SPECIFIC CAPACITANCE OF NB/ALOX/NB JOSEPHSON-JUNCTIONS WITH CRITICAL-CURRENT DENSITIES IN THE RANGE OF 0.1-18 KA/CM(2)

The specific capacitance Cs of Nb/AlOx/Nb Josephson tunnel junction has been measured by means of the superconducting quantum interference device (SQUID) resonance technique. We have investigated the junctions with critical current densities Jc in the range of 0.1-18 kA/cm2 and found that 1/Cs linearly depends on a logarithm of Jc. This suggests that the barrier thickness is moderately uniform in the junction area and increases continuously during growth. The results also show that increasing Jc reduces time constants of the junction.© 1995 American Institute of Physics.