A new design of tunable ferroelectric capacitors in RF applications

Abstract

Epitaxial SrTiO 3 films are deposited by on-axis magnetron sputtering on CeO 2 buffered r-cut sapphire. The ferroelectric films indicate low losses (e.g. tan δ≈0.002–0.004 at 300 K) and a large tunability at small electric fields. Different complex designs for ferroelectric capacities are prepared via dry etching. The resulting capacity data can be explained in terms of an analytic model for parallel plate capacitors. The quality factors K [J. Supercond. 12 (2) (1999) 325] of a new capacity design exceeds the requirement for most applications K>50 already for small applied voltages U dc≈18 V, which demonstrates the good properties of the new design in combination with the quality of our ferroelectric films.