Fabrication and Characterization of Ultrathin MgB2 Films for Hot-Electron Bolometer Applications

Hot-electron bolometer mixers employing thin films of conventional superconducting materials have already been successfully fabricated in the past. Magnesium diboride (MgB₂) is a promising alternative to conventional superconductors, and we report the fabrication and study of ultrathin MgB₂ films of down to 10 nm deposited by hybrid physical-chemical vapor deposition technique. The MgB₂ films showed T_c of above 36 K, while residual resistivities of up to 26 μΩ · cm were achieved. Critical currents of more than 6 × 10⁶ A · cm^-2 at 20 K have been measured for the films with thicknesses ranging from 10 to 100 nm. Fishtail structures have been observed in the magnetic field dependence of the critical current density for the thinnest of these films, indicating the presence of defects, which act as vortex pinning centers. From the magnetic field dependence, an average distance between adjacent pinning centers of 35 nm has been obtained for the thinnest films.