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.
Nb/Al-AlOx/Nb tunnel junctions with controllable critical current density Jc are fabricated using the standard selective Nb etching process.Tunnel barriers are formed in different oxygen exposure conditions (oxygen pressure P and oxidation time t),giving rise to Jc ranging from 100 A/cm2 to above 2000 A/cm2.Jc shows a familiar linear dependence on P × t in logarithmic scales.We calculate the energy levels of the phaseand flux-type qubits using the achievable junction parameters and show that the fabricated Nb/Al-AlOx/Nb tunnel junctions can be used conveniently for quantum computation applications in the future.
