Development of superconducting electrode capacitor using a YBa2Cu3O7-x thick film and Y2BaCuO5 dielectric

Different phases in the YO_1.5-BaO-CuO phase diagram were evaluated for dielectric properties and compatibility with subsequent firing of a YBa₂Cu₃O_7-x thick film. Y₂BaCuO₅ (211) was chosen for capacitor manufacture because it showed no reaction with the YBa₂ Cu₃O_7-x (123) thick film upon sintering. AC field exclusion confirmed the superconductivity of the 123 thick film on the 211 substrate with T_c at 93 K. Scanning electron microscopy of the interface between the 211 substrate and the 123 thick film showed neither a reaction nor the formation of a third phase. Capacitor samples were manufactured in various sizes. All sizes were found to have the following characteristics. For a range from 0.1-110 MHz, at 77K, the phase angle of the impedance remains constant at -90°. The same is true at 298 K. This would be an improvement over a commercial chip capacitor for which the curve is constant only for a small range. The dielectric constant remains at 24 over the 0.1-110-MHz frequency range at 77 and 298 K. The capacitance of the sample was found to be constant over frequency. It is concluded that 211 substrates are suitable for the formation of a low-loss capacitor with superconducting electrodes