• Journal of The Korean Astronomical Society
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• v.29 no.spc1
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• pp.231-232
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• 1996

The local instabilities of accretion disks were extensively studied, with the considerations of radial advection, thermal diffusion and different disk geometry, dominated pressure and optical depth. Two inertial-acoustic modes in a geometrically thin, radiative cooling dominated disk depart from each other if very little advection is included. A geometrically slim, advection-dominated disk is found to be always stable if it is optically thin. However, if it is optically thick, the thermal diffusion has no effect on the stable viscous mode but has a significant contribution to enhance the thermal instability.

• JSTS:Journal of Semiconductor Technology and Science
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• v.8 no.2
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• pp.111-114
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• 2008

We studied the influence of nanocrystalline silicon (nc-Si) thin film thickness on top gate nc-Si thin film transistor (TFT) fabricated at $180^{\circ}C$. The nc-Si thickness affects the characteristics of nc-Si TFT due to the nc-Si growth similar to a columnar. As the thickness of nc-Si increases from 40 nm to 200 nm, the grain size was increased from 20 nm to 40 nm. Having a large grain size, the thick nc-Si TFT surpasses the thin nc-Si TFT in terms of electrical characteristics such as field effect mobility. The channel resistance was decreased due to growth of the grain. We obtained the experimental results that the field effect mobility of the fabricated devices of which nc-Si thickness is 60, 90 and 130 nm are 26, 77 and $119\;cm^2/Vsec$, respectively. The leakage current, however, is increased from $7.2{\times}10^{-10}$ to $1.9{\times}10^{-8}\;A$ at $V_{GS}=-4.4\;V$ when the nc-Si thickness increases. It is originated from the decrease of the channel resistance.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.407-408
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• 2013

Thin transparent conductive oxides (TCOs) having a thickness lower than 30 nm have been widely usedin touch screen panels. However the resistivity of the TCO films significantly increases as the thickness decreases, due to the poor crystallinity at very thin thickness of TCO films. In this study, we have investigated the effect of electron beam irradiation during the sputtering on the electrical properties and transmittance of 30 nm-thick ITO films, which have a different SnO2 atomic percent, prepared by magnetron sputtering at room temperature. Fig. 1 shows the variation of resistivity of ITO films with a different SnO2 atomic percent for both the normal ITO films and electron beam irradiated ITO films. As shows in Fig. 1, the electron beam irradiation to the ITO (SnO2 weight percent 10%) films during the sputtering resulted in a significantly decreased in resistivity from $7.4{\times}10^{-4}{\Omega}-cm$ to $1.5{\times}10^{-4}{\Omega}-cm$ and it also increased in transmittance from 84% to 88% at a wavelength of 550 nm. These results can be attributed to energy transfer from electron to ad-atoms of ITO films during the electron beam irradiated sputtering, which can enhance the crystallinity of 30 nm-thick ITO films. It is strongly indicate that electron beam irradiation can greatly improve the electrical properties and transmittance of very thin ITO films for touch screen panels, flexible displays and solar cells.

• Progress in Superconductivity
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• v.8 no.1
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• pp.27-32
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• 2006

[$YBa_2Cu_3O_{7-x}$] thin films were deposited on various buffered-templates by a metal organic chemical vapor deposition(MOCVD). Three different templates of $CeO_2/YSZ/CeO_2/pure-Ni(CYC),\;CeO_2/YSZ/Y_2O_3/Ni-3at.%W(YYC)$ and $CeO_2/IBAD-YSZ$/stainless steel were used. The Ni and Ni-W alloy tapes were biaxially textured by cold rolling and annealing heat treatment. The dense YBCO films were grown on both the IBAD and YYC templates with no microcrack, while the YBCO films on the CYC templates were grown with the formation of microcracks and NiO. The YBCO film on the YYC template showed the higher $I_c$ than that on CYC template. Especially, the IBAD templates with a thin $CeO_2$(type I) and thick $CeO_2$(type II) top layer were used to compare the deposition nature of the YBCO on them. Comparing the current property of the YBCO films on IBAD templates, the YBCO film deposited on thick $CeO_2$ layer was better than the film on thin $CeO_2$ layer.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.278-279
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• 2005

The crystallization of FePt/MgO(100) magnetic thin films of various thicknesses has been studied using synchrotron x-ray scattering, atomic force microscope, and vibrating sample magnetometer. In film with a 500-${\AA}$-thick, ordered (fct) FePt phase was dominantly crystallized into perpendicular (001) grains keeping the magnetically easy c-axis normal to the film plane during annealing. In film with a 812-${\AA}$-thick, however, longitudinal (110) grains keeping the c-axis parallel to the film plane were grown on top of the perpendicular (001) grains. The behavior of the magnetic properties was consistent with the thickness dependence of the crystallization. We attribute the thickness dependence of the crystallization to the substrate effect, which prefers the growth of the c-axis oriented perpendicular grains near the film/substrate interfacial area.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.543-543
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• 2013

Thin-film transistors (TFTs) based on oxide semiconductors have been regarded as promising alternatives for conventional amorphous and polycrystalline silicon TFTs. Oxide TFTs have several advantages, such as low temperature processing, transparency and high field-effect mobility. Lots of oxide semiconductors for example ZnO, SnO2, In2O3, InZnO, ZnSnO, and InGaZnO etc. have been researched. Particularly, zinc-tin oxide (ZTO) is suitable for channel layer of oxide TFTs having a high mobility that Sn in ZTO can improve the carrier transport by overlapping orbital. However, some issues related to the ZTO TFT electrical performance still remain to be resolved, such as obtaining good electrical contact between source/drain (S/D) electrodes and active channel layer. In this study, the bottom-gate type ZTO TFTs with staggered structure were prepared. Thin films of ZTO (40 nm thick) were deposited by DC magnetron sputtering and performed at room temperature in an Ar atmosphere with an oxygen partial pressure of 10%. After annealing the thin films of ZTO at $400^{\circ}C$ or an hour, Cu, Mo, ITO and Ti electrodes were used for the S/D electrodes. Cu, Mo, ITO and Ti (200 nm thick) were also deposited by DC magnetron sputtering at room temperature. The channel layer and S/D electrodes were defined using a lift-off process which resulted in a fixed width W of 100 ${\mu}m$ and channel length L varied from 10 to 50 ${\mu}m$. The TFT source/drain series resistance, the intrinsic mobility (${\mu}i$), and intrinsic threshold voltage (Vi) were extracted by transmission line method (TLM) using a series of TFTs with different channel lengths. And the performances of ZTO TFTs were measured by using HP 4145B semiconductor analyzer. The results showed that the Cu S/D electrodes had a high intrinsic field effect mobility and a low effective contact resistance compared to other electrodes such as Mo, ITO and Ti.

• Journal of Information Display
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• v.4 no.2
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• pp.1-6
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• 2003

In this paper, we demonstrate that the organic electrophosphorescent device is driven by the organic thin film transistor with spin-coated photoacryl gate insulator. It was found that electrical output characteristics in our organic thin film transistors using the staggered-inverted top-contact structure showed the non-saturated slope in the saturation region and the sub-threshold nonlinearity in the triode region, where we obtained the maximum power luminance that was about 90 $cd/m^2$. Field effect mobility, threshold voltage, and on-off current ratio in 0.45 ${\mu}m$ thick gate dielectric layer were 0.17 $cm^2/Vs$, -7 V, and $10^6$ , respectively. In order to form polyimide as a gate insulator, vapor deposition polymerization process was also introduced instead of spin-coating process, where polyimide film was co-deposited by high-vacuum thermal evaporation from 4,4'-oxydiphthalic anhydride (ODPA) and 4,4'-oxydianiline (ODA) and cured at 150${\sqsubset}$for 1hr. It was also found that field effect mobility, threshold voltage, on-off current ratio, and sub-threshold slope with 0.45 ${\mu}m$ thick gate dielectric films were 0.134 $cm^2/Vs$, -7 V, and $10^6$ A/A, and 1 V/decade, respectively.

• Korean Journal of Metals and Materials
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• v.47 no.8
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• pp.466-473
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• 2009

Our group previously observed the intrinsic stress evolution of Cu thin films during deposition by changing the deposition rate. Intrinsic stress of Cu thin films, which show Volmer-Weber growth, is reported to display three unique stress stages, initial compressive, broad tensile, and incremental compressive stress. The mechanisms of the initial compressive stress and incremental compressive stages remain subjects of debate, despite intensive research inquiries. The tensile stress stage may be related to volume contraction through grain growth and coalescence to reduce over-accumulate Cu adatoms on the film surface. The in-situ intrinsic stresses behavior in Cu thin films was investigated in the present study using a multi-beam curvature measurement system attached to a thermal evaporation device. The effect of substrate surface roughness was monitored by observed the in-situ intrinsic stress behavior in Cu thin films during deposition, using $100{\mu}m$ thick Si(111) wafer substrates with three different levels of surface roughness.

• 한국정보디스플레이학회:학술대회논문집
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• 2007.08b
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• pp.1075-1078
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• 2007

Negative Bias Temperature Instability (NBTI) in Eximer Laser Annealing (ELA) based Low Temperature polysilicon (LTPS) Thin-Film Transistors (TFT) was investigated. Even though NBTI is generally appeared in devices with thin gate oxide, the TFT with gate oxide thickness of 120 nm, relatively thick, also showed NBTI effect and dynamic NBTI effect is dependent on operational frequency.

• Journal of Korea Foundry Society
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• v.5 no.4
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• pp.289-297
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• 1985

Thin sections in castings solidify faster than thick sections. Solidification rates increase because of an increase in heat transfer from molten meltals to molds through these solidified thin sections. The cooling fin effect in pure zinc casting was studied about the solidification time, superheat, and fin size by adopting the pourout test. The following results could be obtained from the study: (1) The fin effect could be represented by the effective cooling surface area ($A_f/S$) increased. (2) The fin effect could be obtained as functions of solidification time, superheat, and fin size.