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IEICE Technical Report; IEICE Tech. Rep.

Fabrication of Magnetic Josephson Junctions on Nb 4-layer Structure for Large Scale Half Flux Quantum Circuits

Daiki Hasegawa, Yuto Takeshita, Feng Li, Kyosuke Sano, Masamitsu Tanaka, Taro Yamashita, Akira Fujimaki

Published Jan 9, 2020• 0 citations
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Magnetic Josephson Junctions on Nb Four-layer Structure for Half Flux Quantum Circuits

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We successfully fabricated magnetic Josephson junctions integrated on a Nb four-layer superconducting structure for demonstrating half flux quantum (HFQ) circuits. In the developed process, we adopted a 0-0-π SQUID instead of the 0-π SQUID as the basic element of the HFQ circuits. In this work, we characterized the Nb/PdNi/Nb magnetic Josephson junctions on the Nb four-layer structures fabricated by two different processes. We measured the I-V characteristics of junctions in liquid helium at 4.2 K. The results showed that the fabricated junctions had properties comparable to conventional ones on Si wafers.

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Magnetic Josephson Junctions With Superconducting Interlayer for Cryogenic Memory

I. V. Vernik, V. V. Bol'ginov, Sergey V. Bakurskiy +4 more

We investigate a Magnetic Josephson Junction (MJJ) - a superconducting device with ferromagnetic barrier for a scalable high-density cryogenic memory compatible with energy-efficient single flux quantum (SFQ) circuits. The superconductor-insulator-superconductor-ferromagnet-superconductor (SIS'FS) MJJs are analyzed both experimentally and theoretically. We found that the properties of SIS'FS junctions fall into two distinct classes based on the thickness of S'layer. We fabricate Nb-Al/AlOx-Nb-PdFe-Nb SIS'FS MJJs using a co-processing approach with a combination of HYPRES and ISSP fabrication processes. The resultant SIS'FS structure with thin superconducting S'-layer is substantially affected by the ferromagnetic layer as a whole. We fabricate these type of junctions to reach the device compatibility with conventional SIS junctions used for superconducting SFQ electronics to ensure a seamless integration of MJJ-based circuits and SIS JJ-based ultra-fast digital SFQ circuits. We report experimental results for MJJs, demonstrating their applicability for superconducting memory and digital circuits. These MJJs exhibitIcRnproduct only ~ 30% lower than that of conventional SIS junctions co-produced in the same fabrication. Analytical calculations for these SIS'FS structures are in a good agreement with the experiment. We discuss application of MJJ devices for memory and programmable logic circuits.

arXiv:1212.0815•IEEE Transactions on Applied Superconductivity•Dec 10, 2012•150 citations
We successfully fabricated magnetic Josephson junctions integrated on a Nb four-layer superconducting structure for demonstrating half flux quantum (HFQ) circuits. In the developed process, we adopted a 0-0-π SQUID instead of the 0-π SQUID as the basic element of the HFQ circuits. In this work, we characterized the Nb/PdNi/Nb magnetic Josephson junctions on the Nb four-layer structures fabricated by two different processes. We measured the I-V characteristics of junctions in liquid helium at 4.2 K. The results showed that the fabricated junctions had properties comparable to conventional ones on Si wafers.
We report a hybrid fabrication process for superconductor large-scale integrated circuits (ICs) with ferromagnetic π-shifted Josephson junctions (π junctions) and conventional 0 junctions. π junctions have a Nb/PdNi/Nb sandwich structure and are formed on the reliable Nb four-layer structure used for Nb/AlOx/Nb 0-junction-based ICs. The additional process for making π junctions causes little damage to the 0 junctions. The π phase shift for the superconducting macroscopic wave function is confirmed by forming 0-0-π SQUIDs that have two 0 junctions and one π junction in a superconducting loop. The π junction serves as the π phase shifter because the critical currents of the π junctions are much larger than those of the 0 junctions. The modulation patterns of the 0-0-π SQUIDs show a clear shift by the magnetic field corresponding to the half flux quantum (HFQ). The critical currents of the 0-0-π SQUIDs without fields, which are referred to as the nominal critical currents, are reduced depending on the product of the loop inductance and the critical current of the 0 junction. The nominal critical current reaches 1/5 of the critical current of the single 0 junction. The small values of the nominal critical currents contribute to the reduction of the power consumption in the HFQ circuit directly.
We investigate a Magnetic Josephson Junction (MJJ) - a superconducting device with ferromagnetic barrier for a scalable high-density cryogenic memory compatible with energy-efficient single flux quantum (SFQ) circuits. The superconductor-insulator-superconductor-ferromagnet-superconductor (SIS'FS) MJJs are analyzed both experimentally and theoretically. We found that the properties of SIS'FS junctions fall into two distinct classes based on the thickness of S'layer. We fabricate Nb-Al/AlOx-Nb-PdFe-Nb SIS'FS MJJs using a co-processing approach with a combination of HYPRES and ISSP fabrication processes. The resultant SIS'FS structure with thin superconducting S'-layer is substantially affected by the ferromagnetic layer as a whole. We fabricate these type of junctions to reach the device compatibility with conventional SIS junctions used for superconducting SFQ electronics to ensure a seamless integration of MJJ-based circuits and SIS JJ-based ultra-fast digital SFQ circuits. We report experimental results for MJJs, demonstrating their applicability for superconducting memory and digital circuits. These MJJs exhibitIcRnproduct only ~ 30% lower than that of conventional SIS junctions co-produced in the same fabrication. Analytical calculations for these SIS'FS structures are in a good agreement with the experiment. We discuss application of MJJ devices for memory and programmable logic circuits.