Low-loss substrate for microwave application of high-temperature superconductor films

We have shown that strontium lanthanum aluminate (SrLaAlO4) has considerable potential as a substrate material for high-temperature superconductor (high Tc) microwave applications. Excellent lattice match is obtainable on a 14° tilt from the c axis. The lattice dimensions encourage ab plane epitaxial growth. The thermal expansion was found to be 7.4×10−6 °C−1. Patterned sputtered niobium resonators on SrLaAlO4 exhibit Q values at 5 K comparable to similar niobium resonators on polycrystalline alumina, (Q≳10 000 from 2 to 15 GHz). Deposited YBa2Cu3O7−x (YBCO) films on this substrate show sharp ac susceptibility transitions indicating good homogeneity and ab plane orientation.