SrBi4Ti4O15 Thin Films Research Articles

Effect of Oxygen Mixing Percentage on Mechanical and Microwave Dielectric Properties of SrBi4Ti4O15 Thin Films

Effect of Oxygen Mixing Percentage on Mechanical and Microwave Dielectric Properties of SrBi4Ti4O15 Thin Films

Tailoring the optical properties of SrBi4Ti4O15 thin films by RF sputtering process parameters

SrBi4Ti4O15 is a bismuth layered perovskite structure material, its thin film form gained much interest due to their geometrical flexibility and thickness. In the present study, SrBi4Ti4O15 thin films are deposited on amorphous substrate using radio frequency sputtering technique. SrBi4Ti4O15 thin films found to be single phase orthorhombic structure by using X-ray diffraction technique. Surface morphology studies such as grain size, shape and roughness were explored through atomic force microscopy. EDX analysis identified the individual elements and its percentage in the compound. Optical properties (refractive index and bandgap) were determined with varying the oxygen mixing percentage (OMP). The best optical properties (refractive index ~ 2.35 and bandgap ~ 3.4 eV) were obtained for films deposited at 50% OMP. These results shows the potential of using SrBi4Ti4O15 thin films in electro-optic devices.

Effects of Substrate and Annealing Temperatures on the Characteristics of SrBi4Ti4O15 Thin Films

In this study, radio frequency (RF) sputtering was used as the method and the layer-structured bismuth compound of SrBi4Ti4O15 + 4 wt% Bi2O3 ferroelectric ceramic was used as the target to deposit the SrBi4Ti4O15 (SBT) thin films. The addition of excess Bi2O3 content in the target ceramic was used to compensate the vaporization of Bi2O3 during the sintering and deposition processes. SBT ferroelectric thin films were deposited on Pt/Ti/SiO2/Si under optimal RF magnetron sputtering parameters with different substrate temperatures for 2 h. After that the SBT thin films were post-heated using rapid temperature annealing (RTA) method. The dielectric and electrical characteristics of the SBT thin films were measured using metal-ferroelectric-metal (MFM) structure. From the physical and electrical measurements of X-ray diffraction pattern, scanning electronic microscope (SEM), I-V curve, and C-V curve, we had found that the substrate temperature and RTA-treated temperature had large influences on the morphology, the crystalline structure, the leakage current density, and the dielectric constant of the SBT thin films.

Nanomechanical and microwave dielectric properties of SrBi4Ti4O15 thin films sputtered on amorphous substrates by rf sputtering

SBTi (SrBi4Ti4O15) thin films were prepared on amorphous fused silica substrates by rf magnetron sputtering technique and crystallized in a microwave oven and conventional furnace. The difference in crystalline perfection was observed for both conventional and microwave annealed films. Nanoindentation and nanoscratch test were preformed to extract the mechanical properties of the films. Microwave annealed films exhibited higher hardness (6.2 GPa), Young’s modulus (103 GPa) and low friction coefficient than conventional annealed films. Microwave dielectric properties are measured at 10 and 20 GHz using spilt post dielectric resonator technique. Microwave annealed films have shown good microwave dielectric properties even at high temperatures by controlling the Bi volatization.

Crystal orientation dependent microwave dielectric properties of sputtered SBTi thin films on fused silica substrates

Thin films of SBTi (SrBi4Ti4O15) were deposited on fused silica substrates by rf-magnetron sputtering at substrate temperatures from 600 to 725 °C. The effect of substrate temperature on preferential orientation, microstructure, Raman scattering characteristics and microwave dielectric properties of SBTi thin films were investigated. Microwave dielectric properties were investigated using the Split Post Dielectric Resonator (SPDR) technique. As the substrate temperature increases, the preferential orientation changes from (119) to (0010). Films deposited at 700 °C exhibits less lattice distortion. It exhibits a dielectric constant about 110 and loss tangent about 0.06 at 10 GHz. It is seen from the Raman analysis that the films deposited at higher temperatures orients more towards c-axis which releases the torsional vibration mode involving TiO6 octahedra with a higher oscillator strength resulting in larger values of dielectric constant and dielectric loss for those films.

Anisotropic electrical properties in bismuth layer structured dielectrics with natural super lattice structure

Dielectric property of epitaxial SrBi4Ti4O15 thin films with (001)-, (1110)-, (105)/(015)-, and (100)/(010)-orientations was investigated as a function of film thickness. As the tilting angle of c-axis from the surface normal is smaller, the relative dielectric constant begins to degrade at thinner thickness; eventually, the (001)-oriented films for which the c-axis is vertical to the substrate do not show noticeable degradation. The leakage current density also strongly depends of the tilting angle of the c-axis. The results indicate that the layer structure of SrBi4Ti4O15 exhibits a small size effect with high insulation performance.

The Influences of Annealing Temperatures on the Properties of the Sol-Gel Deposition SrBi<sub>4</sub>Ti<sub>4</sub>O<sub>15</sub> Thin Films

In this study, SrBi4Ti4O15 (SBT) thin films were deposited onto the SiO2/p-Si(100) and Pt/Ti/SiO2/p-Si(100) substrates by using sol-gel method. After deposition, the SBT thin films were then heated by a rapid thermal annealing (RTA) process conducted in air for 1min at 600-800°C. The surface morphologies and the crystalline structures of the SBT thin films were investigated by using SEM and XRD patterns. The grain sizes increased and the pores decreased with rising RTA temperature. In addition, the coercive field decreased and the remanent polarization and saturation polarization increased with rising RTA temperature. The lnJ-E1/2 curves of the SBT thin films were also investigated to find the leakage current mechanisms correspond either to the Schottky emission or to the Poole-Frenkel emission.

Structure and ferroelectric properties of stoichiometric and Sr-deficient–SrBi4Ti4O15 thin films

SrBi4Ti4O15 (SBTi) and Bi-excess and Sr-deficient SBTi (Sr-deficient SBTi, Sr0.8Bi4.13Ti4O15) thin films were deposited on Pt/Ti/SiO2/Si (100) substrates using a sol–gel method. Structure and electric properties were investigated systematically. These films were random oriented. The remnant polarization (2P r) of SBTi film was about 25.3 μC/cm2, which was larger than the reported value of SBTi thin film. The film with Sr-deficient and Bi-excess composition showed a very large remnant polarization of 36.6 μC/cm2. The capacitance–voltage (C–V) characteristics of both the films showed normal ferroelectric behavior. The Curie temperatures of the same Sr-deficient and Bi-excess component ceramics sample increased slightly in comparison with that of SBTi. More importantly, the Sr-deficient and Bi-excess SBTi thin film showed high fatigue resistance against continuous switching up to 4.4 × 1010 cycles.

Crystal Structure and Dielectric Property of Bismuth Layer-Structured Dielectric Films with c-Axis Preferential Crystal Orientation

Thin films of bismuth layer-structured dielectrics (BLSDs), CaBi4Ti4O15, and SrBi4Ti4O15, were prepared by a chemical solution deposition (CSD) technique on various substrates, such as (111)Pt/TiO2/(100)Si, (100)LaNiO3/(111)Pt/TiO2/(100)Si, and (100)SrRuO3∥(100)SrTiO3 substrates. Conductive perovskite oxide LaNiO3 with (100) preferential crystal orientation was introduced into the interface between the BLSD film and the (111)Pt/TiO2/(100)Si substrate to control the crystal orientation of BLSD by lattice matching between pseudo-perovskite blocks in the BLSD crystal and the (100)LaNiO3 plane with the perovskite structure. The (00l) planes of BLSD crystals were preferentially oriented on the substrate surface of the (100)LaNiO3/(111)Pt/TiO2/(100)Si, whereas randomly-oriented BLSD crystals with lower crystallinity were only obtained on the surface of (111)Pt/TiO2/(100)Si substrate. The (001)-oriented BLSD films exhibited the leakage current densities below 10-7 A/cm2 at ±50 kV/cm, which is significantly lower than those for randomly-oriented films, above 10-6 A/cm2, The room-temperature dielectric constants (εr) of CaBi4Ti4O15 and SrBi4Ti4O15 thin films on the (100)LaNiO3/(111)Pt/TiO2/(100)Si substrate were both approximately 250, while those on the (100)SrRuO3∥(100)SrTiO3 substrate were approximately 220. The temperature dependence of the capacitances for the CaBi4Ti4O15 and SrBi4Ti4O15 films on the (100)LaNiO3/(111)Pt/TiO2/(100)Si substrate were approximately +17 and +10%, respectively, in the temperature range from 25 to 400 °C. These values were slightly larger than those of epitaxial BLSD films, but smaller than those of (Ba,Sr)TiO3 films.

Preparation of (001)-Oriented CaBi4Ti4O15 and SrBi4Ti4O15 Films Using LaNiO3 Nucleation Layer on Pt-passivated Si Wafer

Thin films of CaBi4Ti4O15 and SrBi4Ti4O15 with preferential crystal orientation were prepared by the chemical solution deposition (CSD) technique on a (100)LaNiO3/(111)Pt/(100)Si substrate. The films consisted of a crystalline phase of bismuth-layer-structured dielectric (BLSDs). The (00l) planes of a BLSD crystal were preferentially oriented to the surface of the (100)LaNiO3/(111)Pt/(100)Si substrate, which is ascribed to the lattice matching between pseudo perovskite blocks in the BLSD crystal and the (100)LaNiO3 plane with a perovskite structure. Frequent heat treatment for crystallization, i.e., once after each coating, also enhanced the degree of crystallinity and crystal orientation of the BLSD films. The dielectric constants (εr) of SrBi4Ti4O15 and CaBi4Ti4O15 thin films were approximately 250 at room temperature. The εr values of both films increased with ambient temperature. The variations in capacitance in the temperature range from 25 to 200 °C were approximately 3 and 5% respectively, which were significantly smaller than that in the (Ba,Sr)TiO3 thin film.

Dielectric properties of highly c‐axis oriented chemical solution deposition derived SrBi4Ti4O15 thin films

AbstractC‐axis oriented thin films of SrBi4Ti4O15 were prepared by a chemical solution deposition method. The influence of precursor chemistry and processing conditions on the resulting film morphology and the dielectric properties of SrBi4Ti4O15 thin films were investigated. By controlling the film formation process, highly c‐axis oriented SrBi4Ti4O15 thin films on (111)Pt/Si substrates were obtained at temperatures of 600 °C and 700 °C. The dielectric constant of the films is about 200 and it is independent of film thickness ranging from 55 to 160 nm. The dielectric constant also shows stable value with an increase in temperature from 25 °C to 200 °C. The leakage current of the film at 125 °C is in the order of 10–7 A/cm2 at an applied electric field of 500 kV/cm. These films exhibit stable dielectric constant and excellent insulating properties. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Dielectric Spectroscopy Analyses of SrBi4Ti4O15 Films Obtained from Soft Chemical Solution

SrBi4Ti4O15 (SBTi) thin films were deposited by the polymeric precursor method on Pt bottom electrodes. The obtained films were characterized by X‐ray diffraction, scanning electron microscopy, Raman spectroscopy, and dielectric spectroscopy analyses. The capacitance‐voltage (C‐V) characteristics of perovskite thin film showed normal ferroelectric behavior. The remanent polarization and coercive fields were 5.4 μC/cm2 and 85 kV/cm, respectively. Dielectric spectroscopy was employed to examine the polycrystalline behavior of ferroelectric material and the mechanisms responsible for the dielectric performance of the thin film.

Preparation and ferroelectric properties of (124)-oriented SrBi4Ti4O15 ferroelectric thin film on (110)-oriented LaNiO3 electrode

A (124)-oriented SrBi4Ti4O15 (SBTi) ferroelectric thin film with high volume fraction of {\alpha}SBTi(124)=97% was obtained using a metal organic decomposition process on SiO2/Si substrate coated by (110)-oriented LaNiO3 (LNO) thin film. The remanent polarization and coercive field for (124)-oriented SBTi film are 12.1 {\mu}C/cm2 and 74 kV/cm, respectively. No evident fatigue of (124)-oriented SBTi thin film can be observed after 1{\times}10e9 switching cycles. Besides, the (124)-oriented SBTi film can be uniformly polarized over large areas using a piezoelectric-mode atomic force microscope. Considering that the annealing temperature was 650{\deg}C and the thickness of each deposited layer was merely 30 nm, a long-range epitaxial relationship between SBTi(124) and LNO(110) facets was proposed. The epitaxial relationship was demonstrated based on the crystal structures of SBTi and LNO.

Notable enlargement of remnant polarization for fatigue-free SrBi4Ti4O15 thin films by La-substitution

La-doped SrBi4Ti4O15, SrBi4–xLaxTi4O15 (SBLT-x, x = 0.00, 0.10 and 0.25), thin films have been successfully prepared by the sol–gel method. Structures, surface morphology and ferroelectric properties were investigated. Compared with undoped SBTi, SBLT-0.10 shows a notable larger remnant polarization (2Pr = 46 μC/cm2). Meanwhile, the SBLT-0.10 film shows little change of Pnv and −Pnv up to 4.4 × 1010 switching cycles, suggesting an excellent fatigue-endurance characteristics.

Nature of defects for bismuth layered thin films grown on Pt electrodes

The authors investigated the influence of defects on the piezoelectric and dielectric properties of Bi4Ti3O12 (BIT), SrBi4Ti4O15 (SBTi) and CaBi4Ti4O15 (CBTi144) thin films by x-ray photoemission spectroscopy measurements. In the SBTi film, Sr which is a nonpolarizable ion restricting the movement of Ti4+ ions and thus leads to a low piezoresponse. Meanwhile, the oxygen environment is quite different in the BIT and CBTi144 films exhibiting excellent piezoelectric properties. The piezoelectric coefficient and the dielectric behavior were larger for a-b axis oriented than for c axis-oriented films due to the defects created during the films crystallization.

DOPING EFFECT OF LA AND V IN SrBi4Ti4O15 THIN FILMS

ABSTRACT SrBi4Ti4O15 (SBTi), SrBi4−x La x Ti4O15 (x = 0.10, 0.25: SBLT), and SrBi4−y/3Ti4−y V y O15 (y = 0.03: SBTV) thin films have been prepared by the sol-gel method. The ferroelectric properties of the SBTi thin films have been improved by La and V substitution. The SBLT-0.10 and SBTV-0.03 films exhibit large remnant polarization (2P r) of 45.9 μC/cm2 and 34.0 μC/cm2 respectively. V doping brings about the more significant improvement of the fatigue resistance of the SBTi. After being subject to 2.2 × 109 switching cycles at the low frequency of 50 kHz, the P nv of SBTV-0.03 change little.

Large remnant polarization and excellent fatigue property of vanadium-doped SrBi4Ti4O15 thin films

We report the enhancement of electric and fatigue-endurance properties of vanadium-doped SrBi4Ti4O15 (SBTi) thin films deposited by a refined sol-gel method. The structures and surface morphologies of the films were characterized by x-ray diffraction, atomic force microscopy, and scanning electron microscopy. Their electric properties were investigated systematically. Compared to the undoped SBTi, V-doped SBTi [(SrBi3.99Ti3.97V0.03O15) (SBTV)] showed a larger remnant polarization (2Pr), lower coercive electric field, lower leakage current density, and a better fatigue resistance. The 2Pr of SBTV was 35.9μC∕cm2, which was much higher than that of SBTi (25.3μC∕cm2). Importantly, at a low frequency of 50kHz, the SBTV film showed no variation of Pnv and −Pnv after 2.2×109 switching cycles, suggesting excellent fatigue-endurance characteristics.

Raman study of anharmonic phonons in SrBi4Ti4O15 thin films

Raman spectra of SrBi4Ti4O15 (SBTi4) thin films were measured as a function of temperature from 80to820K. Below room temperature, no phonon modes were detected between 200 and 815cm−1, which indicates the existence of a phonon band gap in this material. Differences between the Raman spectra of the thin film and bulk polycrystalline samples are discussed. The asymmetric Raman band at high frequency can be interpreted as the superposition of two main distinct Raman lines. Temperature dependence of the Raman shifts and full widths at half maximum (FWHMs) for the two phonon modes is discussed as well, which provides information about the vibration energy levels within the film. Theoretical fittings of their FWHMs indicate that the higher-energy phonon mode is apparently more anharmonic than the lower one.

Ferroelectric characteristics of SrBi4Ti4O15 thin films grown on Pt/Ti/SiO2/Si substrates by the soft chemical method

Ferroelectric SrBi4Ti4O15 thin films were successfully prepared on a Pt (111)/Ti/SiO2/Si(100) substrate for the first time by spin coating, using the polymeric precursor method. X-ray diffraction patterns of the films indicate that they are polycrystalline in nature. Atomic force microscopy (AFM) analyses showed that the surface of these films is smooth, dense and crack-free with low surface roughness (6.4 nm). At room temperature and at a frequency of 1 MHz, the dielectric constant and the dissipation factor were, respectively, 150 and 0.022. The C–V characteristics of perovskite thin film prepared at low temperature show normal ferrolectric behaviour. The remanent polarization and coercive field for the films deposited were 5.4 μC/cm2 and 85 kV/cm, respectively. All the capacitors showed good polarization fatigue characteristics at least up to 1×1010 bipolar pulse cycles indicating that SrBi4Ti4O15 thin films can be a promising material for use in nonvolatile memories.

Fabrication and Optical Properties of SrBi4Ti4O15/BaBi4Ti4O15 Graded Ferroelectric Thin Films

SrBi4Ti4O15 (SBTi) and BaBi4Ti4O15 (BBTi) thin films as well as SBTi/BBTi graded thin films with gradients in composition were prepared by sol-gel technique. A special heating treatment procedure was employed in this study to form the uniform composition gradients at the temperature below 850°C. The smooth graded thin films were obtained by rapid thermal annealing (RTA) at 750°C for 10 min and then annealing at 800°C for 60 min. The microstructural evolution of SBTi, BBTi and SBTi/BBTi graded films and their optical properties were studied. The band edge absorption of SBTi/BBTi graded thin films is between that of BBTi and SBTi in the wavelength 250 nm–400 nm from the results of spectrophotometric measurements of the transmittance. The band gap energy of SBTi/BBTi graded film is found to be 4.10 eV, which is between that of BBTi (3.59 eV) and SBTi (4.44 eV). It indicates that the structure of the graded thin films will affect the band gap energy and optical absorbancy of this material. Annealing conditions also have a great influence on the optical properties of graded thin films. It is found that the impurity absorption beyond the intrinsic absorption appears in the graded films, and the impurity absorption peak blue-shifts with the increase in the annealing time.