Synthesis of BaTiO₃ Thin Films for Electro-Optic Applications

Electro-optic modulators form the backbone of efficient data transfer necessary for modern optical communications. These modulators directly connect a driving electric field with optical properties of a material, efficiently converting an electrical signal to an optical signal. Modern data centers and high speed internet, as well as sensing systems, heavily rely on these devices. The electro-optic modulators are often bulk crystals of lithium niobate with indiffused waveguides, limiting their size, speed, and efficiency. Although thin film lithium niobate offers improved scalability and higher bandwidth over its bulk counterpart, lithium oxides are not CMOS compatible and there is a growing need for higher bandwidth modulators with lower voltage requirements. Barium titanate (BaTiO₃) is an alternative material platform which exhibits an extremely high electro-optic coefficient (r₄₂ ~ 900 pm/V), a reasonably high band gap (> 3eV), a relatively high refractive index (n = 2.4), and is compatible with traditional CMOS processing. Scalable methods for creating high quality, single ferroelectric domain films of barium titanate are therefore extremely attractive for highly efficient modulators and integrated optical devices. Here we present our work using reactive sputtering to make thin films of BaTiO₃ and characterize this materials for electro-optic applications.