• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.105-106
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• 2008

Structural, optical and electrical properties of CdS films deposited by chemical bath deposition (CBD), which are a very attractive method for low-cost and large-area solar cells, are presented. Cadmium sulfide (CdS) is II-VI semiconductor with a wide band gap of approximately 2.42 eV. CdS films have a great application potential such as solar cell, optical detector and optoelectronics device. In this paper, effects of Rapid Thermal Process (RTP) on the properties of CdS films were investigated. The CdS films were prepared on a glass by chemical bath deposition (CBD) and subsequently annealed at standard temperature $(400^{\circ}C)$ and treatment time (10 min) in various atmospheres (air, vacuum and $N_2$). The CdS films treated RTP in $N_2$ for to min were showed larger grain size and higher carrier density than the other samples.

• 한국태양에너지학회:학술대회논문집
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• 2012.03a
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• pp.108-112
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• 2012

Crystalline silicon solar cell remains the major player in the photovoltaic marketplace with 90 % of the market, despite the development of a variety of thin film technologies. Silicon's excellent efficiency, stability, material abundance and low toxicity have helped to maintain its position of dominance. However, the cost of silicon photovoltaic remains a major barrier to reducing the cost of silicon photovoltaics. Using the crystalline silicon wafer with thinner thickness is the promising way for cost and material reduction in the solar cell production. However, the thinner thickness of silicon wafer is, the worse bow phenomenon is induced. The bow phenomenon is observed when two or more layers of materials of different temperature expansion coefficiencies are in contact, in this case silicon and aluminum. In this paper, the solar cells were fabricated with different thicknesses of Al layer in order to reduce the bow phenomenon. With lower paste applications, we observed that the bow could be reduced by up to 40% of the largest value with 130 micron thickness of the wafer even though the conversion efficiency decrease of 0.5 % occurred. Since the bowed wafers lead to unacceptable yield losses during the module construction, the reduction of bow is indispensable on thin crystalline silicon solar cell. In this work, we have studied on the counterbalance between the bow and conversion efficiency and also suggest the formation of enough back surface field (BSF) with thinner Al paste application.

• Journal of the Korean Solar Energy Society
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• v.34 no.4
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• pp.17-22
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• 2014

The design of a fuel cells stack is important to get optimal output power. This study focuses on the evaluation of fuel cell system for unmaned aerial vehicles (UAVs). Low temperature proton exchange membrane (LTPEM) fuel cells are the most promising energy source for the robot applications because of their unique advantages such as high energy density, cold startup, and quick response during operation. In this paper, a 600 W open cathode LTPEM fuel cell was tested to evaluate the performance and to determine optimal operating conditions. The open cathode design reduces the overall size of the system to meet the requirement for robotic application. The cruise power requirement of 600 W was supported entirely by the fuel cell while the additional power requirements during takeoff was extended using a battery. A peak of power of 900 W is possible for 10 mins with a lithium polymer (LiPo) battery. The system was evaluated under various load cycles as well as start-stop cycles. The system response from no load to full load meets the robot platform requirement. The total weigh of the stack was 2 kg, while the overall system, including the fuel processing system and battery, was 4 kg.

• Applied Chemistry for Engineering
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• v.30 no.6
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• pp.659-666
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• 2019

Proton exchange membrane fuel cells (PEMFCs) generate electricity by electrochemical reactions of hydrogen and oxygen. PEMFCs are expected to alternate electric power generator using fossil fuels with various advantages of high power density, low operating temperature, and environmental-friendly products. PEMFCs have widely been used in a number of applications such as fuel cell vehicles (FCVs) and stationary fuel cell systems. However, there are remaining technical issues, particularly the long-term durability of each part of fuel cells. Degradation of a carbon supported-platinum catalyst in the anode and cathode follows various mechanistic origins in different fuel cell operating conditions, and thus accelerated stress test (AST) is suggested to evaluate the durability of electrocatalyst. In this article, comparable protocols of the AST durability test are intensively explained.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.4 s.181
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• pp.153-161
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• 2006

Micro-forming is a suited technology to manufacture very small metallic parts(several $mm{\sim}{\mu}m$). Micro-forming of $Zr_{62}Cu_{17}Ni_{13}Al_8$ bulk metallic glass(BMG) as a candidate material for this developing process are feasible at a relatively low stress in the supercooled liquid state without any crystallization during hot deformation. In this study, micro- formability of a representative bulk metallic glass, $Zr_{62}Cu_{17}Ni_{13}Al_8$. was investigated for micro-forging of U-shape pattern. Micro-formability was estimated by comparing $R_f$ values ($=A_f/A_g$), where $A_g$ is cross-sectional area of U groove, and $A_f$ the filled area by material. Micro-forging process was simulated and analyzed by applying finite element method. FEM simulation results showed reasonable agreement with the experimental results when the material properties and simulation conditions such as top die speed, remeshing criteria and boundary conditions were tightly controlled. The micro-formability of $Zr_{62}Cu_{17}Ni_{13}Al_8$ was increased with increasing load and time in the temperature range of the supercooled liquid state. Also, FEM simulation using a commercial software, DEFORM was confirmed to be applicable for the optimization of micro-forming process.

• Journal of the Microelectronics and Packaging Society
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• v.14 no.3
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• pp.15-20
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• 2007

Low temperature processed ZnO-TFTs on glass below $270^{\circ}C$ for plastic substrate applications were fabricated and their electrical properties were investigated. Films in ZnO-TFTs with bottom gate configuration were made by RF magnetron sputtering system except for $SiO_2$ gate oxide deposited by ICP-CVD. ZnO channel films were grown on glass with various Ar and $O_2$ flow ratios. All of the fabricated ZnO-TFTs showed perfectly the enhancement mode operation, a high optical transmittance of above 80% in visible ranges of the spectrum. In the ZnO-TFTs with pure Ar process, the field effect mobility, threshold voltage, and on/off ratio were measured to be $1.2\;cm^2/Vs$, 8.5 V, and $5{\times}10^5$, respectively. These characteristic values are much higher than those of the ZnO-TFTs of which ZnO channel layers were processed with additional $O_2$ gas. In addition, ZnO-TFT with pure Af process showed smaller swing voltage of 1.86v/decade compared to those with $Ar+O_2$ process.

• Journal of the Korean Ceramic Society
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• v.45 no.3
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• pp.157-160
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• 2008

A series of $La_2O_3$-added zincborosilicate glasses was fabricated by systematically varying $La_2O_3$ addition up to 15mol% under the constraint of a ZnO:$B_2O_3$ ratio of 1:2. The degree of water leaching after ball milling of the prepared glasses in water medium was relatively quantified by the change in zinc peak intensity in energy dispersive spectroscopy. 8mol% of $La_2O_3$ was the most efficient addition in inhibiting the glass leaching by water. The role of $La_2O_3$ in inhibiting the leaching was explained in terms of change of structural units in the glass network. When the optimum 8mol% $La_2O_3$-added ZnO-$B_2O_3$ glass was used as sintering aid for $Al_2O_3$, the fabricated alumina-glass composite at $875^{\circ}C$ demonstrated dielectric constant of 6.11 and quality factor of 15470 GHz, indicating the potential of leaching-minimized $La_2O_3-ZnO-B_2O_3$ glass for application to low temperature co-firing ceramic technology.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.38 no.4
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• pp.20-30
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• 2001

A novel 200 MHz CMOS transconductor using translinear cells is proposed. The proposed transconductor consists of voltage followers and current followers based on translinear cells and a resistor. For wide applications, a single-input single-output, a single-Input differential-output, and a fully-differential transconductor are systematically designed, respectively. The theory of operation is described and computer simulation results are used to verify theoretical predictions. The results show that the fully-differential transconductor has a linear input voltage range of ${\pm}2.7$ V, a 3 dB frequency of 200 MHz, and a temperature coefficient of less than 41 $ppm/^{\circ}C$ at supply voltages of ${\pm}3$ V. In order to certify the applicability of the fully-differential transconductor, A ladder-type 3th-order cllitic low pass filter is also designed based on the inductance simulation method. The filter has a ripple bandwidth of 22 MHz, a pass-band ripple of 0.36 dB, and a cutoff frequency of 26 MHz.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.3
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• pp.245-249
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• 2007

The liquid crystal display (LCD) applications treated on the organic overcoat thin film surfaces by ion beam irradiation was successfully studied. The good LC aligning capabilities treated on the organic overcoat thin film surfaces with ion beam exposure of $60^{\circ}$ for 2 min above ion beam energy of 1200 eV can be achieved. But, the alignment of defect of NLC on the organic overcoat surface at low energy of 600 eV was measured. The pretilt angle of NLC on the organic overcoat thin film surface with ion beam exposure of $60^{\circ}$ for 2 min at energy of 1800 eV was measured about 1 degree. Finally, the good thermal stability of LC alignment on the organic overcoat thin film surface with ion beam exposure of $60^{\circ}$ for 2 min until annealing temperature of $200^{\circ}C$ can be measured.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.05c
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• pp.83-87
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• 2002

Plasma enhanced chemical vapor deposited (PECVD) silicon nitride ($SiN_X$) is widely used as a gate dielectric material for the hydrogenated amorphous silicon(a-Si:H) thin film transistors (TFT's). We investigated $SiN_X$ films were deposited PECVD at low temperature ($300^{\circ}C$). The reaction gases were used pure nitrogen and a helium diluted of silane gas(20% $SiH_4$, 80% He). Experimental investigations were carried out with the variation of $N_2/SiH_4$ flow ratios from 3 to 50 and the rf power of 200 W. This article presents the $SiN_X$ gate dielectric studies in terms of deposition rate, hydrogen content, etch rate and C-V, leakage current density characteristics for the gate dielectric layer of thin film transistor applications. Electrical properties were analyzed through high frequency (1MHz) C-V and current-voltage (I-V) measurements. The thickness and the refractive index on the films were measured by ellipsometry and chemical bonds were determined by using an FT-IR equipment.