Postprocessing of YBCO He-FIB Josephson junction arrays

High-temperature superconductors like yttrium barium copper oxide (YBCO) are good candidates for a voltage standard working at liquid nitrogen temperatures. Their ability to be operated at THz frequencies is advantageous, as this significantly reduces the number of Josephson junctions (JJs) needed for an array with comparable voltage output. To achieve this, JJs with low parameter variation (Ic and Rn) are necessary [1]. Such JJs can be fabricated using a direct-write helium-focused ion beam (He-FIB) process [2]. Another requirement for synchronized JJs within an array is sufficient hf excitation with uniform power across all JJs. Recent studies have shown progress in the field of YBCO He-FIB JJ arrays, but even with this method, synchronizing multiple JJs within an array is not trivial [3]. Therefore, in this work we investigate postprocessing steps to modify the YBCO He-FIB JJ arrays to optimize the synchronization of the individual JJs. These steps include shunting of the JJs and modification of the YBCO microbridge width using Ga-FIB [4] and He-FIB. The dc current-voltage characteristics of the JJ arrays are analyzed. Furthermore, the appearance and synchronization of Shapiro steps under high-frequency excitation are characterized.



[1] R. Behr, et.al., Meas. Sci. Technol., vol. 23, p. 124002, 2012.

[2] B. Müller, et.al., Phys. Rev. Appl., vol. 11, p. 044082, 2019.

[3] M. Pröpper, et.al. IEEE Trans. Appl. Supercond., vol. 34, 2024.

[4] D. Hanisch, et.al., IEEE Trans. Appl. Supercond., vol. 33, 2023.