ELECTRICAL RESPONSE OF FERROELECTRIC SUPERCONDUCTING DIELECTRIC BAXSR1-XTIO3 YBA2CU3O7-DELTA/LAALO3 THIN-FILM MULTILAYER STRUCTURES/

Multilayered structures of ferroelectric and superconducting films dep osited on dielectric substrates are being developed for use in low-los s tunable microwave components for satellite and ground-based communic ations. In this paper, we report on the electrical characterization of BaxSr1-xTiO3 (x = 0, 0.08 and 0.10)/YBa2Cu3O7-delta/LaAlO3 thin-film multilayer structures. These structures were formed in situ using a pu lsed laser deposition method by the sequential deposition of the YBa2C u3O7-delta (YBCO) high-temperature superconductor (HTS) and the SrTiO3 (STO) or Ba0.10Sr0.90TiO3 (BST) films on 20 mil (0.5 mm) thick (100) LaAlO3 single-crystal substrates and by using a metal organic depositi on method to deposit the Ba0.08Sr0.92TiO3 films. These processes produ ced YBCO films with thicknesses of 300 nm and ferroelectric films with thicknesses of 250 and 500 nm. The YBCO films showed a transition tem perature (T-c) above 89 K after deposition and processing of the ferro electric layers. Electrical characterization of these structures was p erformed by measuring the capacitance (C), relative dielectric constan t (epsilon(r)), and loss tangent (tan delta) of the ferroelectric film in the temperature range from 300 to 40 K and at electric fields (E) from zero to 2.0 x 10(5) V cm(-1). For 500 nm and 250 nm thick BST fil ms having the same stoichiometry, epsilon(r) values of 191 and 126, re spectively, were obtained at 300 K, 1.0 MHz, and zero E. Corresponding tan delta values of 0.096 and 0.021 were measured for the 500 nm and 250 nm thick samples, respectively, at the aforementioned temperature, frequency and E. It was observed that the amount of variation of epsi lon(r) as a function of E was closely related to the microstructure of the films. Evidence of conductive pathways in the ferroelectric film as well as of ferroelectric domain 'lock-in' under a d.c. bias is pres ented.