Superconductor digital circuits with π junctions alone.

This article focuses on the development and application of superconductor/ferromagnet/insulator/superconductor (SFIS) Josephson junctions (JJs) as both switching elements and intrinsic π phase shifters in superconductor digital circuits. The SFIS junctions exhibit a critical current density of about 22 A/cm² and a characteristic voltage of 22 μV, enabling their use in single-flux-quantum (SFQ) circuits without the need for hybrid integration with conventional 0-JJs. Experimental results demonstrate intrinsic π phase shifts through modulation patterns in π–π–π superconducting quantum interference devices (SQUIDs) and show that SFIS-based SFQ circuits can reduce energy dissipation by 80% due to self-biasing effects from circulating currents. Additionally, half-flux-quantum (HFQ) SQUIDs fabricated solely with π-JJs reveal propagation of HFQ signals, suggesting potential for more complex SFQ and HFQ circuits using SFIS technology in future superconducting electronics.