Effect of growth defects on microwave properties in epitaxial Ba_0.5Sr_0.5TiO₃ thin films grown on (001) MgO by pulsed laser deposition

Abstract

Ba_0.5Sr_0.5TiO₃ (BSTO) films have been grown heteroepitaxially on (001) MgO substrates by pulsed laser deposition (PLD) to fabricate microwave phase shifters for the wide frequency range 45 MHz–50 GHz. Both as-grown and ex situ annealed films have a cube on cube epitaxial relationship with ⟨100⟩BSTO//⟨100⟩MgO. Threading dislocations are the dominant defects, mostly with Burgers vectors b = ⟨101⟩. Growth at 10⁻¹ mbar oxygen pressure, compared to 10⁻⁴ mbar, resulted in significantly better properties. Ex situ annealing of the film grown at 0.1 mbar resulted in a reduction of 40% in threading dislocation density and a 40% increase in dielectric tunability.

Keywords:

• ferrolectric thin gilms
• TEM
• dislocations
• tunability

Acknowledgements

The authors thank Professor M. Aindow (University of Connecticut) for helpful discussions and EPSRC for financial support of this research project (GR/S60471).