Microstructure and ferroelectric characteristics of ultra-thin BaTiO3 films

Microstructure studies of ultra-thin BaTiO3 thin films (2-10 nm thick) show nanodomains having a width as small as one unit cell. Only 180degrees nano-domains are formed in multi-domains structures. The domain-boundaries are formed at (001) twin boundaries. Most of the domains are oriented in parallel to the film plane but out-of-plane orientations are also observed. The films exhibit ferroelectric behavior characterized by a polarization hysteresis loop and a relatively fast switching time. A remnant polarization of about 0.5 muC/cm(2) and coercive field of 2.7 V/cm were measured in parallel to the film plane. Temperature-dependent measurements show two peaks of the dielectric constant at about 60degreesC and 115degreesC. These peaks are attributed to two transition temperatures associated with the orientation of the nano-domains relative to the film plane and stress.