Derived PZT Thin Films Research Articles

One-axis-oriented growth of PZT thin films on transparent glass substrates using metal oxide nanosheets

Aiming at applications of ferroelectric and optical devices, we investigated the fabrication of one-axis-oriented lead zirconate titanate Pb(Zr,Ti)O3 (PZT) thin films on glass substrates with a processing temperature below the glass-transition point of the substrate. Chemical solution deposition (CSD)-derived PZT thin films with a preferential crystal orientation of (00l)/(h00)PZT were grown on an ITO/glass substrate with a crystalline buffer layer of calcium niobate Ca2Nb3O10 (ns-CN). This ns-CN buffer layer lowered the crystallization temperature of the CSD-derived thin films, resulting in crystalline PZT thin films with one-axis (00l) orientation and ferroelectricity of P r = 4 μC cm−2 deposited on transparent glass substrates at a crystallization temperature of 500 °C.

Electrochemically driven degradation of chemical solution deposited ferroelectric thin-films in humid ambient

The ambient humidity significantly accelerates the degradation of lead zirconate titanate (PZT) films in microelectromechanical systems; the cause of such degradation is under debate. Here, it is shown that the degradation of chemical solution derived PZT thin-films in humid conditions is driven by the system's electrochemical activity toward water electrolysis. The layer stacks with Pt-based electrodes exhibited a faster degradation rate owing to their higher electrocatalytic activity compared to Au. A degradation model is proposed based on the electrolysis of liquid or gaseous H2O, involving the evolution of oxygen and hydrogen gas at the top and bottom electrodes. Degradation proceeds above the threshold voltage for a given electrode system and is driven by the evolution and pressure build-up of gaseous species at the PZT/electrode interfaces. The pressure build-up causes film cracking, delamination of the film and electrodes, electrothermal breakdown events, and eventually time-dependent dielectric breakdown. Significantly larger post-breakdown crater sizes in humid than in dry conditions suggests that larger cracks through which dielectric breakdown through humidified air can occur. Overall, these effects are shown to cause sample failure up to six orders of magnitude of time earlier than for operation in dry conditions. Thus, in order to improve the resilience of thin-film systems in humid conditions, it is imperative to protect the electrochemically active electrode components of the device.

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.

Microstructure and Electrical Properties of R.F Magnetron Sputtering Derived PZT Thin Films Deposited on Interlayer for Pyroelectric IR Sensor

The PZT thin film was deposited by R.F. Magnetron sputtering with Pb 1.1Zr0.53Ti0.47O3 target. When interlayers were inserted at the between PZT and Pt, The grain growth of the PZT thin films was considerably improved by various interlayers (PbO, TiO2, TiO2/PbO) and had low-processing temperature. Compared to the pure PZT thin films, pyroelectric properties of the PZT thin films inserted by interlayers were relatively measured high value. In particular, PZT thin film deposited on interlayer(PbO) was appeared the best pyroelectric properties (P=189.4μ C/㎠K, FD=12.7×10-6Pa-1/2, FV=0.018㎡/C) respectively. As a result of XPS depth profile analysis, both PZT thin film and interlayers were confirmed as independently existing layer respectively.

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.

Microstructure and Electrical Properties of R.F. Magnetron Sputtering Derived PZT Thin Films Deposited on PbO Buffer Layer

The MFS and MFIS structures were prepared on the Si and PbO/Si substrate by the r.f. magnetron sputtering method. When the PbO buffer layer was inserted between the PZT thin film and Si substrate, the crystallization of the PZT thin films was considerably improved, and the processing temperature was lowered. Compared with the MFS structure, memory window values of the MFIS structure with the buffer layer were considerably improved. In particular, in the MFIS structure, the maximum value of the memory window is 2.0 V under the applied voltage of 9V for Pt/PZT (200 nm, 400ı)/PbO (80 nm)/Si structures with the PbO buffer layer deposited at the substrate temperature of 300ı.

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.

Microstructure and ferroelectric properties of r.f. magnetron sputtering derived PZT thin films deposited on interlayer (PbO/TiO 2)

Lead zirconate titanate (PZT) thin films were deposited on Pt/Ti/SiO 2/Si and interlayer/Pt/Ti/SiO 2/Si substrate by radio frequency (r.f.) magnetron sputtering with a Pb 1.1Zr 0.53Ti 0.47O 3 target. The crystallization of the PZT thin films was formed only by substrate temperature. When interlayer (PbO/TiO 2) was inserted between the PZT thin film and the Pt electrode, the grain growth and processing temperature of the PZT thin films were considerably improved. Compared to PZT/Pt structure, the dielectric constant and polarization properties of the PZT/interlayer/Pt structure were fairly improved. In particular, PZT/interlayer/Pt at the substrate temperature of 400 °C showed prevalent ferroelectric properties ( ɛ r=475.97, tan δ=0.0591, P r=23 μC/cm 2). As a result of an X-ray photoelectron spectroscopy (XPS) depth-profile analysis, it was found that PZT/interlayer/Pt deposited only by substrate temperature without the post-annealing process via r.f. magnetron sputtering method remained independent of each other regardless of substrate temperatures.

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.

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

Preparation and Characterization of Laser Ablation Derived PZT Thin Films for Micro Actuators

Pb (Zr0.52Ti0.48)O3(PZT) thin films with thickness of 1.8-2.0μm were fabricated using laser ablation onto Pt/Ti/SiO2/Si substrate. Crystalline phases in the PZT films were investigated by X-ray diffraction analysis (XRD). The microstructure and composition of the films were studied by scanning electron microscopy (SEM) and electron probe microanalysis (EPMA), respectively. The PZT films with well-crystallized perovskite phase were obtained by 20% excess PbO to the target and annealing at 750°C for 90min. The remnant polarization and the coercive field of this film were 23.6μC/cm2 and 60.0kV/cm, while the dielectric constant and loss values measured at 1kHz were approximately 935 and 0.04, respectively. The device of micro scanning beams and micro mirrors were successfully fabricated through the PZT film deposition, lithography, electron cyclotron resonance (ECR), reactive ion etching (RIE) and inductively coupled plasma (ICP) releasing processes. The scanning performed by applying AC voltages at resonance frequencies to the actuating bimorph beams.

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