COMMENTS ON THE EFFECTS OF SOLUTION PRECURSOR CHARACTERISTICS AND THERMAL-PROCESSING CONDITIONS ON THE CRYSTALLIZATION BEHAVIOR OF SOL-GEL DERIVED LEAD-ZIRCONATE-TITANATE THIN-FILMS

Lead zirconate titanate (PZT 40/60) thin films were fabricated on elec troded silicon wafers using chemical solution deposition. Two differen t chelating agents, acetic acid and acetylacetone, were used in the sy nthesis of the precursor solutions. The microstructure of the acetylac etone-derived film was characterized by nucleation at the platinum ele ctrode and a columnar growth morphology (similar to 100-200 nm lateral grain size). In contrast, the acetic acid-derived film was characteri zed by both columnar grains nucleated at the electrode, and larger (si milar to 1 mu m) grains nucleated at the surface of the film. Using Fo urier transform infrared (FTIR) diffuse reflectance spectroscopy, we a lso noted that the pyrolysis behavior of the films was dependent on th e chelating agent employed. The acetylacetone-derived films, which dis played only one nucleation event, were also characterized by a higher pyrolysis temperature than the acetic acid-derived films. Previously, microstructural differences of this nature were attributed to variatio ns in ''precursor structure.'' In this paper, we discuss an alternativ e mechanism for the observed microstructural variations in films prepa red from different solution precursors. In the model proposed, we disc uss how changes in film pyrolysis temperature result in a change in hi m crystallization temperature, and hence, a change in the effective dr iving force for crystallization. We show how the change in crystalliza tion driving force is expected to impact the thin film microstructure due to the accompanying variations that occur in the barrier heights f or interface (lower electrode) and surface nucleation A standard appro ach to nucleation in glasses is used as the basis of the proposed mode l. Finally, we also discuss how the model can be used to understand th e observed effects of heating rate and thickness on the microstructure of solution-derived thin films.