THE CAPACITANCE OF BICRYSTAL JOSEPHSON-JUNCTIONS DEPOSITED ON SRTIO3 SUBSTRATES

We have investigated the capacitance of grain boundary Josephson junct ions deposited on symmetric 24 degrees misoriented SrTiO3 bicrystal su bstrates using hysteresis and Fiske resonances in their current voltag e characteristics, Our measurements show that the total junction capac itance is proportional to the junction area. The capacitance per unit area is (140 +/- 30)fF mu m(-2) and this implies that the main effect of the large relative permittivity of the substrate is to scale-up the grain boundary capacitance by a factor of around 10, We also find tha t in the planar geometry of bicrystal grain boundary junctions the vel ocity of light in the junction depends upon film thickness.