Energy/Space-Efficient Rapid Single-Flux-Quantum Circuits by Using π-Shifted Josephson Junctions

Tomohiro KAMIYA  Masamitsu TANAKA  Kyosuke SANO  Akira FUJIMAKI  

Publication
IEICE TRANSACTIONS on Electronics   Vol.E101-C   No.5   pp.385-390
Publication Date: 2018/05/01
Online ISSN: 1745-1353
DOI: 10.1587/transele.E101.C.385
Type of Manuscript: Special Section PAPER (Special Section on Innovative Superconducting Devices Based on New Physical Phenomena)
Category: 
Keyword: 
energy-efficient circuit,  π-shifted Josephson junctions,  rapid single-flux-quantum,  superconducting spintronics,  

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Summary: 
We present a concept of an advanced rapid single-flux-quantum (RSFQ) logic circuit family using the combination of 0-shifted and π-shifted Josephson junctions. A π-shift in the current-phase relationship can be obtained in several types of Josephson junctions, such as Josephson junctions containing a ferromagnet barrier layer, depending on its thickness and temperature. We use a superconducting quantum interference devices composed of a pair of 0- and π-shifted Josephson junctions (0-π SQUIDs) as a basic circuit element. Unlike the conventional RSFQ logic, bistability is obtained by spontaneous circular currents without using a large superconductor loop, and the state can be flipped by smaller driving currents. These features lead to energy- and/or space-efficient logic gates. In this paper, we show several example circuits where we represent signals by flips of the states of a 0-π SQUID. We obtained successful operation of the circuits from numerical simulation.