Contact Resistance of Several Metals on YBa2Cu3O7-δ

The contact resistance of metal electrodes deposited on high T c superconductor YBa2Cu3O7-δ (YBCO) ceramics has been studied. Several metals such as Au, Ag, Cu, Pb, Sb and Al were employed. They have very different tendencies for oxidation, which can be measured by the free energy of oxide formation. The lower the free energy of the metal oxide is, the larger the electrode resistivity becomes. The electrode resistivity is defined by the inverse of conductance per unit area of the electrode. It is suggested that the main sources of contact resistance are the formation of an oxide layer on the metal side of the interface and the appearance of an oxygen-deficient layer on the YBCO surface. Using Au, Ag and Cu, for which free energy is high, electrodes of good quality were obtained where the electrode resistivity was less than 10-6 Ω·cm2.