Epitaxial growth of ferroelectric oxide films

This review paper begins with a brief overview of the most common ferroelectric materials, the perovskites and the Aurivillius families. The epitaxial growth of ferroelectric epitaxial films can be a viable approach to improve the ferroelectric properties, in particular for the layered perovskites. Defects related to a polycrystalline structure, which lead to a degradation of ferroelectric properties like remanent polarisation, piezoelectric coefficient, charge retention, and may cause time-dependent fatigue problems, can be prevented. However, it is also to be considered that effects connected with thin films like substrate clamping, strain or finite thickness may limit the film properties. Substitution of elements allows the adjustment of the film characteristics to the device function. Additionally, the orientation of the films can be controlled by the appropriate choice of the substrate, which is important due to the anisotropy of the ferroelectrics.The deposition methods commonly used for ferroelectric oxide layers are reviewed, particularly with regard to epitaxial growth. The conditions under which stoichiometric, crystalline growth can be obtained are described. The paper primarily focuses on the MO-CVD technique.Furthermore whether epitaxial growth of ferroelectric films occurs or not depends on several conditions like lattice mismatch between film and substrate, surface orientation and crystal symmetry of the substrate, thermal expansion of film and substrate. The influence of these parameters on epitaxial growth is discussed. Local epitaxial growth of ferroelectric layers on metallic electrodes is also mentioned due to its importance in device fabrication. The site-engineering concept is shortly reviewed as the substitution of elements constitutes a simple way to modify film properties in thin film technology.