Epitaxial∕amorphous Ba0.3Sr0.7TiO3 film composite structure for tunable applications

Abstract

A Ba0.3Sr0.7TiO3 (BST) thin film composite structure was fabricated by means of a selective epitaxial growth process. The epitaxial growth of BST on SrRuO3 electrode surface was selectively achieved at 485°C using a prepatterned ultrathin amorphous BST layer that locally prevented crystallization. This self-buildup mechanism resulted in a columnar composite structure, where epitaxial and amorphous BST columns are electrically connected in parallel. The effective permittivity of the composite capacitors decreased linearly upon increasing the amorphous BST concentration, while the tunability stayed fairly unchanged until it reached 70%. The results agree with the theoretical ferroelectric∕dielectric parallel composite model.