Bismuth Titanate Films Research Articles

Pulsed laser deposition (PLD) of oriented bismuth titanate films for integrated electronic applications

Abstract : In this paper we describe recent successes of growth of epitaxial bismuth titanate (BTO) films by pulsed laser deposition (PLD) suitable for electro-optic and electrical switching device structures, and fabrication of an improved gate structure for a ferroelectric memory FET (FEMFET). TEM and x-ray results indicate that excellent crystalline quality BTO films were achieved on LaAlO3. Polarization switching was demonstrated for BTO capacitors with epitaxial superconducting YBaCu3Oy as the lower electrode. Using an SiO2 buffer layer, a BTO/Si structure was fabricated and direct charge modulation in the Si by polarization reversal in the BTO was demonstrated.

Pulsed excimer laser deposition of ferroelectric thin films

Abstract Pulsed UV excimer laser ablation was employed to deposit multi-axial, bi-axial and uni-axial ferroelectric compositions of PZT, bismuth titanate and lead germanate respectively. In general, a fluence lower than 2 J/cm2 caused a preferential evaporation of volatile components, resulting in stoichiometric imbalance. However, the fluences beyond 2 J/cm2 enabled the deposition of stoichiometric thin films of multi-component oxide systems. The intrinsic bombardment due to the energetic ablated species during the thin film deposition seemed to influence the composition, structure, orientation and the electrical properties. The electrical characterization of ferroelectric films indicated a dielectric constant of 800–1000, a Pr of 32μC/cm2 and Ec of 130KV/cm for polycrystalline PZT films and the corresponding quantities were measured to be 150, 7 μC/cm2 and 20 KV/cm for in-situ crystallized c-axis preferred oriented bismuth titanate films. Lead germanate thin films oriented along c-axis (003) showed a di...

ＥＣＲプラズマスパッタリング法によるチタン酸ビスマス膜の作製と光学特性

ＥＣＲプラズマスパッタリング法によるチタン酸ビスマス膜の作製と光学特性

Pulsed laser deposition and ferroelectric characterization of bismuth titanate films

Stoichiometric films of bismuth titanate, Bi4Ti3O12, have been grown for the first time by the technique of pulsed excimer laser deposition. Ferroelectric films were obtained at temperatures as low as 500 °C on Si(100), MgO(110), and Pt-coated Si(100) substrates. Hysteresis measurements using a Pt-coated Si sample yielded a saturation polarization value of about 28 μC/cm2, consistent with a randomly oriented titanate film structure. A preliminary metal-insulator-semiconductor sandwich structure of the form Bi4Ti3O12-CaF2(100 Å)-Si was grown and used to examine polarization induced memory switching effects.

Sol-Gel Derived Barium Sodium Niobate and Bismuth Titanate Films

AbstractSol-gel derived barium sodium niobate and bismuth titanate films were successfully prepared from precursor solutions of chelated Ba[Nb(OEt)6]2 and NaNb(OEt)6 and from bismuth 2-ethyl hexanoate and Ti(OEt)4 respectively. Single phase Ba2NaNb5O15 was formed at 750C on platinized Si and at 850C on fused SiO2. Monoclinic (pseudo-orthorhombic) Bi4Ti3O12 was formed at temperatures as low as 500C. Both film compositions showed significant second harmonic generation. The dielectric constant of the bismuth titanate film was comparable to that of sputtered films.

Ferroelectric Thin Films of Bismuth Titanate Prepared by Mocvd

AbstractThe ferroelectric thin films of bismuth titanate (Bi4Ti3O12) have been prepared by metalorganic chemical vapor deposition ( MOCVD) technique at atmosphere. The triphenyl bismuth (Bi(CaH5 ) 3)and tetrabutyl titanate (C16H36O4Ti) were used as precursors. Dense Bi4Ti3 O12 films with smooth shinning surface have been grown on Si( 100) substrates at 550°C whithout postannealing. The as- grown films were characterized by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and energy dispersion analysis ( EDAX). The films showed well-ordered crystallinity with an (001)preffered orientation. The influence of growth parameters on deposition rate, composition and morphology of as-grown films was also discussed.

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.

Domain switching effects in epitaxial films of ferroelectric bismuth titanate

Domain switching effects in epitaxial films of ferroelectric bismuth titanate

Optical switching characteristics of epitaxial bismuth titanate films for matrix-addressed displays

Abstract Electro-optic switching properties of (010) epitaxial Bi4Ti3O12 films grown on (110) MgAl2O4 substrates have been investigated. The measurements were carried out on large-area films in situ on the spinel substrate using an inter-digitated electrode array. A contrast ratio higher than 7:1 was obtained. Switching times of less than 5 μsec were measured at fields >60 kV/cm. Due to substrate clamping the field needed for switching the epitaxial film was about seven times higher than that for bulk single crystal at a same switching speed. The films exhibit an apparent switching threshold and grey scale capability. Finally, an experimental X-Y matrix-addressed display has been designed and evaluated.

Optimization of epitaxial quality in sputtered films of ferroelectric bismuth titanate

Earlier phases of this study demonstrated the feasibility of growing epitaxial films of Bi 4 Ti 3 O 12 by rf sputtering from ceramic targets containing excess Bi 2 O 3 . These films were unsuitable for device exploitation of the unusual electro-optic display properties of bulk crystals of the titanate because of their twinned, multidomain character. During the present phase, clamping effects exerted by the MgO substrate were shown to prevent conversion by electrical poling to the single domain state. Other substrates were investigated, TiO 2 and sapphire giving the (001) orientation desired for the differential retardation display mode, and MgAl 2 O 4 giving the (010) orientation required for the extinction mode. The latter is obtained untwinned, a result attributed to the thermal expansion and lattice mismatch properties of the system, which, however, also lead to cracking and peeling due to large stresses along the film c -axis. The peeling problem was alleviated by a novel stress compensation growth technique resulting in films on MgAl 2 O 4 , showing minimal substrate clamping effects, and good electro-optic switching properties.

The growth of single crystalline waveguiding thin films of piezoelectric sillenites

We report for the first time the epitaxial growth of single crystalline thin films of bismuth gallate 12 Bi 2O 3 : 1 Ga 2O 3 and bismuth titanate, 6 Bi 2O 3 : 1 TiO 2. The growth process takes advantage of the difference in the melting points between bismuth germanate, Bi 12GeO 20, the substrate, and that of several lower melting isostructural bismuth compounds as the film material. Liquid phase epitaxial growth via dipping can be made directly in melts of the desired film composition and requires no additional fluxes to effect solubility. The indices of refraction of the films can be made greater than that of the substrate, thus the waveguiding characteristics of the films can be combined with their acoustooptic, electrooptic and nonlinear optic properties. Waveguiding thin films of bismuth gallate and bismuth titanate have been deposited on bismuth germanate substrates in thicknesses ranging up to 100 μm and at growth rates in the order of 1–2 μm/min. These epitaxial layers appear to possess excellent waveguiding characteristics. Using a rutile prism-film coupler, waveguide modes have been observed at 0.6328, 0.5145 and 0.4880 μm laser wavelengths.

Electro-optic contrast observations in single-domain epitaxial films of bismuth titanate

Electro-optic switching has successfully been demonstrated on untwinned (010) epitaxial bismuth titanate films grown on (110) MgAl2O4 substrates. This result is achieved on large-area films using an interdigitated electrode array structure which can be used both for electrical poling and subsequent electro-optic address. A contrast ratio higher than 7:1 between the on and off states is obtained with a 10-μm-thick film. A gradual variation of the contrast ratio with switching field is observed, which gives the film a capability for grey scale.

The Research Status and Device Potential of Ferroelectric Thin Films

Some of the problems of fabricating thin films of mixed oxide ferroelectrics possessing electrical properties comparable to those of the bulk material are discussed. It is shown that crystallographic disorder and non-stoichiometry can lead to anomalous behavior in dielectric properties such as permittivity and loss. If care is taken to produce homogeneous and well-crystallized structures, polarization reversal effects closely similar to those characteristic of the bulk ferroelectric can be obtained. In particular. thecrystalline anisotropy of polarization and optical properties in epitaxial bismuth titanate films follows closely that observed in single crystals. Moreover. bulk-type electro-optic switching behavior is observed in these structures. offering good prospects of using them as display media. The optimization of ferroelectric properties for capacitors. memories and displays is discussed and some of the new device potentialities for ferroelectric films in general are evaluated.

Domain Structure and Polarization Reversal in Films of Ferroelectric Bismuth Titanate

A preliminaly study has been made of the structure, optical properties and polarization reversal behavior of epitaxial bismuth titanate films grown by sputtering on MgO substrates. As grown, the films are twinned on a coarse scale, with alternate regions oriented with the monoclinic (100) and (010) plane parallel to the (I IO) MgO surface. Optical birefringence measurements on these regions yielded An, and An, values as a function of temperature which were in general agreement with those measured for bulk crystals. By annealing film sections detached from the substrate, a single orientation of the type (010) was obtained, and regions of such samples could be poled to a single-domain condition. Hysteresis data, with the field applied along the U and c axes, for single domain regions yielded spontaneous polarization results comparable to those reported previously for bulk crystals, but indicated somewhat higher coercive fields. Similar measurements with the field along the [l011 axis showed that it is possible either to pole the film along the a-axis or switch it along the c-axis using a single electrode geometry

Domain structure and polarization reversal in films of ferroelectric bismuth titanate

A preliminary study has been made of the structure, optical properties and polarization reversal behavior of epitaxial bismuth titanate films grown by sputtering on MgO substrates. As grown, the films are twinned on a coarse scale, with alternate regions oriented with the monoclinic (100) and (010) plane parallel to the (110) MgO surface. Optical birefringence measurements on these regions yielded Δna and Δnb values as a function of temperature which were in general agreement with those measured for bulk crystals. By annealing film sections detached from the substrate, a single orientation of the type (010) was obtained, and regions of such samples could be poled to a single-domain condition. Hysteresis data, with the field applied along the a and c axes, for single domain regions yielded spontaneous polarization results comparable to those reported previously for bulk crystals, but indicated somewhat higher coercive fields. Similar measurements with the field along the [101] axis showed that it is possib...

The research status and device potential of ferroelectric thin films

Some of the problems of fabricating thin films of mixed oxide ferroelectrics possessing electrical properties comparable to those of the bulk material are discussed. It is shown that crystallographic disorder and non-stoichiometry can lead to anomalous behavior in dielectric properties such as permittivity and loss. If care is taken to produce homogeneous and well-crystallized structures, polarization reversal effects closely similar to those characteristic of the bulk ferroelectric can be obtained. In particular, the crystalline anisotropy of polarization and optical properties in epitaxial bismuth titanate films follows closely that observed in single crystals. Moreover, bulk-type electro-optic switching behavior is observed in these structures, offering good prospects of using them as display media. The optimization of ferroelectric properties for capacitors, memories and displays is discussed and some of the new device potentialities for ferroelectric films in general are evaluated.