Characterizing piezoelectric response of thin-film barium titanate using surface acoustic wave resonators

Ferroelectric materials, with their strong piezoelectricity and optical nonlinearity, are crucial in modern electronic and photonic integrated circuits. Advances in nanofabrication now enable high-quality ferroelectric thin films that satisfy requirements for compact, low-cost, and energy-efficient devices. Among them, thin-film barium titanate (BTO) is a promising material widely explored for electro-optic modulation, though its piezoelectric properties lack a systematic study. This work investigates the piezoelectric response of RF-sputtered BTO thin films on silicon using surface acoustic waves (SAWs) excited by interdigital transducers. Acoustic resonators operating up to 7.6 GHz and electromechanical coupling of 8% are demonstrated. The extracted compliance tensor and piezoelectric coefficients are comparable to bulk BTO. Leveraging its switchable polarization, tunable microwave acoustic resonators are realized, relevant for next-generation reconfigurable RF systems. Furthermore, cryogenic characterizations down to millikelvin show only a modest reduction in piezoelectric response. These results highlight the excellent piezoelectric performance of thin-film BTO with the potential for advanced classical and quantum transducers.