The Nb/Al-AlOx/Nb Josephson junction serves as the core component of mainstream low-temperature superconducting devices. With the growing demand for scaling up superconducting circuits, increasing the process temperature has become a key technical direction. However, during higher-temperature processing, the difference in the coefficient of thermal expansion between niobium and the substrate introduces significant thermal stress, which degrades junction quality. To mitigate the adverse effects of thermal stress, this paper proposes a stress pre-compensation method: by pre-tuning the residual stress of the bottom niobium electrode, the thermal stress generated in subsequent high-temperature steps is counteracted, thereby maintaining the total stress in the bottom electrode at a low level. In experiments, a series of Josephson junctions with different bottom-electrode stresses were electrically characterized at 4.2 K before and after annealing. The results show that controlling the residual stress of the bottom electrode within a specific tensile range can improve the post-annealing yield. After annealing at 250 ℃ for 30 min, junctions with an initially tensile-stressed bottom Nb electrode exhibited approximately a 14% higher yield compared to those with compressive stress. This trend was also verified in the annealing process of Nb/Al-AlOx-Al*/Nb Josephson junctions.
WANG et al. (Wed,) studied this question.