Kromann, Rasmus

This report contains the results of an experimental study of YBa2Cu3O7 thinfilms. The study involved deposition methods, structural characterization, andapplication of the thin films for SQUID devices. Chapter 1 describes the principles of thin film deposition by RF sputtering, followed by an account of the optimization procedure for the YBCO thin films. The sputter system was used in two different configurations. The first of these, a parallel plate geometry with an unheated, rotating substrate table, was abandoned relatively early because of the poor quality of post annealed films as compared to films made by an in-situ technique. The second configuration of the sputter system involved an inverted cylindrical magnetron gun in combination with a heated substrate table. By varying the deposition parameters (such as the deposition temperature and the gas composition) systematically, it was possible to obtain films that were fully superconducting at 77 K and with an X-ray spectrum consisting of essentially only (00/) reflections from the 1:2:3 phase of YBCO. The composition of the films were analyzed by EDX and the results showed that the films contained excess Ba. The relatively low Tc is ascribed to this fact. In the last part of Chapter 1 thin film deposition by laser ablation is described. This technique was used for the SQUID devices described in Chapter 3. Chapter 2 presents the results of an X-ray diffraction study of the structure of laser ablated YBCO thin films. Four films were examined, two of which were deposited on MgO, while the other two were deposited on SrTiO3. The two films on MgO differ by 75 % in the critical current density and this is ascribed to the fact that about 5 % of the grains in the low Jc film grow 45° miscriented with respect to the dominant orientation in the a-b plane. The low Jc film also has a higher density of small-angle grain boundaries as evidenced by transmission electron microscopy. The two films on SrTiO3 differ by 70 % in Jc and this is ascribed to the presence of 8.3 % a-axis oriented material in the low Jc film as compared to only 0.6 % in the high Jc film. In general, the critical current density is higher in the films on SrTiO3 than in the films on MgO and this is attributed to the closer lattice match between SrTiO3 and YBCO

Online Research Database In Technology

Deposition, Qiaracterization, and Electronic Applications of YBa2Cu307 Thin Films

http://orbit.dtu.dk/ws/files/170890534/RISOR642.pdf

Deposition, Qiaracterization, and Electronic Applications of YBa2Cu307 Thin Films

Abstract

Similar works

Full text

Available Versions

Online Research Database In Technology