Lead Titanate Thin Films Research Articles

Multistep polarization switching and reduced coercive field in lead titanate thin films

Multistep polarization switching and reduced coercive field in lead titanate thin films

Magnetron-Sputtered Lead Titanate Thin Films for Pyroelectric Applications: Part 2-Electrical Characteristics and Characterization Methods.

Pyroelectric materials are naturally electrically polarized and exhibits a built-in spontaneous polarization in their unit cell structure even in the absence of any externally applied electric field. These materials are regarded as one of the ideal detector elements for infrared applications because they have a fast response time and uniform sensitivity at room temperature across all wavelengths. Crystals of the perovskite lead titanate (PbTiO3) family show pyroelectric characteristics and undergo structural phase transitions. They have a high Curie temperature (the temperature at which the material changes from the ferroelectric (polar) to the paraelectric (nonpolar) phase), high pyroelectric coefficient, high spontaneous polarization, low dielectric constant, and constitute important component materials not only useful for infrared detection, but also with vast applications in electronic, optic, and MEMS devices. However, the preparation of large perfect and pure single crystals PbTiO3 is challenging. Additionally, difficulties arise in the application of such bulk crystals in terms of connection to processing circuits, large size, and high voltages required for their operation. In this part of the review paper, we explain the electrical behavior and characterization techniques commonly utilized to unravel the pyroelectric properties of lead titanate and its derivatives. Further, it explains how the material preparation techniques affect the electrical characteristics of resulting thin films. It also provides an in-depth discussion of the measurement of pyroelectric coefficients using different techniques.

Influence of the Annealing Environment on the Structure and Ferroelectric Properties of Lead Titanate Thin Films

Lead titanate thin films of pyrochlore phase were deposited using layer-by-layer reactive magnetron sputtering on a heated platinized silicon substrate. It was found that the pyrochlore phase transition to the perovskite phase was initiated at 700 °C, and the properties of the PbTiO3 films could be controlled by changing the annealing environment. The thin films annealed in air and oxygen environments (1.33 Pa) have a tetragonal structure. The highest values of remnant polarization and the coercive field were 38 μC/cm2 and 130 kV/cm, respectively, but the largest dielectric loss was determined for the films annealed in air. The remnant polarization, coercive field and dielectric loss were reduced when the annealing of films was performed using oxygen gas at 1.33 Pa pressure. The films annealed in vacuum showed a rhombohedral (and ferroelectric) structure with the lowest remnant polarization and coercive field values. Such a structure was not observed for lead titanate at room temperature. It was observed that the surface morphology strongly depended on the reaction rate, which was influenced by the oxygen concentration in the environment.

Self-aligned single-electrode actuation of tangential and wineglass modes using PMN-PT

Considering the evolution of rotation sensing and timing applications realized in micro-electro-mechanical systems (MEMS), flexural mode resonant shapes are outperformed by bulk acoustic wave (BAW) counterparts by achieving higher frequencies with both electrostatic and piezoelectric transduction. Within the 1–30 MHz range, which hosts BAW gyroscopes and timing references, piezoelectric and electrostatic MEMS have similar transduction efficiency. Although, when designed intelligently, electrostatic transduction allows self-alignment between electrodes and the resonator for various BAW modes, misalignment is inevitable regarding piezoelectric transduction of BAW modes that require electrode patterning. In this paper transverse piezoelectric actuation of [011] oriented single crystal lead magnesium niobate–lead titanate (PMN–PT) thin film disks are shown to excite the tangential mode and family of elliptical compound resonant modes, utilizing a self-aligned and unpatterned electrode that spans the entire disk surface. The resonant mode coupling is achieved by employing a unique property of [011] PMN–PT, where the in-plane piezoelectric coefficients have opposite signs. Fabricating 1-port disk transducers, RF reflection measurements are performed that demonstrate the compound mode family shapes in the 1–30 MHz range. Independent verification of mode transduction is achieved using in-plane displacement measurements with Polytec’s laser Doppler vibrometer (LDV). While the tangential mode achieves a 40o/s dithering rate at 335 kHz resonant frequency, the n = 2 wine-glass mode achieves 11.46 nm tip displacement at 8.42 MHz resonant frequency on a radius of 60 μm disk resonator in air. A single electrode resonator that can excite both tangential and wine-glass modes with such metrics lays the foundation for a BAW MEMS gyroscope with a built-in primary calibration stage.

Ferroelectric properties and structural characterisation of lead titanate thin films prepared by polymeric precursor method

ABSTRACT Ferroelectric thin films of lead titanate (PbTiO3) have been prepared on SiO2/Si(100) and LaNiO3(110)/SiO2/Si(100) substrates by a sol-gel spin coating method, using lead acetate trihydrate, and titanium isopropoxide as precursors along with 2-methoxyethanol as a solvent and acetic acid as catalyst. X-Ray Diffraction patterns show the formation of the perovskites structure of PbTiO3 thin films deposited on SiO2/Si substrates at 650°C. A SEM micrograph of the film cross-section is used to measure the thickness, which gave a value of 0.65 μm. Analysis of its ferroelectric hysteresis measurements gave values of remanent polarisation of Pr = 18.37 μC/cm2 and a coercive field of Ec = 121.53 kV/cm which are essential for non-volatile memories application. The current-voltage characteristic was found to be space charge conduction in the high voltage region and its piezoelectric coefficient d33, as measured by a Laser Scanning Doppler vibrometry, showed small linear decreases from 75 pm/V at 45 kV/cm to 67 pm/V at the highest applied field (330 kV/cm).

Cascaded pyroelectric conversion: Optimizing the ferroelectric phase transition and electrical losses

The dramatic increase in the pyroelectric coefficient around the ferroelectric–paraelectric phase transition suggests high potential energy conversion efficiencies, but the reality is more complicated when thermal and electrical losses are considered. The performance of prototype mono-domain lead titanate thin films is simulated around phase transition using a phenomenological modeling approach. Thermodynamic properties are calculated using a modified Landau–Devonshire potential that is a function of temperature, applied electric field, and uniaxial tensile stress for bulk films. Significant performance enhancement near the ferroelectric–paraelectric phase transition is observed. However, increases in both the specific heat and the dielectric constant reduced the anticipated improvement. Critically, electrical losses during charging and discharging processes within the energy conversion cycle are included and calculated using the dielectric dissipation factor. Cascaded pyroelectric conversion cycles are considered where heat for each subsequent stage is provided by the previous stage, allowing for the segmentation of large temperature changes into multiple cycles. The implementation of a multi-stage or cascade approach could greatly increase the cycle efficiency over a large temperature range while utilizing lower, more realistic, electric field strengths. We show how each stage could be optimized through a secondary multi-caloric effect where the ferroelectric–paraelectric transition temperature is shifted using an applied biaxial stress. Loss tangents as low as 5% are shown to negate the benefits of cascading for high number of stages (n > 10). Using a stress-tuned optimum phase transition temperature for cascade stages provides roughly a 100% increase in thermal efficiency vs the unoptimized material for low electric field cycles.

Mechanical-force-induced non-local collective ferroelastic switching in epitaxial lead-titanate thin films

Ferroelastic switching in ferroelectric/multiferroic oxides plays a crucial role in determining their dielectric, piezoelectric, and magnetoelectric properties. In thin films of these materials, however, substrate clamping is generally thought to limit the electric-field- or mechanical-force-driven responses to the local scale. Here, we report mechanical-force-induced large-area, non-local, collective ferroelastic domain switching in PbTiO3 epitaxial thin films by tuning the misfit-strain to be near a phase boundary wherein c/a and a1/a2 nanodomains coexist. Phenomenological models suggest that the collective, c-a-c-a ferroelastic switching arises from the small potential barrier between the degenerate domain structures, and the large anisotropy of a and c domains, which collectively generates much larger response and large-area domain propagation. Large-area, non-local response under small stimuli, unlike traditional local response to external field, provides an opportunity of unique response to local stimuli, which has potential for use in high-sensitivity pressure sensors and switches.

Texture and phase variation of ALD PbTiO3 films crystallized by rapid thermal anneal

PbTiO3 (lead titanate) thin films were deposited by atomic layer deposition (ALD) and crystallized via rapid thermal anneal. The films were grown using lead bis(3-N,N-dimethyl-2-methyl-2-propanoxide) and tetrakis dimethylamino titanium as cation precursors. A combination of H2O and ozone was used as oxidizers. Phase-pure, stoichiometric PbTiO3 was confirmed using x-ray diffraction, Rutherford backscattering spectroscopy, and scanning transmission electron microscopy. Ferroelectric hysteresis loops obtained by patterning circular capacitors with areas of 4.92 × 10−4 cm2 indicate a Pmax = 48 μC/cm2, 2Pr = 60 μC/cm2, Ec1 = −73 kV/cm, Ec2 = 125 kV/cm, and a leakage current density of 15 μA/cm2 at 138 kV/cm. Capacitance versus voltage measurements were used to obtain a maximum dielectric constant of 290 at 85 kV/cm and loss tangent under 4% tested in the range of ±275 kV/cm. ALD PbTiO3 grown with near-ideal cation ratios crystallized into randomly oriented perovskite grains when grown on a sputtered Pt-coated Si substrate. A variation of rapid thermal anneal temperatures, ramp rates, and nucleation layers was investigated and did not have a significant effect on perovskite grain orientation.

Calculation of the thickness and optical constants of lead titanate thin films grown on MgO from their transmission spectra

Calculation of the thickness and optical constants of lead titanate thin films grown on MgO from their transmission spectra

Thickness‐dependent domain wall reorientation in 70/30 lead magnesium niobate‐ lead titanate thin films

AbstractContinued reduction in length scales associated with many ferroelectric film‐based technologies is contingent on retaining the functional properties as the film thickness is reduced. Epitaxial and polycrystalline lead magnesium niobate‐lead titanate (70PMN‐30PT) thin films were studied over the thickness range of 100‐350 nm for the relative contributions to property thickness dependence from interfacial and grain‐boundary low permittivity layers. Epitaxial PMN‐PT films were grown on SrRuO3/(001)SrTiO3, while polycrystalline films with {001}‐Lotgering factors >0.96 were grown on Pt/TiO2/SiO2/Si substrates via chemical solution deposition. Both film types exhibited similar relative permittivities of ~300 at high fields at all measured thicknesses with highly crystalline electrode/dielectric interfaces. These results, with the DC‐biased and temperature‐dependent dielectric characterization, suggest irreversible domain wall mobility is the major contributor to the overall dielectric response and its thickness dependence. In epitaxial films, the irreversible Rayleigh coefficients reduced 85% upon decreasing thickness from 350 to 100 nm. The temperature at which a peak in the relative permittivity is observed was the only measured small signal quantity which was more thickness‐dependent in polycrystalline than epitaxial films. This is attributed to the relaxor nature present in the films, potentially stabilized by defect concentrations, and/or chemical inhomogeneity. Finally, the effective interfacial layers are found to contribute to the measured thickness dependence in the longitudinal piezoelectric coefficient.

Declamped Piezoelectric Coefficients in Patterned 70/30 Lead Magnesium Niobate–Lead Titanate Thin Films

Lateral subdivision of blanket piezoelectric thin films increases the functional properties through both increased domain wall mobility and declamping of the intrinsic response. This work presents the local effects of substrate declamping on the piezoelectric coefficient d33,f of 300 nm thick, rhombohedral, {001}‐oriented lead magnesium niobate–lead titanate thin films at the 70/30 composition (70PMN–30PT). Films grown by chemical solution deposition on platinized Si substrates are patterned into strip structures ranging from 0.75 to 9 µm in width. The longitudinal piezoelectric coefficient, d33,f, is interrogated as a function of position across the patterned structures by three approaches: finite element modeling, piezoresponse force microscopy, and nanoprobe synchrotron X‐ray diffraction. It is found that d33,f increases from the clamped value of 40–50 to ≈160 pm V−1 at the free sidewall under 200 kV cm−1 excitation. The sidewalls partially declamp the piezoelectric response 500–600 nm into the patterned structure, raising the piezoelectric response at the center of features with lateral dimensions less than 1 µm (3:1 width to thickness aspect ratio). The normalized data from all three methods are in excellent agreement, with quantitative differences providing insight to the field dependence of the piezoelectric coefficient and its declamping behavior.

Block Copolymer-Assisted Nanopatterning of Porous Lead Titanate Thin Films for Advanced Electronics

Chemical self-assembly of functional ferroelectric PbTiO3 using amphiphilic block copolymers is used to prepare low-cost nanopatterned porous thin films with nanostructure control down to ∼22 nm of lateral size. The approach developed in this work is highly effective in patterning PbTiO3 and avoids costly high-resolution lithography techniques and harmful etching processes. Nanopatterned films presenting a honeycomb-like arrangement of pores with diameters between 80 and 140 nm are obtained. The ordering and thickness of the films are discussed as a function of the precursors concentration and withdrawal rate used for films dip-coating. The nanopatterned porous films with thickness of 22 nm exhibit tetragonal perovskite crystallographic phase and ferroelectric response at the nanoscale. These films display vertical open porosity from the film surface to the substrate, leading to nearly 50% of the substrate surface being accessible to further functionalization toward low-cost, sustainable, multifunctional ...

Management of Lead Content for Growth of {001}‐Oriented Lead Magnesium Niobate‐Lead Titanate Thin Films

A scalable growth process for domain engineered {001}‐oriented lead magnesium niobate—lead titanate (PMN‐PT) thin films with Lotgering factors of 0.98–1.0, without an orienting perovskite seed layer, is presented. Deposition of a 2–3‐nm‐thick PbO buffer layer on {111} Pt thin film bottom electrodes, prior to chemical solution deposition of PMN‐PT reduces the driving force for Pb diffusion from the PMN‐PT to the bottom electrode, and facilitates nucleation of {001}‐oriented perovskite grains. Energy dispersive spectroscopy demonstrated that up to 10% of the Pb from a PMN‐PT precursor solution may diffuse into the bottom electrode. PMN‐PT grains with a mixed {101}/{111} orientation in a matrix of Pb‐deficient pyrochlore phase were then promoted near the interface. When this is prevented, phase‐pure films with {001} orientation can be achieved.

In situ deposition of PbTiO3 thin films by direct current reactive magnetron sputtering

The lead titanate thin films were deposited using in situ layer-by-layer reactive magnetron sputtering. The synthesis of films was performed on platinized silicon (Pt/Ti/SiO2/Si) substrates at 450–600°C temperatures using Ti2O seed layer. The influence of the substrate temperature on the surface morphology, phase composition, and electrical properties of PbTiO3 films were investigated. Experimental results demonstrated that the deposition at higher substrate temperatures resulted in the formation of films with the lower surface roughness values. The increase of the substrate temperature has no effect on the tetragonality value of the films. The preferential orientation in the films was changed and the crystallites size slightly increased with the increased substrate temperature from 450°C to 550°C. Hysteresis measurements show that the films exhibit ferroelectric properties with a maximum coercive field of Ec=150kV/cm and of Pr=60μC/cm2. Coercive field dependence on the frequency measurements indicated that the creep regime of domain wall motions dominated till 1kHz of frequency.

Sol–gel synthesis and characterization of lead titanate films

Lead titanate thin films have been deposited by spin coating on stainless steel substrate using the precursor sol, which was synthesized from acetylacetone chelating with titanium isopropoxide and ethylene glycol as a solvent, in the sol–gel process. The influence of film thickness, pyrolysis temperature, and heating rate on (the formation of thin films) microstructure and morphology of thin films have been systematically investigated. The phase purity, particle size, and morphology are studied using X-ray diffraction and scanning electron microscopy (SEM) measurements. It is observed that the preferred oriented thin films could be obtained by pyrolysis of wet films at 150°C and annealed at 600°C at a slow heating rate of 4°C/min. It is also confirmed from X-ray patterns that the tetragonal perovskite structure of the titanate exists without any impurity peaks in the films formed. The TGA/DSC curves of the PT precursor show weight loss of ~7% and two exotherms at 492 and 522°C. They are attributed to the crystallization of tetragonal PbTiO3. SEM shows that the PbTiO3 thin films annealed at 600°C for 1 h crystallized well. The FTIR analysis showed the characteristic absorption bands of Pb–O groups at 663 cm−1 and Ti–oxo groups at 600 cm−1.

Formation of PbTiO3 thin films on seed layers using DC magnetron layer-by-layer deposition

Lead titanate thin films were produced without and with seed layers on platinized silicon substrates by reactive DC magnetron layer-by-layer sputter-deposition on high (350–700 °C) temperature substrates. To achieve perovskite PbTiO3 phase the films after deposition were annealed in an oxygen atmosphere (1.33 Pa) at 600 °C temperature. The surface morphological, structural and ferroelectric properties of the lead titanate thin films were studied by x-ray diffraction, scanning electron microscopy, optical microscopy and polarization–electric field (P-E) measurements. The results show that Ti (5 nm) and Ti/TiO2 (5 nm) seed layers change the nucleation density and therefore change the morphology, crystal structure, adhesion and ferroelectric properties. The best results were obtained using Ti/TiO2 seed layers. These seed layers increase the density of nucleation centers of growing thin films and therefore increase the density of grains, decrease crystal sizes and increase tetragonality up to 1.057 and remnant polarization up to 25 μC/cm2.

Dielectric and I-V Characteristic of Lead Titanate Thin Films Prepared on ITO Glass Substrate

Performance of lead titanate, (PbTiO3) thin films have been successfully investigated on microstructural properties, I-V characteristic, dielectric properties, and ferroelectric properties. PbTiO3offers variety of application as transducer, ferroelectric random access memory, transistor, high performance capacitor, sensor, and many more due to its ferroelectric behavior. Preparation of the films are often discussed in order to improve the structural properties, like existence of grain boundaries, particle uniformity, presents of microcrack films, porosities, and many more. Yet, researchers still prepare PbTiO3thin films at high crystallization temperature, certainly above than 600 ̊C to obtain single crystal perovskite structure that would be the reason to gain high spontaneous polarization behavior. Although this will results to high dielectric constant value, the chances that leads to high leakage current is a major failure in device performance. Thus, preparation the thin films at low annealing temperature quite an essential study which is more preferable deposited on low-cost soda lime glass. The study focuses on low annealing temperature of PbTiO3thin films through sol-gel spin coating method and undergo for dielectric and I-V measurements.

Surface Morphological Study of Lead Titanate Thin Films Prepared on ITO Glass Substrate

The most important thing in preparing thin films ceramic material such lead titanate, PbTiO3 is the behavioral of microstructural changes due to the applying heat treatment during crystallization process. In general, the imperfection of PbTiO3 surface morphology such as porosity, grain boundaries, existence of microcrack films, films out-diffusion and others are caused by this factor, heat transfer element and found very interesting to be discussed towards next electrical characterization. However, the present study only focuses on the surface morphology of PbTiO3 thin films that observed by both field emissions scanning electron microscopy (FESEM) and atomic force microscopy (AFM). The details of measurement for observation will be explained later. The preparation of PbTiO3 thin films were done trough simple sol-gel spin coating method deposited on ITO coated glass substrate.

Inhomogeneity of phase transition in lead titanate thin films formed by magnetron layer-by-layer deposition

The formation of deposited ferroelectric perovskite PbTiO3 thin films using layer-by-layer reactive magnetron sputtering was investigated in this work. Deposition rates of each layer (PbO and TiO2) for 7.2 and 9.2 nm/min, respectively, were chosen there. Silicon (110) substrate with the heater was moved periodically and parallel to the magnetron cathodes during deposition. The heater temperature (380 °C–700 °C) has influence on the stoichiometry of thin films. Perovskite phase of lead titanate was not obtained without post annealing. The reasons for this are discussed in the work. The results of the structure of thin layers deposited on silicon substrates at 380 °C and annealed for one hour at 700 °C in air have shown that a pure perovskite phase of PbTiO3 is formed there.

Modified lead titanate thin films for pyroelectric infrared detectors on gold electrodes

Pyroelectric infrared detectors provide the advantage of both a wide spectral response and dynamic range, which also has enabled systems to be developed with reduced size, weight and power consumption. This paper demonstrates the deposition of lead zirconium titanate (PZT) and lead calcium titanate (PCT) thin films for uncooled pyroelectric detectors with the utilization of gold electrodes. The modified lead titanate thin films were deposited by pulsed laser deposition on gold electrodes. The PZT and PCT thins films deposited and annealed at temperatures of 650°C and 550°C respectively demonstrated the best pyroelectric performance in this work. The thin films displayed a pyroelectric effect that increased with temperature. Poling of the thin films was carried out for a fixed time periods and fixed dc bias voltages at elevated temperature in order to increase the pyroelectric coefficient by establishing a spontaneous polarization of the thin films. Poling caused the pyroelectric current to increase one order of magnitude.