High-Temperature Superconductor Resonators and Phase Shifters

High-Tc superconductor resonators and phase shifters are reported in this paper. The YBa2Cu3O7-δ (YBCO) films used in this work were off-axis sputtered onto 0.5-mm thick [100] LaA1O3 substrates and have surface impedances at 10 GHz as low as 20 μΩ at 4.2 K and 300 μΩ at 77 K. The dielectric constant of the LaA1O3 substrates was measured carefully using both straight-line and ring-resonator techniques. The superconductor straight-line resonator, which uses silver as its ground plane, has a moderately high Q factor and has an electromagnetic feedthrough level below - 65 dB up to 10 GHz. We also report the first demonstration of a semiconductor /superconductor microwave digital phase shifter. We utilized YBCO film to form the circuit, with semiconductor PIN diodes serving as switches. A 4-bit superconductor phase shifter design is also presented along with a simulation that indicates maximum total insertion loss (which occurs with all bits forward-biased) at 77 K to be 1.1 dB at 10 GHz, which is about 1.5-2.0 dB less than that of a similar copper phase shifter at room temperature (radiation loss is not taken into consideration in either case). This insertion loss difference will, to some extent, depend on the details of the designed circuit, and it will increase significantly if thinner substrates are used, in which case the microstrip loss is more significant.