Comments on the effects of solution precursor characteristics and thermal processing conditions on the crystallization b
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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 R. W. Schwartz, J. A. Voigt, and B. A. Tuttle Sandia National Laboratories, Materials and Process Sciences Center, Albuquerque, New Mexico 87185
D. A. Payne Department of Materials Science and Engineering, Seitz Materials Research Laboratory, and Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801
T. L. Reichert and R. S. DaSalla Sandia National Laboratories, Materials and Process Sciences Center, Albuquerque, New Mexico 87185 (Received 31 January 1996; accepted 14 August 1996)
Lead zirconate titanate (PZT 40/60) thin films were fabricated on electroded silicon wafers using chemical solution deposition. Two different chelating agents, acetic acid and acetylacetone, were used in the synthesis of the precursor solutions. The microstructure of the acetylacetone-derived film was characterized by nucleation at the platinum electrode and a columnar growth morphology (,100 –200 nm lateral grain size). In contrast, the acetic acid-derived film was characterized by both columnar grains nucleated at the electrode, and larger (,1 mm) grains nucleated at the surface of the film. Using Fourier transform infrared (FTIR) diffuse reflectance spectroscopy, we also noted that the pyrolysis behavior of the films was dependent on the chelating agent employed. The acetylacetone-derived films, which displayed 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 variations in “precursor structure.” In this paper, we discuss an alternative mechanism for the observed microstructural variations in films prepared from different solution precursors. In the model proposed, we discuss how changes in film pyrolysis temperature result in a change in film crystallization temperature, and hence, a change in the effective driving force for crystallization. We show how the change in crystallization driving force is expected to impact the thin film microstructure due to the accompanying variations that occur in the barrier heights for interface (lower electrode) and surface nucleation. A standard approach to nucleation in glasses is used as the basis of the proposed model. Finally, we also discuss how the model can be used to understand the observed effects of heating rate and thickness on the microstructure of solution-derived thin films.
I. INTRODUCTION
Lead zirconate titanate (PZT) thin films have been widely investigated for use in a number of electronic applications including decoupling capacitors,1 nonvolatile memories,2 and optical storage media.3 In the preparation of these materials, chemical solution deposition (CSD) methodologies have been extensively employed. Two of the most widely used approaches are sol-gel processing, which for PZT fil
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