Design and Demonstration of Directly Coupled Quantum-Flux-Parametron Circuits With Optimized Parameters

We have been developing the adiabatic quantum-flux-parametron (AQFP), which is an ultra-low-power superconductor logic family. To date, somewhat large AQFP circuits, such as a 4-bit microprocessor and an 8-bit adder, have been demonstrated. To design much larger devices, space-efficient logic circuits are needed. Therefore, in a previous study, we proposed the directly coupled quantum-flux-parametron (DQFP). DQFP circuits propagate data via a direct connection, whereas AQFP circuits propagate data via transformers, which can occupy a large part of the gate area. Thus, DQFP circuits are more space-efficient than AQFP circuits. In this study, we optimized the circuit parameters for DQFP logic cells using numerical simulations from the viewpoint of excitation current margins, component parameter margins, and energy dissipation. We also designed the physical layout of the optimized DQFP cells, fabricated chips, and demonstrated basic DQFP circuits with the optimized cells.