• 한국초전도학회:학술대회논문집
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• v.9
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• pp.147-151
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• 1999

YBCO step-edge Josephson junction were fabricated on sapphire substrates. The steps were formed on R-plane sapphire substrates by using Ar ion milling with PR masks. The step angle was controlled in the wide range from 25$^{\circ}$ to 50$^{\circ}$ by adjusting both the Ar ion incident angle and the photoresist mask rotation angle relative to the incident Ar ion beam. CeO$_2$ buffer layer and in-situ YBa$_2Cu_3O_{7-{\delta}}$ (YBCO) thin films was deposited on the stepped R-plane sapphire substrates by pulsed laser deposition method. The YBCO film thickness was varied to obtain the ratio of film thickness to step height in the range from 0.5 to 1. The step edge junction exhibited RSJ-like behaviors with I$_cR_n$ product of 100 ${\sim}$ 300 ${\mu}$V, critical current density of 10$^3$ ${\sim}$ 10$^5$ A/ cm$^2$ at 77 K.

• Progress in Superconductivity
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• v.9 no.2
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• pp.177-182
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• 2008

[ $MgB_2$ ] thin films were fabricated using hybrid physical-chemical vapor deposition (HPCVD) method on silicon substrates with buffers of alumina grown by using atomic layer deposition method. The growth war in a range of temperatures $500\;{\sim}\;600^{\circ}C$ and under the reactor pressures of $25\;{\sim}\;50\;Torr$. There are some interfacial reactions in the as-grown films with impurities of mostly $Mg_2Si$, $MgAl_2O_4$, and other phases. The $T_c$'s of $MgB_2$ films were observed to be as high as 39 K, but the transition widths were increased with growth temperatures. The magnetization was measured as a function of temperature down to the temperature of 5 K, but the complete Meissner effect was not observed, which shows that the granular nature of weak links is prevailing. The formation of mostly $Mg_2Si$ impurity in HPCVD process is discussed, considering the diffusion and reaction of Mg vapor with silicon substrates.