Nonlinear ceramics for tunable microwave devices part I: materials properties and processing

Nonlinear dielectrics are promising materials for tunable microwave components. However, dielectric loss, tunability, and temperature dependence of such dielectrics are crucial parameters and have to be optimized for an application as microwave device. In part I of this split publication, the impact of doping and processing on the material performance of Ba0.6Sr0.4TiO3 (BST) ceramics and thick films are presented. A phenomenological model developed by Vendik (Vendik and Zubko 2000) was used to characterize the influence of doping on the material performance of BST as tunable microwave dielectrics. It is shown that acceptor (iron, Fe)-donor (fluoride, F) codoping can positively influence the tunability of BST fundamentally. This impact is interpreted by charged defects influenced by doping and/or related defect formations. In addition to doping, it is shown that thermal treatment of powders and thick films as well as the deposition method show a strong impact on dielectric performance of the final thick-films. In the following part II, metallization, component design, and RF-characterization of tunable microwave devices will be discussed.