Long baseline LTS SQUID gradiometers with sub-μm sized Josephson junctions

Abstract

In this paper, we present new integrated on-chip planar-type superconducting quantum interference device (SQUID) first order gradiometers, which are manufactured by a new mix and match fabrication technology combining sub-μm sized Josephson junctions (JJs) with cm-scale pickup loops. The fabrication technology is described and the design is schematically shown. These sensors have high voltage swing and low flux noise and provide thus the best so far reported gradient resolution of aboutHz . These gradiometers were developed and implemented in instruments for applications in mineral exploration. They allow a better system dynamic range (ratio of maximal to minimal detectable signals) and a more effective use of the chip area. The gradiometer performance in terms of gradient resolution is compared against state of the art planar-type SQUID based gradiometers. Two models predicting a gradient noise limit as a function of the chip area and baseline of the gradiometer are discussed. The small geometric dimensions of the gradiometers are very important for future miniaturized instruments in mineral exploration. The comparison of our results with those models highlights the importance of a smaller JJs size for the reduction of the intrinsic gradiometer noise and geometrical dimensions.

SQUIDs for magnetic and electromagnetic methods in mineral exploration

“…and also the SNR (Stolz et al 2020). In future, the readout principle introduced for the vector magnetometer instrument which uses the periodic characteristics of the SQUID will overcome these limitations for system noise and SNR.…”

Dual on-chip SQUID measurement protocol for flux detection in large magnetic fields

“…Previous measurements involving a single DC-SQUID have been performed with Gd spin systems [15]. Measurements involving multiple DC-SQUIDs in a gradiometer setup have been performed, but these methods are usually done with the SQUID isolated from the magnetic field in a shielded enclosure and coupled to the sample via a flux transformer [18], [19], [20]. Direct coupling to spins placed in the planar magnetic field allows for a much more sensitive detection.…”

Consequences of Brian Josephson’s Theoretical Discovery

“…However, the highest albeit indirect economic impact thus far has the use of SQUID-magnetometry-based equipment methods for geophysical exploration of minerals [7,8]. In the 1st decade of this century, portable ground-based and airborne geophysical instrumentation attained performance clearly superior to conventional equivalents and became generally accepted in mineral exploration and mining.…”

“…To give just one example of exploration successes: thanks to the use of low-T c SQUID instrumentation for large depths, Anglo American discovered in 2009 the main Sakatti Ore Body in Finland-the largest ever found resource in Europe with significant grade of ore at large depth (principal base metals copper, nickel and cobalt, lesser amounts of platinum, palladium, gold, and silver). 8 In most practical applications, the main obstacle to a broad use of SCE is operation at low and moderate cryogenic temperatures, and the related capital and maintenance cost. While many such applications were investigated and their significant technical or other benefits demonstrated, the tradeoffs have not been sufficiently attractive to warrant a broad implementation.…”

“…Low-Tc equipment developed and tested by SIMIT (Shanghai Institute of Microsystem and Information Technology). Private information by Dr. Xiaoming Xie, SIMIT 8. Information provided by R. Stolz, IPHT-Jena, based on information by exploration and mining companies.…”