Multilayered YBCO/LaA103/YBCO films for microwave applications

Multilayered YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} (YBCO)/LaAlO{sub 3}/YBCO films deposited on (100)-oriented LaAlO{sub 3} substrates have been studied for potential use in microwave circuits. The thickness of the LaAlO{sub 3} layer was either 100, 300 or 500 nm thick, and the YBCO films were 350 nm. Metallic normal state resistance was observed in the top YBCO layers, but the transition temperature was higher for films deposited on 100 nm LaAlO{sub 3} layers than for films on 300 nm thick LaAlO{sub 3} layers (88 vs. 83 K). Electrical impedance measurements across the dielectric indicate there was extensive shorting between the YBCO layers, and transmission electron microscopy (TEM) micrographs suggests that the shorting occurred along high-angle grain boundaries in the LaAlO{sub 3} film. The LaAlO{sub 3} films grew with columnar structures; at LaAlO{sub 3} thicknesses greater than approximately 150 nm the columns were no longer parallel, and a chevron-shaped structure emerged.