Microwave losses and structural properties of large-area YBa/sub 2/Cu/sub 3/O/sub 7/ films on r-cut sapphire buffered with [001]/(111) oriented CeO/sub 2/

Abstract

YBa/sub 2/Cu/sub 3/O/sub 7-x/ thin films were prepared on 2 inch in diameter (11_02) sapphire substrates buffered with CeO/sub 2/ layer of mixed [001]/(111) orientation. The thickness of the YBa/sub 2/Cu/sub 3/O/sub 7-x/ films was typically /spl sim/250 nm. The YBa/sub 2/Cu/sub 3/O/sub 7-x/ thin films exhibited smooth surfaces (peak-to-valley roughness of less than 20 nm) free of cracks and outgrowths. The critical temperatures of these films were 87-89 K, the critical current densities (2-3).10/sup 6/ A/cm/sup 2/ at 77 K and zero magnetic field. The low field microwave surface resistance (R/sub S/) of the YBa/sub 2/Cu/sub 3/O/sub 7-x/ films was measured at 18.7 GHz. Values of /spl sim/1.4 m/spl Omega/ were obtained at 77 K and <70 /spl mu//spl Omega/ below 20 K. Such low R/sub S/ values are comparable to the lowest reported values for thicker YBa/sub 2/Cu/sub 3/O/sub 7-x/ films grown epitaxially on structurally well-matched substrates, e.g. LaAlO/sub 3/. The elevation of the microwave power produced a weak increase of R/sub S/. No drastic changes in R/sub S/ occur up to the maximum magnetic field of /spl sim/35 Oe at 79 K and /spl sim/63 Oe at 50 K. The properties of the YBa/sub 2/Cu/sub 3/O/sub 7-x/ films do not degrade with time.