Y. Poplavko

Epitaxial Ba0.5Sr0.5TiO3 thin films for microwave phase shifters

Abstract A tunable phase shifter was fabricated with epitaxial Ba0.5Sr0.5TiO3 (BST) thin film and gold coplanar waveguide. BST thin film of the thickness ∼0.5 μm was deposited by laser ablation on the MgO(OOl) single crystalline substrate. Gold electrode of the thickness ∼2 μm was prepared by the sequence of thermal evaporation, electroplating, and wet etching. Epitaxial quality of the BST thin film was confirmed by X-ray diffraction. The microwave performance of phase shifter was measured at room temperature in the frequency range of 8–12 GHz, and with applied bias voltage of up to 30 V. Effect of Mn dopant in the epitaxial films was also considered.

Electrically Tunable Phase Shifters With Air-Dielectric Sandwich Structure

Abstract : Electrically tunable microwave phase shifter was developed by inserting dielectric slab and piezoelectric actuator inside a waveguide. Air-dielectric sandwich structure of dielectric material and thin air gap was placed inside a waveguide, where the thickness of air gap is controlled by the actuator. Small changes in the ratio between the thickness of dielectric material and air gap induce significant changes in the effective dielectric constant of the air-dielectric sandwich structure. Phase shifts of 20 ^ 200 degrees were realized with the dielectric materials such as (Mg, Ca)TiO3 while the thickness of air gap is changed between 0 to 30 micrometers by piezoelectric control. Since the dielectric ceramics has very small loss (tan delta ^ 10 (exp-4)) and the air gap has practically no loss, the total structure shows low insertion loss.

Low Loss Microwave Piezo-Tunable Devices

Tunable by the mechanical reconfiguration low loss dielectric filter and wide-band phase shifter are elaborated. Dielectric or metallic parts of device should have a piezo-dirigible air gap between them. Key idea is to provide strong perturbation in electromagnetic field in the region influenced by the mechanical control. Energy distribution within the device is controlled by fast piezo-actuator, and can be described as a change in the effective dielectric permittivity. Highly tunable devices are realized experimentally

Microwave examination of ferroelectric film quality

Abstract Microwave methods for thin ferroelectric film parameter investigations are classified, discussed and improved. Being non-electrode and in some cases non-contact these methods are non-destructive and the information about parameters of films can be obtained from a distance and even during the technological process. High-resistivity silicon or semi-insulated gallium arsenide wafer adds little to microwave absorption or reflection. On the contrary, the crucial factor for the latter is the ferroelectric film with its microwave dielectric dispersion. It is assumed that some of microwave methods would be used in various stages of ferroelectric-semiconductor device characterisation.

Tunable microstrip filter with piezo-moved ground electrode

New principle of microstrip resonators and filters tuning is developed and studied. Realized idea is the operation by the effective dielectric constant (/spl epsiv//sub eff/) of substrate using piezo-control. For that, between substrate and ground electrode a narrow air gap (/spl Delta/) is created, and its size is controlled by the piezoelectric plate. The change in /spl epsiv//sub eff/(/spl Delta/) leads to the variation of filter resonant frequency while quality factor is preserved.

Piezo-controlled microwave frequency agile dielectric devices

A novel approach, utilizing piezoelectric actuators to control filters, resonators, and phase shifters with the minimum insertion loss, is described. Tunable, low-loss microwave devices can be fabricated using composite structures in which effective dielectric constant, /spl epsi//sub ef/, is controlled by piezoelectrically induced changes in the energy distribution within the devices. With this approach, a high degree of tunability is possible while utilizing high Q dielectrics. These devices usually consist of two dielectric parts with an air gap between them. This gap has to be arranged to provide the largest perturbation in the electromagnetic field. By means of a fast piezoelectric mini-actuator, the size of the air gap is changed and as a result, the /spl epsi//sub ef/ can be tuned. This tuning is used for device control. Highly tunable (more than 20%) dielectric and metal ring resonators, as well as wide-band, low-loss phase shifters are realized experimentally.

Low loss phase shifter based on piezo-controlled layered dielectric structure

Layered structure made of high-/spl epsiv/ dielectric and piezo-controlled air slot, filling various type waveguides, is used as tunable low loss wide-band phase shifter. A contemporary piezoelectric actuator is employed for fast variation of air slot width. This alteration results in considerable change in effective dielectric constant /spl epsiv//sub ef/ of the structure. Using high quality microwave dielectrics, it is possible to realize low loss phase shifters in the microwave as well as in the millimeter wave region.

Non-resonant, electrode-less method for measuring the microwave complex permittivity of ferroelectric thin films

A procedure is described for measuring the complex permittivity of dielectric thin films with relatively large dielectric constants (e: about 102–104) and considerable losses (tan δ: about 10−3–1). The ferroelectric films studied here are deposited on a relatively low-e dielectric substrate and placed in the centre of a rectangular waveguide parallel to the direction of wave propagation. The dielectric constants and losses of thin films are determined not by the shift of the resonant peak, but by numerical analysis of measured scattering parameters using a vector network analyser. The proposed method does not require electrode deposition on the film surface, and provides the natural properties of the film without complications due to conductive electrodes and their interfaces.

Dielectric-air structure as a component of electromechanically controlled microwave devices

Dielectric-air structure located between ideal metal plates is analyzed. It is shown that efficient mechanical alteration of propagation constant in this structure could be achieved only for those modes with non-zero component of electrical field perpendicular to border between dielectric and air. Scattering problem for the structure was reduced by partial domain method to set of 1-rst type Fredholm integral equations for the unknown tangential components of electric and magnetic fields at the boundaries of partial domains. The set of integral equations was solved by method of moments.

Piezo-controlled dielectric phase shifter with microstrip and coplanar lines

Report presents design, simulation and study of new kind of microwave device, namely piezo-driven dielectric phase shifter. The study develops principles of hybrid type piezo-controlled devices.