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IEEE Transactions on Applied Superconductivity

Computational Modeling of bi-Superconducting Quantum Interference Devices for High-Temperature Superconducting Prototype Chips

Susan A. E. Berggren, B. J. Taylor, E.E. Mitchell, Kirsty Hannam, Jeina Lazar, Anna Leese de Escobar

Published May 17, 2016• 9 citations
Publisher

Abstract

We explore bi-superconducting quantum interference device (bi-SQUID) designs suitable for the fabrication process of high-temperature superconducting step-edge Josephson junctions. The bi-SQUID offers increased linearity and improved signal detection performance over a SQUID. The realization of high-temperature superconducting (HTS) bi-SQUIDs opens up new potential applications given the reduced constraints of the cryogenic package. In this paper, we explore the effects of Josephson junction and temperature variations through modeling a bi-SQUID system of equations for different designs based on step-edge Josephson junctions.

DOI
10.1109/tasc.2016.2569502

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We explore bi-superconducting quantum interference device (bi-SQUID) designs suitable for the fabrication process of high-temperature superconducting step-edge Josephson junctions. The bi-SQUID offers increased linearity and improved signal detection performance over a SQUID. The realization of high-temperature superconducting (HTS) bi-SQUIDs opens up new potential applications given the reduced constraints of the cryogenic package. In this paper, we explore the effects of Josephson junction and temperature variations through modeling a bi-SQUID system of equations for different designs based on step-edge Josephson junctions.
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We develop a two-dimensional (2-D) superconducting quantum interference filter (SQIF) array based on the recently introduced high-linearity tri-junction bi-SQUIDs (superconducting quantum interference device). Our bi-SQUID SQIF array design is based on a tight integration of individual bi-SQUID cells sharing inductances with adjacent cells. We provide extensive computer simulations, analysis, and experimental measurements, in which we explore the phase dynamics and linearity of the array voltage response. The nonuniformity in inductances of the bi-SQUIDs produces a pronounced zero-field single antipeak in the voltage response. The antipeak linearity and size can be optimized by varying the critical current of the additional junction of each bi-SQUID. The layout implementation of the tight 2-D array integration leads to a distinct geometrical diamond shape formed by the merged dual bi-SQUID cells. Different-sized 2-D arrays are fabricated using the standard HYPRES niobium 4.5 kA/cm2fabrication process. The measured linearity, power gain, and noise properties will be analyzed for different array sizes and the results will be compared with circuit simulations. We will discuss a design approach for the electrically small magnetic field antenna and low-noise amplifiers with high bandwidth based on these 2-D bi-SQUID SQIF arrays. The results from this work will be used to design chips densely and completely covered in bi-SQUIDs that have optimized parameters such as linearity and power gain.
Abstract A numerical model based on a lumped circuit element approximation for a bi-superconducting quantum interference device (bi-SQUID) operating in the presence of an external magnetic field is presented in this paper. Included in the model is the novel ability to capture the resultant behaviour of the device when a strong electric field is applied to its Josephson junctions by utilising gate electrodes. The model is used to simulate an all-metallic SNS (Al-Cu-Al) bi-SQUID, where good agreement is observed between the simulated results and the experimental data. The results discussed in this work suggest that the primary consequences of the superconducting field effect induced by the gating of the Josephson junctions are accounted for in our minimal model; namely, the suppression of the junctions super-current. Although based on a simplified semi-empirical model, our results may guide the search for a microscopic origin of this effect by providing a means to model the voltage response of gated SQUIDs. Also, the possible applications of this effect regarding the operation of SQUIDs as ultra-high precision sensors, where the performance of such devices can be improved via careful tuning of the applied gate voltages, are discussed at the end of the paper.
The predominantly dx2−y2-pairing symmetry in most high-Tc superconductors provides the opportunity to fabricate Josephson junction circuits in which part of the junctions are biased by a phase difference of the superconducting order parameter of π. We present fabrication and measurements of an all high-Tc dc superconducting quantum interference device (dc SQUID) realized with thin-film technology, of which the Josephson junctions consist of one standard junction and one junction with a π-phase shift. The characteristics of the π-SQUID are compared with the properties of a standard high-Tc SQUID.
The CSIRO Applied Superconductivity Group has a long-term effort in research and development of superconducting electronic devices and systems for various practical applications. In this talk, I will give an overview of CSIRO research activities in developing high-Tcsuperconducting (HTS) Josephson junction devices for various applications. I will firstly describe the CSIRO-developed HTS step-edge Josephson junction technology and its basic application in Superconducting Quantum Interference Devices (SQUIDs). I will then describe in more detail our recent research progress on developing high-Tcsuperconducting (HTS) Josephson devices for microwave and terahertz (THz) applications.
We report on the fabrication and characterization of micrometer-sized superconducting quantum interference devices (SQUIDs) based on nanoscale vanadium/copper/vanadium Josephson weak links. Magnetically driven quantum interference patterns have been measured for temperatures in the 0.24–2 K range. As DC SQUIDs, these devices obtain flux-to-voltage transfer function values as high as 450 μV/Φ0 leading to promising magnetic flux resolution ΦN<3 μΦ0/Hz, being here limited by the room temperature preamplification stage. Significant improvement in the flux noise performance figures is expected with the adoption of cryogenic preamplification. The presented devices are suitable for operation as small-area SQUIDs at sub-Kelvin temperature, but their design can also be upscaled to include input coils enabling their use as sensitive magnetometers via the adoption of optimized electronic readout stages based on flux feedback schemes.