Abstract Body

We report on thermal effects induced superconducting nanowire arrays fabrication based on nano laser direct writing (NLDW). The superconducting nanowire arrays are fabricated by growing of 20 nm-thick Nb films via sputtering deposition on high-resistivity silicon substrates. Nano patterning is performed by optical lithography and followed by nano laser direct writing. By harnessing the advantages such as cost-effectiveness, efficiency, and design flexibility of NLDW, large-scale superconducting nanowire arrays up to 190 μm × 190 μm fabrication process was demonstrated. Furthermore, the thermal effect induced the degradation of Nb films was analyzed with simulated temperature distribution, electron probe x-ray microanalysis, and electrical transport measurements respectively by shrinking the spacing of nanowires step by step. Compared with the traditional micro-nano fabrication techniques such as electron beam and ion beam processes, the NLDW technique could provide a reliable, cost-effective, and reproducible pathway for scaling up superconducting circuits as well as an avenue to conduct nanoscale thermal engineering on superconducting materials studies for basic science.

References

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Acknowledgment

This work was supported by the National Natural Science Foundation of China (Grant No. 12104112), and the Natural Science Foundation of Shandong Province (Grant No. ZR2021QA036).

Figure 1. Schematic of NLDW system components. (a) Schematic of the NLDW system: The red laser is used for focusing, while the blue laser (405 nm) is used for writing. (b) Laser etching of nanowire arrays with different spacing on Nb film.

Figure 2. Heat transfer simulation of laser acting on Nb film. (a) Schematic of NLDW on Nb film to fabricate a nanowire array. (b) YZ and XZ sections indicate laser path. (c) Temperature distribution at different times in the YZ-plane. (d) Variation of XZ-plane temperature distribution with spacing between nanowires. (e) Temperature distribution versus time in the YZ-plane. (f) Temperature distribution of nanowires with a spacing of 600 nm versus time in the XZ-plane.

Figure 3. Optical microscope and SEM images of nanowire arrays. (a) 190 μm × 190 μm nanowire array fabricated by NLDW system. (b-c) The SEM images of nanowire arrays.

Figure 4. Characterization of electrical transport properties of Nb nanowire arrays. (a) I-V characteristics of the microbridge without NLDW at different temperatures (from 4.0 K to 8.0 K). (b) Normalized resistance versus temperature for different spacing of nanowires. (c) I-V characteristics of nanowire arrays with different spacing. (d) The relationship between Jc and the spacing of nanowire arrays.

Keywords: Superconducting nanowire, laser direct writing, Thermal effect