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

Abstract 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)YBa 2 Cu 3 O 7− δ /(600 nm)Ba 0.9 Sr 0.1 TiO 3 /(200 nm)YBa 2 Cu 3 O 7− δ and (200 nm)NdBa 2 Cu 3 O 7− δ /(600 nm)Ba 0.9 Sr 0.1 TiO 3 /(200 nm)NdBa 2 Cu 3 O 7− δ were laser deposited on (100)LaAlO 3 substrates. The relative dielectric permittivity e / e 0 of Ba 0.9 Sr 0.1 TiO 3 was in the range 900–1250 at T =300 K and f =1 MHz, values considerably higher than those for conventional metal electrodes. e ( T ) had a sharper maximum at a lower temperature (below room temperature) for Ba 0.9 Sr 0.1 TiO 3 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. e 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  δ , for the Ba 0.9 Sr 0.1 TiO 3 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 Ba 0.9 Sr 0.1 TiO 3 between NdBa 2 Cu 3 O 7− δ electrodes could be described by the same model at both low and high electric fields.