Tunable dielectric properties of BST thin films for RF/MW passive components

Heteroepitaxial Ba0.6Sr0.4TiO3 films were deposited on (100) LaAlO3 and (100) MgO substrates via pulsed laser deposition. Film thickness varied from 22 nm to 1.15 mum. All films were examined with x-ray diffraction and cross-section FESEM to determine both epitaxy and thickness, and stoichiometry was confirmed with RBS measurements. Microwave dielectric measurements were carried out in the range of 1-20 GHz, using an interdigitated electrode array. The state of strain in the films as a function of thickness and substrate type was correlated with the observed capacitive tunability. The tunability for both film series was shown to exhibit markedly different behavior depending on the type of strain, compressive or tensile. Maximum dielectric tunabilities of similar to65% were achieved for the thickest films in both film sets, however the tunability of the thinnest films were much higher for the films grown on MgO.