Strontium Bismuth Tantalate Research Articles

Electrophoretic sol–gel synthesis of SrBi2Ta2O9 nanowires

We report the independent invention of perovskite ferroelectric nanowires strontium bismuth tantalate (SrBi2Ta2O9, SBT). Electrophoretic sol–gel techniques have been used successfully. The morphology and structures are analyzed via SEM, TEM and XRD. SBT nanowires and nanoparticles filled template revealed 30 and 40 μm long, respectively. SBT are proved to be a single phase of orthorhombic perovskite structure. As it indicated, SBT nanowires has been crystallized at 700 °C. To minimize surface polarity, SBT nanowires oriented preferentially along the growing axis (c axis) by translation and rotation of atomic clusters of SBT.

CHARACTERIZATION OF SECOND GENERATION ADVANCED DYNAMIC PYROELECTRIC FOCAL PLANE ARRAY

ABSTRACT The pyroelectric effect has been characterized for single-pixel elements consisting of strontium bismuth tantalate (SBT) ferroelectric material as the sensing element. The pixels include also a thermal insulating layer and an infrared (IR) absorber layer. These MEMS-less devices are operated in active mode, a technique that eliminates the need for a radiation chopper found in passive pyroelectric IR imagers. Test results of the SBT pixels of dimensions 7.5 μm × 7.5 μm to 200 μm × 200 μm have shown high endurance to polar cycling, high responsivity values, and very low noise-equivalent temperature difference for focal plane array applications. This paper describes and analyses the results of precursor 2 × 2 arrays using discrete sensing elements, the active detection mechanism, and its unique read-out electronics. A second-generation 32 × 32 pixels array being implemented to demonstrate the performance of a 1k-pixel array as precursor to larger size arrays is also described. The active mode detection, in addition to eliminating the use of a chopper, enables the dynamic partition of the array into pixel domains in which the pixel sensitivities in each domain can be adjusted independently. This unique feature in IR detection is not readily found in other types of IR imagers and can be applied to the simultaneous tracking of diverse contrast objects. By controlling the absorber material thickness, the arrays can be optimized for maximum response at specified wavelengths by means of quarter-wavelength interferometric technique.

Sol–Gel synthesis of SrBi 2Ta 2O 9 nanowires

We report the synthesis of perovskite ferroelectric nanowire strontium bismuth tantalate (SrBi 2Ta 2O 9, SBT). Sol–gel techniques have been used. The morphology and structures are analyzed via SEM, TEM and XRD. The XRD and TEM analysis show that the structure of SBT nanowires is single orthorhombic perovskite with A2 1 am structure space group. The obtained SBT nanowires with an average length of 35 μm and a diameter of 200 nm are c-axis preferred orientation in the templates. The formation mechanism of SBT nanowires with complex crystal structure was discussed.

Halogen-Light-Enhanced Metallorganic Decomposition of SrBi2Ta2O9 Ferroelectric Thin Films

We investigated the influence of the halogen-light exposure on the metallorganic decomposition of strontium bismuth tantalate [ (SBT)] thin films deposited by chemical-solution deposition (CSD) on platinum (Pt) capacitors. The UV absorption spectrum obtained using Fourier transform infrared showed that the removal of the residual organic species from the SBT solution layer was enhanced by the halogen light during drying at . The halogen-light exposure improved ferroelectric properties and the formation of a (200)-preferred film structure, a superior ferroelectric property. In addition, the decomposition of oxidated bismuth (Bi–O bonds) in SBT as a result of the halogen-light exposure was also observed. Some reduction in metallic Bi from the oxidated state that occurred during the high temperature rapid thermal annealing was enhanced by the halogen-light exposure. The high ratio in the SBT film samples exposed to the halogen light was responsible for their high leakage current. At , the annealing in a ambient was effective in oxidizing Bi and in reducing the leakage current densities by about 2 orders of magnitude. Although the specific interaction between the halogen light and the CSD film remains unclear, the cost-effective and safe halogen lamp may be an appropriate choice for photoassisted thermal processes for the production of ferroelectrics.

Effect of annealing on microstructure and P–E hysteresis of vanadium doped SrBi2Ta2O9

The vanadium modified strontium bismuth tantalate (SBT) was prepared by conventional mixed oxide method using faster firing technique. Ceramics were characterised with the help of scanning electron microscopy and the ferroelectric P–E loop analysis after subsequent annealing. Microstructural analysis suggested a completed densification in undoped SBT after sintering and had not shown modification in microstructure after annealing. However, in the vanadium doped SBT samples the densification is achieved only during the reoxidation or annealing process. Ferroelectric hysteresis could be switched in the doped samples after 24 h of annealing despite the fact that it was not possible to obtain a P–E loop in as sintered and 7·5 h annealed samples of SBTV. The best Pr and Ec (Pr=1·75 μC cm–2, Ec=12·05 kV cm–1) combination was observed with 15% vanadium doping in SBT system which also suggested a great decrease in the coercive field value as observed earlier (∼30 kV cm–1). Current study has shown that improved ferroelectric properties were obtained in the synthesised SBT and V doped SBT even at reduced processing temperatures, which could aid in simplifying the integration of silicon based devices.

Effect of Eu/Sr Ratios on Ferroelectric and Fluorescent Properties of Eu-Substituted Strontium Bismuth Tantalate Films

The ferroelectric and fluorescent properties of Eu-substituted strontium bismuth tantalate (Eu-SBT) films grown on Pt/Ti/SiO2/Si substrates by spin coating were investigated. The polycrystalline Eu-SBT films with Aurivillius phases were grown at Eu/Sr ratios between 0 and 0.25. Moreover, the lattice constants along the a- and c-axes at Eu/Sr=0.25 in comparison with Eu/Sr=0 decreased by approximately 0.36 and 0.19%, respectively. The remnant polarization values of the Eu-SBT films with Eu/Sr ratios of 0 and 0.25 were approximately 6.6 and 5.8 µC/cm2, respectively. The 80%-fatigue endurance of a Eu-SBT film with Eu/Sr=0.25 was approximately 3.1×109 cycles when a 10 kHz triangular wave with an amplitude of 8 V (approximately 530 kV/cm electric field) was used. The photoluminescence intensity of the Eu-SBT films was increased by Eu doping with negligible change of the remnant polarization. Emission peaks at approximately 600 nm in wavelength, which were associated with the 5D0–7F transitions of Eu3+, were observed in the Eu-SBT films.

Effects of acetoin as chelating agent on the preparation of SrBi2Ta2O9 thin films from non-hydrolyzing precursors

Ferroelectric thin films of strontium bismuth tantalate (SBT) have been fabricated by a chemical solution deposition technique using non-hydrolyzing precursors. Strontium acetate, bismuth nitrate and tantalum ethoxide were used as precursor materials, with methanol and glacial acetic as solvents. We investigate the effects of the precursor chemistry, by the selection of the chelating agent, on the elimination of residual organic compounds, thermal evolution of phase formation, and microstructure evolution of derived films. We found that the utilization of alkanolamines as chelating agent produce the segregation of metallic bismuth in as-prepared powders. On the other hand, acetoin, one of the hydroxyketones, showed the elimination of residual organics at low temperature, an earlier onset of crystallization, and no segregation of secondary phases during the whole crystallization process. A comparative investigation of the surface microstructure, grain size distribution, crystallinity, and degree of crystal orientation of films fabricated with the different chelating agents is presented. The dielectric and ferroelectric properties of films prepared with acetoin are investigated.

Correlation Between Ferroelectric and Fluorescent Properties by Introducing Eu Atoms Into Strontium Bismuth Tantalate Films

AbstractElectrical and fluorescent properties of Sr-deficient strontium bismuth tantalate co-doped with excess-Bi and Eu atoms (BiEu-SBT) were investigated, in which the Eu/Bi ratio was changed between 0 and 0.1. BiEu-SBT were synthesized on Pt (200 nm)/Ti (50 nm)/SiO2/Si substrates by using Sr0.8Bi2.2Ta2O9 and Sr0.8(Bi2, Eu0.2)Ta2O9 mixed precursor solutions with a concentration of 0.33 mol/kg, in which Sr concentration was fixed at 0.8. From X-ray diffraction analysis, the diffraction peaks from Aurivillius phases were observed in the synthesized BiEu-SBT as well as in pure SBT. In BiEu-SBT, the lattice parameters along a- and c-axes at the Eu/Bi ratio of 0.1 in comparison with those of 0 decreased approximately 0.27 and 0.19 %, respectively. The remnant polarization (2Pr) values of the synthesized BiEu-SBT with Eu/Bi ratio of 0 and 0.1 were approximately 8.4 and 6.8 μC/cm2, respectively. From photoluminescence (PL) measurement at a wavelength of 615 nm as a function of Eu/Bi ratio, the PL intensity of the synthesized BiEu-SBT was proportional to the Eu/Bi ratio, whereas, the 2Pr values were slightly decreased by Eu-doping.

JITTER ANALYSIS AND PREDICTION FOR PHASE LOCKED LOOPS UTILIZING FERROELECTRIC CAPACITORS

ABSTRACT The non-linear nature of charge versus polarization in ferroelectric capacitors offers the unique opportunity to minimize jitter in phase locked loops (PLL). During the low effective capacitance state, the clock generation signal within the PLL has a high slew rate offering excellent timing characteristics. During the rest of the clock period, the high effective capacitance state is used to average inherent PLL noise. In this paper, we present the improved jitter that results when a PLL is implemented utilizing a strontium bismuth tantalate niobate based ferroelectric capacitor compared to conventional linear capacitor. In addition, we present the analysis of jitter in terms of capacitance characteristics of ferroelectric capacitor. When integrated on CMOS technology, PLLs based on ferroelectric capacitors have great potential for producing reduced jitter clock sources usable in future clock recovery and communication circuits.

PRECURSOR CHEMISTRY FOR POLAR NANOTUBES

ABSTRACT The strategy for synthesising a precursor solution for Misted Chemical Deposition of strontium bismuth tantalate is described and the importance of attention to detail is illustrated. With a view towards eventual commercial exploitation, emphasis is laid upon robustness and adaptability of the synthesis process in terms of raw material availability, impurity elimination, solution formulation and stoichiometry control.

Ferroelectric and Luminescent Properties of Eu-Doped SrBi2Ta2O9 Films

Sr-deficient and Bi-excess strontium bismuth tantalate (SBT) films doped with Eu atoms with concentrations from 1.25 to 5 mol % (SBT:Eu) were grown on Pt/Ti/SiO2/Si substrates by spin coating. The crystallinity of the SBT:Eu films was characterized by X-ray diffraction analysis. The ferroelectric and luminescent properties of the SBT:Eu films were measured at room temperature. Polycrystalline SBT:Eu films with the Aurivillius phase were grown, in which the Eu concentration was less than 5 mol %. The remnant polarization values of the 260-nm-thick SBT:Eu films with Eu concentrations of 1.25 and 5 mol % were approximately 4.0 and 0.86 µC/cm2, respectively. The PL intensity of the SBT:Eu films was significantly dependent on both annealing temperature and Eu concentrations. The maximum PL intensity was obtained in a 5 mol %-Eu-doped SBT film at an annealing temperature of 850 °C.

Synthesis of complex ceramics by mechanochemical activation

Solid state synthesis of three complex ceramics, nickel ferrite, manganese ferrite and strontium bismuth tantalate, by mechanochemical activation in a high energy ball mill was investigated. It was shown that mechanochemical activation prior to reaction synthesis at elevated temperatures is generally beneficial to reduce the necessary synthesis temperature. Synthesis of manganese ferrite occurred even during the ball milling but not to completion. Subsequent heating to complete the synthesis resulted in deterioration of the manganese ferrite back into the constituent oxides. In strontium bismuth tantalate, the other oxides dissolved initially in bismuth oxide during the activation process.

Influence of redeposition on the plasma etching dynamics

This work reports on measurements of the degree of redeposition of sputtered species during the etching of platinum (Pt), barium-strontium-titanate (BST), strontium-bismuth-tantalate (SBT), and photoresist (PR) in a high-density argon plasma. While PR exhibits a redeposition-free behavior, the degree of redeposition of Pt, BST, and SBT species increases from 10% to 95% as the argon pressure increases from 0.5to10mTorr. These results are in good agreement with the predictions of a simple model accounting for the backscattering of sputtered species following their interaction with the gas phase. Based on these results and using other experimental data reported in the literature, it is further demonstrated that, depending on the plasma etching conditions, redeposition effects can induce misinterpretation of the etch rate data.

Enhanced pyroelectric sensitivity using ferroelectric active mode detection

Active pyroelectric detection (APD), using ferroelectrics as the sensing materials, is described and compared to traditional-passive pyroelectric modes of operation. The active approach yields a number of distinct advantages over its passive counterparts, including greater effective pyroelectric coefficient and improved signal to noise ratio. Thin film test structures formed from strontium bismuth tantalate (SrBi2Ta2O9) are used to demonstrate the APD principle.

Behavior of the ferroelectric polarization as a function of temperature in sol-gel derived strontium bismuth tantalate thin films

Strontium bismuth tantalate (SBT) thin films of nominal composition Sr0.8Bi2.2Ta2O9 have been prepared on (111)Pt/TiO2/SiO2/(100)Si substrates by Chemical Solution Deposition (CSD) methods, using two different thermal treatments of crystallization. The evolution of the ferroelectric polarization as a function of temperature has been studied using hysteresis loops, thermo stimulated current (TSC) measurements and the evolution of the pyroelectric coefficient (γM) with temperature. The results of remnant polarization (Pr) obtained from hysteresis loops and γM as a function of temperature showed different trends, indicating the presence of polarizing bias field in the prepared thin films due to induced asymmetry of the electrical and mechanical conditions produced at the top and bottom film electrode interfaces. The competition between internal bias fields due to differences in contact potentials of bottom and top electrodes and flexoelectric bias fields induced by stress gradient, can be in the origin of the γM fluctuation with temperature. A critical temperature (T*) is found that can be explained as the crossover between the dominant effects. It can be related to a possible ferroelectric-ferroelectric phase transition previously reported. The results also indicate that the Pr is not stable for temperatures over ≈425 K.

Influence of Ta content on the physical properties of SrBi2Ta2O9 ferroelectric thin films

We have investigated the effect that the Ta content has on the ferroelectric properties of strontium bismuth tantalate (SBT) thin films synthesized using metalorganic decomposition (MOD) and spin coating techniques. The physical properties of these SBT samples were strongly dependent upon the Ta ratio. Polarization measurements revealed that Ta-deficient SBT exhibited a relatively low coercive field (2Ec ∼ 87 kV/cm) and a high remanent polarization (2Pr ∼ 15 μC/cm2). The value of 2Pr decreased as the Ta ratio in SBT increased. The improved ferroelectric properties of the Ta-deficient SBT samples may have resulted from the uniformly well-grown bismuth-layered-structured (BLS) phases of the films and their highly preferential orientation along the a and b axes. We suggest that the incorporation of Ta vacancies plays an important role in enhancing the crystallinities and microstructures of Ta-deficient SBT films.

Piezoelectric properties of SrBi2M2− xVxO9 (M = Nb and Ta) ceramics

Vanadium-substituted strontium bismuth tantalate, Sr0.8Bi2.2Ta2− xVxO9 (SBTVx), and strontium bismuth niobate, SrBi2Nb2− xVxO9 (SBNVx), ceramics were synthesized by a low-temperature processing, and their dielectric, ferroelectric and piezoelectric properties were characterized. With the partial substitution of tantalum or niobium by vanadium cations, the single phase of the ABi2M2O9-type structure was preserved and the sintering temperature was significantly decreased. For the SBNV ceramics, the T c of 437∘C for x = 0.0, the vanadium content hardly changed. On the other hand, the T c of the SBTV ceramics increased from 408∘C for the non-substituted SBTV to 414∘C for x = 0.05 and then with the increasing vanadium content, the T c decreased to 379∘C for x = 0.20. The remanent polarizations, P r, of SBTV and SBNV at room temperature were 4.9 and 5.4 μC/cm2, respectively. All the obtained independent electromechanical coupling factors of the SBTV0.05 ceramics were as follows: k p = 0.119, k 31 = 0.073, k 33 = 0.165, k 15 = 0.051 and k t = 0.134, and the SBNV0.05 ceramics were as follows: k p = 0.074, k 31 = 0.045, k 33 = 0.175, k 15 = 0.106 and k t = 0.140. These coupling factors were higher than those of the non-substituted materials. From these results, the vanadium-substituted SBT and SBN-based materials can be expected to be lead-free piezoelectric resonator materials that can be prepared at low sintering temperatures.

TRIBUTYLBISMUTH AS A LIQUID BISMUTH PRECURSOR IN AN AVD SYSTEM FOR STRONTIUM BISMUTH TANTALATE THIN FILM DEPOSITION

ABSTRACT In this study, tributylbismuth has been tested as a bismuth source for strontium bismuth tantalate (SBT) deposition using atomic vapor deposition (AVD) system. The effects of annealing temperature on the structural and electrical properties of deposited films were investigated. SBT films annealed at 750°C were crystallized in ferroelectric perovskite phase. Ferroelectric hysteresis loops of the SBT films have been measured, from which a remnant polarization of 3.5 μC/cm2 and a coercive voltage of 3 V of the crystallized SBT layer have been evaluated. SBT thin films annealed at 750°C also showed good fatigue properties. Fatigue was found to be about 4% after 109 cycles.

Oxygen ion implantation in Strontium Bismuth Tantalate thin films

Strontium Bismuth Tantalate (SBT) ferroelectric thin films have attracted considerable attention for the development of non-volatile ferroelectric random access memories (NV-FRAMs). These films, however, have a critical problem: a high processing temperature ( > 700oC) is required for the crystallization of the perovskite phase. The thermal evolution of the SBT films prepared by Chemical Solution Deposition (CSD) techniques showed the formation of an intermediate oxygen-deficient fluorite phase at ~ 550oC. The SBT perovskite phase crystallizes at higher temperatures. To favor an earlier perovskite crystallization, SBT thin films were implanted with oxygen ions pulses produced by a Plasma Focus (1 kJ). The samples were annealed at different temperatures in oxygen atmosphere and characterized by GI-XRD and Atomic Force Microscopy techniques. It was found that oxygen addition into the SBT structure promotes a better crystallization of the perovskite phase.

Deterioration Process of Strontium Bismuth Tantalate Induced by Hydrogen Reduction

We studied the effect of annealing in a hydrogen gas on the crystal structure of strontium bismuth tantalate (SBT) by means of X-ray diffraction measurements. The hydrogen reduction happens mainly in bismuth oxide layers followed by the decomposition of pseudo-perovskite layers. With increasing the annealing time and/or temperature, new crystalline products such as bismuth, strontium tantalate, and bismuth oxide, and an unidentified crystal are observed along with non-crystalline materials. Decomposition of SBT and recrystallization of the decomposed materials occur even from the initial stage of the hydrogen reduction process.