Showing papers on "Lead zirconate titanate published in 1998"

Piezoelectric Sensors and Sensor Materials

Abstract: This paper reviews the current trends and historical development of piezoelectric sensors and sensor materials technology. It begins with a discussion of the bases of piezo- and ferroelectric activity, followed by an overview of the most commonly used piezoelectric ceramic: lead zirconate titanate (PZT). A discussion of the properties and applications of piezoelectric crystals and additional piezoelectric ceramics is followed by a description of several sensor configurations prepared from bulk ceramics. An extensive review and comparison of piezoelectric ceramic—polymer composite sensors based on the connectivity of the constituent phases is also presented. We conclude our discussion of sensor configurations with recent examples of piezoelectric ceramic—metal composite sensors, and expected future developments in the area of piezoelectric sensors.

Crystal orientation dependence of piezoelectric properties of lead zirconate titanate near the morphotropic phase boundary

Abstract: The piezoelectric and dielectric constants in different crystal orientations of the lead zirconate titanate (PZT) have been phenomenologically calculated for the compositions near the morphotropic phase boundary at room temperature. For a tetragonal PZT, the effective piezoelectric constant d33 monotonously decreases as the crystal cutting angle from the spontaneous polarization direction [001] increases. However, for a rhombohedral PZT, the effective piezoelectric constant d33[001]// along the perovskite [001] direction was found to be much larger than those along the spontaneous polarization direction [111]. This crystal orientation-related enhancement is emphasized as the composition approaches the morphotropic phase boundary. This suggests that by adopting the perovskite [001] orientation with a rhombohedral composition near the morphotropic phase boundary, the piezoelectric constant d33 for PZT can be greatly enhanced.

Influence of temperature on the electromechanical and fatigue behavior of piezoelectric ceramics

Abstract: This paper presents research results on the electro–thermomechanical behavior of piezoelectric ceramics for use in actuator applications with an emphasis on ferroelectric fatigue. The material being investigated is a lead zirconate titanate piezoelectric ceramic with the composition PbZr0.53Ti0.47O3 (PZT-5H). Results presented in this paper include an augmented constitutive model that accounts for the temperature-dependent piezoelectric properties. Using this model, nonlinear effects measured at one temperature can be extrapolated to other temperatures with good accuracy. Experimental studies into 180° and 90° polarization switching of PZT-5H indicate that the dielectric flux to dipole the material appears to be an adequate criterion for predicting this nonlinear switching behavior. Fatigue studies show that material degradation is strongly influenced by temperature and by the magnitude of the applied electric field. Above a critical temperature, PZT-5H no longer fatigues in the presence of large electric...

The wafer flexure technique for the determination of the transverse piezoelectric coefficient (d31) of PZT thin films

Abstract: This paper describes a simple and inexpensive method for evaluating the transverse piezoelectric coefficient ( d 31 ) of piezoelectric thin films. The technique is based upon the flexure of a coated substrate which imparts an ac two-dimensional stress to the piezoelectric film. The surface charge generated via the mechanical loading is converted to a voltage by an active integrator. Plate theory and elastic stress analyses are used to calculate the principal stresses applied to the film. The d 31 coefficient can then be determined from knowledge of the electric charge produced and the calculated mechanical stress. For 52/48 sol-gel lead zirconate titanate (PZT) thin films, the d 31 coefficient was found to range from − 5 to − 59 pC/N and is dependent on poling field.

A novel micromachined pump based on thick-film piezoelectric actuation

Abstract: A new silicon-based micropump is described in this paper. The key element of the device is a thick-film/silicon micromachined hybrid actuator. The actuation principle relies on the flexure of a screen printed piezoelectric lead zirconate titanate (PZT) layer on a silicon membrane (8 mm × 4 mm × 70 μm). An investigation into the deposition technology of the bottom electrode for the piezoelectric material showed that a gold resinate or Pt evaporated electrode on a 500 nm thick SiO 2 covered silicon wafer achieved best results for the membrane actuator. Inlet and outlet valves are of the cantilever type and use deep boron diffusion together with KOH etching. Pump rates of up to 120 μl min −1 have been achieved. A maximum backpressure of 2 kPa was measured when using a 600 V pp sinusoidal drive voltage at 200 Hz across a 100 μm thick PZT layer. The pump was compared with a conventional surface mounted piezoelectric driven micropump. The conventional pump achieves a performance which was a factor of 3–6 more efficient, but does not allow mass production.

Sintering Model for Mixed‐Oxide‐Derived Lead Zirconate Titanate Ceramics

Abstract: The properties of lead zirconate titanate (PZT) ceramics are determined by the microstructure and chemical homogeneity of Zr, Ti, and dopants within the grains as well as the presence of secondary grain boundary phases. Stoichiometric 53/47 PZT and compositions with 3 mol% PbO excess were prepared by the mixed-oxide process, and were densified by pressureless sintering in oxygen. The influence of PbO content and different La concentrations on the densification behavior was analyzed by dilatometric measurements. Quantitative image analysis showed a different relative density and grain size dependence for samples containing >0.5 mol% additives compared to samples with <0.5 mol% La. On the basis of a model experiment and by using different analytical methods (microprobe analysis, HRTEM, STEM, and Auger spectroscopy) three types of inhomogeneities could be detected in conventionally prepared PZT ceramics: the existence of Ti and La enrichment in the core of PZT grains, and PbO-rich secondary phases in triple junctions as well as in grain boundary films. The results of the microstructural characterization and the analysis of the densification behavior were finally combined to deduce a sintering model based on a Pb-vacancy concentration gradient within the PZT grains.

Charge release of lanthanum-doped lead zirconate titanate stannate antiferroelectric thin films

Abstract: The charge release speed and backward phase switching time of lanthanum-doped lead zirconate titanate stannate antiferroelectric thin films were investigated by directly measuring the switching current upon removal of the applied electric field. The backward switching time is about 6 ns. The maximum switching current density can reach 9400 A/cm2, and more than half of the stored charge can be released in 10 ns. These results show that the obtained antiferroelectric thin films are very promising for decoupling capacitor applications in high speed multichip modules.

Influence of sample thickness on the performance of photostrictive ceramics

Abstract: Ferroelectric materials with high photovoltaic properties are of interest for new optical devices such as photostrictive ceramic actuators. However, fabrication of these devices requires development of materials exhibiting high photovoltage and photocurrent. In pursuit of these high performance photostrictive materials, the present research examines the influence of illumination intensity, degree of polarization, and sample thickness on the photostrictive response of WO3 doped lanthanum-modified lead zirconate titanate (Pb, La)(Zr, Ti)O3 ceramics prepared by oxide mixing process. A model for calculating the optimum sample thickness for maximum photostrictive response is proposed. This model agrees well with experimental results, and should be useful in designing photostrictive devices.

Effect of external stress on polarization in ferroelectric thin films

Abstract: The polarization changes caused by applying mechanical stresses to a lead zirconate titanate (PZT) thin film were investigated. Both the remnant and spontaneous polarizations decreased when the PZT film was loaded with tensile stress. For compressive stresses, the remnant polarization increased, but spontaneous polarization did not change. In fatigue with tensile stress state, the polarization decreased earlier than when there was no stress, which depend on whether or not the initial polarization value was high. Conversely, in fatigue with compressive stress, the initial higher remnant polarization value was maintained compared with the polarization in the unstress condition.

A cylindrical micro ultrasonic motor using PZT thin film deposited by single process hydrothermal method (/spl phi/2.4 mm, L=10 mm stator transducer)

Abstract: A micro ultrasonic motor using PZT (lead zirconate titanate) thin film has been improved by a single process hydrothermal method. The hydrothermal method is a unique method for depositing PZT thin film in a solution. An earlier reported hydrothermal method consisted of two linked processes. Our new method, however, has only a single process. Hence, less distribution of chemical components of the PZT film contributes to a higher efficiency of the stator transducer. The piezoelectric factor d/sub 31/ was -30 pC/N for this new method, which is six times larger than that of the previous method. The output torque of the micro ultrasonic motor fabricated by the single process hydrothermal method was measured. The output torque was 7.0 /spl mu/Nm, and the maximum revolution speed was 880 rpm at 15 Vp-p driving voltage.

Electrophoretic and electrolytic deposition of ceramic coatings on carbon fibers

Abstract: Alumina, zirconia, titania, lead zirconate titanate, hydroxyapatite and chemically bonded ceramics in the system CaO-SiO 2 -P 2 O 5 were deposited via electrophoretic or/and electrolytic deposition methods on individual carbon fibers, bundles and felts, which served as cathodic substrates. Experimental conditions were determined for formation of uniform deposits of controlled thickness. After burning out of carbon fibers the corresponding ceramic replicas can be obtained. The possibility to form multilayer alumina/zirconia hollow fibers with sharp interfaces between alumina and zirconia layers has been demonstrated. Obtained coatings and fibers were studied by SEM. Experimental results obtained by electrophoretic and electrolytic deposition methods were compared.

Effects of quenched disorder on La-modified lead zirconate titanate: Long- and short-range ordered structurally incommensurate phases, and glassy polar clusters

Abstract: Structure–property relationship studies have been performed in the La-modified lead zirconate titanate (PLZT) solution as a function of quenched La impurity content and Zr/Ti ratio by transmission electron microscopy, lattice imaging, and dielectric spectroscopy. Investigations were performed for 65/35⩽Zr/Ti⩽90/10. These investigations have demonstrated a general trend in domain structure and polar order with increasing quenched impurity concentration. For Zr/Ti ratios of 90/10 and 85/15, a structurally incommensurate antiferroelectric (AFEin) state was found to be stabilized with increasing La. Temperature dependent investigations demonstrated that the incommensurate structure becomes pinned into long-time metastable states, rather than transforming to a commensurate phase. Also, the modulation wavelength (λ) was found to increase significantly with increasing Ti. When λ increased to ∼40 A, polar clusters began to condense from the AFEin order. For Zr/Ti ratios of 80/20 and 65/35, increasing quenched dis...

Behavior of soft piezoelectric ceramics under high sinusoidal electric fields

Abstract: The behavior of piezoelectric, dielectric, and elastic characteristics of soft piezoelectric lead zirconate titanate (PZT) ceramics was investigated under sinusoidal electric field E applied along the poling direction and under mechanical stress-free conditions for a frequency range 10 Hz–10 kHz. Electrical displacement D3 along the poling direction, mechanical strain S1 in the direction perpendicular to the poling direction, and the resonant frequency νr of electromechanically uncoupled bending vibrations of polarized plates were measured. Commercial ceramics PZT5H, 3203HD, and PKI550 with chemical composition near the morphotropic phase boundary were used in the study. It was found that the amplitude and phase of the first harmonic of the relative strain S1(1)/Em and of the relative electrical displacement D3(1)/Em increase similarly with increasing amplitude Em of the electric field if the amplitude is less than coercive field. The corresponding increase in the square of the resonant frequency is more ...

Low‐Temperature Preparation of Nanocrystalline Lead Zirconate Titanate and Lead Lanthanum Zirconate Titanate Powders Using Triethanolamine

Abstract: Nanocrystalline lead zirconate titanate (PZT) powders, with a Zr:Ti ratio of 60:40, have been prepared from a solution of triethanolamine (TEA) and Ti4+, Zr4+, and Pb2+ ions. The metal ions were in solution through complex formation with TEA. The soluble metal-ion–TEA complex formed the precursor material when it was completely dehydrated. Heat treatment of the precursor at 450°C resulted in single-phase PZT powders. The precursor and the heat-treated powders have been characterized by using thermal analysis and X-ray diffractometry (XRD) studies. The average particle size, as measured from X-ray line broadening and transmission electron microscopy studies, was ∼20 nm. PZT powders modified with 3 mol% of lanthanum (PLZT) also were prepared through this route and were investigated via XRD studies. The dielectric constants of the PZT and PLZT powders were 12475 and 11262, and their corresponding Curie temperatures were 362° and 315°C, respectively.

Point defect chemistry of metal oxide heterostructures

Abstract: ▪ Abstract This article reviews the defect chemistry of perovskite ferroelectric oxides such as barium titanate and lead zirconate titanate. Such metal oxides are being considered for a wide range of applications that include nonvolatile memories and dynamic random access memories. Time-dependent degradation of these devices is controlled at least in part by point defects, which are determined by the defect chemistry of the material. The role of point defects on Pb(Zr,Ti)O3 thin film device properties such as fatigue, switching, polarization relaxation and imprint is discussed.

Subsurface defect detection in materials using optical coherence tomography

Abstract: We have used optical coherence tomography to study the internal structure of a variety of non-biological materials. In particular, we have imaged internal regions from a commercial grade of lead zirconate titanate ceramic material, from a sample of single-crystal silicon carbide, and from a Teflon-coated wire. In each case the spatial positions of internal defects were determined.

Transient photocurrents in lead zirconate titanate thin films

Abstract: Transient photocurrents are investigated in ferroelectric lead zirconate titanate (PZT) films illuminated by laser pulses in the spectral range of 340–380 nm. At low electric fields, the photocurrent is sensitive to the ferroelectric polarization state and changes sign upon the polarization switching. At higher fields, the polarization-independent current proportional to the applied electric field is dominant. The spectral dependence of polarization-dependent current is controlled by the excitation of charge carriers over the forbidden band of PZT having a maximum near 3.5 eV. Possible mechanisms of the observed effect are discussed and the possibilities of a nondestructive read out of polarization state in the ultraviolet spectral range are demonstrated.

Shear response of lead zirconate titanate piezoceramics

Abstract: The piezoelectric shear strain S5 of several commercial lead zirconate titanate (PZT) piezoceramics was evaluated under the nonresonant condition in a sinusoidal ac-field E1(t) applied perpendicular to the poling direction. Results obtained on donor doped (soft PZT) and acceptor doped (hard PZT) ceramics are compared. At fields sufficiently below the limiting field Elim necessary to electrically depole the sample, we find a linear, nonhysteretic relationship between S5 and the polarization P1. In soft PZT ceramics, the effective piezoelectric shear coefficient d15=S5/E1 shows a pronounced ac-field dependence which was fitted according to d15(E1)=dlin[1+(dnlE1)α] with α≈1.2. The results indicate that irreversible motion of non-180° walls causes the nonlinearity of PZT and the contribution of 180° walls to the linear and nonlinear coefficients is negligible. The analysis of the relationship between linear and nonlinear coefficients obtained at different ceramic systems suggests that there exists another ext...

Nonlinearity and scaling behavior in donor-doped lead zirconate titanate piezoceramic

Abstract: Two different effective thresholds for the onset of nonlinearity in the dielectric and piezoelectric coefficients of donor-doped lead zirconate titanate (soft PZT) piezoceramics at electric ac fields Ec1≈100 V/cm and Ec2≈1 V/cm are found. Both are characterized by a scaling behavior x=x0+A[E−Ec)/Ec]φ above the respective threshold, where x is the dielectric or piezoelectric coefficient. The values of the effective exponent φ are apparently independent of the particular ceramic system which suggests a universal behavior in soft PZT. We suggest that the nonlinearity is dominated by the dynamics of domain walls in a randomly pinned medium.

Growth of highly oriented Pb(Zr, Ti)O3 films on MgO-buffered oxidized Si substrates and its application to ferroelectric nonvolatile memory field-effect transistors

Abstract: We have grown highly oriented lead zirconate titanate [Pb(Zr, Ti)O3 or PZT] films on oxidized silicon substrates using a thin MgO buffer layer (7–70 nm thick). Ferroelectric nonvolatile memory field-effect transistors (FETs) were successfully fabricated using the metal/PZT/MgO/SiO2/Si structure in conjunction with radio-frequency sputter deposition of PZT and MgO films. The fabricated devices show excellent performance in ferroelectric polarization switching and memory retention. The results indicate that a thin MgO buffer serves well not only as a template layer for the growth of oriented PZT films on amorphous substrates, but also as a diffusion barrier between a ferroelectric and a substrate during device fabrication, protecting the SiO2/Si interface and the FET channel region.

Correlation between structure, microstructure, and ferroelectric properties of PbZr0.2Ti0.8O3 integrated film: Influence of the sol-gel process and the substrate

Abstract: The properties of a ferroelectric material deposed as a thin film on a substrate depend on the method of preparation and on the nature of the substrate used. The present work reports fine characterization by x-ray diffraction of structural modifications (cell parameters, preferential orientations) and microstructural modifications (ferroelectric domain arrangement) and electric measurements of a ferroelectric film as a function of its method of preparation (sol-gel process, pyrolysis, annealing) and the nature of its substrate (crystalline structure, crystallographic orientation, thermal coefficient of dilation). Due to the elaboration process, lead zirconate titanate (PZT) films have grain size smaller than 0.3 μm and consequently modified cell parameters (higher a parameter, smaller c parameter, and consequently smaller c/a tetragonality). Thermal treatment induces specific stresses between the PZT film and the substrate that modify the ferroelectric domain microstructure of the PZT grains: the microstr...

Piezoelectric paints as one approach to smart structural materials with health-monitoring capabilities

Abstract: Piezoelectric paints have a potential to change a conventional structural material into an intelligent material system with health-monitoring capabilities such as vibration sensing and damage detection. Such paints were prepared using lead zirconate titanate (PZT) ceramic powder as a pigment and epoxy resin as a binder. The obtained paints were coated on aluminum test specimens, and were cured at room temperature or at 150 , thus forming the paint films having different thicknesses of 25-300 . These films were then poled at room temperature, and were evaluated with regard to the sensitivities as vibration and acoustic emission sensors in the frequency ranges of 0-250 Hz and 0-1.0 MHz, respectively. This paper mainly describes the effects of the film thickness and the cure temperature on the poling behavior of the PZT/epoxy paint film. This paper describes also the application of the paint film as a vibration modal sensor integrated into a structural material.

Microstructural characterization of sol–gel lead–zirconate–titanate thin films

Abstract: The techniques of x-ray diffraction, x-ray photoelectron spectroscopy (XPS), Auger analysis, and transmission and scanning transmission electron microscopy (TEM) have been applied to the analysis of thin films of Pb(Zr0.30Ti0.70)O3 (PZT30/70) deposited at low temperatures (510 °C) by a sol–gel process onto Pt/Ti electrodes on SiO2/Si 100 substrates. It is found that the platinum film is highly oriented with the [111] axis perpendicular to the substrate plane. The ferroelectric film tends to crystallize epitaxially upon this as columnar crystals. There are indications from the TEM of the existence of a second metallic phase at the interface between the platinum and the PZT30/70 film, which may be associated with its nucleation. The TEM shows the boundaries between the individual sol–gel layers, although the growing crystallites of the PZT30/70 propagate through these boundaries unhindered. The XPS and Auger analyses have shown that Pb penetrates through the Pt layer to the underlying Ti layer, even at the ...

Film structure, electronic device, recording medium, and method for forming conductive oxide thin films

Abstract: A film structure includes a conductive oxide thin film formed on a substrate having a silicon (100) face at its surface. The conductive oxide thin film is an epitaxial film composed mainly of strontium ruthenate. At least 80% of the surface of the conductive oxide thin film has a Rz of up to 10 nm. On the conductive oxide thin film having excellent surface flatness and crystallinity, a ferroelectric thin film, typically of lead zirconate titanate, having surface flatness and spontaneous polarization can be formed.

Ultrasonic wire-bond quality monitoring using piezoelectric sensor

Abstract: This paper describes an ultrasonic wire-bond quality monitoring technique which involves the detection of changes in the mechanical impedance of the bond zone during bond formation by monitoring the changes in the ultrasonic vibrations of an ultrasonic wire-bonding transducer system. A lead zirconate titanate (PZT) piezoelectric ceramic having properties similar to the commercial PZT-5A has been selected as the sensor material. A PZT piezoelectric sensor is installed on an appropriate location on the transducer in order to measure the ultrasonic amplitude and bonding time during the bonding process. This sensor has dimensions 1 mm × 1 mm × 0.245 mm to avoid excessive loading on the transducer and to obtain a flat frequency response. A bond quality monitoring system has been developed to process and record the non-linear signal detected by the sensor. More significant changes are observed at the higher-frequency harmonics (second harmonic) of the ultrasonic signal. Good correlation is found between the change in the second harmonic and the bond quality. Bonding process drift towards unacceptable bond quality can be identified. This technique will be used to develop a multiparameter-based automatic process-control system for wire bonding.

Schottky barrier effects in the electronic conduction of sol–gel derived lead zirconate titanate thin film capacitors

Abstract: Pure and Fe-doped Pb(Zr0.53Ti0.47)O3 (PZT) thin film capacitors were fabricated by the sol–gel method and the leakage current versus voltage characteristics of these films were investigated at several temperatures and initial polarization states. After the initial poling of ferroelectric thin films, we measured two kinds of leakage current: (i) the full-switching current measured against an initial polarization direction and (ii) the nonswitching current measured toward an initial polarization direction. In the case of the full-switching current measurement, the anomaly of leakage current due to the switching of space charges was observed, which we suggest to be accumulated at a Schottky barrier region near an electrode or a gain boundary. In the case of the nonswitching current measurement, the Schottky diode rectifier current and the field-enhanced Schottky (ES) emission current came out without the switching current. The Poole–Frenkel emission process was dominant over ES emission for a Fe-doped PZT th...

Multilayer ferroelectric capacitor structure

Abstract: Multilayer ferroelectric capacitor structures comprising a ferroelectric film having a combination of different ferroelectric materials or compositions such as strontium bismuth tantalate, strontium bismuth niobate, bismuth titanate, strontium bismuth tantalate niobate, lead zirconate titanate, lead lanthanum zirconate titanate are disclosed. A method of preparing the multilayer ferroelectric film containing at least two different ferroelectric materials and/or more than one composition of ferroelectric material is also disclosed.