Preparation and Non-Destructive Characterization of YBa sub 2 Cu sub 3 O sub 7-- delta Films for Microwave Applications

• Published in: Journal of alloys and compounds 1992-11, Vol.195, p.559-562
• Main Authors: Lenkens, M, Aschermann, B, Hensen, S, Jeck, M, Orbach, S, Schlick, H, Chaloupka, H, Muller, G, Piel, H
• Format: Article
• Language: English
• ISSN: 0925-8388

High-quality YBa sub 2 Cu sub 3 O sub 7-- delta films with a thickness between 200-500 nm and a size of 1 cm exp 2 were deposited on YSZ, MgO and NdGaO sub 3 substrates. Shielding measurements show that critical temperatures T sub c between 89-93K and transition widths Delta T sub c between 0.7-0.2K can be obtained reproducibly on all of these substrates. A contactless inductive j sub c measurement technique, based on the detection of the third harmonic, has given critical current densities up to (5.1 plus/minus 0.5) MA/cm exp 2 at 77K. For the best films, values of the surface resistance R sub s at 87 GHz and 77K of (16 plus/minus 3) m Omega have been derived from measurements in a copper host cavity. Furthermore, these films show a significant reduction of the residual microwave losses at temperatures < 60K, leading to R sub s values < 3 m Omega at 4.2K. From such high-quality YBa sub 2 Cu sub 3 O sub 7-- delta films on MgO, standard patterning techniques were used to fabricate and optimize the design of microwave devices. As an example, a narrow nonlinear coplanar-line device is presented. "Fast" and "slow" nonlinear responses which limit the output power were observed.