• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.358-359
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• 2006

In the Langmuir-Blodgett (LB) technique, a monolayer on the water surface is transferred onto a substrate, which is raised and dipped through the surface. From this, multilayers can be obtained in which constituent molecules are periodically arranged. The LB technique has attracted considerable interest in the fabrication of electrical and electronic devices. Many researchers have investigated the electrical properties of monolayer and multiplayer films. Dendrimers represent a new class of synthetic macromolecules characterized by a regularly branched treelike structure. Multiple branching yields a large number of chain ends that distinguish dendrimers from conventional star-like polymers and microgels. The azobenzene dendrimer is one of the dendritic macromolecules that include the azo-group exhibiting a photochromic character. Due to the presence of the charge transfer element of the azo-group and its rod-shaped structure, these compounds are expected to have potential interest in electronics and ptoelectronics, especially in nonlinear optics. In the present paper, we give pressure stimulation to organic thin films and detect the induced displacement current.

• Current Applied Physics
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• v.18 no.11
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• pp.1300-1305
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• 2018

The tunable electronic performance of the solution-processed semiconductor metal oxide is of great significance for the printing electronics. In current work, transparent thin-film transistors (TFTs) with indium-zinc oxide (IZO) were fabricated as active layer by a simple eco-friendly aqueous route. The aqueous precursor solution is composed of water without any other organic additives and the IZO films are amorphous revealed by the X-ray diffraction (XRD). With systematic studies of atomic force microscopy (AFM), X-ray photoemission spectroscopy (XPS) and the semiconductor property characterizations, it was revealed that the electrical performance of the IZO TFTs is dependent on the concentration of precursor solution. As well, the optimum preparation process was obtained. The concentrations induced the regulation of the electronic performance was clearly demonstrated with a proposed mechanism. The results are expected to be beneficial for development of solution-processed metal oxide TFTs.

• Korean Journal of Metals and Materials
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• v.47 no.4
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• pp.261-266
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• 2009

The mechanical and electrical properties of ball grid array (BGA) solder joints were measured, consisting of Sn-3.5Ag, with organic solderability preservative (OSP)-finished Cu pads and Electroless Nickel/Immersion Gold (ENIG) surface finishes. The mechanical properties were measured by die shear test. When ENIG PCB was upper joint and OSP PCB was lower joint, the highest shear force showed at the third reflow. When OSP PCB was upper joint and ENIG PCB was lower joint, the highest shear force showed at the forth reflow. For both joints, after the die shear results reached the highest shear force, shear force decreased as a function of increasing reflow number. Electrical property of the solder joint decreased with the function of increasing reflow number. The scanning electron microscope results show that the IMC thickness at the bonding interface gets thicker while the number of reflow increases.

• Korean Journal of Metals and Materials
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• v.46 no.2
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• pp.80-87
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• 2008

Many researches related to the reliability of Pb-free solder joints with PCB (printed circuit board) surface finish under thermal or vibration stresses are in progress, because the electronics is operating in hash environment. Therefore, it is necessary to assess Pb-free solder joints life with PCB surface finish under thermal and mechanical stresses. We have investigated 4-points bending fatigue lifetime of Pb-free solder joints with OSP (organic solderability preservative) and ENIG (electroless nickel and immersion gold) surface finish. To predict the bending fatigue life of Sn-3.0Ag-0.5Cu solder joints, we use the test coupons mounted 192 BGA (ball grid array) package to be added the thermal stress by conducting thermal shock test, 500, 1,000, 1,500 and 2,000 cycles, respectively. An 4-point bending test is performed in force controlling mode. It is considered that as a failure when the resistance of daisy-chain circuit of test coupons reaches more than $1,000{\Omega}$. Finally, we obtained the solder joints fatigue life with OSP and ENIG surface finish using by Weibull probability distribution.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.5-5
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• 2009

Thin-film-transistors (TFTs) that can be prepared at low temperatures have attracted much attention because of the great potential for transparent and flexible electronics. One of the mainstreams in this field is the use of organic semiconductors such as pentacene. But device performance of the organic TFTs is still limited due to low field-effect mobility and rapid degradation after exposing to air. Alternative approach is the use of amorphous oxide semiconductors as a channel. Amorphous oxide semiconductors (AOSs) based TFTs showed the fast technological development, because AOS films can be fabricated at room temperature and exhibit the possibility in application like flexible display, electronic paper, and larges solar cells. Among the various AOSs, a-IGZO has lots of advantages because it has high channel mobility, uniform surface roughness and good transparency. [1] The high mobility is attributed to the overlap of spherical s-orbital of the heavy post-transition metal cations. This study demonstrated the effect of the variation in channel thickness from 30nm to 200nm on the TFT device performance. When the thickness was increased, turn-on voltage and subthreshold swing was decreased. The a-IGZO channels and source/drain metals were deposited with shadow mask. The a-IGZO channel layer was deposited on $SiO_2$/p-Si substrates by RF magnetron sputtering, where RF power is 150W. And working pressure is 3m Torr, at $O_2/Ar$ (2/28 sccm) atmosphere. The electrodes were formed with electron-beam evaporated Ti (30 nm) and Au (70 nm) bilayer. Finally, Al (150nm) as a gate metal was thermal-evaporated. TFT devices were heat-treated in a furnace at 250 $^{\circ}C$ and nitrogen atmosphere for 1hour. The electrical properties of the TFTs were measured using a probe-station. The TFT with channel thickness of 150nm exhibits a good subthreshold swing (SS) of 0.72 V/decade and on-off ratio of $1{\times}10^8$. The field effect mobility and threshold voltage were evaluated as 7.2 and 8 V, respectively.

• Proceedings of the IEEK Conference
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• 2000.06b
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• pp.80-83
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• 2000

In this work we deposited Pentacene thin film by OMBD at the various substrate temperatures, deposition rate and the various annealing temperatures for the fabrication of organic TFT and investigated the electrical and film surface characteristics such as sheet resistance, contact resistance and conductance Film thickness were measured by $\alpha$-step and the sheet resistance, contact resistance and conductance were extracted from the relation between the distance of the contacts and the resistance. During the film deposition the substrate temperature was held at 3$0^{\circ}C$, 4$0^{\circ}C$, 5$0^{\circ}C$, 6$0^{\circ}C$, 8$0^{\circ}C$ and 10$0^{\circ}C$, respectively. After the film deposition, Au contact was deposited by thermal evaporation. For the effect of annealing, the thin film was annealed in the nitrogen environment at 10$0^{\circ}C$ and 14$0^{\circ}C$ for 10 seconds, respectively. Film surface characteristics at the vatious substrate temperatures were measured by AFM. The crystallization of thin film was improved as the substrate temperatures were increased and the maximum gram size was 4${\mu}{\textrm}{m}$. The conductivity of thin film was found to be 7.40 $\times$10$^{-7}$ ~ 7.78$\times$10$^{-6}$ S/cm and the minimum contact resistance was 2.5324 ㏁.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.137-137
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• 2009

Thin-film transistors (TFTs) that can be prepared at low temperatures have attracted much attention due to the great potential for flexible electronics. One of the mainstreams in this field is the use of organic semiconductors such as pentacene. But device performance of the organic TFTs is still limited by low field effect mobility or rapidly degraded after exposing to air in many cases. Another approach is amorphous oxide semiconductors. Amorphous oxide semiconductors (AOSs) have exactly attracted considerable attention because AOSs were fabricated at room temperature and used lots of application such as flexible display, electronic paper, large solar cells. Among the various AOSs, a-IGZO was considerable material because it has high mobility and uniform surface and good transparent. The high mobility is attributed to the result of the overlap of spherical s-orbital of the heavy pest-transition metal cations. This study is demonstrated the effect of thickness channel layer from 30nm to 200nm. when the thickness was increased, turn on voltage and subthreshold swing were decreased. a-IGZO TFTs have used a shadow mask to deposit channel and source/drain(S/D). a-IGZO were deposited on SiO2 wafer by rf magnetron sputtering. using power is 150W, working pressure is 3m Torr, and an O2/Ar(2/28 SCCM) atmosphere at room temperature. The electrodes were formed with Electron-beam evaporated Ti(30nm) and Au(70nm) structure. Finally, Al(150nm) as a gate metal was evaporated. TFT devices were heat treated in a furnace at $250^{\circ}C$ in nitrogen atmosphere for an hour. The electrical properties of the TFTs were measured using a probe-station to measure I-V characteristic. TFT whose thickness was 150nm exhibits a good subthreshold swing(S) of 0.72 V/decade and high on-off ratio of 1E+08. Field effect mobility, saturation effect mobility, and threshold voltage were evaluated 7.2, 5.8, 8V respectively.

• Korean Journal of Microbiology
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• v.43 no.1
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• pp.19-22
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• 2007

Acetohydroxyacid synthase (E.C.2.2.1.6., AHAS) is the enzyme that catalyses the first step in the synthesis of the branched-chain amino acids valine, leucine and isoleucine. The AHAS gene (TIGR access code HI2585) from Heamophilus influenzae was cloned into the bacterial expression vector pET-28a and expressed in the Escherichia coli strain BL21(DE3). The expressed enzyme was purified by $Ni^{2+}-charged$ HiTrap chelating HP column. The purified enzyme appears as a single band on SDS-PAGE with a molecular mass of about 63.9 kDa. The enzyme exhibits absolute dependence on the three cofactors FAD, $MgCl_{2}$ and thiamine diphosphate for activity. Specific activity of purified enzyme has 3.22 unit/mg and optimum activity in the pH 7.5 at $37^{\circ}C$. This enzyme activity has an effect on the buffer. When comparing the enzyme activity against the organic solvent, it followed in type and the difference it is but even from the aqueous solution where the organic solvent is included with the fact that the enzyme activity is maintained.

• Journal of the Institute of Electronics and Information Engineers
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• v.53 no.8
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• pp.129-135
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• 2016

This study is about ionic water generator filter Recently, a lot of people feel deep interest in health and drinking water. Evaluation of the stability of oxidation-reduced potential (ORP) using the filter of the alkaline water. This study utilizes the three filter of activated carbon, UF, carbon block in alkaline reduced water equipment. Passing the water to the filter is evaluated that the OPR values are stability in accordance with the change of the volume in the bucket. Alkaline reduced water equipment is a system that has the function of making the water reduction. This system is the values of the human body beneficial minerals and ORP are made in the functional water has a very low value than general water. Which has passed through the filter the water in the water negative ions and positive ions through the electrolytic. After electrolysis, the cathode side by water, including $Ca^+$, $K^+$, $Mg^+$, $Na^+$ water gets Alkaline Reduced Water containing the minerals beneficial to the human body. A positive electrode side is made of the organic materials that have an anion such as chlorine (Cl), phosphorus (P), sulfur(S). This experiment uses the Alkaline Reduced Water to adjust the magnitude of the voltage of the electrolysis in the Alkaline Reduced Water. That is 1st step(pH8) 2nd step (pH8.5) 3th step (pH9), 4th step (pH9.5) in the Alkaline Reduced Water and -1st step (pH6.0), -2nd step (pH5.0) used as the acidic oxidation water. When the water passes through the three filter in this system was evaluated whether the ORP values are changed and stabilized. When about 100 liters of water passing through the filter was confirmed that the ORP values are stability and evaluation.

• Journal of the Korean Vacuum Society
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• v.20 no.4
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• pp.288-293
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• 2011

We investigated the effects of piezoelectric field on the electro-absorption characteristics in InGaN/GaN multiple-quantum well (MQW) green light emitting diodes (LED). Double crystal X-ray diffraction measurement was performed to study the crystalline property and indium (In) composition in the MQW active layer. To measure the electro-luminescence and electro-reflectance (ER) spectroscopy, we fabricated the $1{\times}1\;mm^2$ large-area green LED chip. The piezoelectric field inside the LED structure was evaluated from the Vcomp in active layer by the ER spectra. Finally, we analyzed the electro-absorption characteristics of the green LED by using the photo-current spectroscopy.