All-refractory weak-link SQUIDs for use in Josephson logic and memory applications

We report on the fabrication of all-refractory submicron-dimensioned superconductor-normal metal-superconductor (SNS) weak links between two coplanar electrodes. This unique geometry allows two or more weak links to be placed in parallel (dc SQUID) underneath an overlying control line for use in Josephson logic and memory applications. The method of fabrication is described and is amenable to incorporation in large-scale integrated circuit production. Depending upon geometry, weak links with a broad range of parameters may be obtained. Resistances are in the range of 0.01 to 2Ω and critical currents range from a few μA to a few mA. When incorporated into dc SQUIDs, inductances of one or two pH are typically obtained. Data are presented on the I-V characteristic, the dependence of critical current on temperature and magnetic field, and the rf response. In addition to their potential for use in superconducting microcircuitry, these devices closely approximate an ideal three-dimensional point contact, and as such are of basic interest.