NEW CONTACT DESIGN FOR THE EX-SITU FABRICATION OF SMALL-SIZE, LOW-RESISTIVITY NORMAL-METAL CONTACTS TO EPITAXIAL C-AXIS YBCO FILMS

We report a new method for the ex situ fabrication of low resistance o hmic contacts between planar epitaxial c-axis YBCO films and Ag/Au met allizations. The process involves the etching of slots into the superc onductor prior to metal deposition and annealing at 450 degrees C. We confirmed the optimum dimensions of the superconductor line and slot w idth to be 1 mu m. The patterning processes was investigated which per mitted us to fabricate these dimensions with no discernible degradatio n of the high temperature superconductors (HTSC) edges and surface deg radations below 30 nm thickness. Specific contact resistivities in the 10(-6) ... 10(-7) Omega . cm(2) region have been achieved which is an advantage over planar contacts of up to two orders of magnitude and c an be obtained for contact pads of widths above 10 mu m. Contacts prov ided with slots are characterized by a significant increase in homogen eity and reproducibility compared to annealed planar contacts. The tem perature and size dependence of the contact resistances of planar and slotted contacts have been compared and studied as a function of film morphology and contact metal. The resulting contact resistance can be related to the interface resistance in ab- and c-directions as well as to the formation of point contacts and a contribution of the spreadin g resistance of the contact layer.