Investigating the Intrinsic Noise Limit of Dayem Bridge NanoSQUIDs

Abstract

NanoSQUIDs made from Nb thin films have been produced with nanometre loop sizes down to 200 nm, using weak-link junctions with dimensions less than 60 nm. These composite (W/Nb) single layer thin film devices, patterned by FIB milling, show extremely good low-noise performance ∼170 nΦ 0 at temperatures between 5 and 8.5 K and can operate in rather high magnetic fields (at least up to 1 T). The devices produced so far have a limited operating temperature range, typically only 1-2 K. We have the goal of achieving operation at 4.2 K, to be compatible with the best SQUID series array (SSA) preamplifier available. Using the SSA to readout the nanoSQUIDs provides us with a means of investigating the intrinsic noise of the former. In this paper we report improved white noise levels of these nanoSQUIDs, enabling potential detection of a single electronic spin flip in a 1-Hz bandwidth. At low frequencies the noise performance is already limited by SSA preamplifier noise.Index Terms-NanoSQUIDs, noise measurements, T c suppression. 1051-8223

Nano Superconducting Quantum Interference device: A powerful tool for nanoscale investigations

“…The heater consists in a normal metal thin film separated from the superconductor by an insulating layer. Finally, it is worth to mention that several experimental studies about the noise properties of nanoSQUIDs based on nanobridges have been carried out [153,[158][159][160]184]. These investigations included measurements of both white and low frequency magnetic noise as a function of the applied magnetic field, the temperature and the nanoSQUID design.…”

A Self-Flux-Biased NanoSQUID with Four NbN-TiN-NbN Nanobridge Josephson Junctions

“…Two methods are usually used to pattern nanostructures of TiN, NbN, and Nb: electron beam lithography (EBL) in combination with reactive ion etching (RIE) [7,24,25] and focused ion beam (FIB) milling [25,29]. The high selectivity and isotropy of RIE allow the realization of variable thickness nJJs down to 10 nm resolution [7], but these are sensitive to sample temperature and surface contamination, to the configuration of nearby current leads, and to the granular structure of the etched film, as well as previous processes in the RIE machine: the etch rate of a second sample can then be lower than the etch rate of a first sample.…”

Low-Noise Diamond-Based D.C. Nano-SQUIDs

“…Nanoscale superconducting quantum interference devices (nano-SQUIDs) are considered a promising tool for achieving the goal of single-electron spin detection on account of their performance as a flux-to-voltage transformer and low sensitivity to external flux noise . Over the last 2 decades, a wide range of nano-SQUIDs have been demonstrated using a variety of materials, − device geometries, and fabrication techniques − and applied to magnetometry of magnetic nanoparticles. − Many of these have exploited weak links formed using Dayem bridges, which are desirable due to their low capacitance, high current density, and insensitivity to in-plane magnetic fields, suitable for high-magnetic-field applications. − However, the operational magnetic fields reported so far for nano-SQUIDs are below 1 T, and focus has been on cases where the high magnetic field is applied only parallel to the plane of the SQUID loop. , Superconducting diamond, achieved through boron doping with a density exceeding 4.5 × 10 20 cm –3 , is considered an excellent candidate for D.C. SQUID technology because of its high critical field and critical current density. A micrometer-sized D.C. SQUID has been demonstrated using thin-film, boron-doped nanocrystalline diamond (NCD) with a Dayem bridge architecture and a loop size of 2.5 μm, reporting operation in a perpendicular applied magnetic field of up to 4 T, and a flux noise sensitivity of in an applied field of 0.3 mT.…”