A MODIFICATION OF THE 3-POINT METHOD OF MEASURING CONTACT RESISTIVITIES OF METAL-SUPERCONDUCTOR INTERFACES

Axisymmetric three-point measurement of the contact resistance between a metal electrode and a superconductor substrate shows significant va riation as a function of the placement of the voltage measuring probe on the metal electrode. This study explored this variation by the use of an analytical model simulating the voltage variation in the metal e lectrode. The model used a simplified scheme of mapping the electrode- superconductor interface to an equivalent layer with the same resistiv ity as the metal electrode. The voltage in the electrode was obtained by solving Laplace's equation. Using a numerical approximation process , three simplified equations for calculating the contact resistivities from the voltage measured from the three-point method were developed. The contact resistivities calculated from the modified equations and those measured from the lap-joint method were compared in order to sho w the validity of the modified equations. The radii of the electrode a nd current leads, and the ratio of the voltage measured at the top edg e of the electrode to the voltage measured at the current lead determi ne the selection of the modified equations.