Fabrication of Al/AlO x /Al Josephson junctions on silicon and sapphire substrates using a cold-development technique

In order to obtain high-quality superconducting qubits, we employed a cold-development technique, using temperatures down to −20°C, to fabricate Al/AlO x /Al Josephson junctions. Cold development greatly reduced the sensitivity of the electron-beam resist to the developer, eliminated molecules of the electron-beam resist at trench edges, and improved the repeatability and reliability of the nanopatterning process. The fabricated samples have well-defined geometries and increased dose margins, with lateral sizes of 100 nm×100 nm on both silicon and sapphire substrates. Together with the bridge-free fabrication method we used in these experiments, we believe that the cold-development technique can play an important role in quantum information technology that employs superconducting qubits.