Tunable Ferroelectric Acoustic Resonators in Monolithic Thin-Film Barium Titanate

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.

Figures (6)

• Figure 1: Device optical image showing dimensions and electrode layout.
• Figure 2: COMSOL admittance simulation shows S0 overtones and their stress profiles.
• Figure 3: XRD 2$\theta$ scan measurements showing peak slightly lower than 45 degrees, with inset of RHEED pattern.
• Figure 4: (a) 0V versus 20V DC Bias wide admittance measurement (b) zoom of mode at 300 MHz showing $k^2$ and $Q$, and (c) same zoom of mode at 700 MHz.
• Figure 5: Mode 1 at 300 MHz and mode 2 at 700 MHz behaviors versus applied DC bias showing electromechanical coupling, series quality factor, and series resonance frequency.