Michael M. Eddy

Measured performance at 77 K of superconducting microstrip resonators and filters

Results on three types of passive microwave devices fabricated and tested using epitaxial thin films of Tl/sub 2/CaBa/sub 2/Cu/sub 2/O/sub 8/ grown on LaAlO/sub 3/ are reported. A microstrip ring resonator with unloaded Q of 2740 at 77 K and 33 GHz is described. A superconducting 4.6 GHz band-reject filter with unloaded Q greater than 15000 when operated at 77 K is reported. In addition, results on a multiple microstrip bandpass filter are presented. >

Preparation of superconducting Tl‐Ca‐Ba‐Cu thin films by chemical deposition

A chemical deposition process for the preparation of superconducting thin films of Tl2CaBa2Cu2O8 (2122) and Tl2Ca2Ba2Cu3O10 (2223) has been developed. Oriented, superconducting 2122 and 2223 thin films have been successfully fabricated on single‐crystal yttria‐stabilized zirconia and magnesium oxide substrates (〈100〉 orientation). Epitaxial films have been prepared on magnesium oxide. Chemical analysis of the film composition by energy dispersive x‐ray analysis is in agreement (2122 vs 2223) with the phases indicated by powder x‐ray diffraction. The thin films of these compounds exhibited superconducting transition temperatures above 105 K as determined by variable‐temperature resistivity and ac magnetic susceptibility measurements. In addition, microwave surface resistance measurements at 150 GHz show that these films have very low losses at 77 K (1 mΩ).

Microwave surface resistance in Tl‐based superconducting thin films

We report measurements of microwave surface resistance in Tl‐based superconductor thin films made by laser ablation followed by a post‐deposition thermal process. The films were measured by using cavity methods. The data at 9.5 and 148 GHz indicate that the residual resistance scales as f2. At 77 K, the 9.5 GHz surface resistance is ten times smaller than oxygen‐free high‐conductance copper at the same temperature and frequency. The 9.5 GHz measurement also indicates that the film‐substrate interface does not cause more microwave loss than the film surface.

Performance of superconducting microwave devices passivated with dielectric materials

We present a set of experiments which show that three dielectric processing variables in particular affect the performance of superconducting microwave devices: processing time and temperature, moisture content of the dielectric material, and surface interactions with the high temperature superconductor (HTS). The changes in microwave performance of a straight-line microstrip resonator before and after passivation were quantified by measurements of the loaded and unloaded quality factors for each resonator. Dielectric materials of varying moisture content were used. The dielectrics were processed at different times and temperatures. This study shows that the degradation of the microwave devices can be minimized by choosing dielectrics which (i) have a low moisture content, (ii) interact as little as possible with the HTS surface, and (iii) can be rapidly processed at relatively low temperatures.

Tl-Ca-Ba-Cu-O Thin Film Passive Microwave Devices

We report results on several passive microwave devices fabricated and tested using epitaxial thin films of Tl2CaBa2Cu2O8 grown on LaAlO3. We report microstrip resonators with unloaded Q’s of 15,000 at 80K and 4.83 GHz, and 1440 at 80K and 33 GHz. We report a superconducting 4.6 GHz bandreject filter with unloaded Q greater than 15,000 when operated at 77K.