Off-axis RF-sputtered barium titanate thin films for next-generation electro-optic devices

In this work, we report the growth of 300 nm c-axis oriented barium titanate (BTO) films on (001)-strontium titanate (STO) substrates via off-axis radio frequency (RF) sputtering. The as-grown films exhibit exceptional crystallinity, with a rocking curve full width at half maximum of ∼0.03°, and atomically smooth surface morphology with a root mean square roughness of 0.23 nm, ensuring minimal optical losses. Transmission ellipsometric characterization of the film reveals a record-high electro-optic (EO) coefficient, r51 ∼ 550 pm V−1 that exceeds by a factor of 3 compared to the previously reported values for RF-sputtered BTO. This high-quality, industry-compatible material paves the way for the development of efficient and compact EO modulators based on hybrid BTO-on-silicon waveguides.