Nb 9-Layer Fabrication Process for Superconducting Large-Scale SFQ Circuits and Its Process Evaluation

Shuichi NAGASAWA  Kenji HINODE  Tetsuro SATOH  Mutsuo HIDAKA  Hiroyuki AKAIKE  Akira FUJIMAKI  Nobuyuki YOSHIKAWA  Kazuyoshi TAKAGI  Naofumi TAKAGI  

Publication
IEICE TRANSACTIONS on Electronics   Vol.E97-C   No.3   pp.132-140
Publication Date: 2014/03/01
Online ISSN: 1745-1353
DOI: 10.1587/transele.E97.C.132
Print ISSN: 0916-8516
Type of Manuscript: INVITED PAPER (Special Section on Leading-Edge Technology of Superconductor Large-Scale Integrated Circuits)
Category: 
Keyword: 
superconducting fabrication technology,  Nb/AlOx/Nb Josephson junction,  single flux quantum,  planarization,  shift register,  

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Summary: 
We describe the recent progress on a Nb nine-layer fabrication process for large-scale single flux quantum (SFQ) circuits. A device fabricated in this process is composed of an active layer including Josephson junctions (JJ) at the top, passive transmission line (PTL) layers in the middle, and a DC power layer at the bottom. We describe the process conditions and the fabrication equipment. We use both diagnostic chips and shift register (SR) chips to improve the fabrication process. The diagnostic chip was designed to evaluate the characteristics of basic elements such as junctions, contacts, resisters, and wiring, in addition to their defect evaluations. The SR chip was designed to evaluate defects depending on the size of the SFQ circuits. The results of a long-term evaluation of the diagnostic and SR chips showed that there was fairly good correlation between the defects of the diagnostic chips and yields of the SRs. We could obtain a yield of 100% for SRs including 70,000JJs. These results show that considerable progress has been made in reducing the number of defects and improving reliability.