• 한국초전도학회:학술대회논문집
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• v.12
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• pp.49-49
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• 2002

• Progress in Superconductivity
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• v.2 no.2
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• pp.76-80
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• 2001

We have fabricated YBa$_2$Cu$_3$$O_{7-x}$ (YBCO) ramp-edge Josephson junctions by modifying ramp edges of the base electrodes without depositing any artificial barrier layer. YBa$_2$Cu$_3$O/7-x//SrTiO$_3$ (YBCO/STO) films were deposited on SrTiO$_3$(100) by on-axis KrF laser deposition. After patterning the bottom YBCO/STO layer, the ramp edge was cleaned by ion-beam and then reacted with deionized water under various conditions prior to the deposition of counter-electrode layers. The top YBCO/STO layer was deposited and patterned by photolithography and ion milling. We measured current-voltage (I-V) characteristics, magnetic field modulation of the critical current at 77 K. Some showed resistively shunted junction (RSJ)-type I-V characteristics, while others exhibited flux-flow behaviors, depending on the dipping time of the ramp edge in deionized water. Junctions fabricated using optimized conditions showed fairly uniform distribution of junction parameters such as I$_{c}$R$_{n}$ values, which were about 0.16 mV at 77 K with 1$\sigma$~ 24%. We made a dc SQUID with the same deionized water treated junctions, and it showed the sinusoidal modulation under applied magnetic field at 77 K. 77 K.

• 한국초전도학회:학술대회논문집
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• v.9
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• pp.13-15
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• 1999

A Josephson sampler circuit using high-Tc superconductor (HTS) ramp-edge junctions has been designed, fabricated, and experimentally tested. It consists of five ramp-edge junctions with a stacked groundplane and is based on single-flux-quantum (SFQ) operations. The sampler was used to measure current waveforms at picosecond and microampere resolutions. We are developing a system based on the sampler for measuring the current waveform in a room-temperature sample. And measuring current flowing through wiring in a semiconductor large-scale integrated circuit is a promising application for the HTS sampler system.

• Progress in Superconductivity
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• v.1 no.2
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• pp.81-84
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• 2000

A Josephson sampler circuit using high-Tc superconductor (HTS) ramp-edge junctions has been designed, fabricated, and experimentally tested. It consists of five ramp-edge junctions with a stacked groundplane and is based on single-flux-quantum (SFQ) operations. The sampler was used to measure current waveforms at picosecond and microampere resolutions. We are developing a system based on the sampler for measuring the current waveform in a room-temperature sample. And measuring current flowing through wiring in a semiconductor large-scale integrated circuit is a promising application for the HTS sampler system.

• Progress in Superconductivity
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• v.1 no.1
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• pp.31-35
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• 1999

We have fabricated and tested a simple circuit of the rapid single-flux-quantum(RSFQ) four-stage shift register using a single layer high-$T_c$ superconducting (HTS) $YBa_2Cu_3O_{7-x}$ (YBCO) thin film structure with 9 step-edge Josephson junctions. The circuit includes two read superconducting quantum interference devices(SQUID) and four stages. To establish a robust HTS RSFQ device fabrication process, we have focussed on the reproducible process of sharp and straight step-edge formation as well as the ratio of film thickness to step height, t/h. The spread of step-edge junction parameters was measured from each 13 junctions with t/h=1/3, 1/2, and 2/3 at various temperatures. We have demonstrated the simplified operation of the shift register at 65 K.

• Progress in Superconductivity and Cryogenics
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• v.4 no.1
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• pp.8-12
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• 2002

Since the high performance analog-to-digital converter can be built with Rapid Single Flux Quantum (RSFQ) logic circuits the development of superconductive analog-to-digital converter has attracted a lot of interests as one of the most prospective area of the application of Josephson Junction technology. One of the main advantages in using Rapid Sng1e Flux Quantum logic in the analog-to-digital converter is the low voltage output from the Josephson junction switching, and hence the high resolution. To design an analog-digital converter, first we have used XIC tool to compose a circuit schematic, and then studied the operational principle of the circuit with WRSPICE tool. Through this process, we obtained the proper circuit diagram of an 1-bit analog-digital converter circuit. The optimized circuit was laid out as a mask drawing. Inductance values of the circuit layout were calculated with L-meter.

• Progress in Superconductivity
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• v.5 no.1
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• pp.1-4
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• 2003

A five-year project for Nb-based single flux quantum (SFQ) circuits supported by Japan's Ministry of Economy Trade and Industry (METI) in Japan was started in September 2002. Since April 2003, the New Energy and Industrial Technology Development Organization (NEDO) has supported this Superconductor Network Device Project. The aim of the project is to improve the integration level of Nb-based SFQ circuits to several ten thousand Josephson junctions, in comparison with their starting integration level of only a few thousand junctions. Actual targets are a 20 GHz dual processor module for the servers and a 0.96 Tbps switch module for the routers. Starting in April 2003, the Nb project was merged with SFQ circuit research using a high-T$_{c}$ superconductor (HTS). The HTS research targets are a wide-band AD converter for mobile-phone base stations and a sampling oscilloscope for wide-band waveform measurements.

• 한국초전도학회:학술대회논문집
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• v.9
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• pp.133-133
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• 1999

We have fabricated and tested a simple circuit of the rapid single-flux-quantum(RSFQ) four-stage shift register using a single layer high-T$_c$ superconducting (HTS) YBa$_2Cu_3O_{7-x}$ (YBCO) thin film structure with 9 step-edge Josephson junctions. The circuit includes two read superconducting quantum interference devices(SQUID) and four stages. To establish a robust HTS RSFQ device fabrication process, we have focussed the reproducible process of sharp and straight step-edge formation as well as the ratio of film thickness to step height t/h. The spread of step-edge junction parameters was measured from each13 junctions with t/h=l/3, l/2, and 2/3 at various temperatures. We have demonstrated the simplified operation of the shift register at 65 K..

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2002.02a
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• pp.131-134
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• 2002

In this work, we have developed a systematic way of utilizing the basic design tools for superconductive electronics. This include WRSPICE, XIC, margin program, and L-meter. Since the high performance analog-to- digital converter can be built with Rapid Single Flux Quantum (RSFQ) logic circuits the development of superconductive analog-to-digital converter has attracted a lot of interests as one of the most prospective area of the application of Josephson Junction technology. One of the main advantages in using Rapid Single Flux Quantum logic in the analog-to-digital converter is the low voltage output from the Josephson junction switching, and hence the high resolution. To design an 1-bit analog-digital converter, first we have used XIC tool to compose a circuit schematic, and then studied the operational principle of the circuit with WRSPICE tool. Through this process, we obtained the proper circuit diagram of an 1-bit analog-digital converter circuit. Based on this circuit we performed margin calculations of the designed circuits and optimized circuit parameters. The optimized circuit was laid out as a mask drawing. Inductance values of the circuit layout were calculated with L-meter. Circuit inductors were adjusted according to these calculations and the final layout was obtained.

• Progress in Superconductivity and Cryogenics
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• v.17 no.4
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• pp.38-42
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• 2015

In terms of food safety,mixture of contaminants in food is a serious problem for not only consumers but also manufacturers. In general, the target size of the metallic contaminant to be removed is 0.5 mm. However, it is a difficult task for manufacturers to achieve this target, because of lower system sensitivity. Therefore, we developed a food contaminant detection system based on high-Tc RF superconducting quantum interference devices (SQUIDs), which are highly sensitive magnetic sensors. This study aims to improve the signal to noise ratio (SNR) of the system and detect a 0.5 mm diameter steel ball. Using a real time digital signal processing technique along with analog band-pass filters, we improved the SNR of the system. Owing to the improved SNR, a steel ball with a diameter as small as 0.3 mm, with stand-off distance of 117 mm was successfully detected. These results suggest that the proposed system is a promising candidate for the detection of metallic contaminants in food products.