Self-aligning fabrication and DC characterization of Nb/AlOx/Nb superconducting Josephson junctions

Superconducting qubit systems are one way to implement large-scale quantum computations. Nb/AlOx/Nb superconducting Josephson junctions were fabricated using a planar process as the groundwork for fabricating reliable qubits. The junction area was formed by a self-aligning technology, which effectively protected the device and reduced the fabrication complexity. A low temperature system was constructed to characterize the Josephson junctions with automatic generation and acquisition of signals. The I-V characteristics of the Josephson junctions were measured at different temperatures with an observed jump at the niobium superconducting gap voltage of 2.85 mV. The critical currents of the Josephson junctions were measured at different temperatures, which agree well with the theoretical result of Ambegaokar and Baratoff.