Bi-SQUID: design for applications

Abstract

A review of the theory of bi-SQUIDs and the experimental studies of bi-SQUID-based devices is presented. The reported output voltage linearity of the fabricated devices ( ∼ 40 to 45 dB) is much higher than that observed for dc SQUIDs ( ∼ 20 dB). Recent numerical simulation evidence indicates that the linearity can be further improved to at least 60 to 70 dB. Results from a wide, multi-parameter optimization analysis are considered in the form of parameter domains for the voltage-response linearity. Thermal–noise influence, load impact and interfacing requirements are examined. Potential applications of the devices are discussed.

Ultra-Highly Linear Magnetic Flux-to-Voltage response in Proximity-based Mesoscopic bi-SQUIDs

“…Such method, which is valid in the ω 1 → 0 limit, yields a theoretical maximum value for L ranging from ∼ 70 dB (at I B /I 0 = 0.85) to ∼ 120 dB (at I B /I 0 = 1.3), for Φ = φ 0 /16. As discussed in many other previous works 8,[23][24][25][26][28][29][30] , the inability associated to many real bi-SQUIDs technologies to achieve performances similar to the ones anticipated theoretically is a critical problem. One of the main results in this paper is that the technology we propose is one of the first that enable real performance for a single bi-SQUID close to the theoretical ones.…”

“…SNS JJs gained a growing interest in device physics thanks to a negligible parasitic capacitance and, even more, to a convenient and reproducible fabrication process, which allows their critical current and the functional form of their current-phase-relation 41,42 to be tailored to specific application needs just through the geom- etry of the weak link. Similarly to what conventional done for tunnel junctions devices 8 , in bi-SQUIDs based on SNS weaklinks, the linearity of the magnetic-field-to-voltage response can be controlled through the ratios of the critical current of the three JJs. The latter, indeed, can be regulated during the fabrication by properly setting the section and the length of the weak-links, and the relative thickness and the size of the overlapping area of the S and N regions.…”

“…Superconducting quantum interference devices (SQUIDs) provide the reference standard for magnetic flux detectors [1][2][3][4][5][6][7] and for the measurement of all those physical quantities that can be transduced from magnetic to electrical properties. In this sense, SQUIDs can be integrated into larger systems and used for signal processing applications 8 . In their simplest implementation, direct-current (DC) SQUIDs comprise a pair of Josephson junctions (JJ) 9 closed in a superconducting ring, whose critical current is modulated by the magnetic flux threading the loop with a periodicity equal to the magnetic flux quantum φ 0 = h/2e 1,2,10,11 .…”

“…A mitigation of these restrictions came from the introduction of a class of superconducting interferometers containing a third a) Electronic mail: giorgio.desimoni@sns.it b) Electronic mail: francesco.giazotto@sns.it JJ connected in parallel with the inductance loop of a DC SQUID. In such devices, namely called bi-SQUIDs [23][24][25][26] , the third JJ, is used as additional non-linear element operating in parallel to compensate for the non-linear response of the DC-SQUID resulting in a highly linear voltage response [23][24][25] . Although such promising premises, Nb bi-SQUIDs with shunted Josephson tunnel junctions 27 , due to the large junction area and inductance, showed non ideal voltage response, with a linearity performance far from the expected one 8 .…”

“…In such devices, namely called bi-SQUIDs [23][24][25][26] , the third JJ, is used as additional non-linear element operating in parallel to compensate for the non-linear response of the DC-SQUID resulting in a highly linear voltage response [23][24][25] . Although such promising premises, Nb bi-SQUIDs with shunted Josephson tunnel junctions 27 , due to the large junction area and inductance, showed non ideal voltage response, with a linearity performance far from the expected one 8 . Instead, Nb bi-SQUIDs based on arrays of different numbers of interferometers, ranging between tens and hundreds of unit cells, have proven to be extremely effective for low-noise signal amplification and magnetic field sensing, exhibiting excellent performance in terms of linearity of the flux-to-voltage response [28][29][30] .…”