Fabrication of Micro-Superconducting Quantum Interference devices based on Nano Laser Direct Writing

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 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 μΦ 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.