Bridge Type Josephson Junction Devices and Integrated Circuits

Takuo Sugano, Yoichi Okabe, Hirotaka Tamura +2 more

Sueli Skinner Ramos, Matthew Freeman, Douglas V. Pete +3 more

Josephson junctions are the principal circuit element in numerous superconducting quantum information devices and can be readily integrated into large-scale electronics. However, device integration at the wafer scale necessarily depends on having a reliable, high-fidelity, and high-yield fabrication method for creating Josephson junctions. When creating Al/AlO x based superconducting qubits, the standard Josephson junction fabrication method relies on a sub-micron suspended resist bridge, known as a Dolan bridge, which tends to be particularly fragile and can often times fracture during the resist development process, ultimately resulting in device failure. In this work, we demonstrate a unique Josephson junction lithography mask design that incorporates stress-relief channels. Our simulation results show that the addition of stress-relief channels reduces the lateral stress in the Dolan bridge by more than 70% for all the bridge geometries investigated. In practice, our novel mask design significantly increased the survivability of the bridge during device processing, resulting in 100% yield for over 100 Josephson junctions fabricated.

Hideo Suzuki, Takeshi Imamura, S. Hasuo

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.

Thomas F. Finnegan

The design, operation and details of construction of a fully shielded microwave-integrated-circuit holder suitable for use with thin-film superconducting microstrip circuitry including couplers, filters, impedance transformers and devices such as Josephson junctions are described. Several simple microwave coupling schemes for use with Josephson junction 2e/h frequency-to-voltage transducers illustrate the flexibility of the microstrip approach for coupling to thin-film Josephson junctions and semiconductor devices at cryogenic temperatures.

W. Jutzi