Fabrication of high-quality submicron Nb/Al-AlO_x/Nb tunnel junctions

【摘要】：Nb/Al–AlOx/Nb tunnel junctions are often used in the studies of macroscopic quantum phenomena and supercon- ducting qubit applications of the Josephson devices. In this work, we describe a convenient and reliable process using electron beam lithography for the fabrication of high-quality,submicron-sized Nb/Al–AlO x /Nb Josephson junctions. The technique follows the well-known selective Nb etching process and produces high-quality junctions with V m =100 mV at 2.3 K for the typical critical current density of 2.2 kA/cm 2 , which can be adjusted by controlling the oxygen pressure and oxidation time during the formation of the tunnelling barrier. We present the results of the temperature depen- dence of the sub-gap current and in-plane magnetic-field dependence of the critical current, and compare them with the theoretical predictions.