Saturation Polarization Values Research Articles

Growth and characterization of excimer laser-ablated BaBi2Nb2O9 thin films

The pulsed-laser ablation technique has been employed to deposit polycrystalline thin films of layered-structure ferroelectric BaBi2Nb2O9 (BBN). Low-substrate-temperature growth (Ts=400 °C) followed by ex situ annealing at 800 °C for 30 min was performed to obtain a preferred orientation. Ferroelectricity in the films was verified by examining the polarization with the applied electric field and was also confirmed from the capacitance–voltage characteristics. The films exhibited well-defined hysteresis loops, and the values of saturation (Ps) and remanent (Pr) polarization were 4.0 and 1.2 μC/cm2, respectively. The room-temperature dielectric constant and dissipation factor were 214 and 0.04, respectively, at a frequency of 100 kHz. A phase transition from a ferroelectric to paraelectric state of the BBN thin film was observed at 220 °C. The dissipation factor of the film was observed to increase after the phase transition due to a probable influence of dc conduction at high temperatures. The real and imaginary part of the dielectric constant also exhibited strong frequency dispersion at high temperatures.

Single-grained PZT thin films for high level FRAM integration—fabrication and characterization

A new method for formation of large single grains as large as 40 μm in length of the sputter-deposited PZT(65/35) thin films has been developed in this research group. Crystallized PZT dots were used as a seed and the grains were laterally grown to form a square pattern on the Pt substrate. It turned out that the electrical characteristics of the single grained PZT thin films were much superior to those of the poly-grained PZT thin films. The leakage current was measured to be less than 8x10−8 A/cm2, the breakdown field more than 1,240 kV/cm, the value of saturation polarization and remanent polarization as high as 42 μC/cm2, 30 μC/cm2, respectively. No degradation of the polarization properties was observed even after the 2×1011 cycles at 1 MHz using a ± 10 V wave form in Pt/PZT/Pt structure. The accelerated retention test revealed that it takes more than 6×107 years for the remanent polarization to be reduced down to 80% of the original value.

(FeCoNi)–ZrBCu base alloys, the influence of transition metal composition and heat treatment on structure and magnetic properties

Magnetic properties of amorphous and partially crystallized (Fe : Co : Ni) 86Zr 7B 6Cu 1 alloys were investigated. Primary formation of BCC as well as FCC nanocrystals takes place at the first stage of crystallization. Low coercivities (H c <10 A/m) and low magnetostrictions are observed only in the Fe-rich corner. Maximum value of saturation polarization J S =1.63–1.67 T are obtained in the partially crystallized (Fe : Co) 86Zr 7B 6Cu 1 alloys with 30–35 Co-parts.

Structural and electrical characterization of epitaxial, large area ferroelectric films of Ba2Bi4Ti5O18 grown by pulsed excimer laser ablation

Excimer laser ablation was used to deposit epitaxial thin films of Ba2Bi4Ti5O18 having mostly c-axis oriented grains. The ferroelectric layer was deposited on an epitaxial conducting oxide electrode layer of LaNiO3, the electrode layer in turn being grown on an epitaxial buffer layer stack on single crystalline (100)-oriented silicon wafers of 3 in. diameter. X-ray diffraction measurements indicate a strong c-axis orientation of the ferroelectric layer. Scanning electron microscopy and atomic force microscopy were used to observe the microstructure of the films and these revealed the homogenous quality of the film with good uniformity over the wafers. Well-defined, saturated ferroelectric hysteresis loops were observed in the compound with values of 1.3 and 0.6 μC/cm2 as saturation and remnant polarization values, respectively, and a coercive field of 47 kV/cm. The results of I–V measurements and complex impedance spectroscopy measurements are presented and a defect formula is proposed for the compound.

Investigations on sol-gel derived lanthanum doped lead titanate (PLT) films

Pb1.05−xLax(Ti1−x/4)O3 (x = 0.00, 0.05, 0.1, 0.15, 0.20, 0.25 and 0.30) thin films were deposited on sapphire (0001) substrates by an acetic acid modified sol-gel technique. The films were characterized, using various techniques, in terms of their phase formation behavior, composition, microstructure and electrical characteristics. It was observed that the sol-gel derived films crystallize into the perovskite phase without any paraelectric cubic pyrochlore phase formation. For less than 15 at% lanthanum composition, the films show a tetragonal phase which transforms into a cubic phase for higher lanthanum content. The observed reduction of the tetragonal distortion with La addition is due to the pronounced shrinkage of the ‘c’ axis. X-ray photoelectron spectroscopy (XPS) was used to analyze the chemical composition. The XPS results are in excellent agreement with the nominal composition of the films. All films are extremely smooth, crack- and pinhole-free, and have a dense uniform microstructure. The grains are not single crystalline, instead each grain is the aggregate of numerous tiny perovskite crystallites. The apparent grain size increases with La addition. The values of dielectric constant, remnant polarization, saturation polarization and coercive field are comparable with the best reported values of sol-gel derived PLT thin films.

Piezoelectric and pyroelectric behavior of lead zirconate titanate–lead sulfide–glass nanocomposites

Composites containing micron-sized lead zirconate titanate and nanometer-sized lead sulfide in a glass matrix were prepared using a sol-gel technique. The PbS size ranged from 3.5 to 15.3 nm. It was possible to pole some of these nanocomposites. The measured values of saturation polarization, remanent polarization, and coercive field showed an increase as the PbS particle size was enhanced. The composites exhibited improvement in the piezoelectric and pyroelectric behavior as compared to that of the base glass-ceramic.

In situ growth of highly oriented Pb(Zr0.5Ti0.5)O3 thin films by low-temperature metal–organic chemical vapor deposition

Highly oriented, polycrystalline Pb(Zr0.5Ti0.5)O3 (PZT) thin films were successfully grown on RuO2/SiO2/(001)Si using metal–organic chemical vapor deposition (MOCVD) at 525 °C. The orientation of the PZT film was controlled by using MOCVD-deposited highly textured RuO2 bottom electrodes. A (001)-oriented PZT film was observed for growth on (101)-textured RuO2. In contrast, for (110) RuO2, the growth of (001) PZT was greatly suppressed while the growth of both (110) and (111) were enhanced, resulting in a poorly (001)-textured polycrystalline film. The as-grown PZT films exhibited a dense columnar microstructure with an average grain size of 150–250 nm. Both PZT films showed excellent ferroelectric properties without any postgrowth annealing. The (001) highly oriented PZT films showed significantly higher values of remnant polarization (Pr=49.7 μC/cm2) and saturation polarization (Ps=82.5 μC/cm2). In comparison, for the PZT films grown on (110) RuO2, Pr and Ps were 21.5 and 35.4 μC/cm2, respectively.

Lanthanum doped lead zirconate titanate stannate antiferroelectric thin films from acetic acid-based sol–gel method

Abstract Lanthanum doped lead zirconate titanate stannate antiferroelectric thin films with `square' hysteresis loops and zero remanent polarization were prepared, for the first time, from acetic acid-based sol–gel processing. The method has the advantages of simple procedure in solution preparation, less sensitivity to moisture and the potential to make thick films. The thin films obtained have very distinctive phase transition field, and the saturated polarization value of 37 μ C/cm 2 , which are suitable for high-energy-storage or decoupling capacitor applications in advanced multichip modules, as well as microactuation applications.

Influence of texture on the switching behavior of Pb(Zr0.70Ti0.30)O3 sol-gel derived thin films

Rhombohedral Pb(Zr0.70Ti0.30)O3 thin films of four different well-defined textures, namely, (100), (111), bimodal (110)/(111), and (100)/(111), were prepared by a sol-gel method. The films were characterized in terms of grain size, presence of second phases, surface roughness, columnarity of grains, and other microstructural features. The dielectric, ferroelectric, and fatigue properties were investigated, with emphasis on the hysteresis switching characteristics. Results are discussed from the reference point of the allowable spontaneous polarization directions available for the different textures. The values of coercive field, remanent and saturation polarization, and slope of the loop at the coercive field, at saturating fields can be qualitatively explained based on the texture, independent of microstructural differences. The occurrence of surface pyrochlore, however, is observed to affect the functionality of the saturation curves, particularly for the samples of bimodal texture. Shearing of the hysteresis curves of the bimodal films is also attributed to surface microstructural features. The occurrence of nonswitching 71° or 109° domains in the (111) and (110)/(111) textured films is hypothesized based on a comparison with the data from the (100) textured film. Corrected saturation polarization values agree with the spontaneous polarization values of rhombohedral PZT single crystals and published calculated values for rhombohedral PZT ceramics. The fatigue characteristics show increases in the switching component of polarization in the range 103−107 bipolar cycles, particularly for the (111) textured sample. Onset of fatigue is observed for all samples between 107 and 108 switching cycles.

Synthesis of Ferroelectric Strontium Bismuth Tantalate Films from Metal Alkoxide Precursors

AbstractFerroelectric SrBi2Ta2O9 (SBT) films were prepared by the spin coating technique on platinum, quartz and YBa2Cu3O7-x/LaA1O3 substrates from a methoxyethanol solution of bismuth isopropoxide (Bi(OCH(CH3)2)3) and strontium tantalum isopropoxide (SrTa2(OCH(CH3)2)12). X-Ray diffraction studies showed some crystallization occurred after annealing the films under oxygen flow at 600 °C and excellent crystallinity was achieved after annealing at 750 °C for 0.5 h. Electron microprobe analysis gave a composition close to that expected for SBT, and atomic force microscopy gave a root mean square surface roughness of 101 A. An hysteresis measurement (1 kHz) gave remnant polarization (2Pr), saturation polarization (Ps) and coercive field (Ec) values of 14.5 μC/cm2, 14.5 μ/cm2 and 59 kV/cm, respectively.

Oriented ferroelectric La-Sr-Co-O/Pb-La-Zr-Ti-O/La-Sr-Co-O heterostructures on [001] Pt/SiO2 Si substrates using a bismuth titanate template layer

We demonstrate the growth of c-axis oriented La-Sr-Co-O/Pb-La-Zr-Ti-O/La-Sr-Co-O ferroelectric capacitor heterostructures on a highly [001] oriented Pt film which was grown on a thermally oxidized Si (SiO2/Si) substrate. The [001] growth orientation in the Pt film is induced by depositing it on a thin c-axis oriented bismuth titanate template layer which is previously grown on the SiO2/Si substrate. The test capacitors show saturation and remnant polarization values comparable with that obtained on single-crystal LaAlO3 substrates. The use of a Pt layer reduces the sheet resistance of the bottom electrode stack by at least 3–5 times. Since the Pt layer is strongly [001] oriented, it favors the growth of [001] La-Sr-Co-O (LSCO) and lead zirconate titanate layers. The use of the LSCO top and bottom electrodes in contact with the ferroelectric thin film provides the resistance to bipolar fatigue, consistent with our earlier results.

Influence of doping on the early stages of precipitation in CuCo-base alloys

Magnetic properties of a Cu-0.7at.%Co and a Cu-0.7at.%Co-0.3at.%Ge alloy have been studied during isothermal precipitation in the temperature range from 743 to 803 K. Magnetization curves have been determined in the temperature range from 5 to 300 K. Since the precipitate particles exhibit superparamagnetic behaviour, the average size and particle density per unit volume of the precipitates could be estimated from the initial magnetic susceptibility and the saturation polarization values. Both of these parameters have been utilized to characterize the different stages of the decomposition processes. The chemical volume diffusion is slower in the ternary alloy than in the binary.

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.

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.

Dielectric Properties of Sodium and Potassium Niobates

The following paper deals with evidence of ferroelectricity in KNb${\mathrm{O}}_{3}$ and NaNb${\mathrm{O}}_{3}$. Temperatures at which both materials undergo crystallographic changes and corresponding changes in dielectric constant and loss tangent are reported. Photographs of dielectric hysteresis loops and values of saturation polarization taken at various points over a temperature range are given for KNb${\mathrm{O}}_{3}$.