Reliability Studies of Nb/AlOx/Al/Nb Josephson Junctions Through Accelerated-Life Electrical Stress Testing

Reliability studies have been performed on Nb/AlOx/Al/Nb trilayer Josephson junctions with a critical current density of 100 μA/μm
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with emphasis on reliability of the thin AlOx dielectric tunnel barrier. High current stress tests at 4.2 K involving ramp-to-failure and time-dependent stress profiles have been used to accelerate the barrier degradation process while monitoring changes through dc characterization of the tunnel junctions. Tunneling characteristics of the junctions have been found to deteriorate with increasing stress magnitudes, suggesting breakdown mechanisms depending on the magnitude and polarity of the applied stress or the time-duration of applied stress. The typically observed stress effects can be ascribed to a reduction in the effective barrier thickness or increase in barrier transparency, and corresponding to the formation of conduction channels through the barrier above a threshold stress current. Significant stress current polarity dependence has been observed and described.