MICROSTRUCTURE AND MICROWAVE PROPERTIES OF YBCO THIN-FILMS GROWN ON MGO AND SRTIO3 BY CVD

The microstructure and microwave properties of YBa2Cu3O7-delta thin films grown on SrTiO3 (100) and MgO (100) substrates by chemical vapor deposition have been studied. Both 100 GHz cavity measurement of surface resistance and ground plane substitution in a 5 GHz microstrip resonator show that films on SrTiO3 have better microwave properties than those on MgO. Although there are some a-axis grains and secondary phases on the surface, a large fraction of each film on SrTiO3 is epitaxial with its c axis normal to the substrate. The 100 GHz surface resistance of these films is less than copper for temperature less-than-or-equal-to 82 K, and approaches the detection limit at 10-20 K. For the films on MgO, c-axis grains of different in-plane rotation are found together with some a-axis needle-like grains. The grain boundaries are detrimental to the microwave properties, and the resulting surface resistance at 100 GHz and 10-20 K is about 20 m-OMEGA higher than that of films on SrTiO3.