Properties Of Lead Zirconate Titanate Films Research Articles

Effect of Dy doping on the crystal orientation, microstructure, and electrical properties of PDZT thin films prepared by sol–gel method

Dysprosium-doped lead zirconate titanate thin films (PbDyx(Zr0.40Ti0.60)1−(3x/4)O3) (x = 0%, 1%, 2%, 3%, 4%, 5%), abbreviated as PDZT, were prepared by sol–gel method. The effects of Dy doping on the crystal orientation, microstructure, and electrical properties of lead zirconate titanate (PZT) films were studied. X-ray diffraction (XRD) analysis shows that PDZT thin films with Dy concentration less than 3% exhibit (111) preferred orientation, and the samples doped with 3%, 4%, and 5% show (100) preferred orientation. Scanning electron microscope (SEM) analysis results show that all samples exhibit dense perovskite structure. With the increase of doping content, the electrical properties of PDZT films show a trend of first increasing and then decreasing. An enhanced residual polarization strength of 60.89 μC/cm2 and an improved relative dielectric constant of 943.1 at 0.1 kHz are obtained in 2% doped PDZT film. Moreover, the PZT film with 2% Dy doped also exhibits a significantly reduced leakage current density.

The study of the properties of lead zirconate-titanate films on silicon substrate after halogen lamps rapid thermal annealing

Ferroelectric thin films of lead zirconate titanate (PZT) are important is creation of ferroelectric MEMS, memory devices, sensors of physical quantities and converters energy. The thermal annealing is used to obtain satisfactory electro-physical parameters and optimal crystal structure PZT films. The rapid thermal annealing (RTA) in comparison with isothermal annealing has a possibility of selective annealing of individual layers of the multilayer PZT composition by selecting appropriate temperature and duration of the RTA. The purpose of this work is to study the phase-structural state of PZT films formed by high-frequency reactive plasma sputtering and subjected to rapid thermal annealing by halogen lamps. The PZT thin films with a thickness of 1.0 ± 0.1 µm were deposited by oxygen atmosphere high-frequency reactive plasma sputtering on silicon (100) substrates and silicon substrates with SiO2 on surface. After applying, PZT film underwent RTA at temperatures of 600-800 °C and with speed 60 degrees/s. With X-ray phase analysis, the structure-phase composition of the PZT film is revealed. Besides that, the effect of RTA was investigated using electron microscopy. It is established that temperature change at RTA leads to a qualitative change in the phase-structural state of the PZT films as compared to their initial state. This gives a chance to use RTA in formation of the PZT films with given parameters.

Microstructure and Properties of PZT Films with Different PbO Content-Ionic Mechanism of Built-In Fields Formation.

Experimental studies were conducted on the effects of lead oxide on the microstructure and the ferroelectric properties of lead zirconate-titanate (PZT) films obtained by the method of radio frequency (RF) magnetron sputtering of a ceramic PZT target and PbO2 powder with subsequent heat treatment. It is shown that the change in ferroelectric properties of polycrystalline PZT films is attributable to their heterophase structure with impurities of lead oxide. It is also shown that, even in the original stoichiometric PZT film, under certain conditions (temperature above 580 °C, duration greater than 70 min), impurities of lead oxide may be formed. The presence of a sublayer of lead oxide leads to a denser formation of crystallization centers of the perovskite phase, resulting in a reduction of the grain size as well as the emergence of a charge on the lower interface. The formation of the perovskite structure under high-temperature annealing is accompanied by the diffusion of lead into the surface of the film. Also shown is the effect of the lead ions segregation on the formation of the self-polarized state of thin PZT films.

Effect of neodymium substitution on crystalline orientation, microstructure and electric properties of sol-gel derived PZT thin films

Pb(NdxZr0.52Ti0.48)O3 (PNZT) (x = 0%, 1%, 2%, 3%, 4%, 5%) thin films were prepared by sol-gel process to investigate the effects of neodymium substitution on crystalline orientation, microstructure and electric properties of lead zirconate titanate (PZT) films. X-ray diffraction (XRD) and scanning electron microscope (SEM) analysis showed that PNZT films with Nd doping concentration below 3% exhibited dense perovskite structure with (100) preferred orientation. The average grain size of PNZT films decreased as the Nd substitution increased. The maximum dielectric constant, remnant polarization and minimum coercive field were obtained in 2% Nd-doped PZT films. Fatigue resistance was also improved significantly with 2% Nd dopant.

Dependence of the ferroelectric properties of modified spin-coating-derived PZT thick films on the crystalline orientation

The effects of crystalline orientation on the ferroelectric properties of lead zirconate titanate (PZT) thick films deposited on (111)-oriented Pt/Ti/SiO2/Si substrates by using a modified spincoating method have been studied. The texture and the microstructure of the thick films were characterized by using X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis, respectively. The XRD results implied that the texture of the PZT films was sensitive to the pyrolysis conditions after spin-coating, but less dependent on the film’s thickness. The texture had mainly a (111)-orientation for pyrolysis temperatures from 330 to 400 ◦C, and changes in the (100)- orientation occurred for pyrolysis temperatures at or above 450 ◦C after annealing at 650 ◦C for 5 min. The formation of a preferred texture could be explained by using the intermetallic phases and the internal stress energies between the substrate and the film. The ferroelectric properties of the PZT films fabricated by using this method have been found to be enhanced as compared to those of the PZT films fabricated by using the conventional spin-coating method and to be correlated to the microstructure of the film.

Ferroelectric Properties of Lead Zirconate Titanate Thin Film on Glass Substrate Crystallized by Continuous-Wave Green Laser Annealing

The ferroelectric properties of lead zirconate titanate (PZT) films crystallized by a continuous-wave (CW) green laser are discussed in this paper. After CW green laser annealing, two kinds of typical crystallization modes of the PZT thin films were observed: island crystallization and lateral crystallization. In the island crystallization region, the PZT film was crystallized uniformly over the thin films. However, poor surface roughness was found in lateral crystallization region. Significant improvements of ferroelectric characteristics have been achieved in the island crystallization region after optimizing with a low energy density. By varying energy density from 4.5 to 7.1 kW/cm2 and fixing annealing time at 42.5 ms, significant features were found at an energy density of 5.3 kW/cm2. A maximum remanent polarization of 27 µC/cm2 was obtained.

EFFECT OF PRE-HEATING TEMPERATURE ON THE CHARACTERISTICS OF SOL–GEL DERIVED LEAD ZIRCONATE TITANATE FILMS

Effect of pre-heating temperature on the properties of Lead zirconate titanate (PZT) powders and films was investigated. PZT powders and films were prepared via a triol-based sol–gel route. The PZT powders prepared at various heating temperatures were characterized. The preheating temperature range of 200°C–400°C and annealing temperature of 600°C were chosen to make the films. AFM micrograph revealed the thin films with homogeneous, dense, and crack-free properties. The pre-heating temperature was found to have a significant effect on phase formation, prefer orientation, and dielectric properties of the films. Higher dielectric constant and dielectric loss were observed at higher pre-heating temperature. However, all films showed the dielectric loss less than 0.04.

Scanning Capacitance Microscopy Evaluation of Lead Zirconate Titanate Film Formed by Aerosol Deposition Method

The local electric properties of lead zirconate titanate (PZT) film prepared by the aerosol deposition method (ADM) were investigated by scanning capacitance microscopy (SCM) using a self-sensing probe. Although an obvious ferroelectric response cannot be observed from macroscopic polarization versus applied electric field (P–E) measurements for the as-deposited PZT film, capacitance images showed a distinctive contrast as the result of the spatial variation of local dielectric permittivity. The scanning capacitance spectroscopy (SCS) measurements show that there are localized regions which have poor ferroelectricity, and this is the cause of the nominal ferroelectric properties of as-deposited PZT film.

Experimental, analytical, and finite element analyses of nanoindentation of multilayer PZT/Pt/SiO2 thin film systems on silicon wafers

The mechanical properties of lead zirconate titanate (PZT) multilayer systems are needed to model and design micro-electromechanical systems (MEMS) devices. Nanoindentation is a promising tool for obtaining the elastic properties of thin films. However, no means exist to obtain the elastic modulus of the lead zirconate titanate (PZT) in the multilayer system. The indentation modulus versus a/t behavior of the multilayered PZT/Pt/SiO2 film system on a silicon substrate was investigated and compared with finite element models and a new analytical solution. Six different PZT film thicknesses were indented (100, 140, 400, 700, 1500, and 2000 nm), using 5-, 10-, and 20-μm radius indenters. Good agreement was shown between the finite element analysis (FEA) and analytical solutions, and the experimental data. However the behavior of multilayer systems is complex, making deconvolution of properties difficult for films of less than a micron thick.

Influence of processing parameters on PZT thick films

We have studied influence of processing parameters on the microstructure and ferroelectric properties of lead zirconate titanate (PZT)-based thick films in the range of 5–25 μm. PZT and 2% La-doped PZT thick films were processed using a modified sol–gel process. In this process, PZT- and La-doped PZT powders were first prepared via sol–gel. These powders were calcined and then used with respective sols to form a slurry. Slurry composition was optimized to spin-coat thick films on platinized Si substrate (Si/SiO 2/Ti/Pt). Spinning rate, acceleration and slurry deposition techniques were optimized to form thick films with uniform thickness and without any cracking. Increasing solids loading was found to enhance the surface smoothness of the film and decrease porosity. Films were tested for their electrical properties and ferroelectric fatigue response. The maximum polarization obtained was 40 μC/cm 2 at 250 kV/cm for PZT thick film and 30 μC/cm 2 at 450 kV/cm for La-doped PZT thick film. After 10 9 cycles of fatiguing at 35 kHz, La-doped PZT showed better resistance for ferroelectric fatigue compared with un-doped PZT films.

Ferroelectric Properties of Dysprosium-Substituted Lead Zirconate Titanate Thin Films Fabricated by Chemical Solution Deposition

Dysprosium (Dy3+)-substituted lead zirconate titanate (PDZT) thin films were synthesized in order to improve the ferroelectric properties of lead zirconate titanate (PZT) films by crystal anisotropy enhancement. Thin films of Pb1.00-(3x/2)Dyx(Zr0.40Ti0.60)O3 (A-PDZT) and Pb1.00Dyx(Zr0.40Ti0.60)1-(3x/4)O3 (B-PDZT) were deposited on (111)Pt/Ti/SiO2/(100)Si substrates by chemical solution deposition (CSD). The ferroelectric properties of A- and B-PDZT thin films were compared with those of a non-substituted PZT film. Dy3+-substitution based on B-PDZT (x=0.02) enhanced the tetragonality of PZT film, which increased the Pr value of B-PDZT from 20 µC/cm2 up to 25 µC/cm2. On the other hand, both the c/a ratio and Pr value of the A-PDZT film decreased with increasing x continuously. These results suggest that the ferroelectric property was enhanced by the Dy3+-substitution for B-site in PZT crystal.

Enhanced Spontaneous Polarization of Dysprosium-substituted Lead Zirconate Titanate Thin Films by a Chemical Solution Deposition Method

ABSTRACTInfluences of the B-site substitution using Dy3+ ion on the crystal structure and ferroelectric properties of lead zirconate titanate (PZT) films were investigated. Dy3+-substituted PZT films with nominal chemical compositions of Pb1.00Dyx (Zr0.40Ti0.60)1-(3x/4)O3 (x = 0 ∼ 0.06) were fabricated by a chemical solution deposition (CSD). Polycrystalline PZT films with preferential orientation of (111)PZT were obtained on (111)Pt/TiO2/SiO2/(100)Si substrates, while epitaxially-grown (111)PZT films were fabricated on (111)SrRuO3//(111)Pt//(100)YSZ//(100)Si substrate. Ratio of PZT lattice parameters (c/a), which corresponds to its crystal anisotropy, was enhanced by the Dy3+-substitution with x = 0.02. Spontaneous polarization (Ps) of Dy3+-substituted PZT film (x = 0.02) along polar [001] axis of PZT lattice was estimated from saturation polarization (Psat) value of the epitaxially-grown (111)PZT film on (111)SrRuO3//(111)Pt//(100)YSZ//(100)Si to be 84 μC/cm2 that was significantly larger than that of non-substituted PZT (= 71 μC/cm2). We concluded that the enhancement of Ps value could be achieved by the Dy3+-substitution that promoted the crystal anisotropy of PZT lattice.

Electrical properties of PZT thin films by photochemical deposition

The electrical properties of lead zirconate titanate (PZT) thin film prepared by photochemical metal–organic deposition (PMOD) using photosensitive starting precursors were characterized. Unlike sol–gel procedure based on the chemical reaction including hydrolysis and condensation, by PMOD, metallic state is obtained through the removal of organic ligand by exposure to UV. This metallic state usually turns to oxide state through oxidation reaction with atmospheric oxygen during exposure to UV. Fourier transform infra-red spectroscopic observation showed that a complete removal of organic group was possibly obtained by exposure of spin-coated PZT precursor film to UV at room temperature. After anneal treatment of the UV-exposed PZT precursor film to crystallize, a highly preferred growth orientation was found in PZT film according to the orientation of substrate Pt. The characteristics of ferroelectric properties (remnant polarization and coercive field) and leakage current behavior were almost the same as those of conventional PZT film prepared by sol–gel processing. However, a slight shift of hysteresis curve and more leaky behavior with negative direction of bias were found and it seemed to be due to the presence of micro-defects formed during PMOD reaction.

Electrical properties of PZT thin films by photochemical deposition

The electrical properties of lead zirconate titanate (PZT) thin film prepared by photochemical metal–organic deposition (PMOD) using photosensitive starting precursors were characterized. Unlike sol–gel procedure based on the chemical reaction including hydrolysis and condensation, by PMOD, metallic state is obtained through the removal of organic ligand by exposure to UV. This metallic state usually turns to oxide state through oxidation reaction with atmospheric oxygen during exposure to UV. Fourier transform infra-red spectroscopic observation showed that a complete removal of organic group was possibly obtained by exposure of spin-coated PZT precursor film to UV at room temperature. After anneal treatment of the UV-exposed PZT precursor film to crystallize, a highly preferred growth orientation was found in PZT film according to the orientation of substrate Pt. The characteristics of ferroelectric properties (remnant polarization and coercive field) and leakage current behavior were almost the same as those of conventional PZT film prepared by sol–gel processing. However, a slight shift of hysteresis curve and more leaky behavior with negative direction of bias were found and it seemed to be due to the presence of micro-defects formed during PMOD reaction.

Comparison of the Electrical Characteristics of PZT and SBT Thin Films

The electrical properties of lead zirconate titanate (PZT) and strontium bismuth tantalate (SBT) thin films are compared for nonvolatile random access memory applications. PZT thin films have high switchable polarization with poor fatigue resistance and higher leakage current densities as compared to SBT thin films deposited on platinized silicon substrates. Characterization of these films in terms of their domain dynamics under application of sub-switchable and switchable electric fields give valuable insight about the observed differences in the electrical behavior. In the present work the dielectric behaviors of SBT and PZT thin films at sub-switchable electric field were analyzed in terms of Rayleigh law. The reversible and irreversible polarization component of switchable polarization was separated by the measurement of capacitance-voltage (C-V) and polarization hysteresis loops. The conduction mechanisms in these films were evaluated by measuring field dependence of leakage current densities at various temperatures. The observed differences in electrical properties are explained in terms of the intrinsic defects and defect-domain interaction of these two materials.

Specific properties of the PZT-based thin-film capacitor structures with excess lead oxide

The effect of excess lead oxide on the microstructure and ferroelectric properties of lead zirconate titanate (PZT) films was studied in PZT-based thin-film capacitor structures. It is shown that excess lead in the form of lead oxide is localized at the grain boundaries and film-platinum electrode interfaces, which can result in the appearance of internal electric fields and the self-polarization of PZT films. It is suggested that the selfpolarization effect is related to the formation of a built-in electric charge with different densities at the bottom and top metal electrode-ferroelectric film interfaces.

Improved dielectric properties of lead zirconate titanate thin films deposited on metal foils with LaNiO3 buffer layers

Improved dielectric properties of lead zirconate titanate (PZT) films deposited on a variety of foils using buffer layers are reported. Foils include titanium, stainless steel, and nickel with LaNiO3(LNO) buffer layers which were prepared by sol–gel processing. High dielectric constant (330 for stainless steel, 420 for titanium, and 450 for nickel foils), low dielectric loss (<2.2% for titanium and 8% for stainless steel), symmetric ferroelectric C–V characteristics and P–E curves were obtained. The LNO layers are shown to provide an effective diffusion barrier for Ni and Cr and to restrict oxide layer formation (i.e., TiOx or NiOx) between the PZT film and the metallic foils during annealing in air.

The effects of solvent on the properties of sol-gel derived PZT thin films

The effects of various solvents on the material properties of lead zirconate titanate (PZT) thin films were investigated. PZT films have been made from alkoxide precursor by sol-gel method using four kinds of solvent (2-methoxyethanol, iso-propyl alcohol, ethanol, and methanol). It was found that phase formation temperature decreases as molecular weight of solvent decreases. And the stock solution using light alcohol such as ethanol or methanol induced decrease of grain size and increase of (111) preferred orientation in PZT films. Furthermore, remnant polarization value was also decreased.

Effects of Electrodes on the Electric Properties of Pb(Zr,Ti)O3 Films Deposited by Electron Cyclotron Resonance Plasma Enhanced Chemical Vapor Deposition

The effects of electrodes on the deposition characteristics and electrical properties of lead zirconate titanate (PZT) films deposited by electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR-PECVD) were investigated. Pt/Ti/SiO2/Si and RuO2/SiO2/Si were used as bottom electrodes (substrates) for PZT capacitors. Pt and RuO2 were used as top electrodes. The nucleation of the perovskite phase was more difficult on RuO2 substrates than on Pt/Ti substrates, and the PZT films grown on RuO2 substrates tend to have Pb-based second phases. Precise control of the flow rates of metalorganic sources (particularly the lead source) and the introduction of a proper seed layer are required to obtain films of the single perovskite phase and good electrical properties on the RuO2 substrate. An excellent leakage current density of 10-6 A/cm2 at 150 kV/cm was obtained from the Pt(top)/PZT/RuO2(bottom) capacitor with the introduction of a 4 nm-thick Ti-oxide seed layer. The polarization fatigue and current leakage characteristics of the PZT capacitors with four different electrode configurations (Pt ∥Pt, RuO2 ∥Pt, Pt ∥RuO2, and RuO2 ∥RuO2) were also investigated. Only the RuO2/PZT/RuO2 capacitor did not show any polarization fatigue even after 1010 cycles, while the other capacitors, whose either top or bottom electrode was Pt, showed distinct polarization fatigues. The RuO2/PZT/RuO2 capacitor, however, showed a leakage current density of as high as 10-4 A/cm2 at 100 kV/cm.

Ferroelectric Properties of Crystalline-Oriented Lead-Zirconate-Titanates Formed by Sol-Gel Deposition Technique

Ferroelectric properties of lead-zirconate-titanate (PZT) films formed by the sol-gel deposition technique have been discussed from the standpoint of ferroelectric random-access memory (FRAM) and dynamic random-access memory (DRAM) applications. PZT films with <111>-preferred orientation and random orientation were formed on Pt/Ti/SiO2/Si substrates by optimizing fabrication conditions. Remanent polarization of the <111>-preferred film was 23.5 µ C/cm2 which is somewhat higher than that of the randomly oriented one. An abrupt saturation of remanent polarization was observed only for the <111>-preferred film. The voltages which provide saturations of remanent polarization densities for the <111>-preferred films are almost constant between 3.5 V to 4 V independent of thickness. The dielectric constant of the randomly oriented film was 730 which is larger than that of the <111>-preferred one and gradually decreased depending on the applied electric field. The <111>-preferred PZT film is appropriate for FRAM application, and the randomly oriented one is preferred for DRAM application.