Ferroelectric domain architecture and poling of BaTiO3 on Si

Controlling the ferroelectric polarization at macroscopic or microscopic levels is crucial in the framework of the development of ferroelectric materials used in yet challenging photo-electrochemical (PEC) cells and spintronic applications. We report here on polarization methods allowing to electrically polarize prototypical samples of BaTiO 3 (001) films. Epitaxial single crystalline layers were grown up to a thickness of 25 nm by atomic oxygen assisted molecular beam epitaxy on 1 at.% Nb doped SrTiO 3 (001) single crystals. The samples were both microscopically and macroscopically polarized using Piezoresponse Force Microscopy and electrochemical poling in an electrolyte respectively. In addition we demonstrate the possibility to retrieve a quasi-native mixed ferroelectric polarization state after annealing. These polarization methods may be applied to many other ferroelectric thin films. Atomic oxygen molecular beam epitaxial method (AO-MBE) Piezo response and atomic force microscopy (PFM and AFM) Annealing Overcurrent

Scientific Reports, 2020

Skewed band structures have been empirically described in ferroelectric materials to explain the functioning of recently developed ferroelectric tunneling junction (FTJs). Nonvolatile ferroelectric random access memory (FeRAM) and the artificial neural network device based on the FTJ system are rapidly developing. However, because the actual ferroelectric band structure has not been elucidated, precise designing of devices has to be advanced through appropriate heuristics. Here, we perform angle-resolved hard X-ray photoemission spectroscopy of ferroelectric BaTiO3 thin films for the direct observation of ferroelectric band skewing structure as the depth profiles of atomic orbitals. The depth-resolved electronic band structure consists of three depth regions: a potential slope along the electric polarization in the core, the surface and interface exhibiting slight changes. We also demonstrate that the direction of the energy shift is controlled by the polarization reversal. In the f...

Journal of Physics: Condensed Matter, 2012

Recent works suggest that the surface chemistry, in particular the presence of oxygen vacancies, can affect the polarization in a ferroelectric material. This should, in turn, influence the domain ordering driven by the need to screen the depolarizing field. Here we show using density-functional theory that the presence of oxygen vacancies at the surface of BaTiO 3 (001) preferentially stabilizes an inward pointing, P-, polarization. Mirror electron microscopy measurements of the domain ordering confirm the theoretical results.

The potential distribution of BaTiO 3 single crystal ferroelectric domains was investigated by scanning Kelvin probe microscopy at room temperature with and without an electric field applied parallel to the (001) top surface. Immediate c domain surface potential inversion was observed after reaching the 6 V/mm critical electric field intensity followed by complete recovery upon switching the electric field off. Piezoresponse force microscopy was used to characterize domain structure evolution during the electric field application, which caused c domain motion. Newly formed domain patterns were stable for a month after switching the electric field off. Screening surface charges and their mobility play a dominant role in this experiment.

The potential distribution of BaTiO 3 single crystal ferroelectric domains was investigated by scanning Kelvin probe microscopy at room temperature with and without an electric field applied parallel to the (001) top surface. Immediate c domain surface potential inversion was observed after reaching the 6 V/mm critical electric field intensity followed by complete recovery upon switching the electric field off. Piezoresponse force microscopy was used to characterize domain structure evolution during the electric field application, which caused c domain motion. Newly formed domain patterns were stable for a month after switching the electric field off. Screening surface charges and their mobility play a dominant role in this experiment.

Physical Review Letters, 2007

We present molecular dynamics simulations of a realistic model of an ultrathin film of BaTiO3 sandwiched between short-circuited electrodes to determine and understand effects of film thickness, epitaxial strain and the nature of electrodes on its ferroelectric phase transitions as a function of temperature. We determine a full epitaxial strain-temperature phase diagram in the presence of perfect electrodes. Even with the vanishing depolarization field, we find that ferroelectric phase transitions to states with in-plane and out-of-plane components of polarization exhibit dependence on thickness; it arises from the interactions of local dipoles with their electrostatic images in the presence of electrodes. Secondly, in the presence of relatively bad metal electrodes which only partly compensate the surface charges and depolarization field, a qualitatively different phase with stripe-like domains is stabilized at low temperature.

Physical Review Materials, 2021

BaTiO 3 (BTO) is an emergent material in the field of silicon-integrated photonics, as its thin films have been demonstrated to have a very large electro-optic (Pockels) coefficient that can be used for optical modulators. However, BTO grown directly on SrTiO 3 (STO)-buffered Si (STO is required for epitaxial growth) initially grows with a polarization direction not suitable for the geometries currently used in photonic devices. Here, we grow BTO on a BaSnO 3-buffered STO substrate to form orthorhombic mm2 BTO, which has in-plane polarization orientation needed for photonic devices. Extensive crystalline characterization is done to confirm the high quality of the films, along with electro-optic measurements. Theoretical simulations coupled with the experimental results provide a foundational understanding of the properties of strain-stabilized orthorhombic BTO. Large electro-optic coefficients of 121 pm/V are observed in films as thin as 40 nm.

Physical Review Materials

Recent advances in epitaxial oxide deposition have enabled the fabrication of thick films of ferroelectric perovskite BaTiO3 capable of providing a robust electro-optic response via the Pockels effect in silicon photonic devices. We report a microstructure analysis of such films integrated on Si(001) by molecular beam epitaxy, showing how the crystallographic and polarization orientation change as a function of thickness. The measured electro-optic properties of the film correlate well with the microstructural analysis and demonstrate the potential of Siintegrated BaTiO3 for silicon photonics. An effective Pockels coefficient of up to 268 pm/V has been demonstrated in 110-nm-thick films in transmission measurements and 352 pm/V in waveguide measurements.

Integration of epitaxial complex ferroelectric oxides such as BaTiO 3 on semiconductor substrates depends on the ability to finely control their structure and properties, which are strongly correlated. The epitaxial growth of thin BaTiO 3 films with high interfacial quality still remains scarcely investigated on semiconductors; a systematic investigation of processing conditions is missing although they determine the cationic composition, the oxygen content, and the microstructure, which, in turn, play a major role on the ferroelectric properties. We report here the study of various relevant deposition parameters in molecular beam epitaxy for the growth of epitaxial tetragonal BaTiO 3 thin films on silicon substrates. The films were grown using a 4 nm-thick epitaxial SrTiO 3 buffer layer. We show that the tetragonality of the BaTiO 3 films, the crystalline domain orientations, and SiO 2 interfacial layer regrowth strongly depend on the oxygen partial pressure and temperature during the growth and on the post-deposition anneal. The ferroelectricity of the films, probed using piezoresponse force microscopy, is obtained in controlled temperature and oxygen pressure conditions with a polarization perpendicular to the surface. V

Journal of Applied Physics, 2001

The domain microstructure in an epitaxial thin film of Bi4Ti3O12 on a SrTiO3(001) substrate is studied by second harmonic generation measurements. The input polarization dependence of the second harmonic signal exhibits spatial symmetries that reflect the presence of eight different domain variants present in the film. A theoretical model is presented that explains the observed symmetries and extracts quantitative information on the nonlinear optical coefficients of the material and statistics of domain variants present in the film area being probed. The following ratios of nonlinear coefficients and birefringence was determined: d12/d11=−3.498±0.171, |d26/d12|=0.365±0.010, |d26/d11|=1.273±0.036, and |nb−na|=0.101±0.018 (at 532 nm).