Interface-mediated dc electro-optic instability in lithium niobate nanophotonics

In certain materials, the linear electro-optic (Pockels) effect allows direct control of the refractive index with an applied electric field. In practice, material inhomogeneities and defects cause the field inside the material to drift over macroscopic time scales. Such phenomena degrade the reliability and stability of integrated electro-optic devices. Here, we combine systematic measurements of dc electro-optic response, electronic transport, and elemental composition to examine the microscopic origins of dc instability in nanofabricated thin-film lithium niobate (TFLN) devices. We identify two key sources of instability: the metal-LN contact interface where Schottky barriers impede charge injection, and the oxide-LN cladding interface where lithium diffusion occurs. Our work provides an electronic understanding of a long-standing photonics issue, advancing a potential pathway toward high-performance integrated electro-optic devices through materials-motivated design.