Structural and electrical properties of YBa₂Cu₃O₇ [1 0 0]-tilt grain boundary Josephson junctions with large I_cR_n-products on SrTiO₃ bicrystals

The microstructure of 2 × 12° [1 0 0]-tilt grain boundary Josephson junctions was investigated by atomic force and cross-sectional transmission electron microscopy. The junctions were prepared by depositing about 100 nm thick epitaxial YBa₂Cu₃O₇ films on the vicinal bicrystal substrates of SrTiO₃ with high pressure oxygen sputtering and showed a 2 × 12° tilt of the YBa₂Cu₃O₇ c-axis towards the grain boundary. The film grain boundary was very straight and followed the bicrystal substrate boundary. It showed a low degree of meandering in comparison to the behaviour of conventional [0 0 1]-tilt grain boundaries. Due to step bunching the film surface exhibited a profile of 12° inclined terraces with a valley depth of 5-20 nm and at the grain boundary a straight V-shaped surface suppression of about 40 nm depth was observed. The fact that the I_cR_n-products of such Josephson junctions showed high values of up to 1.2 mV at 77 K and up to 8 mV at 4.2 K as well as a smaller scattering of the values for I_c and R_n in comparison to [0 0 1]-tilt grain boundaries is attributed to the observed microstructure. The junctions showed clear Shapiro steps as a response to 94 GHz microwave radiation.