Lead Titanate Thin Films Research Articles

Preparation of thicker PbTiO3 thin film by a metallo- organic solution deposition process

Using a metallo-organic solution deposition (MOSD) process, the thicker lead titanate thin films were prepared on platinum-coated silicon substrates. The working solution was synthesized by heating lead acetate and titanium butoxide in a solvent. Then a polymer was mixed into the solution. The thickness of crackfree single PbTiO3 layer is approximately 0.25um. This value is almost three times larger than that of the film prepared by conventional metallo-organic deposition (MOD) methods. The effects of polymer on solution properties and film structures were investigated.

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.

Pyroelectricity of spontaneously poled La-modified lead titanate thin films on silicon based substrates

Multiple deposition by spin-coating and RTP crystallisation have been used to obtain La-modified lead titanate thin films of composition Pb 0.88 La 0.08 TiO 3 (PTL) onto two types of substrates : Ti/Pt/Ti/(100)Si annealed at 650°C and Pt/TiO 2 /(100)Si. The films on Ti/Pt/Ti/(100)Si present a main preferred crystallographic orientation, whereas the films on Pt/TiO 2 /(100)Si present a mixed / preferred orientation. All the films developed a net polarisation in the direction perpendicular to the film plane and a spontaneous pyroelectric coefficient. The hysteresis and switching characteristics of the films were dependent on the type of substrate. Results as a function of the number of deposited layers are presented. Poling was carried out under different electrical signals at 150°C. The highest pyroelectric coefficient achieved at room temperature was γ ∼40×10 -9 C cm -2 K -1 .

Effect of bottom electrodes on the structural and electrical characteristics of lanthanum doped lead titanate thin films

Ferroelectric Pb0.90La0.15TiO3 (PLT15) thin films were deposited by sol-gel method on Pt, Pt/Si, ruthenium oxide (RuO2)/Si and RuO2/Pt/Si bottom electrodes. X-ray diffraction, and micro-Raman spectroscopy techniques were used for structural characterization of these films. PLT15 films deposited on RuO2 electrodes show (100) preferred orientation of growth and result in larger crystallites. Films on Pt electrode exhibited higher dielectric constant (1300 at 100 kHz) and high values of Pm, Pr values, 68 and 46 μC/cm2 respectively. AC field dependence of dielectric permittivity at sub-switching fields was fitted using the Rayleigh law. The reversible polarization components estimated from the CV and quasi-static hysteresis measurements for films on Pt/Si (24%), was larger than that of Pt (11%) bottom electrodes. The observed results were correlated with the domain wall pinning at the disturbed film-electrode interface.

Thickness dependence of stress in lead titanate thin films deposited on Pt-coated Si

Thickness dependence of the soft mode E(1TO) of tetraganol lead titanate thin film, deposited on Pt-coated Si by a chemical solution deposition, was determined with Raman scattering measurements. A downshift of the soft mode was attributed to the residual stress in the thin film, which was estimated in the range of 1.3–2.6 GPa, corresponding to film thickness of 400–50 nm. The variation of the clamped dielectric constants determined by observed mode frequencies was found to agree with the prediction of stress dependence of dielectric constants by Devonshire theory.

Raman Studies of the Effects of Nb Dopant on the Ferroelectric Properties in Lead Titanate Thin Film

Raman spectroscopy was used to study the effects of Nb additives in ferroelectric lead titanate thin films. Raman spectra were measured from lead titanate thin films with Nb concentrations between 0 and 5%. The Nb additive was found to significantly influence the profile of the A1(2TO) mode, which is the relative vibration between the Ti atom and other atoms along the c-axis, indicating that the doped Nb occupied a Ti position. A decrease of all transverse modes followed the increase in Nb. The observed mode frequencies were used to extract the dependence on Nb addition of the clamped dielectric constants. The dielectric constants along both the a- and c-axes increase with increasing Nb concentration.

Pyroelectric Properties of Sol–Gel Derived (Pb,Ca)TiO3 Thin Film Detectors

Calcium-modified lead titanate (PCT) thin film pyroelectric infrared (IR) detectors were fabricated on Pt(111)/SiO2/Si(100) substrates using a diol-based sol–gel process. The randomly oriented PCT thin film, which has not undergone the poling treatment, exhibits a relatively small dielectric constant and a large pyroelectric coefficient. The pyroelectric properties of PCT thin film point detectors with various Ca contents on modulation frequency are measured and compared. The optimized composition of PCT thin film IR detectors was found to be the PCT(25), which exhibits a large voltage responsivity of 4533 (V/W) at 20 Hz and a specific detectivity (D*) of 6.45×107 cmHz1/2/W at 100 Hz. The results show that Pb1-xCaxTiO3 thin film with x = 0.25 [PCT(25)] was most suitable for application to the pyroelectric thin film IR detector.

Characterization of Calcium-Modified Lead Titanate Thin Films Derived from a Diol-Based Sol–Gel Process

Polycrystalline thin films of Ca-modified lead titanate (PCT) were deposited on Pt/SiO2/Si substrates using a diol-based sol–gel process. Calcium acetylacetonate hydrate was adopted as a starting material instead of the calcium acetate or calcium nitrate tetrahydrate used conventionally. By changing the Ca content (5–35 mol%) and heating temperature (500–800°C), the influences of various processing parameters on the characteristics of thin films were studied. With the increase of the Ca content, the relative dielectric constant (εr) of PCT thin film increased from 43 to 70 at the heating temperature of 700°C. It was found that the coercive field (Ec) and the remanent polarization (Pr) decreased, but the pyroelectric coefficient (γ) increased with an increase of Ca content. The results reveal that PCT thin film with a Ca content of 25 mol% exhibits the largest figures of merit for the voltage responsivity and the specific detectivity at a heating temperature of 700°C.

Study of electrolytic laminated ferroelectric thin films from electroded substrates

An electrolytic process is described to peel off ferroelectric thin films from electroded substrates. This procedure was used to study the evolution of stress in ferroelectric calcium-modified lead titanate thin films. Stresses developed during the different steps of the preparation of the film on the substrate were calculated from curvature radii of the deposited films after each step. During the film preparation, the substrate was permanently deformed by the generated stresses. This was shown by curvature of the substrate after the electrolytic separation of the film. The laminated film liberated a large amount of stresses, as deduced from the lattice parameters of the deposited and laminated film, obtained by x-ray diffraction. The moderate residual stress that the laminated film maintained could be associated with intrinsic defects of the film.

Preparation and properties of lead titanate thin ferroelectric films

A new technique is proposed for preparing lead titanate ferroelectric films. The technique involves a solid-phase reaction in an oxygen environment between titanium and lead layers deposited on a substrate. The thicknesses of the component films being deposited are chosen based on the stoichiometric ratio in the compound to be synthesized. The composition and structure of the film obtained are checked by x-ray phase analysis. The films exhibit a dielectric hysteresis loop and a temperature dependence of the permittivity characteristic of ferroelectrics. A study has been made of the temperature and thickness dependences of the film coercive field. They also are shown to follow a pattern typical of ferroelectrics.

Optical functions of Ca-modified PbTiO 3 thin films determined by spectroscopic ellipsometry

Calcium-modified lead titanate thin films deposited on Si(100) substrate have been prepared by sol–gel processing. The structural properties of the thin films have been studied by X-ray diffraction. The ellipsometric spectra of the Pb 1− x Ca x TiO 3 ( x=0.0–0.4) films have been obtained in the spectral range of 2.2–5.0 eV, and their optical constants (the refractive index n and the extinction coefficient k) determined. The results show that after doping Ca, the refractive indexes of the Pb 1− x Ca x TiO 3 films increase, the maximum value of refractive indexes and the absorption edges shift to lower energy.

Structural and optical characterization of PLT thin films prepared by a sol-gel process

Lanthanum-modified lead titanate (PLT) thin films were deposited on fused-quartz substrates using a sol-gel process. The crystallization behaviour and structural changes were studied as a function of the annealing temperature by differential thermal analysis, thermogravimetry, infrared spectroscopy, and X-ray diffraction. The surface morphology of the films was characterized in a scanning electron microscope. The absorption edge was found to shift to longer wavelength with increasing crystallite size.

Short range structural disorder in lanthanum doped lead titanate thin films

Spin coated Pb1−xLaxTi1−x/4Q3 thin films (x ' 0.00, 0.05.…0.30) on (0001) sapphire were studied using x-ray diffraction, atomic force microscopy, and Raman scattering in order to investigate the phase formation, surface morphology, and the phase transition behavior in them. The x-ray and Raman scattering reveal a decrease in tetragonality with La substitution in lead titanate. Microscopy estimated surface roughness was also found to be decreasing with the La doping. Raman scattering, in the temperature range 75–783K, shows the transition temperature about 730, 680, 614, and 563 K for x'0.05, 0.10, 0.15, and 0.20 compositions, respectively. The diffuse nature of the ferroelectric phase transition owing to a short-range structural disorder in the paraelectric cubic phase and an increase in the diffuseness with La doping indicates the relaxor behavior and its relationship with the local disorder in these materials.

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.

Silicate formation at the interface of a calcium-modified lead titanate thin film deposited on Si(100)

A calcium-modified lead titanate (Pb0.76Ca0.24TiO3) thin film has been prepared by spin-on sol–gel on an Si(100) substrate. The film deposited from a stoichiometric solution was subjected to thermal treatment at 650 °C for 720 s with a heating rate of 8 °C s−1. The film presents a perovskite-type structure, as indicated from x-ray diffraction powder pattern data, giving it ferroelectrical properties. The chemical composition at the film surface and at increasing depth into the substrate was studied by XPS combined with 4 keV Ar+ depth profiling. Ion bombardment gives rise to compositional and chemical changes in the sample surface, in which case lead and oxygen are sputtered preferentially. After 50 min of 4 keV Ar+ bombardment, a steady-state composition is reached. At further depth (>200 min) an increase of the Pb 4f signal indicates a non-homogeneous Pb distribution in the film. At the interface between the ferroelectric film and the Si(100) substrate, silicon is found as Si(IV), as well as chemical shifts of the O 1s and Ca 2p3/2 peaks to higher binding energies are observed. Both facts support the formation of calcium silicate. At the same time, titanium is reduced from Ti(IV), Ti(III) and Ti(II) to Ti(0). Copyright © 2000 John Wiley & Sons, Ltd.

Effect of UV-Irradiation on Processing of Lead Titanate Thin Film Derived from Photoreactive [Pb-Ti] Precursor Modified with Alkanolamine.

A photoreactive [Pb-Ti] precursor was successfully synthesized by chemical modification of metallo-organics with alkanolamine. The synthesized precursor showed strong absorption at wavelengths shorter than 350nm, being effective for the absorption of ultra-violet light. Photolithographic patterning of [Pb-Ti] precursor film on MgO (100) substrate could be prepared by UV-irradiation. The patterned precursor film yielded highly oriented lead titanate (PbTiO3) of perovskite single phase by rapid heating at 550°C. PbTiO3 films with a thickness of about 100nm could also be synthesized on a Pt/quartz substrate using cyclic treatments of coating/UV-irradiation. Compared with the conventional method, this synthetic method was found to be useful from the following viewpoints: (1) preparation of thicker film was possible within short time; and, (2) synthesis of PbTiO3 single phase with a uniform microstructure could be obtained.

ANALYSIS OF SUBSTRATE EFFECTS ON THE RESPONSE OF PYROELECTRIC THIN-FILM INFRARED SENSORS

An infrared (IR) sensor with a lead titanate (PbTiO3) thin film using the technology of microelectromechanical systems (MEMS) has been designed, fabricated, and developed. Anisotropic wet etching of Si(111) orientation in ethylenediamine/pyrocatechol (EDP) solution is used to process a micromachined cantilever beam for better thermal isolation and the array form available. The major IR-sensing part on the cantilever beam consists of a 5-nm PbTiO3 layer deposited by RF sputtering, and a gold (Au) black layer evaporated as an IR radiation absorber, with the active cantilever dimensions of 200 x 100 x 5 mu m3 formed by the etching processes. The substrate effect on the performance of the IR sensor has been studied in both experimental and theoretical analysis. The cantilever structure exhibits much superior performance in both theory and experiment to that of a traditional IR-sensing bulk structure under incident radiation at a wavelength of 970 nm.

Pyrochlore-to-perovskite transformation during rapid heating of sol-gel (Pb,La)TiO3 thin films

Phases appearing in lanthanum-modified lead titanate thin films prepared by a diol-based sol-gel method and crystallized by rapid heating were studied. The results clearly indicate that a phase transformation from a pyrochlore structure to the perovskite phase occurs in Pb-deficient films during the thermal treatment, which involves a heating rate higher than 500 °C min−1. The rate of this transformation is a function of the lead content of the films, decreasing as lead volatilizes. Temperatures higher than 650 °C or soak times longer than 2 h make possible the complete pyrochlore-to-perovskite transformation without any lead excess in the films.

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.

XPS depth profile analysis of sol–gel calcium-modified lead titanate thin films

X-ray photoelectron spectroscopy (XPS) combined with 4 keV Ar + depth profiling has been used for the study of calcium-modified lead titanate thin films obtained by the spin-on sol–gel technique. Amorphous films were prepared on Pt/TiO 2/Si(100) substrates. These films were deposited from solutions with a nominal composition of Pb 0.76Ca 0.24TiO 3 and with this composition plus a 10 mol% surplus of Pb. Crystallisation of the films was carried out at 650°C/720 s, with a heating rate of 8°C/s and 650°C/50 s with a heating rate of 30°C/s. The chemical composition at the film surface and in depth of the crystalline films were analysed by XPS. A non-uniform Pb distribution with depth was found for the films crystallised with the slower heating rate, whereas the more rapidly heated films show a homogeneous Pb distribution. The film heated with a rate of 30°C/s and deposited from the stoichiometric solution shows Pb deficiency and Pt diffusion into the film, in the proximity of the Pt electrode. A homogeneous composition throughout the film down to the interface with the Pt electrode was obtained for the film heated with a rate of 30°C/s, but deposited from the solution with 10-mol% Pb excess. This explains the well defined ferroelectric response of this film.