Sub-micron Josephson junctions fabricated with cross-line process

Abstract We have developed a cross-line process to fabricate sub-micron Josephson tunnel junctions using i-line stepper lithography and RIE etching. In the process, step sidewall was introduced to achieve the passivation of the junction utilizing the Al-AlOx layer in situ and a self-aligned insulating layer. The effect of junction area shrinkage in the process enables one to form smaller junction with dimension even at or below lithography limitation. Josephson junction with minimum area of 0.7 × 0.35 μm2 was obtained. The junction with gap current density of 1 kA/cm2 demonstrated high junction quality with a gap voltage of 2.8 mV and small sub-gap leakage current. The cross-line process for sub-micron junctions could be used in SQUID or other superconducting circuits where a low capacitance is desired. To verify the process, a SQUID magnetometer was also presented.