Publication Type:Journal Article
Source:Journal of Applied Physics, Volume 100, Number 5 (2006)
Keywords:Epitaxial ferroelectric heterostructures, Epitaxial growth, Ferroelectric materials, Heterojunctions, Piezoelectric response, Polarization, Polydomain state, Switchable polarization, transmission electron microscopy, Ultrathin films
Scaling of the structural order parameter, polarization, and electrical properties was investigated in model ultrathin epitaxial SrRuO 3/PbZr 0.2Ti 0.8O 3/SrRuO 3/SrTiO 3 heterostructures. High-resolution transmission electron microscopy images revealed the interfaces to be sharp and fully coherent. Synchrotron x-ray studies show that a high tetragonality (c/a∼1.058) is maintained down to 50 Å thick films, suggesting indirectly that ferroelectricity is fully preserved at such small thicknesses. However, measurement of the switchable polarization (Δ3) using a pulsed probe setup and the out-of-plane piezoelectric response (d 33) revealed a systematic drop from ∼140 μC/cm 2 and 60 pm/V for a 150 Å thick film to 11 μC/cm 2 and 7 pm/V for a 50 Å thick film. This apparent contradiction between the structural measurements and the measured switchable polarization is explained by an increasing presence of a strong depolarization field, which creates a pinned 180° polydomain state for the thinnest films. Existence of a polydomain state is demonstrated by piezoresponse force microscopy images of the ultrathin films. These results suggest that the limit for a ferroelectric memory device may be much larger than the fundamental limit for ferroelectricity. © 2006 American Institute of Physics.
cited By 85