The loss factor $(\tan \mathrm{ \delta )}$ of ferroelectric material at microwaves and the tunability (n) defined as a ratio of the dielectric permittivity at zero dc field to the dielectric permittivity at the given field are strongly connected with the softness of so-called ferroelectric soft mode. The loss factor and the tunability are generalized by the commutation quality factor (CQF). The dielectric response of a ferroelectric material allows one to determine the CQF and to compare it to the theoretical CQF obtained for a perfect ferroelectric sample. In order to compare the theoretical prediction and experimental data, the influence of deposition parameters on microwave properties of ${\mathrm{Ba}}_x{\mathrm{Sr}}_{\text{1−x}}{\mathrm{TiO}}_3$ (BSTO) films deposited on sapphire and alumina substrate has been investigated in a wide frequency range (1–30 GHz). The highest CQF at room temperature was obtained for the 30% Ba content target and the deposition temperature 905 °C. The best BSTO films exhibited $\mathrm{CQF}{\text{≅1.6×10}}^4$ with $\text{n=2.1}$ and $\tan \text{\hspace{0.05em}δ=0.012}$ at 1 GHz and zero bias. This result is among the best reported for sputtered BSTO films both on sapphire and alumina substrates. Nevertheless the obtained CQF is 3–5 times lower than the upper theoretical limit.

Planar capacitors, consisting of a thin $(\approx 1\mathrm{\mu }\mathrm{m})$ ferroelectric film and a dielectric substrate, widely used at microwaves, are normally designed on the basis of the conformal mapping technique and the use of the traditional formula for electric field in the capacitor gap: $E=U∕s$ . $U$ is applied voltage and $s$ is the width of the gap. The important characteristic of the planar capacitor is its tunability defined as $n=C\left(0\right)∕C\left(U\right)$ . The dependence of the tunability on the ferroelectric film thickness $\left(h_f\right)$ has been experimentally investigated. The saturation or feebly marked maximum on the dependence of $n$ on $h_f$ was observed. The appearance of the maximum can be explained using the corrected formula for the field in the gap: $E\cong U∕(s+h_f)$ . The formula was earlier theoretically developed on the basis of minimization of the free energy accumulated in the planar capacitor and using the Ginzburg–Devonshire equation for the nonlinear polarization of the ferroelectric film. The result should be considered as a correction of the model of a planar capacitor based on the conformal mapping technique.

Ferroelectric films in the paraelectric phase exhibit two undesirable properties: hysteresis in the voltage-capacitance characteristics and a significant relaxation time of the capacitance. Our experiments show that suppression of both of these is achieved by using UV radiation with wavelengths corresponding to the material forbidden gap. Experimentally we also observed UV radiation induced modulation of thin film permittivity without an applied electric field. The observed phenomena are believed to have the same origin: UV light generates nonequilibrium charge carriers that screen out local electric field induced by defects and interfaces inside ferroelectric thin films and change films effective dielectric properties.

The split-cylinder resonator method was adapted to measure the microwave properties (dielectric permittivity and loss tangent) of thin ferroelectric films on a dielectric substrate. The mathematical model for calculating the resonance frequency of the split-cylinder resonator was adjusted for the “ferroelectric film—substrate” structure. An approach for correcting the gap effect based on calibrating with a single-layer dielectric was introduced and used to study two-layer dielectrics. The prototype of a split-cylinder resonator designed to measure single-layer dielectric plates at a frequency of 10 GHz was presented. The resonator calibration was performed using dielectric PTFE samples and fused silica, and an example of the correction function was suggested. The measurement error was estimated, and recommendations on the acceptable parameter range for the material under investigation were provided. The method was demonstrated to measure the microwave properties of a ferroelectric film on a fused silica substrate.

The design and microwave characteristics of a ferroelectric thin film slotline-waveguide phase shifter operating in the millimeter wavelength range ( f∼60 GHz) are presented. In this frequency range,...

Thin ferroelectric barium strontium titanate (BST) layers of high structure quality have been grown for the first time directly on semi-insulating silicon carbide substrates by RF magnetron sputtering of a ceramic target. The structural and microwave properties of the films were substantially improved by an intermediate annealing of the layers during the growing process. Prepared under this approach, BST films have a well-formed crystal structure, which has a positive effect on their electrical properties, specifically on nonlinearity and dielectric losses. Planar capacitors based on these BST films demonstrate the best combination of high tunability and low losses for BST/SiC structures at microwaves.