Preparing Ultrathin MgB₂ Thin Film by Ex Situ Annealing of Mg-B Precursor Film

Ultrathin MgB2 film is essential for the fabrication of MgB2 superconducting single photon detectors (SSPDs). In this paper, we prepared 20nm and 10nm MgB2 film using ex-situ annealing of Mg-B multilayer method. The precursor films were prepared by electron beam evaporation. A flowing Mg vapour and H2 was introduced in the annealing process to keep MgB2 thin film thermodynamically stable. The annealing temperature was between 680 and 740 and annealing time was 1-10min. 20nm MgB2 films on MgO(111) substrates had the critical temperature (Tc) of 32.2K. The films grew along c-axes direction. As the substrate changed to SiC(001) and Al2O3(001), Tc decreased to 30.3K and 10.2K respectively. For 10nm MgB2 film on SiC(001) substrate, Tc was 24.2K. The self-field critical current density for 10nm and 20nm film on SiC(001) substrate was 2.1×106A/cm2 and 2.3×106A/cm2, respectively. AFM image showed that the film had a flat surface with mean roughness of 0.899nm for 10nm MgB2 film.