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

BaSrTiO (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 mbar oxygen pressure, compared to 10 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.