Ferroelectric Bismuth Research Articles

Preparation and Characterization of Ferroelectric Bi 4Ti 3O 12 Thin Films Grown on (100)-Oriented Silicon Wafers

Ferroelectric bismuth titanate (Bi4Ti3O12) thin films were prepared directly on (100) silicon substrate by rf planar magnetron sputtering using a Bi2TiO5 ceramic target. Highly c-axis-oriented films were obtained at a high deposition rate of about 17 nm/min. The deposited thin films, consisting of plate-like grains about 2 µm in diameter, were grown uniformly parallel to the substrate surface. The remanent polarization (P r) and the coercive field (E c) of this film at 50 Hz were estimated to be 0.8 µC/cm2 and 20 kV/cm, respectively.

Characteristics of some (MOD) thin film layer type compounds in the bismuth titanate-lead titanate system

Abstract Layer type Aurivillius compounds of complex ferroelectric bismuth oxides have become important as thin films for nonvolatile, random-access memories(DRAMS). This paper reports the investigation of the formation of these compounds and their electrical properties, in the bismuth titanate-lead titanate system. Films were formed using the metallo-organic decomposition (MOD) spin-on solution process. These solutions were spun onto a platinized Si substrate and then fired at 700°C to form 1 μm thick films of bismuth titanate and lead titanate. The films were analyzed using microprobe and x-ray diffraction analyses. Next, the solutions were blended to give compounds from m = 4 to m = 7; where m is defined as the potential number of perovskite-like units between (Bi2O2)+2 layers. The blended solutions were processed exactly like the bismuth titanate and lead titanate solutions. X-ray diffraction analysis was used to determine if Aurivillius layer compounds were formed. Ferroelectric hysteresis loops were...

Grain-oriented ferroelectric bismuth titanate thin film prepared from acetate precursor

Bismuth titanate (Bi 4Ti 3O 12) thin films were fabricated by a spin coating deposition and rapid thermal processing (RTP) technique. The acetate-derived solution for deposition was synthesized by blending dissolved bismuth acetate in aqueous acetic acid and then adding titanium acetate. A series of electrically insulating, semiconducting and conducting substrates were evaluated for Bi 4Ti 3O 12 films deposition. X-ray diffraction indicated that the initial crystallization temperature of the Bi 4Ti 3O 12 films was 500 °C or less; a 700 °C crystallization treatment was used to obtain single phase films. The Bi 4Ti 3O 12 film crystallographic orientation is shown to depend on three factors: substrate type; number of coating layers; and thermal processing. While preferred c-direction orientation was observed for films deposited on silver foil substrates, preferred a-direction orientation was obtained for films deposited on both Si and Pt coated Si wafers. The films were dense, smooth, crack-free and had grain sizes ranging from 20 to 400 nm. Film thickness and refractive index were determined using a combination of ellipsometry, waveguide refractometry and TEM techniques. The refractive index is close to the value of single crystal BIT.

Structural and electrical properties of ferroelectric bismuth titanate thin films prepared by the sol gel method

Crystalline bismuth titanate films were fabricated using a modified sol gel method. The process was simplified using stock titanium and bismuth solutions. Films were fabricated using rapid thermal processing with a ramp rate of 100 °C/s to 700 °C for 30 s. The average grain size of films was 175 nm. A dielectric constant in the typical range of 220 and tanδ of 0.01 were measured. P- E hysteresis loops were observed with the ferroelectric properties of P s = 22 μC/cm 2, P r = 10 μC/cm 2 and the coercive force E c = 165 kV/cm. The leakage current density was of the order of 10 nA/cm 2 at 60 kV/cm. An almost flat C- V characteristic and a charge storage density of 42 fC/μm 2 at 220 kV/cm were measured.

Preparation of Bismuth Titanate Thin Films by Laser Ablation

Ferroelectric bismuth titanate thin films have been prepared on Si substrates at low temperature by the laser ablation method using an ArF laser. Dependences of crystallographic property of the film on substrate temperature, O2 gas pressure, laser repetition frequency and annealing temperature are presented. The preferentially c-axis-oriented films have been obtained on Si substrates at a substrate temperature of 400° C with annealing at 700° C, and on Pt substrates at a low substrate temperature of 450° C.

Ferroelectric properties of Bi2VO5.5 thin films on LaAlO3 and SiO2/Si substrates with LaNiO3 base electrode

Ferroelectric bismuth vanadate Bi2VO5.5 (BVO) thin films have been grown on LaAlO3 (LAO) and SiO2/Si substrates with LaNiO3 (LNO) base electrodes by the pulsed laser deposition technique. The effect of substrate temperature on the ferroelectric properties of BVO thin films, has been studied by depositing the thin films at different temperatures. The BVO thin films grown on LNO/LAO were textured whereas the thin films grown on LNO/SiO2/Si were polycrystalline. The BVO thin films grown at 450 °C exhibited good ferroelectric properties indicating that LNO acts as a good electrode material. The remanent polarization Pr and coercive field Ec obtained for the BVO thin films grown at 450 °C on LNO/LAO and LNO/SiO2/Si were 2.5 μC/cm2, 37 kV/cm and 4.6μC/cm2, 93 kV/cm, respectively.

Grain size effects on the dielectric properties of ferroelectric Bi2VO5.5 ceramics

Dielectric properties and microstructural characteristics of ferroelectric bismuth vanadate (Bi2VO5.5) ceramics exhibiting grain sizes of 7, 10, 20 and 25 μm have been studied. Microstructural studies indicate the presence of ferroelectric 90° domain patterns on the surface as well as in the bulk of the coarse-grained ceramics. The dielectric constant and the loss tangent both at room temperature and in the vicinity of the Curie temperature have been found to increase with increasing grain size. The Curie temperature (725 K) is found to shift slightly (by about 7 K) towards higher temperatures as the grain size increases (7–25 μm). The magnitude of the dielectric anomaly around 725 K is found to be higher for coarse-grained ceramics. The dielectric constant and the loss have been found to decrease with increase in frequency (1–100 kHz) for all the ceramics studied. The increase in dielectric constant with increasing grain size is attributed to a decrease in thickness of the relatively more insulating grain boundary layer.

Studies on structural and electro-optic properties of ferroelectric bismuth titanate thin films

Abstract Ferroelectric bismuth titanate thin films have been deposited on LaAlO3, SrTiO3, MgO, A12O3, and ZrO2/SiO2/Si substrates using a Q-switched Nd:YAG laser. X-ray diffraction studies show that most films on single crystal substrates have preferential crystallographic orientation. The film on MgO(110) shows large electro-optic characteristics with an effective electro-optic coefficient of about 3.8×10−-15 m2/V2. Using a lens coupling method, it is demonstrated that light can propagate along the Bi4Ti3O12 layer in a Bi4Ti3O12/ZrO2/SiO2/Si(100) heterostructure.

Preparation and Use of Mosaic Target for the Deposition of Ferroelectric Bismuth Titanate Thin Films

ABSTRACTIon beam sputter deposition using a Kaufman source is a well-established technique for fabricating thin films. This method has the capability for yielding smooth surfaces and depositing uniform films over a large area. We have used this technique, in the past, with a 5″ diameter target to deposit smooth ferroelectric bismuth titanate (Bi4Ti3O12) films. One of the major obstacles was fabricating the large target with the desired composition. To reduce cost by simplifying the target preparation process we developed a ‘mosaic’ target to deposit ferroelectric Bi4Ti3O12films. Films were deposited at different substrate temperatures. Measurements show that the post-annealing of the deposited films results in measurable ferroelectric properties and enhanced low field dielectric behavior in the films. The discussion will include the target fabrication, the observed properties of the resultant films, and the effect of the deposition and post-annealing temperatures on the film properties.

Growth and ferroelectric properties of Bi2VO5.5 thin films with metallic LaNiO3 electrodes

Novel ferroelectric bismuth vanadate, Bi2VO5.5 (BVO), thin films have been grown between lattice matched metallic LaNiO3 (LNO) layers deposited on SrTiO3 (STO) by the pulsed laser deposition technique. LNO/BVO/LNO/STO and Au/BVO/LNO/STO trilayer structures exhibited c-oriented (001) growth of BVO. LNO has been found to be a good metallic electrode with sheet resistance ∼20 Ω in addition to aiding c-axis oriented BVO growth. The dielectric constant, εr of LNO/BVO/LNO/STO, at 300 K was about 12. However, when an Au electrode was used on top of BVO/LNO/STO film, it showed a significant improvement in the dielectric constant (εr=123). The ferroelectric properties of BVO thin films have been confirmed by hysteresis behavior with a remnant polarization, Pr=4.6×10−8 C/cm2 and coercive field, Ec=23 kV/cm at 300 K.

Ferroelectric bismuth titanate films by hot wall metalorganic chemical vapor deposition

Ferroelectric bismuth titanate thin films were successfully deposited on Si, sapphire disks, and Pt/Ti/SiO2/Si substrates by hot wall metalorganic chemical vapor deposition. Triphenyl bismuth [Bi(C6H5)3] and titanium ethoxide [Ti(C2H5O)4] were used as the precursors. The deposition rates were in the range of 3.9–12.5 nm/min. The Bi/Ti ratio was easily controlled by precursor temperature, carrier gas flow rate, and deposition temperature. As-deposited films were pure Bi4Ti3O12 phase. The films were specular and showed uniform and fine grain size. Optical constants as a function of wavelength were calculated from the film transmission characteristics in the ultraviolet-visible-near infrared (UV-VIS-NIR) region. The 550 °C annealed film showed a spontaneous polarization of 26.5 μC/cm2 and a coercive field of 244.3 kV/cm.

The crystal chemistry and dielectric properties of the Aurivillius family of complex bismuth oxides with perovskite-like layered structures

Many Aurivillius phases of ferroelectric complex bismuth oxides are currently known. With the formula Bi 2A m−1 B m O 3m+3, they all consist of Bi 2O 2 layers interleaved with perovskite-like A m−1 B m O 3m+1 layers. Their crystal chemistry and their chemical stability in relation to the number, m of octahedral sheets within the perovskite-like layers and to various cationic substitutions, have been analysed. The possibility of their ordered intergrowth, i.e. the formation of the homologous series Bi 4 A 2n−1 B 2n+1 O 6n+9 of mixed-layer structures has been examined and a comprehensive review of their dielectric properties with respect to various chemical substitutions and to different formation processes has been achieved, permitting an outline of their future potential applications.

Ac impedance analysis on crystalline layered and polycrystalline bismuth titanate

A comparison is made on the dielectric properties of the ferroelectric perovskite bismuth titanate for both crystalline (along different directions) and polycrystalline (with and without flux) samples, using the complex ac impedance technique. Results for the impedance, conductivity activation energies, bulk dielectric constant, and temperature behavior of the low-frequency dielectric constant are presented. We discuss these results in terms of the conduction mechanisms depending on the nature of the sample, and compare results for crystalline and polycrystalline samples. Also, we show the important influence of the flux on the dielectric properties of the different samples, which must be taken into account in the use of these materials as substrates for the growth of superconducting thin-film ceramic oxides.

Epitaxial growth of ferroelectric bismuth titanate thin films by pulsed laser deposition

Epitaxial thin films of ferroelectric bismuth titanate Bi4Ti3O12 have been grown by pulsed laser deposition on single-crystal [100] SrTiO3 substrates. Bismuth titanate has a high Curie temperature (675 °C) and saturation polarization values of 4 and 50 μC/cm2 along the c and b axis, respectively. Its a,b lattice parameters allow thin-film growth on substrates such as SrTiO3, LaAlO3, MgO, etc. These single crystalline films exhibit good quality as evidenced by x-ray diffraction, Rutherford backscattering, and transmission electron microscopy. Applications for these films include memory devices and optical displays.

Material syntheses of thallium-substituted ferroelectric bismuth layer-oxides

Abstract Material syntheses of thallium-substituted bismuth layer-oxides were performed and the dielectric properties were investigated.

Ferroelectric Films-Growth, Properties and Applications

ABSTRACTThin films of ferroelectric and piezoelectric materials are playing a growing role as critical elements in microwave acoustic devices, infrared imagers, integrated optic circuits, optical displays and high-performance semiconductor memories. In this review, we discuss recent progress in the control of growth, structure and properties of the main candidate materials, such as piezoelectric ZnO and AlN, and ferroelectric PZT-based solid solutions, KNbO3, bismuth titanate (Bi4Ti3O12), LiNbO3, LiTaO3 and KNO3. Brief mention is also made of the role and status ferroelectric polymers and of the BaMF4 class of fluorides. The emphasis of the review is primarily on vacuum-processed films, and optimization of characteristics required for integration into solid-state or semiconductor components.

Polarization reversal and film structure in ferroelectric Bi4Ti3O12 films deposited on silicon

A study has been made of the film structure and polarization reversal in ferroelectric bismuth titanate films deposited on silicon. Most films exhibited a fiber-textured c-axis (001) orientation. The structure of the films appeared not to depend on the orientation, resistivity, or conductivity type but on the surface conditions of the silicon substrate. The study on the polarization reversal of the films using the metal-ferroelectric-semiconductor structure yielded spontaneous polarization of 5.7 μC/cm2. The coercive field was about 130 kV/cm. An anomalous kink was observed on some hysteresis loops and the physical mechanism associated with this unusual phenomenon is attributed to the minority carrier of the silicon substrate.

Flux growth of Bi 2WO 6 single crystal below the transformation temperature

The growth of single crystals of ferroelectric bismuth tungstate, Bi 2WO 6, by the flux method was carried out in the pseudobinary system Bi 2WO 6-Na 2WO 4. It was found that the grown crystals cracked upon cooling through the destructive transformation at 860°C; accordingly, crystal growth had to be accomplished at temperature below the transformation point, so as to obtain strain-free large single crystals. The optimum composition range was between 23 to 30 mole% Bi 2WO 6, which yielded single crystals with dimensions up to 3 × 3 × 0.2 mm.

Electron microscopy of ferroelectric bismuth oxides containing perovskite layers

Ferroelectric bismuth oxides of the general formula (Bi 2 O 2 ) 2+ (A n-1 B n O 3n+1 ) 2- (A = Ba, etc., B = Ti or other transition metal) have been examined by high-resolution lattice imaging electron microscopy. The lattice images show dark bands at the positions of the Bi 2 0 2 layers, with n -1 lines between them due to the layers of the perovskite A cations or, in favourable circumstances, the fully resolved 0.4 nm square perovskite grid. Dislocations and domain boundaries have been imaged for the first time in ferroelectric crystals. The structure of the dislocations and domain walls is discussed in the light of the microstructural evidence.

Domain switching effects in epitaxial films of ferroelectric bismuth titanate

Domain switching effects in epitaxial films of ferroelectric bismuth titanate