Orientation of rapid thermally annealed lead zirconate titanate thin films on (111) Pt substrates
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The nucleation, growth, and orientation of lead zirconate titanate thin films prepared from organometallic precursor solutions by spin coating on (111) oriented platinum substrates and crystallized by rapid thermal annealing was investigated. The effects of pyrolysis temperature, post-pyrolysis thermal treatments, and excess lead addition are reported. The use of post-pyrolysis oxygen anneals at temperatures in the regime of 350-450 °C was found to strongly affect the kinetics of subsequent amorphous-pyrochlore-perovskite crystallization by rapid thermal annealing. The use of such post-pyrolysis anneals allowed films of reproducible microstructure and textures [both (100) and (111)] to be prepared by rapid thermal annealing. It is proposed that such anneals and pyrolysis temperature affect the oxygen concentration/average Pb valence in the amorphous films prior to annealing. Such changes in the Pb valence state then affect the stability of the transient pyrochlore phase and thus the kinetics of perovskite crystallization.
I. INTRODUCTION The crystallization of and, hence, resultant microstructure, texture, and ferroelectric properties of lead zirconate titanate (PZT) thin films are known to depend upon numerous parameters.1-2 Published techniques for the synthesis of PZT thin films can be divided into two categories: those that use in situ crystallization (i.e., crystallization during deposition) and those that involve post-deposition crystallization of a pre-existing amorphous layer. MOCVD and physical deposition at elevated temperatures fall into the former category.3'4 For in situ crystallization, O 2 partial pressure is known to be a critical process control parameter. The second category includes most chemical and low temperature physical deposition techniques. Fox and Krupanidhi5 demonstrated that the oxygen content of as-sputtered lead lanthanum titanate films had a profound effect on the transformation to perovskite during subsequent annealing. Oxygen deficient films fully transformed to perovskite, whereas pyrochlore formed when an excess of oxygen was present. This was shown to be related to Pb valence state, and independent of Pb content.5 The effects of annealing atmosphere (i.e., Po 2 ) o n perovskite crystallization from an amorphous phase have also been reported. Other thermal treatments, pre- and post-crystallization, are known to influence the nucleation, microstructure, texture, and electrical properties of PZT films.2 An investigation of the critical
a*On
leave from School of Physics, The University of Melbourne, Parkville, 3052, Victoria, Australia.
2540
http://journals.cambridge.org
J. Mater. Res., Vol. 9, No. 10, Oct 1994
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parameters for post-deposition crystallization of amorphous films derived from spin casting of sol-gel solutions is presented below. The chemical and thermal stability, crystallographic structure, and quality of the substrate material(s) also play key roles in the preparation of high quality PZT thin films.1'2'6'7 The most frequently reported s
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