We have examined the thickness dependence of the growth morphology and surface resistance R-s of laser ablated YBa2Cu3O7-x films with transition temperatures over 89 K and critical current densities greater than 10(6) A/cm(2) at 76 K. The thickness was varied from 50 to 1600 nm while all other deposition conditions were maintained constant. The microstructure has been characterized by scanning electron microscopy and scanning tunneling microscopy (STM). The films exhibit two-dimensional island growth at all thicknesses and the island density continuously decreased with film thickness as a power law with an exponent of -0.5. The surface resistance was measured at 76 K with a dielectric rod resonator. for films less than 300 nm thick, the fields penetrated the superconducting films, causing a rapid increase in the apparent R-s with decreasing film thickness. Films thicker than 800 nm showed microcracks and the R-s increased sharply, and no resonance was observed above 1000 nm.
