Composition/structure/property relations of multi-ion-beam reactive sputtered lead lanthanum titanate thin films: Part I
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K. L. More and L. F. Allard Oak Ridge National Laboratory, High Temperature Materials Laboratory, Oak Ridge, Tennessee 37831-6064 (Received 9 March 1992; accepted 22 July 1992)
Material properties are greatly dependent upon the structure of the material. This paper, the first of three parts, discusses how composition influences the crystallographic structure and microstructure of lead lanthanum titanate (PLT) thin films grown by the multi-ion-beam reactive sputtering (MIBERS) technique. A transmission electron microscopy (TEM) study detailing the relationship between crystallographic texturing and microstructure development will be presented in a second paper. The dependence of the ferroelectric properties on observed crystallographic structure and microstructure is presented in the third paper of this series. As-deposited PLT microstructures coincide with the structure zone model (SZM) which has been developed to describe the microstructure of thin films deposited by physical vapor deposition. The as-deposited PLT structures are altered during post-deposition annealing as a result of crystallization and PbO evaporation. Amorphous films with more than 10 mole % excess PbO become polycrystalline with porous microstructures after annealing. When there is less PbO in the as-deposited film, (100) texture and dense structures are observed. Porosity results from PbO evaporation, and (100) texture is inhibited by excess PbO.
I. INTRODUCTION The engineering of ferroelectric thin film devices, such as nonvolatile memories,1 pyroelectric sensors,2 piezoelectric SAW devices,3 and electrooptic modulators,4 is governed by the properties of the ferroelectric thin film material. These properties are controlled by the material structure from the device scale down to the atomic scale.5'6 Composition influences material structure on all scales, but composition generally becomes more important in smaller scale structures. At the atomic scale, the work of investigators, such as Goldschmidt and Pauling, has established a set of empirical rules that relate composition to crystallographic structure and predict phase formation.7'8 Many researchers have shown how composition influences microstructure through the formation of second phases or defects.9 Understanding of the relation among composition, crystallographic structure, and microstructure becomes critical to the production of Pb-based perovskite materials having optimum electrical properties.10 In thin films, composition and structural interdependencies remain influential, but the relations are extended to include the macroscopic or device structure. Since the scale of thin film device structure approaches the scale of thin film microstructure, composition can indirectly affect device structure through changes in microstructureJ. Mater. Res., Vol. 7, No. 11, Nov 1992 http://journals.cambridge.org
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controlled surface morphology. Therefore, the primary concern in ferroelectric thin film deposition must be the stringent control of composition. This three-part
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