Surface resistance of large-area Tl2Ba2CaCu2O8 thin films at microwave and millimeter wave frequencies measured by three noncavity techniques

The surface resistanceRs of Tl2Ba2CaCu2O8 films fabricated on LaAlO3 wafers up to 3 inches (7.6 cm) in diameter through a post-deposition anneal process was measured over the frequency range 5.55–94.1 GHz by the following techniques: 5.55 and 27.5 GHz high-temperature superconductor (HTS)-sapphire resonators, 10 GHz parallel plate resonator, and 94.1 GHz scanning confocal resonator.Rswas found to exhibit a quadratic dependence on frequencyf at 77 K:Rs∝f2.0±0.1. The highest-quality films yieldRs=145±15μΩ at 10 GHz and 77 K. Scanning confocal resonator mapping ofRsacross a 2-inch (5.1 cm) diameter wafer yielded a base value forRsof 16±1 mΩ at 77 K and 94.1 GHz (equivalent to 180±10μΩ at 10 GHz) and good uniformity inRsacross the wafer. HTS-sapphire resonator measurements ofRsfor fifteen 1.2 cm square parts cut from a 3-inch diameter wafer yieldedRsvalues scaled to 10 GHz of 196±10μΩ at 80 K. Similar values were measured for Tl2Ba2CaCu2O8 films prepared on both sides of a 2-inch diameter wafer.Rs values at 10 GHz and 80 K of 147−214μΩ were maintained over the course of 40 independent and successive deposition runs and corresponding anneals under nominally identical film fabrication conditions. Surface resistance at 5.55 GHz remained below 80μΩ for maximum rf magnetic fields up to 85 Oe at 4.2 K and 7 Oe at 80 K, respectively. Results are compared with predictions of the two-fluid model. The relative advantages and disadvantages of the different techniques for measuring surface resistance are discussed.