Metallorganische Chemische Gasphasenabscheidung (MOCVD) ferroelektrischer Dünnschichten: Herstellung und Charakterisierung

Puchalla, Jochen

Dissertation / PhD Thesis/Book

Metallorganische Chemische Gasphasenabscheidung (MOCVD) ferroelektrischer Dünnschichten: Herstellung und Charakterisierung

Puchalla, J. (Corresponding author)FZJ*

2007
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich
ISBN: 978-3-89336-492-3

Jülich : Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag, Schriften des Forschungszentrums Jülich. Reihe Informationstechnik / Information Technology 17, 164 S. (2007) = RWTH Aachen, Diss., 2007

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Please use a persistent id in citations: http://hdl.handle.net/2128/3127

Abstract: The extended use of digital communication requires ever more powerful and faster memory with concurrently minimized energy consumption. Novel non-volatile memory using ferroelectric crystalline thin films (FeRAM) are a possible replacement for Flash- and DRAM-memory with equivalent or superior performance. Ferroelectric films consisting of lead zirconate titanate (PZT) are a promising candidate for the application in these memory devices. One problem for the application of PZT in memory devices is its high switching voltage which cannot be further reduced at film thicknesses below 100 nm. One aim of this work has been to study the effect of a material modification on the electronic properties of PZT based films with thicknesses in the area of 100 nm. For the first time a systematic examination on polycrystalline and epitaxial thin films of ferroelectric barium substituted lead zirconate titanate (Pb$_{1−x}$Ba$_{x}$)(Zr$_{1−y}$Ti$_{y}$)O$_{3}$ (PBZT) has been undertaken. These PBZT films have been synthesized by metal organic chemical vapour deposition (MOCVD). A process has been developed to deposit single-phase PZT based perovskite films with varying barium content, both in polycrystalline form on iridium covered silicon substrates and hetero-epitaxially on strontium ruthenate covered strontium titanate single crystals. By modification of the processing of polycrystalline PBZT films, a significant improvement of interface quality in comparison to pure PZT films has been shown successfully. The shifting of the morphotropic phase boundary to lower zirconium content, which has been observed by the insertion of barium into PZT ceramics, could also be verified in thin films by X-ray diffraction. The tetragonality in PBZT films decreases linearly with barium content. In epitaxial films it could be shown by the method of reciprocal space mapping that the tilting angle of a-domains in c-axis oriented films is also being decreased by increasing barium content. This tilting effect is partially compensated by substrate induced compressive stress, which is comparable in all films. The substitution of PZT with barium allows for the first time to study the influence of the tetragonality on the structural and electrical properties of the films. Only by variation of the zirconium content in pure PZT this influence is limited by the phase transition from the tetragonal to the rhombohedral structure. In epitaxial 110 nm thick films with tetragonal structure and (001) orientation the switching voltage has been successfully reduced from 1.5 V for pure PZT(29/71) to 0.9 V by the substitution of 11 at% barium in PZT. At the same time the remanent polarisation is being decreased by less than a factor of two from 52 μC/cm$^{2}$ to 29 μC/cm$^{2}$.

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