The dependence of current–voltage characteristics upon thin film deposition conditions was investigated using MgB2/AlN/NbN SIS junctions. By increasing the substrate temperature in AlN insulator deposition, the current density decreased and the normal resistance increased. The results indicated that an additional insulator layer between the MgB2 and AlN formed, either before or during the AlN deposition. The thickness of the additional insulator layer was increased with an increase in the AlN deposition temperature. From the dependence of current density on the thickness of AlN in low temperature depositions, the thickness of the additional insulator layer was estimated to be 1 to 1.5nm when the AlN insulator was deposited from 0.14 to 0.7nm. Moreover, with the current density of MgB2/AlN/MgB2 SIS junctions, further insulator layer formation was confirmed.

Insulator Layer Formation in MgB2 SIS Junctions. H.Shimakage, K.Tsujimoto, Z.Wang, M.Tonouchi: Physica C, 2005, 426-431[2], 1469-73