Improving the temperature stability of tunable devices by using composition-spread epitaxial ferroelectric films
Phys. Rev. Materials 9, 064410 – Published 23 June, 2025
DOI: https://doi.org/10.1103/zm8l-nxct
Abstract
Achieving frequency tunability by utilizing material properties rather than altering geometric structures is highly attractive due to its lightness and processability. (BSTO) has been a widely used ferroelectric in tunable microwave devices due to its large dielectric constants, high electric field tunability, and low microwave losses. However, due to the narrow temperature range of the high tunability for conventional single-composition ferroelectric material, which can only be achieved in the vicinity of the Curie temperature (), this results in difficulty for the resulting devices to work stably in harsh operating environments. To overcome this challenge, thin films with gradient composition have emerged as a promising strategy to achieve improved dielectric tunability across a wide temperature range. In this study, we employed an advanced combinatorial synthesis technique to fabricate composition-spread BSTO films from to (i.e., ) on a single piece of substrate. By characterizing the complex impedances of interdigital capacitors (IDCs) with 270-µm width fabricated at different compositions of the film, we extract the doping dependencies of tunability and ferroelectric transition temperature, which qualitatively agree with the results from single-composition films. A comparison between short IDCs (nearly single-component) and composition-span IDCs demonstrated improvement in the temperature stability of composition-spread BSTO film. These findings prove the effectiveness of the combinatorial technique for optimizing the dielectric properties of ferroelectric materials.
