Improved designs of tunable ferroelectric capacities for microwave applications

Epitaxial SrTiO3 films are deposited by on-axis magnetron sputtering on CeO2-buffered r-cut sapphire. The ferroelectric films possess low losses (e.g., tan δ≈0.001–0.004 at 300 K) and a large tunability at small electric fields. Different complex designs for ferroelectric capacities are prepared via dry etching ranging from standard designs to those in which the ferroelectric material is restricted to the gap of the capacity. The resulting capacity data can be explained in terms of an analytic model for parallel capacities. Due to modifications and optimization of the design, the quality factors for an improved capacity design exceeds the requirement for most applications K>45 already for extremely small voltages U≈18 V, which demonstrates the good properties of the design in combination with the quality of our ferroelectric films.