%0 Journal Article
%K transmission electron microscopy
%K Polarization
%K Ferroelectric materials
%K Epitaxial growth
%K Heterojunctions
%K Piezoelectric response
%K Ultrathin films
%K Epitaxial ferroelectric heterostructures
%K Polydomain state
%K Switchable polarization
%A V Nagarajan
%A J Junquera
%A J.Q He
%A C.L Jia
%A R Waser
%A K Lee
%A Y.K Kim
%A Sunhee Baik
%A T Zhao
%A Ramamoorthy Ramesh
%A Ph Ghosez
%A K.M Rabe
%B Journal of Applied Physics
%D 2006
%G eng
%R 10.1063/1.2337363
%T Scaling of structure and electrical properties in ultrathin epitaxial ferroelectric heterostructures
%V 100
%X <p>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.</p>