Design and Operation of HTS SFQ Circuit Elements

Koji TSUBONE  Hironori WAKANA  Yoshinobu TARUTANI  Seiji ADACHI  Yoshihiro ISHIMARU  Keiichi TANABE 

Publication
IEICE TRANSACTIONS on Electronics  Vol.E90-C  No.3  pp.570-578
Publication Date: 2007/03/01
Online ISSN: 1745-1353
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Section on Innovative Superconducting Devices and Their Applications)
Category: INVITED
Keyword: 
single flux quantum (SFQ) circuit,  ramp-edge junction technology,  toggle flip-flop,  thermal noise,  high-temperature superconductor, 

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Summary: 
Single flux quantum (SFQ) circuit elements have been designed and fabricated using the YBa2Cu3O7-δ ramp-edge junction technology. Logic operations of SFQ circuit elements, such as a toggle flip-flop (T-FF), a set-reset flip-flop (RS-FF), and a 96-junction Josephson transmission line (JTL), were successfully demonstrated, and dc supply current margins were confirmed up to temperatures higher than 30 K. The circuit layout was improved in order to suppress the critical current (Ic) spread that appears during the junction fabrication procedure. By employing the new circuit layout rule, correct operations at temperatures from 27 K to 34 K with dc supply current margins wider than 7% were confirmed for the T-FF with a single output. Moreover, the maximum operating frequencies of T-FFs were measured to be 360 GHz at 4.2 K and 210 GHz at 41 K, which are substantially higher than the values for the circuits with the conventional layout. According to the simulation result, the maximum operating frequency at 40 K was expected to be approximately 50% of the characteristic frequency at a bit error rate (BER) less than 10-6.