All-NbN Single Flux Quantum Circuits Based on NbN/AlN/NbN Tunnel Junctions

Hirotaka TERAI, Zhen WANG

Summary :

We report on the fabrication and operation of all-NbN single flux quantum (SFQ) circuits with resistively shunted NbN/AlN/NbN tunnel junctions fabricated on silicon substrates. The critical current varied by about 5% in 400 NbN/AlN/NbN junction arrays, where the junction area was 88 µm². Critical current densities of the NbN/AlN/NbN tunnel junctions showed exponential dependence on the deposition time of the AlN barrier. By using the 12-nm-thick Cu film as shunted resistors, non-hysteretic current-voltage characteristics were achieved. From dc-SQUID measurements, the sheet inductance of our NbN stripline was estimated to be around 1.2 pH at 4.2 K. We designed and fabricated circuits consisting of dc/SFQ converters, Josephson transmission lines, and T flip-flop-based SFQ/dc converters. The circuits demonstrated correct operation with a bias margin of more than 15% at 4.2 K.

• Publication: IEICE TRANSACTIONS on Electronics Vol.E83-C No.1 pp.69-74
• Publication Date: 2000/01/25
• Type of Manuscript: Special Section PAPER (Special Issue on Superconductive Devices and Systems)
• Category: Digital Applications

Authors

Hirotaka TERAI
Zhen WANG

Keyword

NbN integrated circuit,  NbN/AlN/NbN tunnel junction,  overdumped junction,  sheet inductance,  SFQ circuit,  operating margin