Modified Lead Titanate Thin Films Research Articles

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.

High pyroelectric coefficient modified lead titanate thin films deposition using gold electrode

Reported is the deposition and characterisation of lead zirconium titanate (PbZr0.4Ti0.6O3) (PZT) and lead calcium titanate (Pb0.7Ca0.3Ti03) (PCT) deposited on a gold electrode with a gold top electrode to form a capacitor structure. Pulsed laser deposition was utilised to deposit the thin films. The thin films were characterised for their dielectric constant and loss tangent variation with temperature as well as the pyroelectric coefficient. The thin films were poled to improve the pyroelectric effect. The highest pyroelectric coefficient was found to be 280 µC/m2 K for PZT film and 400 µC/m2 K for the PCT film after poling.

Effect of annealing temperature on microstructure of chemically deposited calcium modified lead titanate thin films

Thin ferroelectric films of calcium modified lead titanate Pb1−xCaxTiO3(PCT) have been prepared by chemical deposition process. The as deposited amorphous films were thermally treated for crystallization and formation of perovskite structure. Characterization of these films by X-ray diffraction (XRD) have been carried out for various amounts of calcium (Ca)-doping (0.20, 0.24, and 0.28) on indium tin oxide (ITO) coated corning glass substrates. For a better understanding of the crystallization mechanism, the investigations were carried out at various annealing temperatures (450, 550, and 650 °C). Characterization of these films by XRD shows that the films exhibit tetragonal phase with perovskite structure. Atomic force microscope images (AFM) are characterized by slight surface roughness with a uniform crack-free, densely-packed structure. Also, Fourier transform infrared spectra (FT-IR) of the as deposited film and annealed thin films (x=0.24) at 650 °C on silicon (Si) substrates were taken to get more information about the film formation. Dielectric studies of the films were carried out and reported.

Effect of annealing temperature on microstructure of chemically deposited calcium modified lead titanate thin films

Thin ferroelectric films of calcium modified lead titanate Pb 1− x Ca x TiO 3(PCT) have been prepared by chemical deposition process. The as deposited amorphous films were thermally treated for crystallization and formation of perovskite structure. Characterization of these films by X-ray diffraction (XRD) have been carried out for various amounts of calcium (Ca)-doping (0.20, 0.24, and 0.28) on indium tin oxide (ITO) coated corning glass substrates. For a better understanding of the crystallization mechanism, the investigations were carried out at various annealing temperatures (450, 550, and 650 °C). Characterization of these films by XRD shows that the films exhibit tetragonal phase with perovskite structure. Atomic force microscope images (AFM) are characterized by slight surface roughness with a uniform crack-free, densely-packed structure. Also, Fourier transform infrared spectra (FT-IR) of the as deposited film and annealed thin films ( x=0.24) at 650 °C on silicon (Si) substrates were taken to get more information about the film formation. Dielectric studies of the films were carried out and reported.

Structural, Dielectric and Pyroelectric properties of Lanthanum modified Lead Titanate Thin Films

ABSTRACTFerroelectric lead lanthanum titanate (Pb1−xLaxTi1−x/4O3) (PLTx) thin films (x=0.04,0.08 and 0.12) have been prepared by sol-gel spin coating process on ITO coated 7059 Corning glass substrates. Investigations have been made on the crystal structure, surface morphology, dielectric and ferroelectric properties of the thin films. For a better understanding of the crystallization mechanism, the structural investigations were carried out at various annealing temperatures (350°C, 450°C, 550°C and 650°C). Characterization of these films by X-ray diffraction shows that the films annealed at 650°C exhibit tetragonal structure with perovskite phase. Replacement of lanthanum in lead titanate results in reduction of tetragonal ratio (c/a), resulting in better mechanical stability. Microstructural analysis of the films are carried out by taking the Atomic Force Microscope (AFM) pictures. AFM images are characterized by slight surface roughness with a uniform crack free, densely packed structure. Dielectric, pyroelectric and ferroelectric studies carried out on these films have been reported. Dielectric constant and pyroelectric coefficient increase while Curie temperature decreases with increase in La content. The pyroelectric figures of merit of the films have also been calculated which suggest that 8% lanthanum is best suited material for pyroelectric detectors owing to its high pyroelectric coefficient (∼ 29nC/cm2 K), high voltage responsivity (∼420Vcm2/J), high detectivity (∼1.04×10−5Pa−1/2) and low variation of pyrocoefficient with temperature.

Texture Development in Modified Lead Titanate Thin Films Obtained by Chemical Solution Deposition on Silicon‐Based Substrates

An advanced method of X‐ray diffractometry analysis, the quantitative texture analysis, is used in this work to study the preferential orientations of ferroelectric lanthanum‐modified lead titanate thin films, to establish the factors affecting their development. The new, more reliable, texture data obtained allows us to discuss previous models of texture development in chemical‐solution‐deposited films. The results show that a fiber type, mixed <100>,<001> preferential orientation, is obtained when high heating rates are used during crystallization. The degree of texture of these films decreases when successive layers are deposited before a simultaneous crystallization of the ensemble is conducted. This undesirable effect is avoided through layer‐by‐layer crystallization, because of the preferential nucleation of <100>,<001> crystals at the interface between layers. The use of a titanium layer on the platinized silicon‐based substrate leads to the development of an additional fiber <111> texture component. In this case, the layer‐by‐layer crystallization process cannot avoid the loss of the degree of orientation (texture index) with the increase of film thickness. This is mainly caused by the appearance of interlayer porosity, which disrupts the growth of <111>‐oriented grains into upper layers.

Tailoring of the Elastic Properties by Texture Control in Ferroelectric Thin Films for MEMS

The use of piezoelectric thin films in advanced devices such as microelectromechanical systems (MEMS), not only rests on high piezoelectric coefficients, as the ones achieved in some ferroelectric lead titanate derived compositions, but also on their mechanical properties. This makes the study of the correlation between texture and elastic properties of high interest for the processing of piezoelectric thin films with tailored properties, regardless of which, not much related work has been reported up to now. In this paper we present the analysis of the variations observed in the elastic tensor of a series of modified lead titanate thin films with different orientations. The different textures were induced either by deposition on modified substrates or by changes of the annealing scheme. Orientation distribution functions (ODF) for all films were obtained by an advanced texture quantitative analysis of x-ray diffraction data of several pole figures. From the ODF and the single crystal tensor, we are able to calculate the effective elastic properties of the films by a geometric averaging procedure. This is a promising result in the tailoring of the mechanical properties of these piezoelectric thin films for applications.

Preferential orientation of ferroelectric calcium modified lead titanate thin films grown on various substrates

La aparicion de orientaciones preferentes o textura en laminas delgadas policristalinas se puede potenciar de muchas maneras, pero probablemente el factor mas importante a tener en cuenta es la naturaleza del substrato. Si se logra una orientacion preferente de los cristales de la lamina con el eje polar perpendicular al plano de la lamina el comportamiento ferroelectrico del material mejora. Englobado en la busqueda del substrato mas adecuado para obtener laminas delgadas ferroelectricas orientadas, este trabajo estudia por medio de analisis cuantitativo de texturas laminas delgadas de titanato de plomo modificado con calcio depositadas sobre substratos de Si, MgO y SrTiO3 con electrodos de Pt. Se obtiene una orientacion preferente mixta a lo largo de y . A partir de los datos obtenidos se analizan los factores que contribuyen a las diferentes texturas obtenidas. Por un lado se discute el diferente grado de texturacion del Pt sobre los tres substratos, y la formacion de la lamina ferroelectrica sobre ellos, cuya orientacion parece desarrollarse independientemente del Pt en este caso. Y por otro, se estudia el efecto de las tensiones presentes durante el proceso de cristalizacion provocadas por las diferencias entre los coeficientes de expansion de cada uno de los substratos y la lamina, especialmente en el paso de la fase paraelectrica cubica a ferroelectrica tetragonal,

Effect of the substrate heterostructure on the texture of lanthanum modified lead titanate thin films

Abstract Modified lead titanate thin films with a nominal composition of Pb 0.88 La 0.08 TiO 3 (PTL) have been prepared by chemical solution deposition (CSD) onto annealed Ti/Pt/Ti/(100)Si and Pt/TiO 2 /(100)Si. Composition and heterostructure of the PTL films on the two substrates have been studied by Rutherford backscattering spectroscopy (RBS). Composition of the PTL films on the two substrates is similar and close to the nominal one. However, the Ti/Pt/Ti/(100)Si and Pt/TiO 2 /(100)Si substrates induces different textures in the PTL films. The films on Ti/Pt/Ti/(100)Si developed a preferred orientation, whereas the films on Pt/TiO 2 /(100)Si have a mixed preferred orientation.

Quantitative analysis of preferential orientation components of ferroelectric thin films

A quantitative study of the preferred orientation of lanthanum and calcium modified lead titanate thin films, including the measurement of pole figures and calculation of orientation distribution function (OD), is presented. The main preferential orientation components are identified as <001> and <100> perpendicular to the film surface. Variations of the texture strength and the contribution of these components to the final texture are observed with changes in the film thickness or the substrate used. These variations are correlated to the ferroelectric properties of these films. This information can be used to optimise the preparation process to obtain improved thin films for pyroelectric and piezoelectric applications.

Effect of processing parameters and substrate on the preferred orientation of Sol-Gel calcium modified lead titanate thin films

In this work the characteristics of the texture of sol-gel Pb 0.76 Ca 0.24 TiO 3 deposited onto three different substrates : Pt/Ti/SiO 2 /Si, Ti/Pt/Ti/SiO 2 /Si y Pt/TiO 2 /SiO 2 /Si, are studied. The films were prepared by spin-coaling the precursor solution, with a low concentration, onlo the substrates and by further drying at 350°C and crystallisation at 650°C, with a heating rate of ∼30.4s°C/s. Each of the deposited layers had a thickness of ∼75 nm. Four successive layers were deposited to obtain a tilm thiesness of ∼ 300 nm. Texture of the Pb 0.76 Ca 0.24 TiO 3 films on the different substrates was studied by means of X-ray diffraction. The crystalline phases present at the substrates surfaces were identify by means of grazing incidence X-ray diffraction. The Pb 0.76 Ca 0.24 TiO 3 film on the Ti/Pt/Ti/SiO 3 /Si substrate developed a preferred orientation. A spontaneous pyroelectric coefficient of γ∼-6.49×10 -9 Ccm -2 K -1 was measured in this sample.

In Situ Deposition of Highly C-axis Oriented Lanthanum Modified Lead Titanate Thin Films by Multi-Ion-Beam Reactive Co-sputtering Technique

Highly c-axis oriented La-modified PbTiO 3 (PLT) thin films were in situ grown on Pt(100)/MgO(100) and MgO(100) substrates by multi-ion-beam reactive co-sputtering (MIBRECS) technique at the substrate temperature range of 450°C-540°C. The orientation degree α of the films is more than 90%. The chemical composition is in good agreement with the designed one and is almost uniform across the surface of the substrates. The remanent polarization (P r ) and coercive field (E c ) were found to be 5.3 μC/cm 2 and 78 kV/cm, respectively.

In Situ Deposition of Highly C-axis Oriented Lanthanum Modified Lead Titanate Thin Films by Multi-Ion-Beam Reactive Co-sputtering Technique

In Situ Deposition of Highly C-axis Oriented Lanthanum Modified Lead Titanate Thin Films by Multi-Ion-Beam Reactive Co-sputtering Technique

Microstructure-ferroelectric properties relationships in sol–gel prepared lanthanum modified lead titanate thin films

Transmission electron microscopy is used to investigate the effect of the excess of PbO and the temperature of crystallization on the grain size of sol–gel lanthanum modified lead titanate thin films. Grain size is found to increase from ∼100 nm to ∼1 μm when the excess of PbO in the precursor solution is reduced from 20 to 10 mol%, but it is not significantly affected by raising the temperature from 650 to 700°C. Films ferroelectric characterization shows that the switchable polarization is higher in the films with a smaller grain size. This effect is explained by taking into account the presence of a tensile stress at the film–substrate interface, which clamps 90° domain walls. This stress is higher in coarse grained films, most of whose grains are in contact with the substrate, than in the fine grained films. Therefore, 90° domain wall movement is easier in fine grained films.

The effect of film thickness on the ferroelectric properties of sol–gel prepared lanthanum modified lead titanate thin films

Lanthanum modified lead titanate (PTL) thin films with a thickness ranging between 100 and 650 nm have been prepared by a sol–gel method. Hysteresis loops have been measured in two sets of films: thermally crystallized with 10°C min −1 and more than 500°C min −1. A thickness dependence of the ferroelectric parameters has been found in both sets. This dependence is related to the presence of a modified layer near the bottom electrode, with a different origin in the two sets of films. In those treated with 10°C min −1, the layer is a Ti deficient one, most probably with the perovskite structure but La deficient. In those treated with more than 500°C min −1, it is a layer that bears the ferroelectric-substrate interfacial stress.

Structural and optical properties of (Pb,Ca)TiO3 thin films prepared by a sol-gel technique

Transparent and crack-free calcium modified lead titanate thin films were prepared on platinum-coated silicon and fused quartz substrates by a sol-gel technique. Lead acetate trihydrate, calcium nitrate tetrahydrate and titanium tetra-n-butoxide were used as starting materials. Methanol and ethanolamine were used as solvent and stabilizing agent, respectively. The structural properties of the thin films were studied by x-ray diffraction technique. Optical transmission and absorption properties of the thin films were measured in the wavelength range of 200-1100 nm. The thin films possess good optical transmissitivity. By using an approximate formula, the refractive index and band gap were evaluated. The optical transitions of the thin films are direct in nature. The dispersion relation of refractive index and wavelength follows the single electron oscillation model.

Calcium modified lead titanate thin films for electromechanical applications

Electromechanical properties of Pb 1-x Ca x TiO 3 (PCT) thin films prepared by sol-gel technique are investigated as a function of Ca content. Crystallization of a perovskite phase is observed for the films subjected to the rapid thermal anneal at 650 °C. A small amount of pyrochlore phase is found for low Ca concentration (x=0.08). Tetragonality of the films is gradually decreased with Ca addition in qualitative agreement with bulk ceramics data. Piezoelectric coefficient, d 33 , measured by optical interferometry initially increases with Ca content reaching a maximum at x=0.24. At this concentration, d 33 of 70 pm/V is observed which matches well the value for bulk PCT ceramics. The strain developed at 400 kV/cm is progressively decreased with Ca reflecting a decrease in tetragonality of the films. The observed difference in piezoelectric coefficients of PCT films and bulk ceramics is qualitatively explained by the clamping effect of the substrate and by depoling of the films due to the influence of depolarizing field.

Conditioning effects on RTP (Pb,Ca)TiO 3 thin films

Calcium modified lead titanate thin films have been spin-coated on Pt/TiO 2/SiO 2/(100)Si substrates from sol-gel synthesized solutions containing a 10 mol% excess of PbO. Amorphous layers have been crystallized by a rapid thermal treatment at 650°C for 50 s, using a heating rate of ∼30°C/s. Further thermal conditioning treatments were applied to the films, to study their effects on the ferroelectric response, by means of measurements of hysteresis loops, switching current curves, pyroelectricity, permittivity and leakage current densities. The origin of the leakages in these films is related with the nature of the electrode-ferroelectric interfaces. A mechanism based on the redistribution of charged defects after the thermal conditioning treatments is suggested. These treatments influence the trapping level and lead to the control of pinning of ferroelectric domains. This causes a direct effect on the switching process.

Solution processing and crystallization of ferroelectric samarium modified lead titanate thin films

Samarium-doped lead titanate thin films have been prepared by a sol–gel technique. The processing of precursor solutions through two different synthetic routes and containing differing excesses of PbO is described. The films deposited from these solutions are crystallized by thermal treatments at temperatures higher than 550 °C. The crystalline structure, composition and microstructure of the resulting films are studied by grazing incidence X-ray diffraction analysis, energy dispersive spectroscopy, quantitative scanning electron microscopy and transmission electron microscopy. It is observed that the film microstructure and the development of non-ferroelectric phases in these films are influenced by both the solution chemistry and the lead oxide stoichiometry. Preliminary results concerning the ferroelectric behaviour of these films are also given.

Study by Rutherford Backscattering Spectroscopy of the Heterostructure of Lead Titanate Thin Films

A depth profile analysis of modified lead titanate thin films was performed by means of Rutherford Backscattering Spectroscopy (RBS). These films were deposited from sol-gel synthesized solutions onto platinized silicon substrates and crystallized by thermal treatments at temperatures of about 650°C. The chemistry of the solution and the thermal treatment for crystallization affect the heterostructure of the resulting films. Losses of lead and formation of substrate-film interfaces are produced during the crystallization of the films. These film characteristics determine their ferroelectric response.