Properties Of BST Thin Films Research Articles

Enhanced dielectric responses of Ba0.6Sr0.4TiO3 thin films onto BaxSr1−xTiO3-buffered stainless steel substrates

Misfit strain, lattice parameter, polarization, permittivity, and tunability of Ba[Formula: see text]Sr[Formula: see text]TiO3 thin films onto Ba[Formula: see text]Sr1−xTiO3-buffered stainless steel (SS) substrates are computed via a modified phenomenological model. When the Ba/Sr ratio of Ba[Formula: see text]Sr1−xTiO3 buffer layer grows, the permittivity and tunability first increase and then decrease with the maximum at [Formula: see text] = 0.75. The highest tunability of such films prepared by the sol-gel technique can reach 32.5% at the electric field of 320 kV/cm when [Formula: see text] = 0.8. The strains are qualitatively analyzed through combining XRD, Raman, and theoretical calculation. The computed data are generally supported by experimental lattice parameters, permittivities, and tunabilities, which show that polycrystalline BST thin films with smaller compressive strain obtain higher dielectric response, and that inserting buffer layer could regulate the strains and dielectric properties of BST thin films.

Effects of electrolyte on micro-structure and properties of BaxSr(1−x)TiO3 films prepared by micro-arc oxidation

BaxSr(1−x)TiO3(BST) films are deposited on titanium substrate by micro-arc oxidation (MAO) technique under three electrolytes. The micro-structure and electrical properties of the BST thin films are analyzed and compared. The results show that the BST films obtained with these three electrolytes are all mainly composed of tetragonal BaxSr(1−x)TiO3. Compared with electrolyte without additive, both PVP30 and EDTA, as additive, significantly inhibit the growth of BST films, and the BST films become flat and dense. Moreover, the dielectric and ferroelectric properties of BST thin films are positively correlated with their micro-structure, and flat and dense BST film possesses good dielectric and ferroelectric properties. The residual polarization intensity of BST film prepared with the electrolyte involving PVP30 or EDTA is about 18 and 13 times of that of BST film prepared without additive, respectively.

Enhanced recoverable energy storage density of Mn-doped Ba0.4Sr0.6TiO3 thin films prepared by spin-coating technique

Mn-doped barium strontium titanate Ba0.4Sr0.6TiO3-x mol%Mn (x = 0, 1, 3 and 5; BSTMx) thin films were deposited on Pt/Ti/SiO2/Si(100) substrates by spin-coating and annealed at 800 °C. X-ray diffraction patterns revealed that all the thin films were a typical cubic perovskite structure and no impurity peaks were observed. The effect of Mn doping on the ferroelectric properties and energy storage performance of the samples was investigated. The results showed that the recoverable energy storage density Urec and the difference ∆P(Pmax − Pr) between maximum polarization Pmax and remnant polarization Pr firstly increased, then decreased with the increase of Mn doping amount. The optimized energy storage performance was obtained in Pt/BSTM3/Pt thin films: energy storage density of 8.48 J/cm3 and energy storage efficiency of 42.4% at 1.63 MV/cm, electrical resistivity of 4.19 × 1010 Ω cm and leakage current density of 7.77 × 10−6 A/cm2 at 163 kV/cm. Moreover, the effect of different top electrodes on energy storage performance was studied, which displayed that the energy density of Au/BSTM3/Pt films was higher than that of Pt/BSTM3/Pt films. The results indicated that Mn doping and Au electrodes could be effective ways to improve the energy storage properties of BST thin films.

Microstructure and dielectric properties of (Ba0.6Sr0.4)TiO3 thin films grown on super smooth glazed-Al2O3 ceramics substrate

Modified substrates with nanometer scale smooth surface were obtained via coating a layer of CaO–Al2O3–SiO2 (CaAlSi) high temperature glaze with proper additives on the rough-95% Al2O3 ceramics substrates. (Ba0.6Sr0.4)TiO3 (BST) thin films were deposited on modified Al2O3 substrates by radio-frequency magnetron sputtering. The microstructure, dielectric, and insulating properties of BST thin films grown on glazed-Al2O3 substrates were investigated by X-ray diffraction (XRD), atomic force microscope (AFM), and dielectric properties measurement. These results showed that microstructure and dielectric properties of BST thin films grown on glazed-Al2O3 substrates were almost consistent with that of BST thin films grown on LaAlO3 (100) single-crystal substrates. Thus, the expensive single-crystal substrates may be substituted by extremely cheap glazed-Al2O3 substrates.

Impedance spectroscopic studies of sol–gel derived barium strontium titanate thin films

In the present work electroceramic thin films of barium strontium titanate (Ba 1− x Sr x TiO 3 – BST) were deposited on stainless steel substrates by sol–gel technique. Homogeneous Ba 0.6Sr 0.4TiO 3 thin films as well as spatially inhomogeneous BST thin films exhibiting artificial gradients in composition normal to the growth surface were deposited. Both up- and down-graded BST films were fabricated by depositing successive layers with Sr mole fraction x ranging from x = 0.5 to x = 0.3. In the present study the tool of impedance spectroscopy has been used to study the dielectric properties of BST thin films at room temperature. To analyze the impedance spectroscopy data the Nyquist ( Z″ vs. Z′) plots as well as the simultaneous representation of the imaginary part of impedance and electrical modulus ( Z″, M″) vs. frequency were used. Experimental data were fitted using the CNLS fitting method. Agreement between experimental and simulated data was established. The data indicated that the thin film samples fabricated can be represented by an equivalent circuit with two relaxation frequencies.

Low-temperature fabrication of Ba 1− xSr xTiO 3 thin films with good dielectric properties on platinized silicon substrates

Ba 0.7Sr 0.3TiO 3 (BST) thin films 500 nm in thickness were prepared on technologically desirable Pt/TiO 2/SiO 2/Si(1 0 0) substrates by ion beam sputtering (IBS) and post-deposition annealing method. The effect of annealing temperature on the structural and dielectric properties of BST thin films was systematically investigated. A sharp transition in their tunable dielectric behaviours was observed in good agreement with the evolution of crystal structure from amorphous to crystalline phase. It was demonstrated that the perovskite phase could crystallize in BST films at a very low temperature, around 450 °C. The lowering of perovskite crystallization temperature in the BST films was explained in terms of the high energetic process nature of IBS technique. A high dielectric tunability of 42% at E (electric field intensity) = 500 kV/cm and a low loss tangent of 0.013 at zero bias were both obtained in the 450 °C-annealed film, thereby resulting in the highest figure-of-merit factor among all the different temperature annealed films. Moreover, the 450 °C-annealed film showed superior leakage current characteristics with a low leakage current density of about 10 −4 A/cm 2 at E = 800 kV/cm.

Optical Properties of BST Thin Films by Spectroscopic Ellipsometry and Optical Reflectivity

Optical properties of Ba 0.25 Sr 0.75 TiO 3 thin films fabricated by pulsed laser deposition (PLD) have been investigated using variable angle spectroscopic ellipsometry (VASE) and near-normal spectroscopic reflectivity (NNSR). The measurements were carried out from 5 K to 450 K in the spectral range 1–6 eV by VASE, and in the range 1–12 eV by NNSR at the room temperature. Both types of the experimental data (VASE and NNSR) were simultaneously fitted to obtain the optical functions (e.g. complex refractive index, dielectric function) and thicknesses of the films. To determine the optical response functions and parameters of the material we used several models to fit the experimental data. The Cauchy-Urbach formula was applied in the transparent spectral range and the direct fit procedure and the Cody-Lorentz model were applied around and beyond absorption edge. In the entire spectral range the reflectivity spectra were analyzed by Kramers-Kronig analysis. The behavior of the refractive index obtained in this way was studied and some anomalies were found. The x-ray diffraction was used for a study of sample texture. Some correlation with the optical study was found. The optimal deposition temperature can be found from both studies.

Preparation of Epitaxial Pt Bottom Electrode and Tunability of (Ba,Sr)TiO3 Thin Film Deposited on Si Substrate

(001) oriented epitaxial Pt bottom electrode was prepared on Si(001) substrate using four fold buffer layer of ST/LSCO/CeO 2 /YSZ. On the epitaxial Pt bottom electrode, we found that both epitaxial and polycrystalline BST thin film can be prepared by the change of oxygen gas flow procedure during heating up to deposition temperature of BST. Without oxygen gas flow on the heating process of the Pt bottom electrode, BST thin film was changed into polycrystalline, on the other hand, when the Pt bottom electrode was heated in 100 mTorr of oxygen pressure, epitaxial grown BST thin film was realized. This means that the orientation of BST thin film can be controlled by the oxygen flow procedure during heating of the Pt bottom electrode. Dielectric constant and tunability of epitaxial BST thin film changed with the oxygen pressure during heating and deposition of BST thin film. This suggests that oxygen pressure during heating and deposition is the key to control the orientation and properties of BST thin film.

Study on dielectric and tunable properties of Cr-doped Ba0 .6Sr0.4TiO3 thin films by rf sputtering

Ba0.6Sr0.4TiO3 dielectric thin films doped by Cr(0, 1, 2.5, 5, 10 mol%) (BSTC) were prepared by radio frequency magnetron sputtering on Pt/Ti/SiO2/Si substrates. The structure and morphology of the BSTC thin films were studied by atomic force microscopy and X-ray diffraction. The effect of Cr doping on the dielectric properties of BST thin films were analyzed. The results show that the dielectric loss of Cr doping BST thin films is lower than that undoped, and the tunability increased with Cr doping. The thin film doped with 5 mol% Cr has the best dielectric properties. The tunability, loss and figure of merit (FOM) at 1 MHz were 38.9%, 0.0183, and 21.3, respectively.

OPTICAL AND STRUCTURAL PROPERTIES OF NANO-SIZED BARIUM STRONTIUM TITANATE (Ba0.6Sr0.4TiO3) THIN FILM

Barium strontium titanate ( Ba0.6Sr0.4TiO3) or BST thin films on quartz substrates have been prepared by using a modified sol-gel processing technique. The starting materials are barium 2-ethylhexanoate Ba[CH3( CH2)3CH(C2H5) CO2]2, strontium 2-ethylhexanoate Sr[CH3( CH2)3CH(C2H5) CO2]2and titanium (IV) isopropoxide Ti[CH3CH3CHO ]4. The precursors Ti[CH3CH3CHO ]4except were synthesized in the laboratory. Transparent and crack-free films were fabricated on quartz substrates by spin coating. The as-fired films were found to be amorphous, which crystallized to cubic phase after annealing at 550°C in air for 1 hr. In this paper, we report the structural and optical properties of BST thin films prepared by the modified sol-gel process.

Improved dielectric and electrical behaviour of low-temperature deposited (Ba0.6Sr0.4)TiO3 films by thin SrTiO3 buffer layer

(Ba0.6Sr0.4)TiO3 (BST) thin films were deposited at a low temperature of 420 °C using thin SrTiO3 (STO) buffer layers on (1 0 0)LaNiO3/Si substrates by radio frequency magnetron sputtering. BST thin films showed a pure perovskite phase and preferred (h 0 0) orientation. The effect of the SrTiO3 layer thickness on crystallinity, dielectric and electrical properties of BST thin films was investigated. Compared with single BST films, the BST/STO multilayer thin films exhibited improved crystallinity when the STO layers were thicker than 10 nm. The dielectric constant clearly increased and the dielectric loss decreased with a 10 nm thick STO buffer layer. As a result, the figure of merit of films at a certain frequency reached the maximal value of 19.7 with the applied voltage of 6 V. In addition, the multilayer films exhibited a reduced leakage current density, which could be attributed to the improved crystallinity of the BST films by using the thin STO buffer layer.

Enhanced tunable properties of Ba0.6Sr0.4TiO3 thin films grown on Pt∕Ti∕SiO2∕Si substrates using MgO buffer layers

Ba 0.6 Sr 0.4 Ti O 3 (BST) thin films were prepared on MgO buffered Pt(111)∕Ti∕SiO2∕Si substrates by pulsed laser deposition. The crystallographic structure, interface characteristics, and dielectric properties of BST thin films are strongly dependent on MgO thickness. BST thin films exhibit (111) preferred orientation when MgO layer is thicker than 5nm. The MgO layer can mitigate the interdiffusion between BST and Pt, causing the dielectric loss and leakage current of BST thin films to decrease significantly. The dielectric loss, tunability, and the largest figure of merit of BST thin films on 10nm MgO achieve 0.009, 30%, and 33.4, respectively.

Impact of in-plane anisotropic strains on the dielectric and pyroelectric properties of Ba0.7Sr0.3TiO3 thin films

A modified Landau-Devonshire phenomenological thermodynamic theory is used to describe the influence of in-plane anisotropic strains on the dielectric and pyroelectric properties of epitaxial Ba0.7Sr0.3TiO3 thin films grown on dissimilar tetragonal substrates. The in-plane anisotropic strain factor-temperature phase diagram is developed. The in-plane anisotropic strains play a crucial role in the dielectric and pyroelectric properties of BST thin films. The theoretical maximum dielectric tunability approaching 100% can be attained at the critical anisotropic strain factor corresponding to the structural phase transformation from ca1 to a1 phase. Moreover, the anisotropic strain factor has an opposite effect on the figure of merit and pyroelectric coefficient, respectively. Furthermore, in the case of isotropic strains, our theoretical results are well consistent with the experimental results.

Effect of (Ba+Sr)/Ti ratio on dielectric and tunable properties of Ba 0.6Sr 0.4TiO 3 thin film prepared by sol-gel method

Ba 0.6Sr 0.4TiO 3(BST) thin films were fabricated on Pt coated Si (100) substrates by sol-gel techniques with molar ratio of (Ba+Sr) to Ti changing from 0.76 to 1.33. The effect of (Ba+Sr)/Ti ratio deviating from the stoichiometry on microstructure, grain growth, dielectric and tunable properties of BST thin films were investigated. TiO 2 and (Ba,Sr) 2TiO 4 were found as a second phase at the ratios of 0.76 and 1.33, respectively. The variation of the ratio reveals more significant effect on the grain size in B-site rich samples than that in A-site rich samples. The dissipation factor decreases rapidly from 0.1 to 0.01 at 1 MHz with decreasing (Ba+Sr)/Ti ratio. The tunability increases with decreasing ratio from 1.33 to 1.05, and then decreases with decreasing ratio from 1.05 to 0.76. The film with (Ba+Sr)/Ti ratio of 1.05 has a maximum tunability of 32% and a dissipation factor of 0.03 at 1 MHz.

Electrical Properties of (Ba,Sr)TiO<sub>3</sub> Thin Films with Self-Seed Layer Deposited by R.F. Magnetron Sputtering

Barium strontium titanate (Ba0.66Sr0.34TiO3) thin films and seed-layers were deposited on the Pt/Ti/SiO2/Si substrate by R.F. magnetron sputtering method. Effects of the substrate temperature on electrical properties of BST thin films were studied. The effect of seed-layer was also studied. From the XRD results, we could confirm that the seeding layer of BST thin film plays a key role in lowering the crystallization temperature of BST thin films. When seed-layer was inserted between BST and Pt, the crystallization of the BST thin films was considerably improved and the processing temperature was lowered. Compared to the pure BST thin films, dielectric constant, dielectric loss, and leakage current of BST thin films deposited on the seed-layer were considerably improved. It could be revealed that electrical properties are influenced by the substrate temperatures of BST thin films and are enhanced by the seed-layer.

Influence of Solvents on the Microstructure and Dielectric Properties of Ba0.5Sr0.5TiO3 Thin Films Prepared by a Diol-Based Sol−Gel Process

BaxSr1-xTiO3 (BST, x = 0.5) thin films were prepared on Pt/TiO2/SiO2/Si substrates using a diol-based sol−gel method. Two different solvents were employed, ethylene glycol and propylene glycol (1,2-propanediol). The influence of the solvent on the sol structure, microstructure development, and dielectric properties of BST thin films is analyzed and discussed. It is observed that films prepared with ethylene glycol show higher values of the dielectric permittivity (∼40% higher) and lower values of dielectric losses when compared with films prepared from propylene glycol precursors. The dielectric permittivitty is 459 and 302 at 1 kHz for films prepared with ethylene glycol and 1,2-propanediol, respectively, and annealed at 800 °C. IR studies revealed that the stabilization of a titanium precursor with propylene glycol is incomplete. During the phase-formation process, a higher content of a second phase is formed for the propylene glycol-delivered films. However, microstructure analyses revealed smaller grain size and surface roughness and higher density for films prepared with ethylene glycol. These differences are attributed to the relative high boiling point and latent heat of vaporization and to the linear molecular structure of ethylene glycol. Ethylene glycol as a solvent allows for the preparation of BST thin films with improved dielectric properties.

High pyroelectric Ba 0.65Sr 0.35TiO 3 thin films with Ba 0.65Sr 0.35RuO 3 seeding-layer for monolithic ferroelectric bolometer

Ba 0.65Sr 0.35TiO 3 (BST) thin films were deposited by RF sputtering with a very thin Ba 0.65Sr 0.35RuO 3 (BSR) seeding-layer on Pt/Ti/SiO 2/Si substrate. The crystallization of BST thin films and the surface morphology of BSR seeding-layer were characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM), respectively. XRD patterns show that the BSR seeding-layer affected the orientation of BST thin film, which is highly a-axis textured. It was also found that the BSR seeding-layer had a marked influence on the dielectric properties of BST thin films. Comparing with BST thin films directly deposited on Pt electrode, the dielectric relaxation can be suppressed and dielectric constant increased due to a possible reduction of interface oxygen vacancies at BST/BSR interface. Moreover, J– V measurement indicates that the leakage current density of BST thin films on BSR seeding-layer were greatly reduced compared with that of BST thin films directly on Pt electrodes. The pyroelectric coefficient of BST thin films with BSR seeding-layer is 7.57 × 10 −7 C cm −2 K −1 at 6 V/μm at room temperature (RT). Our results reveal that high pyroelectric property of BST thin film could be achievable using BSR seeding-layer as a special buffer.

Influence of TiO2 Adhesion Layer Thickness on Properties of (Ba,Sr)TiO3 Thin Films

(Ba0.5Sr0.5)TiO3 thin films were deposited on Pt/TiO2/SiO2/Si substrates with various TiO2 adhesion layer thicknesses. The crystallinity of Pt thin films with (111) direction and the electrical properties of BST thin films strongly depend on the TiO2 adhesion layer thickness. TiO2 adhesion layers between the Pt and SiO2 layers with thicknesses smaller than 5 nm show good adhesion properties and a low leakage current density of BST thin films deposited on the Pt/TiO2/SiO2/Si substrate, which is lower than 8.8×10-8 A/cm2 at an applied voltage of 1 V. The optimal thickness of the TiO2 adhesion layer in the Pt/TiO2/SiO2/Si structure is very important to obtain good electrical properties of BST thin films as well as good adhesion properties.

Effect of bottom electrodes on the dielectric properties of barium strontium titanate thin films

Barium strontium titanate (Ba0.5Sr0.5TiO3, BST) thin films were prepared on Pt/Ti/SiO2/Si and Pt/Cr/SiO2/Si substrates by sol–gel method. The effects of Pt/Ti and Pt/Cr bottom electrodes on the microstructure and dielectric properties of BST thin films were studied. The X-ray diffraction patterns show that both these films crystallize into a perovskite structure. The atomic force micrographs indicate that the films using Pt/Ti and Pt/Cr as bottom electrodes have different grain distributions and grain sizes. The dielectric constant of the films using Pt/Cr as bottom electrodes decreases significantly and the loss tangent and tunability decrease slightly. However, the figure of merit of the films using Pt/Cr as bottom electrodes still increases from 24.3 to 27.6.

Electrical Properties of BST Thin Films Fabricated by a Modified Sol—Gel Processing

ABSTRACT A modified Sol-Gel process was used to get the higher-performance BST thin films. The BST thin films possessed different composites and structures in the substrate of Pt/Ti/SiO2/Si. The microstructure, morphology and the electrical properties of the prepared BST thin films were investigated via X-ray diffractometry, scanning electron microscopy techniques and measurement techniques. The results show that the optimum processing for BST films is RTA750°C × 20 min and with sandwich structure seed layers. BST20 film with good resistivity, comparatively dielectric and ferroelectric properties is practical for the detecting materials of UFPA. The system with dielectric constant of 405, loss tangent of 0.011, remanent polarization of 2.3 μC cm−2, a coercive field of 45 kV cm−1 can be obtained by the modified Sol-Gel processing.