• Korean Journal of Materials Research
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• v.20 no.11
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• pp.623-627
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• 2010

Semiconducting metal oxides have been frequently used as gas sensing materials. While zinc oxide is a popular material for such applications, structures such as nanowires, nanorods and nanotubes, due to their large surface area, are natural candidates for use as gas sensors of higher sensitivity. The compound ZnO has been studied, due to its chemical and thermal stability, for use as an n-type semiconducting gas sensor. ZnO has a large exciton binding energy and a large bandgap energy at room temperature. Also, ZnO is sensitive to toxic and combustible gases. The NO gas properties of zinc oxide-single wall carbon nanotube (ZnO-SWCNT) composites were investigated. Fabrication includes the deposition of porous SWCNTs on thermally oxidized $SiO_2$ substrates followed by sputter deposition of Zn and thermal oxidation at $400^{\circ}C$ in oxygen. The Zn films were controlled to 50 nm thicknesses. The effects of microstructure and gas sensing properties were studied for process optimization through comparison of ZnO-SWCNT composites with ZnO film. The basic sensor response behavior to 10 ppm NO gas were checked at different operation temperatures in the range of $150-300^{\circ}C$. The highest sensor responses were observed at $300^{\circ}C$ in ZnO film and $250^{\circ}C$ in ZnO-SWCNT composites. The ZnO-SWCNT composite sensor showed a sensor response (~1300%) five times higher than that of pure ZnO thin film sensors at an operation temperature of $250^{\circ}C$.

• Journal of the Korean Vacuum Society
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• v.20 no.4
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• pp.294-299
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• 2011

In this study, single-walled carbon nanotubes (SWCNTs) were synthesized on a Fe/$Al_2O_3$/Si layer by thermal chemical vapor deposition. Metallic SWCNTs were selectively removed by microwave irradiation. Electrical and structural characterizations of the SWCNTs clearly revealed that the metallic SWCNTs were almost removed by microwave irradiation for 120 sec. The remained semiconducting SWCNTs with a high crystalline structure were obtained over 95%. This method would provide useful information for applications to SWCNTs-based field effect transistors and multifaceted nanoelectronics.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.7
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• pp.531-536
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• 2012

We herein present results of flat and uniform polymer-blended small molecular semiconductor thin films. Which were produced for organic thin film transistors (OTFTs), using a simple pre-metered horizontal dipping process. The organic semiconducting thin films were composed of 6,13-bis(triisopropylsilylethynyl)-pentacene (TIPS-PEN) composite blended with a polymer binder of poly(${\alpha}$-methylstyrene) (PaMS). We show that the pre-metered horizontal-dip-coating(H-dip-coating) process allowed the critical control of the thickness of the blended TIPS-PEN:PaMs thin film. The fabricated OTFTs using the TIPS-PEN:PaMs films exhibited maximum field-effect mobility of $0.22\;cm^2\;V^{-1}\;s^{-1}$. These results demonstrated that H-dip-coated TIPS-PEN:PaMS films show considerable promise for the production of reliable, reproducible, and high-performance OTFTs.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.456-456
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• 2008

In the past few years, the deposition and characterization of cadmium sulfide semiconducting thin films has received a considerable amount of interest due to their potential application in the area of electronic and opto-electronic devices fabrications. Polycrystalline CdS thin films posses good optical transmittance, wide band-gap and electrical properties makes it as one of the ideal material for their application to solar cell fabrication. Cadmium sulfate thin films were deposited by the chemical bath deposition method using tartaric acid and triethanolamine as a complexing agent. Deposition parameters such as pH, temperature, deposition time and concentration of the reactant species were optimized so as to obtain reflecting, good adherent uniform thin films on the glass substrate. Reaction mechanism of the thin film formation is also reported. The crystallographic structure and the crystallite size were studied by the X-ray diffraction pattern. The optical band-gap of deposited film is identified by measuring the transmittance in the visible region. Temperature dependence of resistivity confirmed the semiconducting behavior of the film. Scanning electron micrographs (SEM) showed the presence of grain particles of size 50 nm.

• Journal of IKEEE
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• v.22 no.2
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• pp.420-426
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• 2018

In the near future, CNTFET(Carbon NanoTube Field Effect Transistor) is considered as one of the most promising candidate for the replacement of modern silicon-based transistors by utilizing the ballistic or near-ballistic transport capability of CNT(Carbon NanoTube). For the large-scale fabrication of high performance CNTFET, semiconducting CNTs have to be well-aligned with a fixed pitch and high densities in the each CNTFET. However, due to the immaturity of the CNTFET fabrication process, CNTs can be unevenly positioned in a CNTFET and existing HSPICE library file cannot support the circuit level evaluation of performance variation caused by the unevenly positioned CNTs. To evaluate the performance variation, linear programming methodology was suggested previously, but the errors can be made during the calculation of the current and the gate capacitance of a CNTFET. In this paper, the reasons causing errors will be discussed in detail and the new methodology to reduce the errors will be also suggested. Simulation results shows that the errors can be reduced from 7.096% to 3.15%.

• Proceedings of the Korean Vacuum Society Conference
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• 1999.07a
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• pp.168-168
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• 1999

Recently, Fe/Si multilayered films (MLF) have been a focus of interest due to the strong antiferromagnetic (AF) coupling observed in such kind of MLF originates from the same nature as in the metal/metal MLF. In particular, a question of whether the spacer layer in the Fe/Si MLF is metallic or semiconducting is of interest. In spite of various experimental techniques envolved in the study, the chemical composition and the properties of the interfacial regions in the MLF exhibiting the AF coupling is still questionable. The nature of the AF coupling and the interfacial properties of Fe/Si MLF are investigated in this study. A series of Fe/Si MLF with a fixed nominal thickness of Fe(3nm) and a variable thickness of Sk(1.0-2.2nm) were deposited by RF-sputtering onto glass substrates at room temperature. The atomic structures and the actual sublayer thicknesses of the Fe/Si MLF are investigated by using x-ray diffraction. The magnetic-field dependence of the equatorial Kerr effect clearly shows an appearance of the AF coupling between Fe sublayers at tsi = 1.5 - 1.8 nm. the drastic discrepancies between the experimental magnetooptical (MO) and optical properties, and based on the assumption of sharp interfaces between Fe and Si sublayers leads to a conclusion that pure si is absent in the AF-coupled Fe/Si MLF. Introducing in the model nonmagnetic semiconducting FeSi alloy layers between Fe and Si sublayers or as spacer between pure Fe sublayers only slightly improves the agreement between model and experiment. A reasonable agreement between experimental and simulated MO spectra was reached with using the fitted optical properties for the spacer with a typical metallic type of behavior. The results of the magnetic properties measured by vibrating sample magnetometer and magnetic circular dichroism are also analyzed in connection with the MO and optical properties.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.361.2-361.2
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• 2014

Transition metal dichalcogenides (MoS2, WS2, WSe2, MoSe2, NbS2, NbSe2, etc.) are layered materials that can exhibit semiconducting, metallic and even superconducting behavior. In the bulk form, the semiconducting phases (MoS2, WS2, WSe2, MoSe2) have an indirect band gap. Recently, these layered systems have attracted a great deal of attention mainly due to their complementary electronic properties when compared to other two-dimensional materials, such as graphene (a semimetal) and boron nitride (an insulator). However, these bulk properties could be significantly modified when the system becomes mono-layered; the indirect band gap becomes direct. Such changes in the band structure when reducing the thickness of a WS2 film have important implications for the development of novel applications, such as valleytronics. In this work, we report for the controlled synthesis of large-area (~cm2) single-, bi-, and few-layer WS2 using a two-step process. WOx thin films were deposited onto a Si/SiO2 substrate, and these films were then sulfurized under vacuum in a second step occurring at high temperatures ($750^{\circ}C$). Furthermore, we have developed an efficient route to transfer these WS2 films onto different substrates, using concentrated HF. WS2 films of different thicknesses have been analyzed by optical microscopy, Raman spectroscopy, and high-resolution transmission electron microscopy.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.273.2-273.2
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• 2014

Sputtering process has been widely used in Si-based semiconductor industry and it is also an ideal method to deposit transparent oxide materials for thin-film transistors (TFTs). The oxide films grown at low temperature by conventional RF sputtering process are typically amorphous state with low density including a large number of defects such as dangling bonds and oxygen vacancies. Those play a crucial role in the electron conduction in transparent electrode, while those are the origin of instability of semiconducting channel in oxide TFTs due to electron trapping. Therefore, post treatments such as high temperature annealing process have been commonly progressed to obtain high reliability and good stability. In this work, the scheme of electron-assisted RF sputtering process for high quality transparent oxide films was suggested. Through the additional electron supply into the plasma during sputtering process, the working pressure could be kept below $5{\times}10-4Torr$. Therefore, both the mean free path and the mobility of sputtered atoms were increased and the well ordered and the highly dense microstructure could be obtained compared to those of conventional sputtering condition. In this work, the physical properties of transparent oxide films such as conducting indium tin oxide and semiconducting indium gallium zinc oxide films grown by electron-assisted sputtering process will be discussed in detail. Those films showed the high conductivity and the high mobility without additional post annealing process. In addition, oxide TFT characteristics based on IGZO channel and ITO electrode will be shown.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.11a
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• pp.134-135
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• 2005

To improve mean-life and reliability of power cable, we have investigated volume resistivity and thermal conductivity showed by changing the content of acetylene black which is the component parts of semiconductive shield in underground power transmission cable. The sheets were primarily kneaded in their pellet form material samples for 5 minutes on rollers ranging between 70[$^{\circ}C$] and 100[$^{\circ}C$]. Then they were produced as sheets after pressing for 20 minutes at 180[$^{\circ}C$] with a pressure of 200[kg/cm]. The content of conductive acetylene black was the variable, and their contents were 20, 30 and 40[wt%], respectively. Volume resistivity of specimens was measured by volume resistivity meter after 10 minutes in the preheated oven of both $25\pm1[^{\circ}C]$ and $90\pm1[^{\circ}C]$. Thermal conductivity was measured by Nano Flash Diffusivity. The measurement temperatures of thermal conductivity using Nano Flash Diffusivity were both 25[$^{\circ}C$] and 55[$^{\circ}C$]. From these experimental results, volume resistivity was high according to an increase of the content of acetylene black. And thermal conductivity was increased to an increase of the content of acetylene black. And thermal conductivity were increased by heating rate because volume of materials was expanded according to rise in temperature.

• Macromolecular Research
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• v.17 no.7
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• pp.491-498
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• 2009

New $\pi$-conjugated multi-branched molecules were synthesized through the Homer-Emmons reaction using alkyl-substituted, 3,4-ethylenedioxythiophene-based, thiophenyl aldehydes and octaethyl benzene-l,2,4,5-tetrayltetrakis(methylene) tetraphosphonate as the core unit; these molecules have all been fully characterized. The two multi-branched conjugated molecules exhibited excellent solubility in common organic solvents and good self-film forming properties. The semiconducting properties of these multi-branched molecules were also evaluated in organic field-effect transistors (OFET). With octyltrichlorosilane (OTS) treatment of the surface of the $SiO_2$ gate insulator, two of the crystalline conjugated molecules, 7 and 8, exhibited carrier mobilities as high as $2.4({\pm}0.5){\times}10^{-3}$ and $1.3({\pm}0.5){\times}10^{-3}cm^2V^{-1}s^{-1}$, respectively. The mobility enhancement of OFET by light irradiation ($\lambda$ = 436 nm) supported the promising photo-controlled switching behavior for the drain current of the device.