Microwave surface resistance of magnetron-sputtered Tl-Ba-Ca-Cu-O films on silver substrates

Surface resistance measurements on Tl-Ba-Ca-Cu-O thick films (∼15 μm) magnetron sputtered onto BaF2-buffered, silver-based (Consil 995) substrates have been made at a microwave frequency of 22 GHz. The relatively large-area films (∼5 cm2) are characterized by surface resistance values of 6.9±2 mΩ at 11.3 K and 30.2±1 mΩ at 77 K; the corresponding values for Cu are 10 and 22 mΩ, respectively. These results demonstrate that Tl-Ba-Ca-Cu-O can be deposited onto large-area, metallic substrates with characteristic surface resistance values lower than Cu at 4 K. Orientation of the film should improve the surface resistance at 77 K, thereby making the fabrication of microwave cavities that are superior to Cu possible.