Microwave properties and strain-induced lattice defects of c-axis-oriented YBa₂Cu₃O_7-δ thin films on silicon

The microwave properties and the crystal structure of YBa₂CU₃O_7-δ thin films are examined as a function of film thickness. Already below the critical thickness for the formation of macroscopic fractures, we observe an increase of the residual surface resistance with thickness. Cross-sectional transmission electron microscopy reveals that this behavior is caused by structural changes of antiphase boundaries leading to normal-conducting regions between superconducting grains. The surface resistance is calculated within the weak-link picture.