AN EXPERIMENTAL-STUDY OF HIGH-TC SUPERCONDUCTING MICROSTRIP TRANSMISSION-LINES AT 35 GHZ AND THE EFFECT OF FILM MORPHOLOGY

Microstrip transmission lines in the form of ring resonators have been fabricated from a number of in-situ grown laser ablated films and post-annealed co-sputtered YBa2Cu3O7-x (YBCO) films. The properties of these resonators have been measured at 35 GHz and the observed performance is examined in light of the critical temperature (Tc) and film thickness and also the film morphology which is different for the two deposition techniques. We find that Tc is a major indicator of the film performance for each growth type with film thickness becoming important as it decreases towards 1000 angstrom. We find that the films with a mixed grain orientation (both 'a' axis and 'c' axis oriented grains) have poorer microwave properties as compared with the primarily 'c' axis oriented material. We speculate that this is due to the significant number of grain boundaries between the different crystallites, which may act as superconducting weak links and contribute to the surface resistance.