Optimization of SrTiO/sub 3/ for applications in tunable resonant circuits

Abstract

A series of SrTiO/sub 3/ (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/sub 2/ (40 mTorr<P/sub dep/<800 mTorr) and substrate temperature (750/spl deg/C<T/sub sub/<850/spl deg/C) were varied independently while the fluence was held constant at 2.0 J/cm/sup 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/sub z/(film)) of the deposited films was found by XRD to be a strong function of the deposition pressure: a/sub z/(film)<a(bulk) at low pressures (P/sub dep/<65 mTorr) and a/sub z/(film)>a(bulk) at higher pressures (P(dep)>65 mTorr). The dielectric constant (/spl epsiv//sub r/) and loss tangent (tan/spl 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.