Growth Of BaTiO3 Thin Films Research Articles

Stoichiometric Control and Optical Properties of BaTiO3 Thin Films Grown by Hybrid MBE

AbstractBaTiO3 is a technologically relevant material in the perovskite oxide class with above‐room‐temperature ferroelectricity and a very large electro‐optical coefficient, making it highly suitable for emerging electronic and photonic devices. An easy, robust, straightforward, and scalable growth method is required to synthesize epitaxial BaTiO3 thin films with sufficient control over the film's stoichiometry to achieve reproducible thin film properties. Here the growth of BaTiO3 thin films by hybrid molecular beam epitaxy is reported. A self‐regulated growth window is identified using complementary information obtained from reflection high energy electron diffraction, the intrinsic film lattice parameter, film surface morphology, and scanning transmission electron microscopy. Subsequent optical characterization of the BaTiO3 films by spectroscopic ellipsometry revealed refractive index and extinction coefficient values closely resembling those of stoichiometric bulk BaTiO3 crystals for films grown inside the growth window. Even in the absence of a lattice parameter change of BaTiO3 thin films, degradation of optical properties is observed, accompanied by the appearance of a wide optical absorption peak in the IR spectrum, attributed to optical transitions involving defect states present. Therefore, the optical properties of BaTiO3 can be utilized as a much finer and more straightforward probe to determine the stoichiometry level present in BaTiO3 films.

Novel fractal analysis of nanograin growth in BaTiO3 thin film

The grain size and the ferroelectric morphology are the two most important factors in the research and development of advanced dielectric devices. It is important to synthesize nanostructures in order to achieve optimal grain size and inhibit grain growth while controlling the sintering parameters. It is also important to find new methods to study the grain growth during densification. BaTiO3 films were successfully obtained via the sol-gel spin coating method.In this paper, we report the deposition of nanostructured BaTiO3 thin film by spin coating of sol-gel precursors. The densification, grain growth and microstructure evolution have been studied. Moreover, a novel physical and mathematical fractal analysis have been applied successfully to the densification and nano grain growth of BaTiO3 thin film. The discrepancy between the fractal dimension and the grain growth with increasing temperatures and soaking time are presented and discussed.

Solvothermal growth of BaTiO3 thin films on Ti foils at T ≤ 200 °C with ferroelectric behavior

Polycrystalline BaTiO3 thin films were grown solvothermaly on titanium foil by introducing barium hydroxide solution in a Teflon line and allowed to react with the foil during the autoclave process. Different molar concentration of Ba(OH)2 were investigated: 0.5, 1 and 2 mol·L−1 with three heating temperatures: 150, 175 and 200 °C. The films were characterized by XRD and revealed characteristic peaks of BTO with a slight preferential orientation along the [00l] directions. The SEM characterizations showed dense thin films with spherical grains. The relative permittivity is about 400 and dielectric losses below 0.05 in the frequency range 102 to 107 Hz.

Theoretical Study of the Reaction Mechanism Ba, Ti, O in the Early Growth of BTO Thin Films

We use the DMol3 program based on density functional theory(DFT) to clarify the processes of microcosmic reactions and the particle states in the early growth of BaTiO3 (BTO) thin films. This research is important for optimal preparation and structure control of BTO thin films. After designing and optimizing some possible intermediate states, we find that the molecules may serve as nucleation sites for BTO growth. This occurs by combining TiO2 with BaO molecules to form BaTiO3 with the G conformation, which is similar to a quarter of a BTO unit cell. By virtue of understanding these mechanisms, perovskite-structured BTO thin films are formed.

In-situ x-ray diffraction study of the growth of highly strained epitaxial BaTiO3 thin films

In-situ synchrotron x-ray diffraction was performed during the growth of BaTiO3 thin films on SrTiO3 substrates using both off-axis RF magnetron sputtering and pulsed laser deposition techniques. It was found that the films were ferroelectric during the growth process, and the presence or absence of a bottom SrRuO3 electrode played an important role in the growth of the films. Pulsed laser deposited films on SrRuO3 displayed an anomalously high tetragonality and unit volume, which may be connected to the previously predicted negative pressure phase of BaTiO3.

Piezoresponse Force Microscopy Study of Ferroelectric BaTiO<sub>3</sub> Thin Film Directly Deposited on Si(001) by Magnetron Sputtering

Direct integration of ferroelectrics with semiconductors is critical to lower the cost and simplify the production procedures for data storage/processing components and miniature sensor/actuator development. By optimizing magnetron sputtering parameters, highly <001> preferential growth of BaTiO3 thin films with reproducible ferroelectric responses have been achieved on Si (001) substrates. The thin film ferroelectric characteristics were systematically studied by piezoresponse force microscopy, and a piezoelectric coefficient d33 of 24pm/V has been measured. It is found that the scanning tip sidewall angle and cantilever tilt affect the contour and size of polarized area.

Surface composition of BaTiO3/SrTiO3(001) films grown by atomic oxygen plasma assisted molecular beam epitaxy

We have investigated the growth of BaTiO3 thin films deposited on pure and 1% Nb-doped SrTiO3(001) single crystals using atomic oxygen assisted molecular beam epitaxy and dedicated Ba and Ti Knudsen cells. Thicknesses up to 30 nm were investigated for various layer compositions. We demonstrate 2D growth and epitaxial single crystalline BaTiO3 layers up to 10 nm before additional 3D features appear; lattice parameter relaxation occurs during the first few nanometers and is completed at ∼10 nm. The presence of a Ba oxide rich top layer that probably favors 2D growth is evidenced for well crystallized layers. We show that the Ba oxide rich top layer can be removed by chemical etching. The present work stresses the importance of stoichiometry and surface composition of BaTiO3 layers, especially in view of their integration in devices.

Molecular beam epitaxy growth of BaTiO3 thin films and crucial impact of oxygen content conditions on the electrical characteristics

In this study, high quality crystalline BaTiO3 films were fabricated in different oxygen content conditions on Nb-doped SrTiO3 (001) substrates by molecular beam epitaxy (MBE). BaTiO3 epitaxial film presents a critical thickness of 6.4nm and is almost entirely relaxed on SrTiO3 with a thickness of ~50nm. The electrical properties of 50nm strain-free BaTiO3 films were investigated by both macro- and microscopic measurements. Their electrical characteristics were found to be strongly influenced by different oxygen content conditions used during the preparation or annealing of the samples. Limited molecular oxygen partial pressure in a MBE chamber probably leads to a great amount of oxygen vacancies in the oxide film and results in rectification behavior of the oxygen-deficient BaTiO3-x/SrTiO3:Nb interface. Several approaches such as using atomic oxygen ambiance during the growth, annealing under elevated oxygen pressure were employed in order to decrease the oxygen vacancy density and these approaches eventually permit obtaining BaTiO3 films with good ferroelectric characteristics.

Submonolayer growth of BaTiO3 thin film via pulsed laser deposition: A kinetic Monte Carlo simulation

Distinguishing with the traditional solid-on-solid model, the adatom bonding is specially considered to describe the atom combined according to the perovskite structure, and the pulsed laser deposition growth of the perovskite thin film on the surface of square lattice substrate of homoepitaxial system is considered as three stochastic incidents such as the deposition, diffusion, and bonding of adatoms. We proposed an energy-dependent kinetic Monte Carlo approach to simulate BaTiO3 thin film growth via pulsed laser deposition within the submonolayer regime, in which the coverage θ is less than 1. In the simulation, first- and second-nearest-neighbor interactions are taken into account by the Born–Mayer–Huggins potential. Varying the values of the laser repetition rate and pulse duration, the relative curves of the island density and island size versus coverage were obtained. The simulation results show that the island density increases, while the island size decreases with the pulse frequency. When the pulse repetition rate is less than 1 kHz, there is no obvious variation for the curves of the island density and island size versus coverage. However, when the pulse repetition rate is larger than 1 kHz, the island density does not change for θ<0.1, and with the pulse duration, the island density increases while the island size decreases for θ>0.1. They are in good agreement with the previous experimental observations. It provides an understanding of the evolution of the morphology of the BaTiO3 thin film in submonolayer growth and a basic exploration of the epitaxial growth process of ionic oxides with perovskite-type structures.

Kinetic Monte Carlo simulation of RHEED from BaTiO3 thin films

Abstract We proposed an energy-dependent kinetic Monte Carlo approach to simulate the reflection high-energy electron diffraction intensity during the three-dimensional growth of BaTiO3 thin film using pulsed laser deposition. In the simulation, we employed the Born–Mayer–Huggins potential and assumed the overhanging of atoms in the deposition and diffusion process. The factors considered include the incident kinetic energy, laser repetition rate and mean deposition rate. By changing the values relative to every factor, the effects on the reflection high-energy electron diffraction (RHEED) intensity were studied. Being in good agreement with the experimental observations, the results provide an understanding on the evolution of the morphology about BaTiO3 thin film and a basic exploration of the epitaxial growth process of ionic oxides with perovskite-type structures.

Kinetic Monte Carlo simulation of growth of BaTiO3 thin film via pulsed laser deposition

Considering the characteristics of perovskite structure, a kinetic Monte Carlo(KMC) model, in which Born-Mayer-Huggins(BMH) potential was introduced to calculate the interatomic interactions and the bonding ratio was defined to reflect the crystallinity, was developed to simulate the growth of BaTiO3 thin film via pulsed laser deposition(PLD). Not only the atoms deposition and adatoms diffusion, but also the bonding of adatoms were considered distinguishing with the traditional algorithm. The effects of substrate temperature, laser pulse repetition rate and incident kinetic energy on BaTiO3 thin film growth were investigated at submonolayer regime. The results show that the island density decreases and the bonding ratio increases with the increase of substrate temperature from 700 to 850 K. With the laser pulse repetition rate increasing, the island density decreases while the bonding ratio increases. With the incident kinetic energy increasing, the island density decreases except 6.2 eV<Ek<9.6 eV, and the bonding ratio increases at Ek<9.6 eV. The simulation results were discussed compared with the previous experimental results.

Influences of particle size upon room temperature structure of BaTiO3 thin films on p-Si substrates

The current study performed the growth of BaTiO3 thin film on p-Si substrate by using RF-Magnetron sputtering system and the effects of thickness and particle size of the thin film on several structural characteristics of thin film were investigated. Initially, the interrelationship between the thickness and particle size of thin film was elucidated. Based upon the results obtained, the systematic study was made to evaluate the influences of particle size of BaTiO3 thin film on crystal quality, crystal structure, lattice parameter, tetragonality, and stress. In case of BaTiO3 thin film made of specific particle size less than 45 nm as in the current study, the XRD peak at (200) and Raman’s 630 cm−1 band, both typical for cubic BaTiO3, were observed at room temperature. In addition, the lattice parameter was increased and the tetragonality was decreased with the decrease of particle size. It was thus found that the particle size of that range could lead to the formation of cubic crystal structure even at room temperature. It was also shown that the decease of particle size results in the reduction of the stress applied to thin film. It was therefore demonstrated for the first time in this study that one can determine the room temperature crystal structure of BaTiO3 thin film simply by controlling its particle size.

Hydrothermal growth of BaTiO3 thin films on printed circuit boards for integral capacitor applications

Polycrystalline BaTiO3 films were hydrothermally grown on Ti-coated substrates from 80∘C to 200∘C. Films grown at 200∘C exhibited the lowest dielectric loss of around 0.1. Proton incorporation was more severe for the 80∘C film resulting in higher dielectric losses and leakage currents about two orders of magnitude higher. Post deposition oxygen plasma treatment removed incorporated protons and reduced the loss tangent but did not reduce defect density. As such, the leakage current of the 80∘C film remained high. The films had dielectric constants of 275 to 675 from 100 Hz to 100 kHz and a value of 67 from 100 MHz to 3 GHz.

A Very Low-Temperature Growth of BaTiO3 Thin Film by Hydrothermal Treatment Following Sol-Gel Coating at 200 Degree Celsius

BaTiO3 thin films with perovskite structure have been prepared on Pt/Ti/SiO2/Si substrate using a combined process of conventional sol-gel process and a hydrothermal treatment at 200°C. The sol-gel films were spin-coated on Pt/Ti/SiO2/Si. After drying, were treated in an autoclave with Ba(OH)2 solution, and finally followed by post-baking at 200°C for 60 minutes. The crystallization temperature of the organic gel film can be much lowered by reaction with OH− solution in a high hydrothermal pressure. The structure development, stoichiometry, spectroscopic, and dielectric properties of BaTiO3 thin films have been systematically investigated. X-ray diffraction patterns show that well-developed crystallites with a pure perovskite phase have been formed. It was found from XPS analysis that the peak of carbon contained in the gel film was diminished by the hydrothermal treatment. From dielectric characterizations, the 500 nm BaTiO3 film showed dielectric constant of 20, and leakage current density of less than 1 × 10−7 A/cm2 at 50 kV/cm, respectively.

A Very Low-Temperature Growth of BaTiO3 Thin Film by Hydrothermal Treatment Following Sol-Gel Coating at 200 Degree Celsius

A Very Low-Temperature Growth of BaTiO3 Thin Film by Hydrothermal Treatment Following Sol-Gel Coating at 200 Degree Celsius

Epitaxial Growth of BaTiO3 Thin Films by High Gas Pressure Sputtering

Heteroepitaxial BaTiO3 thin films with lattice-misfit strain were prepared on SrRuO3/SrTiO3 substrates by rf magnetron sputtering under high gas pressure, in order to realize large area deposi-tion with uniform ferroelectric properties. Lattice constants, composition and ferroelectric properties of the epitaxial BaTiO3 films were characterized as a function of pressure as well as the incident angle of sputtered particles, under the assumption that the sputtered particles were eradiated from the eroded area of the target surface. Although ferroelectric properties of films sputtered under low gas pressure had remarkable place dependability, they have been drastically improved by high gas pressure sputtering. X-ray diffraction analyses revealed that the BaTiO3 film deposited with a pressure of 6.3 Pa had a large lattice strain of 5%, even though the substrate was placed at a position directly facing the erosion area of the target, where a number of high-energy ions such as oxygen ions are thought to collide against the film surface if the pressure is low. The BaTiO3 film exhibited a ferroelectric hysteresis loop with remnant polarization of 43 µC/cm2. These results indicate that high gas pressure sputtering is effective for achieving large area uniformity of ferroelectric properties in heteroepitaxial BaTiO3 thin films.

Atomic scale epitaxial growth of BaTiO3 thin films by laser molecular beam epitaxy

By using laser molecular beam epitaxy (L-MBE), atomic scale epitaxid growth of BaTiO3(BTO) thin films on SrTiO3 (STO) substrates is achieved. Measurements of reflection high energy electron diffraction (RHEED), X-ray diffraction (XRD), scanning electron microscopy, and transmission electron microscopy reveal that the BTO films arec-axis oriented single crystals with smooth surface. The multi-layer ferroelectric/superconducting heterostructures are also prepared and the ferroelectric properties of BTO films are studied. The results show that by using L-MBE technique, high quality BTO films and improved device performance can be obtained.

Epitaxial growth of BaTiO3 thin films by plasma-enhanced metalorganic chemical vapor deposition

High-quality BaTiO3 thin films have been epitaxially grown on (001) LaAlO3 and (001) NdGaO3 substrates by plasma-enhanced metalorganic chemical vapor deposition at a substrate temperature of 680 °C. X-ray diffraction θ–2θ, ω, and φ scan results all indicate that single-crystalline BaTiO3 thin films were epitaxially grown on the substrates with 〈100〉 orientation perpendicular to the substrates. The high degree of epitaxial crystallinity is further confirmed by Rutherford backscattering spectrometry which gives a minimum yield of 7.5% and 11% for films deposited on LaAlO3 and NdGaO3, respectively. Cross-section high-resolution electron microscopy images also showed that the layer epitaxy of BaTiO3 was characterized by an atomically abrupt film/substrate interface. Scanning electron micrographs showed that these films had very smooth surface morphologies.

Epitaxial growth of BaTiO3 thin films by organometallic chemical vapor deposition

Epitaxial BaTiO3 thin films were grown in situ on (100) LaAlO3 by low-pressure organometallic chemical vapor deposition using the precursors Ba (hexafluoroacetylacetonate)2 (tetraglyme) and titanium tetraisopropoxide. The phase composition and epitaxial quality were sensitive to the reactant partial pressures and growth temperature. Deposition at 800 °C yielded [100]-oriented BaTiO3 films. In-plane epitaxy was confirmed for the BaTiO3 films by x-ray diffraction.

Preparation of Epitaxial BaTiO3 Thin Films by Plasma-Enhanced Metalorganic Chemical Vapor Deposition (Pe-Mocvd)

AbstractThe plasma-enhanced metalorganic chemical vapor deposition (PE-MOCVD) process has been successfully used to achieve high quality epitaxial growth of BaTiO3 thin films on (001) LaA103 and (001) NdGaO3 substrates at a substrate temperature of 680°C. The PEMOCVD system, which incorporates a 300-Watt microwave cavity, introduces excited species from an oxygen plasma to lower the required deposition temperature, as compared to thermal MOCVD growth of BaTiO3. X-ray diffraction (XRD) θ-20 scan patterns indicate that there are few randomly oriented grains and impurity phases in the epitaxial BaTiO3 films. Results of XRD ϕ-scans of the BaTiO3 (202) reflection show a modulation pattern of peaks every 90°, which demonstrates that the BaTiO3 thin films have no misorientation along the [100] and [010] directions of the substrates. An XRD ω rocking curve of the BaTiO3 (200) reflection had a narrow FWHM of 0.25°, indicating that the films have a high degree of preferred orientation of &lt;100&gt; perpendicular to the substrates. The high degree of epitaxial crystallinity is further confirmed by Rutherford Backscattering Spectrometry which gives a minimum yield of 7.5% and 11% for the films deposited on LaAIO3 and NdGaO3, respectively. Scanning electron micrographs show that these films have very smooth surface morphologies, which are desirable for device applications.