A review of molecular beam epitaxy of ferroelectric BaTiO3 films on Si, Ge and GaAs substrates and their applications

SrTiO3 epitaxial growth by molecular beam epitaxy (MBE) on silicon has opened up the route to the monolithic integration of various complex oxides on the complementary metal-oxide-semiconductor silicon platform. Among functional oxides, ferroelectric perovskite oxides offer promising perspectives to improve or add functionalities on-chip. We review the growth by MBE of the ferroelectric compound BaTiO3 on silicon (Si), germanium (Ge) and gallium arsenide (GaAs) and we discuss the film properties in terms of crystalline structure, microstructure and ferroelectricity. Finally, we review the last developments in two areas of interest for the applications of BaTiO3 films on silicon, namely integrated photonics, which benefits from the large Pockels effect of BaTiO3, and low power logic devices, which may benefit from the negative capacitance of the ferroelectric. © 2015 National Institute for Materials Science161711sciescopu

Atomic-layer deposited thulium oxide as a passivation layer on germanium

A comprehensive study of atomic-layer deposited thulium oxide (Tm2O3) on germanium has been conducted using x-ray photoelectron spectroscopy (XPS), vacuum ultra-violet variable angle spectroscopic ellipsometry, high-resolution transmission electron microscopy (HRTEM), and electron energy-loss spectroscopy. The valence band offset is found to be 3.05 ± 0.2 eV for Tm2O3/p-Ge from the Tm 4d centroid and Ge 3p3/2 charge-corrected XPS core-level spectra taken at different sputtering times of a single bulk thulium oxide sample. A negligible downward band bending of ∼0.12 eV is observed during progressive differential charging of Tm 4d peaks. The optical band gap is estimated from the absorption edge and found to be 5.77 eV with an apparent Urbach tail signifying band gap tailing at ∼5.3 eV. The latter has been correlated to HRTEM and electron diffraction results corroborating the polycrystalline nature of the Tm2O3 films. The Tm2O3/Ge interface is found to be rather atomically abrupt with sub-nanometer thickness. In addition, the band line-up of reference GeO2/n-Ge stacks obtained by thermal oxidation has been discussed and derived. The observed low reactivity of thulium oxide on germanium as well as the high effective barriers for holes (∼3 eV) and electrons (∼2 eV) identify Tm2O3 as a strong contender for interfacial layer engineering in future generations of scaled high-κ gate stacks on Ge

Structural and electrical properties of Er-doped HfO2 and of its interface with Ge (001)

International audienceEr-doped HfO"2 thin films with Er content ranging from 0% to 15% are deposited by atomic layer deposition on native oxide free Ge(001). The crystallographic phase is investigated by X-ray diffraction and is found to depend on the Er%. The cubic fluorite structure develops on Ge for Er% as low as 4% and is stable after annealing at 400^oC in N"2. Microstrain increases with increasing the Er content within the fluorite structure. Time of flight secondary ion mass and electron energy loss spectroscopy evidence a Ge diffusion from the substrate that results in the formation of a Ge-rich interfacial region which does not present a structural discontinuity with the oxide. The diffusion of Ge is enhanced by the annealing and causes a reordering of the crystal lattice. In annealed films the interface defect density measured by low temperature conductance measurements is found to decrease with decreasing the Er content

Quantitative mapping of strain and displacement fields over HR-TEM and HR-STEM images of crystals with reference to a virtual lattice

International audienceA method for the reciprocal space treatment of high-resolution transmission electron microscopy (HR-TEM) and high-resolution scanning transmission electron microscopy (HR-STEM) images has been developed. Named “Absolute strain” (AbStrain), it allows for quantification and mapping of interplanar distances and angles, displacement fields and strain tensor components with reference to a user-defined Bravais lattice and with their corrections from the image distortions specific to HR-TEM and HR-STEM imaging. We provide the corresponding mathematical formalism. AbStrain goes beyond the restriction of the existing method known as geometric phase analysis by enabling direct analysis of the area of interest without the need for reference lattice fringes of a similar crystal structure on the same field of view. In addition, for the case of a crystal composed of two or more types of atoms, each with its own sub-structure constraint, we developed a method named “Relative displacement” for extracting sub-lattice fringes associated to one type of atom and measuring atomic columns displacements associated to each sub-structure with reference to a Bravais lattice or to another sub-structure. The successful application of AbStrain and Relative displacement to HR-STEM images of functional oxide ferroelectric heterostructures is demonstrated

Combining HRTEM-EELS nano-analysis with capacitance-voltage measurements to evaluate high-kappa thin films deposited on Si and Ge as candidate for future gate dielectrics

International audienceAberration corrected transmission electron microscopy and electron spectroscopy are combined with electrical measurements for the quantitative description of the structural, chemical and dielectric parameters of rare earth/transition metal oxides thin films. Atomic structure near the interface and elemental profiles across the interface up to the surface of La-doped ZrO2 and Er-doped HfO2 films prepared by atomic layer deposition on Si(100) and Ge(100) are determined. Interfacial layers unavoidably form between the semiconductor substrate and the dielectric oxide after deposition and annealing. They are evidenced from a structural and chemical point of view. From the knowledge of the chemical extent of the interfacial layer and of the accumulation capacitance of the stack, it is possible to recover the dielectric constant of both the interfacial layer and the high-κ oxide layer constituting the stack using a multi-layers capacitor model approach. Oxides with permittivities higher than 30 are stabilized. Interfacial layers, silicate/germanate in composition, with permittivites, respectively, tripled/doubled compared to the one of SiO2 are evidenced

Influence of La on the electrical properties of HfSiON: From diffusion to Vth shifts

We investigated the dependence of the electrical properties of TiN/La2O3/HfSiON/SiO2/Si-substrate stacks with 15 nm thick HfSiON layers on annealing temperature and time. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and capacitancevoltage (CV) measurements were used to characterize the La depth profiles and the electrical properties. We found that the threshold voltage (Vth) shift after annealing correlates linearly with the total amount of La diffused into the HfSiON rather than with the La concentration at the HfSiON/SiO2 interface. This unexpected behavior can be explained by the decreased thermal stability of thick (>2 nm) HfSiON layers which probably leads to phase separation during annealing and therefore to HfO2/SiO2 interfaces all over the stack

Multi-scale analysis of the dielectric properties and structure of resin/carbon-black nanocomposites

Dielectric properties of resin/carbon-black nanocomposites were measured and shown to differ from results given by a random sets modeling approach. The origin of the discrepancies was traced back to the presence of sets of carbon planes, detached from the carbon-black particles during the composite preparation. These planes are dispersed in the resin matrix and are nearly invisible, even in HRTEM images. EELS measurements revealed the signature of bonding states typical of graphite-like compounds, in regions of the matrix previously supposed to be free of carbon-black. A new approach to texture characterization of HRTEM images, using Haralick parameters based on pixel intensity co-occurrence matrices, showed strong differences between pure resin and regions of the composite between carbon particles. The nano-scale characterization results explain the values obtained in macroscopic measurements

Atomic layer deposition of LaxZr1-xO2-delta (x=0.25) high-k dielectrics for advanced gate stacks

International audienceThin LaxZr1−xO2−δ (x=0.25) high permittivity (k) films are grown on Si(100) by atomic layer deposition at 300 °C using (PirCp)3La, (MeCp)2ZrMe(OMe) and O3 species. Their properties are studied by grazing incidence x-ray diffraction, high resolution transmission electron microscopy, electron energy loss spectroscopy, x-ray photoelectron spectroscopy, and electrical measurements on the as-grown films and after vacuum annealing at 600 °C. Annealed films feature resistance to hygroscopicity, a large k value of around 30 and an acceptable leakage current density. A low-k silica-rich interlayer is also evidenced at both pristine and annealed high-k/Si interfaces

Ultra Low Energy Ion Beam Synthesis: An Original Method for the Fabrication of Nanocrystals in Dielectrics for Nanoelectronics, Nano-Optics and Plasmonic Applications

International audienc

Epitaxial growth by molecular beam epitaxy of ferroelectric BaTiO3 on silicon

8-9 décembre 2014International audienceno abstrac