The Contact Resistance of the YBa₂Cu₃O_7-δ-Metal Film System

Abstract

The electrical properties and X-ray photoelectron spectroscopy (XPS) of Y 1 Ba 2 Cu 3 O 7-δ (YBCO) contacts formed by Ag, Au, Sn, Zn, In and Al metal films have been studied. The Cu, In, Zn and Sn film contacts show high resistivities with semiconductive temperature dependence. The Au, Ag, and Pt film contacts have low resistivities with metallic temperature dependence. The XPS analyses show that Sn and Al react with the oxygen on the YBCO surface. However, little change in copper and oxygen states can be observed in Ag/YBCO and Au/YBCO systems. It is assumed that the oxygen-deficient layer at the interfaces of Sn/YBCO and Al/YBCO systems makes the contact resistance high, while the semiconductive layer is insignificant at the Ag/YBCO and Au/YBCO interfaces, and their resistance is low. Analyses indicate that Ag/YBCO and Au/YBCO systems provide very effective ohmic contacts.