Microstructure of YBCO and YBCO/SrTiO 3 /YBCO* PLD Thin Films on Sapphire for Microwave Applications
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M. LORENZ', H. HOCHMUTH', D. NATUSCH', T. THARIGEN', V. L. SVETCHNIKOV 2, H. W. ZANDBERGEN 2, C. SCHAFER ', G. KASTNER 3, D. HESSE
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1 Universitt Leipzig, Fakultlit ffir Physik und Geowissenschaften, D-04103 Leipzig, Germany, [email protected] 2 National Center for High Resolution Electron Microscopy, 2628 AL Delft, The Netherlands 3 Max-Planck-Institut fUr Mikrostrukturphysik, D-06120 Halle/Saale, Germany
ABSTRACT A large-area pulsed laser deposition process for high-quality YBa 2Cu 3 OT-8 (YBCO) thin films on both sides of R-plane sapphire substrates with CeO2 buffer layer is used routinely to optimize planar microwave filters for satellite and mobile communication systems. With the experience of more than 700 double-sided 3-inch diam. YBCO:Ag films a high degree of reproducibility of jc values above 3.5 MA/cm 2 and of state of the art R, values is reached. TEM cross sections of the large-area and double-sided PLD-YBCO:Ag thin films on R-plane sapphire with CeO 2 buffer layers show typical defects like stress modulation, stacking faults, a-axis oriented grains, precipitates and interdiffusion layers. YBCO films on SrTiO 3 / YBCO* / CeO 2 film systems on R-plane sapphire wafers have more growth defects compared to bare CeO 2 buffers on sapphire but show as microwave resonators encouraging electrical tunability. INTRODUCTION High-T, superconducting (HTS) YBa2 Cu 3 07-8 (YBCO) and dielectric or ferroelectric thin films on low dielectric loss substrates are suitable candidates for applications as passive microwave devices in future communication systems. There is a huge number of activities in many countries to develop microwave devices using HTS thin films, because in this field real market applications of HTS subsystems seem to be possible in the nearest future. Very recently, the physical and technological aspects of HTS thin films at microwave frequencies were summarized in the excellent book by Hein [1]. To develop electrically tunable microwave filters and devices, combinations of HTS and dielectric or ferroelectric thin films are necessary. A highly reproducible PLD process for large-area 3-inch diameter and double-sided YBCO films on sapphire substrates for microwave applications is developed and continuously improved by Lorenz et al [2 - 5]. The electrical and microwave performance of this PLD-YBCO films is comparable to high-quality films deposited by other techniques as e. g. thermal coevaporation developed by Kinder et al [6]. Reproducible deposition processes are base technologies for the successful application of HTS microwave devices in commercial products. Several processes are now ready to fulfill the demands of the device developing community. This paper describes the state of the art of a highly reproducible large-area PLD technique for HTS-YBCO and dielectric SrTiO 3 and ferroelectric Sr(Ba)TiO 3 thin films on buffered sapphire wafers by comparing TEM cross sections and maps of the critical current density jc.
163 Mat. Res. Soc. Symp. Proc. Vol. 603 © 2000 Materials Research Societ
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