HIGHLY EPITAXIAL FERROELECTRIC LEAD STRONTIUM TITANATE ((Pb,Sr)TiO3) THIN FILMS WITH EXTRA LARGE DIELECTRIC TUNABILITY: A GOOD CANDIDATE FOR ROOM TEMPERATURE TUNABLE MICROWAVE ELEMENTS

Lead Strontium Titanate ((Pb, Sr)TiO3, PST) thin films were epitaxially grown on (001) magnesium oxide (MgO), (001) lanthanum aluminate (LaAlO3, LAO), and (110) neodymium gallate (NdGaO3, NGO) substrates by pulsed laser deposition. Microstructural studies revealed that the as-grown PST films are with excellent epitaxial quality. PST films on MgO and LAO substrates exhibit a tetragonal distortion whereas the films on NGO substrates show an orthorhombic distortion. Dielectric property measurements at 1.0 MHz revealed that the room temperature dielectric constant is about 1500 with an extra large dielectric tunability value of 65% at 50 kV/cm for the PST film on the MgO substrate, and dielectric constant of 3100 with a dielectric tunability value of 48% at 50 kV/cm for the PST film on the LAO substrate. PST films on NGO substrates show anisotropic in-plane dielectric properties due to the anisotropic in-plane strain. A high zero-field dielectric constant of 4220 with a dielectric tunability value of 59% at 50 KV/cm was achieved along the a-axis of the PST film on the NGO substrate. All the films show dielectric losses smaller than 0.01. These excellent results suggest the highly epitaxial PST thin films can be a good candidate for developing room temperature tunable microwave device applications.