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(Zr_0.52Ti_0.48)O₃ (PZT) thin films, 10-nm thick (Pb_0.72La_0.28)Ti_0.93O₃ (PLT) and Pb(Zr_0.52Ti_0.48)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.     

Ferroelectric properties of bilayer structured Pb(Zr0.52Ti0.48)O3/SrBi2Ta2O9 (PZT/SBT) thin films on Pt/TiO2/SiO2/Si substrates

Pb(Zr_0.52Ti_0.48)O₃ (PZT) thin films with large remanent polarization and SrBi₂Ta₂O₉ (SBT) thin films with excellent fatigue-resisting characteristic have been widely studied for non-volatile random access memories, respectively. To combine these two advantages_, bilayered Pb(Zr_0.52Ti_0.48)O₃/SrBi₂Ta₂O₉ (PZT/SBT) thin films were fabricated on Pt/TiO₂/SiO₂/Si substrates by chemical solution deposition method. X-ray diffraction patterns revealed that the diffraction peaks of PZT/SBT thin films were completely composed of PZT and SBT, and no other secondary phase was observed. The electrical properties of the bilayered structure PZT/SBT films have been investigated in comparison with pure PZT and SBT films. PZT/SBT bilayered thin films showed larger remanent polarization (2P_r) of 18.37 μC/cm² than pure SBT and less polarization fatigue up to 1 × 10⁹ switching cycles than pure PZT. These results indicated that this bilayered structure of PZT/SBT is a promising material combination for ferroelectric memory applications.     

(111)择优取向的Pb(Zr0.52Ti0.48)O3铁电薄膜的制备及研究

选用不同浓度的Pb(Zr_0.52Ti_0.48)O₃溶胶，用Sol-gel法在Pt/Ti/SiO₂/Si基片上沉积一层厚度不同的Pb(Zr_0.52Ti_0.48)O₃ (PZT52)过渡层，经400℃烘烤、550℃退火等程序后，再用Sol-gel法在PZT52过渡层上沉积Pb(Zr_0.52Ti_0.48)O _{关键词： PZT铁电薄膜 择优取向 过渡层 剩余极化强度}     

Highly (100) oriented Pb(Zr<Subscript>0.52</Subscript>Ti<Subscript>0.48</Subscript>)O<Subscript>3</Subscript>/LaNiO<Subscript>3</Subscript> films grown on amorphous substrates by pulsed laser deposition

Pb(Zr_0.52Ti_0.48)O₃ (PZT)/LaNiO₃ (LNO) thin films with highly (100) out of plane orientation were produced on SiO₂/Si(100) and alkaline earth aluminosilicate glass substrates by pulsed laser deposition (PLD). Orientations of both PZT and LNO films were evaluated using X-ray diffraction. The pure (100)-oriented PZT/LNO films were obtained under optimized deposition conditions. Time of flight-secondary ion mass spectrometry analysis showed that LNO could effectively block interdiffusion between the PZT films and the substrates. Fairly smooth surfaces of the PZT films with roughness of about 4 nm were observed using an atomic force microscope. Cross sectional examination revealed that the films grew in columnar grains. The PZT films grown on both SiO₂/Si and glass substrates demonstrated very good ferroelectric characteristic at room temperature with remnant polarization of up to 26 μC/cm². PACS 79.20.DS; 77.84.DY; 78.70.Ck     

Polarization fatigue resistance of Ca-doped Pb(Zr<Subscript>0.52</Subscript>Ti<Subscript>0.48</Subscript>)O<Subscript>3</Subscript> thin films prepared by the sol–gel method

The ferroelectric and polarization fatigue characteristics of Pb_1-xCa_x(Zr_0.52Ti_0.48)O₃ (PCZT) thin films prepared using the sol–gel method were studied. The Ca-doping slightly suppresses the ferroelectricity of Pb(Zr_0.52Ti_0.48)O₃ (PZT) because of the quantum paraelectric behavior of CaTiO₃. Compared with PZT thin films, the PCZT (x=0.2) thin films show enhanced fatigue resistance at room temperature, further emphasized by the almost fatigue-free behavior at 100 K. The temperature-dependent dc-conductivity suggests a decrease of the oxygen vacancy density by almost 20 times and a slightly declined activation energy U for oxygen vacancies, upon increasing of the Ca-doping content from 0.0 to 0.2. It is argued that the improved fatigue endurance is ascribed to the decreasing density of oxygen vacancies due to the Ca-doping, although the lowered activation energy of oxygen vacancies is unfavorable. PACS 77.84.Dy; 66.30.-h; 68.35.Fx     

Electric and magnetic properties of CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/Pb(Zr<Subscript>0.52</Subscript>Ti<Subscript>0.48</Subscript>)O<Subscript>3</Subscript> bilayer thin films prepared by pulsed-laser deposition

CoFe₂O₄ (CFO) thin film with highly (111)-preferential orientation was first deposited on the silicon substrate by a pulsed-laser deposition, and then Pb(Zr_0.52Ti_0.48)O₃ (PZT) layers were deposited with different oxygen pressures to form the bilayer CFO/PZT nanocomposite thin films. X-ray diffraction showed that the PZT preferential orientation was strongly dependant on the oxygen pressure. The smooth film surface was obtained after depositing the CFO and PZT layers. The bilayer thin films exhibit good ferromagnetic and ferroelectric properties, and a low leakage current density of 0.004 μA/cm² at 50 kV/cm. The leakage current density curves show loops for the electric polarized field when the electric field reverses. PACS 77.84.Lf; 75.80+q; 81.05.Zx; 81.15.Fg     

Preparation and crystallization of Pb(Zr0.95Ti0.05)O3 thin films deposited by radio-frequency magnetron sputtering with a stoichiometric ceramic target

0.95 Ti_0.05)O₃ (PZT 95/5) thin films of perovskite structure were prepared on various substrates by the radio-frequency magnetron sputtering with a stoichiometric ceramic target. The crystal structure of the films showed a strong dependency on the crystal structure of the substrates. After conventional-furnace annealing at 750 °C, crack-free and transparent epitaxial PZT 95/5 films were successfully obtained on SrTiO₃(100) substrates, and highly oriented films on LaAlO₃(012). The films on r-sapphire exhibit slightly preferred orientation along both the (040) and (122) axes of the orthorhombic PZT 95/5 phase. The films on YSZ(100) consist principally of the perovskite PZT 95/5 phase with random orientation with a small portion of unknown phase. However, the formation of the perovskite PZT 95/5 phase was not observed in the films on Si(110) or (111)Pt-coated Si substrates. The crystallization of the perovskite PZT 95/5 on these substrates could be improved by rapid thermal annealing (RTA). Single perovskite phase was obtained in the films on (111)Pt/Si which had RTA at 750 °C for 1 min. No tangible loss of Pb from the films occurred during either the sputtering or annealing. Received: 17 April 1997/Accepted: 18 November 1997     

Crystallization kinetics and growth mechanism of Pb(Zr0.52·Ti0.48)O3 nanopowders

In this study, Pb(Zr_0.52·Ti_0.48)O₃ nanopowders were synthesized via sol–gel process. Particle morphology, crystalline phases and thermal behavior were characterized by scanning electron microscopy, X-ray diffraction and simultaneous thermal analyzer, respectively. The X-ray diffraction pattern showed perovskite phase clearly. The non-isothermal activation energy for the perovskite crystallization in Pb(Zr_0.52·Ti_0.48)O₃ gel powders was 224.91 kJ mol^?1. Both growth morphology parameter (n) and crystallization mechanism index (m) are close to 3.0, indicating that the bulk nucleation is dominant in the perovskite PZT formation. To determine dielectric properties, the calcined Pb(Zr_0.52·Ti_0.48)O₃ nanopowders were pressed using uniaxial press. It was found that the Pb(Zr_0.52·Ti_0.48)O₃ disks, by sintering at 1,200 °C for 2 and 10 h, and at 1 kHz frequency, had 966 and 1,490 of the dielectric constant, respectively.     

Excimer laser-induced transformation in laser ablated Pb(Zr0.52Ti0.48)O3 amorphous thin films

Pb(Zr_0.52Ti_0.48)O₃ (PZT) amorphous thin films were deposited on Si substrates at room temperature and 573?K by pulsed laser deposition. The as-deposited films were subsequently annealed at various laser power densities using a KrF pulsed excimer laser irradiation to induce the phase transformation from amorphous to ferroelectric perovskite structure. Structural analysis shows the possibility of transformation from pyrochlore to perovskite transformation when irradiated above a laser power density of 1.4?MW/cm², which is in agreement with the thermal simulation. The surface quality of the PZT films deposited on 573?K is remarkably superior to that deposited at room temperature due to the enhanced thin structure and composition homogeneity. Almost all the pyrochlore phase transformed into perovskite structure after annealing at 2.8?MW/cm² for 120?s for both PZT films deposited at room temperature and 573?K, respectively. P-E hysteresis measurement of the laser-treated PZT shows relatively low remnant polarization P _r of about 1.2?μC/cm².     

In-situ X-ray microdiffraction analysis of local strain-field across the interface in a Pb(Zr0.52Ti0.48)O3/Ni0.8Zn0.2Fe2O4/Pb(Zr0.52Ti0.48)O3 tri-layered structure

We have performed a synchrotron X-ray microdiffraction to investigate the variation of the local strain-field across the interface in Pb(Zr_0.52Ti_0.48)O₃/Ni_0.8Zn_0.2Fe₂O₄/Pb(Zr_0.52Ti_0.48)O₃ (PZT–NZFO–PZT) tri-layered structure. In this study, we show that the in-plane lattice parameters of the NZFO lattice depend strongly on the piezoelectric strain of the PZT layer. This result explains that an electric-field-induced piezoelectric strain from the PZT layer is effectively transferred to the NZFO layer. Furthermore, the local strain persists within 20 μm away from the interface, inducing changes of magnetic responses via the inverse magnetostrictive effect.     

Lead zirconate titanate–barium titanate by mechanical activation of mixed oxides

For the first time, the perovskite phase in 0.9Pb (Zr_0.52Ti_0.48)O₃-0.1BaTiO₃(0.9PZT-0.1BT) is triggered to form in an oxide matrix consisting of PbO, ZrO₂, BaO, and TiO₂. Unlike in the solid-state reaction activated by calcination at an intermediate temperature, intermediate phases, such as PbTiO₃, were not observed with increasing degree of mechanical activation prior to the formation of perovskite 0.9Pb(Zr_0.52Ti_0.48)O₃-0.1BaTiO₃ phase. This suggests that the nucleation and subsequent growth of perovskite crystallites in the activated oxide composition are not a result of the interfacial reactions that normally occur in the temperature-driven solid-state reaction. The mechanical activation-derived powders can be sintered to a relative density of >97% theoretical at 1100 °C. Sintered 0.9Pb(Zr_0.52Ti_0.48)O₃-0.1BaTiO₃ derived from mechanical activation of constituent oxides exhibits a maximum dielectric constant of 775 and a minimum dielectric loss of <2% at room temperature when measured at 1.0 kHz. Received: 3 December 1998 / Accepted: 18 March 1999 / Published online: 24 June 1999     

Electrodynamic properties of lead Zirconate-Titanate thin films in the terahertz frequency range

The transmission/reflection spectra of bilayer structures consisting of thin amorphous and polycrystalline Pb(Zr_0.52Ti_0.48)O₃ ferroelectric films deposited on dielectric substrates of magnesium oxide MgO and sapphire α-Al₂O₃ were measured in the frequency range of 5–4000 cm^?1. Based on these spectra and using the dispersion analysis method, the spectra of complex dielectric permittivity ?*(ν) and dynamic conductivity σ′(ν) of the films were simulated, the electrodynamic parameters of the films were determined, and the dielectric dispersion responsible for the formation of static permittivity was found.     

Effect of buffer layers on the property of Pb(Zr,Ti)O3-Pb(Mn,W,Sb,Nb)O3 thin films grown by pulsed laser deposition

New ferroelectric Pb(Zr,Ti)O₃-Pb(Mn,W,Sb,Nb)O₃ (PZT-PMWSN) thin film has been deposited on a Pt/Ti/SiO₂/Si substrate by pulsed laser deposition. Buffer layer was adopted between film and substrate to improve the ferroelectric properties of PZT-PMWSN films. Effect of a Pb(Zr_0.52Ti_0.48)O₃ (PZT) and (Pb_0.72La_0.28)Ti_0.93O₃ (PLT) buffer layers on the stabilization of perovskite phase and the suppression of pyrochlore phase has been examined. Role of buffer layers was investigated depending on different types of buffer layer and thickness. The PZT-PMWSN thin films with buffer layer have higher remnant polarization and switching polarization values by suppressing pyrochlore phase formation. The remnant polarization, saturation polarization, coercive field and relative dielectric constant of 10-nm-thick PLT buffered PZT-PMWSN thin film with no pyrochlore phase were observed to be about 18.523 μC/cm², 47.538 μC/cm², 63.901 kV/cm and 854, respectively.     

Investigation the effects of the excess Pb content and annealing conditions on the microstructure and ferroelectric properties of PZT (52-48) films prepared by sol-gel method

The effects of the PbO volatilization, excess Pb content of PbZr_0.52Ti_0.48 (PZT) precursor, PbTiO₃ (PT) seeding layers and annealing condition on the microstructures, surface morphologies, preferred orientation and ferroelectric properties of PbZr_0.52Ti_0.48 films were systematically investigated. PZT films with a variety of excess Pb (0-20%) were spin-deposited on Si(1 0 0) and Pt(1 1 1)/Ti/SiO₂/Si(1 0 0) substrates by sol-gel technique. The films composition, Pb/Zr/Ti/O atom rate and Pb loss were semiquantitative analyzed by X-ray photoelectron spectrometer (XPS). When the excess Pb of PZT precursor was 10%, the Pb/Zr/Ti/O atomic rate of the fabricated films was very close to the designed rate of 1:0.52:0.48:3. The XRD and AFM investigations confirmed that PT seeding layer promoted the PZT films perovskite phase transformation and grains growth with (1 1 0) plane preferred orientation, accordingly lowered perovskite phase crystallization temperature and reduced Pb loss. The PZT films annealed in O₂ flow demonstrated better microstructure and ferroelectric properties comparing with films annealed in air by double remnant polarization increase and 8% coercive field increase. The underlying mechanism was also investigated.     

Preparation and characterization of poled nanocrystal and polymer composite PZT/PC films

Pb(Zr_0.52Ti_0.48)O₃ (PZT) nanocrystals and transparent polycarbonate (PC) composite thin films with useful properties for ferroelectric, piezoelectric and electro-optic devices were prepared by a spin-coating technique. Ultra-fine PZT (∼40–50 nm) nanocrystals with pure perovskite tetragonal phase were synthesized by a hydrothermal method. The structure and morphology of the composite thin films were studied by means of X-ray diffraction and scanning electron microscopy. To obtain the optimum electro-optic properties of poled composite films, the poling condition under an external electric field was optimized through the dielectric properties of PZT and PC polymer and effective field intensity theory. The electro-optic coefficient of the poled PZT/PC composite film is estimated to be 30.5 pm/V. The transparency spectra were measured and the optical band gaps of the unpoled, poled at 145 °C and poled at 165 °C composite thin films are estimated to be 4.26 eV, 4.21 eV and 4.18 eV, respectively. The measured dielectric constants of PZT/PC are in good agreement with the calculated values for the composite with a very small PZT volume fraction, based on the Onsager effective-field theory. This offers a reliable and indirect way to predict the dielectric constant of nanocrystals. PACS 81.40.Tv; 78.66.Sq; 78.66.Vs     

Pyroelectric and photoelectric responses of capacitors based on thin PZT films

The influence of 0.63-μm laser radiation and an external electric field on the photo-and pyroelectric response of thin ferroelectric Pb(Zr_0.54Ti_0.46)O₃ (PZT) films is studied at various temperatures. The films are grown by RF magnetron sputtering of a PZT ceramic target on platinum-coated substrates. It is found that the photosensitivity of PZT films increases after switching of the applied static electric field, as well as after an increase in temperature.     

Synthesis, microstructures, and magnetoelectric couplings of electrospun multiferroic nanofibers

Multiferroic materials with two or more types of ferroic orders have attracted a great deal of attention in the last decade for their magnetoelectric coupling, and new ideas and concepts have been explored recently to develop multiferroic materials at nano-scale. Motivated by theoretical analysis, we synthesized single-phase BiFeO₃ (BFO) nanofibers, Pb(Zr_0.52Ti_0.48)O₃-CoFe₂O₄ (PZT-CFO) and Pb(Zr_0.52Ti_0.48)O₃-NiFe₂O₄ (PZT-NFO) composite nanofibers, and CoFe₂O₄-Pb(Zr_0.52Ti_0.48)O₃ (CFO-PZT) core-shell nanofibers using sol-gel based electrospinning. These nanofibers typically have diameters in the range of a few hundred nanometers and grain size in the range of 10s nanometers, and exhibits both ferroelectric and ferromagnetic properties. Piezoresponse force microscopy (PFM) based techniques have also been developed to examine the magnetoelectric coupling of the nanofibers, which is estimated to be two orders of magnitude higher than that of thin films, consistent with our theoretical analysis. These nanofibers are promising for a variety of multiferroic applications.     

Experimental evidence of breakdown strength and its effect on energy-storage performance in normal and relaxor ferroelectric films

Normal-ferroelectric Pb(Zr_0.52Ti_0.48)O₃ (PZT) and relaxor-ferroelectric Pb_0.9La_0.1(Zr_0.52Ti_0.48)O₃ (PLZT) thin-films are deposited on SrRuO₃-covered SrTiO₃/Si substrates. An ultrahigh recoverable energy-storage density (U_reco) of 68.2 J/cm³ and energy efficiency (η) of 80.4% are achieved in the PLZT thin-films under a large breakdown strength (E_BD) of 3600 kV/cm. These values are much lower in the PZT thin-films (U_reco of 10.3 J/cm³ and η of 62.4% at E_BD of 1000 kV/cm). In addition, the remanent polarization (P_r) and dielectric-constant are also investigated to evaluate the breakdown strength in thin-films. Polar nano-regions (PNRs) are created in the PLZT thin-films to enable relaxor behavior and lead to slim polarization loops along with very small P_r. The excellent operating temperature of energy-storage performance and also the breakdown strength obtained in the PLZT thin-films are mainly ascribed to the presence of PNRs. Moreover, both PZT and PLZT thin-films exhibit superior performance up to 10¹⁰ times of charge-discharge cycling.     

Low temperature crystallization behavior of multi-walled carbon nanotubes/Pb(Zr0.52Ti0.48)O3 nanocomposite thin films through annealing in various atmosphere and duration control

We report a successful fabrication of 300 nm thick carbon nanotubes and Pb(Zr_0.52Ti_0.48)O₃ (CNT–PZT) nanocomposite thin films with annealing temperature as low as 500 °C in H₂/N₂ atmosphere. Realizing the thickness of CNT–PZT nanocomposite thin films down to few hundred nanometers is one way to reduce the operating voltage of its application to micro- or nano-electromechanical system. The field emission scanning electron microscopic and atomic microscopic analysis revealed that the nanocomposite thin films annealed in H₂/N₂ atmosphere exhibits the most favorable surface morphology with adequate perovskite (111) reflection of PZT based on X-ray diffraction analysis. The measured dielectric constant and loss tangent of the nanocomposite thin films show that the annealing duration of 30 min promotes the optimum dielectric properties of the nanocomposite thin films. Our observations suggest that the annealing atmosphere and duration are important parameters in controlling the crystallization behavior hence the dielectric properties of the nanocomposite thin films, which can be readily applicable to other nanocomposite thin films.     

Texture control of Pb(Zr, Ti)O3 thin films with different post-annealing processes

The non-crystalline Pb(Zr, Ti)O₃ thin films sputtered on Pt(1 1 1)/Ti/SiO₂/Si(1 0 0) substrates at room temperature were crystallized by conventional furnace annealing (CFA) and rapid thermal annealing (RTA), respectively. It was found that the RTA process favored the (1 1 1)-preferred orientation in lead zirconate titanate (PZT) thin films while the CFA process favored the (1 0 0)-preferred orientation. The origin of the different orientation selection might be due to the different epitaxial nucleation mechanism. The long heating duration would lead to the aggregation of Pb and the formation of PbO(1 0 0) on film surface; therefore, the nucleation at the PbO(1 0 0)/PZT interface on film surface might lead to the (1 0 0)-preferred orientation. However, the nucleation at the PZT/Pt(1 1 1) electrode interface by RTA process would result in the formation of (1 1 1)-preferred orientation. The RTA-derived (1 1 1)-preferentially oriented PZT thin films exhibited a high remnant polarization of 35 μC/cm².