Tunable Ferroelectric Acoustic Resonators in Monolithic Thin-Film Barium Titanate

TL;DR

This paper demonstrates the use of epitaxial barium titanate on silicon to create tunable, low-loss acoustic resonators operating in the sub-GHz range, with potential for reconfigurable RF filtering.

Contribution

It introduces a novel lateral excitation method for ferroelectric acoustic resonators in BTO membranes, enabling frequency tuning and mode coupling in a monolithic silicon platform.

Findings

Resonances at 300 MHz and 700 MHz with up to 8% electromechanical coupling.

Frequency tuning achieved with applied DC bias, showing a transition near 20 V.

Lateral excitation of symmetric Lamb modes in BTO membranes.

Abstract

The increasing development of wireless communication bands has motivated the development of compact, low-loss, and frequency adjustable RF filtering technologies. Acoustic resonators are the ideal solution to these requirements, and tunable implementations offer a path toward reconfigurable front ends. In this work, we investigate epitaxial barium titanate (BTO) grown on silicon as a platform for tunable acoustic resonators operating in the sub-GHz regime. We demonstrate lateral excitation of symmetric lamb (S0) modes in X-cut BTO membranes, in contrast to prior thickness-defined ferroelectric resonators. Devices are designed using finite-element simulations and fabricated with laterally patterned electrodes that enable overtone coupling to multiple resonant modes. Under applied DC bias, ferroelectric domains align, allowing electrical excitation, frequency tuning, and quality-factor enhancement of acoustic modes. Resonances near 300 MHz and 700 MHz exhibit electromechanical coupling up to 8% and bias-dependent frequency tuning, with a distinct transition in behavior near 20 V. These results highlight monolithic BTO on silicon as a promising material system for laterally excited, tunable acoustic resonators for reconfigurable RF applications.