Composition-spread Epitaxial Ferroelectric Thin Films for Temperature Insensitive Functional Devices

Abstract

Ba_xSr_1-xTiO₃(BST) ferroelectric thin films are widely used in microwave tunable devices due to their high dielectric constant, strong electric field tunability and low microwave loss. However, because of the temperature dependence of dielectric constant in ferroelectric materials, the high-tunability for conventional single component ferroelectric thin films can only be achieved in the vicinity of Curie Temperature (T_C) which results in that the ferroelectric thin films are difficult to apply to wide temperature range. To obtain ferroelectric thin films available for temperature stable functional devices, single composition Ba_0.2Sr_0.8TiO₃ thin films, Ba_0.5Sr_0.5TiO₃ thin films and heterostructure ofBa_0.2Sr_0.8TiO₃/Ba_0.5Sr_0.5TiO₃ thin films are deposited by pulsed laser deposition (PLD). By comparing with their dielectric properties in a wide temperature range, it’s found that the temperature sensitivity of BST films can be effectively reduced by introducing a composition gradient along the epitaxial direction. However, the heterostructure engineering may bring extra troubles caused by interfaces, which may limit the quality factor Q. In this paper, we extend our combinatorial film deposition technique to ferroelectric materials, and successfully fabricated in-plane composition-spread Ba_1-xSr_xTiO₃ thin films, which are expected to broaden the phase transition temperature range of BST films while avoiding the problem of interface control.