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.