Dependence of Electrical Characteristics of NbN/TiN/NbN Josephson Junctions on Barrier Thickness and Temperature

The dependence of the product of critical current I c and normal-state resistance R n for NbN/TiN/NbN Josephson junctions on TiN barrier thickness and temperature has been measured. From a comparison of measured results and theoretically calculated I c R n values, the coherence lengths in TiN films at 4.2 K and 10 K have been estimated to be 6.0 nm and 3.9 nm, respectively. At 4.2 K, the I c R n product in the range of 20 to 400 µV is obtained for junctions with TiN film thickness ranging from 30 nm to 48 nm. At 10 K, the I c R n product up to 50 µV can be obtained when the TiN film thickness is decreased to 25 nm.