Optimization of SrTiO3 for applications in tunable resonant circuits

A series of SrTiO3 (STO) films have been grown at a wide range of deposition conditions in order to determine the optimal growth parameters to maximize ferroelectric tuning while maintaining the lowest dielectric losses. The deposition pressure of the ambient O-2 (40m Torr<P-dep<800m Torr) and substrate temperature (750 degrees C<T-sub<850 degrees C) was varied independently while the fluence was held constant at 2.0 J/cm(2). The deposited films were characterized by x-ray diffraction (XRD) and low frequency dielectric measurements (1 MHz). The out-of-plane STO lattice parameter (a(z)(film)) of the deposited films was found by XRD to be a strong function of the deposition pressure: a(z)(film) < a(bulk) at low pressure (P-dep <65 mTorr) and a(z)(film) > a(bulk) at higher pressures (P-dep>65 mTorr). The dielectric constant (epsilon(r)) and loss tangent (tan delta) were determined as a function of applied field at room temperature (300 K) and at liquid nitrogen temperature (77 K). The low frequency dielectric properties of the STO films were found to be a weak function of the strain of the ferroelectric film.