Surface resistance of large-area Tl2Ba2CaCu2O8 thin films at microwave and millimeter wave frequencies measured by three noncavity techniques |
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Authors: | W L Holstein L A Parisi Z -Y Shen C Wilker M S Brenner and J S Martens |
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Affiliation: | (1) Du Pont Central Research and Development, P. O. Box 80304, 19880-0304 Wilmington, Delaware;(2) Dept. 1140, Sandia National Laboratory, 87185 Albuquerque, New Mexico;(3) Present address: Conductus, 969 W. Maude Ave., 94086 Sunnyvale, California |
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Abstract: | The surface resistanceR
s
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.R
s
was found to exhibit a quadratic dependence on frequencyf at 77 K:R
s
f
2.0±0.1. The highest-quality films yieldR
s
=145±15 at 10 GHz and 77 K. Scanning confocal resonator mapping ofR
s
across a 2-inch (5.1 cm) diameter wafer yielded a base value forR
s
of 16±1 m at 77 K and 94.1 GHz (equivalent to 180±10 at 10 GHz) and good uniformity inR
s
across the wafer. HTS-sapphire resonator measurements ofR
s
for fifteen 1.2 cm square parts cut from a 3-inch diameter wafer yieldedR
s
values scaled to 10 GHz of 196±10 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 147–214 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 80 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. |
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Keywords: | Superconductor microwave surface resistance measurement techniques Tl2Ba2CaCu2O8 |
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