Orest Vendik

Ferroelectric Tuning of Planar and Bulk Microwave Devices

Benefits of ferroelectric component applications at microwaves is discussed. Experience recently gained in the high-temperature film-production technology has been used for obtaining high-quality ferroelectric tunable components. The disk made from bulk SrTiO3 single crystal covered with double-sided YBa2Cu3Y7 films was used as a high-quality TM010 mode tunable resonator. Planar structures containing thin film ferroelectric layers: planar capacitor, sandwich capacitor, coplanar line, and fin line have been studied. Modeling dielectric response of low-temperature incipient ferroelectrics (SrTiO3, KTaO3) has been applied for simulation of tunable planar structures. The quality factor of a tunable component (QFCT) is suggested to characterize the validity of the component for practical applications. The high-quality planar capacitors are pioneered for the applications. The wide frequency band fin line phase shifter has been studied and simulated. The prospects for applications of ferroelectric planar structures at room temperature is discussed.

Empirical model of the microwave properties of high-temperature superconductors

This paper presents simple correct models of high-temperature superconductor (HTS) film parameters at microwave frequencies. The models are based on the enhanced two-fluid model of a superconductor. The quasi-particle scattering and peculiarities of the normal conductivity of the HTS at microwaves, including residual resistance of a material, are taken into account. The difference between the known Gorter and Casimir two-fluid model of low-temperature superconductor and the enhanced two-fluid model of HTS is proven. A simple quasi-static model of current distribution across the microstrip line and coplanar waveguide is used for a simulation of a contribution of the superconductor transport processes into impedance per unit length of the transmission lines considered. The models developed were applied to a simulation of microstrip line and coplanar waveguide resonators. Good agreement of simulated results and measurements in a wide temperature range has been demonstrated. The model presented can be considered as a starting point for the formation of the computer-aided design (CAD) package of HTS microwave components.

Microwave losses in incipient ferroelectrics as functions of the temperature and the biasing field

The dielectric constant of ferroelectric materials can be controlled by an applied electric field. That is promising for applications using the microwave technique. The widespread use of ferroelectric materials at microwaves is retarded by a considerable high dielectric loss by the materials at high frequencies. The goal of this article is to model the essential mechanisms of losses in incipient ferroelectrics at microwave frequencies. The following materials are studied: strontium titanate (SrTiO3) and potassium tantalate (KTaO3). The following loss mechanisms are considered: fundamental loss determined by multiphonon scattering of the soft ferroelectric mode and transformation of microwave electric field oscillations into acoustic oscillations due to residual ferroelectric polarization.

Modeling the dielectric response of incipient ferroelectrics

Interest in incipient ferroelectrics has been renewed due to their promise for applications at cryogenic temperatures. The dependence of the dielectric constant of an incipient ferroelectric on temperature and the applied biasing field can be modeled correctly by solution of the Ginsburg–Devonshire equation. A set of simple and correct formulas is derived to provide simulation of the dielectric constant of an incipient ferroelectric as a function of temperature and the biasing field. As a typical representative of this, SrTiO3 is used. The inhomogeniety of the composition or/and structure of the material is quantitatively described by a specially introduced coefficient. The correlation effect is used to describe the size effect for a thin film capacitor. The boundary conditions for a ferroelectric polarization on the surface of electrodes are considered. The boundary conditions are specified for the interface between the ferroelectric and the metal or the high temperature superconductor. Comparison of the...

HTS/ferroelectric devices for microwave applications

High Temperature Superconducting (HTS, e.g. YBCO) microwave devices based on bulk or thin film ferroelectrics (e.g. Strontium Titanate-STO) are studied theoretically and experimentally. YBCO/STO/YBCO parallel-plate resonators and based on bulk single crystal STO are for electrically tunable high power filters, phase shifters and other devices in the frequency band 0.5-2.0 GHz of advanced microwave communication systems. Thin film YBCO/STO Inter-digital Capacitors (IDC), Coplanar Waveguides (CPW) phase shifters/delay lines are also designed and studied experimentally for low microwave power applications. Modelling problems of these devices and microwave losses in ferroelectrics are also discussed.

Experimental evidence of the size effect in thin ferroelectric films

The phenomenological model based on the Ginsburg–Devonshire equation has been applied to investigate the size effect in thin SrTiO3 and BaxSr1−xTiO3 films. The size effect is caused by two phenomena: spatial correlation of the polarization and boundary conditions for the ferroelectric polarization on electrodes. The experimental data obtained by different groups were used to investigate the boundary conditions. The most remarkable result was found for the SrRuO3/BaxSr1−xTiO3/SrRuO3 structure which is characterized by free boundary conditions for the ferroelectric polarization. Such boundary conditions provide the highest value of the effective dielectric constant of a dielectric layer in the sandwich structure. The strain dependence of the dielectric permittivity of SrTiO3 at finite temperatures was taken into account as well.

Commutation quality factor of two-state switchable devices

A unified way to characterize a two-state one-port switchable network is discussed in this paper. A figure-of-merit of the two-state one-port, called the commutation quality factor (CQF), is introduced. It can be applied to different types of switching devices (semiconductor, ferroelectric, superconductor, etc.) and used for a design of two-state components with optimal characteristics. The CQF is defined as the ratio of the input impedances of a lossless reciprocal two-port terminated in the impedance pair Z/sub 1/ and Z/sub 2/, provided the imaginary parts of both input impedances are zero. A simple formula is derived for a calculation of the CQF. The invariance of the CQF with respect to lossless reciprocal transformation is shown. The applicability of the CQF does not depend on the physical nature of the device. The CQF is a working tool for a selection of switching devices while designing electronically controlled microwave components and subsystems. The CQF is recommended to be used for determining the available minimum of insertion loss of a switching microwave component. Thus, the introduced CQF can be used for optimization of the switching microwave component designed.

Nonlinearity of superconducting transmission line and microstrip resonator

The simplest model of nonlinear response of a superconducting thin film is used for modeling the nonlinear phenomena in a superconducting transmission line and a microstrip resonator. The specified characteristic power of the transmission line is suggested to use as a fitting parameter for numerical description of the microstrip line nonlinearity at microwaves. Quantitative agreement of simulated and experimental data has been obtained for the incident power dependent transmission coefficient of a microstrip line section and a high quality microstrip resonator. Numerical results have also been obtained for the power of the third harmonic radiated from the nonlinear resonator.

Broadband digital phase shifter based on switchable right- and left-handed transmission line sections

A novel approach to design digital phase shifters with the operational bandwidth extended to one octave is presented. An original design of the broadband phase shifter based on switching between transmission lines (TLs) with positive and negative dispersions is considered. An artificial TL with the negative dispersion was implemented as a quasilumped-element coplanar structure using a multilayer technology. The simulated and measured performance of the 180/spl deg/ phase shifter is presented.

Modeling tunable bulk acoustic resonators based on induced piezoelectric effect in BaTiO[sub 3] and Ba[sub 0.25]Sr[sub 0.75]TiO[sub 3] films

Modeling tunable bulk acoustic resonators based on induced piezoelectric effect in BaTiO[sub 3] and Ba[sub 0.25]Sr[sub 0.75]TiO[sub 3] films