Structures and dielectric properties of multilayer BST/ST/BST and ST/BST/ST sandwich structures

Multilayer thin films with sandwich structures of BST/ST/BST and ST/BST/ST were designed and prepared by sol-gel method on Pt/Ti/SiO2/Si substrates, and their structures and dielectric properties have been studied. Pure BST and ST films were also studied for comparison. X-ray diffraction reveals that all films grow along (110) orientation and show polycrystalline cubic perovskite structures. SEM shows that the BST/ST/BST film exhibits smaller grain size and better uniformity than the pure BST film. BST/ST/BST and ST/BST/ST films almost keep significantly high tunable capabilities of 40-50% at low applied voltage of +/- 10 V like the pure BST film, but show lower dielectric losses, resulting in higher figure of merit (FOM). Related mechanisms on such dielectric properties are analyzed by resistor-capacitor (RC) equivalent circuit models. Such sandwich structure design is a novel route for BST films to fulfill the tunable microwave application.