YBa₂Cu₃O_7-δ α-Axis Films and Planar Junctions

In order to prepare planar junctions, multilayers were sputtered, using YBa₂Cu₃O_7-δ as superconductor and PrBa₂Cu₃O_7-δ as barrier material. The sandwiches are a-axis oriented. Out of these, single junctions were etched, planarized with CeO₂. Finally gold contacts were sputtered. The junctions are squares of size 20x20 to 100x100 μm². A prerequisite for successful preparation of junctions from a-axis oriented multilayers is a study of such films. Films deposited by RF off-axis sputtering were characterized electrically, Their morphology was investigated by XRD, AFM and TEM. The films are very smooth and have a grain size of below 100x100 nm². To improve T_c and crystal quality, template layers were used. The T_c of a single film is about 62 K; by using a template layer up to 78 K can be reached. For α-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.