BT Thin Films Research Articles

Phase diagrams of bismuth ferrite barium titanate thin films with misfit strains and their improved electrical properties

Phase diagrams of BiFeO3-BaTiO3 (BF–BT) thin films were constructed via thermodynamic model calculation, as well as their electrical properties. The calculated morphotropic phase boundary (MPB) of BF–BT thin films without strain is located near the composition of 0.663BF–0.337BT, which agrees well with the experimental results of reported BF–BT ceramics (between 0.66BF–0.34BT and 0.71BF–0.29BT). The permittivity, tunability and [Formula: see text]of BF–BT thin films on Si substrates are higher than those on SrTiO3(ST) plates, which are also in accordance with the measured data in the literature. Further calculation indicates that 0.7BF–0.3BT and 0.6BF–0.4BT thin films can achieve enormous piezoelectric coefficient [Formula: see text] ([Formula: see text]1200 and [Formula: see text]1000 pm/V, respectively) by selecting the substrates with the TEC respectively of 0.3 and 3.1 × 10[Formula: see text]/[Formula: see text]C, because of the phase transition from aa phase to rhombohedral phase. Such results help to clarify the phase diagrams of BF–BT thin films, implying that huge [Formula: see text]can be achieved by choosing the composition near MPB on the substrates with small TEC.

Structural and microstructural features of lead‐free BNT–BT thin films: Nanoscale electromechanical response analysis

AbstractThe structural, microstructural, and electromechanical properties have been investigated at the nanoscale, as a function of the lanthanum concentration, in Bi0.506Na0.46Ba0.08–3x/2LaxTiO3 (x = 0, 2 and 3 at %) (BNLBT–x) lead‐free thin films. The structural characterization, investigated from X‐ray diffraction and Raman spectroscopy, confirmed the formation of the perovskite structure and suggests the coexistence of both antiferroelectric (tetragonal) and ferroelectric (rhombohedral) phases. The surface morphology, characterized by atomic force microscopy, has shown a dense and crack‐free nanostructured surface for all the studied compositions, noting that the increase in the lanthanum content promoted a decrease in both the grain size and surface roughness. PFM imaging analyses have evidenced the ferroelectric domain structure over the surface, as well as the presence of non–piezoelectric regions attributed to the antiferroelectric phase. PFM spectroscopy measurements revealed a reliable switching behavior for locally probed ferroelectric domains, yielding a noticeable local piezoactivity, which indeed shows to increase with the increase in the doping content. The static domain wall was also analyzed in terms of the nanoscale domain structure, and the obtained dimensionality indicated a local electric field‐induced structural disorder. The clear local piezo/ferroelectric nature highlighted on the studied materials underlines the potential for applications of the BNLBT–x films for their integration into advanced electronic nanodevices.

Enhanced energy storage properties of BaTiO3 thin films by Ba0.4Sr0.6TiO3 layers modulation

Electrostatic dielectric energy storage capacitors have attracted much attention recently for their fast charging-discharging speed and high power density. Trilayered Ba0.4Sr0.6TiO3/BaTiO3/Ba0.4Sr0.6TiO3 (BST/BT/BST) thin films were prepared by spin-coating technique. The sandwich-structured thin films showed high dielectric constant (εr = 952) and low dielectric loss (tanδ = 0.034) at room temperature (10 kHz). Moreover, the dielectric constant of the thin films demonstrated good frequency stability within the measured frequency range and broad capacitance variation (20 °C–160 °C, ΔC/C25°C<±10%). The electric-field dependence of dielectric response was investigated and the dielectric tunability was 13.3% at 100 kV/cm. Compared with pure BT thin films, the heterostructure exhibited enhanced electric breakdown strength and energy storage density. The recoverable energy storage density and efficiency of BST/BT/BST thin films were 14.69 J/cm3 and 33.9% at 1.44 MV/cm, respectively. The results indicated that BST/BT/BST heterostructure films would be an alternative way to improve the energy storage density of dielectrics for applications.

Low Frequency Piezoelectric Energy Harvesters Based on Pb-Free Thin Films

The successful utilization of Pb-free piezoelectric materials for the most useful cantilever-type energy-harvesters has been a critical interest for better performance. Here, we introduce the piezoelectric energy-harvesting characteristics of Bi0.5Na0.5TiO3-BaTiO3 (BNT-BT) thin films. The BNT-based thin films have not been reported so far for the energy-harvesting applications. 0.94BNT-0.06BT thin films, which are in the morphotropic phase boundary, showed the best dielectric and piezoelectric performance. The poling effect on the 0.94BNT-0.06BT thin films was also investigated by varying poling electric field, poling temperature and poling time. The 0.94BNT-0.06BT with poling process showed the improved piezoelectric constant of 3.13 C/m2 in the poling condition of 700 kV/cm, 60 oC and 20 min, compared to that of 3.04 C/m2 for films without poling process. XRD patterns showed the increased intensity of (002) peak indicating the increase in the volume fraction of the c-domain of BNT-BT film by applied external electric field, and thus the figure of merit (FOM) values were improved with increased poling field. As a result, the cantilever type energy harvester showed the output power of 2.22 µW from the vibration source with 42 Hz.

Enhanced energy-storage performance of 0.94NBT-0.06BT thin films induced by a Pb0.8La0.1Ca0.1Ti0.975O3 seed layer

0.94(Na0.5Bi0.5TiO3)-0.06BaTiO3 ferroelectric thin films with and without the Pb0.8La0.1Ca0.1Ti0.975O3 seed layer were deposited on platinum-buffered silicon substrates by using Sol–Gel process. The influence of Pb0.8La0.1Ca0.1Ti0.975O3 seed layer and annealing temperatures on the microstructures, ferroelectric properties and energy-storage performances of the as-prepared films were investigated in details. The low annealing temperature and Pb0.8La0.1Ca0.1Ti0.975O3 seed layer could improve the values of electric break-down field strength and Pmax-Pr, which play a vital role for high recoverable energy-storage density. Owing to the high electric break-down field strength value of 3310kV/cm, a large recoverable energy density of W=17.2J/cm3 and a high energy efficiency of η=74.3% were obtained for the 0.94(Na0.5Bi0.5TiO3)-0.06BaTiO3 thin film with the Pb0.8La0.1Ca0.1Ti0.975O3 seed layer, which was annealed at 450°C.

Large piezoelectric properties of (1 − x)Na0.5Bi0.5TiO3–xBaTiO3 thin films prepared by sol–gel method

(1 − x)Na0.5Bi0.5TiO3–xBaTiO3 (BNT–xBT) thin films with x = 0, 0.04, 0.06, 0.08 were prepared on Pt(111)/Ti/SiO2/Si substrates via water-based sol–gel method. A new crystallization process called stepwise crystallization was used to obtain pure perovskite phase observed by XRD. Piezoelectric property and ferroelectric property of BNT–xBT thin films are investigated, and BNT–BT0.06 shows best piezoelectric and ferroelectric properties among the different compositions. The maximum strain value of 1.4–1.8 % and d 33 of 83 pm/V are observed for BNT–BT0.06 thin films. AFM and PFM images reveal the dense morphology and large piezoresponse of BNT–BT thin films without orientation.

Investigation of thickness dependence of electric properties of sol&amp;ndash;gel BNT&amp;ndash;BT thin films with stepwise crystallization

Investigation of thickness dependence of electric properties of sol&amp;ndash;gel BNT&amp;ndash;BT thin films with stepwise crystallization

Effects of LaNiO3 seeding layers on the crystal structure and electrical properties in 0.94(Bi0.5Na0.5)TiO3–0.06BaTiO3 thin films

In this work, the high-quality 0.94(Bi0.5Na0.5)TiO3–0.06BaTiO3 (hereafter abbreviated as BNT–BT) lead-free piezoelectric thin films were synthesized by introducing LaNiO3 (hereafter abbreviated as LNO) seeding layers. The effects of LNO seeding layers on the crystal structure and electrical properties were systematically investigated. The X-ray diffraction patterns indicate that highly (100)-oriented BNT–BT films were prepared through utilizing LNO seeding layers. The maximum piezoelectric coefficient d33⁎ of ~100pm/V, remanent polarization 2Pr of ~18μC/cm2 and dielectric constant ɛr ~410 have been obtained in the highly (100)-oriented BNT–BT films. The observed tremendous enhancement of piezoresponse, ferroelectric and dielectric properties in LNO-seeded films can be attributed to the better crystallization quality, higher degree of (100)-preferred orientation and reduced leakage current density. These findings demonstrate that LNO-seeded BNT–BT thin films integrating with silicon substrates may provide a wide range of applications in high-performance MEMS devices.

Piezoelectric properties of lead-free (Na0.5Bi0.5)0.95Ba0.05TiO3 thin films on polycrystalline nickel foils

Lead-free (Na0.5Bi0.5)0.95Ba0.05TiO3 (0.95NBT–0.05BT) thin films were deposited on polycrystalline Ni substrates by using the RF high-pressure sputtering system. Microstructural studies by high resolution X-ray diffraction reveal that the as-deposited 0.95NBT–0.05BT thin films are polycrystalline structures. The piezoelectric property measurements by a piezoresponse force microscopy exhibit that the polycrystalline 0.95NBT–0.05BT thin films have an excellent piezoelectric response. It is indicated that the as-grown 0.95NBT–0.05BT thin films have the potential for the development of the structural health monitoring systems and related device applications.

Thickness dependence of structural, optical and luminescence properties of BaTiO3 thin films prepared by RF magnetron sputtering

BaTiO3 thin films were deposited onto quartz substrates by RF magnetron sputtering. X-ray diffraction pattern showed the formation of BT thin films with a tetragonal structure with orientations along (101) plane. Average crystallite size increased from 12.52 to 14.87 nm as the film thickness increased from 207 to 554 nm. With the increase in film thickness, the structural disorder decreases and the crystalline quality of the films gradually improved. The film exhibited good adherence to the substrate and are crack free. X-ray photoelectron spectroscopy revealed the presence of barium, titanium and oxygen in BT film. An average transmittance of >80 % was observed for all the films. This high transmittance BT films in the visible region is suitable for various electro-optic applications. The transmittance spectra showed high UV-shielding properties. Optical band gap was found to decrease from 4.55 to 3.70 eV with increase of film thickness, whereas the refractive index was found to increase. The refractive index of the BT films can be tuned between 2.11 and 2.21 at 550 nm. The real and imaginary dielectric constants with increase in film thickness were investigated. The low dissipation factor of BT thin films makes it a promising material for frequency agile applications. The emission spectra of BT thin films consist of near band edge excitonic UV emission and defect related emission in the visible range. The PL emission bands in UV and visible region of BT thin films make them suitable for electro-optic devices and light emitters.

Effect of Rb doping on ferroelectric and piezoelectric properties of Bi0.5Na0.5TiO3–BaTiO3 thin films

Rb doped 0.94Bi0.5Na0.5TiO3–0.06BaTiO3 (BNT–BT–Rbx) thin films with xmol% Rb (x=0, 2.5, 5, 7.5, 10) were deposited on Pt/Ti/SiO2/Si substrate by metal-organic solution deposition method. Experiments were conducted to investigate the effect of Rb doping on phase formation, microstructure, leakage current, and the resulting ferroelectric and piezoelectric property. It was found that substantial enhancement in structural, morphological and electrical properties can be achieved by Rb doping of BNT–BT thin films. Optimal electrical properties were obtained for 5mol% Rb doped BNT–BT thin films, with a dielectric constant, remnant polarization, and effective piezoelectric constant of ∼681, ∼28.9μC/cm2 and ∼86pm/V, respectively. It was suggested that the enhanced electrical properties in the case of 5mol% Rb BNT–BT thin films can be attributed to domain wall movement induced by A-site substitutions, large grain size, and lattice distortion.

Growth and Characterization of Na0.5Bi0.5TiO3 Thin Films with BaTiO3 Buffer Layer (Study of Au/Na0.5Bi0.5TiO3/BaTiO3/Pt Capacitor)

Lead free bilayer capacitor structure has been fabricated as a combination of sodium bismuth titanate (Na0.5Bi0.5)TiO3 (NBT) thin films with barium titanate, (BaTiO3) (BT) buffer layer in situ using pulsed laser deposition (PLD). PLD control parameters have been optimized using Taguchi approach to obtain good quality NBT and BT thin films. It has been observed that dielectric properties of NBT thin films enhanced by inserting BT buffer layer. This improvement in the dielectric properties of NBT thin films have been discussed in relation to the effect of the buffer layer on the structure, microstructure and interface of the NBT/BT multilayer capacitor.

Structure and Properties of BT and BST Thin Films

Barium titanate [BT] and barium strontium titanate [BST] solid solution films have been fabricated by a modified sol-gel processing technique from barium acetate {Ba(CH3COOH)2}, strontium acetate [Sr(CH3COOH)2] and titanium (IV) Isopropoxide [Ti[(CH3)2CHO]4] precursors. The as-fired films were found to be amorphous that crystallized to perovskite phase after annealing the films at 550°C in air for one hour. The dielectric constant (ϵ) and loss tangent (tanδ) of the BaTiO3 film at 1 kHz was found to be 360 and 0.01 respectively. The dielectric constant showed a broad anomaly peak at 130°C that confirms ferroelectric-paraelectric transition. The room temperature dielectric constant and loss factor of this film were found to be 450 and 0.005 respectively. The dielectric anomaly peak of the BST film was found to shift towards lower temperature with Sr content. Both BT and BST showed butterfly capacitance-voltage (C-V) and conductance-voltage (G-V) loops, confirming the existence of ferroelectricity in these films.

Structural Modification and Large Piezoelectricity of Strained (Na,Bi) TiO3–BaTiO3 Epitaxial Thin Films

The crystal structure and ferroelectric and piezoelectric properties of the (1−x)(Na0.5Bi0.5)TiO3–xBaTiO3 (NBT−BT) thin films grown on Pt/MgO(100), (111), and (110) substrates were systematically investigated around the morphotropic phase boundary (MPB) composition (x = 0.05–0.15). X‐ray diffraction and transmission electron microscopy revealed the successful epitaxial growth of high‐quality thin films of NBT–BT with a thickness of 3 μm. Due to compressive thermal strain caused by the difference in thermal expansion between NBT–BT and MgO planes, all the NBT–BT thin films grown on MgO(100), (111), and (110) substrates were distorted to form single‐crystal lattices with tetragonal, rhombohedral, and orthorhombic symmetries, respectively. This is quite different from the case of free bulk NBT–BT in which rhombohedral‐to‐tetragonal transformation of the crystal lattice occurs at MPB compositions of x = 0.06–0.07. Nonetheless, the piezoelectric coefficient, −e31*, of the present NBT–BT thin films was largest when x = 0.07 for tetragonal and rhombohedral thin films and 0.09 for orthorhombic ones, with values as high as 18.1, 15.0, and 20.6 C/m2, respectively. These −e31* values are the highest found for lead‐free piezoelectric thin films to date, and larger than those of Pb(Zr,Ti)O3 thin films.

Dielectric enhancement of BaTiO 3/BaSrTiO 3/SrTiO 3 multilayer thin films deposited on Pt/Ti/SiO 2/Si substrates by sol–gel method

Polycrystalline BaTiO 3/Ba 0.6Sr 0.4TiO 3/SrTiO 3 (BT/BST/ST) multilayer thin films with different periodicities have been deposited on Pt/Ti/SiO 2/Si substrates by using a sol–gel method. The multilayer thin films were crack free, compact and crystallized in a perovskite structure. The dielectric constant of the multilayer thin films was significantly increased and the dielectric loss was almost the same as those of uniform BT, ST and BST thin films. The dielectric constant increased with increasing stacking periodicity as the thickness of each individual layer decreased. The multilayer thin films showed excellent dielectric properties and can be promisingly used for the dielectric layer of silicon-based embedded capacitors in package substrate.

Lead‐Free Ferroelectric (Na1/2Bi1/2)TiO3–BaTiO3 Thin Films in the Morphotropic Phase Boundary Composition: Solution Processing and Properties

Ferroelectric (Na1/2Bi1/2)TiO3–BaTiO3 (BNT–BT) single perovskite thin films have been prepared, for the first time, by chemical solution deposition onto Pt/TiO2/SiO2/(100)Si substrates. A solution process has been developed for the preparation of precursor solutions. The handling of all the chemical reagents, refluxes, and distillations was carried out in air. In addition, the resulting solutions are stable in air, presenting a low gelation and trend to the formation of precipitate. Solutions containing a 10 mol% of Na excess, and a 10 mol% excess of Na+10 mol% excess of Bi, were prepared. These solutions were spin‐coated onto the substrates, obtaining amorphous layers that were crystallized in O2 by rapid thermal processing. Multiple deposition and crystallization were carried out to grow crystalline films with a thickness between 125 and 140 nm. At temperatures below 600°C, the perovskite phase coexists with a pyrochlore phase. At temperatures over 700°C or soaking times over 60 s, an interdiffusion substrate/film interface is formed. Single perovskite BNT–BT thin films are obtained at 650°C, with soaking times of only 6 s. There is an effect of the Na excess and Na+Bi excess on the film microstructure and the dielectric/ferroelectric properties. The films containing Na+Bi excess have a larger grain size, higher dielectric permittivities (at room temperature K′∼400), and higher saturation and polarization values (Ps∼23 μC/cm2 and Pr∼12 μC/cm2). The results of this work prove the feasibility of preparing these lead‐free compositions in thin film form, resulting in materials with promising functional properties when integrated with Si semiconductor substrates.

Structural evolution of nanostructured barium titanate thin film sol–gel derived

Ferroelectric nanostructured barium titanate (BT) thin films derived by a modified sol–gel process were formed by a deep coating method on Si (100) substrate. In this work was investigated the influence of different types and amounts of water (free water directly added in process and crystalline water from barium precursors) and of different barium precursors (hydroxide and acetate) on the gel-structure evolution and the barium titanate thin film crystallization. The IR-spectroscopy and X-ray diffraction analysis were used for sample characterization. Experimental results show that crystalline water from barium hydroxide octahydrate stabilizes the cubic phase of barium titanate. Barium titanate crystallizes in the tetragonal form in thin films when sols were prepared with free water and Ba-acetate or Ba-hydroxide monohydrate as precursors. The type of Ba-precursor used in preparation of sols effects the rate of crystallization of the BT in thin films, making it slower in the case when as precursor was used Ba-acetate than Ba-hydroxides. The prepared BT-thin films demonstrated good adhesion towards substrate and were smooth and uniform.

Effects of buffer layer on the dielectric properties of BaTiO 3 thin films prepared by sol–gel processing

Ferroelectric BaTiO 3 (BT) thin films were deposited on Pt/Ti/SiO 2/Si substrates by sol–gel technique. The thickness of the La 0.5Sr 0.5CoO 3 (LSCO), serving as a buffer layer, was varied from 0 nm to 210 nm, to study the dependence of dielectric properties of the BT thin films on the buffer layer thickness and stress. The influence of buffer layer thickness on the phase and microstructure of the thin films was also examined. Dielectric properties of the thin films were investigated as a function of temperature and direct current (dc) electric field. The results showed that the LSCO buffer layer strongly influenced the microstructure and the dielectric properties of the films. The BT thin film with 150 nm thickness LSCO buffer layer had the least loss, smallest leakage current and largest dielectric constant.

Pulsed laser deposition of perovskite relaxor ferroelectric thin films

Structural, dielectric and ferroelectric properties of thin films of La-doped lead zirconate titanate (PLZT) and sodium bismuth titanate–barium titanate (NBT–BT) perovskite relaxor ferroelectric have been investigated. PLZT films were deposited on Pt/Si substrates in oxygen atmosphere by pulsed laser deposition (PLD) and radio frequency (RF) discharge-assisted PLD, using sintered targets with different La content and Zr/Ti ratio, near or at the boundary relaxor ferroelectric. The films are polycrystalline with perovskite cubic or slightly rhombohedral structure. A slim ferroelectric hysteresis loop, typical for relaxors, has been measured for all film sets. Dielectric characterization shows a large value of capacitance tunability and low dielectric loss. However, common problems related to lead diffusion into the metallic electrode layer do not allow one to obtain high capacitance values, due to the formation of an interface layer with low dielectric constant. Lead-free NBT–BT thin films have been deposited on single crystal (1 0 0)-MgO substrates starting from targets with composition at the morphotropic phase boundary between rhombohedral and tetragonal phase. Films deposited by PLD are polycrystalline perovskite with a slight (1 0 0) orientation. Capacitance measurements were performed using interdigital metallic electrodes deposited on the film's top surface and showed high relative dielectric constant, on the order of 1300.