Longitudinal Electrooptic Effects and Photosensitivities of Lead Zirconate Titanate Thin Films

The feasibility of storing and reading high-density optical information in lead zirconate titanate (PZT) and in lead lanthanum zirconate titanate (PLZT) thin films depends on both the longitudinal electrooptic coefficients and the photosensitivities of the films. This paper describes the methods used to measure the longitudinal electrooptic effects and the photosensitivities of the films. The results of these measurements were used to evaluate a longitudinal quadratic electrooptic R coefficient, a longitudinal linear electrooptic r_c coefficient, and the wavelength dependence of the photosensitivity of a composition of PZT polycrystalline thin film. The longitudinal electrooptic R and r_c coefficients are about an order of magnitude less than the transverse R and r_c coefficients of bulk ceramics of similar compositions. This is attributed to clamping of the film by the rigid substrate. The large birefringence of the films after poling (>10⁻²) suggests that the optic axes of the films are preferentially oriented normal to the film surface. The techniques used in this paper for evaluating the photosensitivities of thin films are based on measuring the photocurrent generated rather than the reduction in coercive voltage (as in bulk ceramics) when the film is exposed to light. The thin film photosensitivities appear to be significantly higher than those of bulk ceramics of similar compositions. The high photosensitivities coupled with the substantial longitudinal electrooptic coefficients combine to establish the feasibility of using PZT or PLZT thin films for optical information storage applications.     

钛酸铅系薄膜的溶胶-凝胶法制备及其应用

简单介绍了钛酸铅系薄膜的制备方法，分析了溶胶-凝胶法较其它方法的优点。探讨了钛酸铅溶胶的稳定因素，如原料、溶剂、添加剂的选取。阐述了热处理温度、时间，退火温度、时间，基片和过渡层对促进钛酸铅系薄膜晶化的影响，并对钛酸铅系薄膜的应用现状进行了概括，展望了钛酸铅系薄膜的发展前景。     

Phase formation in pulsed laser-deposited ferroelectric thin films

PZT and modified lead titanate thin films were prepared by pulsed excimer laser irradiation of dense ceramic targets. The amorphous phase of the lead titanate was crystallized to pyrochlore and/or perovskite by post annealing and the ratio, perovskite to pyrochlore, was found to depend on the depositional P₀₂. Formation of two types of pyrochlore was discussed. A PZT film formed from a target having the morphotropic phase boundary composition showed no tetragonal X-ray peak splitting. However, Raman spectroscopy suggested that this film had mixed tetragonal and rhombohedral phases, the same as the target.     

Single-target sputter deposition and post-processing of perovskite lead titanate thin films

The growth of ferroelectric lead titanate (PT) thin films by RF magnetron sputtering using a single mixed-oxide target is described. This study has been focused on producing perovskite thin (2000 Å) films with the desired composition on different substrates. Depositions were performed at room temperature and the process gas is pure argon. The effects of deposition and post-annealing conditions on film composition and microstructure were evaluated. Optimization of process conditions is discussed in terms of stoichiometry, structure and reproducibility. The optical properties of the films have also been characterized.     

掺锶对钛酸铅薄膜结晶性能的影响

钛酸锶铅(PST)薄膜是一类重要的铁电薄膜材料.采用溶胶-凝胶法在硅(100)衬底上制备了钛酸锶铅薄膜.利用X射线衍射(XRD)、原子力显微镜(AFM)等表征手段,表征了不同锶掺杂量及不同退火温度对薄膜结晶性能的影响.通过实验发现:锶掺杂对薄膜的微观结构和表面形貌有重要的影响.由XRD谱图发现,随着锶掺入量的增加,Pb 1-xSrxTiO3薄膜中的晶轴比、晶胞体积都逐渐减小,晶化温度降低.通过AFM发现,相同掺锶量的薄膜随着退火温度的升高,结晶性能增强,颗粒增大,粗糙度增加.     

Electrochemical synthesis of ba- and Sr-based titanate thin films using Ti electrode prepared by RF sputtering

Barium and strontium titanate films were electrochemically synthesized onto Ti thin film prepared by RF sputtering. Applied current waveform was modulated to investigate the film growth mechanism. Superimposed cathodic pulses accelerated the formation of titanate thin films, and both the electrode surface pH and (Ba²⁺, Sr²⁺) ion size had a strong influence on film formation. Titanate film formation mechanism was investigated with a scanning electron microscope, an X-ray diffractometer and an electrochemical quartz crystal microbalance (EQCM).Insitu mass change of Ti electrode during electrolysis indicated that electrochemical method sets a limit to film growth.     

Recent Materials Characterizations of [2D] and [3D] Thin Film Ferroelectric Structures

A review is given of ceramic and single-crystal thin film ferroelectric oxides, emphasizing perovskite phases, together with some new developments on hafnia films. It is shown that single-crystal barium titanate films behave as bulk down to at least 77 nm, with no finite size effects, no phase transition temperature shifts, and no dielectric peak broadening or change from first- to second-order transitions, suggesting that the gradient defect model of Bratkovsky and Levanyuk correctly describes such effects as extrinsic in experimental studies of equally thin ceramic thin films. In ceramic barium–strontium titanate (BST) thin films, it is shown that there is also no intrinsic broadening or shifts in phase transitions, with sharp, unshifted, bulk-like transitions observed only as re-entrant upon warming from cryogenic temperatures; this shows that phase transitions in ceramic thin films are dominated by kinetics and not thermodynamics and are definitely not equilibrium measurements. At high fields (>1 GV/m), the films exhibit space charge-limited conduction; no variable-range hopping is observed, contrary to recent studies on SrTiO₃. Some novel, unconventional switching processes are discussed, comparing the "perimeter effect" (non-equilibrium, ballistic) with Molotskii's equilibrium model. Theory and experiment are described for [3D] nanotubes, nanorods, and nano-ribbons (or micro-ribbons). The layered-structure-perovskite–pyrochlore conversion in bismuth titanate is described together with the PbO+TiO₂ phase separation in lead zirconate titanate during electrical breakdown, as are novel HfO₂ precursors that demonstrate enhanced temperature crystallization from the amorphous state and hence commercial advantages for front-end processing.     

Influence of film structure on mobilities of charge carriers in conducting polymers

Two sorts of poly(3-hexylthiophene) (PHT) films with the same chemical compositions were prepared, and their electrochemical, spectroscopic, and transport properties were studied with a special interest in a possible influence of film structure on mobilities of charge carriers. One of the PHT films was electrochemically synthesized using 3-hexylthiophene as a monomer (as-grown film) and the other was obtained by dissolving the as-grown film in chloroform and then casting the polymer solution (cast film). A clear difference was observed in the mobility versus doping level plot between the two sorts of PHT films, demonstrating that the difference is caused only by a distinction in film structure. An initial decreasing feature of the mobility plot observed for the cast films was accounted for in terms of swelling of the films at an early stage of doping.     

Dielectric investigations of PLT(28) thin film prepared by reactive magnetron sputter

Paraelectric PLT(lead lanthanium titanate) thin films were prepared by dc magnetron sputtering with multi element metal target. In order to crystallize the as-deposited PLT thin films to the cubic perovskite phase, post-heat treatment was applied at the temperatures from 450 to 750 °C. The composition of PLT(28) thin film was: Pb, 0.72; La, 0.28; Ti, 0.88; O, 2.9. The dielectric characteristics were essentially dependent on the changes in the chemical composition and crystalline phase with variation of annealing treatment. The dielectric constant increased and dissipation factor decreased slightly, as the post-annealing temperature increased. The dielectric constant and dissipation factor at low electric field measurement of the capacitors with highest dielectric properties were 1216 and 0.018, respectively.     

Sol-Gel Preparation of Pb(Zr0.50Ti0.50)O3 Ferroelectric Thin Films Using Zirconium Oxynitrate as the Zirconium Source

Lead zirconium titanate (Pb(Zr_0.5Ti_0.5)O₃, PZT) ferroelectric thin films were successfully deposited on platinum-coated silicon substrates and platinum-coated silicon substrates with a PbTiO₃ interlayer by using a modified sol–gel spin-coating process, using zirconium oxynitrate dihydrate as the zirconium source. The precursor solution for spin coating was prepared from lead acetate trihydrate, zirconium oxynitrate dihydrate, and tetrabutyl titanate. The use of zirconium oxynitrate instead of the widely used zirconium alkoxide provided more stability to the PZT precursor solution and a well-crystallized structure of PZT film at a relatively low processing temperature. PZT films that were annealed at a temperature of 700°C for 2 min via a rapid thermal annealing process formed a well-crystallized perovskite phase of PZT films and also had nanoscale uniformity. The microstructure and morphology of the prepared PZT thin films were investigated via X-ray diffractometry, transmission electron microscopy, and atomic force microscopy techniques. The values for the remnant polarization ( P ) and coercive electric field ( E ) of the PZT films that were obtained from the P–E loop measurements were 3.67 μC/cm² and 54.5 kV/cm, respectively.     

Fabrication of Perovskite-Based High-Value Integrated Capacitors by Chemical Solution Deposition

Projected trends for capacitors include increasing capacitance density and decreasing operating voltages, dielectric thickness and process cost. Advances in the fabrication and processing of barium strontium titanate (BST) and lead zirconate titanate (PZT)-based thin films are presented toward attaining these goals in next-generation high-value integrated capacitors. Increasing capacitance density has been demonstrated through the use of large-area electrodes, multilayer structures, and decreased dielectric layer thickness. Capacitance values as high as 10 μF were obtained in a single-layer, 10 cm² film, and layer thicknesses as small as 9 nm have been achieved using chemical solution deposition. Base metal integration results for BST and PZT films are discussed in terms of additional cost and volume reduction; such films have achieved capacitance densities as high as 1.5 μF/cm² and electric fields of 25 V/μm.     

Effect of Switching Atmospheric Conditions during Crystallization on the Phase Evolution of Solution‐Derived Lead Zirconate Titanate Thin Films

The crystallization behavior of solution‐derived lead zirconate titanate (PZT) thin films in different atmospheric environments was studied using in situ X‐ray diffraction. The stability of the transient intermetallic Pt₃Pb phase and perovskite PZT is dependent on oxygen partial pressure during crystallization. Based on the relationship between oxygen partial pressure and the resultant phase stability of intermediate phases, a new route to produce PZT thin films was developed. The new route involves switching atmospheres during crystallization and is shown to mitigate the formation of the transient intermetallic Pt₃Pb phase and to promote the perovskite PZT phase. The route evidences a new and significant variable controlling film synthesis and film microstructure.     

Low-temperature preparation of hydrothermal lead zirconate titanate thin films

In preparing lead zirconate titanate thin films under hydrothermal conditions, we investigated the effects of concentrations of nutrient and mineralizer, reaction time and reaction temperature on crystallinity, grain size and shape. Experiments were performed in the ranges of 0.1-1.0M Pb(NO₃)₂, and 0-6.0M KOH with varying reaction time from 0 to 48 hours at 60-200 °C. In the experiment, lead zirconate titanate thin film of homogeneous crystalline grain was obtained through a 24 hour reaction with 0.4M Pb(NO₃)₂ and 5.0M KOH at 140 °C. The thickness of the film was 0.9-1.6 μm, and it exhibited a saturation polarization (Ps) of 18.3 μC/cm², remnant polarization (Pr) of 7.4 μC/ cm₂ and coercive field (Ec) of 0.41 kV/cm. The dielectric constant and loss (δ) measured at 1 kHz were approximately 1020 and 0.15, respectively.     

Nano-embossing technology on ferroelectric thin film Pb(Zr0.3,Ti0.7)O3 for multi-bit storage application

In this work, we apply nano-embossing technique to form a stagger structure in ferroelectric lead zirconate titanate [Pb(Zr0.3, Ti0.7)O3 (PZT)] films and investigate the ferroelectric and electrical characterizations of the embossed and un-embossed regions, respectively, of the same films by using piezoresponse force microscopy (PFM) and Radiant Technologies Precision Material Analyzer. Attributed to the different layer thickness of the patterned ferroelectric thin film, two distinctive coercive voltages have been obtained, thereby, allowing for a single ferroelectric memory cell to contain more than one bit of data.     

Sol–Gel Preparation of Thick PZN–PZT Film Using a Diol-Based Solution Containing Polyvinylpyrrolidone for Piezoelectric Applications

Dense and crack-free lead zinc niobate–lead zirconate titanate (PZN–PZT) films were deposited on silicon and glass substrates by spin coating using a sol containing propanediol and polyvinylpyrrolidone. Single-layer PZN–PZT films as thick as 0.80 μm were deposited by a single spin coating with successive heat treatments at 250° and 700°C. After heat treatment, the films were dense, crack free, and optically transparent. In addition, the crystallographic orientation of the thick film was controllable by adjusting the heat-treatment conditions. The ferroelectric properties of the (111)-oriented film were superior to those of the (100)-oriented film. On the other hand, the piezoelectric and dielectric properties of the (100)-oriented film were better than those of the (111)-oriented film. The piezoelectric coefficients ( d ₃₃) of the PZN–PZT films of 4.0-μm-thickness were 192 and 110 pC/N for the (100)-and (111)-oriented films, respectively.     

Formation of Monoclinic Hafnium Titanate Thin Films Via the Sol–Gel Method

Hafnium titanate films are generating increasing interest because of their potential application as high- k dielectrics materials for the semiconductor industry. We have investigated sol–gel processing as an alternative route to obtain hafnium titanate thin films. Hafnia-titania films of different compositions have been synthesized using HfCl₄ and TiCl₄ as precursors. The HfO₂–TiO₂ system composition with 50 mol% of TiO₂ and 50 mol% of HfO₂ has allowed the formation of a hafnium titanate film after annealing at 1000°C. The films exhibited a homogeneous nanocrystalline structure and a monoclinic hafnium titanate phase that has never been obtained before in thin films. The films resulted in the formation of homogeneously distributed nanocrystals with an average size of 50 nm. Different compositions, with higher or lower hafnia contents, produced anatase crystalline films after annealing at 1000°C.     

Piezo and dielectric properties of PHB–PZT composite

Flexible piezoelectric composite films made of poly(3‐hydroxybutyrate) (PHB) in powder form and lead zirconate titanate (PZT) ceramic powder were obtained by mixing both powders and pressing at 180°C. The effect of PZT on PHB crystallization was investigated using differential scanning calorimetry (DSC). The relative dielectric constant and dielectric loss factor were analyzed by dielectric spectroscopy and the α‐relaxation of amorphous phase of PHB was observed. After suitable polarization, the composite film displayed piezoelectric activity indicating the possibility of using that material as a sensor. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Relaxor Ferroelectric Behavior in Barium Strontium Titanate

The development of barium strontium titanate‐based tunable dielectrics is currently hindered by high losses in the paraelectric phase. Barium strontium titanate (BST) thin films and ceramics show a range of ferroelectric transition behavior, from normal, diffuse, and relaxor‐like ferroelectric responses, depending on the sample preparation route. Rayleigh analysis, the temperature‐dependent dielectric response, and the optical second harmonic generation were used to characterize the ferroelectric response of bulk and thin film BST. Ferroelectricity is observed to persist in BST for 30°C above the global phase transition temperature in ceramics and over 50°C in thin films. Piezoresponse force microscopy on BST ceramics with extensive residual ferroelectricity reveals the coexistence of nanoscale polar regions, typical of relaxor ferroelectrics, as well as micrometer scale domain structures. The nature of the phase transition was probed using electron energy loss spectroscopy and found to correlated with the nanoscale A‐site chemical inhomogeneity in the samples.     

Role of the PbTiO3 Seed Layer on the Crystallization Behavior of PZT Thin Films

The role of a highly crystalline and oriented lead titanate (PTO) seed layer on the subsequent phase and texture evolution of lead zirconate titanate (PZT) thin films is investigated in situ using X‐ray diffraction (XRD) during crystallization. Crystalline PTO seed layers were first prepared via a 2‐methoxyethanol route. Amorphous PZT with a Zr/Ti ratio of 52/48 was then deposited on the seed layer using the same synthesis route and subsequently crystallized in situ during XRD. During heating, a tetragonal‐to‐cubic transformation of the seed layer occurs prior to the formation of perovskite PZT. Subsequent nucleation of the crystalline PZT occurs in the cubic phase. Simultaneous to nucleation of PZT, development of a dominant 100 texture component was observed in the PZT phase of the thin films. The results indicate that 100 textured PTO nucleates 100 texture of PZT thin films during crystallization.     

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.