Microwave power handling in engineered YBa2Cu3O7-δ grain boundaries

Microwave-frequency (rf) power-dependence measurements performed on thin-film YBa2Cu3O7-delta grain boundaries engineered on sapphire bicrystal substrates with misorientation angles of theta=2 degrees, 5 degrees, 10 degrees, and 24 degrees are presented. The data are compared to measurements on films grown on single-crystal substrates. A stripline-resonator measurement technique is employed. The rf results are compared to dc measurements performed on a four-point test structure on the same substrate as the resonator. The measurements demonstrate that low-angle grain boundaries (theta less than or equal to 10 degrees) have little effect on the rf power handling, while the high-angle grain boundaries (theta=24 degrees) cause large nonlinear losses due to Josephson vortices created by rf currents. (C) 1998 American Institute of Physics. [S0003-6951(98)04541-0].