Figure of Merit and Limiting Characteristics of Tunable Ferroelectric Microwave Devices

Microwave application of ferroelectrics is very promising for electrically tunable microwave devices based on the electric field dependence of the dielectric permittivity. Tunable filters and controllable phase shifters are successfully designed as integrated circuits based on multilayer structures containing thin epitaxial ferroelectric (FE) film. As a rule lumped ferroelectric capacitors are used as the tunable components. Quality of the capacitor can be evaluated using Commutation Quality Factor (CQF). There is a unique connection between the Figure of Merit of a tunable microwave device and the CQF of the FE capacitors used. The Figure of Merit gives the upper limit of the quality of a tunable device based on the FE components.