Properties Of PZT Thin Films Research Articles

Bottom Electrode Effects on Piezoelectricity of Pb(Zr0.52,Ti0.48)O3 Thin Film in Flexible Sensor Applications

Piezoelectric thin films grown on a mechanical, flexible mica substrate have gained significant attention for their ability to convert mechanical deformation into electrical energy though a curved surface. To extract the generated charge from the PZT thin films, bottom electrodes are typically grown on mica substrates. However, this bottom electrode also serves as a buffering layer for the growth of PZT films, and its impact on the piezoelectric properties of PZT thin films remains understudied. In this work, the effect of Pt and LaNiO3 bottom electrodes on the piezoelectric effect of a Pb(Zr0.52,Ti0.48)O3 thin film was investigated. It was observed that the PZT thin films on LNO/Mica substrate possessed weaker stress, stronger (100) preferred orientation, and higher remanent polarization, which is beneficial for a higher piezoelectric response theoretically. However, due to insufficient grain growth resulting in more inactive grain boundaries and lattice imperfections, the piezoelectric coefficient of the PZT thin film on LNO/Mica was smaller than that of the PZT thin film on a Pt/Mica substrate. Therefore, it is concluded that, under the current experimental conditions, PZT films grown with Pt as the bottom electrode are better suited for applications in flexible piezoelectric sensor devices. However, when using LNO as the bottom electrode, it is possible to optimize the grain size of PZT films by adjusting the sample preparation process to achieve piezoelectric performance exceeding that of the PZT/Pt/Mica samples.

Improving the microstructure and properties of PZT thin films via annealing prepared by RF magnetron sputtering using Pb(Zr0.52Ti0.48)O3 target

PZT thin films are one of the most effective materials attractive for MEMs applications. In this research, high-quality PZT thin films were deposited on (111)Pt/Ti/SiO2/(100)Si substrates by RF magnetron sputtering from a Pb(Zr0.52Ti0.48)O3 ceramic target. The sputtered PZT films with deposition times of 90 min–180 min were annealed at different temperatures; 550°C-700 °C. The results indicated that the film's crystallinity, density, and morphology were affected by the sputtering time and the annealing conditions due to grain growth. Post-annealing improved the microstructure and properties of PZT thin films. The increase in annealing temperatures virtually caused the decrease of PZT thin-film thickness. Densification and PZT grain size were found to increase with increasing annealing temperatures. The XRD and SEM results demonstrated that the PZT thin films were well-crystallized and contained a uniform grain distribution. With sputtered time of 90 min, 120 min, 150 min, and 180 min, the thickness of PZT thin films were 168 nm, 228 nm, 266 nm, and 275 nm, respectively. WDS results showed that the atomic percentages of zirconium content decreased by increasing annealing temperature. At the 180 min-sputtered time, the remaining lead content after annealing temperatures of 550°C–700 °C showed an estimated 1.0 at%. Increased annealing temperatures affected significantly lead loss due to volatilization. The surface roughness was confirmed by AFM analysis of the proposed systems. The roughness values of films increased from 1.28 nm to 4.25 nm with increasing annealing temperature. The dielectric functions (ε1) and (ε2) of sputtered PZT thin films at different annealed temperature and different thicknessess were analyzed by Spectroscopic Ellipsometry (SE). The (ε1) and (ε2) of as-deposited PZT thin film showed different dispersion shapes, and (ε2) amplitude was shifted to the lower photon energy in comparison with annealed PZT thin films, which can correspond to differences in the crystal structure.

Robust ferroelectricity enhancement of PZT thin films by a homogeneous seed layer

With its excellent ferroelectric properties such as large dielectric constant and large remanent polarization, PZT thin films are extensively used in micro-sensors and other devices. In this study, the sol–gel process was used to fabricate Pb(Zr0.52Ti0.48)O3 thin films with Pb(ZrxTi1–x)O3 seed islands. The experimental consequences demonstrate that all the Pb(Zr0.52Ti0.48)O3 thin films with Pb(ZrxTi1−x)O3 seeds show pure perovskite phase with no other impurity phases, and the electrical properties of Pb(Zr0.52Ti0.48)O3 thin films modified by Pb(ZrxTi1–x)O3 seed islands with different Zr/Ti ratios are improved, such as remanent polarization increased, dielectric properties increased, coercive electric field decreased, leakage current density decreased. In particular, the electrical properties of the Pb(Zr0.52Ti0.48)O3 thin films with Pb(ZrxTi1–x)O3 seed islands are the most optimal when the x is 0.52. This paper provides a new technique for optimizing the electrical properties of PZT thin films, which is of great significance for breaking through the bottleneck of the development of ferroelectric memory.

Effects of Annealing Temperature on Crystal Structure and Microstructure of PZT Thin Films (52/48) Prepared by RF Magnetron Sputtering

In this research, the effects of annealing temperatures on the crystallization and morphology of Pb(Zr0.52Ti0.48)O3 (PZT) thin films on (111) Pt/Ti/SiO2/(100)Si and (111) Au/Cr/(100)Si substrates prepared by RF magnetron sputtering were investigated. Two types of thin films: PZT/Pt/Ti/SiO2/Si and PZT/Au/Cr/Si were obtained from a Pb(Zr0.52Ti0.48)O3 ceramic target and were annealed at different temperatures of 600 °C, 650 °C, and 700 °C for 1 h, in air, with heating rate of 5 °C/min. The XRD studies showed that the crystal structures of the PZT thin films could be affected by varying annealing temperatures. The annealed PZT thin films exhibited perovskite structures that crystallographic orientations increased remarkably with annealing temperatures. Phases of PZT thin films on two types of substrates oriented differently. The FE-SEM images along with energy dispersive spectroscopy (EDS) studies confirmed the homogeneous and compact films. The increase of annealing temperatures virtually caused the decrease of PZT thin-film thickness, increase of densification of the films, and increase of PZT grain size. Moreover, the phase composition state of the PZT thin films changed quantitatively with increase in annealing temperatures. The dielectric, ferroelectric and piezoelectric properties of PZT thin films will be further investigated.

Irradiation behavior and recovery effect of ferroelectric properties of PZT thin films* *Project supported by the National Natural Science Foundation of China (Grant No. 51802056), the Science Foundation of the National Key Laboratory of Science and Technology on Advanced Composites in Special Environments, and the Key Laboratory of Micro-systems and Micro-structures Manufacturing (Harbin Institute of Technology), Ministry of Education, China.

Lead zirconate titanate piezoelectric ceramics have important applications in space and aerospace technology, but the effect and physical mechanism of charged particle radiation on their performance yet to be clarified. In this study, we characterized PbZr0.52Ti0.48O3 (PZT) thin films, and changes in the ferroelectric properties of the films before and after electron and proton irradiation were investigated. The natural and heat treatment recoverability of the ferroelectric properties were studied, and the damages and mechanisms of different types of radiation in PZT films were also investigated. The results show that, in addition to ionization damages, electron irradiation causes certain structural damage on the PZT film, and the large structural damage caused by proton irradiation reduces drastically the ferroelectricity of the PZT film.

Effect of Ba(Mg1/3Nb2/3)O3 buffer layer on electrical properties of PZT-based films

Pb[Nbx(Zr0.52Ti0.48)1−x]O3 (PNZT) thin films were deposited on Pt/Ti/SiO2/Si(100) by the sol–gel method using Ba(Mg1/3Nb2/3)O3 (BMN) buffer layer. The effects of Nb doping and BMN buffer layer on fatigue endurance and ferroelectric properties of PZT thin film were investigated. The optimum ferroelectric properties of PNZT film: Pr = 43.4 µC/cm2, Ec = 29.3 kV/cm and J = 2.73 × 10− 6 A/cm2 were obtained by doping 3 mol% Nb in PZT film. After 1010 cycles, the Pr of PZT film reduces by 50%. After 1012 cycles, the Pr of PNZT film only reduces by 20%. The reason for enhanced ferroelectric properties and fatigue endurance of PNZT thin film is that Nb doping effectively prevents the generation of oxygen vacancies. The Pr of the PNZT/BMN film remains 85% after 1010 cycles, and it remains stable even till to 1012 cycles. Moreover, the leakage current of PNZT/BMN film is 5.40 × 10− 7 A/cm² under 100 kV/cm electric field, which is about one order of magnitude lower than that of PNZT (2.73 × 10− 6 A/cm²). The effect of BMN on improving the fatigue endurance and ferroelectric properties of PNZT thin film could be ascribed to blocking of Pt diffusion at the PNZT–Pt interface. Moreover, PNZT/BMN film with excellent ferroelectric and fatigue endurance shows the promising application in FeRAM.

On the influence of pyrochlore phase on ferroelectric and dielectric properties of PZT thin films

The intrinsic contribution of dielectric permittivity was obtained in thin films of PZT pyrolyzed at different temperatures. Pyrochlore phases were observed in films pyrolyzed at temperatures above 350 °C, while only the perovskite phase grows in films pyrolyzed at temperatures lower than 300 °C. Dielectric and ferroelectric properties were characterized, and their behaviors were related to pyrolysis temperature. The dielectric permittivity dependence on the bias electric field was investigated at room temperature for different PZT thin films, and these curves were used to reconstruct the hysteresis loops. In this work, a model was used to reconstruct the hysteretic behavior of the films. The experimental results are in excellent agreement with the applied model.

Adjustable response of PZT thin film based piezoelectric micro-actuator through DC bias pre-polarization

PZT piezoelectric thin film based technology is promising in the field of micro-actuators. This paper discusses the effects of pre-polarization on the key properties of PZT thin film, and explores the improvement rules of pre-polarization from the material to device level experiments. At the material level, the pre-polarization treatment increases the piezoelectric strain coefficient by 25%, and improves dielectric properties. Meanwhile, in ferroelectric properties the pre-polarization treatment increases the residual polarization by 50% and coercive field by 25%, respectively. At the device level, pre-polarization treatment greatly increases the output characteristics of the devices, such as maximum output displacement increasing by at least 45% and withstand voltage enhancing by 2 V, which is consistent with the material level enhancement. In addition, the optimal pre-polarization process conditions and the long-term stability of the performance improvement are investigated. The pre-polarization treatment has proved to be meaningful for the improvement of the output capability of the piezoelectric thin film actuators.

Enhancement of relaxor behavior by La doping and its influence on the energy storage performance and electric breakdown strength of ferroelectric Pb(Zr0.52Ti0.48)O3 thin films

La-doped Pb1-xLax(Zr0.52Ti0.48)O3 (PLZT) thin films with dopant concentrations of up to 12% were fabricated on (111)Pt/Ti/SiO2/Si substrates by a sol-gel spin-coating method to investigate the effects of La content on the phase transition, ferroelectric and energy-storage performance properties of PZT thin films. The compositional-induced relaxor behavior was increased with the doping of La, due to the presence of polar nano-regions (PNRs). The existence of PNRs in the relaxor ferroelectric, as opposed to the microscopic long-range ordered domains in the normal ferroelectric, induced the difference between the polarizations of the normal and relaxor ferroelectrics. The results indicated that the decrease in remanent polarization and coercive field in the PLZT thin films with increasing La content was associated with the phase transition from normal ferroelectric behavior in undoped PZT to relaxor behavior in PLZT thin films due to the substitution of Pb2+ ions by La3+ ions. The maximum recoverable energy-storage density (27.5 J/cm3) and efficiency (62.2%) were obtained for the 8% La-doped film due to the large electric breakdown strength (2200 kV/cm) and slimmer polarization hysteresis loop. Because of the thinner films (250 nm), the low driven voltage of 55 V can be used to charge the thin film capacitors to obtain the above energy-storage properties. Moreover, an excellent charge-discharge cycling life with fatigue-free performance up to 1010 cycles was also realized in the thin films. All of the excellent results indicated that the relaxor PLZT thin films with 8% La doping possess excellent potential for low voltage operation advanced capacitors with high energy-storage performance.

Study of acetic acid addition on properties of PZT films prepared by sol–gel method

In order to improve the property of PZT, a method of adding acetic acid was proposed in this paper, and the effects of acetic acid addition on the crystal orientation, microstructures, leakage current, dielectric and ferroelectric properties of PZT thin films were investigated. The Pb1.1(Zr0.53Ti0.47)O3 (1 µm) thin film samples with acetic acid were prepared on Pt(111)/Ti/SiO2/Si(100) substrate by sol–gel method. The addition of acetic acid (36%) in the 0.025 mol PZT solution are 0 ml, 10 ml, 15 ml, 20 ml, respectively. All samples obtained dense columnar perovskite structures. X ray diffraction (XRD) analysis showed that the addition of 15 ml acetic acid made the orientation of the (110) crystals the highest, and the maximum leakage current decreased from 1.19 × 10−9 to 9.08 × 10−10 A. The relative dielectric constant reached 1034 at 100 Hz, which was 10% higher than the PZT film without acetic acid. For ferroelectric properties, the + Pr increased from 14.1 to 17.0 µC/cm2, and the −Pr increased from 8.1 to 11.9 µC/cm2.

Mechanism of grain growth and excellent polarization, dielectric relaxtion of La3+, Nd3+ modified PZT nano-films prepared by sol–gel technique

Ferroelectric PbZr0.52Ti0.48O3 film and its partial substitutions by rare earth ions La3+ and Nd3+ Pb0.9(La/Nd)0.1Zr0.52Ti0.48O3, grown on Pt(111)/Ti/SiO2/Si(100) substrates, were prepared via sol–gel and rapid thermal processes. Structural characterization by X-ray diffraction and scanning electron microscopy showed that Pb(Zr0.52Ti0.48)O3 and Pb0.9La0.1(Zr0.52Ti0.48)O3 films are of (111) preferred orientation but Pb0.9Nd0.1(Zr0.52Ti0.48)O3 is more inclined to (100) reflection though both are of tetragonal perovskite structure. The results indicate that the piezoelectric properties of PZT thin films can be improved by doping La3+ and Nd3+ substituted A-site. The d33 can be dramatically improved by doping La3+. Moreover, Pr of Pb(Zr0.52Ti0.48)O3 films reaches up to 120.53 µC/cm2, while the doping samples present relatively inferior ferroelectric hysteresis loops (PrLa = 64.32, PrNd = 53.17 µC/cm2), greater dielectric constants, higher dielectric loss and lower leakage current than the undoped Pb(Zr0.52Ti0.48)O3 sample. And meanwhile, the samples showed a typical non-Debye dielectric spectroscopy of multiple quantum relaxation time distribution observing from the Cole–Cole plot at room temperature.

Effect of La and W dopants on dielectric and ferroelectric properties of PZT thin films prepared by sol–gel process

La or W-doped lead zirconate titanate thin films (PLZT or PZTW) were prepared on platinized silicon substrates by sol–gel process. The effects of La or W dopant on the phase development, microstructure, dielectric and ferroelectric characteristics of films were studied. For PLZT films, the optimum doping concentration was found to be 2 mol%. While for PZTW films, the dielectric and ferroelectric properties were found to be improved as the doping concentration increased. The fatigue properties of PLZT and PZTW thin films were also investigated, the results showed that A- or B-site donor doping could improve the fatigue properties of PZT thin films. The theory of oxygen vacancy was used to explain the performance improvement caused by donor doping.

Effect of La doping on crystalline orientation, microstructure and dielectric properties of PZT thin films

Abstract Lanthanum (La)-modified lead zirconate titanate (PLZT) thin films with doping concentration from 0 to 5 at.-% have been fabricated by sol-gel methods to investigate the effects of La doping on crystalline orientation, microstructure and dielectric properties of the modified films. The characterization of PLZT thin films were performed by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and precision impedance analysis. XRD analysis showed that PLZT films with La doping concentration below 4 at.-% exhibited (100) preferred orientation. SEM results indicated that PLZT films presented dense and columnar microstructures when La doping concentration was less than 3 at.-%, while the others showed columnar microstructures only at the bottom of the cross section. The maximum dielectric constant (1502.59 at 100 Hz) was obtained in a 2 at.-% La-doped film, which increased by 53.9 % compared with undoped film. Without introducing a seed layer, (100) oriented PLZT thin films were prepared by using conventional heat treatment process and adjusting La doping concentration.

Effect of seed layer with low lead content on electrical properties of PZT thin films

Abstract

Enhanced dielectric and ferroelectric properties of PZT thin films derived by an ethylene glycol modified sol–gel method

PbZr0.52Ti0.48O3 thin films on stainless steel substrates were fabricated by an ethylene glycol modified sol–gel method. Perovskite structure of PbZr0.52Ti0.48O3 thin films was examined by the X-ray diffraction analysis. With the increase of ethylene glycol, PbZr0.52Ti0.48O3 thin films with enhanced dielectric and ferroelectric properties were got. Crack-free PbZr0.52Ti0.48O3 thin films with thickness of 1.6 μm were prepared for ethylene glycol content of 50%, and the dielectric permittivity and dielectric loss were 224 and 5.4% respectively at the frequency of 1 kHz showing better dielectric properties compared with PbZr0.52Ti0.48O3 thin films without ethylene glycol modified. The remnant polarization (P r) of 50% content ethylene glycol modified PbZr0.52Ti0.48O3 thin films was nearly twice reaching 12.3 μC/cm2, and lower leakage current density was obtained with 4.6 × 10−6 A· cm−2 under the field of 50 kV· cm−1. Such enhanced performance indicated that the PbZr0.52Ti0.48O3 thin films prepared on stainless steel substrates by the ethylene glycol modified sol–gel process exhibited their potentiality in applications.

Effect of sol temperature on structural, morphological and magnetic properties of PZT thin films on alumina substrate

In the present study, we investigate the structural, morphological and magnetic properties of sol–gel spin-coated PZT thin films on alumina substrate. The morphotropic phase boundary (MPB) of PZT [Pb (Zr1−xTix)03] between the tetragonal and rhombohedral phases occurs at the Zr/Ti ratio of 52/48. At the MPB the physical properties of PZT are of far-reaching importance due to their possible crystalline phases. In this study Pb(Zr0.52Ti0.48)03 sols are prepared at room temperature and at 125 °C. The gels are coated onto alumina substrate using a spin-coating unit as two and three layers. The structural studies using XRD confirm the perovskite phase formation at an annealing temperature of 660 °C for both films. The structural parameter grain size, dislocation density, lattice parameters and strain were dependent on the sol temperature. The SEM morphology of the samples represents well-developed dense grain structure and thickness in micrometer ranges. The VSM analysis shows diamagnetic and ferromagnetic hysteresis loop. The ferromagnetism at low fields in PZT films is confirmed by studying the magnetic properties of powder made of the same gel. The effect of heat treatment on the gel preparation is observed on structural, morphological and magnetic properties of PZT thin films. The ferromagnetism in PZT can be attributed to oxygen vacancies. The squareness ratio of the films shows the application of the films as a high-density recording medium.

Influence of oxygen partial pressure on the properties of PZT thin film deposited by RF magnetron sputtering

In magnetron sputtering systems, lead-zirconium-titanium oxide (PbZr1−xTixO3 or PZT) thin films were prepared in a mixture atmosphere of Ar and O2 with various oxygen partial pressures (0, 0.5, 1, 1.5 and 2% oxygen). About 600 nm PZT ferroelectric thin films were deposited on substrates, and then annealed at 600°C for 35 s. The structural, electrical and ferroelectric properties of PZT films were studied. As the oxygen partial pressure increased, the remanent polarisation rose first and went down later, and the leakage current density decreased first and then increased. At the oxygen partial pressure of 0.5%, we obtained the largest remanent polarisation and the minimum leakage current density. The XRD diffraction spectrum of all films displayed predominant (111) preferred orientation, and there was a weak XRD diffraction peak of pyrochlore phase in the PZT films deposited in pure Ar.

Improvement in temperature dependence and dielectric tunability properties of PbZr0.52Ti0.48O3 thin films using Ba(Mg1/3Ta2/3)O3 buffer layer

In this paper, Pb(Zr0.52Ti0.48)O3 (PZT) thin films were prepared via sol-gel method. The effects of Ba(Mg1/3Ta2/3)O3 (BMT) buffer layer on the temperature dependence and dielectric tunability properties of PZT thin films were studied. As the thickness of BMT buffer layer increases, the tan δ and tunability of PZT thin films decrease while tunability still maintains above 10%. This result shows that BMT buffer layer can improve the dielectric tunability properties of PZT thin films. Furthermore, the temperature coefficient of the dielectric constant decreases from 2333.4 to 906.9ppm/°C with the thickness of BMT buffer layer increasing in the range from 25 to 205°C, indicating that BMT buffer layer can improve the temperature stability of PZT thin films. Therefore, BMT buffer layer plays a critical role in improving temperature dependence and dielectric tunability properties of PbZr0.52Ti0.48O3 thin films.

Effect of heating rates on the crystallization process of (111)-oriented lead zirconate titanate thin films prepared by the sol–gel method

We prepared Pb(Zr0.52Ti0.48)O3 (PZT) thin films with a (111)-preferred orientation on Pt/Ti/SiO2/Si substrates by a sol–gel method, and investigated the effects of heating rates on the crystallization process and kinetics by X-ray diffraction, transmission electron microscopy and Avrami׳s model. We found that the (111)-orientated initial crystallites directly formed on the top of Pt in the early stage of crystallization, and had smaller lattice parameters and an enhanced Ti content than the standard perovskite PZT. The quantity and distribution of the initial crystallites were dependent on the heating rates. The initial crystallite acted as a nucleation site for the perovskite PZT, which grew with a columnar grain structure into the pyrochlore matrix throughout the film. Using Avrami׳s model, we found that the effective activation energy for crystallization of the PZT films heated at a fast heating rate of 35°C/s to be 241kJ/mol, much lower than 325kJ/mol for crystallization of the PZT films heated at a low heating rate of 25°C/min. These results show that a fast heating rate in annealing process can reduce the effective activation energy for crystallization, improve the microstructure including the crystalline orientation, grain size and shape and thus the electrical properties of PZT thin films.

Effects of residual stress on the electrical properties in PbZr0.52Ti0.48O3 thin films

In this paper, Pb(Zr0.52Ti0.48)O3 (PZT) thin films were prepared on Pt/Ti/SiO2/Si substrates via sol–gel method. The effects of residual stress on the electrical properties in PZT thin films were investigated. There is no significant difference in grain size and orientation for PZT thin films, indicating that the influences of grain size and orientation on electrical properties of PZT thin films can be neglected. The residual stresses in PZT thin films, which decrease with increase in the film thickness, were detected by the phonon mode shift of Raman scattering. In the thin films, the interface between PZT thin films and platinum electrodes is the main factor that affected dielectric properties. As the film thickness increases, the contribution of the interface is increasingly attenuated and the residual stress is the main factor. To relieve some of the residual stress, there are more 90° domains to form, which can improve the ferroelectric and piezoelectric properties of PZT thin films. The value of dielectric constants decreases at 1 MHz, and tan δ increases with the decrease in film thickness. In this paper, the processing was designed to control grain size and crystal orientation. Therefore, residual stress and interface are the main factors that affect the dielectric constant. For the sample with the thickness of 162 and 324 nm, there is a ~45 % increase in measured dielectric constant and this change appears to be too much to be accounted for by the residual stress alone. The main factor that affects dielectric constant in the thinner films is the interface which can dilute the effective dielectric constant. As the film thickness increases, the contribution of the interface is increasingly attenuated and there is only 4 % change in the dielectric constant, indicating that residual stress is the main factor that affected dielectric constant.