BTO Thin Films Research Articles

Periodic Domain Inversion in Single Crystal Barium Titanate-on-Insulator Thin Film.

Experimentally achieving the first-ever electric field periodic poling of single crystal barium titanate oxide(BTO, or BaTiO3) thin film on-insulator is reported. Owing to the outstanding optical nonlinearities of BTO, this result is a key step toward achieving quasi-phase-matching (QPM). First, the BTO thin film is grown on a dysprosium scandate substrate using pulsed laser deposition with a thin layer of strontium ruthenate later serving as the bottom electrode for poling. The characterization of the BTO thin film using x-ray diffraction (XRD) and piezo-response force microscopy to demonstrate single crystal, single domain growth of the film that enables the desired periodic poling, are presented. To investigate the poling quality, both non-destructive piezo force response microscopy and destructive etching-assisted scanning electron microscopy (SEM) are applied, and it is shown that high quality, uniform, and intransient poling with 50% duty cycle and periods ranging from 2µm to 10µm is achieved. The successful realization of periodic poling in BTO thin film unlocks the potential for highly efficient nonlinear processes under QPM that seemed far-fetched with prior polycrystalline BTO thin films which predominantly relied on efficiency-limited random or non-phase matching conditions and is a key step toward integration of BTO photonic devices.

Fabrication and photonic applications of Si-integrated LiNbO3 and BaTiO3 ferroelectric thin films

Silicon, renowned for its applications in electronic circuits, also offers significant advantages in the realm of integrated optics. While silicon does have inherent limitations in fabricating active devices, these challenges can be overcome through heterogeneous integration with other materials. Ferroelectric materials like lithium niobate (LN) and barium titanate (BTO) exhibit exceptional electrical and nonlinear optical properties, making them ideal candidates for integrated silicon photonics. Over the past few decades, the LN platform has made substantial progress, surmounting obstacles such as manufacturing difficulties, high waveguide losses, and low modulation bandwidth caused by wide electrode spacing. Consequently, LN-based devices have found widespread application in various fields. With the advent of high-quality, large-size LN on insulator wafers, LN photonics has become a burgeoning research area. At the same time, the ferroelectric material BTO, with its tremendous electro-optic response, shows promise for the next generation of integrated photonics. Recent studies have highlighted the remarkable performance of BTO-based modulators, which offer smaller device sizes compared to LN by achieving lower half-wave voltages. This comprehensive review presents various fabrication methods for integrating LN and BTO thin films on silicon, focusing on recent advancements. We discuss their electro-optic responses and provide an overview of the diverse applications enabled by these platforms. Finally, we summarize the current state of integrated LN and BTO photonics research and offer insights into future directions.

Ultrahigh UV Responsivity Quasi-Two-Dimensional BixSn1-xO2 Films Achieved through Surface Reaction.

In this study, quasi-two-dimensional BixSn1-xO2 (BTO) thin films were fabricated using a liquid metal transfer method. The ultraviolet (UV) photodetector based on BTO thin films was constructed, and the ultrahigh responsivity of 589 A/W was observed at 300 nm UV light illumination. Interestingly, by dropping ethanol during light-off period, the recovery time induced by the persistent photoconductivity (PPC) effect is reduced from 1.65 × 103 s to 5.71 s. Furthermore, the recovery time can also be reduced by dropping methanol, propylene glycol, NaNO2, and Na2SO3 after light termination. The working mechanisms are attributed to the rapid consumption of holes stored in BTO thin films by reaction with those solutions. This work demonstrates that the BTO thin films have potential applications in high-performance UV detectors and present an innovation route to weaken the PPC effects in semiconductors by introducing chemical liquids on their surface.

High energy storage properties of calcium-doped barium titanate thin films with high breakdown field strength

Barium titanate (BaTiO3; BTO) has excellent energy storage properties; however, the breakdown field strength of BTO thin films must be improved for high energy storage. In this study, calcium (Ca)-doped BTO thin films, Ba1−xCaxTiO3 (x = 0, 0.03, 0.06, 0.09, 0.12, and 0.15), were prepared on Pt(111)/Ti/SiO2/Si substrates using the sol–gel method. Further, the energy storage properties of Ba1−xCaxTiO3 thin films with different Ca concentrations were characterized and analyzed. Results revealed that the only 165-nm-thick Ba0.91Ca0.09TiO3 film exhibits a high-energy storage density of 32.0 J/cm3 and a high energy storage efficiency of 87.8 % at a high breakdown field strength of 7879 kV/cm. Moreover, Ca-doped BTO thin films have excellent energy storage potential and can be used for fabricating high-breakdown-field, lead-free, and miniaturized dielectric capacitors.

Design and fabrication of novel Tb doped BaTiO3 thin film with superior light-harvesting characteristics for dye sensitized solar cells

Herein propose a high performance dye sensitized solar cell based terbium (Tb) doped barium titanate (BaTiO3) thin films prepared by three different techniques such as chemical bath deposition method (CBD), screen printing (SP) and spray pyrolysis coating (SPC) techniques respectively. XRD, SEM and HRTEM results suggest that tetragonal phase of BaTiO3 with three different morphologies like spherical, nanosheets and nanofibers for CBD, SP and SPC assisted Tb:BTO thin films, respectively. Enhancing the visible light absorption, narrowing the band gap energy and prevent the recombination process of electron-hole pair of SPC assisted Tb:BTO thin films were also examined by UV and PL spectra analysis. Moreover, the SPC assisted Tb:BTO thin films show high surface area (102.5 m2/g) and specific porous nature (14.7 nm), studied by N2 adsorption-desorption analysis. Sandwich type DSSC was fabricated and studied the current-voltage characteristic of all the Tb:BTO thin film photoanode samples. The device utilizing in the SPC assisted Tb:BTO thin film photoanode produced the highest photo-conversion efficiency (η) of 15.15% than compared with CBD assisted Tb:BTO (6.57%) and SP assisted Tb:BTO (8.67%). This is due to highest porosity, surface area, lowest leak current and charge transfer resistance Rct of Tb:BTO photoanode. The improved mechanism of the proposed work is also discussed in detail.

Microstructure analysis of epitaxial BaTiO3 thin films on SrTiO3-buffered Si: Strain and dislocation density quantification using HRXRD methods

Barium titanate (BTO) is a promising perovskite-like material, exhibiting interesting functionalities, such as ferroelectricity, piezoelectricity, high dielectric constant, and electrooptic coefficients. All these properties are closely related to the orientation, density of linear defects and the stability of the tetragonal phase, which depends in turn on its fabrication conditions.High-vacuum Chemical Vapor Deposition (HVCVD) is a method allowing to deposit epitaxial BTO thin films on suitable substrates. In this study, we correlate the microstructure of BTO thin films to the Ba and Ti precursors flow parameters applied in the HVCVD process. In particular, strain, texture, and mosaicity of the crystalline blocks of BTO are investigated in both out-of-plane and in-plane orientation to assess the epitaxial relationships and the crystalline quality. The size of the BTO crystalline domains that scatter the X-ray radiation coherently is calculated using three methods. The mosaicity of the films has been correlated to the concentration of line defects. The value of the screw-type dislocations density has been derived and we discuss its close relationship with the coating deposition conditions.

Ultra-Low-Power Tuning in Hybrid Barium Titanate–Silicon Nitride Electro-optic Devices on Silicon

As the optical analogue to integrated electronics, integrated photonics has already found widespread use in data centers in the form of optical interconnects. As global network traffic continues its rapid expansion, the power consumption of such circuits becomes a critical consideration. Electrically tunable devices in photonic integrated circuits contribute significantly to the total power budget, as they traditionally rely on inherently power-consuming phenomena such as the plasma dispersion effect or the thermo-optic effect for operation. Here, we demonstrate ultra-low-power refractive index tuning in a hybrid barium titanate (BTO)-silicon nitride (SiN) platform integrated on silicon. We achieve tuning by exploiting the large electric field-driven Pockels effect in ferroelectric BTO thin films of sub-100 nm thickness. The extrapolated power consumption for tuning a free spectral range (FSR) in racetrack resonator devices is only 106 nW/FSR, several orders of magnitude less than many previous reports. We demonstrate the technological potential of our hybrid BTO-SiN technology by compensating thermally induced refractive index variations over a temperature range of 20 {\deg}C and by using our platform to fabricate tunable multiresonator optical filters. Our hybrid BTO-SiN technology significantly advances the field of ultra-low-power integrated photonic devices and allows for the realization of next-generation efficient photonic circuits for use in a variety of fields, including communications, sensing, and computing.

Broadband mid-infrared second harmonic generation using epitaxial polydomain barium titanate thin films

The mid-infrared (mid-IR) second-order optical nonlinearity of the barium titanate (BTO) thin films was characterized by second harmonic generation (SHG). The epitaxial BTO thin films were grown on strontium titanate substrates by pulsed-laser deposition. From the azimuthal-dependent polarized SHG measurements, the tensorial optical nonlinear coefficients, dij, and ferroelectric domain fraction ratio, δAY/δAz, were resolved. Strong SHG signals were obtained at the pumping laser wavelength λ between 3.0 and 3.6 μm. The SHG intensity was linearly dependent upon the square of the pumping laser power. The broadband mid-IR optical nonlinearity enables BTO thin films for applications in chip-scale quantum optics and nonlinear integrated photonic circuits.

Electrochemical sensor for the detection of lead ions of B-site-doped bismuth titanate perovskite thin film

The perovskite thin film was fabricated using cobalt (Co)-doped B-site on bismuth titanate (Bi4Ti3−xCoxO12) on FTO substrate by spin coating technique. The fabricated substrate was annealed at 700 °C and employed as an electrochemical sensor for the detection of lead ions. The obtained device was investigated for their structural, optical and morphological features using X-ray diffraction (XRD), UV–V is spectroscopy (UV), photoluminescence and scanning electron microscopy (SEM). XRD patterns reveal that the grains were orientated along c axis with (117) plane providing decreased crystallite size upon increasing dopant concentrations in BTO. UV–Vis diffusion reflectance spectrum showed that bismuth titanate thin films exhibited good optical transmittance in the visible region. BTO thin films displayed particles are in spherical in shape which was confirmed using SEM. The acquired thin film was employed as an electrochemical sensor for the detection of lead ions. The detection technique was carried out using cyclic voltammetry which delivered high sensitivity. On examining the physical and chemical properties of the obtained product, it can also be further employed as real-time applications.

Investigation of barium titanate thin films as simple antireflection coatings for solar cells

Barium titanate (BaTiO3, BTO) is a perovskite class material of remarkable dielectric, ferroelectric and ferromagnetic properties. Our previous studies on optical properties of BTO thin films proved high visible transmittance and sharp absorption edge at ∼300 nm. Therefore the usage of BTO as a UV blocker or an antireflection (AR) coating in visible region is straightforward. AR coatings are agreed to be important parts of many photonic devices, among them also of solar cells. In this paper, single layers of amorphous BTO are numerically and experimentally investigated as promising AR coatings for achieving increased light trapping in thin film silicon solar cells. Reduced reflections achieved by BTO thin films deposited using RF magnetron sputtering on a-Si:H/SiO2 compared with pristine a-Si:H/SiO2 system are clearly demonstrated. Antireflection effects are analyzed using simple AR systems comprising BTO.

Deposition of transistion metal Mn doped BTO thin films by sol–gel technique

This present work reports about bismuth titanate [Bi4Ti3O12, BTO] thin films with Mn doped coating on a glass substrate by applying spin coating method. The prepared films are characterized by X-ray diffraction (XRD), scanning electron microscopy, photoluminescence (PL) and Ultra Violet–Visible spectroscopy (UV–Vis). XRD analysis reveals the polycrystalline nature and orthorhombic structure of BTO thin films. Surface morphology discloses the influence of Mn doped on surface texture. Optical band gap values of BTO films decrease with respect to doping concentration. PL spectra of BTO films display broad green emission peaks at 520 nm under an excitation of 380 nm. The optical parameters like refractive index (n), extinction coefficient (α), dielectric constant (e), optical conductivity (σ), electrical susceptibility (χ) are calculated and reported for the first time by using UV–Vis transmittance measurements.

Monolithic Mid-Infrared Integrated Photonics Using Silicon-on-Epitaxial Barium Titanate Thin Films.

Broadband mid-infrared (mid-IR) photonic circuits that integrate silicon waveguides and epitaxial barium titanate (BTO) thin films are demonstrated using the complementary metal-oxide-semiconductor process. The epitaxial BTO thin films are grown on lanthanum aluminate (LAO) substrates by the pulsed laser deposition technique, wherein a broad infrared transmittance between λ = 2.5 and 7 μm is observed. The optical waveguiding direction is defined by the high-refractive-index amorphous Si (a-Si) ridge structure developed on the BTO layer. Our waveguides show a sharp fundamental mode over the broad mid-IR spectrum, whereas its optical field distribution between the a-Si and BTO layers can be modified by varying the height of the a-Si ridge. With the advantages of broad mid-IR transparency and the intrinsic electro-optic properties, our monolithic Si on a ferroelectric BTO platform will enable tunable mid-IR microphotonics that are desired for high-speed optical logic gates and chip-scale biochemical sensors.

Microstructure and ferroelectricity of BaTiO3 thin films on Si for integrated photonics

Significant progress has been made in integrating novel materials into silicon photonic structures in order to extend the functionality of photonic circuits. One of these promising optical materials is BaTiO3 or barium titanate (BTO) that exhibits a very large Pockels coefficient as required for high-speed light modulators. However, all previous demonstrations show a noticable reduction of the Pockels effect in BTO thin films deposited on silicon substrates compared to BTO bulk crystals. Here, we report on the strong dependence of the Pockels effect in BTO thin films on their microstructure, and provide guidelines on how to engineer thin films with strong electro-optic response. We employ several deposition methods such as molecular beam epitaxy and chemical vapor deposition to realize BTO thin films with different morphology and crystalline structure. While a linear electro-optic response is present even in porous, polycrystalline BTO thin films with an effective Pockels coefficient reff = 6 pm V−1, it is maximized for dense, tetragonal, epitaxial BTO films (reff = 140 pm V−1). By identifying the key structural predictors of electro-optic response in BTO/Si, we provide a roadmap to fully exploit the linear electro-optic effect in novel hybrid oxide/semiconductor nanophotonic devices.

Intermediate pinning states engineering in Bi-doped SnO2 for transparent semi-insulator applications

Bi-doped SnO2 (BTO) thin films were prepared by the magnetron reactive sputtering technique. The BTO thin films were characterized by x-ray photoelectron core level and valence band spectroscopy. Bi was introduced into an SnO2 lattice dominated with Bi5+ states accompanied with Bi3+ minority states. The BTO films exhibited a high optical transparency (>85% @550 nm) in the whole range of solar radiation spectrum without compromising the band gap alignment. The sheet resistance dramatically increased up to 108 Ω/sq after Bi doping. The reduction of electron concentration can be attributed to the electrons pinning to the intermediate state within the band gap. The BTO films have promising applications in high performance optoelectronic and photovoltaic devices.

Fabrication of Crack-Free Barium Titanate Thin Film with High Dielectric Constant Using Sub-Micrometric Scale Layer-by-Layer E-Jet Deposition.

Dense and crack-free barium titanate (BaTiO3, BTO) thin films with a thickness of less than 4 μm were prepared by using sub-micrometric scale, layer-by-layer electrohydrodynamic jet (E-jet) deposition of the suspension ink which is composed of BTO nanopowder and BTO sol. Impacts of the jet height and line-to-line pitch of the deposition on the micro-structure of BTO thin films were investigated. Results show that crack-free BTO thin films can be prepared with 4 mm jet height and 300 μm line-to-line pitch in this work. Dielectric constant of the prepared BTO thin film was recorded as high as 2940 at 1 kHz at room temperature. Meanwhile, low dissipation factor of the BTO thin film of about 8.6% at 1 kHz was also obtained. The layer-by-layer E-jet deposition technique developed in this work has been proved to be a cost-effective, flexible and easy to control approach for the preparation of high-quality solid thin film.

Effect of ion beam irradiation on dielectric properties of BaTiO3 thin film using surface plasmon resonance

The effects of swift heavy ions on the structure, surface morphology and dielectric behaviour of barium titanate (BaTiO3, known as BTO) thin films have been investigated by irradiating the films with 100 MeV Au+8 ions at an ion fluence of 1 × 1012 ions cm−2. BTO thin films were deposited on Pt/Si substrate by pulsed laser deposition technique. The structure of the film was crystalline with tetragonal phase. Surface topography was studied by atomic force microscope. The dielectric properties of BTO have been studied using surface plasmon resonance (SPR) technique in Otto configuration. SPR is a highly sensitive technique for investigating the dielectric and optical properties of dielectrics. Gold-coated glass prisms have been utilized to excite the surface plasmon waves (SPWs) at the metal–air interface. When BTO thin film is integrated with the surface of Au thin film, a significant shift in the SPR curve has been observed due to change in the propagation constant of SPW at metal–dielectric interface. The optical and dielectric parameters of BTO thin film were obtained by fitting the experimental SPR data with the Fresnel’s equations. The observed increase in the dielectric constant of BTO thin film after irradiation may be attributed to packing density.

Effect of Fe substitution on microstructure and properties of bismuth titanate thin films

Bi4Ti3O12 and Fe doped Bi4Ti3O12 (Bi4Ti2.94Fe0.03O12, BTFO) thin films were prepared on FTO/glass (SnO2:F) substrates by the sol–gel method. The effects of Fe doping on the microstructures, dielectric and ferroelectric properties of the films were investigated. X-ray diffraction analyses reveal a lattice distortion for the BTFO thin film. At an applied field of 500kV/cm, the leakage current density of the BTFO thin film is 1.15×10−5A/cm2, which is about 2 orders of magnitude lower than that of the pure BTO thin film (2.73×10−3A/cm2). The electrical conduction mechanisms of the BTO and BTFO thin films are dominated by Ohmic conduction at the low electric field region and gradually transite to space-charge-limited conduction at the higher electric field region. The dielectric constant and dielectric loss of BTFO thin film at 100kHz are 313 and 0.05, respectively. The BTFO thin film shows an enhanced ferroelectric property (Pr=30.88μC/cm2), which is mainly attributed to the lower leakage current density, the distorted lattice structure and the improved surface microstructure.

Multiferroic BiFeO3/BaTiO3 thin films fabricated by chemical solution deposition technique

ABSTRACTThe BiFeO3/BaTiO3 (BFO/BTO) multilayers were deposited on Pt/Ti/SiO2/Si substrates using sol-gel spin coating technique. The electric and magnetic studies on BFO/BTO multilayer structures were carried out for different number of layers. Enhancement in multiferroic properties were seen for all the prepared multilayers as compared to individual BTO and BFO thin films. Maximum value of ferroelectric polarization 71.18 µC/cm2 and saturation magnetization 69.85 emu/cm3 was obtained for multilayer structure having five layers. The observed enhancement in the multiferroic properties of the multilayer system is due to the increased interfacial stress and multiferroic coupling between the alternating layers.

Characteristics and mechanisms of aerosol deposition-based barium titanate by sulfur hexafluoride inductively coupled plasma etching

Aerosol deposition (AD)-derived barium titanate (BTO) micropatterns are etched in SF6/O2/Ar plasmas using inductively coupled plasma (ICP) etching technology. The reaction mechanisms of the proposed sulfur hexafluoride on BTO thin films are verified through X-ray photoelectron spectroscopy (XPS) and static time-of-flight secondary ion mass spectrometry (ToF-SIMS) results. The exact peak positions and chemical shifts of Ba 3d, Ti 2p, O 1s, and F 1s are deduced by fitted XPS narrow-scan spectra on both the as-deposited and etched BTO surfaces. Compared to the as-deposited BTOs, the etched Ba 3d5/2, Ba 3d3/2, Ti 2p3/2, Ti 2p1/2, and O 1s peaks shift towards higher binding energy regions by amounts of 0.55, 0.45, 0.4, 0.35, and 0.76eV, respectively. ToF-SIMS analysis is used to obtain elemental and molecular data for quantitatively studying the interaction between reactive gases and BTO. The combined use of these two techniques is to systematically investigate and analyze the sulfur hexafluoride-based BTO etching mechanisms.

Phase field simulations of the poling behavior of BaTiO3 nano-scale thin films with SrRuO3 and Au electrodes

Abstract A continuum phase field model is used to investigate the poling behavior of BaTiO 3 (BTO) thin films with thicknesses ranging from 1 nm–80 nm. The finite element simulations focus on the influence of the electrode material on the electrical hysteresis curves. The 15 nm thick electrodes consist of either SrRuO 3 (SRO) or Au and are explicitly included in the simulations. Experimental evidence suggests that there is a depolarization field in SRO-electroded BTO thin films. This depolarization field, which is due to an imperfect charge compensation by the electrodes, causes a suppression of ferroelectricity for film thicknesses of a few unit cells. The depolarization field and its effect on the electrical behavior is captured by a Robin type boundary condition for the order parameter of the phase field model. This boundary condition is applied at the interface between the thin film and the top and bottom electrode. The simulation results show that the overall poling behavior strongly depends on the lattice parameter of the electrode material. Films with SRO electrodes, which have a lattice parameter smaller than the a -parameter of tetragonal BTO, observe a switchable polarization larger than the spontaneous polarization. If Au is used (which has lattice parameter larger than the a -parameter of tetragonal BTO) then switching is inhibited for films which are less than 20 nm thick. It is also shown that the Robin boundary condition induces a depolarization field which has the effect of dramatically reducing the switchable polarization in ultrathin films.