YBa2Cu3O7−δ superconducting quantum interference devices with metallic to insulating barriers written with a focused helium ion beam

Abstract

In this work, we demonstrate the ability to fabricate superconducting quantum interference devices (SQUIDs) by directly writing Josephson junctions into the plane of YBa2Cu3O7−δ thin films with a focused helium ion beam. This technique allows for the control of the Josephson barrier transport properties through the single parameter, ion dose. SQUIDs written with a dose of 4 × 1016 ions/cm2 had metallic barrier junctions that exhibited nearly ideal electrical transport characteristics at 50 K and a flux noise of 20 μΦ0/Hz at 10 Hz. At higher irradiation doses, the SQUIDs had insulating barrier Josephson junctions with a quasi particle energy gap edge at 20 meV.

Direct-Write Ion Beam Irradiated Josephson Junctions

“…At doses near 4 × 10 16 ions/cm 2 ρ N (T ) is independent of temperature and constant. Although there has between some individual reports of HTS junctions with insulating barriers [17] only the HI-JJ process has been able to demonstrate a continuous transition from SNS to SIS junctions [14]. Additionally, the ρ N (T ) of the junction barriers from FHIB irradiation agrees very well with ρ(T ) obtained from bulk film and broad beam irradiation [18].…”

Josephson Junctions and SQUIDs Created by Focused Helium-Ion-Beam Irradiation ofYBa2Cu3O7

“…This approach has been successfully used by Cybart and co-workers to fabricate JJs by focused Helium ion beam (He-FIB) irradiation of YBCO thin films, and they demonstrated that the barriers in such He-FIB JJs can be changed continuously from conducting to insulating by varying the irradiation dose 28 . Moreover, the same group demonstrated already the integration of He-FIB JJs into SQUID devices 29 , and the feasibility to use high-dose irradiation for nanoscale patterning (without removing material) in YBCO devices 30,31 . For a short review on this approach, also including irradiation with a focused Ne ion beam, see Ref.…”

Ultradense Tailored Vortex Pinning Arrays in Superconducting YBa2Cu3O7−δThin Films Created by Focused He Ion Beam Irradiation for Fluxonics Applications

“…As a first application in YBCO, the fabrication of Josephson junctions and superconducting quantum interference devices has been demonstrated via forming thin barriers of insulating material with the focused ion beam across pre-patterned microbridges. [27][28][29][30] However, for the fabrication of vortex pinning defects, the HIM in its original operation mode is less suitable. On the one hand, it is known that the diameter of defects suitable for vortex pinning must not be smaller than the superconducting coherence length, which is ξ ab (0) 1.2 nm in YBCO.…”