Epitaxial BaTiO₃ on Si(100) with In-Plane and Out-of-Plane Polarization Using a Single TiN Transition Layer

The integration of BaTiO3 with Si(100) is essential to exploit its ferroelectric capabilities in the well-established Si-complementary metal–oxide–semiconductor (CMOS) technological platform. To enable this goal, epitaxial BaTiO3 films with both in-plane and out-of-plane polarization are demonstrated on Si(100) with just a single TiN layer that is also CMOS-compatible. This change in polarization direction is brought about very simply by changing the growth temperature. Piezo force microscopy and optical second-harmonic generation measurements confirm the presence of out-of-plane and in-plane polarization. Films deposited at relatively higher temperatures of 800 °C have polarization lying in-plane at room temperature. The nonlinear dielectric susceptibilities were found to be comparable to the state-of-the-art films integrated with more complex transition schemes. Films deposited at a relatively lower temperature of 600 °C are defective and revert to 800 °C like films on annealing. The defects however confer on them an out-of-plane polarization with a large tetragonality of 1.6% at 500 °C. The changes in anomalous lattice expansion in out-of-plane coupled with coefficient of thermal expansion (CTE) strain result in orientation selection in our films.