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 cycle

Dynamical Dark Matter: II. An Explicit Model

In a recent paper (arXiv:1106.4546), we introduced "dynamical dark matter," a new framework for dark-matter physics, and outlined its underlying theoretical principles and phenomenological possibilities. Unlike most traditional approaches to the dark-matter problem which hypothesize the existence of one or more stable dark-matter particles, our dynamical dark-matter framework is characterized by the fact that the requirement of stability is replaced by a delicate balancing between cosmological abundances and lifetimes across a vast ensemble of individual dark-matter components. This setup therefore collectively produces a time-varying cosmological dark-matter abundance, and the different dark-matter components can interact and decay throughout the current epoch. While the goal of our previous paper was to introduce the broad theoretical aspects of this framework, the purpose of the current paper is to provide an explicit model of dynamical dark matter and demonstrate that this model satisfies all collider, astrophysical, and cosmological constraints. The results of this paper therefore constitute an "existence proof" of the phenomenological viability of our overall dynamical dark-matter framework, and demonstrate that dynamical dark matter is indeed a viable alternative to the traditional paradigm of dark-matter physics. Dynamical dark matter must therefore be considered alongside other approaches to the dark-matter problem, particularly in scenarios involving large extra dimensions or string theory in which there exist large numbers of particles which are neutral under Standard-Model symmetries.Comment: 45 pages, LaTeX, 10 figures. Replaced to match published versio

Orientation of rapid thermally annealed lead zirconate titanate thin films on (111) Pt substrates

The nucleation, growth, and orientation of lead zirconate titanate thin films prepared from organometallic precursor solutions by spin coating on (111) oriented platinum substrates and crystallized by rapid thermal annealing was investigated. The effects of pyrolysis temperature, post-pyrolysis thermal treatments, and excess lead addition are reported. The use of post-pyrolysis oxygen anneals at temperatures in the regime of 350-450 °C was found to strongly affect the kinetics of subsequent amorphous-pyrochlore-perovskite crystallization by rapid thermal annealing. The use of such post-pyrolysis anneals allowed films of reproducible microstructure and textures [both (100) and (111)] to be prepared by rapid thermal annealing. It is proposed that such anneals and pyrolysis temperature affect the oxygen concentration/average Pb valence in the amorphous films prior to annealing. Such changes in the Pb valence state then affect the stability of the transient pyrochlore phase and thus the kinetics of perovskite crystallizatio

Microstructure of PZT sol-gel films on Pt substrates with different adhesion layers

The influence of Ta, Ti and TiO2 adhesion layers with Pt bottom electrodes and the deposition temperature of the metallization on the nucleation and growth of sol-gel derived Pb(Zr0.53Ti0.47)O-3 thin films is reported. Several different PZT annealing profiles were simultaneously investigated to determine the role of PZT annealing on resultant PZT film microstructures for a given metallization. The adhesion layer was found to primarily influence PZT grain size. Largest grain sizes were observed for substrate structures with TiO2 adhesion layers. Slower heating rates resulted in rosette type structures and a large volume of residual pyrochlore, particularly in the case of TiO2 adhesion layers, while yielding only a grain size increase on Ti and Ta bonded substrates. These results were correlated to the stability of the adhesion layers in terms of diffusion through Pt and thus changes in the chemistry and structure of the film/Pt interface where the perovskite nucleation was observed to occur. The Pt metallizations were found to be more strongly (111) textured on the purely metallic adhesion layers and independent of the adhesion layer deposition temperature. PZT texture was found to be influenced by adhesion layer deposition temperature and PZT annealing profile. The perovskite texture was altered through annealing conditions only on TiO2 bonded substrates. The above results suggested a reduction of the number of perovskite nucleation sites on metallizations with TiO2 adhesion layer. This result is in agreement with Rutherford backscattering evidence from previous investigations

Processing of sol-gel PZT films for microactuators

Sol-gel derived lead zirconate titanate (PZT) thin films are being investigated for micromechanical applications. A synthesis technique which involves the spin coating of several thin layers followed by rapid thermal annealing to crystallize the perovskite phase and repetition to achieve thicker films is described. Methods of improving the PZT-PZT interfaces between subsequently annealed layers are described. Specifically, the effects of introducing thin (≈ 15 nm) Pb or Ti-rich layers at the PZT-PZT interfaces were investigated by transmission electron microscopy (TEM). Both the Pb and Ti-rich interlayers are shown to yield films of improved microstructure compared to films prepared without such compositional modifications

Ferroelectric thin films for microsystems

Deposition, integration and application issues of ferroelectric thin films are briefly reviewed. Applications in ultrasonic micromotors and infra-red sensors are treated in more detail. Current results on stress measurements across the ferroelectric phase transition and on pyroelectric devices are presented

Fabrication and characterization of PZT thin films for micromotors

Piezoelectric membranes consisting of PbZrxTi1-xO3 (PZT) films on silicon diaphragms have been fabricated, investigated, and applied for micromotors. The PZT films were deposited by sputtering and sol gel techniques. Resonance amplitudes of up to 1000 nm/V have been measured for 16 mu m thick, 2 mm diameter membranes with 0.6 mu m PZT. The PZT films show a preferred direction of polarization, which seems to depend on the deposition technique. Membranes of 4 mm diameter have been successfully applied as a vibrator of a micro motor, allowing for the first time the characterization of a PZT thin film micro motor. The motor could be operated with voltages as low as 1.0 V-rms, which is much less than has been obtained with ZnO micro motors and is sufficiently low for standard battery and IC supply voltages. A 100 h degradation test of frequency and amplitude has revealed a 5 % drop in amplitude, possibly due to depolarization

NbSe3: Effect of Uniaxial Stress on the Threshold Field and Fermiology

We have measured the effect of uniaxial stress on the threshold field ET for the motion of the upper CDW in NbSe3. ET exhibits a critical behavior, ET ~ (1 - e/ec)^g, wher e is the strain, and ec is about 2.6% and g ~ 1.2. This ecpression remains valid over more than two decades of ET, up to the highest fields of about 1.5keV/m. Neither g nor ec is very sensitive to the impurity concentraction. The CDW transition temperature Tp decreases linearly with e at a rate dTp/de = -10K/%, and it does not show any anomaly near ec. Shubnikov de-Haas measurements show that the extremal area of the Fermi surface decreases with increasing strain. The results suggest that there is an intimate relationship between pinning of the upper CDW and the Fermiology of NbSe3.Comment: 4 pages, 5 figure

Interferometric study of piezoelectric degradation in ferroelectric thin films

Degradation of piezoelectric properties has been studied in ferroelectric PZT films by means of optical interferometry. The degradation under de bias and aging of poled films have been observed. The decay of piezoelectric coefficient with time is described by a logarithmic law with aging rates comparable to those of switching polarization. The aging rates are shown to be sensitive to poling conditions and to orientation of the poling field with respect to the direction of preferred polarization. The fatigue measurements revealed a decrease of piezoelectric coefficient with a simultaneous shift of piezoelectric hysteresis loops. Degradation tests on thin membranes covered by PZT films have been reported