Characterization Of PZT Thin Films Research Articles

Sol–gel synthesis and characterization of PZT thin films on FTO/aluminoborosilicate glass substrates

Sol–gel synthesis and characterization of PZT thin films on FTO/aluminoborosilicate glass substrates

Synthesis, Microstructure and Properties of Magnetron Sputtered Lead Zirconate Titanate (PZT) Thin Film Coatings

Compared to aluminum nitride (AlN) with simple stoichiometry, lead zirconate titanate thin films (PZT) are the other promising candidate in advanced micro-electro-mechanical system (MEMS) devices due to their excellent piezoelectric and dielectric properties. The fabrication of PZT thin films with a large area is challenging but in urgent demand. Therefore, it is necessary to establish the relationships between synthesis parameters and specific properties. Compared to sol-gel and pulsed laser deposition techniques, this review highlights a magnetron sputtering technique owing to its high feasibility and controllability. In this review, we survey the microstructural characteristics of PZT thin films, as well as synthesis parameters (such as substrate, deposition temperature, gas atmosphere, and annealing temperature, etc.) and functional proper-ties (such as dielectric, piezoelectric, and ferroelectric, etc). The dependence of these influential factors is particularly emphasized in this review, which could provide experimental guidance for researchers to acquire PZT thin films with expected properties by a magnetron sputtering technique.

Preparation and characterization of PZT thin films deposited on PZT buffer layer with different lead content

ABSTRACTLead zirconate titanate (PZT) thin films deposited on Pt electrode and Pb1+x(Zr0.52,Ti0.48)O3 (x = 0.10, 0.15, 0.25, 0.30) buffer layer have been prepared by sol-gel methods to investigate the effects of lead content in the buffer layer on crystalline orientation, electric and fatigue properties of PZT films. XRD and SEM showed that all films exhibited dense perovskite structure with (100) preferential orientation. The maximum dielectric constant (1571 at 100 Hz) was obtained in the PZT film with buffer layer containing 25% excess lead, which increased by 42.5% compared with the film without buffer layer. Fatigue resistance was improved by introducing buffer layer.

High resolution X-ray and electron microscopy characterization of PZT thin films prepared by RF magnetron sputtering

Pb(Zr0.52Ti0.48)O3 (PZT) thin films grown on Pt/TiO2/SiO2/Si(1 0 0) substrates in the thickness range of ∼30–550 nm by radio frequency (RF) magnetron sputtering method under different sputtering pressures were studied in the present work. High resolution grazing incidence X-ray diffraction method for residual stress and electron microscopy, particularly cross sectional transmission electron microscopy (XTEM), were used to identify the crystalline phases, and structure of the thin films at the nano-scale. Microstructure of the ultrathin films in <50 nm thickness range, consists predominantly of para-electric, oxygen deficient pyrochlore phase of Pb2Ti2O6 structure co-existing with ferroelectric perovskite PZT phase in tetragonal form. In films with thickness around 500 nm, sputtering pressure shows a strong influence on the purity of PZT phase grown. High resolution X-ray diffraction method for wafer curvature measurement and Stoney's equation were used to evaluate the biaxial stress in the films. It is found that the ultrathin films are compressively stressed with high magnitude of the order of 2 GPa which gets reduced with increasing film thickness. In the thickness range of ∼500 nm, at an optimum sputtering pressure of 4.5 Pa, the stress becomes tensile in nature with a small magnitude of 2.3 MPa. At this pressure, the film consists of almost pure perovskite phase and comparatively better electrical characteristics. X-ray reflectometry study indicates very low density of PZT films with an interlayer formed at the interface with Pt. XTEM study throws valuable insight into the nano-scale structure and reveals the presence of nano-porosity along the interface as well as within the film microstructure. This has been attributed to the observed interface roughness, reduced density, tensile residual stress as well as the poor ferroelectric properties encountered.

Synthesis and Characterization of PZT Thin Films Embedded with WO3 Nanoparticles by a Hybrid Chemical Solution Route

PZT thin films embedded with WO3 nanoparticles were prepared by a hybrid chemical solution process. WO3 at 0, 0.1, 0.2, 0.3, 0.4, 0.5 and 1 wt% nanopowders were suspended in an organometallic precursor solution of PZT, and then coated on platinized silicon substrate using spin-coating technique. The increase of WO3 resulted in a reduction of densification of the films. However, at 1 wt% WO3 concentration, the reaction between PZT and WO3 occurred during heat-treatment process at 600°C and seemed to improve the film's density. The WO3 nanoparticles were also found to affect both dielectric and ferroelectric properties of PZT films. Moreover, the addition of WO3 nanoparticles was found to improve a fatigue phenomenon in ferroelectric PZT thin films.

Mechanical properties of sol–gel derived lead zirconate titanate thin films by nanoindentation

Lead zirconate titanate (PZT) thin films are deposited on platinized silicon substrate by sol–gel process. The crystal structure and surface morphology of PZT thin films are characterized by X-ray diffraction and atomic force microscopy. Depth-sensing nanoindentation system is used to measure mechanical characteristics of PZT thin films. X-ray diffraction analyses confirm the single-phase perovskite structures of all PZT thin films. Nanoindentation measurements reveal that the indentation modulus and hardness of PZT thin films are related with the grain size and crystalline orientation. The increases of the indentation modulus and hardness with grain size are observed, indicating the reverse Hall–Petch effect. Furthermore, the indentation modulus of (1 1 1)-oriented PZT thin film is higher than those of (1 0 0)- and random-oriented films. The consistency between experimental data and numerical results of the effective indentation moduli for fiber-textured PZT thin films using Voigt–Reuss–Hill model is obtained.

Phase evolution and effect of pre-heating temperature on the characteristics of PZT thin films grown by using a triol sol--gel route

Lead zirconate titanate (PZT) films were fabricated on Pt(111)/Ti/SiO2/Si(100) using the triol sol--gel method. The effect of the pre-heating temperature on the phase transformations, microstructures, electrical properties and ferroelectric properties of the PZT thin films was investigated. Randomly-oriented PZT thin films pre-heated at 400°C for 10 min and annealed at 600°C for 30 min showed well-defined ferroelectric hysteresis loops with a remanent polarization of 26.57 µC cm−2 and a coercive field of 115.42 kV cm−1. The dielectric constant and dielectric loss of the PZT films were 621 and 0.0395, respectively. The microstructures of the thin films are dense, crack-free and homogeneous with fine grains about 15–20 nm in size.

Nano-tribological characteristics of PZT thin film investigated by atomic force microscopy

In this work, the nano-scale tribological characteristics of PZT thin films (Pb(Zr x Ti 1 − x )O 3: PZT) with various Zr/Ti ratios were investigated using an Atomic Force Microscope (AFM). The PZT thin films deposited by the sol–gel method were characterized by using an AFM, X-Ray Diffraction (XRD), and a nano-indentation technique. From the experimental results, the friction coefficient of the PZT thin film was found to be about 0.1–0.2 under a 0.1–10 μN normal force. It was determined that the wear rate of the PZT thin film was in the order of 10 − 8 mm 3/N·cycle. Also, it was observed that the crystalline structure of the PZT was amorphized due to mechanical stress.

Extensive electromechanical characterization of PZT thin films for MEMS applications by electrical and mechanical excitation signals

In this work we present a unique measurement method to estimate the effective transverse piezocoefficient e31,f of piezoelectric thin films which is often used in micro electromechanical systems (MEMS). This method utilizes basically a 4-point bending setup specially adapted to be used with thin film samples. It allows the application of very homogeneous well defined mechanical stresses to the device. Stress and corresponding strain distribution are verified by Finite Element simulations. Measurements are shown to demonstrate the capability and repeatability of the setup on sol-gel processed PZT thin film samples. In conjunction with additional measurement results it is possible to fully determine the electromechanical characteristics.

The effect of LaNiO 3 buffer layer thickness on the electric properties of Pb(Zr 0.53Ti 0.47)O 3 thin films deposited on titanium foils

Sol-gel derived Pb(Zr 0.53Ti 0.47)O 3 (PZT) thin films were prepared on LaNiO 3 (LNO) buffered titanium foils. The effect of LNO buffer layer thickness on the electric properties of PZT thin films was investigated. The room temperature dielectric constant of PZT thin films increased with increasing LNO thickness. The remnant polarization of PZT thin films on 150 and 250 nm LNO was about 20 uC/cm 2. Curie temperatures of PZT thin films were 310, 330 and 340 °C for LNO of 250, 150 and 50 nm respectively. The current-voltage characteristics of PZT thin films were examined for different LNO buffer layer thicknesses, and the space charge limited conduction model was followed in PZT thin films on 50 nm LNO.

Preparation and Characterization of PZT Thin Films on ITO/Glass Substrate by CSD

This paper describes the deposition of PZT thin films on soda-lime glass substrate with ITO bottom electrode by CSD (Chemical Solution Deposition). The transmittance of the obtained PZT thin film on ITO/glass substrate was about 60 % in the visible light region. The deposited transparent PZT thin film exhibited the ferroelectricity of Pr=36.3 μC/cm2 and Ec=71.3 kV/cm. In addition, the piezoelectric property of the resultant PZT thin film was relatively large and exhibited the measured effective d33 of 120 pC/N after the polarization.

Interface Effects on Fatigue Properties of Pt/PZT/Pt Thin Film Capacitors

To investigate the mechanism of the polarization fatigue of ferroelectric thin films, we analyzed the relationship between the crystalline defects of electrode/ferroelectric interface and fatigue characteristics of PZT thin films. Pt/PZT/Pt thin films were prepared by the chemical solution deposition method, and conditions of Pt/PZT interface were analyzed by TEM-EDX analysis, thermally stimulated current methods and I-V Properties. The PZT layers of about 30nm near the top Pt electrodes became an n-type due to the oxygen vacancies and they formed the contact similar to the top electrode of Pt/n-type PZT/p-type PZT. Because the height and width of the Schottky barrier in the Pt/PZT interface had reduced with the increase of the fatigue, this band structure was observed in the electric field where the Fowler-Nordheim currents were lower than usual. This is considered to be caused by the increase of crystalline defects near the interface due to the impressing of the bipolar pulse. This phenomenon was observed quantitatively by TSC analysis, and the TSC peak of 490K became larger with the increase of the fatigue. The activation energy of the TSC peak was 0.8ev and the defect density was 2.5×1019/cm3, which is consider to be produced by Pb defects.

Comparison of the effect of PLT and PZT buffer layers on PZT thin films for ferroelectric materials applications

In order to study the effect of different buffer layers on the Pb(Zr0.52Ti0.48)O3 (PZT) thin films, 10-nm thick (Pb0.72La0.28)Ti0.93O3 (PLT) and Pb(Zr0.52Ti0.48)O3 buffer layers have been deposited on the Pt(1 1 1)/Ti/SiO2/Si substrates by pulsed laser deposition, respectively. The top buffer layers were also deposited on PZT thin films with the same thickness of the seed layers in order to enhance the fatigue characteristics of PZT thin films. We compared the results of dielectric constant, hysteresis loops and fatigue resistance characteristics. It was found that the dielectric properties of PZT thin films with PLT buffer layers were improved by comparing with PZT thin films with PZT buffer layers. The polarization characteristics of PZT thin films with PLT buffer layers were observed to be superior to those of PZT thin films using PZT buffer layers. The remanent polarization of PZT thin films showed 36.3 μC/cm2 and 2.6 μC/cm2 each in the case of use PLT and PZT buffer layers. For the switching polarization endurance analysis, PZT thin films with PLT buffer layers showed more excellent result than that of PZT thin films with PZT buffer layers.

Fatigue Characteristics of PZT Thin Films Deposited by ECR-PECVD

Fatigue characteristics of lead zirconate titanate (PZT) films deposited by electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR-PECVD) were investigated. The fatigue characteristics were investigated with respect to PZT film thickness, domain structure, fatigue pulse height, temperature, electrode materials and electrode configurations. The used top and bottom electrode materials were Pt and <TEX>$RuO_2$</TEX>. In the fatigue characteristics with fatigue pulse height and PZT film thickness, the fatigue rates are independent of the applied fatigue pulse height at the electric field regions to saturate the P-E hysteresis and polarization <TEX>$(P^*,\;P^A)$</TEX> characteristics. The unipolar and bipolar fatigue characteristics of PZT capacitors with four different electrode configurations <TEX>$(Pt//Pt,\;Pt//RuO_2,\;RuO_2//Pt,\;and\;RuO_2//RuO_2)$</TEX> were also investigated. The polarization-shifts during the unipolar fatigue and the temperature dependence of fatigue rate suggest that the migration of charged defects should not be expected in our CVD-PZT films. It seems that the polarization degradations are attributed to the formation of charged defects only at the Pt/PZT interface during the domain switching. The charged defects pin the domain wall at the vicinity of Pt/PZT interface. When the top and bottom electrode configurations are of asymmetric <TEX>$(Pt//RuO_2,\;RuO_2//Pt)$</TEX>, the internal fields can be generated by the difference of charged defect densities between top and bottom interfaces.

Effect of PLT Buffer Layers on the PZT Thin Films for Scaling-Down Ferroelectric Materials

AbstractThe Hysteresis characteristics of below 400 nm- thick Pb(Zr0.52Ti0.48)O3 (PZT) thin films grown on Pt (111) /Ti/SiO2/Si substrates have showed very poor with remanent polarization of 1∼3 μC/cm2 in our previous research. To study the further scaling-down, we introduced the method of our previous research that the (Pb0.72La0.28)Ti0.94O3 (PLT) buffer layers play an important role in enhancing the ferroelectric properties of the PZT thin films. As a result, the remanent polarization of 300 nm-thick PZT thin films with the 10 nm-thick PLT buffer layers have showed 32 μC/cm2 at applied voltage of 8 V and 24 μC/cm2 at applied voltage of 5 V. Inserted the PLT seed layers between the PZT thin films and substrate, the hysteresis characteristics of PZT thin films were improved a lot. The dielectric and leakage current properties of PZT thin films were also investigated.

Optical characterization of PZT thin films for waveguide applications

In order to develop an electro-optic waveguide, Pb(Zr, Ti)O 3 ceramic ferroelectric thin films were elaborated by a modified sol–gel process on glass substrate. In the aim to study the optical properties of the PZT films, an accurate refractive index and thickness measurement apparatus was set up, which is called M-lines device. An evaluation of experimental uncertainty and calculation of the precision of the refractive index and thickness were developed on PZT layers. Two different processes of PZT elaboration were made and studied with this apparatus. The reproducibility of one fabrication process was tested and results are presented in this paper.

Study on the etching damage characteristics of PZT thin films after etching in Cl-based plasma

In present work, we carried out the investigations of plasma-induced etching damage for the PZT thin films etched using the various Cl-based gas chemistries. The basic gas mixture was Cl 2/CF 4 (8/2) while Ar or O 2 were used as the additive gases (up to 20%). It was found that the etching in Cl 2/CF 4/Ar plasma provides higher a rate but degrades the remnant polarization more compared with Cl 2/CF 4/O 2 plasma. X-ray photoelectron spectroscopy showed the contamination of the etched surfaces by ZrCl x for both gas mixtures. The Auger electron spectroscopy and X-ray diffraction analyses show that Cl 2/CF 4/Ar plasma provides more significant etching damage, which cannot be recovered by the O 2 annealing. For the Cl 2/CF 4/O 2 plasma, annealing under the O 2 atmosphere helps to restore the ferroelectric properties resulting in good recovering of the remnant polarization.

Ferroelectric Properties of Highly (111) Oriented Pb(Zr0.4Ti0.6)O3 Thin Films Fabricated Using Sol-Gel Process

The well-crystallized and highly (111)-oriented Pb(Zr0.4Ti0.6)O3(PZT) thin films were prepared using sol-gel process. The P-V curves and switching current characteristics of PZT thin films were investigated as a function of annealing temperature. With increasing the annealing temperature from 400°C to 700°C, the P-V hysteresis loop became more rectangular shaped, the remnant and saturated polarizations increased, and the activation field decreased. The remnant polarization (P r ) of the film annealed at 400°C and 700°C was 23 μC/cm2 and 29 μC/cm2, respectively. The switching current behavior depending on the annealing temperature was successfully observed. The value of activation field (α) decreased from 422 ± 27 kV/cm to 339 ± 28 kV/cm with increasing the annealing temperature. These ferroelectric properties of highly (111)-oriented PZT films were discussed in terms of the change in the grain size and domain configuration.

Preparation and characterization of PZT thin films deposited by pulsed laser deposition on template layer

Pb(Zr x Ti 1− x )O 3 thin films were prepared by pulsed laser deposition using the target of Pb(Zr 0.45Ti 0.55)O 3 with excess PbO (20 wt.%) on Pt/Ti/SiO 2/Si(100) substrates with and without a template layer derived by the sol-gel process. Crystalline phases and microstructure of the PZT films were investigated using X-ray diffraction analysis and scanning electron microscopy, respectively. The electrical properties of the PZT films were evaluated by measuring the polarization versus electric field hysteresis loop and the dielectric constant. In comparison with the experimental results, it was found that the template layer derived by the sol-gel process could effect the crystallographic orientation, and improve the electrical properties of the PZT films. It is clear that 1–3 μm thick films with good electrical properties can be fabricated by the pulsed laser deposition process on the template layer in a shorter time.

Plasma-induced damage in PZT thin films etched by inductively coupled plasma

We investigated the etching damage induced by Ar/(Cl 2+CF 4) plasma and improvement in etching damage by O 2 annealing. PZT thin films were etched for 1 min in an ICP using a gas mixture of Cl 2 80%/CF 4 20% with 20% Ar addition. The etching conditions were fixed at a substrate temperature of 30 °C, RF power of 700 W, DC bias voltage of −200 V and a chamber pressure of 15 mTorr. To improve the ferroelectric properties of PZT thin films after etching, the samples were annealed for 10 min at 600 °C in O 2 atmosphere. After O 2 annealing, the remanent polarization-on-fatigue property was recovered to the characteristics of the as-deposited film. According to X-ray diffraction (XRD) analysis, an increase in (100) and (200) phases showed the improvement in structure of the PZT thin films after the O 2 annealing process. In addition, transmission electron microscope (TEM) images showed that the etched PZT surface is damaged by the bombardment of energetic particles, but that the damaged surface can be recovered by O 2 annealing. The results of electron probe microanalysis (EPMA) and Auger electron spectroscopy (AES) showed that O 2 annealing supports the substitution of oxygen vacancies on the PZT surface by O atoms. This decrease in oxygen vacancies improves the fatigue characteristics of PZT thin films.