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Journal of Physics D Applied Physics

Fabrication of micro-superconducting quantum interference devices based on nano laser direct writing

Wenqian Liu, Shuo Xiang, Yicong Huang, Wenzhi Zhang, Shangqing Li, Enhua Chen, Chaoyun Zhang, Xiaoliang Wang, Haohui Zhang, Songling Xiao, Tuo Zhang, Hao Zhang, Yu Liu, Jianxin Lin

Published Aug 13, 2025• 2 citations

Abstract

Abstract We propose the fabrication of micro-superconducting quantum interference devices via nano laser direct writing (NLDW). A 20 nm thick Nb film with a critical transition temperature of 9.2 K was deposited on a silicon substrate by sputtering, and nanopatterning was performed with NLDW. After optimizing parameters such as the laser pulse width and power, we investigated the electrical performance of SQUIDs by varying the laser power between 245 mW and 270 mW in 5 mW steps. Experimentally, the voltage–flux (V–Φ) characteristics of micro SQUIDs exhibited typical periodic modulation, confirming the Josephson effect and magnetic flux quantization effect based on the NLDW process. The noise spectral density measurements of SQUID fabricated with laser power of 265 mW achieved a white noise level of 3 μ Φ 0 /Hz 1 / 2 , demonstrating comparable flux noise sensitivity compared to electron beam and ion beam fabrication processes. Furthermore, the devices retained stable superconducting and electrical performance after 101 days, illustrating excellent long-term stability. To some extent, the NLDW shows the potential to perform micro-nanopatterning of superconducting devices efficiently and cost-effectively, as well as an avenue for conducting nanoscale thermal engineering on superconducting devices for basic science research.

DOI: 10.1088/1361-6463/adfae9

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Science and industry demand ever more sensitive measurements on ever smaller systems, as exemplified by spintronics, nanoelectromechanical system, and spin-based quantum information processing, where single electronic spin detection poses a grand challenge. Superconducting quantum interference devices (SQUIDs) have yet to be effectively applied to nanoscale measurements. Here, we show that a simple bilayer deposition route, combining photolithography with focused ion beam patterning, produces high performance nanoscale SQUIDs. We present results of noise measurements on these nanoSQUIDs which correspond to a magnetic flux sensitivity of around 0.2μΦ0∕Hz1∕2. This represents one of the lowest noise values achieved for a SQUID device operating above 1K.

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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.

Nano-Superconducting Quantum Interference Devices (nano-SQUIDs) are usually fabricated from a single layer of either Nb or Al. We describe here a simple method for fabricating suspended nano-bridges in Nb/Al thin-film bilayers. We use these suspended bridges, which act as Josephson weak links, to fabricate nano-SQUIDs which show critical current oscillations at temperatures up to 1.5 K and magnetic flux densities up to over 20 mT. These nano-SQUIDs exhibit flux modulation depths intermediate between all-Al and all-Nb devices, with some of the desirable characteristics of both. The suspended geometry is attractive for magnetic single nanoparticle measurements.