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Microstructure and microwave surface resistance of YBaCuO thin films

1999; IEEE Council on Superconductivity; Volume: 9; Issue: 2 Linguagem: Inglês

10.1109/77.784898

1558-2515

G. Kästner, C. Schäfer, Stephan Senz, D. Hesse, Michael Lorenz, H. Hochmuth, M. Getta, Matthias Hein, Thomas Kaiser, G. Müller,

Magnetic properties of thin films

Epitaxial YBaCuO thin films on 73 mm diam. sapphire and 50 mm LaAlO/sub 3/ wafers prepared for microwave applications were characterized by optical and electron microscopy as well as by X-ray diffraction in order to guide optimizing the film properties. The surface resistance R/sub s/, measured at 8.5, 19 or 145 GHz, partially as a function of microwave field amplitude B/sub s/, was taken as the key parameter. Typical results scaled quadratically in frequency to 0.25-0.75 m/spl Omega/ at 10 GHz, 77 K, and low field levels. In case of sapphire substrates, a challenge for applications is microcracking of the films. However, cracks are less deleterious if "dispersed" by other heterogeneities such as a-oriented grains. Narrow microcracks should allow for tunnel currents and flux pinning. In case of LaAlO/sub 3/, films sensitive to high microwave power exhibited some in-plane rotational misorientation and a-oriented grains as well as inhomogeneous layering of these grains and of additional Cu-O planes within the film thickness, with possible influence on R/sub s/.