Showing papers on "Lead zirconate titanate published in 1993"

Domain wall clamping in ferroelectrics by orientation of defects

Abstract: A quantitative model which describes the aging of the material properties in acceptor doped ferroelectric ceramics as a result of the reorientation of defects in time is proposed. By this reorientation the domain walls are clamped by a time dependent force leading to the observed decrease of the material properties during aging. The model is experimentally confirmed with aging and deaging measurements on barium titanate and lead zirconate titanate ceramics.

Low temperature perovskite formation of lead zirconate titanate thin films by a seeding process

Abstract: A two-step seeding process has been developed to lower the transformation temperature and modify the grain structure of ferroelectric lead zirconate titanate (PZT) thin films with high Zr/Ti ratio. Previous study has shown that nucleation is the rate-limiting step for the perovskite formation. Therefore, any process that enhances the kinetics of nucleation is likely to decrease the transformation temperature. In this process, a very thin (45 nm) seeding layer of PbTiO3, which has a low effective activation energy for perovskite formation, was used to provide nucleation sites needed for the low temperature perovskite formation. In this study, we have shown that the pyrochlore-to-perovskite phase transformation temperature of PbZrxTi1−xO3 films of high Zr/Ti ratio (e.g., x = 53/47) can be lowered by as much as 100 °C. The grain size of these films can also be substantially modified by this two-step approach.

Dielectric properties of tetragonal lanthanum modified lead zirconate titanate ceramics

Abstract: Tetragonal La‐modified lead zirconate titanate ceramics with a Zr/Ti ratio of 40/60 (x/40/60) with La contents (x) between 0 and 21 at. % were prepared by the mixed oxide method and were subsequently characterized using dielectric spectroscopy. Small La contents tended to diffuse the dielectric response in the temperature region around the phase transition, however, no distinct changes were observed in the paraelectric region. Compositions with intermediate La contents showed a thermally driven (spontaneous) transformation from a relaxor to a normal ferroelectric, i.e., micro‐macro domain switching. Materials with a high La content exhibited typical relaxor ferroelectric behavior. The relative thermodynamic stability of the ensemble of micropolar regions is then discussed in reference to that of the long‐range ferroelectric state.

Effects of porosity on electric fatigue behaviour in PLZT and PZT ferroelectric ceramics

Abstract: Electric fatigue, namely the decay of the polarization and the consequent elastic strain with increased number of switching cycles under high a.c. field, severely limits the applications of ferroelectric and piezoelectric materials in high-strain electro-mechanical actuators and in thin films used in non-volatile memory devices. Electric fatigue tests have been conducted on lead zirconate titanate (PZT) and lanthanum-doped lead zirconate titanate (PLZT) ferroelectric ceramics. It was found that electric fatigue can be initiated by various factors, the porosity being one of them. Electric fatigue occurred in low-density(93%–97%) PLZT 7/65/35 ceramics after 104 switching cycles, while the high-density (>99%) PLZT specimens of the same composition did not fatigue after 109 switching cycles. It was also observed that for PZT ceramics, fatigue proceeded much more slowly in the samples with higher density (∼98%) than those with lower densities (92%–96%). A tentative explanation for the origin of the fatigue mechanism associated with porosity is proposed.

Proton and carbon-13 NMR investigations of lead zirconate titanate (Pb(Zr,Ti)O3) thin-film precursor solutions

Abstract: Solvent reactions, ligand substitutions, and the oligomer/polymer backbone structure are important factors in the solution preparation of ceramic films. In this study the authors have used H and C NMR spectroscopy to characterize solvent and ligand effects in precursor solutions used for the deposition of ferroelectric PZT (lead zirconate titanate) thin films. Solutions were prepared by a sequential precursor addition method from carboxylate and alkoxide precursors of the three cations, and the solvent, acetic acid, methanol, and water. The results indicate that acetic acid was a key component in the solution preparation process. As observed previously for single metallic component systems, its presence resulted in esterification reactions, leading in the present case to the formation of methyl, isopropyl, and n-butyl acetates. Second, acetic acid functioned as a chemical modifier, or chelating agent, replacing essentially all of the alkoxy ligands of the original precursors. Since alkoxy replacement appeared to be complete, we may describe the PZT species formed in solution as oxo acetate in nature. Finally, the solvent and ligand behavior of a solution prepared by an inverted mixing order was compared to the behavior of the solution prepared by a sequential precursor addition. The spectra for the two solutions weremore » similar, and only differences in the relative intensities of the ester and alcoholic resonances were observed. 29 refs., 5 figs., 3 tabs.« less

Analysis of Bending Displacement of Lead Zirconate Titanate Thin Film Synthesized by Hydrothermal Method

Abstract: Lead zirconate titanate solid-solution (PZT) films with various thicknesses were synthesized on titanium substrates by repeated hydrothermal treatments. Young's modulus and the density of the PZT film were measured by the vibrating-reed technique and Archimedes' method, respectively, and they were lower than those of PZT ceramic. We fabricated bimorph-type bending actuators using those films and analyzed the displacement induced by the electric field. It was found that the piezoelectric constant and electromechanical coupling factor of the PZT film were comparable to those of the ceramic, and also that the displacement was caused by the piezoelectric effect. The actuators were bent by applied voltage without poling, because the polar axes in the as-deposited film were aligned in the direction from the film surface to the substrate.

Shallow Pb3+ hole traps in lead zirconate titanate ferroelectrics

Abstract: A combination of electron paramagnetic resonance and band structure calculations is used to show that the Pb2+ ions in lead zirconate titanate materials can act as shallow hole traps to give Pb3+ centers. The Pb3+ centers are created by optical illumination and are found to be metastable at room temperature. Their decay kinetics follow a stretched exponential function which suggests dispersive transport. The traps have the same character as the upper valence band which is formed from the hybridization of Pb s and O p states.

Crystallization of an amorphous lead zirconate titanate thin film with a dense-plasma-focus device.

Abstract: The pulsed ion beam of highly energetic argon ions that is generated during the focus phase of the dense-plasma-focus (DPF) device is used to crystallize the as-grown rf-sputtered amorphous thin film of lead zirconate titanate (PZT). Many samples of PZT thin films of different thicknesses are exposed to the DPF device. The 0.9-\ensuremath{\mu}m-thick PZT thin film is crystallized to the desired rhombohedral phase. The scanning electron microscopy photograph of this film indicates a reasonably good surface quality.

Preparation of Pb(Zr, Ti)O3 thin films by multi-target sputtering

Abstract: Lead zirconate titanate (PZT) thin films have been prepared with a multi-target sputtering system onto Pt-coated Si substrates. Structure, composition and dielectric properties have been investigated on films ranging in thickness from 60 nm to 1400 nm. The dominant phase of PZT thin films varied from pyrochlore to perovskite with increasing film thickness. An interface PZT layer with about 100 nm thickness, which was confirmed to mainly consist of pyrochlore phase grains, was observed at the PZT/Pt interface in a cross-sectional transmission electron microscopy (TEM) image of an 850 nm thick film. That is, the pyrochlore grains preferentially grow at the early stage of deposition and do not change their structure during subsequent deposition. Dielectric constant and remnant polarization were degraded with decreasing thickness. This can be explained in view of the existence of the interface layer with a low dielectric constant.

Reaction Mechanisms in the Formation of Lead Zirconate Titanate Solid Solutions under Hydrothermal Conditions

Abstract: Reaction mechanisms in the formation of PZT solid solution were studied under hydrothermal conditions (Pb/(Zr+Ti) = 1.0 to 1.9, Zr/Ti = 0/10 to 10/0, 1M to 5M KOH, 100° to 220°C, 2 h). A yellow tabular crystallite with tetragonal symmetry and Pb/Ti ∼ 2 was formed at 100° to 130°C. A PZT crystallite was formed just above 150°C. The crystallite was a mixture of Ti-rich PZT and Zr-rich PZT phases. When the temperature and KOH concentration were increased, the composition of the PZT product tended to be homogeneous. The PZT in the morphotropic phase boundary zone was formed at Zr/Ti = 5/5, 5M KOH, 220°C, 2 h. Neither PbTiO3 nor PbZrO3 was detected as a separate phase under the above hydrothermal conditions.

Correlations Among Degradations in Lead Zirconate Titanate thin Film Capacitors

Abstract: Many attempts have been made to reduce degradation properties of Lead Zirconate Titanate (PZT) thin film capacitors. Although each degradation property has been studied extensively for the sake of material improvement, it is desired that they be understood in a unified manner in order to reduce degradation properties simultaneously. This can be achieved if a common source(s) of degradations is identified and controlled. In the past it was noticed that oxygen vacancies play a key role in fatigue, leakage current, and electrical degradation/breakdown of PZT films. It is now known that space charges (oxygen vacancies, mainly) affect ageing, too. Therefore, a quantitative ageing mechanism is proposed based on oxygen vacancy migration under internal field generated by either remanent polarization or spontaneous polarization. Fatigue, leakage current, electrical degradation, and polarization reversal mechanisms are correlated with the ageing mechanism in order to establish guidelines for simultaneous degradation control of PZT thin film capacitors. In addition, the current pitfalls in the ferroelectric test circuit is discussed, which may cause false retention, imprint, and ageing.

Piezoelectric paints: preparation and application as built-in vibration sensors of structural materials

Abstract: Piezoelectric paints were prepared using lead zirconate titanate (PZT) ceramic powder as a pigment and epoxy resin as a binder. The obtained paints were spread on the surface of an aluminium beam and cured at room temperature, thus forming the final thin films having thicknesses of 35–81 μm and PZT volume fractions of 25%–53%. The thin films were then poled under electric fields of up to 350 kV cm−1 at room temperature, and the resulting piezoelectric activity was evaluated from vibration measurements on the aluminium beam. Although not strictly quantitative, the piezoelectric activity of the thin film showed a tendency to increase with an increase in the film thickness and the PZT volume fraction. From the standpoint of the thin film application as built-in vibration sensors, the piezoelectric activity was confirmed to be high enough to determine the natural frequencies and mode shapes of the aluminium beam.

Evaluation of Imprint Properties in Sol-Gel Ferroelectric Pb(ZrTi)O3 Thin-Film Capacitors

Abstract: Studies of imprint properties have been carried out by electrical evaluation with pulse switching response and circuit modeling on sol-gel lead zirconate titanate (PZT) ferroelectric thin-film capacitors. The imprint properties were evaluated by measuring the switched and nonswitched charges after three different operations at high temperature, which consist of (1) fatigue by cumulative bipolar pulses, (2) exposure to a large number of positive unipolar pulses, and (3) exposure to a large number of negative unipolar pulses. The nonswitched charge without polarization reversal after being exposed to a large number of unipolar pulses was increased to be greater than switched charge with polarization reversal. This causes the decrease of a noise margin when the memory cell is read. This phenomenon is enhanced by the sample temperature above 75°C, the pulse height, and the amount of cumulative fatigue cycles before imprint. This phenomenon is also found in the Nb-doped PZT capacitor, which is a candidate for fatigue-free materials.

Effects of ferroelectric switching on the dielectric and ferroelectric properties in lead zirconate titanate ceramics and their modeling

Abstract: Effects of ferroelectric switching on dielectric and ferroelectric properties in lead zirconate titanate ceramics are investigated. Ferroelectric switching induces rejuvenation of weak field dielectric constant, K, and ferroelectric polarization, P, initially through the ac field deaging effect, and then induces accelerated decrease in K and P through the ferroelectric fatigue effect. ‘‘On shelf’’ aging of K, ferroelectric switching induced decrease of K, ac field deaging induced augmentation in K and P, and ferroelectric polarization fatigue are illustrated and intercompared. The experimental results are modeled and explained by the phenomenological principles and atomistic mechanisms for the participation of domain walls and bulk polarization in on shelf aging, ac field deaging, and ferroelectric fatigue effects.

Hot‐stage transmission electron microscopy studies of phase transformations in tin‐modified lead zirconate titanate

Abstract: The temperature dependence of phase stability for tin‐modified lead zirconate titanate solid solution ceramics Pb(0.98)Nb0.02[(Zr1−x, Snx)1−yTiy]1−zO3 (PZST) was investigated by hot‐stage transmission electron microscopy. Compositions studied included, a material that was antiferroelectric (AFE) at room temperature with x=0.42 and y=0.04, and a material that was ferroelectric (FE) at room temperature with x=0.43 and y=0.08 (abbreviated as PZST 42/4/2 and 43/8/2, respectively). PZST 42/4/2 was found to exhibit a sequence of phase transformations on heating of AFE–multicell cubic (MCC)–simple cubic (SC), whereas PZST 43/8/2 had a sequence of FE‐AFE‐MCC‐SC. Previously referred to F spots (i.e., 1/2[111] superlattice spots) were observed in all four phases. The diffraction intensities for the F spots decreased with increasing temperature, and eventually disappeared above 300 °C. Electron diffraction confirmed the presence of the MCC phase which was characterized by the existence of weak 1/2[110] superlattice ...

Vibration-Level Characteristics for Iron-Doped Lead-Zirconate-Titanate Ceramic

Abstract: Vibration-level characteristics for Fe-doped lead-zirconate-titanate ceramic were studied using the constant current driving method. It was found that mechanical Q was markedly decreased with increasing vibration level, accompanying a lot of heat generation. The other electromechanical characteristics were slightly changed. The heat generation was found to decrease with increasing Fe doping concentration up to ~2 at.%, and was found to show a minimum for lead-zirconate-titanate with the basic composition close to the morphotrophic phase boundary. It was assumed that the heat generation was mainly caused by ferroelectric domain wall hysteresis loss.

Influence of platinum-based electrodes on the microstructure of sol-gel and MOD prepared lead zirconate titanate films

Abstract: The microstructure and preferred orientation of PZT films deposited by spin-coating techniques are shown to depend on the morphology of the Ti/Pt bottom electrode. Annealing of the as-deposited Ti/Pt electrodes results in the formation of hillocks. These hillocks serve as nucleation sites for perovskite formation and thus determine the microstructure and preferred orientation of the crystallized PZT films. The microstructure features are investigated by X-ray diffraction analyses and scanning and transmission electron microscopies.

Characterization of conduction in PZT thin films produced by laser ablation deposition

Abstract: Both direct current (d.c.) and alternating current (a.c.) conductivity measurements were undertaken on lead zirconate titanate (PZT) films synthesized by laser ablation deposition. Direct current (I) displayed an initial time dependence of the form I ∝ t−γ (γ ∝ 0.5–1.0). The possible reasons for this time dependence are discussed. At lower temperatures, the a.c. electrical conductivity shows a frequency dependence of the form σ ∝ ω′ which is explained as electrical charge hopping. At higher temperatures, the d.c. component of electrical conductivity becomes dominant, and is accompanied by a strong low frequency dispersion of the dielectric constant. The results are compared to published data on conductivity in SrTiO3, and discussed in terms of the latest theories for dielectric response of materials.

Switching and Fatigue Characteristics of (Pb, La)(Zr, Ti)O3 Thin Films by Metalorganic Chemical Vapor Deposition

Abstract: Lanthanum-modified lead zirconate titanate (PLZT) thin films (0.3~0.4 µm) have been prepared on Pt/SiO2/Si substrates at 650°C by the metal-organic chemical vapor deposition (MOCVD) method. The electrical properties of the films were examined as a function of lanthanum content. The relative dielectric constants increased as the La content increased to about 5 at%, and beyond this value, it became constant at 600. The remanent polarization and coercive field decreased from 22 to 1 µC/cm2 and from 90 to 20 kV/cm with increasing La content in the range of 0~11 at%, respectively. The leakage current density decreased considerably with the addition of La, and was 8×10-9 A/cm2 at an applied voltage of 5 V. The switched charge densities of PLZT films showed almost no change up to switching cycles of 1×1012 at a bipolar pulse of ±5 V.

Reactive Ion Etching of Lead Zirconate Titanate (PZT) Thin Film Capacitors

Abstract: One of the key processing concerns in the integration of PbZr[sub x]Ti[sub 1[minus]x]O[sub 3](PZT) thin film capacitors into the existing VLSI for ferroelectric or dynamic random access memory applications is the patterning of these films and the electrodes. In this work, the authors have identified a suitable etch gas (CCl[sub 2]F[sub 2]) for dry etching of PZT thin films on RuO[sub 2] electrodes. The etch rate and anisotropy have been studied as a function of etching conditions. The trends in the effect on the etch rate of the gas pressure, RF power and O[sub 2] additions to the etch gas have been determined and an etching mechanism has been proposed. It was found that ion bombardment effects are primarily responsible for the etching of both PZT and RuO[sub 2] thin films. Etch rates of the order of 20--30 nm/min were obtained for PZT thin films under low gas pressure and high RF power conditions. The etch residues and the relative etch rates of the components of the PZT solid solution were determined using XPS. The results show that the etching of PbO is the limiting factor in the etch process.

Liquid spray head and its production method

Abstract: The present invention relates to a liquid spray head provided with a plurality of liquid spray elements arranged in an array on a substrate. Each element comprises a chamber arranged on the substrate for holding a liquid to be sprayed, a nozzle, a liquid path for communication with the nozzle and the chamber, a diaphragm arranged on the liquid chamber, a piezoelectric element comprising a lower electrode arranged on the diaphragm, a piezoelectric film comprising a lead zirconate titanate film arranged on the lower electrode and an upper electrode arranged on the piezoelectric film. Energy is applied to the piezoelectric element so as to bend the diaphragm for deforming a volume of the liquid chambers to spray the liquid. The liquid chambers have a pitch equal to the pitch of the nozzles, and the following relationships are satisfied: 1) 10≦W/L≦150 2) tp≧tv 3) 0.012≦(tp+tv)/L<0.08 where L is a length of the liquid chambers in an array direction, W is a length of the liquid chambers in a depth direction, tp is a thickness of the lead zirconate titanate film and tv is a thickness of the diaphragms.

Dielectric breakdown in high-ε films for ULSI DRAMs

Abstract: Dielectric breakdown has been studied in several materials intended for high-dielectric DRAMs (dynamic random access memories), emphasizing lead zirconate-titanate (PZT) and barium strontium titanate (BST) ceramics. In this paper we present our results on PZT. A second paper will deal with BST. In order to distinguish among impulse thermal breakdown, de thermal breakdown, and avalanche breakdown mechanisms, studies have been carried out as functions of temperature, electrode material and shape, frequency and duration of applied fields, and specimen size and shape. Notable in the results is the fact that maximum breakdown field varies directly with electrode work function but is uncorrelated with electrode thermal conductivity; this militates against a purely thermal breakdown interpretation and instead favors an avalanche mechanism in which the iniation step is impact ionization of Ti ions from electrons emitted from the electrodes, followed by thermal run-away. Thickness dependence also favors a...

Full temperature calibration from 4 to 300 K of the voltage response of piezoelectric tube scanner PZT‐5A for use in scanning tunneling microscopes

Abstract: We have calibrated the displacement/voltage (A/V) response of our piezoelectric scanning tube (PZT‐5A) by imaging graphite at over 40 temperatures between 4 and 300 K. We have also calibrated the (A/V) response as a function of voltage up to 220 V at room temperature, imaging a gold‐plated diffraction grating. We find that the temperature dependence of the (A/V) response is linear to within 10% and is reduced by a factor of 5.5 on decreasing temperature from 300 to 4.2 K. The near linearity with temperature of the (A/V) response makes the PZT‐5A lead zirconate titanate composition a convenient choice for low temperature scanning tunneling microscope piezo tube elements.

Low-temperature synthesis of chemically homogeneous lead zirconate titanate (PZT) powders by a semi-wet method

Abstract: A semi-wet procedure for the synthesis of single-phase Pb(ZrxTi1−x)O3 powders at 600 °C is described. The ultrafine powders so obtained do not exhibit tetragonal/rhombohedral distortions until they are sintered at higher temperatures. The morphotropic phase boundary (MPB) for these powders, which are chemically homogeneous, lies between x=0.52 and 0.53. For x=0.525, the rhombohedral and tetragonal phases coexist.

Origin of F spots and stress sensitivity in lanthanum lead zirconate titanate

Abstract: In this study a systematic microstructural characterization of La‐modified lead zirconate titanate was carried out by hot‐ and cold‐stage transmission electron microscopy and selected area electron diffraction. The existence of 1/2[111] superlattice reflections (F spots) became evident near 300 °C on cooling. The intensity of the F spots was found to increase with decreasing temperature, approaching a near constant intensity below 100 °C. In conjunction with compositional studies, it was proposed that the F spots arise from a doubling of the unit cell associated with a tilting of oxygen octahedra. The presence of F spots at temperatures approaching the onset of local polarization was then interpreted as the existence of a hierarchy of domain states. This hierarchy was proposed to consist of an average‐cubic macroscopic structure containing rhombohedral micropolar regions on the scale of 50–100 A that contain ferroelastic microtwins on the scale of several tens of angstroms.

Domain switching and microcracking during poling of lead zirconate titanate ceramics

Abstract: The application of a DC electric field (poling) to a ferroelectric lead zirconate titanate (PZT) ceramic aligns domains in the field direction. The non 180°-domain switches involve mechanical deformations, which are detected as acoustic emission signals. Concurrent with AE signals, electrical current pulses arise from domain reorientations. When the poling field is large and domain switches are extensive, the resulting deformations, under the constraint of neighboring domains or grains, may exceed the elastic limit and cause microcracking. The onset and propagation of microcracking during poling of PZT is signalled by the appearance of continuous AE signals, unaccompanied by current pulses, in contrast to intermittent AE signals accompanied by corresponding current pulses during domain switching. The onset and extent of microcracking established by this method is confirmed by scanning electron micrographs and decrease in the value of piezoelectric coefficient (d33 ) and mechanical quality factor ...

Method of manufacturing a ferroelectric device using a plasma etching process

Abstract: A method of patterning a film of PZT material comprises the steps of providing a mask over a selected surface portion of the PZT material; and, plasma etching unmasked portions of the thin film material. The method includes the steps of: introducing a gas mixture of halogenated gases into a chamber; ionizing the gas mixture into a plasma in the chamber by imposition of an electric field across the introduced gaseous mixture, chemically reacting the ionized gaseous mixture, chemically reacting the unmasked portions of the lead zirconate titanate thin film material to selectively remove such exposed portion of the thin film material. The gas mixture is a mixture of a chloride and a compound of fluorine. Preferably the compound of fluorine is a halocarbon or fluorocarbon. In particular, the fluorocarbon is a trifluoromethane, CHF 3 , and the chloride is boron trichloride BCl 3 .

Method of forming multilayered electrodes for ferroelectric devices consisting of conductive layers and interlayers formed by chemical reaction

Abstract: A ferroelectric device is constructed using a bottom electrode composed of a conducting oxide such as RuO x , on a substrate such as silicon or silicon dioxide. A ferroelectric material such as lead zirconate titanate (PZT) is deposited on the bottom electrode, and a conducting interlayer is formed at the interface between the ferroelectric and the electrode. This interlayer is created by reaction between the materials of the ferroelectric and electrode, and in this case would be Pb 2 Ru 2 O 7-x . A conductive top layer is deposited over the ferroelectric. This top layer may be a metal, or it may be the same type of materials as the bottom electrode, in which case another interlayer can be formed at the interface. A device constructed in this manner has the property of lower degradation due to fatigue, breakdown, and aging.

Preparation of -oriented Lead-Zirconate-Titanate Films by Sol-Gel Technique

Abstract: A sol-gel technique to control the crystalline orientation of lead-zirconate-titanate (PZT) films on Pt/Ti/SiO2/Si substrates has been studied. It is found that crystalline orientations of sintered films show strong dependence on their thicknesses and -oriented films can be obtained by limiting their thicknesses to 100 nm. It is also found that thicker oriented films can be obtained by stacking up these oriented films. The scanning electron microscopy observation reveals that a well-oriented film surface is smoother than those of non oriented ones. The leakage current of the 240-nm-thick oriented film is about 7 nA/cm2 at 3 V, which is an order of magnitude lower than the best reported lanthanum and iron-doped PZT film.