Noise of dc-SQUIDs with planar sub-micrometer Nb/HfTi/Nb junctions

Beyer, J.; Klemm, Mason; Storm, Jan-Hendrik; Kieler, Oliver; Weimann, Thomas; Morosh, Viacheslav

doi:10.1088/0953-2048/28/8/085011

Cited by 5 publications

(6 citation statements)

References 23 publications

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“…Even if one calculates the flux noise from the nominal value of the SQUID inductance L SQ and takes the contribution of the kinetic inductance L kin into account, the measured noise is higher than expected. This behavior has already been found by other groups for other low-inductance devices as well, for example in [12] or in [14], and is subject to further examination.…”

Section: Characterizationsupporting

confidence: 73%

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Investigation of nanoSQUID designs for practical applications

Bechstein¹,

Köhn²,

Drung³

et al. 2017

Supercond. Sci. Technol.

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In the recent past, considerable effort was spent on the development of superconducting quantum interference device (SQUID) designs for magnetic detection in the micro- and nano-scale. Where these novel nanoSQUIDs were mostly of a simple format, real applications require more elaborate designs including auxiliary components such as coils and transformers. Therefore, we have developed SQUID designs based on a Nb/HfTi/Nb thin-film technology which offers both, nano-patterning and waferscale manufacturing of complex design structures. Employing e-beam lithography and chemical–mechanical polishing process steps, the area of the superconductor–normal conductor–superconductor Josephson junctions of these nanoSQUIDs has been varied between 150 nm × 150 nm and 200 nm × 200 nm, whereas the thickness of the barrier is about 20 nm. In order to enable real practical applications, nanoSQUID designs with a number of implemented auxiliary components and design features, such as gradiometric feedback loops, gradiometric transformers, and rf filters, have been carefully investigated. This paper combines a summary of recent achievements with a presentation of detailed measurements of the device performance in magnetic fields of up to a few tens of millitesla. This investigation is intended to pave the way for future practical complex nanoSQUID tools.

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Section: Characterizationsupporting

confidence: 73%

“…To compare the measured noise data with theory, equation (2) was used-as in [12]. The equation was derived from numerical simulations of the dc SQUID noise if Γβ L =4πk B TL SQUID /Φ 0 2 <0.1 [13].…”

Section: Characterizationmentioning

confidence: 99%

Investigation of nanoSQUID designs for practical applications

Bechstein¹,

Köhn²,

Drung³

et al. 2017

Supercond. Sci. Technol.

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“…The measurements are carried out at T = 4.2 K in a magnetically shielded environment making use of a two-stage cascade readout with a SQUID amplifier as described in Ref. [32]. The noise contribution of our measurement setup is verified to be negligible through measurements of the Johnson-Nyquist noise of a stand-alone cold resistor (R = 1 ) connected instead of a JJ.…”

Section: Noise Propertiesmentioning

confidence: 99%

“…Noise measurements on nano-SQUIDs based on our SNS JJs revealed 1/f noise in the flux noise spectra, which could be suppressed by applying a bias reversal scheme. This indicates that the 1/f noise is due to critical current and resistance fluctuations in our JJs [32,34]. To quantify the strength of those fluctuations in the single JJ discussed here, we follow the analysis described in Refs.…”

Section: Noise Propertiesmentioning

confidence: 99%

“…There have been several earlier realizations of nano-SQUIDs based on self-shunted SNS JJs with Hf-Ti barrier and linear sizes appreciably larger than 100 nm. Because of their low-noise performance and relatively compact design, nano-SQUIDs based on these junctions promise great potential as stand-alone devices [31,32] and as building blocks of complex circuits [33,34]. However, there is still a need for further improvements regarding size reduction of the SQUIDs and tuning of their electrical parameters, including I c , R n , and, therefore, V c .…”

Section: Introductionmentioning

confidence: 99%

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Transport and Noise Properties of sub-100-nm Planar Nb Josephson Junctions with Metallic Hf - Ti Barriers for nano-SQUID Applications

et al. 2020

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We analyze electric transport and noise properties at 4.2 K of self-shunted superconductor-normal metal-superconductor (SNS) sandwich-type Josephson junctions, comprising Nb as the superconductor and Hf-Ti as the normal conducting material, with lateral dimensions down to approximately 80 nm. The junctions are fabricated with an optimized multilayer Nb technology based on nanopatterning by electron-beam lithography and chemical-mechanical polishing. The dependence of transport properties on the junction geometry (lateral size and barrier thickness d Hf-Ti) is studied, yielding a characteristic voltage V c up to approximately 100 μV for the smallest d Hf-Ti = 17 nm. The observed small hysteresis in the current-voltage curves of devices with high V c and large size can be attributed to self-heating of the junctions and fitted with an extended version of the resistively shunted junction model. Measurements of voltage noise of single junctions are consistent with the model including self-heating effects. The potential of our technology for further miniaturization of nanoscale superconducting quantum interference devices and for the improvement of their performance is discussed.

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