• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.352.1-352.1
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• 2014

Indium Tin Oxide (ITO) films are the most extensively studied and commonly used as ones of TCO films. The ITO films having a high electric conductivity and high transparency are easily fabricated on glass substrate at a substrate temperature over $250^{\circ}C$. However, glass substrates are somewhat heavy and brittle, whereas plastic substrates are lightweight, unbreakable, and so on. For these reasons, it has been recently suggested to use plastic substrates for flexible display application instead of glass. Many reaearchers have tried to produce high quality thin films at rood temperatures by using several methods. Therefore, amorphous ITO films excluding thermal process exhibit a decrease in electrical conductivity and optical transparency with time and a very poor chemical stability. However the amorphous Indium Gallium Zinc Oxide (IGZO) offers several advantages. For typical instance, unlike either crystalline or amorphous ITO, same and higher than a-IGZO resistivity is found when no reactive oxygen is added to the sputter chamber, this greatly simplifies the deposition. We reported on the characteristics of a-IGZO thin films were fabricated by RF-magnetron sputtering method on the PEN substrate at room temperature using 3inch sputtering targets different rate of Zn. The homogeneous and stable targets were prepared by calcine and sintering process. Furthermore, two types of IGZO TFT design, a- IGZO source/drain material in TFT and the other a- ITO source/drain material, have been fabricated for comparison with each other. The experimental results reveal that the a- IGZO source/drain electrode in IGZO TFT is shown to be superior TFT performances, compared with a- ITO source/drain electrode in IGZO TFT.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.111.2-111.2
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• 2015

Typical electrodes (metal or indium tin oxide (ITO)), which were used in conventional organic light emitting devices (OLEDs) structure, have transparency and conductivity, but, it is not suitable as the electrode of the flexible OLEDs (f-OLEDs) due to its brittle property. Although Graphene is the most well-known alternative material for conventional electrode because of present electrode properties as well as flexibility, its carrier injection barrier is comparatively high to use as electrode. In this work, we performed plasma treatment on the graphene surface and alkali metal doping in the organic materials to study for its possibility as anode and cathode, respectively. By using Ultraviolet Photoemission Spectroscopy (UPS), we investigated the interfaces of modified graphene. The plasma treatment is generated by various gas types such as O2 and Ar, to increase the work function of the graphene film. Also, for co-deposition of organic film to do alkali metal doping, we used three different organic materials which are BMPYPB (1,3-Bis(3,5-di-pyrid-3-yl-phenyl)benzene), TMPYPB (1,3,5-Tri[(3-pyridyl)-phen-3-yl]benzene), and 3TPYMB (Tris(2,4,6-trimethyl-3-(pyridin-3-yl)phenyl)borane)). They are well known for ETL materials in OLEDs. From these results, we found that graphene work function can be tuned to overcome the weakness of graphene induced carrier injection barrier, when the interface was treated with plasma (alkali metal) through the value of hole (electron) injection barrier is reduced about 1 eV.

• Korean Journal of Materials Research
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• v.21 no.7
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• pp.371-376
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• 2011

We report on the effects of $TiO_2$ doping power on the characteristics of multicomponent $TiO_2$-ITO (TITO) electrodes prepared by a multi-target sputtering system with tilted cathode guns. Both as-deposited and annealed TITO electrodes showed linearly increased sheet resistance and resistivity with increasing $TiO_2$ doping power. However, the TITO electrodes exhibited a fairly high optical transmittance regardless of the $TiO_2$ doping power due to the high transparency of the $TiO_2$. Although the annealed TITO showed much lower sheet resistance and resistivity relative to the as-deposited samples, the electrical properties of the annealed samples exhibited similar dependence on the $TiO_2$ power to the as-deposited samples. In addition, it was found that doping of an anatase $TiO_2$ in the ITO electrode prevented the preferred (222) orientation of the TITO electrodes. Although the TITO electrode showed higher sheet resistance and resistivity than that of the pure ITO electrode, it offers a very smooth surface and usage of a low-cost Ti element. It is thus considered a promising multicomponent transparent conducting electrode for cost-efficient flat panel displays and photovoltatics.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07a
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• pp.309-312
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• 2004

The electronic structure of ZnO oxide semiconductor having high optical transparency and good electric conductivity was theoretically investigated by $DV-X_{\alpha}$(the discrete variation $X_{\alpha}$) method, which is a sort of the first principle molecular orbital method using Hatre-Fock-Slater approximation. The electrical and optical properties of ZnO are seriously affected by the addition of impurities. The imnurities are added to ZnO in order to increase the electric conductivity of an electrode without losing optical transparency. In this study, the effect of impurities of III and IV family on the band structure, impurity levels and the density of state of ZnO were investigated. The cluster model used for calculations was $[MZn_{50}O_{53}]^{-2}$(M=elements belonging to III and IV family).

• Journal of the Korean Ceramic Society
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• v.53 no.1
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• pp.110-115
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• 2016

We prepared a working electrode (WE) coated with 0 ~ 50 nm-thick indium gallium zinc oxide(IGZO) by using RF sputtering to improve the energy conversion efficiency (ECE) of a dye sensitized solar cell (DSSC). Transmission electron microscope (TEM) and energy dispersive spectroscopy (EDS) were used to analyze the microstructure and composition of the IGZO layer. UV-VIS-NIR spectroscopy was used to determine the transparency of the WE with IGZO layers. A solar simulator and a potentiostat were used to confirm the photovoltaic properties of the DSSC with IGZO layer. From the results of the microstructural analysis, we were able to confirm the successful deposition of an amorphous IGZO layer with the expected thickness and composition. From the UV-VIS-NIR analysis, we were able to verify that the transparency decreased when the thickness of IGZO increased, while the transparency was over 90% for all thicknesses. The photovoltaic results show that the ECE became 4.30% with the IGZO layer compared to 3.93% without the IGZO layer. As the results show that electron mobility increased when an IGZO layer was coated on the $TiO_2$ layer, it is confirmed that the ECE of a DSSC can be enhanced by employing an appropriate thickness of IGZO on the $TiO_2$ layer.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.217.2-217.2
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• 2014

We prepared a flexible and transparent CuO/Cu/CuO multilayer electrodes on a polyethylene terephthalate (PET) substrate using a specially designed roll-to-roll sputtering system at room temperature for GFF-type touch screen panels (TSPs). By the continuous roll-to-roll sputtering of the CuO and Cu layer, we fabricated a flexible CuO(150nm)/Cu(150nm)/CuO(150nm) multilayer electrodes with a sheet resistance of $0.289{\Omega}/square$, resistivity of $5.991{\times}10^{-23}{\Omega}-cm$, at the optimized condition without breaking the vacuum. To investigate the feasibility of the CuO/Cu/CuO multilayer as a transparent electrode for GFF-type TSPs, we fabricated simple GFF-type TSPs using the diamond patterned CuO/Cu/CuO electrode on PET substrate as function of mesh line width. Using diamond patterned CuO/Cu/CuO electrode of mesh line $5{\mu}m$ with sheet resistance of 38 Ohm/square, optical transmittance of 90% at 550 nm and an average transmittance of 89% at wavelength range from 380 to 780 nm, we successfully demonstrated GFF-type touch panel screens (TPSs). The successful operation of GFF-type TPSs with CuO/Cu/CuO multilayer electrodes indicates that the CuO/Cu/CuO multilayer is a promising transparent electrode for large-area capacitive-type TPSs due to its low sheet resistance and high transparency.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.300.2-300.2
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• 2016

Increasing of the demand for energy savings for buildings, thermal barrier films have more attracted. In particular, as heat loss through the windows have been pointed out to major problems in the construction and automobile industries, the research is consistently conducted for improving the thermal blocking performance for windows. The main theory of the technology is reflect the infrared rays to help the cut off the inflow of the solar energy in summer and outflow of the heat from indoors in winter to save the energy on cooling and heating. Furthermore, this is well known for prevent glare, reduces fading caused by harmful ultraviolet radiation and easy to apply on constructed buildings if it made as a film. In addition to these advantages, apply the transparent electrode to eliminate condensation by heating. Generally ITO is used as a transparent electrode, but is has a low stability in environmental factors. In this study, ITO and its alternative, ATO, is deposited by sputtering system and then the characteristic is evaluated each material based thermal barrier thin film. The optical property was measured on wide range of wavelength (200 nm 2500 nm) to know the transparency in visible wavelength and reflectivity in IR wavelength range. The electrical property was judged by sheet resistivity. Finally the changes of the temperature and current of the deposited film was observed while applying a DC power.

• 한국신재생에너지학회:학술대회논문집
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• 2007.06a
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• pp.305-308
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• 2007

The field of dye-sensitized solar cell (DSC) is being researched actively at present. Because DSC has several advantages to pass the limits of Si solar cells such as a low manufacturing expense, a simple manufacturing process and its transparency. A lot of researches are underway about materials and processes in the field of dye-sensitized solar cell but its structure has been fixed up as the sandwich structure that both edges are used as positive and negative terminals. But the structure as of present is a factor of decreasing efficiency because the more electrons are recombined the further distance from terminal, considering about the characteristic of dye-sensitized solar cell that electrons generated inside cell are moved by diffusion. In this study, we made experiment on expanding the terminal to shorten internal moving distance of electron and compared the results according to the variation of active area to find out the effect of this trial. As a result, we achieved about 15.5% improvement of maximum power and 0.5% improvement of efficiency from terminal-expanded dye-sensitized solar cell of $2cm^{2}$ active area and concluded that the increasing rate of efficiency is raised as the active area becomes wider.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.276-276
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• 2014

High-performance, fully-transparent, and top-gated oxide thin-film transistor (TFT) was successfully fabricated with Ta2O5 high-k gate dielectric on a glass substrate. Through a self-passivation with the gate dielectric and top electrode, the top-gated oxide TFT was not affected from H2O and O2 causing the electrical instability. Heat-treated InSnO (ITO) was used as the top and source/drain electrode with a low resistance and a transparent property in visible region. A InGaZnO (IGZO) thin-film was used as a active channel with a broad optical bandgap of 3.72 eV and transparent property. In addition, using a X-ray diffraction, amorphous phase of IGZO thin-film was observed until it was heat-treated at 500 oC. The fabricated device was demonstrated that an applied electric field efficiently controlled electron transfer in the IGZO active channel using the Ta2O5 gate dielectric. With the transparent ITO electrodes and IGZO active channel, the fabricated oxide TFT on a glass substrate showed optical transparency and high carrier mobility. These results expected that the top-gated oxide TFT with the high-k gate dielectric accelerates the realization of presence of fully-transparent electronics.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.49-49
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• 2010

Nanopiezotronics is an emerging area of nanotechnology with a variety of applications that include piezoelectric field-effect transistors and diodes, self-powered nanogenerators and biosystems, and wireless nano/biosensors. By exploiting coupled piezoelectric and semiconducting characteristics, it is possible for nanowires, nanobelts, or nanorods to generate rectifying current and potential under external mechanical energies such as body movement (handling, winding, pushing, and bending) and muscle stretching, vibrations (acoustic and ultrasonic waves), and hydraulic forces (body fluid and blood flow). Fully transparent, flexible (TF) nanogenerators that are operated by external mechanical forces will be presented. By controlling the density of the seed layer for ZnO nanorod growth, transparent ZnO nanorod arrays were grown on ITO/PES films, and a TF conductive electrode was stacked on the ZnO nanorods. The resulting integrated TF nanodevice (having transparency exceeding 70 %) generated a noticeable current when it was pushed by application of an external load. The output current density was clearly dependent on the force applied. Furthermore, the output current density depended strongly on the morphology and the work function of the top electrode. ZnO nanorod-based nanogenerators with a PdAu, ITO, CNT, and graphene top electrodes gave output current densities of approximately $1-10\;uA/cm^2$ at a load of 0.9 kgf. Our results suggest that our TF nanogenerators are suitable for self-powered TF device applications such as flexible self-powered touch sensors, wearable artificial skins, fully rollable display mobile devices, and battery supplements for wearable cellular phones.