Growth and characterization of Nb films and Nb/Al-AlOx/Nb trilayers for Josephson junctions

We study the influences of substrates on structure and microstructure characteristics of Nb films deposited onto Si (100), SiO
₂
/Si (100), MgO (100) and C-plane sapphire (Al
₂
O
₃
) by use of magnetron sputtering. Atomic force microscopy shows that elongated columnar shaped grains dominate on these substrates. X-ray diffraction patterns indicate (110)-oriented growth on Si, SiO
₂
/Si and sapphire substrates, while textured growth occurs on MgO substrate. An amorphous oxide layer about 2 nm on the surface of Nb films is confirmed by X-ray reflectometry and transmission electron microscopy analysis. Subsequently, Nb/Al-AlO
_x
/Nb trilayers on Si substrates are fabricated and the interfacial microstructures are also investigated.