Electro-optic effect in thin film strontium barium niobate (SBN) grown by RF Magnetron Sputtering on SrTiO₃ substrates

Ferroelectric strontium barium niobate (Sr_xBa_1-xNb₂O₆ or SBN) is a material with high electro-optic (EO) response. It is currently of interest in low voltage silicon-integrated photonics (SiPh) as electronic integrated circuits have reached their scaling and power limits. We have grown textured SBN films by RF sputtering on a (100)-oriented SrTiO₃ substrate. Grains with predominantly (310) and (001) out-of-plane orientation have been identified. We demonstrate a maximum effective EO coefficient of 230 pm/V in such mixed orientation films using a transmission geometry that is responsive only to the in-plane polarization component. By using a TiO₂-terminated SrTiO₃ substrates, we can partly control the SBN orientation and obtain mostly (001)-oriented SBN films with out-of-plane polarization, which demonstrate a maximum effective Pockels coefficient of 88 pm/V.