Temperature and electric field dependence of the permittivity of Ba0.9Sr0.1TiO3 films epitaxially grown on cuprate electrodes

Cuprate, high-temperature superconductors and perovskite ferroelectrics have similar crystal structures and chemical constituents and, therefore, it can be advantageous to deposit epitaxial trilayer capacitors with high-T-c electrodes and operate these at room temperature, well above the transition temperature T-c, in order to achieve a high dielectric constant, tunability, and relatively low microwave loss. Epitaxial heterostructures (200 nm)YBa2Cu3O7-delta/(600 nm) Ba0.9Sr0.1TiO3/(200 nm)YBa2Cu3O7-delta and (200 nm)NdBa2Cu3O7-delta/600 nm)Ba0.9Sr0.1TiO3/(200 nm)NdBa2Cu3O7-delta were laser deposited on (100)LaAlO3 substrates. The relative dielectric permittivity epsilon/epsilon(0) Of Ba0.9Sr0.1TiO3 was in the range 900-1250 at T = 300 K and f = 1 MHz, values considerably higher than those for conventional metal electrodes. epsilon(T) had a sharper maximum at a lower temperature (below room temperature) for Ba0.9Sr0.1TiO3 layers with Nd- than with Y-based cuprate electrodes while there was no peak at all up to 350 K when one of the electrodes was ordinary In metal. epsilon was suppressed 4-10 times when +/- 15 V bias was applied between the high-T-c electrodes (T = 300 K, f = 1 MHZ), the higher value for the Nd cuprate. Losses, tan delta, for the Ba0.9Sr0.1TiO3 film were high compared to bulk values, they were frequency independent (f = 120 Hz-30 MHz) but decreased with increased bias voltage. The permittivity of Ba0.9Sr0.1TiO3 between NdBa2Cu3O7-delta electrodes could be described by the same model at both low and high electric fields. (C) 1999 Elsevier Science B.V. All rights reserved.