FABRICATION AND CHARACTERIZATION OF BA1-XSR1-XTIO3 TUNABLE THIN-FILM CAPACITORS

Polycrystalline Ba1-xSrxTiO3(x=0.9) thin films have been successfully prepared from sintered stoichiometric ceramic targets by means of the 90 degrees off-axis r.f. sputtering technique at substrate temperatures from 500 to 600 degrees C. Films grown on lanthanum aluminate(100) at 550 degrees C are predominantly c-axis oriented. Those deposited on sapphire(1 $($) over bar$$ 102) did not reveal any preferred growth orientation. Dielectric measurements were performed using planar capacitor geometries. The dielectric constant of these films showed a broad ferroelectric-to-paraelectric transition at 50 to 70 K, depending on the thickness of the films. The dielectric constant of these films also showed a small electric field dependence, changing by 5% at 77 K and at a field strength of 20kVcm(-1). The results are compared with those obtained from bulk samples, and are interpreted in the framework of phenomenological theory.