OXIDE SUPERCONDUCTORS AND FERROELECTRICS - MATERIALS FOR A NEW-GENERATION OF TUNABLE MICROWAVE DEVICES

We describe materials deposition and characterization for a broad clas s of tunable microwave devices using high-temperature oxide supercondu ctor and voltage-tunable oxide ferroelectric thin-film multilayer stru ctures. Tl-Ba-Ca-Cu-O thin films deposited by sputtering or e-beam eva poration were patterned into microwave resonators. each consisting of two colinear microstrip line sections separated by a 5-20 mum gap. A B a0.1Sr0.9TiO3 (BST) layer was then over-coated to fill the gap. The re lative dielectric constant of the BST films deposited by physical vapo r or chemical techniques was measured at 77 K in the 1-10 MHz range an d found to vary by up to a factor of 2 or more with voltage bias in te st capacitor structures using Pt electrodes. In the BST (variable capa citor)-HTSC microwave resonator structures, the change of the relative dielectric constant of the BST under voltage bias has allowed variati on of the fundamental frequency of up to 80 MHz in the 5-10 GHz range at. 4 K. Film deposition by various techniques and associated structur al, morphological, and electronic properties, as well as materials com patibility issues, are discussed.