Nano-bridges based on the superconducting MgB2 thin films

Precursor MgB thin films were prepared on sapphire substrates by magnetron sputtering. Influence of the ex situ annealing process on the roughness of the superconducting MgB2 thin films is discussed. Optimized annealing process of MgB precursor thin films in vacuum results in smooth superconducting MgB2 thin films with roughness below 10 nm, critical temperature Tcon = 31 K and transition width ΔTc less than 1 K. Nano-bridges based on the superconducting MgB2 thin films using optical and focused ion beam lithography were prepared. Critical current density jc (4.2 K) measured on 50 nm wide strip was 7.3 × 106 A/cm2 and no significant loss of superconducting properties was detected.