Nonlinear response of Gd-Ba-Cu-O and Y-Ba-Cu-O microstrip resonators on sapphire

HF power-induced nonlinear effects, including the two-tone intermodulation distortion (IMD), were examined by using 2.3 GHz microstrip resonators prepared from double-sided YBa₂Cu₃O_7-x (YBCO) and GdBa₂Cu₃O_7-x (GBCO) films on CeO₂ buffered sapphire. Both, the YBCO and the GBCO resonators exhibited similarly high performance with low IMD level. The third-order interception points varied linearly with temperature from P_TOI≈1500 W of the circulating power, P_circ, at 4.2 K to P_TOI≈90 W at 77.4 K. The dependence of the IMD products on the P_circ/P_TOI ratio was found to be the same at all measurement temperatures. Similarly, the variation of the microwave surface resistance ΔR_S versus P_circ/P_TOI was found to be temperature-independent. The combination of these dependences provided a universal relation between the power of the IMD signals and ΔR_S, which was exhibited by both YBCO and GBCO resonators in the entire examined temperature range.