Sol-gel Derived Lead Zirconate Titanate Research Articles

Effects of Thickness, Pulse Duration, and Size of Strip Electrode on Ferroelectric Electron Emission of Lead Zirconate Titanate Films

Sol–gel-derived lead zirconate titanate (PZT) thin-film emitters with thickness up to 9.8 μm have been prepared on Pt/TiO2/SiO2/Si wafer via chemical solution deposition with/without polyvinylpyrrolidone (PVP) modification, and the relationship between the film thickness and electron emission investigated. Notable electron emission was observed on application of a trigger voltage of 120 V for PZT film with thickness of 1.1 μm. Increasing the film thickness decreased the threshold field to initiate electron emission for non-PVP-modified films. In contrast, the electron emission behavior of PVP-modified films did not show significant dependence on film thickness, probably due to their porous structure. The emission current increased with decreasing strip width and space between strips. Furthermore, it was observed that increasing the duration of the applied pulse increased the magnitude of the emission current. The stray field on the PZT film thickness was also calculated and found to increase with increasing ferroelectric sample thickness. The PZT emitters were found to be fatigue free up to 105 emission cycles. Saturated emission current of around 25 mA to 30 mA was achieved for the electrode pattern used in this work.

Sol–gel derived lead zirconate titanate: Processing, micrometer and nanometer scale patterning and characterization

To produce good quality films and patterns with high fidelity, the fabrication of PZT by sol–gel process was investigated, and various processing steps were studied. Sol–gel based PZT solutions were prepared and converted into thin films and patterns with spin coating and soft lithographic techniques, respectively. Structural and compositional analysis of the films and patterns was performed with XRD, and surface and topography were studied with HRSEM and AFM. Electrode deposition on the thin films and patterns were done with FIB, PLD and sputtering. The ferroelectric and dielectric properties of the film derived were also investigated.

Effect of heating rate on microstructure and electrical properties of sol–gel derived lead zirconate titanate films crystallized by rapid thermal annealing

In the present work, Ferroelectric Lead zirconate titanate [Pb(ZrxTi1-x)O3: PZT] films with a nominal formula Pb1.1(Zr0.52Ti0.48)O3 were prepared with the sol–gel method and post-annealed by rapid thermal annealing. Different heating rates were adopted to explore their effect on microstructure and electrical properties of PZT films. The results show that heating rate has a significant effect on the orientation and grain size distribution of PZT films under the same annealing temperature, which further results in different dielectric and ferroelectric properties. It is found that the faster heating rate is not favorable for enhancing the ferroelectricity of PZT films although it promotes the phase transition process. The relationship between heating rate and microstructure of PZT films is discussed based on its effect on the nucleation and growth process of PZT perovskite phase. It is proposed that the nucleation and growth process of perovskite phase occurs under different stress states at different heating rates, which leads to the varying orientations of films.

Time-resolved small angle X-ray scattering study of sol–gel precursor solutions of lead zirconate titanate and zirconia

The evolution of nanostructure in sol–gel derived lead zirconate titanate (PZT) and zirconia precursor sols at different hydrolysis ratios was investigated by small angle X-ray scattering (SAXS). The shape of the clusters in the zirconia sol could be described by the length-polydisperse cylindrical form factor. The zirconia-based clusters were characterized by a cross-sectional radius, r0, of 0.28nm and a practically monodisperse length of ca. 1.85nm. These clusters were probably constructed of zirconia-related tetrameric building blocks. Similar cylindrical structural motifs were observed in PZT precursor sols with [H2O]/[Zr+Ti]=9.26 and 27.6, but the polydispersity in length was much higher. Clear scattering contributions from Ti and Pb centers were not detected, which was interpreted in terms of a homogeneous distribution of unbound lead ions in solution and the relatively low scattering intensity from any Ti-based clusters or oligomers that may have been present in the sols.

Development of Nanoscale Inhomogeneities during Drying of Sol–Gel Derived Amorphous Lead Zirconate Titanate Precursor Thin Films

The structural evolution of sol-gel derived lead zirconate titanate (PZT) precursor films during and after physical drying was investigated by transmission electron microscopy (TEM), electron energy loss spectroscopy (EELS), selected area electron diffraction (SAED), and time-resolved X-ray diffraction (XRD). Films were deposited from initial 0.3 mol/dm(3) precursor sols with varying hydrolysis ratios. Zr-rich grains of 1-10 nm size, embedded in a Pb-, Zr-, and Ti-containing amorphous matrix were found in as-dried films. The Zr-rich regions were crystalline at hydrolysis ratios [H(2)O]/[PZT] < 27.6, and amorphous at ratios > 100. X-ray diffraction analysis of PZT and zirconia sols revealed that the crystalline nanoparticles in both sols are identical and are probably composed of nanosized zirconium oxoacetate-like clusters. This study demonstrates that time-resolved X-ray diffraction combined with electron energy loss spectroscopy mapping is a powerful tool to monitor the nanoscale structural evolution of sol-gel derived thin films.

Phase evolution studies of sol–gel derived lead zirconate titanate (PZT) nanopowder using X-ray diffraction and X-ray photoelectron spectroscopy

We report here the formation of single phase lead zirconate titanate (PZT) nanopowder with composition Pb(Zr0.52Ti0.48)O3 and average crystallite size 12–20 nm, synthesized by sol–gel process. The phase evolution of PZT gel powder, heat treated at temperatures 550, 650 and 800°C was monitored by X-ray diffraction (XRD) and X-ray photo-electron spectroscopy (XPS). The high resolution XPS spectra of Pb4f, Zr3d, Ti2p and O1s show that PZT with pure perovskite structure is obtained at 800°C while at lower temperatures pyrochlore phase co-exists with perovskite phase. The XRD results also support this analysis. We have also identified the pyrochlore phase using XPS by analyzing the corresponding variations in the FWHM values, peak positions and the separation between the spin doublets of Pb, Zr and Ti associated with it. The composition of the final powder obtained with pure perovskite structure is calculated and is close to the designed value.

Sol-Gel Derived Nanocrystalline Lanthanum Doped Lead Zirconate Titanate Thin Films Studied for Solitary Waves Propagation

Nanocrystalline PLZT thin films of composition Pb1-xLaxZr0.52Ti0.48 (x = 0, 2, 5%) were deposited on silicon substrates by sol-gel process using lead acetate trihydrate, lanthanum nitrate hydrate, zirconium propoxide and titanium propoxide as lead, lanthanum, zirconium and titanium precursor materials. Experimental studies have been made on solitary waves in 2 mol% lanthanum doped sol-gel derived lead zirconate titanate thin films. The solitary waves are generated under the influence of external alternating electric field, which has the same frequency as the external field. These solitary waves propagate through the thin film upto its boundary and then reflect back. The magnitude of the solitary waves attenuates as they move away from the electrodes and their phase reverses on reflection. For certain frequencies of the external electric field, solitary waves exhibit resonance effect. Distortion in hysteresis loops has been demonstrated on the basis of solitary waves propagation in the film having different electrode area.

Effect of vapor thermolysis on microstructure development of sol–gel-derived lead zirconate–titanate (PZT) and PZT-Sr(K0.25Nb0.75)O3 solid solutions

Ceramic granules of PZT (Pb(Zr53,Ti47)O3) and fibers of SKN-doped PZT (1 Mol-% Sr(K0.25Nb0.75)O3 substitution in PZT) were fabricated from sol–gel precursors. The transformation of the metal–organic gel to the oxide and its crystallization behavior was investigated by thermogravitmetry, and XRD. The formation of pyrochlore or perovskite phase was sensitive to the preceeding heat treatment conditions in moist atmosphere (termed vapor thermolysis). Lower thermolysis temperatures resulted in the preferred formation of metastable pyrochlore phase. Higher thermolysis temperatures favored the formation of perovskite. Investigation of sintered materials revealed a superior sintering activity for samples with pronounced intermediate pyrochlore content whereas low-pyrochlore samples remained highly porous after sintering. For constant chemical precursors the vapour thermolysis conditions (220–280 °C) siginificantly affected crystallization and sintering behavior of the PZT and SKN-PZT material.

Thermal strain measurement in sol-gel lead zirconate titanate thin films

A fluorescence-based digital image correlation (DIC) technique is used to characterize the in-plane strain development of blanket sol-gel derived lead zirconate titanate thin films deposited on platinized silicon substrates. The in-plane strain is also measured within film line features patterned via a mediated octadecyltrichlorosilane (ODS) monolayer. The results indicate that the selective film failure induced by the mediated ODS layer succeeds in slightly reducing the in-plane strain transverse to the line feature direction (∼25% lower), while remaining nearly the same as the blanket film case in the direction parallel to the line direction. Additional in-plane stress estimates from wafer curvature measurements for the two film configurations (blanket and ODS patterned) were consistent with the DIC measured strain results.

Compatibility of Material Processing and Fabrication of Sol-Gel Derived PZT Based Devices

This study investigates the compatibility of material processing and fabrication of micro devices based on sol-gel derived lead zirconate titanate (PZT) thin films. High temperature annealing of sol-gel derived PZT may cause cracking and diffusion of structure layers. The introduction of a buffer layer, (LaxSr 1 − x )MnO 3 , between PZT thin film and metal electrodes improves PZT crystallization and ferroelectricity. Annealing temperature of PZT/LSMO structure using furnace heating is investigated and compared with CO 2 laser annealing. A parameter study of PZT poling shows the improvement of film properties. The fabrication procedures of two exemplar devices, a micro accelerometer and a FPW acoustic sensor illustrate the interaction issues among material structures and processes.

Sensing liquid density using resonant flexural plate wave devices with sol–gel PZT thin films

This study presents the design, fabrication and possible applications in liquid density sensing and biosensing of a flexure plate wave (FPW) resonator using sol–gel-derived lead zirconate titanate ...

Sensing liquid density using resonant flexural plate wave devices with sol–gel PZT thin films

This study presents the design, fabrication and possible applications in liquid density sensing and biosensing of a flexure plate wave (FPW) resonator using sol–gel-derived lead zirconate titanate (PZT) thin films. The resonator has a two-port structure with a reflecting grating on a composite membrane of PZT and SiNx. The design of the reflecting grating is derived from a SAW resonator model using COM theory to generate a sharp resonant peak. A comparison between the theoretical mass and the viscosity effects reveals the applications and the constraints of the proposed device in liquid sensing. Multiple coatings of sol–gel-derived PZT films are employed because of the cost advantage and the strong electromechanical coupling effect over other piezoelectric films. Issues of fabrication of the proposed material structure are addressed. Theoretical estimates of the mass and the viscosity effects are compared with the experimental values. The resonant frequency relates quite linearly to the density of low-viscosity liquids, revealing the feasibility of the proposed device.

Mechanical properties of sol–gel derived lead zirconate titanate thin films by nanoindentation

Lead zirconate titanate (PZT) thin films are deposited on platinized silicon substrate by sol–gel process. The crystal structure and surface morphology of PZT thin films are characterized by X-ray diffraction and atomic force microscopy. Depth-sensing nanoindentation system is used to measure mechanical characteristics of PZT thin films. X-ray diffraction analyses confirm the single-phase perovskite structures of all PZT thin films. Nanoindentation measurements reveal that the indentation modulus and hardness of PZT thin films are related with the grain size and crystalline orientation. The increases of the indentation modulus and hardness with grain size are observed, indicating the reverse Hall–Petch effect. Furthermore, the indentation modulus of (1 1 1)-oriented PZT thin film is higher than those of (1 0 0)- and random-oriented films. The consistency between experimental data and numerical results of the effective indentation moduli for fiber-textured PZT thin films using Voigt–Reuss–Hill model is obtained.

EFFECTS OF RAPID THERMAL ANNEALING ON MICROSTRUCTURES AND PROPERTIES OF PZT-PT/TI STACKS FOR MEMS APPLICATION

ABSTRACT The effects of rapid thermal annealing (RTA) on microstructures, properties, and residual stress of Pt/Ti electrodes and sol-gel derived lead zirconate titanate (PZT) films were investigated. It was found that when heating rate was 3.5°C/s, the Pt/Ti electrode conglomerated to form a typical hillock surface morphology, companied by remarkable degradations in both surface roughness and electric conductivity. When using 10.5°C/s as the heating rate, the Pt/Ti conglomeration and degradation can be effectively retarded. Accordingly, the PZT film exhibited different properties at various RTA conditions. Furthermore, Ti diffusion was found mainly happened in a short period after heat-treatment started.

Effects of rapid thermal annealing on nucleation, growth, and properties of lead zirconate titanate films

The nucleation and growth behavior of solgel-derived lead zirconate titanate (PZT) films was investigated at different rapid thermal annealing (RTA) processes. The effects of RTA on PZT film surface morphology, crystal orientation, residual stress, and properties were also studied and are discussed. PZT nucleation and growth behavior were found to be more sensitive to heating rate than to hold time during RTA. Higher heating rates were preferred for uniform PZT nucleation and grain growth, which resulted in dense microstructures, smooth surfaces, and better film ferroelectric properties. Lower heating rates led to strong PZT (100) orientation, better film piezoelectric properties, and low residual stress, but at the risk of film cracks caused by arbitrarily distributed large crystallites with diameters of approximately 300 nm among crystallites with diameters of approximately 30 nm. Furthermore, the residual stress of the PZT film was found to be effectively reduced by extending the hold time.

Improvement electrical properties of sol–gel derived lead zirconate titanate thick films for ultrasonic transducer application

In this work, a fabrication process of piezoelectric PZT [Pb(Zr0.52Ti0.48)O3] thick films up to 60 μm deposited on silicon and aluminum substrates is reported. Crystalline spherical modified PZT powder about 300 nm in diameter was used as filler. PZT polymeric precursor produced by Chemat Inc. was used as the matrix material. Spinning films were annealed at 700 °C for one hour in the furnace in air. The thickness of the thick films was measured using a scanning electron microscope (SEM). Compared with previous piezoelectric PZT composite films, the modified piezoelectric thick films exhibit better dielectric properties. The dielectric constant is over 780 and dielectric loss is 0.04 at 1 KHz. Using a PiezoCAD model, the high frequency transducer was designed and fabricated. It showed a bandwidth of 75% at 40 MHz.

Residual stress effects on piezoelectric response of sol-gel derived lead zirconate titanate thin films

Piezoelectric properties of three sol-gel derived Pb(Zr0.53Ti0.47)O3 thin film specimens of different thicknesses integrated onto Pt∕Ti∕SiO2‖Si substrates are investigated to delineate the influence of residual stress on the strain-field response characteristics from other thickness related effects. Residual tensile stresses are determined from wafer curvature measurements for films ranging in thickness from 190to500nm. Field-induced strains are measured interferometrically for each film under either a large ac driving voltage or a small ac ripple applied over a range of dc biases. Higher residual stresses decrease measured piezoelectric response, while thickness variations with no accompanying change in residual stress state produce little change in strain-field behavior. The diminished performance associated with high residual stresses is attributed to reductions in both linear and nonlinear contributions, including decreased polarization switching and domain motion.

Effect of drying temperature on structure, phase transformation of sol–gel-derived lead zirconate titanate powders

Lead zirconate titanate (PZT) (53/47) powders were prepared by a cheating acetate sol–gel process. The drying temperature effect on crystallization behavior was conducted to determine the best conditions for preparing high content of perovskite PZT powders in the morphotropic region. DSC/TG analysis, FT-IR spectrum and X-ray diffraction were carried out to identify the reaction sequences and calculated the activation energy of every transition temperature during the drying procedures. In the present work, well-crystallized, single-phase perovskite PZT powders were obtained after drying PZT stock solution at 300 °C for 1 h, then heat treatment at 600 °C for 30 min. The dependence of this crystallization temperature on the drying conditions was discussed.

Relaxation Processes in Dielectric and Electromechanical Response of PZT Thin Films Under Nanoindentation

In this work, stress-induced relaxation processes in sol-gel derived lead zirconate titanate (PZT) films with a Zr/Ti ratio of 30/70 were investigated by nanoindentation with a spherical tipped conductive indenter. The capacitance and electrical current transient flowing through the film under short-circuit conditions were measured as a function of constant nanoindentation force in the time domain. Measurements on piezoelectric films of different thickness indicated a significant mechanical clamping of the ferroelectric domains produced by the substrate. It is demonstrated that both the dielectric and electro-mechanical relaxation behavior are dependent on stress state in the film, which is affected during indentation. The relaxation of the electromechanical response is found to follow a stretched exponential function, the parameters of which are dependent on the indentation force and film thickness. On the other hand, the small signal capacitance measurement showed much slower relaxation characterized by a logarithm-time dependence. The differences observed in time response of dielectric and piezoelectric properties are related to different relaxation mechanisms and discussed in terms of stress-enhanced domain-wall movement. †On leave from the Institute of Materials Research, Slovak Academy of Sciences, Košice, Slovak Republic.

Internal field and self-polarization in sol–gel-derived lead zirconate titanate films

An internal electric field is induced in a sol–gel-derived lead zirconate titanate (PZT) film of thickness 2 μm after the rf-sputtering deposition of the top electrode and this is exhibited as a shift of the P–E loop towards the positive side of the electric field axis. The direction of the internal field is towards the bottom electrode. As the discharge power used for the sputtering decreases, the internal field increases. We suggest that the internal field is induced by the high-energy ion bombardment on the film surface during the rf-sputtering process. Due to the occurrence of the internal field, the as-prepared PZT film becomes self-polarized at a high deposition temperature of 150 °C, thus showing a non-zero pyroelectric coefficient at room temperature. As the internal field increases, the observed pyroelectric coefficient increases and has a large value of 230 μC/m2 K for an as-prepared PZT film with an internal field of 40 kV/cm.