Microstructural issues in c-parallel YBa2Cu3O7-δ thin films

Abstract

Considerable effort has been directed at understanding the microstructures present in YBa2Cu3O7-δ films with the c-axis perpendicular to the plane of the substrate. This work has largely been driven by the high critical currents achieved in this particular film orientation. Although the critical currents are in general lower, the demonstration of high crystal quality, extremely smooth, dense films with their c-axis parallel to the plane of the substrate has opened the possibility of exploiting the highly anisotropic nature of YBa2Cu3O7-δ. To fully utilize such films, a thorough investigation of microstructural issues is as necessary for this film orientation as for the c-perpendicular case. We have used transmission electron microscopy and scanning force microscopy to examine c-parallel films grown on SrTiO3 and LaAlO3 substrates by single-target, off-axis magnetron sputtering. Films were deposited at block temperatures ranging from 600°C to 640°C, in atmospheres ranging from 30 millitorr oxygen and 40 millitorr argon to 60 millitorr oxygen and 90 millitorr argon. In an effort to improve superconducting properties while maintaining as smooth a surface as possible, films were also grown by a template method in which an initial nucleation layer was deposited at 625°C and the remainder of the film deposited at 700°C.