• Transactions on Electrical and Electronic Materials
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• v.6 no.1
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• pp.10-13
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• 2005

$Sr_{0.6}Ba_{0.4}Nb_{2}O_{6}$, hereafter SBN60, thin films of 300 nm thickness were deposited using ion beam sputtering technique, in which sintered ceramic target of the same composition was utilized and the $Ar:O_{2}$ gas ratio was controlled during deposition onto $Pt(100)/TiO_{2}/SiO_{2}/Si$ substrate. Crystallization and orientation behavior as well as electrical properties of the films were examined after annealing treatment at $650{\sim}800{\cric}C$. It was found that the film orientation was dependent upon $Ar:O_{2}$ratio, in which strong (00l) orientation was developed when the gas ratio was about 1:4 at $4.3{\times}10^{-4}$ torr. Typical remanent polarization (2Pr), the coercive field (Ec) and the dielectric constant of Pt/SBN60/Pt thin film capacitor were approximately $10{\mu}C/cm^{2}$, 60 kV/cm, and 615, respectively.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.1
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• pp.7-15
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• 2004

The ferroelectric SBT thin films as a material of capacitors for non-volatile FRAMs have some problems that its remanent polarization value is relatively low and the crystallization temperature is quite high abovc 80$0^{\circ}C$. Therefore, in this paper, SBTN solution with S $r_{0.9}$B $i_{2.1}$T $a_{1.8}$N $b_{0.2}$$O_{9}$ composition was synthesized by sol-gel method. Sr(O $C_2$ $H_{5}$)$_2$, Bi(TMHD)$_3$, Ta(O $C_2$ $H_{5}$)$_{5}$and Nb(O $C_2$ $H_{5}$)$_{5}$ were used as precursors, which were dissolved in 2-methoxyethanol. SBTN thin films with 200 nm thickness were deposited on Pt/Ti $O_2$/ $SiO_2$/Si substrates by spin-coating. UV-irradiation in a power of 200 W for 10 min and rapid thermal annealing in a 5-Torr-oxygen ambient at 76$0^{\circ}C$ for 60 sec were used to promote crystallization. The films were well crystallized and fine-grained after annealing at $650^{\circ}C$ in oxygen ambient. The electrical characteristics of 2Pr=11.94 $\mu$C/$\textrm{cm}^2$, Ps＋/Pr＋=0.54 at the applied voltage of 5 V were obtained for a 200-nm-thick SBTN films. This results show that 2Pr values of the UV irradiated and rapid thermal annealed SBTN thin films at the applied voltage of 5 V were about 57% higher than those of no additional processed SBTN thin films. thin films.lms.s.s.

• JSTS:Journal of Semiconductor Technology and Science
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• v.8 no.1
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• pp.66-79
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• 2008

Several oxides have recently been reported to have resistance-switching characteristics for nonvolatile memory (NVM) applications. Both binary and ternary oxides demonstrated great potential as resistive-switching memory elements. However, the switching mechanisms have not yet been clearly understood, and the uniformity and reproducibility of devices have not been sufficient for gigabit-NVM applications. The primary requirements for oxides in memory applications are scalability, fast switching speed, good memory retention, a reasonable resistive window, and constant working voltage. In this paper, we discuss several materials that are resistive-switching elements and also focus on their switching mechanisms. We evaluated non-stoichiometric polycrystalline oxides ($Nb_2O_5$, and $ZrO_x$) and subsequently the resistive switching of $Cu_xO$ and heavily Cu-doped $MoO_x$ film for their compatibility with modem transistor-process cycles. Single-crystalline Nb-doped $SrTiO_3$ (NbSTO) was also investigated, and we found a Pt/single-crystal NbSTO Schottky junction had excellent memory characteristics. Epitaxial NbSTO film was grown on an Si substrate using conducting TiN as a buffer layer to introduce single-crystal NbSTO into the CMOS process and preserve its excellent electrical characteristics.

• Economic and Environmental Geology
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• v.30 no.6
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• pp.603-612
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• 1997

Cretaceous sedimentary-volcanoclastic formations of the Kyeongsang Supergroup were intruded by granitic rocks in the late Cretaceous and early Tertiary. In the Euiseong and Shinryeong area, these intrusives have various compositions including gabbro, diorite，biotite granite and feldspar porphyry. Associated volcanic rocks consist of two chemically distinct types: the bimodal suite of basalt and rhyolite in the Keumseongsan caldera, and the felsic suite of andesite and rhyolite in the Sunamsan-Hwasan calderas. Most rocks are subalkaline, and follow a typical differentiation path of the calc-alkaline magma. The granitic rocks can be distinguished chemically from the volcanics by high Zr/Y ratios. Differences in Zr/Y and K/Y ratios between the two volcanic suites can be accounted for by mantle source and fractionation. Chondrite-normalized trace element abundances of granitic rocks are depleted in Th and K, whereas those of the Keumseongsan rhyolites are depleted in Sr and Ti. Rb, La and Ce is enriched in rhyolites of the Sunamsan-Hwasan calderas. $Rb-SiO_2$ and Rb-Y+Nb discrimination diagrams suggest that the intrusives and volcanics have a volcanic arc setting. K-Ar ages indicate four plutonic episodes : diorite (89 Ma), granite (66~62 Ma), granite and porphyry (55~52 Ma) and gabbro (52~45 Ma), and two volcanisms : bimodal basaltic and rhyolitic volcanism (71~66 Ma) in the Keumseongsan caldera, and felsic andesitic and rhyolitic volcanism (61~54 Ma) in the Sunamsan-Hwasan calderas. Geochemical and age data thus suggest that the igneous rocks are related to several geologic episodes during the late Cretaceous to early Tertiary.

• Economic and Environmental Geology
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• v.39 no.6 s.181
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• pp.675-687
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• 2006

The purpose of this study is to determine the geochemical characteristics of the stream sediments in the Cheongpung area. So that we can understand the natural background and predict the prospects of geochemical disaster, if any. We collected the stream sediments samples by wet sieving along the primary channels and slow dried the collected samples in the laboratory and ground them to pass a 200 mesh using an alumina mortar and pestle for chemical analysis. Miner-alogical characteristics, major, trace and rare earth elements were determined by XRD, XRF, ICP-AES and NAA analysis methods. For geochemical characteristics on the geological group of stream sediments, the studied area was grouped into granitic gneiss area, metatectic gneiss area, Dado tuff area, Yuchi conglomerate area, and Neungju flow area in the Cheongpung area. Contents of major elements for the stream sediments in the Cheongpung area were $SiO_2\;47.31{\sim}72.81\;wt.%,\;A1_2O_3 \;11.26{\sim}21.88\;wt.%,\;Fe_2O_3\;2.83{\sim}8.39\;wt.%,\;CaO\;0.34{\sim}7.54\;wt.%,\;MgO\; 0.55{\sim}3.59\;wt.%,\;K_2O\;1.71{\sim}4.31\;wt.%,\;Na_2O\;0.56{\sim}2.28\;wt.%,\;TiO_2\;0.46{\sim}1.24\;wt.%,\;MnO\;0.04{\sim}0.27\;wt.%,\;P_2O_5\;0.02{\sim}0.45\;wt.%$. The con-tents of trace and rare earth elements for the stream sediments were $Ba\;700ppm{\sim}8990ppm,\;Be\;1.0{\sim}3.50ppm,\;Cu\;6.20{\sim}60ppm,\;Nb\;12{\sim}28ppm,\;Ni\;4.4{\sim}61ppm,\;Pb\;13{\sim}34ppm,\;Sr\;65{\sim}787ppm,\;V\;4{\sim}98ppm,\;Zr\;32{\sim}164ppm,\;Li\;21{\sim}827ppm,\;Co\;3.68{\sim}65ppm,\;Cr\;16.7{\sim}409ppm,\;Cs\;2.72{\sim}37.1ppm,\;Hf\;4.99{\sim}49.2ppm,\;Rb\;71.9{\sim}649ppm,\;Sb\;0.16{\sim}5.03ppm,\;Sc\;4.97{\sim}52ppm,\;Zn\;26.3{\sim}375ppm,\;Ce\;60.6{\sim}373ppm,\;Eu\;0.82{\sim}6ppm,\;Yb\;0.71{\sim}10ppm$.

• Progress in Superconductivity
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• v.11 no.1
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• pp.47-51
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• 2009

For many large-scale applications of high-temperature superconducting materials, large critical current density ($J_c$) in high applied magnetic fields are required. A number of methods have been reported to introduce artificial pinning centers in $YBa_2Cu_3O_{7-{\delta}}$ films for enhancement of their $J_c$. We studied the microstructures and characteristic of $YBa_2Cu_3O_{7-{\delta}}$ films fabricated on $SrTiO_3$ (100) substrates with ZnO nanorods as pinning centers. Au catalyst nanoparticles were synthesized on STO substrates with self assembled monolayer to control the number of ZnO nanorods. The density of Au nanoparticles is approximately $240{\sim}260{\mu}m^{-2}$ with diameters of $41{\sim}49nm$. ZnO nanorods were grown on STO by hot-walled PLD with Au nanoparticles. Typical size of ZnO nanorod was around 179 nm in diameter and $2{\sim}6{\mu}m$ in length respectively. YBCO films deposited directly on STO substrates show the c-axis orientation, while YBCO films with ZnO nanorods exhibit any mixed phases without any typical crystal orientation.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.410-410
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• 2013

Next-generation nonvolatile memory (NVM) has attracted increasing attention about emerging NVMs such as ferroelectric random access memory, phase-change random access memory, magnetic random access memory and resistance random access memory (RRAM). Previous studies have demonstrated that RRAM is promising because of its excellent properties, including simple structure, high speed and high density integration. Many research groups have reported a lot of metal oxides as resistive materials like TiO2, NiO, SrTiO3 and ZnO [1]. Among them, the ZnO-based film is one of the most promising materials for RRAM because of its good switching characteristics, reliability and high transparency [2]. However, in many studies about ZnO-based RRAMs, there was a problem to get lower current level for reducing the operating power dissipation and improving the device reliability such an endurance and an retention time of memory devices. Thus in this paper, we investigated that highly reproducible bipolar resistive switching characteristics of W doped ZnO RRAM device and it showed low resistive switching current level and large ON/OFF ratio. This may be caused by the interdiffusion of the W atoms in the ZnO film, whch serves as dopants, and leakage current would rise resulting in the lowering of current level [3]. In this work, a ZnO film and W doped ZnO film were fabricated on a Si substrate using RF magnetron sputtering from ZnO and W targets at room temperature with Ar gas ambient, and compared their current levels. Compared with the conventional ZnO-based RRAM, the W doped ZnO ReRAM device shows the reduction of reset current from ~$10^{-6}$ A to ~$10^{-9}$ A and large ON/OFF ratio of ~$10^3$ along with self-rectifying characteristic as shown in Fig. 1. In addition, we observed good endurance of $10^3$ times and retention time of $10^4$ s in the W doped ZnO ReRAM device. With this advantageous characteristics, W doped ZnO thin film device is a promising candidates for CMOS compatible and high-density RRAM devices.

• Restorative Dentistry and Endodontics
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• v.30 no.2
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• pp.95-101
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• 2005

The aim of this study was to evaluate the microleakage of teeth according to root canal preparation with & without apical enlargement in various size of apical foramen. 60 extracted one canal roots were cross-cutted at 5 mm from root apex and divided into two groups according to their apical foramen size of large (L) and small (S). Each group was subdivided into two groups accordance with their cross-sectional configuration at 5 mm from apex, round (R) and ovoid (O); SR Group, SO Group LR Group, LO Group. Each group was shaped in .02 taper by Quantec series Nickel-Titanium (NiTi) rotary file, obturated by lateral condensation method. Leakage was measured using a fluid transport model under 40 $cmH_2O$ pressure. After the leakage test, blocks which had showed the leakage retreated with .04 taper and ,06 taper and evaluated the degree of fluid filtration in each group. The data was analysed statistically using chi-square test and fisher's exact test. The results obtained were as follows : 1. Significant difference in leakage was found in groups which had different apical foramen size in .02 taper instrumentation (p < 0.05), but not in .04 taper instrumentation (p > 0.05) 2. The difference in microleakage according to the shape of canal was not evident at 5 mm from apex (p > 0.05). 3. There was correlation between .02 taper instrumentation and .04 taper instrumentation in LR group, LO group (p < 0.05).

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.3
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• pp.207-213
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• 2003

The Sr$\_$0.7/Bi$\_$2.6/Ta$_2$O$\_$9/(SBT) thin films are deposited on Pt-coated electrode(Pt/TiO$_2$/SiO$_2$/Si) using RF magnetron sputtering method. The structural and electrical properties of SBT capacitors were influenced with annealing atmosphere. In the XRD pattern, the SBT thin films in all annealed atmosphere had (105) orientation. In the SEM images, Bi-layered perovskite phase was crystallized in all annealing atmosphere and grain largely grew in oxygen annealing atmosphere. The maximum remnant polarization and the coercive electric field in oxygen annealing atmosphere are 12.40[${\mu}$C/cm$^2$] and 30[kV/cm] respectively. The dielectric constant and leakage current density of capacitors annealed oxygen atmosphere are 340 and 2.13${\times}$10$\^$-9/ [A/cm$^2$] respectively. The fatigue characteristics of SBT capacitors did not change up to 10$\^$10/ switching cycles.

• Journal of the Korean institute of surface engineering
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• v.29 no.5
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• pp.430-436
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• 1996

We have grown superconducting thin films on various substrates using a pulsed laser deposition (PLD) method. $YBa_2Cu_3O_7-\delta$ (YBCO) superconducting thin films with the superconducting transition temperature ($T_{c. offset}$) of 87K were grown on Si substrates using yittria-stabilized zirconia (YSZ) and $CeO_2$ double buffer layers. We have developed a large area pulsed laser deposition system. The system was designed to deposit up to 6 different materials on a large area substrate up to 7.5cm in diameter without breaking a vacuum. The preliminary runs of the deposition of YBCO superconducting thin films on $SrTiO_3$ substrate using this system showed a very uniform thickness profile over the entire substrate holder area. $T_{c}$ of the deposited YBCO thin film, however, was scattered depending on the position and the highest value was 85K.