Ferroelectric BaTiO3 Thin Films Research Articles

Domain manipulation of ferroelectric BaTiO3 thin films: application to the local reorientation of liquid crystal

A method is reported for local alignment of nematic liquid crystal (NLC) molecules. It consists in the poling of small areas of ferroelectric thin films using scanning probe microscopy. A liquid crystal deposited onto such a surface is aligned via a dipole–dipole interaction. The ferroelectric films are first characterized using X ray diffraction, atomic force microscopy and ellipsometry. The domain manipulation and local poling of the film are achieved and characterized using an electrostatic microscopy type set-up. A hybrid nematic liquid crystal cell (NLC-OFC: nematic liquid crystal – oxide ferroelectric cell) is then constructed and its alignment inspected using polarizing microscopy (in reflection mode). The reorientation is explained by invoking a simple interaction between the dipole moment of the LC and the surface electric field generated by the poled area. In addition, a complimentary experiment is performed to determine the depth to which the poled area affects the liquid crystal alignment. This consists of measuring the deflection of a collimated beam (optical soliton) propagating across the poled area.

Investigations on the infrared optical properties of BaTiO3 ferroelectric thin films by spectroscopic ellipsometry

BaTiO3 thin films have been grown directly on Pt (111)/Ti/SiO2/Si (100) substrates by a modified sol-gel method. X-ray diffraction analysis shows that the BaTiO3 thin films are polycrystalline. The infrared optical properties of the thin films are investigated using the infrared spectroscopic ellipsometry (IRSE) in the spectral range of 2.5–12.5 µm. By fitting the measured ellipsometric parameter (tan Ψ and cos Δ) data with a three-phase model (air/BaTiO3/Pt), and a derived classical dispersion relation for the thin films, the optical constants and thickness of the thin films have been simultaneously obtained. The refractive index decreases, and the extinction coefficient increases with increasing wavelength. Accordingly, the absorption coefficient increases as the wavelength increases. The absorption of the Ni/BaTiO3/Pt multilayer thin films has been calculated and the values in this study are larger than that of the Ni/PZT/Pt structure reported. Finally, the effective static charge obtained is smaller than it would be in a purely ionic material for the BaTiO3 thin films.

RHEED observation of BaTiO3 thin films grown by MBE

Ferroelectric BaTiO3 thin films with a thickness of 10 monolayers (ML) were epitaxially grown on SrTiO3(001) substrates by very slow deposition using molecular beam epitaxy (MBE). The investigations were carried out by two growth methods: (i) codeposition and (ii) alternate deposition of the metal elements in an oxygen atmosphere. In situ observation of reflection high-energy electron diffraction confirmed that an epitaxial cube-on-cube structure was prepared. After the deposition, X-ray diffraction measurements were carried out. The 10-ML-thick BaTiO3 films were highly c-axis oriented single crystals with good film quality.

Synthesis and properties of highly conductive thin films as buffer layer from sol-gel process

We prepared epitaxial growth SrRuO3 thin film on LaAlO3 (001) (LAO) single crystal substrate and highly oriented BaTiO3 ferroelectric thin film on the epitaxial SrRuO3 thin film. A homogeneous precursor solution for preparing SrRuO3 thin film was prepared with Sr(O—i—C3H7)2 and Ru(NO)(NO3)3 as starting materials, and 2-methoxy ethanol as solvents. The as-coated thin films were heat treated at temperatures from 723 to 1273 K for 1 h in air. SrRuO3 grew epitaxially on LAO(001) substrate, which were confirmed by XRD theta-2theta method and XRD pole figure analysis. The crystallographic relationship of the film and substrate was SrRuO3(001) parallel to LAO(001) and SrRuO3[110] parallel to LAO[100]. A homogeneous precursor solution for preparing BaTiO3 thin film was prepared with Ti[O—n—(CH2)3CH3]4 and Ba(OCOCH3)2 as starting materials, and acetic acid, 2-methoxy ethanol. SrRuO3 coated LAO substrates were coated by spin-coating method with the coating solution. The as-coated thin films were heat treated at temperatures from 973 to 1173 K in air. It was confirmed that the thin films were growing orientated for c-axis by measurement of XRD theta-2theta method.

Fabrication of Ferroelectric BaTiO3 Thin Film on Ti Substrate and Formation of Calcium Phosphate in Eagle's MEM Solution

Fabrication of Ferroelectric BaTiO3 Thin Film on Ti Substrate and Formation of Calcium Phosphate in Eagle's MEM Solution

Nonlinear optical absorption in undoped and cerium-doped BaTiO3 thin films using Z-scan technique

BaTiO 3 and BaTiO3:Ce thin films with good surface morphology and tetragonal perovskite structure were fabricated on quartz substrates by pulsed-laser deposition technique at a deposition temperature of 750 °C. The fundamental optical constants (the band gaps, linear refractive indices and absorption coefficients) of the films were obtained through optical transmittance measurements. The nonlinear optical properties of the films were investigated using Z-scan method. The films display large nonlinear absorption effects. The two-photon absorption coefficients of the BaTiO3 and BaTiO3:Ce films were determined to be 51.7 and 59.3 cm/GW, respectively. All the results show that undoped and cerium-doped BaTiO3 ferroelectric thin films have potential applications in absorbing-type optical devices.

Preparation and properties of ferroelectric BaTiO3 thin films produced by the polymeric precursor method

Pb1 − xCaxTiO3 thin films with x = 0.24 composition were prepared by the polymeric precursor method on Pt/Ti/SiO2/Si substrates. The surface morphology and crystal structure, and the ferroelectric and dielectric properties of the films were investigated. X-ray diffraction patterns of the films revealed their polycrystalline nature. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) analyses showed the surface of these thin films to be smooth, dense and crack-free with low surface roughness. The multilayer Pb1 − xCaxTO3 thin films were granular in structure with a grain size of approximately 60–70 nm. The dielectric constant and dissipation factor were, respectively, 174 and 0.04 at a 1 kHz frequency. The 600-nm thick film showed a current density leakage in the order of 10−7 A/cm2 in an electric field of about 51 kV/cm. The C-V characteristics of perovskite thin films showed normal ferroelectric behavior. The remanent polarization and coercive field for the deposited films were 15 μC/cm2 and 150 kV/cm, respectively.

Epitaxial Ferroelectric BaTiO3 Thin Films for Microphotonic Applications

AbstractEpitaxial ferroelectric BaTiO3 thin films have been developed as a material for microphotonics. Efforts have been directed toward developing these materials for thin film electro-optic modulators. Films were deposited by metalorganic chemical vapor deposition (MOCVD) on both MgO and silicon substrates. The electro-optic properties of the thin films were measured. For BaTiO3 thin films grown on (100) MgO substrates, the effective electro-optic coefficient, reff depended on the magnitude and direction of the electric field. Coefficients as high as 260 pm/V have been measured. Investigation of BaTiO3 films on silicon has been undertaken. Epitaxial BaTiO3 thin films were deposited by MOCVD on (100) MgO layers grown on silicon (100) substrates by metal-organic molecular beam epitaxy (MOMBE). The MgO serves as the low index optical cladding layer as well as an insulating layer. X-ray diffraction and transmission electron microscopy (TEM) indicated that BaTiO3 was epitaxial with an orientational relation given by BaTiO3 (100)//Si (100) and BaTiO3[011]//Si [011]. Polarization measurements indicated that the BaTiO3 epitaxial films on Si were in the ferroelectric state.

Phase transition behavior of BaTiO3 thin films using high-temperature x-ray diffraction

Ferroelectric BaTiO3 thin films have been fabricated on SrTiO3(001) substrate using pulsed laser deposition. In order to investigate the phase transition behavior of the thin films, we have conducted high-temperature x-ray diffraction in the process of heating and cooling. Lattice constants, degree of c-axis orientation and crystal quality of the thin films were characterized as a function of temperature. The results show that the temperature of tetragonal-to-cubic phase transition for a BaTiO3 thin film is much higher than that of BaTiO3 bulk single crystal, and the phase transition of BaTiO3 thin film occurs in a wide temperature range (from 500 to 800 °C). The tetragonal-to-cubic phase transition for BaTiO3 thin film is irreversible.

Low-frequency dielectric relaxation of BaTiO3 thin-film capacitors

Ferroelectric BaTiO3 thin films with perovskite structure were grown by sol-gel spin-on processing onto (111)Pt/Ti/SiO2/Si substrates. In order to investigate the effects of space charge in BaTiO3 thin films, we measured the relative dielectric constant and the ac conductivity of the films as a function of frequency, ac oscillation amplitude, and temperature. Dielectric constant and dielectric loss were 147 and 0.03 at 100 kHz, respectively. Also, BaTiO3 thin films exhibited marked dielectric relaxation above the Curie temperature and in the low-frequency region below 100 Hz. This low-frequency dielectric relaxation is attributed to the ionized space-charge carriers such as oxygen vacancies and defects in BaTiO3 film and the interfacial polarization. The thermal activation energy for the relaxation process of the ionized space-charge carriers was 0.72 eV.

Ba Titanate and Barium/Strontium Titanate Thin Films from Hydroxide Precursors: Preparation and Ferroelectric Behavior

Randomly oriented ferroelectric BaTiO3 and (Ba0.6Sr0.4) TiO3 thin films on platinum coated Si (100) were prepared by a sol-gel method. The precursor solutions were derived from barium hydroxide or a mixture of barium/strontium hydroxides dissolved in acetic acid and titanium butoxide. Polarization versus applied voltage hysteresis studies indicated a remanent polarization of 3 µC/cm2 and a coercive field of 43.4 kV/cm for BaTiO3 films annealed at 800°C for 1 h. Corresponding parameters for (Ba0.6Sr0.4)TiO3 films annealed at 800°C were found to be 7.2 µC/cm2 and 102.7 kV/cm, respectively. Microstructural study of the surface morphology of these films indicated grains of less than 0.1 µm in size. The leakage current for (Ba0.6Sr0.4)TiO3 films was found to be two orders of magnitude lower than that for BaTiO3 films.

Electron energy loss spectroscopic study on BaTiO3 ferroelectric thin films

Electron energy loss spectroscopic study on BaTiO3 ferroelectric thin films

Nanolayer BaTiO3thin film capacitors using magnetron sputtering

Abstract Low leakage and high dielectric constant ferroelectric BaTiO3 thin film capacitors, taking advantage of the best properties of both amorphous and polycrystalline materials, were fabricated using radio frequency magnetron sputtering. The leakage current density was reduced to 10−10 A/cm2 at a field intensity of (2 ± 0.5) × 105 V/cm by using a nanolayer structure with an amorphous layer, on a number of alternating stacked layers of polycrystalline on microcrystalline material. This leakage current is believed to be the lowest reported so far for BaTiO3 with a dielectric thickness in the range of 250 nm. The dielectric constant and other electrical properties can be purposely controlled by choosing the number of layers and deposition conditions.

Crystallographic orientation of epitaxial BaTiO3 films: The role of thermal-expansion mismatch with the substrate

Expitaxial ferroelectric BaTiO3 thin films have been grown on (001) MgO and MgO-buffered (001) GaAs substrates by pulsed laser deposition to explore the effect of substrate lattice parameter. X-ray-diffraction studies showed that the BaTiO3 films on both MgO single-crystal substrates and MgO-buffered (001) GaAs substrates have a cube-on-cube epitaxy; however, for the BaTiO3 films grown on MgO the spacing of the planes parallel to the substrate was close to the c-axis dimension of the unconstrained tetragonal phase, whereas the BaTiO3 films on MgO/GaAs exhibited a spacing closer to the a-axis dimension of the unconstrained tetragonal phase. The cube-on-cube epitaxy was maintained through the heterostructures even when thin epitaxial intermediate buffer layers of SrTiO3 and La0.5Sr0.5CoO3 were used. The intermediate layers had no effect on the position of the BaTiO3 peak in θ-2θ scans. Together, these observations indicate that, for the materials combinations studied, it is the thermal-expansion mismatch between the film and the underlying substrate that determines the crystallographic orientation of the BaTiO3 film. Preliminary measurements indicate that the BaTiO3 films are ‘‘weakly’’ ferroelectric.

In Situ Monitoring and Model Simulation of BaTiO3 Pulsed Laser Thin Film Deposition

AbstractWe have applied intensified Charge Coupled Detector (ICCD) imaging to real-time, in situ monitoring of excited vapor species emission during the pulsed excimer (248 nm wavelength) laser deposition (PLD) of BaTiO3 ferroelectric thin films. Molecular beam mass spectrometry (MS) was used for species identification and velocity distribution analysis. Gasdynamic model simulations of the plume formation and transport process are tested by comparison with the ICCD and MS results. Particular attention is given to the time scale during and immediately following the laser pulse (0 - 460 ns), and also to the effects of added 02. atomic oxygen was found to be the predominant species present at the leading edge of the vapor plume. Other, slower species found included neutral Ti, TiO, Ba, and BaO.

Synthesis of BaTiO3/LaNiO3 and PbTiO3/LaNiO3 Multilayer Thin Films by Spray Combustion Flame Technique

In an attempt to utilize LaNiO3 thin film as a bottom electrode for ferroelectric BaTiO3 and PbTiO3 thin films, PbTiO3/LaNiO3 and BaTiO3/LaNiO3 multilayer thin films were prepared on MgO(100) by spraying an ultrasonically atomized nitrate solution into a combustion flame (spray combustion flame technique). Highly oriented BaTiO3(100)/LaNiO3(100) and PbTiO3(001)/LaNiO3(100) multilayer thin films were obtained on MgO(100). BaTiO3 film was pseudocubic while PbTiO3 film was tetragonal. Curie temperature measurement of the PbTiO3 film suggested that the films were free from contamination when LaNiO3 was used as a bottom electrode.

Surface and interface properties of ferroelectric BaTiO3 thin films on Si using RuO2 as an electrode

Ferroelectric BaTiO3 thin films were deposited on Si by rf magnetron sputtering. A conductive oxide, RuO2, was used as the bottom electrode of the capacitors. The performance of the thin film capacitors was found to be a strong function of the surface and interface properties between ferroelectric BaTiO3 and the bottom electrode. A suitable capacitor configuration must be used to preserve the bottom electrode, to enhance the dielectric constant, and to reduce the leakage current density of the films. BaTiO3 thin film on the RuO2/Si substrate, where the BaTiO3 thin film has a bilayer structure of polycrystalline on microcrystalline, showed a dielectric constant of 125 at a frequency of 1 MHz, leakage current density of 10−6 A/cm2 at a field intensity of 2.5 × 105 V/cm, and a breakdown voltage above 106 V/cm.

Preparation of BaTiO3 Thin Films by Metalorganic Chemical Vapor Deposition Using Ultrasonic Spraying

Ferroelectric BaTiO3 thin films were fabricated by metalorganic chemical vapor deposition (MOCVD) at atmospheric pressure. The ultrasonic spraying technique has been used to carry the source materials. The common solutions of barium-diethylhexanoate and diisopropoxy-titanium-bis-acetylacetonate in n-butanol were used as the starting materials. Since the concentration of sources can be controlled in the common solution, this method is more simple and precise than other CVD processes. The films had (110) preferred orientation with increasing temperature. The dielectric constant (ε) and the loss factor (tan δ) of thin film deposited at 550° C were about 250 and 0.1, respectively. The leakage current density was 10-5 A/cm2 at 0.1 MV/cm.

Film Thickness Dependence of Dielectric Properties of BaTiO3 Thin Films Prepared by Sol-Gel Method

Ferroelectric BaTiO3 thin films were prepared on Pt(111)/ SiO2/Si(100) substrates at 650° C by the sol-gel method. Film thickness could be varied by repeating a dip coating/heating cycle. The texture of the BaTiO3 thin films became more dense and homogeneous when the film thickness increased. The crystalline thin films showed microstructure with grains as small as 20–30 nm. The dielectric properties could be measured for films thicker than 0.25 µ m. With increasing film thickness, the dielectric constant and remanent polarization increased and the coercive field decreased. Loss tangent of the thin films was independent of the film thickness. BaTiO3 thin film with a thickness of 0.58 µ m exhibited a dielectric constant of 1000, remanent polarization of 8 µ C/cm2 and coercive field of 30 kV/cm.

Interactions between ferroelectric BaTiO3 and Si

Ferroelectric BaTiO3 thin films were deposited on single crystal Si substrates by radio-frequency magnetron sputtering. Bilayer structures of BaTiO3 thin films, either amorphous on polycrystalline (A/P) or polycrystalline on microcrystalline (P/M), were utilized to reduce the leakage current and to enhance the dielectric constant of the films compared to single polycrystalline and amorphous layer structures, respectively. Relatively lower charge density, determined by the capacitance-voltage measurement on the capacitors with a configuration of Au/ BaTiO/p-Si/Al, was detected for the BaTiO3 thin film with a structure of P/M. The current-voltage characteristics of the Al/SiO2(~1.8 nm)/p-Si/Al diodes fabricated on the Si after removing BaTiO3 layers gave direct evidence of the preservation of the Si surface crystal by using a P/M instead of a A/P structure. This was further confirmed by the Auger electron spectroscopy analysis on the samples.