Abstract Body

Superconducting logic circuits are known for their high-speed performance and low power consumption, making them promising candidates for next-generation digital logic circuits. In particular, adiabatic quantum flux parametron (AQFP) circuits can operate with an energy efficiency over five orders of magnitude superior to the state-of-the-art semiconductor circuit [1]. The team at YNU has previously conducted pioneering research on digital integrated circuits using AQFP logic and demonstrated the world's first operation of an AQFP microprocessor [2].

Despite its significant energy efficiency properties, AQFP encounters challenges related to integration density. This limitation arises because the output superconducting transformer used in AQFP does not adhere to the scaling law required for future reductions in device feature size. To overcome this, we previously proposed the directly coupled AQFP logic (DQFP), where the output superconducting transformer is eliminated. A main challenge in DQFP logic is representing the NOT function without the superconducting transformer. Currently, two DQFP logic families have been proposed: one employs an AQFP NOT gate with a different circuit topology [3], while the other leverages a π-junction to fulfill the NOT function [4].

In this study, we present a novel variant of DQFP logic named dual-rail DQFP (DDQFP) logic. In this approach, AQFP NOT gates are eliminated by adopting the dual-rail logic style. We demonstrate that specific logic circuits can be effectively implemented by using DDQFP logic. We compare three kinds of DQFP logic families regarding circuit size, junction counts, energy efficiency, and robustness with some experimental results.

References

[1] N. Takeuchi, D. Ozawa, Y. Yamanashi and N. Yoshikawa, “An adiabatic quantum flux parametron as an ultra-low-power logic device,” Supercond. Sci. Tech., 26, 2013, 035010 (2013).
[2] C. L. Ayala, T. Tanaka, R. Saito, M. Nozoe, N. Takeuchi and N. Yoshikawa, "MANA: A Monolithic Adiabatic iNtegration Architecture Microprocessor Using 1.4-zJ/op Unshunted Superconductor Josephson Junction Devices," IEEE Journal of Solid-State Circuits, 56, pp. 1152-1165 (2021).
[3] N. Takeuchi, K. Arai, N. Yoshikawa, “Directly coupled adiabatic superconductor logic,” Supercond. Sci. Tech., 33, 065002 (2020).
[4] K. Arai, N. Takeuchi, T. Yamashita, N. Yoshikawa, “Adiabatic quantum-flux-parametron with π Josephson junctions,” Journal of Applied Physics 125, 093901 (2019).

Acknowledgment

This work was supported by JSPS KAKENHI Grant Numbers JP19H05614. The circuits were fabricated in the Superconducting Quantum Circuit Fabrication Facility (Qufab) of National Institute of Advanced Industrial Science and Technology (AIST).