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AIP conference proceedings

Fabrication and characterization of shunted μ-SQUID

Nikhil Kumar, T. Fournier, H. Courtois, Anjan Kumar Gupta

Published Jan 1, 2014• 2 citations
Publisher

Abstract

In order to eliminate hysteresis, we have fabricated and characterized niobium based shunted micron size superconducting quantum interference devices (μ-SQUIDs). We find a wide temperature range where these μ-SQUIDs are non-hysteretic in nature and show a very good Ic vs. B oscillations in hysteretic regime and V vs. B oscillations in non-hysteretic regime. Here we report the characteristics of a shunted- μ-SQUID (Wf38LS72D5). In this device we have achieved a large voltage modulation, in non-hysteretic regime, at various temperatures including such as 1.1 mV at 6.62 K with a transfer function VΦ = 7.2mV/Φ0.The figures within the original article PDF file, as supplied to AIP Publishing, were affected by a PDF-processing error. Consequently, the article re-flowed and pagination increased from 3 to 4 pages. This article was updated on 14 May 2014 to correct the PDF-processing error, with the scientific content remaining unchanged. Readers are advised that the replacement article PDF file contains an additional blank page to preserve the original pagination.

DOI
10.1063/1.4873045

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IEEE Transactions on Applied Superconductivity•May 18, 2018•5 citations
In order to eliminate hysteresis, we have fabricated and characterized niobium based shunted micron size superconducting quantum interference devices (μ-SQUIDs). We find a wide temperature range where these μ-SQUIDs are non-hysteretic in nature and show a very good Ic vs. B oscillations in hysteretic regime and V vs. B oscillations in non-hysteretic regime. Here we report the characteristics of a shunted- μ-SQUID (Wf38LS72D5). In this device we have achieved a large voltage modulation, in non-hysteretic regime, at various temperatures including such as 1.1 mV at 6.62 K with a transfer function VΦ = 7.2mV/Φ0.The figures within the original article PDF file, as supplied to AIP Publishing, were affected by a PDF-processing error. Consequently, the article re-flowed and pagination increased from 3 to 4 pages. This article was updated on 14 May 2014 to correct the PDF-processing error, with the scientific content remaining unchanged. Readers are advised that the replacement article PDF file contains an additional blank page to preserve the original pagination.
Micron-size superconducting quantum interference devices (μ\muμ-SQUIDs) are highly-sensitive magnetic flux sensors where the critical current or the voltage is modulated by the magnetic flux. The so-called voltage read-out mode is nevertheless often hindered by thermal hysteresis. μ\muμ-SQUIDs with improved thermal evacuation and small critical current can feature a phase-dynamic regime over a narrow bias-current and temperature range. Guided by a dynamic thermal model, we could widen these current and temperature ranges by using a shunt resistor. A significant increase in these ranges and, more strikingly, in the voltage oscillations magnitude is observed when the shunt is made of an adequate inductance in series with the resistor. An increase in inductance above a threshold value leads to relaxation oscillations in voltage. The large voltage modulation thus obtained offers an improved flux resolution in the voltage read-out mode down to 1.3 K.
We have fabricated and characterized niobium film based superconducting weak link (WL) devices and micron-size superconducting quantum interference devices (µ-SQUIDs) with superconducting WLs as Josephson Junctions. Here we discuss the effect of WL width on the hysteresis and crossover temperature (Th) while keeping the other dimensions fixed. We find that the critical current reduces linearly with the width and thus Th reduces with decreasing width. This makes some of the devices non-hysteretic down to 1.3K. We also discuss the observed excess current in the current-voltage characteristics of these devices, in terms of Andreev reflection.
In this article, an all-NbN superconducting quantum interference device (SQUID) array was developed for future applications by taking advantage of the higher critical temperature of a NbN film compared with Nb. The NbN SQUID array was composed of 100 SQUIDs with equal loop areas connected in series. The array was fabricated on a single-crystal MgO (100) substrate using 3-μm-diameter NbN/AlN/NbN Josephson junctions. The hysteresis and shielding parameters of the SQUID were 0.67 and 0.15, respectively. The SQUIDs in the array were coherently modulated by injecting current in a common flux control line, which resulted in a modulation voltage of 3.54 mV with consistent periodicity and a flux-to-voltage transfer coefficient of 23 mV/Φ0. Using a flux locked loop circuit, the fabricated NbN SQUID array exhibited excellent performance with a low white flux noise of 1.4 μΦ0/√Hz, which included the preamplifier noise.
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.
A superconducting quantum interference device (SQUID) miniaturized into the nanoscale is promising in the inductive detection of a single electron spin. A nano-SQUID with a strong spin coupling coefficient, a low flux noise, and a wide working magnetic field range is highly desired in a single spin resonance measurement. Nano-SQUIDs with Dayem bridge junctions excel in a high working field range and in the direct coupling from spins to the bridge. However, the common planar structure of nano-SQUIDs is known for problems such as a shallow flux modulation depth and a troublesome hysteresis in current–voltage curves. Here, we developed a fabrication process for creating three-dimensional (3-D) niobium (Nb) nano-SQUIDs with nanobridge junctions that can be tuned independently. Characterization of the device shows up to 45.9% modulation depth with a reversible current–voltage curve. Owning to the large modulation depth, the measured flux noise is as low as 0.34 μΦ 0 /Hz 1/2 . The working field range of the SQUID is greater than 0.5 T parallel to the SQUID plane. We believe that 3-D Nb nano-SQUIDs provide a promising step toward effective single-spin inductive detection.
Superconducting quantum interference devices (SQUIDs) with 3 μm × 3 μm or 4 μm × 4 μm self-shunted Nb/NbxSi1-x/Nb Josephson junctions are designed and fabricated. By adjusting the Nb content and thickness of the NbxSi1-xbarrier, the parameters of the SQUIDs can be easily tuned. The optimal parameters for the barrier are found to be a thickness of around 15 nm and 7% Nb content. The I-V curve, V-Φ curve, and noise spectrum are measured for the SQUID. The high frequency noise for the SQUID is only about several hundred nΦ0/√Hz. Another advantage for these devices is found, that it is not sensitive to the static electricity.