Fabrication and investigation of YBa2Cu3O7-delta/Ba0.05Sr0.95TiO3 thin film structures for voltage tunable devices

High-temperature superconducting/ferroelectric thin film structures were de posited by laser ablation. Three types of voltage tunable devices were fabr icated and investigated-trilayer capacitor, planar interdigital capacitor a nd coplanar waveguide. As ferroelectric the solid solution BaxSr1-xTiO3 was chosen with barium content x = 0.05 because its Curie temperature is close to the liquid nitrogen boiling point (77 K). Temperature and voltage depen dences of the Ba0.05Sr0.95TiO3 dielectric constant epsilon(r,BSTO) were stu died. High epsilon(r,BSTO) values were determined-up to 3000 at 75 K, 20 GH z and zero de bias. Efficient voltage tunability was demonstrated (up to 40 %) at loss level tan delta=0.01-0.1. Compact YBa2Cu3O7-delta/Ba0.05Sr0.95Ti O3 coplanar waveguide with as narrow gap as 18 mu m was tested as electrica lly tunable phase-shifter and field-induced phase shifts of more than 180 d egrees were obtained by 35 V de bias at 20 GHz. This improvement was attain ed by proper choice of the ferroelectric material, accomplished epitaxial g rowth of the films and decrease of the specific dimensions. (C) 1998 Publis hed by Elsevier Science B.V. All rights reserved.