YBA2CU3O7-DELTA A-AXIS FILMS AND PLANAR JUNCTIONS

Among the concepts for Josephson junctions with artificial barriers, p lanar junctions are most favorable, because they can be deposited in s itu. In order to prepare planar junctions, multi-layers were sputtered , using YBa2Cu3O7-delta as superconductor and PrBa2Cu3O7-delta as barr ier material. The sandwiches are a-axis oriented. Out of these, single junctions were etched, planarized with CeO2. Finally gold contacts we re sputtered. The Junctions are squares of size 20 x 20 to 100 x 100 m u m(2). A prerequisite for a successful preparation of junctions out o f a-axis oriented multi-layers is a study of such films. We deposited the films with RF off-axis sputtering. The films were characterized el ectrically. Their morphology was investigated by XRD, AFM and TEM. The films are very smooth and have a grain size of below 100 x 100 nm(2). To improve T-c and crystal quality, template layers were used. The T- c of a single film is about 62 K, using a template layer up to 78 K we re reached. For a-axis oriented growth not only a reduction of the dep osition temperature is important, but also the growth rate must be hig h enough. Best results were obtained at rates higher than 150 nm/h. Th e first planar junctions show a supercurrent, but otherwise rounded I- V-curves.