• 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.

• Polymer(Korea)
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• v.30 no.4
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• pp.338-349
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• 2006

Fully or nearly fully(8-cholesteryloxycarbonyl)heptanoated polysaccharide derivatives were synthesized by reacting cellulose, amylose, chitosan, chitin, alginic acid, pullulan or amylopectin with (8-cholesteryloxycarbonyl)heptanoyl chloride (CH8C), and their thermotropic liquid crystalline behaviors were investigated. Like in the case of CH8C, all the polysaccharide derivatives formed monotropic cholesteric phases with left-handed helicoidal structures whose optical pitches $({\lambda_m}'s)$ decrease with increasing temperature. Amylopectin derivative also formed a monotropic cholesteric phase with lefthanded helicoidal structures but, in contrast with the other derivatives, did not display reflection colors over the full cholesteric range, suggesting that the helicoidal twisting power of the cholesteryl group highly depends on the branched structure in amylopectin. The thermal stability and degree of order in the mesophase, the magnitude of ${\lambda}_m$ at the same temperature, and the temperature dependence of the ${\lambda}_m$ observed for polysaccharide derivatives were entirely different from those reported for the polymers in which the cholesteryl groups are attached to flexible or semiflexible backbones through flexible spacers. The results were discussed in terms of the difference in the chemical structures of the main and side chains and flexibility of the main chain.

• Korean Journal of Applied Biomechanics
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• v.14 no.3
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• pp.83-98
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• 2004

The purpose of this study was to investigate the test-retest of plantar pressures using the F-Scan system over speeds and plantar regions. 6 healthy female subjects in 20's were recruited for the study. Plantar pressure measurements during locomotor activities can provide information concerning foot function, particularly if the timing and magnitude of the loading profile can be related to the location of specific foot structures such as the metatarsal heads. The Tekscan F-Scan system consists of a flexible, 0.18mm thick sole-shape having 1260 pressure sensors, the sensor insole was trimmed to fit the subjects' right. left shoes - sneakers shoes & dress shoes. It was calibrated by the known weight of the test subject standing on one foot. The Tekscan measurements show the insole pressure distribution as a function of the time. This finding has important implications for the development of plantar pressure test protocols where the function of the forefoot is important. According to the result of analysis it is as follows 1) Center of force trajectory in women's dress shoes display direct movement, compare with center of force trajectory in Sneaker shoes displays a little bit curved slow pronation movement. Sneaker shoes in forefoot part display very quick supination movement, therefore, this shoes effects negative effectiveness for ankle's stability Considering center of force trajectory analyzing the more center of force close straight line, the more movement can be quick movement for locomotion. For foot pressure distribution, center of force trajectory in locomotion is better to curved trajectory with pronation movement. So sneaker shoes style is good shoes considering center of pressure distribution trajectory compare with women's dress shoes. 2) Women's dress shoes increased peak pressure in medial, this is effected by high hill's height. The more increased women's dress shoes's height, the more women's peak pressure will increase, pronation can increase compare with before. Supination movement increase, this focused pressure in lateral, also, supination increased more. If the supination movement increased, foot pressure focused in lateral, therefore, it is appeared force distribution in gait direction. This is bad movement in foot's stability. 3) Women's dress shoes in landing phase displayed a long time, this is when women's dress shoes wear, gait movement is unbalance, so, landing phase displayed a long time. For compensation in gait, swing phase quick movement. 4) Women's dress shoes displayed peak pressure distribution in lateral of rearfoot part, Sneakers shoes displayed peak pressure distribution in medial of forefoot part. Its results has good impact absorption compare with women's dress shoes. In forefoot part, sneakers shoes has good propulsive force compare with women's dress shoes.

• Korean Chemical Engineering Research
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• v.50 no.5
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• pp.929-932
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• 2012

Novel platform technology has been developed to replace the photolithography used currently for manufacturing semiconductors and display devices. As a substrate, plastics, especially polycarbonates, have been considered for future application such as flexible display. Other plastics, i.e. polyimide, polyetheretherketon, and polyethersulfone developed for the substrate at this moment, are available for photolithography due to their high glass transition temperature, instead of high price. After thin polystyrene film was coated on the polycarbonate substrate, microstructure of the film was formed with polydimethylsiloxane template over the glass transition temperature of the polystyrene. The surface of the structure was treated with potassium permanganate and octadecyltrimethoxysilane so that the surface became hydrophobic. After this surface treatment, the nanoparticles dispersed in aqueous solution were aligned in the structure followed by evaporation of the DI water. Without the treatment, the nanoparticles were placed on the undesired region of the structure. Therefore, the interfacial interaction was also utilized for the nanoparticle alignment. The surface was analyzed using X-ray photoelectron spectrometer. The evaporation of the solvent occurred after several drops of the solution where the hydrophilic nanoparticles were dispersed. During the evaporation, the alignment was precisely guided by the physical structure and the interfacial interaction. The alignment was applied to the electric device.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.268-268
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• 2016

Chemical sensors have attracted much attention due to their various applications such as agriculture product, cosmetic and pharmaceutical components and clinical control. A conventional chemical and biological sensor is consists of fluorescent dye, optical light sources, and photodetector to quantify the extent of concentration. Such complicated system leads to rising cost and slow response time. Until now, the most contemporary thin film transistors (TFTs) are used in the field of flat panel display technology for switching device. Some papers have reported that an interesting alternative to flat panel display technology is chemical sensor technology. Recent advances in chemical detection study for using TFTs, benefits from overwhelming progress made in organic thin film transistors (OTFTs) electronic, have been studied alternative to current optical detection system. However numerous problems still remain especially the long-term stability and lack of reliability. On the other hand, the utilization of metal oxide transistor technology in chemical sensors is substantially promising owing to many advantages such as outstanding electrical performance, flexible device, and transparency. The top-gate structure transistor indicated long-term atmosphere stability and reliability because insulator layer is deposited on the top of semiconductor layer, as an effective mechanical and chemical protection. We report on the fabrication of InGaZnO TFTs with silver nanowire as the top gate electrode for the aim of chemical materials detection by monitoring change of electrical properties. We demonstrated that the improved sensitivity characteristics are related to the employment of a unique combination of nano materials. The silver nanowire top-gate InGaZnO TFTs used in this study features the following advantages: i) high sensitivity, ii) long-term stability in atmosphere and buffer solution iii) no necessary additional electrode and iv) simple fabrication process by spray.

• Journal of the Microelectronics and Packaging Society
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• v.23 no.2
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• pp.1-10
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• 2016

This paper reports the trends of researches and technologies of electronic packaging using graphene. Electronic packaging is to provide the signal and electrical current among electronic components, to remove the heat in electronic systems or components, to protect and support the electronic components from external environment. As the required functions and performances of electronic systems or components increase, the electronic packaging has been intensively attracted attention. Therefore, technologies such as miniaturization, high density, Pb-free material, high reliability, heat dissipation and so on, are required in electronic packaging. Recently, graphene, which is a single two-dimensional layer of carbon atoms, has been extensively investigated because of its superior mechanical, electrical and thermal properties. Until now, many studies have been reported the applications using graphene such as flexible display, electrode, super capacitor, composite materials and so on. In this paper, we will introduce and discuss various studies on recent technologies of electronic packaging using graphene for solving the required issues.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.188-188
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• 2012

Graphene, with its unique physical and structural properties, has recently become a proving ground for various physical phenomena, and is a promising candidate for a variety of electronic device and flexible display applications. Compared to indium tin oxide (ITO) electrodes, which have a typical sheet resistance of ${\sim}60{\Omega}$/sq and ~85% transmittance in the visible range, the chemical vapor deposition (CVD) synthesized graphene electrodes have a higher transmittance in the visible to IR region and are more robust under bending. Nevertheless, the lowest sheet resistance of the currently available CVD graphene electrodes is higher than that of ITO. In this study, we report a creative strategy, irradiation of microwave at room temperature under vacuum, for obtaining size-homogeneous gold nano-particle doping on graphene. The gold nano-particlization promoted by microwave irradiation was investigated by transmission electron microscopy, electron energy loss spectroscopy elemental mapping. These results clearly revealed that gold nanoparticle with ${\geq}30$ nm in mean size were decorated along the surface of the graphene after microwave irradiation. The fabrication high-performance transparent conducting film with optimized doping condition showed a sheet resistance of ${\geq}100{\Omega}$/sq. at ~90% transmittance. This approach advances the numerous applications of graphene films as transparent conducting electrodes.

• Bulletin of the Korean Chemical Society
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• v.29 no.6
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• pp.1167-1172
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• 2008

We investigated the glass transition temperatures ($T_g$) of dendrons consisting of conformationally mobile aliphatic polyether dendritic cores plus glassy peripheral polystyrenes (PSs), and linear PSs in the molecular weight range of 1000-8500 g/mol. We compared their $T_g$ behavior depending on their polymeric architecture. The linear PSs show a typical growth of $T_g$ up to 92.5 ${^{\circ}C}$ as the molecular weight increases to 8300 g/mol, while the dendrons display nearly constant $T_g$ values of 58-61 ${^{\circ}C}$, despite the increase of molecular weight with each generation. The striking contrast of Tg behavior would be mainly attributed to the fact that the dendrons keep the ratio of $N_e$/M ($N_e$: number of peripheral chain ends, M: molecular weight) over all the generations. Additionally, for the influence of dendritic spacers on glass transition temperature we prepared dimeric PSs with different linkage groups such as aliphatic ether, ester and amide bonds. We found that the dimer with the ether spacer exhibited the lowest glass transition at 55.4 ${^{\circ}C}$, while the amide linked dimer showed the highest glass transition temperature at 74.2 ${^{\circ}C}$. This indicates that the peripheral PS chains are effectively decoupled by the conformationally flexible ether spacer. The results from this study demonstrated that polymeric architecture and dendritic core structures play a crucial role in the determination of glass transition behavior, providing a strategy for the systematic engineering of polymer chain mobility.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.189-189
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• 2016

Recently, many researchers have shown an increased interest in colloidal quantum dots (QDs) due to their unique physical and optical properties of size control for energy band gap, narrow emission with small full width at half maxima (FWHM), broad spectral photo response from ultraviolet to infrared, and flexible solution processing. QDs can be widely used in the field of optoelectronic and biological applications and, in particular, colloidal QDs based light emitting diodes (QDLEDs) have attracted considerable attention as an emerging technology for next generation displays and solid state lighting. A few methods have been proposed to fabricate white color QDLEDs. However, the fabrication of white color QDLEDs using single QD is very challenging. Recently, hybrid nanocomposites consisting of CdTe/ZnO heterostructures were reported by Zhimin Yuan et al.[1] Here, we demonstrate a novel but facile technique for the synthesis of CdTe/ZnO/G.O(graphene oxide) quasi-core-shell-shell quantum dots that are applied in the white color LED devices. Our best device achieves a maximum luminance of 484.2 cd/m2 and CIE coordinates (0.35, 0.28).

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.330-330
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• 2016

투명전극은 디스플레이, 터치스크린, 태양전지 등 폭넓은 분야에서 응용되고 있어 현재 각광 받는 연구 주제 중 하나이다. 특히, ITO(인듐산화물)을 이용한 투명전극은 뛰어난 효율성 때문에 가장 주목 받고 있는 전극 형태 중 하나이다. 그러나 ITO투명전극은 인듐 소재의 희소성으로 인한 자원고갈문제 및 복원력, 투명도 등에서 취약점을 지니고 있는 것으로 보고되어 있다. 이러한 ITO 투명전극의 취약점을 보완하고, 동시에 플렉서블 디스플레이(Flexible Display) 소자에 적용 가능한 대체 투명전극에 관한 연구는 현재 가장 주목할 만한 가치가 있는 연구분야로 부각되고 있다. 본 연구에서는 대체 투명전극 중 하나로 그래핀 투명전극(Graphene Transparent Electrode)을 주목했다. PEN(Polyethylene Naphthalate) 투명기판 상에 Wet-Transfer형식으로 그래핀을 전사하여 그래핀 투명전극을 구현했으며, 복원력 확인을 위해 그래핀에 2가지 (Compressive/Tensile) 압력을 가하며 구부러짐 실험(Bending Test)을 진행하며 그래핀 투명전극의 저항값을 측정했다. 일반 금속전극의 경우, 일정한 수준 이상의 압력 또는 구부러짐이 반복되는 실험의 횟수가 증가되면 원래의 복원력을 상실하며, 저항값이 상승하는 것으로 보고된바 있다. 그러나 이번 연구에서는 그래핀 투명전극을 사용해 PEN 기판 위에 투명전극을 제작한 경우, 일정한 수준의 구부러짐 반복횟수(~1,000회) 및 구부러짐 정도(~10%) 하에서 저항값이 일정하게 유지됨을 확인할 수 있었다. 별도로, 기존에 알려져 있던 순수 그래핀(Pristine Graphene)의 취약점 중 하나인 높은 저항값을 우려하여 본 연구에서는 그래핀에 도핑을 하고, 그 영향을 분석해 보았다. 그 동안 그래핀 도핑법에 대한 적지않은 연구들이 진행되었으며, 본 연구에서는 TFSA(Bis(trifluoromethanesulfonyl)amide)라는 물질을 이용한 그래핀 도핑법을 채택했다. 실험 결과, 도핑된 그래핀 투명전극은 위와 같은 수준의 그래핀 본연의 복원력을 유지하면서 저항값은 순수 그래핀 대비 약 70% 정도 낮아짐을 확인할 수 있었다. 본 연구를 통해 그래핀 투명전극이 그래핀 고유의 특성인 높은 투명도와 복원력, 도핑으로 인한 저항값 감소가능성을 확인함으로써, 그래핀 투명전극이 ITO 투명전극의 좋은 대체자가 될 수 있는 가능성을 확인할 수 있었다.