Josephson junctions fabricated by focused ion beam from ex situ grown MgB2 thin films

Artikel i vetenskaplig tidskrift, 2004

We prepared MgB2 thin films on SrTiO3 (100) and Al2O3 (1 (1) over bar 02) substrates by e-beam evaporation of MgB2 pellet. The films were deposited at room temperature and post-annealed at 900 degreesC in Mg vapour for 5-30 min. Superconducting transition temperatures were observed between 22 and 30 K. Structure and surface morphology of the films were investigated by X-ray diffraction (XRD) and atomic force microscopy (AFM). The films grown on Al2O3 substrates are c-axis oriented while a film grown on SrTiO3 substrate is aligned with the (10 1) direction normal to the substrate planes. The films have grain sizes of about 70 nm. The films were patterned into 4 and 8 mum wide microbridges. The microbridges were observed to carry large critical current densities of approximately 1 MA/cm(2) at 6.7 K. Focused ion beam (FIB) was used on the bridges in order to fabricate Josephson junctions. A cut 50 nm in width was made across the microbridges followed by an in situ platinum (Pt) deposition into the cut made. SNS-like weak-link junctions were formed in the process.