Thick BaTiO₃ Epitaxial Films Integrated on Si by RF Sputtering for Electro-Optic Modulators in Si Photonics

Area of Science:

• Materials Science
• Thin Film Epitaxy
• Nanotechnology

Background:

• Barium titanate (BaTiO3) is a key material for electro-optic applications.
• Achieving high-quality, thick epitaxial BaTiO3 films is challenging but necessary for devices.
• Existing methods like molecular beam epitaxy (MBE) are slow.

Purpose of the Study:

• To develop a faster method for growing high-quality thick epitaxial BaTiO3 films.
• To investigate the structural and polarization properties of sputtered BaTiO3 films.
• To demonstrate the electro-optic performance of these films for integrated photonics.

Main Methods:

• Off-axis RF magnetron sputtering on SrTiO3-templated silicon-on-insulator (SOI) substrates.
• Atomic-resolution scanning transmission electron microscopy (STEM) with geometric phase analysis (GPA).
• Fabrication and testing of Mach-Zehnder modulators using sputtered BaTiO3 films.

Main Results:

• High-quality epitaxial BaTiO3 films grown 10x faster than MBE.
• Detailed analysis of lattice parameter and polarization changes within thick films.
• Demonstrated high effective Pockels coefficients (up to 183 pm/V) and functional modulators.

Conclusions:

• Sputtering is a viable, high-throughput method for producing thick epitaxial BaTiO3 films for electro-optics.
• Sputtered films retain out-of-plane polarization better than MBE films at larger thicknesses.
• These BaTiO3 films are suitable for integrated electro-optic modulators in silicon photonics.