Atomic layer deposition and solid phase epitaxy of BiFeO₃ and BaTiO₃ thin films

Aleksandr Plokhikh

doi:10.17918/00000759

Perovskites are one of the most popular functional materials. They exhibit different chemical and physical properties such as; electronic and ionic conductivity, metal-insulator behavior, high electron mobilities, ferroelectricity, ferromagnetism, multiferroic properties, and catalytic activity. This list of properties makes them a good choice for basic research and for various types of applications in microelectronic devices in form of thin film materials. Perovskites are commonly deposited by physical vapor deposition (PVD) and chemical vapor deposition (CVD), but these methods are limited in achieving high-aspect ratio structures and the use of ALD may extend the boundaries of perovskite applications. Atomic layer deposition (ALD) is a unique self-limiting thin-film deposition technique that allows obtaining conformal coatings on templates of almost any size, shape, and morphology. Unfortunately, ALD is not very suitable for obtaining complex compounds and is mainly used for the deposition of metals, simple oxides (such as Al₂O₃, HfO₂, ZrO₂), sulfides, etc. Another drawback of ALD is the fact that many of the obtained films have an amorphous structure. This work is focused on the investigation of different approaches in the deposition of Bi-Fe-O and Ba-Ti-O films, how they affect films structure, conformality, composition, and morphology. The processes of crystalline phase formation from amorphous phases are explored by various heating in-situ techniques such as X-ray diffraction (XRD), X-ray Photoemission Spectroscopy (XPS), transmission electron microscopy (TEM). The effects of film structure, substrates, and heating rates on crystallization on the nano- and macro-scale were investigated. The obtained results shed light on the problem of solid-state amorphous- crystalline film transformations due to the dearth of comprehensive studies. Obtained insights can be applied to understanding crystallization processes in many other amorphous and semi-crystalline films. The influences of annealing conditions, elemental compositions, and hetero-oxide layers on the morphology and physical properties of the film were investigated. The routes for obtaining films with exceptionally high conformality and attractive dielectric properties were obtained. The routes for low-temperature epitaxial integration of the BiFeO₃ and BaTiO₃/SrTiO₃ superlattices with perovskite buffer-layered Si were determined. Criteria of low-temperature crystallization were also investigated.

Atomic layer deposition and solid phase epitaxy of BiFeO₃ and BaTiO₃ thin films

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Atomic layer deposition and solid phase epitaxy of BiFeO₃ and BaTiO₃ thin films

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