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 hav e similar crystal structures and chemical constituents and, therefore, it c an be advantageous to deposit epitaxial trilayer capacitors with high-T-c e lectrodes 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)YBa 2Cu3O7-delta/(600 nm) Ba0.9Sr0.1TiO3/(200 nm)YBa2Cu3O7-delta and (200 nm)Nd Ba2Cu3O7-delta/600 nm)Ba0.9Sr0.1TiO3/(200 nm)NdBa2Cu3O7-delta were laser de posited on (100)LaAlO3 substrates. The relative dielectric permittivity eps ilon/epsilon(0) Of Ba0.9Sr0.1TiO3 was in the range 900-1250 at T = 300 K an d f = 1 MHz, values considerably higher than those for conventional metal e lectrodes. epsilon(T) had a sharper maximum at a lower temperature (below r oom temperature) for Ba0.9Sr0.1TiO3 layers with Nd- than with Y-based cupra te electrodes while there was no peak at all up to 350 K when one of the el ectrodes 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 independ ent (f = 120 Hz-30 MHz) but decreased with increased bias voltage. The perm ittivity of Ba0.9Sr0.1TiO3 between NdBa2Cu3O7-delta electrodes could be des cribed by the same model at both low and high electric fields. (C) 1999 Els evier Science B.V. All rights reserved.