低温超伝導デバイス作製プロセスと今後の展望

抄録

We are routinely fabricating many superconducting digital devices using three types of Nb-based fabrication process. One of them consists of nine Nb, one Mo and one Nb/AlOx/Nb Josephson junction (JJ) layers. Controllability in the device parameters, such as the critical current density (J_c) of JJ, has been improved. J_c in the Nb 9-layer process was controlled within ±10% of the 10 kA/cm² target value for all 18 wafers fabricated in 2016. Uniformity of the critical current satisfied our criteria for integrated circuit applications up to a JJ size of 0.5 μm². Reliability of the Nb 9-layer process reached the 100,000 JJ circuit level. The digital circuit processes will be improved by introducing advanced fabrication machines and/or integrating new materials. Three-dimensional, analog, analog-digital monolithic and quantum computing devices are being developed based on these digital device processes.