This dissertation, "Fabrication and Characterization of Epitaxial YBa2Cu3Oy Thin Films on Double-buffered Silicon Substrates" by Ho-yi, Eric, Wong, 黃灝頤, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled FABRICATION AND CHARACTERIZATION OF EPITAXIAL YBa Cu O 2 3 y THIN FILMS ON DOUBLE-BUFFERED SILICON SUBSTRATES submitted by WONG HO YI ERIC for the degree of Master of Philosophy at The University of Hong Kong in August 2003 The discovery of perovskite copper oxide YBa Cu O (YBCO) has aroused a 2 3 y constantly increasing interest in this material due to the potential applications in microelectronics devices, such as microwave elements, multilayer junctions, etc. Suitable substrates with a low dielectric constant, good high frequency properties, large size and low cost are necessary. Silicon substrates are widely used and well developed in the semiconductor industry and microwave device applications. Therefore, successful fabrication of high T YBCO films on silicon is of interest for various applications of hybrid superconductor-semiconductor devices and interconnected circuits. In such applications, the epitaxial growth of YBCO on silicon is extremely important. This thesis presents a systematic investigation of the fabrication and characterization of epitaxial YBCO thin films on silicon substrates with a double buffer of Eu CuO (ECO)/YSZ(Yttria-Stabilized Zirconia). Silicon (001) substrates 2 4 were prepared using a chemical etch by dilute HF acid prior to thin film deposition. The YBCO thin films were grown via an entirely in situ process using an on-axis rf magnetron sputtering method with optimized deposition parameters including the deposition temperature, operating pressure and partial oxygen pressure. The crystallinity, surface morphology, electrical properties, and interface of the obtained YBCO/ECO/YSZ thin films were studied by x-ray diffraction, surface profiler, atomic force microscope, optical microscope, standard dc four-probe measurements and small angle x-ray reflection. The X-ray diffraction patterns showed that all the thin films were highly c-axis oriented. A full width of 0.69 at half maximum of the YBCO(005) peak was obtained. This was smaller than reported in previous studies of YBCO thin films on double buffered silicon or nickel substrates. The atomic force microscopy image showed that the ECO buffer surface was flat and smooth. The average roughness over a wide scanning region of 2000m was less than 25nm. The optical microscope images showed that the surface morphology of the grown YBCO thin films was significantly improved by the ECO buffer layer since ECO had a very stable 214-T' crystal structure and very small lattice mismatch with YBCO. The YBCO/ECO/YSZ multilayers were further characterized by small angle x-ray reflection. The surface roughness of the YBCO layers decreased when an ECO buffer was added. No intermediate layer was found at the YBCO/ECO and ECO/YSZ interfaces. The results suggest that ECO is chemically compatible with YBCO and YSZ. The superconductivity of YBCO films was significantly improved by the ECO/YSZ double buffer. This is indicated by the fact that YBCO thin films on silicon substrates with an ECO/YSZ double buffer showed a higher T than that grown on YSZ/Si without the ECO layer. The advantages of using ECO/YSZ double buffer layers in deposition of YBCO on silicon were clearly demonstrated. It would provide a good basis for the potential applications of YBCO on other semiconductors, metallic or me