  Precursor MgB2 thin films were prepared on sapphire substrates by magnetron
sputtering. Influence of ex-situ annealing process on superconducting MgB2 thin
films roughness 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
DTc 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 7.3x106 A/cm2 and no
significant loss of superconducting properties was detected. Resistance vs.
temperature and critical current vs. temperature characteristics were measured
on these structures using standard DC four probe measurements.
