Structure and dielectric properties of barium titanate thin films for capacitor applications

BaTiO₃ is a typical ferroelectric material with high relative permittivity and has been used for various applications, such as multilayer ceramic capacitors (MLCCs). With the tendency of miniaturization of MLCCs, the thin films of BaTiO₃ have been required. In this work, BaTiO₃ thin films have been deposited on Pt-coated Si substrates by RF magnetron sputtering under different deposition conditions. The films deposited at the substrate temperature from 550 °C–750 °C show a pure tetragonal perovskite structure. The films deposited at 550 °C–625  °C exhibit (111) preferential orientation, and change to (110) preferential orientation when deposited above 650 °C. The film morphologies vary with working pressure and substrate temperature. The film deposited at 625 °C and 4.5 Pa has the relative permittivity of 630 and the loss tangent of 2% at 10 kHz.     

Synthesis and properties of multiferroic 0.7BiFeO3−0.3BaTiO3 thin films by Mn doping

Multiferroic BiFeO₃?BaTiO₃ thin films that simultaneously exhibit ferroelectricity and ferromagnetism at room temperature were prepared by chemical solution deposition. Perovskite single-phase 0.7BiFeO₃?0.3BaTiO₃ thin films were successfully fabricated in the temperature range 600–700 °C on Pt/TiO_x/SiO₂/Si substrates. As the crystallization temperature was increased, grain growth proceeded, resulting in higher crystallinity at 700 °C. Although the 0.7BiFeO₃?0.3BaTiO₃ thin films exhibited poor polarization (P)?electric field (E) hysteresis loops owing to their low insulating resistance. The leakage current at high applied fields was effectively reduced by Mn doping at the Fe site of the 0.7BiFeO₃?0.3BaTiO₃ thin films, leading to improved ferroelectric properties. The 5 mol% Mn-doped 0.7BiFeO₃?0.3BaTiO₃ thin films simultaneously exhibited ferroelectric polarization and ferromagnetic magnetization hysteresis loops at room temperature.     

Preparation and tunability properties of Ba(ZrxTi1−x)O3 thin films grown by a sol–gel process

Ba(Zr_xTi_1−x)O₃ (BZT) thin films were deposited via sol–gel process on LaNiO₃, as buffer layer, and Pt-coated silicon substrates. The BZT films were perovskite phase and showed a (1 0 0) preferred orientation dependent upon zirconium content. The grain size decreased and the microstructure became dense with increasing zirconium content. The addition of Zr to the BaTiO₃ lattice decreased the grain size of the crystallized films. The temperature dependent dielectric constant revealed that the thin films have relaxor behavior and diffuse phase transition characteristics that depend on the substitution of Zr for Ti in BaTiO₃. The dependence of electrical properties on film thickness has been studied, with the emphasis placed on dielectric nonlinear characteristics. Ba(Zr_0.35Ti₆₅)O₃ thin films with weak temperature dependence of tunability in the temperature range from 0 to 130 °C could be attractive materials for situations in which precise control of temperature would be either impossible or too expensive.     

Dielectric and ferroelectric properties of multilayer BaTiO3/NiFe2O4 thin films prepared by solution deposition technique

In this work different lead-free multilayered structures, composed of perovskite BaTiO₃ and spinel NiFe₂O₄ thin layers, were obtained by solution deposition method. Structural characterization of the sintered thin films confirmed the well-defined layered structure with overall thickness from 160 to 600 nm, crystalline nature of perovskite BaTiO₃ and spinel NiFe₂O₄ phases without secondary phases (after sintering below 900 °C) and grains on nanometer scale. Dielectric properties of the multiferroic multilayer BaTiO₃/NiFe₂O₄ thin films were analyzed in temperature and frequency range from 30 °C to 200 °C and 100 Hz to 1 MHz, respectively. In comparison to the pure BaTiO₃ films, the introduction of ferrite layer reduces dielectric response and increases low frequency permittivity dispersion of the multilayer thin films. The multilayer samples have shown relatively low dielectric loss with stronger contribution of conductivity at higher temperatures, and characteristic broad peak representing “relaxation” of the interface charge accumulation.     

Preferentially oriented BaTiO3 thin films deposited on silicon with thin intermediate buffer layers

Barium titanate (BaTiO₃) thin films are prepared by conventional 2-methoxy ethanol-based chemical solution deposition. We report highly c-axis-oriented BaTiO₃ thin films grown on silicon substrates, coated with a lanthanum oxynitrate buffer layer of 8.9 nm. The influence of the intermediate buffer layer on the crystallization of BaTiO₃ film is investigated. The annealing temperature and buffer layer sintering conditions are optimized to obtain good crystal growth. X-ray diffraction measurements show the growth of highly oriented BaTiO₃ thin films having a single perovskite phase with tetragonal geometry. The scanning electron microscopy and atomic force microscopy studies indicate the presence of smooth, crack-free, uniform layers, with densely packed crystal grains on the silicon surface. A BaTiO₃ film of 150-nm thickness, deposited on a buffer layer of 7.2 nm, shows a dielectric constant of 270, remnant polarization (2P_r) of 5 μC/cm², and coercive field (E_c) of 60 kV/cm.     

Optical properties of multi-stacked BaTiO3/SrTiO3 thin films synthesized via chemical method

In this work, the BaTiO₃ and SrTiO₃ thin films as well as BaTiO₃/SrTiO₃ lamellar composites are synthesized via sol-gel spin-coating method. The formation of corresponding phases from their sols is investigated by virtue of X-ray diffraction on their powders, which confirms the formation of tetragonal structure for BaTiO₃, but cubic structure for SrTiO₃. The field emission scanning electron microscopy images show that crack-free films with different morphologies are formed in each sample. Likewise, by changing periodicity of the samples, the morphology of the composite samples is changed. As the number of layers increases from 1 to 20, the band gap reduces from 4.38 eV to 4.10 eV for BaTiO₃ samples and from 4.13 eV to 3.80 eV for SrTiO₃ samples confirmed by UV–Vis spectra. The band gap of periodicity = 1 sample is higher than that of BaTiO₃, while band gaps of periodicity = 2 and 5 composites mount between those of BaTiO₃ and SrTiO₃. In addition, the refractive indices of multi-stacked composites are about 0.2 lesser than refractive indices of BaTiO₃ sample in high wavelengths. The periodicity dependence of optical frequency dielectric constant, dielectric loss, impedance, Urbach tail, extinction coefficient, and electric modulus of multi-stacked composites are also studied.     

Ultra-high strain responses in lead-free (Bi0.5Na0.5)TiO3-BaTiO3-NaNbO3 ferroelectric thin films

Lead-free (Bi_0.5Na_0.5)TiO₃ (BNT)-based piezoelectric materials, have a great potential for high-precision actuators’ applications. In this work, the high-quality (0.94-x%)(Bi_0.5Na_0.5)TiO₃-0.06BaTiO₃-x%NaNbO₃ (x = 2–10, BNT-6BT-xNN) thin films have been successfully deposited on Pt/TiO₂/SiO₂/Si substrates by sol-gel method. An ultra-high poling strain S_pol value of 1.7% with a unipolar strain S_uni value of 1.47% was reported in the BNT-6BT-6NN thin films. The coexistence of the ferroelectric phase and relaxor state was observed in the compositions of x = 2–8. Furthermore, the BNT-6BT-6NN thin films show more active domain switching compared to other compositions. It is demonstrated that the optimized strain responses in the BNT-6BT-6NN are attributed to a synergistic reaction of active domain switching and reversible electric-field-induced phase transition between the ferroelectric phase and relaxor state. Our systematic study demonstrates that the BNT-6BT-xNN thin films with an improved strain response are promising candidates for the applications of miniaturized actuators.     

High energy storage efficiency and thermal stability of A-site-deficient and 110-textured BaTiO3–BiScO3 thin films

The development of thin film dielectrics having both high energy density and energy conversion efficiency, as well as good thermal stability, is necessary for practical application in high-temperature power electronics. In addition, there is a demand for the development of new Pb-free high-energy density dielectric materials due to environmental concerns. In this regard, thin films of weakly coupled relaxors based on solid solutions of BaTiO₃–BiMeO₃ have shown good promise, because they exhibit a remarkably large polarization over a wide temperature range. Nevertheless, the performance of Pb-free thin films has lagged behind that of their Pb-based counterparts in terms of thermal stability and energy conversion efficiency. Toward this end, most recent studies on BaTiO₃–BiMeO₃ systems have focused on the optimization of material composition, while relatively less attention has been paid to other aspects such as defect chemistry and crystallographic texture. In this study, we examine the effects of A-site vacancy and crystallographic texture on the energy storage performance of BaTiO₃–BiScO₃ thin films synthesized using pulsed laser deposition (PLD). It is shown that a high energy storage density (W_r) of ~28.8 J/cm³ and a high efficiency of η >90% are achieved through a combination of moderate A-site vacancy concentration and (110) crystallographic texture. Furthermore, W_r remains nearly temperature independent while a high efficiency of η >80% is maintained for temperatures up to 200°C, which constitutes one of the best performances for Pb-free ferroelectric films for high-temperature capacitor applications.     

In-situ X-ray diffraction studies and magneto-optic Kerr effect on RF sputtered thin films of BaTiO3 and Co,Nb co-doped BaTiO3

The effect of annealing on structural and magnetic properties of the RF sputtered BaTiO₃ and Co, Nb co-doped BaTiO₃ thin films on Si (001) substrates were studied. The structure of the as-deposited (amorphous) films was changed into cubic perovskite phase during the in-situ X-ray diffraction from room temperature to 900 °C. The enhancement of crystalline quality with respect to the increase of annealing temperature was observed by the in-situ XRD. The magnetic properties of the films before and after annealing were studied by the measurement of Magneto-Optic Kerr Effect (MOKE). The pure BaTiO₃ revealed a paramagnetic behavior, whereas the Co and Nb co-doped BaTiO₃ films exhibited room temperature ferromagnetism. The increase in ferromagnetic response was observed in the Co and Nb co-doped BaTiO₃ films annealed at 900 °C rather than the as-deposited film.     

Rapid Formation of Nanocrystalline BaTiO3 and Its Highly Stable Sol

Ultrafine BaTiO₃ nanoparticles and their highly stable sols are prepared by a novel and rapid route. In this method, the formation mechanism that lies between the chemical precipitation and the sol–gel process is proposed. The BaTiO₃ nanocrystal sols are synthesized in as fast as 15 min in an air atmosphere. Dynamic light scattering analysis and the observation of the Tyndall effect confirm the existence of crystalline nanoparticles in these sols. After careful separation, nanocrystalline BaTiO₃ powders with an average particle size as small as 2.8 nm are obtained. These particles have perovskite phase structures as determined by X‐ray diffraction and selected‐area electron‐diffraction analysis. Fourier transform infrared spectroscopy (FT‐IR) and thermal analysis are used to detect the characteristic functional groups of the solvents on the particles to reveal the formation mechanism. Uniform BaTiO₃ nanocrystal films with high dielectric constants, low dielectric losses, and paraelectric behavior are prepared through solvent evaporation of the nanocrystal sols, providing a new low‐temperature route for the fabrication of perovskite thin films.     

Effect of Substrate on Structure and Multiferrocity of (La,Mn) CoSubstituted BiFeO3 Thin Films

In this article, we report the substrate effect on ferroelectric and magnetic properties of epitaxial BiFeO₃‐based thin films at room temperature. (La, Mn) cosubstituted BiFeO₃ (BFOLM) thin films were deposited on differently lattice mismatched single‐crystal substrates to manipulate the strain states in the as‐deposited films. All the films with 30‐nm thick CaRuO₃ bottom electrodes exhibited highly epitaxial growth behavior with a slightly monoclinic distorted lattice structure while their strain states are drastically different as confirmed by X‐ray reciprocal space mapping. These films possessed significantly different macroscopic ferroelectric properties with giant remanent polarization of 101 ± 2, 65 ± 2, and 48 ± 2 μC/cm² for the films grown on SrTiO₃, (La, Sr)(Al, Ta)O₃, and LaAlO₃, respectively. It is found that the room‐temperature magnetic properties are also in accordance with their strain state, having a reciprocal relationship with polarization. For example, the enhanced magnetization is associated with the suppressed polarization and vice versa. The stain tunability of multiferroic properties in BFOLM thin films are presumably ascribed to the polarization rotation and oxygen octahedral tilts.     

Optical and Microwave Dielectric Properties of Phase Pure (K0.5Na0.5)NbO3 Thin Films Deposited by RF Magnetron Sputtering

(K_0.5Na_0.5)NbO₃ (KNN) thin films have been deposited onto Pt/Ti/SiO₂/Si and quartz substrates by RF magnetron sputtering. The films were deposited at 400°C with the variation in oxygen mixing percentage (OMP) ratio from 0% to 100% and annealed at 700°C in oxygen atmosphere. The crystallinity of the films is found to be increased with increased OMP. Dielectric properties of the films were examined over the frequency range from 1 kHz to 1 MHz and the temperature range of 30°C to 400°C. The Curie temperature of the films was found to be in the range 369°C–373°C. For the first time, the split postdielectric resonator (SPDR) method was used to measure the microwave (10–20 GHz) dielectric properties of KNN thin films. The optical properties of as‐deposited and annealed KNN thin films were investigated by means of transmittance spectra. The optical bandgap is calculated by using the Tauc relation, and found to be in the range 4.34–4.40 eV and 4.29–4.37 eV for the as‐deposited and annealed films, respectively. The refractive index (n_700nm) of the films found to be in the range 1.98–2.01 and 1.99–2.07 for as‐deposited and annealed films, respectively. The refractive index dispersion is analyzed by using Wemple–DiDomenico (W–D) single‐oscillator model. The effect of annealing and OMP on the refractive index, packing density and W–D parameters has been investigated. The average single oscillator energy (E_o) and dispersion energies (E_d) of the annealed KNN thin films are in the range of 6.17–7.16 eV and 18.77–22.19 eV, respectively. AC‐conductivity of the annealed films was analyzed by using double power law. Ag/KNN/Pt thin films followed the ohmic conduction (J ∝ E^α, where α ~1) and the low leakage current density obtained for the deposited at 100% O₂ is 3.14 × 10^?5 A/cm² at 50 kV/cm.     

Microstructure and grain size dependence of ferroelectric properties of BaTiO3 thin films on LaNiO3 buffered Si

BaTiO₃ films were prepared by radio frequency sputtering on the LaNiO₃/Si substrates and then annealed at different temperatures. The films exhibit a highly (1 0 0)-oriented structure and their grain size range from 14 to 55 nm after annealing. Polarization-reversal characteristics for different BaTiO₃ films were measured. The results show that while obvious ferroelectricity is obtained for films with grain size larger than 22 nm, a weak ferroelectricity is still observed in BaTiO₃ film of 14 nm grains, indicating that if a critical grain size exists for ferroelectricity it is less than 14 nm for polycrystalline BaTiO₃ on LaNiO₃/Si. The suppression of macroscopic ferroelectricity for BaTiO₃ with finest grain size and the grain size dependence of remnant polarization and coercive field are also discussed in detail.     

Crystallographic Orientation Dependence on Electrical Properties of (Bi,Na)TiO3‐based Thin Films

Orientation‐engineered (La, Ce) cosubstituted 0.94(Bi_0.5Na_0.5)TiO₃–0.06BaTiO₃ thin films were epitaxially deposited on CaRuO₃ buffered (LaAlO₃)_0.3(Sr₂AlTaO₆)_0.35 single‐crystal substrates by pulsed laser deposition. The ferroelectric, piezoelectric, dielectric, and leakage current characteristics of the thin films were significantly affected by the crystallographic orientation. We found that the (001)‐oriented film exhibited the best ferroelectric properties with remnant polarization P_r = 29.5 μC/cm² and coercive field E_c = 7.4 kV/mm, whereas the (111)‐oriented film demonstrated the largest piezoelectric response and dielectric permittivity. The bipolar resistive switching behavior, which is predominantly attributed to a combined effect of ferroelectric switching and formation/rupture of conductive filaments, was observed. The conduction mechanisms were determined to be ohmic conduction and Poole–Frenkel emission at high‐ and low‐resistance states, respectively, in all the films.     

Structure and properties of plasma sprayed BaTiO3 coatings

Plasma spraying enables to create layers with thickness in a millimeter range adhering on various substrates. This paper provides a study of electric and mechanical properties of BaTiO₃ coatings prepared by atmospheric plasma spraying. The spraying was carried out by a direct current gas-stabilized plasma gun. BaTiO₃ was fed into the plasma jet as a feedstock powder prepared by a reactive sintering of micrometer-sized powders of BaCO₃ and TiO₂. Microstructure and phase composition are reported and discussed in connection with electric and mechanical properties. The ability of the used techniques to detect precisely the phase transformation temperatures of BaTiO₃ plasma sprayed coatings is discussed as well. A depth-sensing indentation measurement was done between 290 and 520 K to provide local mechanical characterization. The elastic modulus has shown slightly higher values than that reported typically in papers focused on BaTiO₃ ferroelectric thin films. The average Vickers microhardness is tested to characterize the samples in larger scale. A wear resistance in a slurry environment is reported as well. Dielectric properties are reported for the temperature window of existence of the tetragonal ferroelectric phase. Relative permittivity and loss factor are studied at frequency from 50 Hz to 1 MHz and temperature from 260 to 400 K.     

Influence of oxygen pressure on microstructure and dielectric properties of lead-free BaTi0.85Sn0.15O3 thin films prepared by pulsed laser deposition

Lead-free barium tin titanate BaTi_0.85Sn_0.15O₃ (BTS) ferroelectric thin films have been deposited on Pt/Ti/SiO₂/Si substrates by pulsed laser deposition. The structure and dielectric properties of thin films deposited at various oxygen pressures are investigated systematically. By optimizing the oxygen pressure during the deposition, the structure and dielectric properties are improved. The thin films grown at 15 Pa have the best crystal quality and the largest grain size, which result in the enhancement of the dielectric properties. The dielectric constant and loss tangent show the similar trend in the entire oxygen pressure range. The influence mechanisms of the oxygen pressure on the structure and dielectric properties are proposed. The BTS thin films deposited at 15 Pa with large figure of merit (FOM) of 81.1, high tunability of 72.1%, moderate dielectric constant of 341, low loss tangent of 0.009 are considered to be appropriate as a field tunable ferroelectric material for electrically tunable devices.     

Dielectric properties of Mn doped Bismuth Barium Titanate based ceramic thin films prepared by PLD technique

In this article, the effect of Mn doping on the permittivity and dielectric loss in 0.67BiFeO₃-0.33BaTiO₃ (BF-BT) based film bulk acoustic resonator test structures has been investigated. BF-BT thin films were deposited on the fused silica substrates with Pt/TiO₂/Ti as bottom electrode. During the study of the BF-BT based parallel-plate structures, it has been revealed that BF-BT is in the ferroelectric state at room temperature. Higher permittivity (ԑ) is observed at a growth temperature of 600 °C and lower dielectric loss is achieved at 0.3 wt% Mn doping contents. These results show that the proposed BF-BT based FBAR test structure has a great potential for applications in tunable thin Film Bulk Acoustic Resonator (FBAR) devices. Comparison of the measured and simulation results has been made by utilizing the Mason equivalent circuit.     

Preparation and electrical properties of Bi2Zn2/3Nb4/3O7 thin films deposited at room temperature for embedded capacitor applications

Bi₂Zn_2/3Nb_4/3O₇ thin films were deposited at room temperature on Pt/Ti/SiO₂/Si(1 0 0) and polymer-based copper clad laminate (CCL) substrates by pulsed laser deposition. Bi₂Zn_2/3Nb_4/3O₇ thin films were deposited in situ with no intentional heating under an oxygen pressure of 4 Pa and then post-annealed at 150 °C for 20 min. It was found that the films are still amorphous in nature, which was confirmed by the XRD analysis. It has been shown that the surface roughness of the substrates has a significant influence on the electrical properties of the dielectric films, especially on the leakage current. Bi₂Zn_2/3Nb_4/3O₇ thin films deposited on Pt/Ti/SiO₂/Si(1 0 0) substrates exhibit superior dielectric characteristics. The dielectric constant and loss tangent are 59.8 and 0.008 at 10 kHz, respectively. Leakage current density is 2.5 × 10^?7 A/cm² at an applied electric field of 400 kV/cm. Bi₂Zn_2/3Nb_4/3O₇ thin films deposited on CCL substrates exhibit the dielectric constant of 60 and loss tangent of 0.018, respectively. Leakage current density is less than 1 × 10^?6 A/cm² at 200 kV/cm.     

Preparation and ferroelectric properties of (Na0.5Bi0.5)0.94Ba0.06TiO3 thin films deposited on Pt electrodes using LaNiO3 as buffer layer

(Na_0.5Bi_0.5)_0.94Ba_0.06TiO₃ thin films were deposited on Pt/Ti/SiO₂/Si (1 1 1) and LaNiO₃/Pt/Ti/SiO₂/Si (1 1 1) substrates by a sol–gel process. The phase structure and ferroelectric properties were investigated. The X-ray diffraction pattern indicated that the (Na_0.5Bi_0.5)_0.94Ba_0.06TiO₃ thin film deposited on Pt/Ti/SiO₂/Si (1 1 1) substrates is polycrystalline structure without any preferred orientation. But the thin film deposited on LaNiO₃/Pt/Ti/SiO₂/Si substrates shows highly (1 0 0) orientation (f ≥ 81%). The leakage current density for the two thin films is about 6 × 10^?3 A/cm² at 250 kV/cm, and thin film deposited on LaNiO₃/Pt/Ti/SiO₂/Si substrates possessed a much lower leakage current under high electric field. The hysteresis loops at an applied electric field of 300 kV/cm and 10 kHz were acquired for the thin films. The thin films deposited on LaNiO₃/Pt/Ti/SiO₂/Si substrates showed improved ferroelectricity.     

Film thickness dependence of the dielectric properties of SrTiO3/BaTiO3 multilayer thin films deposited by double target RF magnetron sputtering

Four-layer SrTiO₃/BaTiO₃ thin films ((ST/BT)₄) with various thicknesses deposited on Pt/Ti/SiO₂/Si substrates at 500 °C by double target RF magnetron sputtering have been investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), profilometry, capacitance-voltage and current-voltage measurements. The XRD patterns reveal the frame formation of the sputter deposited (ST/BT)₄ with controlled modulation. The adhesion between the Pt bottom electrode layer and the BT layer is excellent. The dielectric constant of the (ST/BT)₄ multilayer thin film increases with increasing film thickness. The effects of temperature, frequency, and bias voltage on the dielectric constant of the (ST/BT)₄ multilayer thin films are discussed in detail. The leakage current density of the (ST/BT)₄ multilayer with a thickness of 450.0 nm is lower than 1.0 × 10⁻⁸ A/cm² for the applied voltage of less than 5 V, showing that the multilayer thin films with such a characteristic could be applied for use in dynamic random access memory (DRAMs) capacitors.