Showing papers on "Lead zirconate titanate published in 1991"

Quantitative measurement of space-charge effects in lead zirconate-titanate memories

Abstract: By combining Auger data on the width of an oxygen depletion layer near the Pt electrodes with a modified Langmuir–Child law for the leakage current: I(V) = aV + bV2, we deduce parameters related to the space‐charge density and field in 210‐nm‐thick PbZr1−xTixO3 memories. The results are compared with the space charge fields inferred by Okazaki (∼10 kV/cm for PZT), which involve measuring the switching speeds ts(E) for positive and negative voltages. Differences in the voltage dependencies of the leakage current are found after fatigue and are related to specific electrochemical processes involving oxygen deposition on electrode surfaces.

The extrinsic nature of nonlinear behavior observed in lead zirconate titanate ferroelectric ceramic

Abstract: The nonlinear electric and electromechanical responses of lead zirconate titanate Pb(ZrxTi1−x)O3 ceramics to an external ac electric field have been measured under different driving levels. The onset of measurable nonlinearity is observed to be accompanied by the appearance of hysteresis loops. This lossy nature suggests that the nonlinearities in a ferroelectric ceramic are generated by the domain‐wall motion. In addition, aging experiments and the bias field dependence of the threshold field (onset of nonlinearity) all indicate the extrinsic nature of the nonlinear behavior of ferroelectric ceramics. A phenomenological theory of Arlt, Dederichs, and Herbiet [Ferroelectrics 74, 34 (1987)] has been extended to include the nonlinear contributions. With only 90° wall vibration being considered, the theory leads to some basic understanding of the experimental results.

Preparation of Lead Zirconate Titanate Thin Film by Hydrothermal Method

Abstract: A hydrothermal method for preparing thin films of crystalline PZT was developed by controlling the rates of nucleation and crystal growth. This method consisted of two steps of hydrothermal reaction. The first step (nucleation process) was that in which the TiO2 substrate reacted with the mixed solution of Pb and Zr to form PZT and/or PZ nuclei on the surface. Subsequently, the crystal growth of PZT was promoted as the next hydrothermal step (crystal growth process) by the reaction of the mixed solution of Pb, Zr and Ti. From the experimental results of PZT powder preparation, the conditions of the nucleation and crystal growth process were determined as at 150°C for 24 h and at 120°C for 48 h, respectively. It was verified that the thin films consisted of PZT polycrystals and showed ferroelectric properties.

Microstructure of Solution‐Processed Lead Zirconate Titanate (PZT) Thin Films

Abstract: Lead zirconate titanate (PZT) thin films with a composition near the morphotropic phase boundary (Zr/Ti = 53/47) were fabricated by spin deposition of an alkoxide-derived solution and annealed at 650°C for 30 min. A complex microstructure is observed in which micrometer-scale rosettes of the desired perovskite phase are surrounded by nanocrystalline (10 to 15 nm) grains of pyrochlore structure. Transmission electron microscopy (TEM) demonstrates that the perovskite rosettes—features of approximately circular cross section which grow rapidly within the confined conditions of the thin film—are single crystals despite being highly porous. Pockets of lead-deficient pyrochlore extend throughout the thickness of the film. The only effects of Nb (2%) doping on the microstructure are to increase the fraction of the perovskite phase and the perovskite grain size. Despite the highly irregular shape of the perovskite particles and the presence of some pyrochlore, reasonable ferroelectric properties are measured (spontaneous polarization Ps∼ 0.2 C/m2).

Characterization of lead zirconate titanate ceramics for use in miniature high-frequency (20-80 MHz) transducers

Abstract: The material properties of lead zirconate titanate (PZT) ceramics for operation in the thickness mode at frequencies as high as 80 MHz are reported. Each of the ceramics tested showed a reduction in k/sub t/ with increasing frequency. In a fine-grained PZT, values of k/sub t/ as high as 0.44 were measured at 80 MHz. The effects of grain size were also evident in the measurement of frequency dependent mechanical losses. Experimental and theoretical analysis of a 1 mm*1 mm, 45 MHz PZT transducer verified the validity of the measurements of the properties and demonstrated excellent insertion loss and bandwidth characteristics. The minimum insertion loss of -17.5 dB is in good agreement with theory and is a marked improvement over the performance of polymer devices. Details on the fabrication and testing of high frequency ceramic transducers are described. >

Preparation and ferroelectric properties of PbZr0.53Ti0.47O3 thin films by spin coating and metalorganic decomposition

Abstract: Films with a composition PbZr0.53Ti0.47O3 were prepared on different platinum bottom electrodes using a spin‐coating process followed by metalorganic decomposition. The film morphology and structure were characterized by scanning electron microscopy and x‐ray diffraction analysis. The morphology was strongly influenced by the heat cycle used to form the PbZr0.53Ti0.47O3 layer. Fast heating and high‐fire temperatures produced smooth films, while slow heating and low‐fire temperatures gave films having a rosette perovskite phase and an inter‐rosette second phase. The films were characterized electrically by measuring hysteresis loops and capacitance and conductance versus bias voltage and by pulse‐switching measurements. The dependence of the switched and nonswitched polarization on the number of switching cycles (i.e., the fatigue behavior) is found to be much better for fast‐heated than for slowly heated films. Switching lifetimes exceeding 1011 cycles were measured. The type of platinum bottom electrode used was found to have a large influence on the ferroelectric properties of the lead zirconate titanate films.

Lead zirconate titanate films by rapid thermal processing

Abstract: Lead zirconate titanate films have been fabricated by a dc sputtering technique with a post deposition rapid thermal annealing treatment at 650 °C for 10 s. The films exhibited good structural, dielectric, and ferroelectric properties compared to conventional furnace‐annealed films. The measured dielectric constant and loss tangent at 1 kHz were 900 and 0.04 and the remanent polarization and coercive field values were 10 μC/cm2 and 23 kV/cm, respectively. No significant fatigue in polarization was observed in the films up to 1010 cycles of bipolar stress. The films were optically transparent and showed a linear electro‐optic (EO) effect after poling with an EO coefficient of 1.5×10 −11 m/V.

Ferroelectric properties of lead‐zirconate‐titanate films prepared by laser ablation

Abstract: Ferroelectric lead‐zirconate‐titanate (PZT) thin films have been deposited by excimer laser ablation on sapphire substrates with and without an electrode. In preparation for the films, O2 gas pressure has greatly influenced the film structure and morphology. For the first time, we have confirmed the ferroelectric properties of PZT films prepared by laser ablation without post‐annealing. It appears to be possible to use these films for nonvolatile random access memories with some additional improvements in the film properties.

PZT Thin Film Preparation on Pt-Ti Electrode by RF Sputtering

Abstract: Pt-Ti alloy films were studied for use as a lower electrode of the ferroelectric lead zirconate titanate (PZT) thin film capacitor. Pt-Ti alloy films with different Ti/Pt atomic ratios were first prepared by rf sputtering. Subsequently, PZT thin films were deposited also by rf magnetron sputtering on the Pt-Ti alloy metals. The Ti/Pt ratio in the alloy was found to strongly affect the crystal structure formation and the composition of the PZT thin films. The Ti/Pt ratio range from 0.02 to 0.17 was shown to bring about a preferable perovskite-type structure and a reproducible constant composition. The effect of Ti atoms in the Pt-Ti lower electrode was discussed in connection with the Pb atom evaporation rate.

Experimental studies on primary and secondary pyroelectric effects in Pb(ZrxTi1−x)O3, PbTiO3, and ZnO thin films

Abstract: The pyroelectric coefficients and pyroelectric response in lead zirconate titanate (Pb(ZrxTi1−x)O3), lead titanate (PbTiO3), and zinc oxide (ZnO) thin films (0.1–2.0‐μm thick) have been studied for possible integrated thermosensor applications. Pyroelectric properties of these films deposited on thick (500‐μm) silicon substrates and thin (1.0‐μm) polysilicon membranes have been investigated. The measured pyroelectric coefficients for these materials are 70, 95, and 1.0 nC/cm2 K for Pb(Zr0.54Ti0.46)O3, PbTiO3, and ZnO, respectively. Coupling effects between the pyroelectric film and substrate were studied. It was observed that the primary pyroelectric effect dominates the pyroelectric response in Pb(Zr0.54Ti0.46)O3 and PbTiO3 thin films while the secondary effect is dominant in ZnO thin films.

Crystallization of sol-gel derived lead zirconate titanate thin films

Abstract: Thin films of lead zirconate titanate (PZT) have been prepared by the sol‐gel processing method using metal alkoxides. The crystallographic and morphological properties of the films have been analyzed by x‐ray diffraction and scanning electron microscopy. The elemental composition of the films was determined by Rutherford backscattering, electron microprobe, and Auger electron spectroscopy, and was compared to that of the precursor solution characterized by inductively coupled plasma spectrophotometry. Results are presented which illustrate the relationships between the properties and the observed structure of the thin films, with the processing conditions. The electrical properties, dielectric constant, and ferroelectric hysterisis response were tested to determine the quality of the films. The experimental observations suggest two competing mechanisms during the PZT formation: lead loss out of the film, and nucleation of the PZT phase with its subsequent crystallization.

Ferroelectric thin film ultrasonic micromotors

Abstract: Ferroelectric thin films of lead zirconate titanate (PZT) of morphotropic phase-boundary composition have been fabricated by a sol-gel spin-on technique for application to a new family of flexure-wave piezoelectric micromotors characterized by low speed and high torque. The high relative dielectric constant (1300) and breakdown strength (1 MV/cm) of the films lead to high stored energy densities. The piezoelectric coefficients d/sub 33/ and d/sub 31/ were measured to be 220 pC/N and -88 pC/N, respectively; the electromechanical coupling factors calculated from these data were k/sub 33/=0.49, k/sub 31/=0.22, and k/sub p/=0.32. The development of the piezoelectric ultrasonic micromotors from the PZT thin films and the architecture of the stator structure are described. Nonoptimized prototype micromotors show rotational velocities of 100-300 rpm and net normalized torques in the pN-m/V/sup 2/ range. >

Excimer laser ablated lead zirconate titanate thin films

Abstract: Lead zirconate titanate (PZT) thin films on platinum coated silicon were prepared by excimer laser ablation and were crystallized by subsequent annealing. Films deposited at various fluences and post‐annealed showed slight variations in lead content which seemed to affect the orientation. The relatively lead rich films showed (110) orientation and the orientation changed to (111) as the Pb content decreased. Crystalline perovskite PZT films showed a dielectric constant of 800, a remnant polarization of 32 μC/cm2 and a coercive field of 130 kV/cm.

Preparation and Properties of Lead Zirconate-Titanate Thin Films

Abstract: Lead zirconate-titanate (PZT, PbZrxTi1-xO3, x=0.2-0.9) films with submicron thickness (600-900 nm) were prepared using an rf-magnetron sputtering technique. The crystal structure and the orientation of the films were studied as a function of the substrate temperature. The relationships between electric properties and the film compositions were elucidated. The films of x=0.90 exhibit a large remanent polarization of 46 µC/cm2 and small coercive force of 28 kV/cm. In addition, no fatigue after >1011 cycles under an accelerated bipolar stressing was observed.

Microstructural development and electrical properties of sol-gel prepared lead zirconate-titanate thin films

Abstract: A systematic investigation of the microstructural evolution of fast fired, sol-gel derived Pb(Zr, Ti)O3 films (Zr/Ti = 54/46) was performed by analytical transmission electron microscopy (TEM). It was found that the nucleation and growth of the sol-gel PZT films were influenced by the precursor chemistry. The precursor solution was composed of Pb 2-ethylhexanoate, Ti isopropoxide, and Zr n-propoxide in n-propanol. Porous and spherulitic perovskite grains nucleated and grew from a pyrochlore matrix for NH4OH-modified films, but no chemical segregation was found. These thin films consisted completely of porous spherulitic PZT grains (∼2 μm) when the firing temperature was increased. Chemical phase separation with regions of Zr-rich pyrochlore particles separated by Zr-deficient perovskite grains was observed in the initial stages of nucleation and growth for CH3COOH-modified PZT films. This phase separation is attributed to the effect of acetate ligands on the modification of molecular structure of the PZT precursor. Firing the acid-modified films at higher temperatures for long times resulted in porous perovskite grain structures. The residual porosity in these films is suggested to be a result of differential evaporation/condensation rates during the deposition process and the gas evolution at high temperatures due to trapped organics in the films. Dielectric and ferroelectric properties were correlated to the microstructure of the films. Lower dielectric constants (∼500) and higher coercive fields (∼65 kV/cm) were found for the acid-modified PZT films with phase separation in comparison to those measured from the sol-gel films with a uniform microstructure (∽ > 600, Ec < 50 kV/cm). All films fired at 650 °C showed relatively good remanent polarization on the order of 20 μC/cm2.

Internal strain relaxation and the glassy behavior of La‐modified lead zirconate titanate relaxors

Abstract: Nonlinear internal friction measurements have been carried out on La‐modified lead zirconate titanate relaxors with a Zr/Ti ratio of 65/35. Measurements have been made as a function of La content and dc bias. The elastic softening is believed to have a ferroelastic contribution due to the tilting of the oxygen octahedra, in addition to the expected electrostrictive effects. The temperatures of the maximum softening form a plausible extension to the rhombohedral‐rhombohedral phase boundary [Proc. IEEE 61, 959 (1973)]. A frequency dependence of the softening has also been found which was interpreted as the existence of fluctuations in the orientations of the tilts. These fluctuations are proposed to arise in an attempt to partially relieve an inhomogeneity in the electrostrictive strains associated with the polarization fluctuations. The results are discussed in context with previously reported transmission electron microscopy work [C. Randall, Ph. D. dissertation, University of Essex (1987)]. Dielectric measurements have also been done as a function of La content and bias, and the freezing temperature of the polarization fluctuations determined as a function of composition. A revised phase diagram has been proposed using this data base which shows different phase fields having various combinations of freezing mechanisms.

Single-Target Sputtring Process for Lead Zirconate Titanate Thin Films with Precise Composition Control

Abstract: The influence of growth conditions on rf-magnetron sputtered lead zirconate titanate (or PZT) thin films has been investigated, and the structural and electrical properties of PZT thin films have been examined. It was found that the Pb content in a sputtered film is proportional to rf power, thereby making it possible to control the film composition precisely. A well-crystallized perovskite structure was obtained by postdeposition annealing at 590°C. A stoichiometric film (i.e., Pb/Zr+Ti=1) had a dielectric constant value of 1180.

Properties of piezoelectric thin films for micromechanical devices and systems

Abstract: Zinc oxide and ferroelectrics of the lead zirconate titanate (PZT) family are candidates for piezoelectric actuation as well as sensing elements in microelectromechanical systems. In this work the relevant properties of the thin film forms of these materials are characterized, including the induced stress, the Young's modulus, and the electromechanical coupling (piezoelectric) constants. Pyroelectric and dielectric properties (permittivity and resistivity) were also investigated. The mechanical properties in thin film ZnO and PZT were found to be favorable for their use in micromachining. The piezoelectric coefficients found for these films are also favorable for microactuation. Electrical properties in both ZnO and PZT were found to be sensitive to substrate material stress surface and surface condition. The relatively high pyroelectric coefficients measured in these films suggest the possible need for ambient temperature-cancellation schemes in micromechanical structures. Demonstration of micromachining using these films suggests that the film deposition technology as it exists now is suitable for achieving piezoelectrically induced motion on the microscale. >

The influence of niobium-doping on lead zirconate titanate ferroelectric thin films

Abstract: Ferroelectric thin films have recently proven viable for nonvolatile memory applications in semiconductor technology. Current research is focused on the development of processing technologies and d...

Fatigue Parameters of Lead Zirconate Titanate Thin Films

Abstract: Temperature and voltage dependence of fatigue parameters were studied for PZT thin film capacitors on the basis of our fatigue model. It was found that the coefficient of dielectric viscosity of PZT and initial internal field difference of PZT capacitors play a key role in determining fatigue rate. Jump distance was calculated from voltage dependence of decay constant, and it turned out to be essentially the same as the lattice parameter. This result indicates that vacancies (oxygen vacancies, mainly) move parallel to the polarization direction during fatigue. Activation energy was calculated from the temperature dependence of the decay constant. It was confirmed that activation energy for domain wall movement determines fatigue rate at various temperatures. This fatigue model can be used to predict the fatigue behavior and can be extended to develop an accelerated test for fatigue.

Sol-gel processing of piezoelectric and ferroelectric films

Abstract: A method of providing a perovskite film having a general chemical formula of ABO₃ over a substrate includes the steps of providing (42,44,46,48,50,52) a sol-gel solution of composition of A and B using alkoxides in organic salts and depositing (54) the sol-gel solution as a thin film over the substrate . The film is converted into the perovskite film by rapidly heating (56) the thin film. Preferred perovskite materials include lead zirconate titanate. In one embodiment the films are deposited from sol-gel solutions containing lead, zirconium, and titanium and are converted (58) to a lead zirconate titante crystalline material in an atmosphere of oxygen to provide a ferroelectric dielectric having a high remanent polarization. In an alternate embodiment (Fig. 3), the sol-gel solution of lead, zirconium, and titanium is converted (62) to lead zirconate titanate crystalline material in a non-oxidizing atmosphere of an inert gas, nitrogen, or forming gas to provide materials having high dielectric constants and high and substantially linear dielectric constants with respect to applied voltages.

Electro-optic variable focal-length lens using PLZT ceramic

Abstract: Proposed is an electro-optic (E-O) variable focal-length lens by combining EO material with numerous transparent fine electrodes on its surface. Coating indium tin oxide transparent electrodes on a lanthanum-modified lead zirconate titanate (9/65/35) ceramic plate and introducing a parabolic index profile with dc voltage, we successfully demonstrate a positive EO variable focal-length lens, obtaining its focal length from ∞ to 1 m with applied voltage up to 300 V to an electrode gap of 50 μm. Theoretical analysis is also given, together with a discussion for improving aberration and resolving power.

Influence of Laser Fluence on Structural and Ferroelectric Properties of Lead-Zirconate-Titanate Thin Films Prepared by Laser Ablation

Abstract: Ferroelectric lead-zirconate-titanate (PZT) thin films were deposited by excimer laser ablation on (100) MgO substrates with and without an electrode. The film composition was approximately the same as that of the target over a laser fluence range of 2.6 and 10 J/cm2shot. Increase in the laser fluence enhances the film deposition rate and the crystallite size. In representative experiments, the remanent polarization and coercive field of the film prepared at a laser fluence of 9.2 J/cm2shot were 28 µC/cm2 and 72 kV/cm, respectively.

Deposition of thin films of multicomponent materials

Abstract: Composite films of multicomponent materials, such as oxides and nitrides, e.g., lead zirconate titanate, are deposited by dc magnetron sputtering, employing a rotating substrate holder, which rotates relative to a plurality of targets, one target for each metal element of the multicomponent material. The sputtering is carried out in a reactive atmosphere. The substrates on which the layers are deposited are at ambient temperature. Following deposition of the composite film, the film is heated to a temperature sufficient to initiate a solid state reaction and form the final product, which is substantially single phase and substantially homogeneous.

Piezoelectric thin film devices

Abstract: A new class of thin-film device structures has become available with the development of thin-film piezoelectric films by sol gel methods or by magnetron sputtering. In particular, sol gel techniques for ceramics such as lead zirconate titanate allow the fabrication of films of 1-4- mu m thickness on surfaces of complex shape with crack propagation within the film being controlled by process methods and buffer layer structures. Rapid thermal annealing methods have recently simplified fabrication procedures for film fabrication on silicon. Devices are described using both planar and coaxial geometry for application in surface acoustic wave (SAW) and bulk wave transducers, coaxial sensors, optical modulators, and silicon-based resonators. Current limitations due to electrodes and mechanical effects are examined. >

Fabrication and characterization of transducer elements in two-dimensional arrays for medical ultrasound imaging

Abstract: Some of the problems of developing a two-dimensional (2-D) transducer array for medical imaging are examined. The authors discuss the fabrication of a 2-D array material consisting of lead zirconate titanate (PZT) elements separated by epoxy. Ultrasound pulses and transmitted radiation patterns from individual elements in the arrays are measured. A diffraction theory for the continuous wave pressure field of a 2-D array element is generalized to include both electrical and acoustical cross-coupling between elements. This theory can be fit to model the measured radiation patterns of 2-D array elements, giving an indication of the level of cross-coupling in the array, and the velocity of the acoustic cross-coupling wave. Improvements in bandwidth and cross-coupling resulting from the inclusion of a front acoustic matching layer are demonstrated. A broadband electrical matching network is described, and pulse-echo waveforms and insertion loss from a 2-D array element are measured. >

Method of laser processing ferroelectric materials

Abstract: Processing methods transform ferroelectric precursor films into a desired crystalline structure without adversely heating nearby materials and circuitry such as those found associated with lead zirconate titanate films. The thin film sample is placed within an appropriate chamber, where a suitable ambient is in contact with the thin film sample. The ambient may be air, oxygen or any other ambient which is known in the art to be appropriate for annealing ferroelectric materials. In this regard annealing in air can done without the processing chamber. The process for annealing relies upon continuous wave (CW) laser annealing, pulse UV annealing with or without a laser and various combinations of thermal pretreatment and processing to allow solid state diffusion in accordance with parameters appropriate for a particular application. Methods of laser patterning thin film ferroelectrics without adversely damaging adjacent or underlying layers, e.g. electrodes, are also disclosed.

Preparation and Properties of Lead Zirconate-Titanate Piezoelectric Ceramics Using Ultrafine Particles

Abstract: Ultraflne particles the order of 0.1-µm have been obtained in the system PbTiO3-PbZrO3-Pb(Ni1/3Nb2/3)O3 by a ball-milling method using zirconia balls of 0.3 mm in diameter. This paper describes the electrical and mechanical properties of these modified PZT ceramics using ultrafine particles. The effect of smaller zirconia balls on grinding is clearly demonstrated. Smaller grain size in the sintered bodies of these modified PZT ceramics gives higher flexural strength. However, the maximum electrical properties have been obtained at a grain size of about 2 µm.

Piezoelectric Thin Film Ultrasonic Micromotors

Abstract: Thin films of lead zirconate titanate have been fabricated for application to a new family of flexure-wave piezoelectric micromotors that are characterized by low speed and high torque. The high relative dielectric constant and breakdown strength of the films lead to high stored energy densities. Evaluation of the film as a bimorph yielded a value of -88 pC/N for the transverse piezoelectric strain coefficient, d31; the relevant electromechanical coupling factor, k31, calculated thereupon was 0.22. The development of the piezoelectric ultrasonic micromotors from the PZT thin films, and the architecture of the stator structure are described. Nonoptimized prototype micromotors show rotational velocities of 100–300 rpm at drives of 3–5 V.

Processing-structure relations for ferroelectric thin films deposited by ion beam sputter deposition

Abstract: This paper emphasizes the need to determine the relationships between processing and structure (including microstructure) in ferroelectric thin films. The use of an automated ion beam deposition system is demonstrated, which allows the controlled deposition of films at low processing temperatures. A key feature is the real-time composition monitoring, during deposition, which allows stoichiometry to be precisely controlled. Microstructures (including defects) in KNbO3 and lead zirconate titanate films are investigated, and differences between the two materials emphasized.