sensitivity for 1 ppm $H_{2}S$ gas, which is higher than the sensors with only $O_{2}$ treatment. The Ni metal was evaporated on Sn thin film on the $Al_{2}O_{3}$ substrate. And the sensor was heated to grow the Sn nanowire in the tube furnace with $N_{2}$ atmosphere. Sn nanowire was thermally oxidized in $O_{2}$ environments. The sensitivity of $SnO_{2}$ nanowire sensor was measured at 500 ppb $H_{2}S$ gas. The selectivity of $SnO_{2}$ nanowire sensor compared with thin film and thick film $SnO_{2}$ was measured for $H_{2}S$, CO, and $NH_{3}$ in this study.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.2
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• pp.98-103
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• 2013

The alumina substrates that Ni electrode was printed on and the multi-layered PTCR thermistors of which composition is $(Ba_{0.998}Ce_{0.002})TiO_3+0.001MnCO_3+0.05BN$ were fabricated by a thick film process, and the effect of re-oxidation temperature on their resistivities and resistance jumps were investigated, respectively. Ni electroded alumina substrate and the multi-layered PTC thermistor were sintered at $1150^{\circ}C$ for 2 h under $PO_2=10^{-6}$ Pa and then re-oxidized at $600{\sim}850^{\circ}C$ for 20 min. With increasing the re-oxidation temperature, the room temperature resistivity increased and the resistance jump ($LogR_{290}/R_{25}$) decreased, which seems to be related to the oxidation of Ni electrode. The small sized chip PTC thermistor such as 2012 and 3216 exhibits a nonlinear and rectifying behavior in I-V curve but the large sized chip PTC thermistor such as 4532 and 6532 shows a linear and ohmic behavior. Also, the small sized chip PTC thermistor such as 2012 and 3216 is more dependent on the re-oxidation temperature and easy to be oxidized in comparison with the large sized chip PTC thermistor such as 4532 and 6532. So, the re-oxidation conditions of chip PTC thermistor may be determined by considering the chip size.