Lead Zirconate Titanate Films Research Articles

Crystallization of piezoceramic films on glass via flash lamp annealing

Integration of thin-film oxide piezoelectrics on glass is imperative for the next generation of transparent electronics to attain sensing and actuating functions. However, their crystallization temperature (above 650 °C) is incompatible with most glasses. We developed a flash lamp process for the growth of piezoelectric lead zirconate titanate films. The process enables crystallization on various types of glasses in a few seconds only. The functional properties of these films are comparable to the films processed with standard rapid thermal annealing at 700 °C. A surface haptic device was fabricated with a 1 μm-thick film (piezoelectric e33,f of −5 C m−2). Its ultrasonic surface deflection reached 1.5 μm at 60 V, sufficient for its use in surface rendering applications. This flash lamp annealing process is compatible with large glass sheets and roll-to-roll processing and has the potential to significantly expand the applications of piezoelectric devices on glass.

Ultra-Stretchable Kirigami Piezo-Metamaterials for Sensing Coupled Large Deformations.

Mechanical metamaterials are known for their prominent mechanical characteristics such as programmable deformation that are due to periodic microstructures. Recent research trends have shifted to utilizing mechanical metamaterials as structural substrates to integrate with functional materials for advanced functionalities beyond mechanical, such as active sensing. This study reports on the ultra-stretchable kirigami piezo-metamaterials (KPM) for sensing coupled large deformations caused by in- and out-of-plane displacements using the lead zirconate titanate (PZT) and barium titanate (BaTiO3 ) composite films. The KPM are fabricated by uniformly compounding and polarizing piezoelectric particles (i.e., PZT and BaTiO3 ) in silicon rubber and structured by cutting the piezoelectric rubbery films into ligaments. Characterizes the electrical properties of the KPM and investigates the bistable mechanical response under the coupled large deformations with the stretching ratio up to 200% strains. Finally, the PZT KPM sensors are integrated into wireless sensing systems for the detection of vehicle tire bulge, and the non-toxic BaTiO3 KPM are applied for human posture monitoring. The reported kirigami piezo-metamaterials open an exciting venue for the control and manipulation of mechanically functional metamaterials for active sensing under complex deformation scenarios in many applications.

Effect of ferroelectric filler nanoarchitectonics on the electrical and mechanical properties of the nanocomposite thick films of polyvinylidene fluoride and lanthanum-doped lead zirconate titanate in 0–3 connectivity

Effect of ferroelectric filler nanoarchitectonics on the electrical and mechanical properties of the nanocomposite thick films of polyvinylidene fluoride and lanthanum-doped lead zirconate titanate in 0–3 connectivity

Film bulk acoustic resonators with 400 MHz ultrawide-range tunability using crystalline PZT thin film

Tunable and switchable film bulk acoustic resonators (FBARs) have great application potential owing to their much-increased flexibility in radiofrequency (RF) circuits. Here, we report on the design and fabrication of a tunable and switchable FBAR based on a thin crystalline lead zirconate titanate (PZT, Pb[Zr0.6Ti0.4]O3) film. The FBAR device has a resonant frequency of 2.42 GHz with a high effective electromechanical coupling coefficient keff2 of 30%. The frequency tunable range of the device is up to 400 MHz (2.11–2.51 GHz, 16.6%) with a DC bias voltage of less than 12 V, and the device can also be switched off when the polarization intensity in the PZT film is zero. Through the investigation, a relationship between the ferroelectric nature of PZT material and the wide tuning range of FBAR is established, providing a theoretical and experimental guideline for further development.

Bottom-up micromachined PZT film-based ultrasonic microphone with compressible parylene tube

This paper reports on a micromachined ultrasonic microphone using a bottom-up fabrication scheme. Starting with a 4 μm-thick titanium foil as the substrate, each functional film and key element was added to the foil substrate to complete the ultrasonic microphone. The piezoelectric lead zirconate titanate film hydrothermally grown on the patterned substrate with low residual stress effectively deflected the unimorph-sensing cantilever array of the microphone under ultrasound pressure. The created cantilever array structure secured on a 250 μm-thick SU8 hollow plate formed an ultrasonic microphone plate that was tested with a sensitivity of −60 dBV Pa−1 at 21 kHz (with 0 dB gain amplification) and an operation bandwidth of 5–55 kHz. Different thicknesses of parylene films ranging from 0.5 to 2 μm overlaid over the entire sensing region and converted the cantilever-to-diaphragm-structured microphone for further investigation. An enhanced result was observed when the deposited parylene film thickness was in the submicron range. The sensitivity of the microphone can be further enhanced by up to 33% by adding a parylene-film-made compressible tube to act as a Helmholtz resonator (HR). The HR model was discussed and compared with the experimental results. The output amplitude of the developed microphone assembled with the compressible tube demonstrates a 15 dB increase compared to that of a commercial capacitive MEMS ultrasonic microphone.

Porous PZT Films: How Can We Tune Electrical Properties?

Porous ferroelectric lead zirconate titanate (PZT) films are a promising material for various electronic applications. This study focuses on understanding how the structure-directing agent, polyvinylpyrrolidone, can alter the structure and electrical properties of porous PZT films prepared through chemical solution deposition. Films with various porosities of up to ~40 vol.% and pore connectivities from 3-0 to 3-3 were prepared and studied by capacitance-voltage, dielectric hysteresis, transient current, photocurrent, and local current techniques. We have found that a linear decrease in material volume in a porous film is not the only factor that determines film properties. The creation of new internal grain boundaries plays a key role in changing electrical properties. This research expands the understanding of physical phenomena in porous ferroelectric films and may facilitate the development of new materials and devices.

Tuning Nb Solubility, Electrical Properties, and Imprint through PbO Stoichiometry in PZT Films.

Lead zirconate titanate (PZT) films with high Nb concentrations (6-13 mol%) were grown by chemical solution deposition. In concentrations up to 8 mol% Nb, the films self-compensate the stoichiometry; single phase films were grown from precursor solutions with 10 mol% PbO excess. Higher Nb concentrations induced multi-phase films unless the amount of excess PbO in the precursor solution was reduced. Phase pure perovskite films were grown with 13 mol% excess Nb with the addition of 6 mol% PbO. Charge compensation was achieved by creating lead vacancies when decreasing excess PbO level; using Kroger-Vink notation, NbTi• are ionically compensated by VPb″ to maintain charge neutrality in heavily Nb-doped PZT films. With Nb doping, films showed suppressed {100} orientation, the Curie temperature decreased, and the maximum in the relative permittivity at the phase transition broadened. The dielectric and piezoelectric properties were dramatically degraded due to increased quantity of the non-polar pyrochlore phase in multi-phase films; εr reduced from 1360 ± 8 to 940 ± 6, and the remanent d33,f value decreased from 112 to 42 pm/V when increasing the Nb concentration from 6 to 13 mol%. Property deterioration was corrected by decreasing the PbO level to 6 mol%; phase pure perovskite films were attained. εr and the remanent d33,f increased to 1330 ± 9 and 106 ± 4 pm/V, respectively. There was no discernable difference in the level of self-imprint in phase pure PZT films with Nb doping. However, the magnitude of the internal field after thermal poling at 150 °C increased significantly; the level of imprint was 30 kV/cm and 11.5 kV/cm in phase pure 6 mol% and 13 mol% Nb-doped films, respectively. The absence of mobile VO••, coupled with the immobile VPb″ in 13 mol% Nb-doped PZT films, leads to lower internal field formation upon thermal poling. For 6 mol% Nb-doped PZT films, the internal field formation was primarily governed by (1) the alignment of (VPb″-VO•• )x and (2) the injection and subsequent electron trapping by Ti4+. For 13 mol% Nb-doped PZT films, hole migration between VPb″ controlled internal field formation upon thermal poling.

Excellent Uniformity and Properties of Micro-Meter Thick Lead Zirconate Titanate Coatings with Rapid Thermal Annealing.

Lead zirconate titanate (PZT) films have shown great potential in piezoelectric micro-electronic-mechanical system (piezo-MEMS) owing to their strong piezoelectric response. However, the fabrication of PZT films on wafer-level suffers with achieving excellent uniformity and properties. Here, we successfully prepared perovskite PZT films with similar epitaxial multilayered structure and crystallographic orientation on 3-inch silicon wafers, by introducing a rapid thermal annealing (RTA) process. Compared to films without RTA treatment, these films exhibit (001) crystallographic orientation at certain composition that expecting morphotropic phase boundary. Furthermore, dielectric, ferroelectric and piezoelectric properties on different positions only fluctuate within 5%. The relatively dielectric constant, loss, remnant polarization and transverse piezoelectric coefficient are 850, 0.1, 38 μC/cm2 and -10 C/m2, respectively. Both uniformity and properties have reached the requirement for the design and fabrication of piezo-MEMS devices. This broadens the design and fabrication criteria for piezo-MEMS, particularly for piezoelectric micromachined ultrasonic transducers.

Process-Controlled Domain Switching and Improved Ferroelectric Properties in Lanthanum-Modified Lead Zirconate Titanate Films

Process-Controlled Domain Switching and Improved Ferroelectric Properties in Lanthanum-Modified Lead Zirconate Titanate Films

Influence of doping and thickness on domain avalanches in lead zirconate titanate thin films

In undoped lead zirconate titanate films of 1–2 μm thick, domain walls move in clusters with a correlation length of approximately 0.5–2 μm. Band excitation piezoresponse force microscopy mapping of the piezoelectric nonlinearity revealed that niobium (Nb) doping increases the average concentration or mobility of domain walls without changing the cluster area of correlated domain wall motion. In contrast, manganese (Mn) doping reduces the contribution of mobile domain walls to the dielectric and piezoelectric responses without changing the cluster area for correlated motion. In both Nb and Mn doped films, the cluster area increases and the cluster density drops as the film thickness increases from 250 to 1250 nm. This is evident in spatial maps generated from the analysis of irreversible to reversible ratios of the Rayleigh coefficients.

Internal stress effects on the piezoelectric properties of Pb(Zr,Ti)O3 superlattice thin films grown on Si substrates

Artificial superlattice thin films of lead zirconate titanate (PZT) were epitaxially grown on silicon substrates, and the influence of superlattice strain on their piezoelectric properties was investigated. The c-axis oriented PZT superlattice thin film consists of two different PZT layers, Pb(Zr0.65Ti0.35)O3 (PZT-65) and Pb(ZrxTi1−x)O3 (PZT-X: x = X/100 = 0.3–0.9), with a 4 nm period. Satellite peaks were clearly observed in x-ray diffraction patterns, and cross-sectional composition measurements confirmed the superlattice structure with good interfaces, showing an alternate change in Zr and Ti compositions. Ferroelectric properties varied significantly depending on the PZT-X composition, and in particular, the PZT-65/PZT-30 superlattice thin film showed nearly the same ferroelectricity as the tetragonal phase under a large compressive strain of PZT-65 from the PZT-30 layer. For the PZT-65/PZT-X (X = 30–58) superlattice thin films, the PZT-65 layers received a compressive strain, and a relatively large piezoelectric coefficient, which did not depend on the PZT-X composition, was obtained. However, a decrease in piezoelectricity was observed in PZT-65/PZT-X (X = 70 and 90), where the PZT-65 layers experienced tensile strain. This result indicates that the piezoelectric properties of PZT superlattice thin films can be controlled by the interlayer strain.

Thin, flexible, and biocompatible medical ultrasound array transducer using a sol–gel composite spray technique

A thin, flexible, and biocompatible medical ultrasonic transducer was developed using a sol–gel composite spray technique to fabricate a single sheet of piezoelectric material. The careful selection of materials prioritized flexibility, with silicone rubber being chosen for its biocompatibility as the material to be in direct contact with the living body. A porous lead zirconate titanate film with a dielectric constant of 134 was generated, and comb-shaped electrodes were printed on the piezoelectric film to form a 64-channel linear array, which successfully suppressed crosstalk values between adjacent elements and at a distance of two elements to −41.5 and −45.8 dB, respectively. Experiments using string targets achieved a spatial resolution of 2 mm in the lateral direction and 0.68 mm in the axial direction. In an imaging experiment of the carotid artery, the transducer was successful in visualizing the vessel wall before and after the carotid artery vessel.

Studying the Effect of Annealing Temperature and Thickness on Electrical Properties of PZT Films Prepared by Sol-Gel Technique

Lead Zirconate Titanate (PZT) film was synthesized by sol-gel technique on a silicon substrate. The raw materials used to synthesize the solution of PZT consist of lead acetate, zirconate nitrate and titanate (IV) isopropoxide and 2methoxy ethanol is used as a stabilizer for Ti structure. Acetic acid is the solvent used to solve lat acetate and zirconate nitrate. The XRD pattern of the sample shows that the film has a tetragonal phase with a perovskite structure. FESEM revealed the surface morphologies and the cross-section of the film. The different thicknesses of film and annealing temperatures are investigated in this work. The dielectric constant was measured at 1 kHz, PZT films have a dielectric constant value ( 312-552 ) and a dielectric loss (0.02-0.08) at ambient temperature. Keywords: PZT film; Lead zirconated titanate; ferroelectric properties; dielectric constant.

Nonlinear Optics for Crystallographic Analysis in Lead Zirconate Titanate

The azimuthal dependences of the optical second harmonic generation signal from crystallized regions (spherulites) of the ferroelectric phase in lead zirconate titanate films are investigated to determine the symmetry and orientation of crystallites. These dependencies in different regions of the same spherulite have different shapes, which indicates a difference in crystallographic orientations and/or symmetry. Based on the assumption of the possible presence of two syngonies and three orientations for each, the fitting of experimental azimuthal dependences by model curves was carried out, which provided information about the ratio of these phases and orientations in different areas of the film.

A two-step wet etching process of PZT thin film with ultra-low undercut for MEMS applications

Wet etching methods of lead zirconate titanate (PZT) film suffer from high residual risk and severe undercut erosion. In this study, a two-step etching approach replace with the traditional concept of multi-acid mixing etchant, which increases the precision of PZT film and fixes the residual issues that were difficult to avoid in the conventional scheme. The two-step etching of the PZT film's mechanism is investigated using XRD and TEM. The impact of the etchant's composition ratio on the etching effect is demonstrated, and the ideal process range and debugging direction can be accurately identified. The undercut ratio (0.62) of the etching method proposed in this study is substantially lower than that in prior studies. In addition, the etching rate and selectivity between photoresists are 60 nm/s and 1.14, respectively. The sidewall forms an inclined plane of around 30 degrees due to the crystal orientation dependent etch rates. The results of the polarization hysteresis loop demonstrate that there is no significant performance loss before and after the wet etching process. A two-step wet etching process of PZT thin film with ultra-low undercut ratio (0.62) is developed. The baseline recipe with a high etch rate, and the selectivity with photoresist is 1.14, and the sidewalls etch into an inclined plane of about 30 degrees. • A new two-step wet etching recipe for PZT film, which use different etchant to etch different phases in PZT film, obtains ultra-low undercut ratio (0.62) and does not generate residual risk, has been developed. • Experimental results have demonstrated that ultra-low undercut, high etch rate, no residual and high selectivity can be simultaneously achieved without using any special processing condition. • Etch results with different acid concentrations in different etchant, processing phenomenon analysis with XRD and TEM, and Interpretation of the etching process and comparison of ferroelectric parameters for the results before and after etching, which can be proven suitability for various etching purposes.

Сегнетоэлектрические свойства тонких пленок цирконата-титаната свинца, полученных методом высокочастотного магнетронного распыления, в области морфотропной фазовой границы

An experimental study of the crystal structure and ferroelectric properties of <110>-textured lead zirconate titanate films with a fine variation in their composition (with a change in the elemental ratio of zirconium and titanium atoms within 1.5%) near the morphotropic phase boundary revealed jump-like changes in the pseudocubic lattice parameter, dielectric permittivity and residual polarization. It is assumed that the observed anomalies correspond to a morphotropic transition from a rhombohedral to a mixture of tetragonal and monoclinic phases.

Ferroelectric properties of lead zirconate titanate thin films obtained by RF magnetron sputtering near the morphotropic phase boundary

An experimental study of the crystal structure and ferroelectric properties of <110>-textured lead zirconate titanate films with a fine variation in their composition (with a change in the elemental ratio of zirconium and titanium atoms within 1.5%) near the morphotropic phase boundary revealed jump-like changes in the pseudocubic lattice parameter, dielectric permittivity and residual polarization. It is assumed that the observed anomalies correspond to a morphotropic transition from a rhombohedral to a mixture of tetragonal and monoclinic phases. Keywords: fine composition variation, phase state, piezoresponse force microscopy, abnormal dielectric and piezoelectric properties.

Increased fatigue resistance in transparent lead zirconate titanate thin films with interdigitated electrodes

This work compares the fatigue behavior of fully transparent lead zirconate titanate films with a composition at the morphotropic phase boundary on fused silica glass or sapphire, respectively, fitted with coplanar interdigitated top electrodes and no bottom electrodes to that of the same systems in a traditional metal–insulator–metal parallel plate capacitor geometry. While the polarization hysteresis in the latter geometry decreases rapidly during bipolar electrical cycling, systems with coplanar electrodes show no notable fatigue up to 107 cycles. The difference is explained based on the columnar microstructure of the films: for coplanar electrode geometries, the grain boundaries of the columnar structure act as trapping sites for oxygen vacancies, preventing the build-up of agglomerates that cause fatigue by domain wall pinning.

Cracking behavior in lead zirconate titanate films with different Zr/Ti ratios

Crack initiation stresses for different lead zirconate titanate (PZT) film compositions were investigated. PZT/Pt/TiO2/SiO2/Si stacks with 2.0 μm thick {100} oriented PZT films at the morphotropic phase boundary (MPB) showed a characteristic strength of 1137 MPa, and the film thickness served as the limiting flaw size for failure of the film/substrate stack. In contrast, for Zr/Ti ratios of 40/60 and 30/70, the characteristic stack strength increased while the Weibull modulus decreased to values typical for that of Si. This difference is believed to be due to toughening from ferroelasticity or phase switching. X-ray diffraction showed that the volume fraction of c-domains increased in Ti-rich compositions. This would allow for more switching from c to a-domains under biaxial tensile stress. Zr/Ti concentration gradients were present for all compositions, which contributed to the observation of a rhombohedral phase off the MPB. Due to the reduced tendency toward cracking, off-MPB compositions are potentially of interest in actuators, albeit with the trade-off of needing a high actuation voltage.

Links between defect chemistry, conduction, and lifetime in heavily Nb doped lead zirconate titanate films

Phase pure PbZr0.52Ti0.48O3 (PZT) films with up to 13 mol. % Nb were prepared on Pt-coated Si substrates using chemical solution deposition; charge compensation for Nb was accomplished by reducing the concentration of lead in the film. For high Nb doping levels, (1) superoxidation of the PZT film surface makes the PZT/Pt interface more p-type and, hence reduces electron injection over the Schottky barrier, (2) the bulk charge transport mechanism changes from electron trapping by Ti4+ to hole migration between lead vacancies, and (3) the ionic conductivity due to migration of oxygen vacancies decreases. For ≤6 mol. % Nb, electrical degradation was controlled via field-induced accumulation of oxygen vacancies near the cathode, which, in turn, leads to Schottky barrier lowering and electron trapping by Ti4+. In phase pure 13 mol. % Nb doped PZT films, on the other hand, the increase in the leakage current during electrical degradation was dominated by hole migration between lead vacancies (2[VPb″]∼[h•]). A much lower lifetime and drastic increase in the leakage current upon electrical degradation was observed in mixed phase PNZT films, which was attributed to (1) a more electrically conductive pyrochlore phase and (2) a high concentration of lead vacancies.