Effect of a Au contact layer on the microwave performance of YBa2Cu3O7-x thin films

The microwave surface resistance (R-s) of YBCO films sputtered simultaneously on both sides of CeO2 coated sapphire wafers of 3 inch diameter was measured using the disk resonator technique at a frequency of 1.92 GHz Gold layers were deposited on the unpatterned side of the resonator, and the microwave losses were measured in the Au-contacted YBCO films. Although the Au layer was not directly exposed to the microwave power, it dramatically increased the effective R-s of the YBCO film, while leaving the effective surface reactance (X-s) almost unchanged. The R-s-enhancement was examined experimentally and theoretically in terms of the impedance transformation approach as a function of the Au nod YBCO film properties. Furthermore, the technique appeared suitable for the determination of the absolute value of the London penetration depths (lambda (L)) in the double-sided YSCO films. The resulting temperature dependencies of lambda (L) were in a good agreement with those estimated by the conventional frequency-shift technique.