Double-sided YBa/sub 2/Cu/sub 3/O/sub 7-∂/ films for planar high-power filters

Abstract

We have extended the planar DC high oxygen-pressure sputtering process for the successive non-scanning deposition of epitaxial YBa/sub 2/Cu/sub 3/O/sub 7-/spl part// (YBCO) films up to 2 in diameter and 600 nm in thickness. Contamination of the heater-facing side of the LaAlO/sub 3/ substrates could be prevented by use of a thin quartz glass plate. For optimized deposition parameters, inductive measurements indicated comparable and homogeneous quality of both film sides, i.e. T/sub c/>88 K and J/sub c/(77 K) >2 MA/cm/sup 2/. Surface resistance measurements at 19 GHz with a Nb-shielded sapphire resonator resulted in R/sub s/<1 (0.2) m/spl Omega/ at 77 (4) K, which, in some cases, did not show any significant increase up to surface field levels B/sub s/=10 (25) mT. In order to obtain planar microwave filters of small size and high power-handling capability, disc resonators for TM/sub 010/-mode operation at 3.5 and 1.8 GHz were patterned from and 2 diameter double-sided YBCO films. Strongly temperature dependent quality factors Q/sub 0/ as high as 7.2/spl middot/10/sup 4/ (6/spl middot/10/sup 5/) have been achieved at 77 K (30 K) and 3.5 GHz, which are limited by losses in both the superconductor and the dielectric. A circulating power of about 1 kW, corresponding to peak B/sub s/-values above 1 mT, could be achieved without significant Q/sub 0/ degradation. Evidences for field limitations by local defects were found.