Laser Ablation Deposited YBa 2 Cu 3 O x Thin Films on YSZ/Si(100)
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LASER ABLATION DEPOSITED YBa 2Cu 3O, THIN FILMS ON YSZ/Si(100) F. SANCHEZ, M. VARELA, X. QUERALT, R. AGUIAR AND J.L. MORENZA Universitat de Barcelona, Departament de Fisica Aplicada i Electr6nica, Avda. Diagonal 647,
E-08028 Barcelona, Spain. ABSTRACT Superconducting YBa 2Cu 3O (YBCO) thin films have been deposited on Si(100) substrates with yttria-stabilized zirconia (YSZ) buffer layers by laser ablation. Buffers have been obtained by laser ablation as well. The films have been characterized by scanning electron microscopy, x-ray diffractometry, secondary ion mass spectrometry, and four-contact electrical resistivity measurements. Secondary ion mass spectrometry results indicate very low interdiffusion between Si, YSZ and YBCO. The best YBCO films are textured with c axis perpendicular to the substrate and their resistance shows a normal state metallic behavior with zero resistance at temperatures higher than 80 K. The properties of YBCO films have been related with the substrate temperature and oxygen partial pressure during deposition. INTRODUCTION High quality superconducting YBa 2Cu 3O (YBCO) films have been grown on several single-crystal substrates such as SrTiO 3(100)' and LaAIO 3(100) 2. The deposition on silicon is more important for the applications, but is not as successful as on SrTiO 3 due to the high chemical interaction between silicon and YBCO. Effectively, the direct growth of YBCO on silicon results in films with bad superconducting properties. Best results are obtained with a buffer layer deposited between both materials. Some materials have been used successfully as 34 56 78 9 buffer layer, for example SrTiO %3 , MgQ ' , CeO 2 and yttria-stabilized zirconia (YSZ) '-. YSZ has been the most used material as buffer layer because it has a very low chemical reactivity with silicon and YBCO, and a lattice constant that depends on the yttria content enables to minimize the mismatch with silicon and YBCO. Although both mismatches exceeds 5%, these considerable values do not prevent the epitaxial growth of YSZ on Si(100) 2"-3 as well as that of YBCO on YSZ' 4" 5 . In this work, we study the properties of YBCO films deposited by laser ablation on Si(100) coated with YSZ buffer layers. The YSZ buffer layers have been deposited by laser ablation too, because it is interesting to grow the YSZ barrier and the YBCO film in a single chamber process. It is known that YBCO films with good superconducting properties can only be obtained if the substrate temperature and the oxygen partial pressure during the deposition have been optimized within narrow intervals'"'l". We have deposited YBCO films with different conditions of substrate temperature and oxygen partial pressure in order to study the influence of these parameters on the oxygen content and crystalline properties of the films. Moreover, we have related the characteristics of resistance versus temperature curves with the texture quality and the oxygen content of the films. EXPERIMENTAL The YBCO films were deposited on Si(100) substrates with YSZ buffer l
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