Josephson junctions and superconducting quantum interference devices made by local oxidation of niobium ultrathin films

Abstract

We present a method for fabricating Josephson junctions and superconducting quantum interference devices (SQUIDs) which is based on the local anodization of niobium strip lines 3 to 6.5 nm-thick under the voltage-biased tip of an Atomic Force Microscope. Microbridge junctions and SQUID loops are obtained either by partial or total oxidation of the niobium layer. Two types of weak link geometries are fabricated : lateral constriction (Dayem bridges) and variable thickness bridges. SQUIDs based on both geometries show a modulation of the maximum Josephson current with a magnetic flux periodic with respect to the superconducting flux quantum h/2e. They persist up to 4K. The modulation shape and depth for SQUIDs based on variable thickness bridges indicate that the weak link size becomes comparable to the superconducting film coherence length ? which is of the order of 10nm.

Classical and Quantum Magnetization Reversal Studied in Nanometer‐Sized Particles and Clusters

“…One might come close to this limit by using shunted SQUIDs [51]. Another possibility could be a reduction of the section of the microbridges [46]. Finally, the micro-SQUID technique could be improved by using superconducting materials with higher critical temperatures allowing measurements at higher temperatures.…”

Niobium and niobium nitride SQUIDs based on anodized nanobridges made with an atomic force microscope

“…All tested SQUIDs show at low temperature hysteretic I-V characteristics [19], see Fig.3. As the current is ramped from zero, the SQUID transits to a finite voltage branch at a switching current I c , which is the main characteristics of the device.…”

“…A pre-patterning using conventional UV photolithography and reactive-ion-etching has been performed. Details of the film fabrications and preliminary results are described elsewhere [19].…”

Nanoscale multifunctional sensor formed by a Ni nanotube and a scanning Nb nanoSQUID

“…Both S and φ μ can be optimized by scaling the SQUID down to nanometer dimensions. [19][20][21][22] Various fabrication techniques, e.g., electron-beam lithography, 23,24 focused ion beam milling, 22,25,26 atomic force microscopy anodization, 27,28 selfaligned shadow evaporation, 29 or a combination of electronbeam lithography with the use of carbon nanotube junctions, 30 have been used to realize nanoSQUIDs.…”