Fabrication of Superconducting Qubits With Al Trilayer Josephson Junctions

• Published in: IEEE transactions on applied superconductivity Vol. 25; no. 3; pp. 1 - 5
• Main Authors: Satoh, T., Noguchi, Y., Yamagishi, M., Nagasawa, S., Hinode, K., Hidaka, M., Maezawa, M., Horikawa, T.
• Format: Journal Article
• Language: English
• Published: IEEE 01-06-2015
• Subjects: CMP planarization; Etching; Fabrication; Josephson junction fabrication; Josephson junctions; Junctions; Planarization; Resists; superconducting qubit; trilayer geometry; Wires; CMP planarization; Josephson junction fabrication; trilayer geometry; superconducting qubit
• ISSN: 1051-8223; 1558-2515
• DOI: 10.1109/TASC.2014.2378033

To implement a large-scale integration of superconducting quantum bits (qubits), we have investigated a process of fabricating submicrometer Al/AlOx/Al trilayer Josephson junctions. Moreover, on the basis of this process, we developed a means of fabricating different kinds of superconducting qubits. Superconducting qubits require not only small junctions, but also peripheral circuit elements, such as a large resonator, on the same chip. As a result, we chose to use planarization in the self-aligned junction contact formation, which suppressed a pattern-area-dependence of the chemical-mechanical polishing rate. In addition, Al fine wires with a width of 0.2 μm were required in some parts of the qubits to increase the coupling strength between the SQUIDs and qubits. We developed a two-step etching process to form such fine wires using i-line photoresist, which had a high etching resistance. The operation of three-junction flux qubits was confirmed in a dilution refrigerator.