YBa/sub 2/Cu/sub 3/O/sub 7/(-δ) a-axis films and planar junctions

Abstract

AbstTact-Among the concepts for Josephson junctions with artificial barriers, planar junctions are most favorable, because they can be deposited in situ.In order to prepare planar junctions, multi-layers were sputtered, using YBa2Cu307-6 as superconductor and PrBa2Cu307-6 as barrier material. The sandwiches are a-axis oriented. Out of these, single junctions were etched, planarized with CeO,. Finally gold contacts were sputtered. The junctions are squares of size 20 x 20 to 100 x 100 pm2.A prerequisite for a successful preparation of junctions out of a-axis oriented multi-layers is a study of such films. We deposited the films with RF off-axis sputtering. The films were characterized electrically. Their morphology was investigated by XRD, AFM and TEM. The films are very smooth and have a grain size of below 100 x 100 nm2. To improve T, and crystal quality, template layers were used. The T, of a single film is about 62 K, using a template layer up to 78 K were reached. For a-axis oriented growth not only a reduction of the deposition temperature is important, but also the growth rate must be high enough. Best results were obtained at rates higher than 150 nm/h.The first planar junctions show a supercurrent, but otherwise rounded I-V-curves.