Abstract
The discovery of high-temperature superconductivity with Tc> 90 K in the Y–Ba–Cu–O system has revived interest in thin-film superconducting devices. By now the preparation of bulk superconducting oxide samples, using conventional ceramic techniques (grinding, firing, and pelletizing), has been well established and reproduced by many groups. On the other hand, preparing thin films has turned out to be relatively more difficult, although a number of groups are beginning to report success. The approaches have primarily been electron-beam evaporation and sputter deposition. Multiple sources1,2 as well as single sources3 have been utilized, and there are problems with both approaches. With multiple-source evaporation, generally for the three metallic constituents, even if the flux of each element is held constant at the right valve the angular distribution of the elements is not a constant. This results in a variation of the stochiometry as a function of the substrate position. If a single-source deposition is used, one faces problems such as differential evaporation or sputtering, as a result of which the source material will have to be of a different composition from that of the film, and furthermore this composition may be strongly dependent on the processing conditions. Of course, once the parameters are determined, preparation of the films could become routine.
© 1988 Optical Society of America
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