• Progress in Superconductivity and Cryogenics
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• v.20 no.3
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• pp.5-10
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• 2018

This study presents that various grain boundary junctions are prepared by controlling the seed orientation combined with an artificial hole in a melt process REBCO bulk superconductor. Large grain YBCO superconductors have been fabricated with various grain boundary junctions that the angle between the grain boundary and the <001> axis of Y123 crystal is $0^{\circ}$, $30^{\circ}$ and $45^{\circ}$, respectively. The presence of the artificial hole is beneficial for the formation of clean grain boundary junction and single peak trapped magnetic field profiles have been obtained. Artificial hole makes two growth fronts meet at a point on a periphery of the artificial hole. The presence of artificial hole is not likely to affect on the distribution of Y211 particles. The newly formed <110> facet lines are explained by the formation of new Y123/liquid interface with (010) crystallographic plane.

• 한국초전도학회:학술대회논문집
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• v.9
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• pp.185-188
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• 1999

Biepitaxial Y$_1Ba_2Cu_3O_{7-x}$ (YBCO) and La$_{0.2}Sr_{0.8}MnO_3$ (LSMO) thin films have been prepared on SrTiO$_3$ buffer layer and MgO seed layer grown on Al$_2O_3$(11${\bar{2}}$0)substrates by dc-sputtering with hollow cylindrical targets, respectively. We charaterized Josephson properties and significantly large magnetoresistance in YBCO and LSMO films with 45$^{\circ}$ grain boundary junction, respectively. The observed working voltage (I$_cR_n$) at 77 K in grain boundary junction was below 10${\mu}$V, which is typical I$_cR_n$ value of single biepitaxial Josephson junction. The field magnetoresistance ratio (MR) of LSMO grain boundary juncoon at 77K was enhanced to 13%, which it was significant MR value with high magnetic field sensitivity at a low field of 250 Oe. These results indicate that inserting the insulating layer instead of the grain boundary layer with metallic phase can be possible to apply a new SIS Josephson junction and a novel magnetic device using spin-polarized tunneling junction.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1997.03a
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• pp.73-76
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• 1997

Nanocrystalline materials have been modeled as a mixture of the crystallite and the grain boundary phases. The mechanical property has been calculated using the rule of mixtures based on the volume fractions. The critical grain size concept suggested by Nieh and Wadsworth and porous material model suggested by Lee and Kim were applied to the calculation. The theoretical results fit very well with the experimental values

• Proceedings of the Korean Magnestics Society Conference
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• 1999.04a
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• pp.26-27
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• 1999

• 한국초전도학회:학술대회논문집
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• v.10
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• pp.293-297
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• 2000

Multiseeding with (100)/(100) grain junctions of top-seeded melt growth (TSMG) processed YBCO superconductors was studied. The effect of the number of seeds and the distance between two seeds on the levitation forces and the trapped magnetic fields of the TSMG-processed YBCO samples was investigated. Multiple seeding shortened the processing time for the fabrication of TSMC-processed YBCO superconductors. The large magnetic field was trapped at the grain junction when two seeds was placed without spacing, while the amount of the magnetic field decreased when the seed distance increased. This is attributed to the increased amount of the residual melt phases around the grain junctions.

• Journal of the Korean Ceramic Society
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• v.42 no.5 s.276
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• pp.366-370
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• 2005

Single gram-boundary varistors were fabricated using hydrothermal and vapor phase grown ZnO single crystals and their voltage-current relation was studied. The single crystal bonded single junction varistor showed various voltage-current relationship and different breakdown voltage of 0.24-3V. The different types of non-linear current voltage behaviors was attributed to the variation of electrical conductivity in ZnO single crystals.

• Electrical & Electronic Materials
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• v.8 no.6
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• pp.737-743
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• 1995

Two step RTD(Rapid Thermal Diffussion) of P into silicon wafer using tungsten halogen lamp was used to fabricated very shallow n$^{+}$p junction. 1st RTD was performed in the temperature range of 800.deg. C for 60 see and the heating rate was in the 50.deg. C/sec. Phosphrous solid source was transfered on the silicon surface. 2nd RTD process was performed in the temperature range 1050.deg. C, 10sec. Using 2 step RTD we can obtain a shallow junction 0.13.mu.m in depth. After RTD, the Ti-silicide process was performed by the two step RTA(Rapid Thermal Annealing) to reduced the electric resistance and to improve the n$^{+}$p junction diode. The titanium thickness was 300.angs.. The condition of lst RTA process was 600.deg. C of 30sec and that of 2nd RTA process was varied in the range 700.deg. C, 750.deg. C, 800.deg. C for 10sec-60sec. After 2 step RTA, sheet resistance was 46.ohm../[]. Ti-silicide n+p junction diode was fabricated and I-V characteristics were measured.red.

• Korean Journal of Materials Research
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• v.3 no.5
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• pp.553-561
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• 1993

In this study, thr effect of $Bi_2O_3$ and BN addition as grain boundary modifiers on sintering and electrical properties of semiconducting PTCR(Positive Temperature Coefficient of Resistivity) mate rial were analyzed using TMA, XRD and Complex Impedance Spectroscopy method. Bismut.h Ox~de and Boron Nitride were added to Y-doped $BaTiO_3$ respectively. Bismuth sesquioxide up to O.lmol%solubil~ ty limit of $Bi_2O_3$ in Y--$BaTiO_3$ ceramics-retarded densification and grain growth, and further addition mitigated these retardation effects. The resistivity at room temperature increased with increasing amount of $Bi_2O_3$ and thus decreased the PTCR effect, probably due to the $Bi_2O_3$ segregation on the grain boundaries. From the complex ~mpedance pattern, it is known that the grain boundary resisitivity is dominant on the whole resistivity of sample. In the result of applying the defect chemistry, $Bi^{3+} \;and \; Bi^[5+}$ are substituted for Ua and Ti site, respectively. Boron nitride decomposed and formed liquid phase among the $BaTiO_3$ grains. The decomposed com~ ponents made the second phase and existed the tr~ple juntion from the result of EPMA. From the complex impendencc pattern, the gram and grain boundary resistivity were small. The grain size increased with increasing BN contents, and decreased grain boundary resistivity enhanced the PTCR effect.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.2
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• pp.111-116
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• 2001

Poly-Si TFT's(Polysilicon thin filmtransistors) have been actively studied due to their applications in active matrix liquid crystal displays and active pull-up devices of CMOS SRAM's. For such applications, the leakage current has to be in the range of sub-picoampere. However, poly-Si TFT's suffer from anomalous high leakage currents, which is attributed to the emission of the traps present at gain boundaries in the drain junction. The leakage current has been analyzed by the field emission via grain-boundary traps and thermionic field emission over potential barrier located at the grain boundary. We found that the models proposed before are not consistent with the experimental results at far as drain-offset poly-Si TFT's we fabricated concern. In this paper, leakage current of drain-offset poly-Si TFT's with different offset lengths was studied. A conduction model based on the thermionic emission of the tunneling electrons is developed to identify the leakage mechanism. It was found that the effective grain size of the drain-offset region is important factor in the leakage current. A good agreement between experimental and simulated results of the leakage current is obtained.

• Journal of the Korean Vacuum Society
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• v.4 no.2
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• pp.194-200
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• 1995

2-3nm의 공간분해능을 갖는 전자에너지손실분광법(Electron Energy Loss Spectroscopy, EELS)을 이용하여, 전기적 특성조사된 YBa2Cu3O7-$\delta$ 고온초전도체 쌍결정의 결정경계(grain boundary)에서 산소의 조성변화를 조사하였다. Misorientation angle이 $14^{\circ}$, $28^{\circ}$,$ 30^{\circ}$인 3개의 쌍결정 중에서 Josephson junction 특성을 보인 $28^{\circ}$ 및 $30^{\circ}$결정경계에서의 oxygen 1s absorption edge는 결정내부에서의 oxygen 1s absorption edge와 매우 다름을 알 수 있었다. 이는 결정경계에서의 산소조성이 결정내부에 비해 낮음을 의미하며, 그 영역이 결정경계 부근 20-40nm로, coherence length에 비해 큼을 알 수 있다. 반면에, flux pinningxmr성을 보인 $14^{\circ}$결정경계에서의 oxygen 1s absorption edge는 결정내부에서와 별 차이를 보이지 않았다. 따라서 일반적으로 관찰되어온, misorientation angle이 큰 결정경계에서의 Josephson junction 특성은 결정경계 부근에서 산소의 조성이 낮아지는데에 기인하며, 그 원인은 결정경계면을 통해 산소가 out-diffusion되기 때문인 것으로 생각된다.