Electrical characteristics of thin-film Ba/sub 2/YCu/sub 3/O/sub 7/ superconducting ring resonators

The microwave performance of superconducting microstrip ring resonators operating between 2 and 22 GHz is reported. The microstrip and ground plane for the resonators were fabricated from Ba/sub 2/YCu/sub 3/O/sub 7/ films deposited on both sides of the same LaAlO/sub 3/ substrate by coevaporation. Two ring resonator geometries differing in ring diameter were studied. The strip width was the same for both to maintain a fixed line impedance. The mean-ring diameters were 10.5 mm and 5.2 mm, giving fundamental resonance frequencies of approximately 2.4 GHz and 4.8 GHz, respectively. By patterning one side with a narrow ring, the resonators are produced with Q factors (at 9.5 GHz) in excess of 7500 at 75 K and 20000 at 25 K. The temperature dependence of the resonant frequency shows the behavior expected for a superconductor with an effective penetration depth of approximately 4500 AA. It is noted that the 75 K value represents an improvement of a factor of 20 over gold.<>