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15 Dec 2006

Volume 100, Issue 12, Articles (12xxxx)

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Ferroelectric crossovers triggered by isovalent A-site substitution in Pb0.7La0.2TiO3

Hwee Ping Soon and John Wang

J. Appl. Phys. 100, 124101 (2006); http://dx.doi.org/10.1063/1.2401026 (7 pages) | Cited 3 times

Online Publication Date: 18 December 2006

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A-site isovalent substitutions trigger ferroelectric transitions in Pb0.7(1−x)A0.7xLa0.2TiO3, where A = Ca, Sr, or Ba. The transitions are dependent on the type and amount of substitutions such as Ca2+, Sr2+, and Ba2+. A transition from normal ferroelectric (FE) to relaxor FE (RFE) is induced by Ca2+, Ba2+, and Sr2+ substitutions at x = 0.30, 0.40, and 0.60, respectively. Interestingly, a further crossover to quantum paraelectriclike behavior occurred in Pb0.7(1−x)Ca0.7xLa0.2TiO3 with x = 0.60, in addition to the transition from FE to RFE. The observed ferroelectric crossovers and temperature dependence of relative permittivity ε′(T) can be correlated to the structural parameters and breakdown in long-range polar order brought by the A-site isovalent substitution.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.B- Phase transitions and Curie point
77.22.Jp Dielectric breakdown and space-charge effects
77.22.Ch Permittivity (dielectric function)

Imprint mechanism in integrated Bi-rich SrBi2Ta2O9 capacitors: Influence of the temperature-dependent polarization

L. Goux and D. J. Wouters

J. Appl. Phys. 100, 124102 (2006); http://dx.doi.org/10.1063/1.2402027 (8 pages) | Cited 1 time

Online Publication Date: 18 December 2006

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In this work, we characterize the imprint properties of three-dimensional Sr0.8Bi2.2Ta2O9 (SBT) ferroelectric capacitors integrated in 0.18 μm technology using metal-organic chemical vapor deposition of SBT. We investigated the dependence of hysteresis loops on the storage temperature and duration after poling the capacitors. Also, the influence of unipolar and bipolar voltage cyclings, respectively, during and after the imprint stress was studied. We show that the imprint-induced shift of the hysteresis is limited for all the investigated stress conditions, and we associate this low shift mainly to a pronounced polarization decrease with the temperature, deviating from the Landau-Devonshire law. Our results also suggest that emission within the SBT layer is dominant over injection from the electrode in the imprint mechanism at 0 V bias. On the other hand, dynamic imprint stress results suggest an increased contribution of carrier injection. Regarding the switchable polarization, it was observed to be higher after an imprint stress due to a wake-up of ferroelectric domains, which may be thermally driven but was evidenced to be prominently field driven. The wake-up and the imprint are discussed in terms of trapping/detrapping mechanisms.
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84.32.Tt Capacitors
85.50.Gk Non-volatile ferroelectric memories

The impact of negative-bias-temperature-instability on the carrier generation lifetime of metal-oxynitride-silicon capacitors

S. N. Volkos, E. S. Efthymiou, S. Bernardini, I. D. Hawkins, A. R. Peaker, and G. Petkos

J. Appl. Phys. 100, 124103 (2006); http://dx.doi.org/10.1063/1.2402346 (9 pages) | Cited 10 times

Online Publication Date: 20 December 2006

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N-type metal-oxynitride-silicon capacitors were subjected to a negative bias voltage at an elevated temperature. Under this condition, Negative-bias-temperature-instability (NBTI) was evidenced in capacitance-voltage (CV) characteristics with an accompanying decrease, as determined from inversion layer-related (i.e., generation lifetime) deep-level-transient-spectroscopy (DLTS) measurements, in the carrier generation lifetime. An analysis of the dominant defect supplying minority carriers to the inversion layer at the silicon-oxynitride interface revealed a significant change brought about by NBTI. A full recovery of the carrier generation lifetime was observed after several days at zero bias voltage, and room temperature conditions had elapsed following NBTI. Concurrently, a passivation, as inferred from conventional DLTS measurements, of the NBTI-induced trap density occurred at the silicon-oxynitride interface. These relaxation and deactivation phenomena were discussed in the context of a plausible model involving a reaction at the silicon-oxynitride interface between trivalent silicon dangling bond defects and hydrogenous species.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
84.32.Tt Capacitors

A semiclassical model of dielectric relaxation in glasses

John R. Jameson, Walter Harrison, P. B. Griffin, J. D. Plummer, and Y. Nishi

J. Appl. Phys. 100, 124104 (2006); http://dx.doi.org/10.1063/1.2397323 (20 pages) | Cited 8 times

Online Publication Date: 20 December 2006

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A semiclassical double-well model of dielectric relaxation current in glasses is extended to (i) nonzero temperature, (ii) complex bias histories, and (iii) strong electric fields. At finite temperature, thermal excitation yields a contribution linear in temperature, which adds to the temperature-independent contribution from tunneling from the zero-temperature case. Both contributions vary linearly with applied field and have a time dependence of 1/tn. Experimental measurements in three different glasses are shown to agree with this prediction, and it is shown how to use such measurements to estimate the material parameters t0 and σ0. For complex bias histories, a principle of superposition is found, as observed experimentally, if the applied fields are weak compared to the material parameter E0, estimated to be on the order of 107 V/m. For an electric field pulsed periodically from 0 to E, the current can be decomposed into a fast contribution due to particles tunneling back and forth every cycle of the field, and a slow residual contribution whose time dependence is the same as that for a continuous bias, but whose magnitude is reduced by the duty cycle of the periodic bias. For a sinusoidal electric field, thermal excitation gives a contribution to the dielectric constant that varies linearly with temperature and has a real part that varies logarithmically with frequency and an imaginary part that varies as the inverse tangent of frequency. For tunneling, both parts are independent of temperature and vary approximately as the logarithm of frequency, a dependence observed experimentally and almost indistinguishable from that suggested by the 1/tn current response to a step voltage. For strong electric fields, the current that flows after the field is removed is found to be dominated by particles that fell forward when the field was on. Since particles fall forward quickly but tunnel back slowly, even strong fields applied for a short period of time can produce a large, long-lasting return current. These analyses lead to a number of testable predictions, and should be useful for understanding the phenomenon of dielectric relaxation and its impact on electronic devices.
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77.22.Gm Dielectric loss and relaxation
73.40.Gk Tunneling
77.22.Ej Polarization and depolarization
61.43.Fs Glasses
81.05.Kf Glasses (including metallic glasses)

Composition influences on the electrical and electromechanical properties of lead zirconate titanate thin films

P. Gerber, U. Böttger, and R. Waser

J. Appl. Phys. 100, 124105 (2006); http://dx.doi.org/10.1063/1.2401047 (8 pages) | Cited 5 times

Online Publication Date: 21 December 2006

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The influences of the Zr content on the structural, electrical, and electromechanical properties of Pb[Zr(x),Ti(1−x)]O3 [PZT(x/1−x)] thin films are investigated in detail. Additionally to measuring all major characteristics of the samples, the electromechanical large-signal behavior is modeled. Raising the Zr content increases the unit cell size and forces the preferred phase to become rhombohedral above the morphotropic phase boundary (MPB). The increased unit cell size changes the switching behavior and increases the intrinsic behavior of the unit cells. The intrinsic behavior is reduced by the phase change, which also introduces non-180° domain wall motion, improving the large-signal strain. Additionally, the domain configuration in saturation is more stable further away from the MPB. Finally, the most suitable materials will be selected for different applications.
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77.80.B- Phase transitions and Curie point
77.80.Dj Domain structure; hysteresis
77.80.Fm Switching phenomena
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.70.+a Pyroelectric and electrocaloric effects
77.65.-j Piezoelectricity and electromechanical effects
77.55.-g Dielectric thin films

Influence of electron-beam and ultraviolet treatments on low-k porous dielectrics

E. Martinez, N. Rochat, C. Guedj, C. Licitra, G. Imbert, and Y. Le Friec

J. Appl. Phys. 100, 124106 (2006); http://dx.doi.org/10.1063/1.2401055 (5 pages) | Cited 6 times

Online Publication Date: 22 December 2006

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The down scaling of complementary metal oxide semiconductor transistors requires materials such as porous low-k dielectrics for advanced interconnects to reduce resistance-capacitance delay. After the deposition of the matrix and a sacrificial organic phase (porogen), postcuring treatments may be used to create porosity by evaporation of the porogen. In this paper, Auger electron spectroscopy is performed to simultaneously modify the material (e-beam cure) and measure the corresponding changes in structure and chemical composition. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy measurements in attenuated total reflection mode confirm the Auger results. The porogen removal and matrix cross-linking result in the formation of a Si–O–Si network under e-beam or ultra violet cure. The possible degradation of these materials, even after cure, is mainly due the presence of Si–C bonds.
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77.55.-g Dielectric thin films
61.82.Ms Insulators
61.80.Fe Electron and positron radiation effects
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
68.55.-a Thin film structure and morphology
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Role of the spin-pair correlation in magnetic relaxor ferroelectrics

Q. S. Xia and Q. Jiang

J. Appl. Phys. 100, 124107 (2006); http://dx.doi.org/10.1063/1.2401646 (5 pages) | Cited 4 times

Online Publication Date: 22 December 2006

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In magnetic relaxor ferroelectrics, for the coupling interaction between the relaxor ferroelectricity and magnetic order, the dielectric susceptibility exhibits a sharp increase around the magnetic phase transition temperature. By adding an appropriate coupling term between the electrical and magnetic subsystems, which is related to the interaction of the Heisenberg spin and the order parameter field, the replica theory based on the spherical random-bond-random-field model and the mean-field theory based on the Heisenberg model are successfully applied to the magnetic relaxor ferroelectrics. We find that the fluctuation of the spin-pair correlation plays an important role in the change of dielectric susceptibility around the magnetic phase transition temperature. The obtained static dielectric susceptibility and the magnetocapacitance are in good agreement with the experimental results.
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77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
77.80.-e Ferroelectricity and antiferroelectricity
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.10.Jm Quantized spin models, including quantum spin frustration
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)

Enhanced magnetoelectric effect in three-phase MnZnFe2O4/Tb1−xDyxFe2−y/Pb(Zr,Ti)O3 composites

Shuxiang Dong, Junyi Zhai, JieFang Li, and D. Viehland

J. Appl. Phys. 100, 124108 (2006); http://dx.doi.org/10.1063/1.2402968 (4 pages) | Cited 14 times

Online Publication Date: 26 December 2006

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Three-phase magnetoelectric (ME) laminate composites made of high-permeability (μ) MnZnFe2O4, magnetostrictive Tb1−xDyxFe2−y, and piezoelectric Pb(Zr,Ti)O3 layers and operated in longitudinal magnetization and transverse polarization (L-T) bending modes have been studied. High-μ MnZnFe2O4 layers act as flux concentrators. This results in increased apparent piezomagnetic coefficients in the magnetostrictive Tb1−xDyxFe2−y layer and consequently larger induced voltages across the piezoelectric Pb(Zr,Ti)O3 layers. We find the enhanced ME field coefficients of up to 8 times for longitudinal magnetization mode, and up to 28 times for transverse magnetization mode, under small dc magnetic field bias.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.80.+q Magnetomechanical effects, magnetostriction
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
77.65.-j Piezoelectricity and electromechanical effects
77.55.-g Dielectric thin films

Structural properties of epitaxial SrTiO3 thin films grown by molecular beam epitaxy on Si(001)

G. Delhaye, C. Merckling, M. El-Kazzi, G. Saint-Girons, M. Gendry, Y. Robach, G. Hollinger, L. Largeau, and G. Patriarche

J. Appl. Phys. 100, 124109 (2006); http://dx.doi.org/10.1063/1.2407273 (5 pages) | Cited 24 times

Online Publication Date: 27 December 2006

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This work reports on the structural properties of an epitaxial SrTiO3 (STO) layer grown by molecular beam epitaxy on a Si(001) substrate with a two step process. The study, which includes a complete characterization of large scale plane-view images of the STO layer, is based on a careful analysis of x-ray spectra and transmission electron microscopy images. The STO layer presents a good crystalline quality and a slight texturation related to the presence of extended defects. A thin Ti-rich amorphous silicate layer (thickness ≈ 1.3 nm) is formed at the interface between the STO and the Si substrate, evidencing the thermodynamic instability of the STO/Si interface. The difference between the thermal expansion coefficients of Si and STO is shown to be at the origin of an increased in-plane lattice parameter (3.927 Å) of the STO layer as compared to its bulk value (3.905 Å). This effect of differential thermal expansion is expected to be responsible for the formation of at least part of the extended defects of the STO layer.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
68.55.-a Thin film structure and morphology
78.70.Dm X-ray absorption spectra
68.37.Lp Transmission electron microscopy (TEM)
61.72.Nn Stacking faults and other planar or extended defects

Sensitivity of synchrotron radiation x-ray diffraction to the chemical ordering in epitaxial perovskite multilayers

Maud Nemoz, Eric Dooryhee, Jean-Louis Hodeau, Catherine Dubourdieu, Hervé Roussel, and Pascale Bayle-Guillemaud

J. Appl. Phys. 100, 124110 (2006); http://dx.doi.org/10.1063/1.2374670 (7 pages) | Cited 1 time

Online Publication Date: 28 December 2006

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The present work shows that the chemical ordering in (BaTiO3/SrTiO3)N chemical-vapor-deposition-grown superlattices can be reliably estimated by synchrotron radiation x-ray diffraction (XRD). XRD (00l) diagrams for l = 1–8 have been simultaneously simulated using a unique set of parameters describing the stack with a model based on periodic structural and chemical profiles. The relative sensitivity of the (00l) reflections to the atomic concentrations of Sr and Ba is presented: the SrTiO3 and BaTiO3 scattering factors partially compensate each other for the l odd, and their respective contributions in the (007) reflection can be disentangled. Using this property, an accuracy as good as 5% can be obtained regarding the Ba and Sr atomic concentrations. Synchrotron radiation reflectivity was performed, and the simulation confirms the observed large atomic interlayer diffusion. Moreover, energy electron loss spectroscopy measurements at the barium and the strontium edges give a very good agreement with the diffusion profiles determined from our XRD diagram simulations. In such oxide multilayers, the extracted chemical profile does not fully obey Vegard’s law.
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68.65.Ac Multilayers
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
68.35.Fx Diffusion; interface formation
79.20.Uv Electron energy loss spectroscopy

Durability properties of piezoelectric stack actuators under combined electromechanical loading

Pavel M. Chaplya, Milan Mitrovic, Gregory P. Carman, and Friedrich K. Straub

J. Appl. Phys. 100, 124111 (2006); http://dx.doi.org/10.1063/1.2407269 (13 pages) | Cited 13 times

Online Publication Date: 29 December 2006

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This paper presents results on the electro-thermo-mechanical behavior of piezoelectric materials for use in actuator applications with an emphasis on durability performance. The objective of this study was to compare the performance of different commercially available actuator systems and to determine the properties necessary for the design of such actuator systems. Basic piezoelectric properties of five stack actuators were determined as a function of mechanical preload and temperature. Changes in these properties during ferroelectric fatigue up to 107 cycles were determined from strain-field relations after a specified number of fatigue cycles. Experimental results indicate a strong dependence of piezoelectric properties and power requirements on mechanical loading conditions. Results indicate that the optimum operating conditions (i.e., mechanical preload) that will improve actuation capabilities of piezoelectric stack actuators can be determined. That is, strain output was found to increase by 60% for some actuators upon the application of certain compressive prestress. Results of fatigue tests indicate negligible degradation in strain output for some stack actuators even when operated under mechanical preload that causes large displacements through domain wall motion. Similar trends in strain output and current degradation curves (as a function of fatigue cycles) suggest that material degradation can be indirectly inferred from simply measuring the current being dissipated by the material and the fatigue predicted by measuring the strain output (quantity related to domain motion). Finally, temperature rise of lead zirconate titanate stacks due to self-heating should be taken into account when designing actuator systems, since temperature changes were found to significantly influence both strain output and power required to drive piezoelectric stack actuators. Physical mechanisms of ferroelectric fatigue are explored.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Electrocaloric and pyroelectric properties of 0.75Pb(Mg1/3Nb2/3)O3–0.25PbTiO3 single crystals

Gael Sebald, Laurence Seveyrat, Daniel Guyomar, Laurent Lebrun, Benoit Guiffard, and Sebastien Pruvost

J. Appl. Phys. 100, 124112 (2006); http://dx.doi.org/10.1063/1.2407271 (6 pages) | Cited 33 times

Online Publication Date: 29 December 2006

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Pyroelectric and electrocaloric characterization has been determined for 0.75Pb(Mg1/3Nb2/3)O3–0.25PbTiO3 relaxor based single crystal and ceramic. Differential scanning calorimetry was used for measuring the electrocaloric response for different electric fields in the vicinity of the Curie temperature. For both ceramic and crystals the maximum activity is found to be around the transition temperature. On the other hand hysteresis loops for different temperatures were used to predict the electrocaloric effect with very good qualitative agreements with direct measurements. Pyroelectric coefficient is found to be much larger for ⟨111⟩ single crystals reaching 1300×10−6 C m−2 K−1 whereas the ceramic reaches only 750×10−6 C m−2 K−1. Higher pyroelectric coefficient and lower dielectric permittivity lead to outstanding figures of merits for sensors and energy harvesting, with a gain of 260% for voltage responsivity and more than 500% for energy harvesting. Although having a much larger pyroelectric activity, the electrocaloric effect is about the same for crystals and ceramics—around 0.40 J/g for 2.5 kV/mm electric field step. This result is interpreted by the decrease of the pyroelectric coefficient for high electric field. The electrocaloric activity is in fact limited by the saturation polarization and difference between Curie transition temperature and the working temperature. Those two parameters are very similar for crystals and ceramics. Single crystals are consequently very interesting materials in the framework of energy harvesting and sensor applications whereas no real improvement of performances can be expected for electrocaloric refrigeration devices.
Show PACS
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.70.+a Pyroelectric and electrocaloric effects
77.80.B- Phase transitions and Curie point
77.80.Dj Domain structure; hysteresis
77.22.Ch Permittivity (dielectric function)
77.22.Ej Polarization and depolarization
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