• Progress in Superconductivity and Cryogenics
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• v.4 no.1
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• pp.50-54
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• 2002

Penetration depth of Nb electrodes in $Nb/A1O_x/Nb$ Josephson junctions has been measured by resistive method. For a given applied field, the total flux through the junction is temperature dependent because the penetration depth of Nb electrode varies with temperature. If the total flux equals an integral multiple of the flux quantum at certain temperatures, resistive peaks appear at those temperatures. The penetration depth of Nb can be determined by applying the above condition, The temperature dependence of penetration depth was found to be well described by the two-fluid model.

• Progress in Superconductivity and Cryogenics
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• v.4 no.1
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• pp.17-20
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• 2002

A complex single flux quantum(SFQ) circuit could be made up of various elementary cells such as JTL(Josephson transmission line), Splitter, XOR, DC/SFQ, SFQ/DC, T flip-flop, ‥‥, etc. In this work, we have designed and simulated a SFQ circuit, which consists of DC/SFQ, JTL and SFQ/DC, based on Nb/AlO$_{x}$Nb Josephson junction technology From the simulation, we could obtain the margins for various circuit parameters. And also we have successfully operated the circuit, which was fabricated with the same design, up to the input signal frequency of about 20 GHz.z.

• Progress in Superconductivity and Cryogenics
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• v.4 no.1
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• pp.4-7
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• 2002

Samples of $Nb/Al-AlO_x/Nb$ tunnel junction with the size of $50 ${\mu}{\textrm}{m}$ {\times} 50 ${\mu}{\textrm}{m}$$ were fabricated by using self-aligning and reactive ion etching technique In the high quality samples, the $V_m$ value (the product of the critical current and subgap resistance measured at 2 mV) was 34 mV at the critical current density of $J_c: 500 A/cm^2 and the V_g$ value (the gap voltage) was 2.8 mV. For the higher $J_c$ sample, voltage fluctuation at the gap voltage was observed. The $V_m and J_c$ values for this sample were 8 mV and 900 A/cm$^2$, respectively. Also, the relationship between critical current density $J_c$ and specific normal conductance $G_s$ of the junctions with $J_c$ in the range of 28 A/cm$^2$~940 A/cm$^2$was investigated.