High Coupling Tunable Acoustic Resonators in Monolithic Barium Titanate

TL;DR

This paper demonstrates the fabrication and characterization of tunable acoustic resonators using epitaxial barium titanate membranes on silicon, achieving high electromechanical coupling and frequency tuning near 700 MHz.

Contribution

It introduces a novel lateral excitation method for BTO-based resonators with high coupling and tunability, advancing reconfigurable RF filter technology.

Findings

Resonators achieve a quality factor of 175 at 700 MHz.

Electromechanical coupling reaches up to 25.1%.

Frequency tuning of 2.3% (series) and 5.6% (parallel) achieved.

Abstract

The growing number of wireless communication bands has driven demand for compact, low-loss, and frequency adjustable RF filtering. Tunable acoustic resonators are well suited to address these needs, offering a path toward reconfigurable front ends with reduced component count. In this work, we extend upon previous conference results to investigate epitaxial barium titanate (BTO) grown on silicon as a platform for tunable acoustic resonators. We demonstrate lateral excitation of symmetric Lamb (S0) modes in 120 nm X-cut BTO membranes using a multi-cell electrode architecture that simultaneously achieves high electromechanical coupling and practical impedance levels. Devices are fabricated with laterally patterned electrodes on released BTO membranes. Under applied DC bias, ferroelectric domains align, allowing electrical excitation, frequency tuning, and quality-factor enhancement of acoustic modes. The primary resonance near 700 MHz exhibits a Bode quality factor of 175, electromechanical coupling up to 25.1%, and series and parallel resonance tunability of 2.3% and 5.6%, respectively. Voltage-dependent material parameters, including permittivity, stiffness, and piezoelectric coefficients, are extracted through a combination of modified Butterworth-Van Dyke modeling and finite-element simulation to explain the observed trends. These results highlight monolithic BTO on silicon as a promising material system for laterally excited, tunable acoustic resonators for reconfigurable RF applications.