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arXiv · 2004.10064

Towards ultra-sensitive SQUIDs based on sub-micrometer-sized Josephson Junctions

Jan-Hendrik Storm·Oliver Kieler·Rainer Körber
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Abstract

We recently demonstrated a 1$^{\textrm{st}}$-order axial gradiometer SQUID system, which is operated in a liquid He dewar with negligible noise contribution. The achieved close to SQUID-limited measured coupled energy sensitivity $\varepsilon_{c}$ of $\sim 30\,h$ corresponds to a white field noise below 180~aT~Hz${^{-1/2}}$. In order to further improve the SQUID noise performance, the junction capacitance was reduced by decreasing its lateral size from $2.5~\mu$m to below $1~\mu$m. This was realized by extending the fabrication process for submicrometer-sized Josephson Junctions based on the HfTi self-shunted junction technology to an SIS process with AlO$_{\textrm{x}}$ as the insulating layer. We achieved energy sensitivities of 4.7$\,h$ and 20$\,h$ at 4.2~K for uncoupled and coupled SQUIDs, respectively. We also investigated the temperature dependence of the noise of the uncoupled SQUIDs and reached an energy sensitivity of 0.65$\,h$ in the white noise regime at 400~mK.

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Jan-Hendrik Storm, Oliver Kieler, Rainer Körber. 2020-04-21. Towards ultra-sensitive SQUIDs based on sub-micrometer-sized Josephson Junctions. https://doi.org/10.1109/tasc.2020.2989630

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