Advances in High-Tc Single Flux Quantum Device Technologies

Keiichi TANABE  Hironori WAKANA  Koji TSUBONE  Yoshinobu TARUTANI  Seiji ADACHI  Yoshihiro ISHIMARU  Michitaka MARUYAMA  Tsunehiro HATO  Akira YOSHIDA  Hideo SUZUKI  

Publication
IEICE TRANSACTIONS on Electronics   Vol.E91-C   No.3   pp.280-292
Publication Date: 2008/03/01
Online ISSN: 1745-1353
DOI: 10.1093/ietele/e91-c.3.280
Print ISSN: 0916-8516
Type of Manuscript: INVITED PAPER (Special Section on Recent Progress in Superconductive Digital Electronics)
Category: 
Keyword: 
superconducting device,  single flux quantum device,  mixed signal device,  high-temperature superconductor,  

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Summary: 
We have developed the fabrication process, the circuit design technology, and the cryopackaging technology for high-Tc single flux quantum (SFQ) devices with the aim of application to an analog-to-digital (A/D) converter circuit for future wireless communication and a sampler system for high-speed measurements. Reproducibility of fabricating ramp-edge Josephson junctions with IcRn products above 1 mV at 40 K and small Ic spreads on a superconducting groundplane was much improved by employing smooth multilayer structures and optimizing the junction fabrication process. The separated base-electrode layout (SBL) method that suppresses the Jc spread for interface-modified junctions in circuits was developed. This method enabled low-frequency logic operations of various elementary SFQ circuits with relatively wide bias current margins and operation of a toggle-flip-flop (T-FF) above 200 GHz at 40 K. Operation of a 1:2 demultiplexer, one of main elements of a hybrid-type Σ-Δ A/D converter circuit, was also demonstrated. We developed a sampler system in which a sampler circuit with a potential bandwidth over 100 GHz was cooled by a compact stirling cooler, and waveform observation experiments confirmed the actual system bandwidth well over 50 GHz.