Sol-gel Derived PZT Thin Films Research Articles

Orientation transition, dielectric, and ferroelectric behaviors of sol-gel derived PZT thin films deposited on Ti–Pt alloy layers: A Ti content-dependent study

Lead zirconate titanate (PZT) films have been deposited on Ti–Pt/Ti/SiO2/Si(100) alloy substrates by sol-gel process. The purpose of the present study was to examine the Ti content in the Ti–Pt alloy layers-dependent preferred orientation and electrical behaviors of PZT films. X-ray diffraction (XRD) shows that Ti–Pt alloy electrodes induces texture transition from (100) to (111), and the maximum peak of (100) and minimum peak of (111) are obtained in the sample on Ti–Pt alloy layer with a sputtering power of 12.5 W/150 W. The film deposited on Ti–Pt alloy layer with a sputtering power of 12.5 W/150 W exhibits a reduced oxygen vacancies concentration, which results in a maximum ε of 1224.25, an enhanced 2Pr of 40.5 μC/cm2, and a relative decreased 2Ec of 108 kV/cm. Therefore, it can be concluded that the Ti–Pt alloy layers with an appropriate Ti content play a very critical role for the preferred orientation, microstructure, and improved electrical properties of the PZT films.

Effect of Pt3Pb on the permittivity and conductivity of lead zirconate titanate thin films

The evolution and interaction of buried interfaces during the synthesis of lead zirconate titanate (PZT) ferroelectric thin film devices have been previously predicted by density functional theory modeling and observed experimentally via in–situ structural characterization. Moreover, the formation and disappearance of an intermetallic phase (Pt3Pb) during the crystallization of the film has been identified as a key process expected to affect the resulting electrical properties of the devices. To elucidate this effect, a combination of direct current (leakage current measurements) and alternating current (impedance spectroscopy) characterization techniques are used to examine the electrical properties of sol–gel–derived PZT thin films. Films with the intermetallic phase exhibit a high potential barrier at the metal–insulator interface (0.83 eV) similar to the fully crystallized films (0.81 eV) and a lower current density than the films without the intermetallic phase, as shown in the Richardson plot. Impedance measurements also revealed that the conductivity of the films with the intermetallic phase, σ = 1.9 × 10−11 S cm−1, and the real part of the relative permittivity at 10 kHz, εr′=42, are lower than the other films (fully crystallized film: σ = 3.5 × 10−10 S cm−1 εr′=566, amorphous crystallized film: σ = 4.6 × 10−11 S cm−1 εr′=121). It is shown that these electrical characterization methods can serve as non–destructive examination tools to track the evolution of secondary phases during device synthesis and fabrication.

Influence of Film Texture on Reliability of Sol-Gel Derived PZT Thin-Film Capacitors

Time-dependent dielectric breakdown (TDDB) of lead titanate zirconate (PZT) thin-film capacitors derived by a sol-gel deposition process has been studied. Without any change in heat treatment conditions such as temperature, ramping rate, and keeping time, the films grain size was varied by adding a small amount of organic additive to PZT sol-gel solution for a control of nucleation to form PZT oxide. The reliability was remarkably improved by fabricating interfaces with multi-annealing process, parallel to film surface when the grain size is greater than film thickness, which seems to suppress conductivity of oxygen vacancies.

Nanomechanical and Dielectric Properties of Sol-Gel Derived PZT Thin Films Annealed with Microwave Energy

Lead zirconium titanate Pb (Zr0.58Ti0.42) O3 (PZT) thin films were deposited on silicon substrates by sol-gel process. The structural, morphological, dielectric and nano mechanical properties of these films have been studied systematically. The thicknesses of the films were around 160 nm. During the deposition of each layer, the films were baked in a microwave oven which in turn resulted in a low temperature crystallization of these thin films compared to the conventional method. The crystallite sizes of the films were ranged between 25–35 nm depending up on the annealing temperature. The dielectric constant of the films decreased with increase in frequency whereas the loss has increased and ranged between (480–100) and (0.03–0.30), respectively. The DFM (Dynamic force microscopy) images of the films shows the spherical grains with uniform microstructure and an average grain size of 80–110 nm. The hardness of the films ranged between 2–5 GPA. The film annealed at 600°C was having a dielectric constant of 400 with hardness of 4.8 GPa which is suitable combination of properties for micromechanical systems.

Enhanced fatigue characteristics of sol–gel derived PZT thin films

Pb(Zr,Ti)O 3 (PZT) thin films with Zr/Ti ratio of 52:48 were deposited on Pt/Ti/SiO 2/Si substrates using the sol–gel method. Since the conditions of heat-treatment play a great role in film growth, post-annealing processes were conducted under different environments. After standard processing, films were annealed at 600 °C in three different atmosphere—air, O 2 and a two-step process conducted in air for 30 min and then in O 2 ambient, all done for 10 min. Through electron microscopy and X-ray diffraction, we found that all films were crack-free and highly (1 1 1) oriented. Hysteresis measurements showed a generally large polarization value. The fatigue properties differ drastically for all processes, showing an abnormal behaviour near the end of the measurement. The hysteresis loops before and after 1 × 10 10 switching cycles have been slightly changed in both shape and magnitude. Such abnormality and fatigue-free property is an unusual result for PZT films prepared on conventional Pt/Ti/SiO 2/Si substrates.

Measurement of longitudinal piezoelectric coefficient of lead zirconate titanate thin/thick films using a novel scanning Mach-Zehnder interferometer

Developing a well accepted method for piezoelectric characterization of piezoelectric thin/thick films is an essential issue in the research of piezoelectric micro-electromechanical systems. This article presents a scanning interferometric technique for piezoelectric characterization of lead zirconate titanate (PZT) thin/thick film on silicon substrate. This technique is established using a newly developed scanning Mach-Zehnder interferometer with ultra-high resolution. The apparent longitudinal piezoelectric coefficients of both sol–gel derived PZT thin films and hybrid PZT thick films are measured using the scanning technique. The roles of several film processing factors on the piezoelectric properties of the resultant films are also discussed.

Impact of low pressure consolidation annealing on electrical properties of sol–gel derived Pb(Zr,Ti)O 3 films

We demonstrate drastic improvement of electrical properties of sol–gel derived PZT thin films by using low-pressure consolidation annealing. PZT thin films have been prepared on Pt/Ti/SiO 2/Si substrates using Pb 1.2Zr 0.4Ti 0.6O 3 source solution. We have employed low-pressure consolidation annealing at 400 °C for 10 min at 35 Torr before the crystallization anneal. The consolidated films were then annealed at 550–600 °C for 15–30 min in O 2 for crystallization. A remanent polarization (Pr) of 35 μC/cm 2 with a coercive filed ( E C) of 64 kV/cm was obtained for the PZT film crystallized at 600 °C with low-pressure consolidation process. Furthermore, it is also demonstrated that the leakage current density of the PZT film fabricated with low-pressure consolidation process is lower than that of the film fabricated by the conventional process. The possible crystallization mechanism of low-pressure consolidation process is discussed.

複合多層PZT薄膜マイクロアクチュエータの開発(マイクロメカトロニクス,IIP2004 情報・知能・精密機器部門講演会)

This paper describes the development of novel PZT thin films. The feature for novel PZT thin films is that double-layered composite PZT thin films which laminate sputtered PZT thin films and sol-gel PZT thin films. The novel PZT thin films are found to have the higher (111) preferred orientation than not only sol-gel PZT thin films but also sputtered PZT thin films. In addition, it is found that composite PZT thin films, which feature is that the sol-gel derived PZT thin films are deposited on the sputtered PZT thin films, shows better characteristics.

Micro-patterning of sol–gel-derived PZT thin film with SAM

Micro-patterns of Pb(Zr 0.53 Ti 0.47)O 3, PZT, thin films with a morphotropic phase boundary (MPB) composition were prepared from molecular-designed PZT precursor solution by using self-assembled monolayer (SAM) as a template. This method includes deposition of SAM followed by the optical etching by exposing the SAM to the UV-light, leading to the patterned SAM as a selective deposition template. The pattern of SAM was formed by irradiating UV-light to the SAM on substrate through a metal mask for the selective deposition of patterned PZT precursor films from alkoxide-derived precursor solution. As a result, patterned ferroelectric PZT films with good electrical properties in micrometer size could be successfully deposited.

Effect of microstructure on reactive ion etching of sol–gel-derived PZT thin film

Micro patterning and etching characteristics of Pb(Zr 0.52Ti 0.48)O 3 (PZT) thin film are very interesting for the fabrication of various ferroelectric micro devices. Besides the effects of plasma, the microstructure of PZT films was very important in etching process. In this article, the characteristics of reactive ion etching (RIE) of PZT films with different microstructure were investigated. The morphology and microstructure were examined by atomic force microscopy (AFM) and X-ray diffraction (XRD). The properties of etching were measured by AFM and X-ray photoelectron spectroscopy (XPS). With the annealing temperature increased, the microstructure became more compact and the etching rate decreased. The highest etching rate was 13 nm/min when the microstructure of PZT film was amorphous.

Design and fabrication of MEMS-based active slider using double-layered composite PZT thin film in hard disk drives

This paper describes a micro-electro-mechanical system (MEMS)-based active slider with microactuators. The proposal active slider uses PZT thin films as a microactuator and to control the slider flying height of less than 10 nm. The design procedure for the active slider is discussed. In addition, novel double-layered composite PZT thin film microactuators, which are very important functional microdevices, are studied. It is shown that the recently developed PZT thin films have better piezoelectric characteristics than conventional sol-gel derived PZT thin films and sputtered PZT thin films. The micromachining process for the active slider is also developed and the pico-size active slider is fabricated. The technical issues related to the fabrication of a MEMS-based active slider are discussed.

Improvement in D-E Hysteresis Curve Squareness of PZT Thin Films—Effect of Oxygen Partial Pressure in High-Pressure Post-Annealing

A high-pressure annealing was applied to a post-annealing process for sol-gel derived PZT thin films. The squareness of D-E hysteresis curves changes depending on both total pressure and oxygen concentration. Moreover, the change follows the product of the total pressure and the oxygen concentration, which correspond to oxygen partial pressure PO2. Where the PO2 is higher than 0.03 MPa, few of the squareness of the hysteresis curve are excellent. The squareness of the hysteresis curves dramatically improve as the PO2 decreases. Where the PO2 is lower than 0.01 MPa, the squareness deteriorates slightly. These changes in the D-E hysteresis curves are thought to be explained by the generation of lead and oxygen vacancies as a function of the PO2.

Effect of cerium doping on the micro-structure and electrical properties of sol-gel derived Pb 1.05(Zr 0.53− δCe δTi 0.47)O 3 ( δ≤10 at.%) thin films

We have studied the effect of Ce on the phase formation behavior, surface morphology and electrical properties of sol-gel derived PZT thin films. Ce doping has been found to have a dramatic influence on the surface morphology and electrical characteristics of PZT thin films. Up to 1 at.% doping content Ce is found to improve the dielectric and ferroelectric properties and also optimal Ce doping is found to be effective in reducing the leakage current density and increasing the dielectric breakdown strength of PZT thin films. The fractional site occupancy of Ce ion has been predicted theoretically and the validity of the prediction has been investigated by XPS analysis. We have observed that Ce ions can exist both in +3 and +4 valence states. Up to 1 at.% content Ce predominantly enters into the A site with +3 valence state and acts as a donor dopant. The observed variation in microstructure and electrical properties have been discussed to be due to the fractional site occupancy of Ce ion either in A or B site, as a function of Ce doping content in PZT thin films.

Investigation of Sol-gel Derived PZT Thin Film on Stainless Steel Substrate

Investigation of Sol-gel Derived PZT Thin Film on Stainless Steel Substrate

Seeding effect on micro- and domain structure of sol–gel-derived PZT thin films

Current trend to miniaturization requires precise control of micro- and domain structure of ferroelectric materials at the nanoscale level. This is essential for future applications of ferroelectric thin films in non-volatile memories, microactuators and pyroelectric arrays. In this work, the seeding effect on the nanoscale properties of ferroelectric Pb(Zr,Ti)O 3 (PZT) thin films is investigated using scanning force microscopy (SFM) capable of simultaneously resolving topographic and domain features on the surface of the films. It is shown that the addition of 5 mol% seeds (fine PZT powder) into the sol–gel precursor solution completely modifies the film's microstructure leading to the improved morphology of the grains, reduced roughness and smaller microporosity. At the same time, significant imprint and instability of the written domain pattern is reduced due to the smaller influence of the bottom electrode interface.

High frequency measurements of P-E hysteresis curves of PZT thin films

Domain switching behavior of sol-gel derived PZT thin films at high frequencies has been investigated for ferroelectric memory applications by measuring P-E hysteresis curves as a function of frequency. The coercive field (Ec ) of the PZT thin films strongly depended on the measuring frequency, nevertheless their remanent polarization was almost independent of it. The domain switching kinetics of PZT thin films could be explained based on the nucleation-controlled model. A guideline to make FeRAM with a high operating speed was proposed based the experimental results obtained.

Effect of rare earth doping on sol-gel derived PZT thin films

We have studied the effect of rare earth dopants (Nd, Gd and Ce) on the phase formation behavior and electrical properties of sol-gel derived Pb1.05(Zr0.53Ti0.47)O3 thin films. In all these films the perovskite phase is obtained up to 5 at% doping and beyond that pyrochlore phase was found to coexist with the perovskite phase. Ce and Gd doping(1-2 at%) exhibited improved ferroelectric and dielectric properties as compared to the undoped PZT films. Nd doping (2 at%) was found to be effective to increase the retained switchable polarization of undoped PZT from 63% to 84%. The transition temperature of undoped PZT film was found to be reduced with Nd doping. The Nd doped films also exhibited typical relaxor behavior and a diffuse phase transition, characteristic of the relaxor material. Introduction of Nd into the PZT lattice probably introduces disorder in the B site of ABO3 lattice which causes the observed relaxor behavior

Dependence of texture development on thickness of single-annealed-layer in sol–gel derived PZT thin films

PbZr0.5Ti0.5O3 thin films have been prepared on Pt (111)/Ti/SiO2/Si substrates by a modified sol–gel technique. The PZT films were annealed layer by layer using a rapid thermal annealing (RTA) method during the spin-coating process. A novel route was used to obtain PZT films with different single-annealed-layer in thickness from the same precursor solution. It is found that the degree of (111) orientation of the films increases with the reduction thickness of single-annealed-layer. As the thickness of single-annealed-layer drops to 40 nm, the film shows a high degree of (111) preferred orientation. The decrease of single-annealed-layer thickness also leads to the increase of the remanent polarization and the dielectric constant.

Fatigue and dielectric properties of undoped and Ce doped PZT thin films

Ce doping improves the ferroelectric properties of sol-gel derived PZT thin films by facilitating easier domain wall movement. It also decreases the leakage current densities by reducing the concentration of free carriers through a decrease in concentration of Pb and O vacancies. Ce-PZT films retain good dielectric dispersion characteristics since the concentration of defects and defect dipoles are reduced. Ce doping dramatically improves the fatigue resistance of PZT thin films. We have studied the frequency dependence of fatigue behavior and shown that the loss of polarization due to fatigue follows a universal scaling behavior with N/f2, where N is the number of the switching cycles and f is the frequency. The origin of the scaling is attributed to the drift of oxygen vacancies, which is the rate limiting process in the growth of the interface layer responsible for fatigue. Empirical fits for both undoped and cerium doped samples show that switchable polarization follows a stretched exponential decay with time or N/f. Cerium doping is believed to improve fatigue resistance by impeding the motion of oxygen vacancies.

Effect of Reactants on the Electrical Properties of Sol-Gel Derived PZT Thin Films

Precursor solutions of lead zirconium titanates were prepared by mixing lead acetate with different combinations of zirconium and titanium alkoxides in a solvent composing of acetic acid and 2-methoxyethanol. PZT thin films were deposited on Pt/Ti/SiO2/Si substrates by spin coating and sintered at temperatures above 400°C. It was found that the crystallization behaviors and the electrical properties showed marked differences for PZT thin films prepared by different reactants. The PZT thin films prepared by the Pb(OAc)2-Zr(OPr)4-Ti(OPri)4 system exhibited superior electrical properties compared with those prepared by other combinations of reactants including the normally used Pb(OAc)2-Zr(OPri)4-Ti(OPri)4 system, which indicates that the selection of reactants has crucial impact on the electrical properties of sol-gel derived PZT thin films.