Microwave characterization of nanostructured ferroelectricBa0.6Sr0.4TiO3 thin films fabricated by pulsed laser deposition

Abstract

A series of nanostructured ferroelectric thin films of barium strontium titanate werefabricated using a pulsed laser deposition system with real-time in situ processcontrol. Pulsed laser deposition parameters were controlled during the growth ofnanostructured thin films for use in the development of high frequency tunable microwavedevices. The thin films were all grown at the same substrate temperature and laserbeam energy density, but the chamber oxygen partial pressure (COPP) was variedsystematically from 19 mTorr through 1000 Torr. Structural and electromagneticcharacterization was performed using atomic force microscopy and evanescent microwavemicroscopy, respectively. Atomic force microscopy showed a linear increase in grain sizewith increases in the ambient oxygen pressure from 38 to 150 mTorr and from300 mTorr to 1000 Torr. The correlation of the microwave properties with the epitaxialfilm microstructure can be attributed to stresses and polarizability in the film.Microwave characterization showed that a COPP of 75 mTorr yielded the mostdesirable film in terms of tunability and loss tangent over a wide frequency range.