This talk will focus on the coupling features of 3D superconducting circuits composed of Josephson junctions. Most of time superconducting electronic circuits, especially digital ones, rely on the microtrip technology for Josephson junction fabrication and also circuitry. One advantage is that magnetic fields associated with the propagation of signals are guided on-chip which limits mutual couplings and simplifies the SPICE schematic models. However, coplanar technologies are sometimes needed or compulsory. In this case mutual couplings are crucial and must be taken into account to properly account for the circuit behavior.
There are two main steps in the design workflow of a superconducting circuit. The synthesis part when the designer converts a finalized schematic electrical circuit into a layout for a given technology. And the analysis part when the designer verifies that the extracted parameters of the layout correspond to the initial parameters from synthesis part. For the synthesis part there are not many tools that allow to directly convert a schematic in a layout for superconductor circuits.
We have developed some tool that simplifies the synthesis of circuits made of monolayers, the ones for which magnetic couplings between adjacent circuits are the most overwhelming. It allows to determine inductances, or the geometry corresponding to a given inductance for simple cases, for applications with important magnetic coupling, either between cells or with respect to an external magnetic field.
I will present the full design process related to 3D nanoSQUIDs fabricated at INRIM and give a few trends about the method, as well as some comparisons with experimental results.