Properties Of PZT Thin Films Research Articles

Fatigue characteristics of Pb(Zr0.3Ti0.7)O3 thin films prepared by metalorganic decomposition

The fatigue properties of PZT thin films with Pt electrodes are strongly influenced by the grain size. A film with smaller grains has better fatigue properties. We assume that the fatigue is mainly due to the pinning of domain walls in PZT grains by space charges or charged point defects near the Pt electrodes. The point defects always accumulate near the PZT/Pt interface because the internal electric field is very strong near the interface. Therefore the film with a lower fraction of grains touching the Pt electrodes has better fatigue properties. The permittivity of the thin film decreases with decreasing grain size. This may arise from a decrease in the mobility of the domain walls.

The effect of stress on the electrical properties of PZT thin films

We have investigated the effect of externally controlled bi-axial stress on the electrical properties of Pb(Zr, Ti)O3 (PZT) thin films. The PZT thin films exhibited a low residual tensile stress, i.e. 120 MPa. It is observed that the intrinsic residual stress of PZT films was independent of the stress state of the Pt bottom electrode, although the residual stress of the Pt bottom electrode is sensitively influenced by processing condition such as sputtering temperature. Under external compressive stress, the switching polarization or remanent polarization increased with the compressive stress. Coercive field also increased with the compressive stress. Upon applying a bi-axial stress of 300 MPa, the switching polarization increased to 40 μC/cm2 while the PZT films with the residual tensile stress had 32 μC/cm2. On the other hand, the polarization and coercive field was less dependent of the degree of the stress under the tensile stress. PZT thin films under the tensile stress exhibited slightly decreasing switching polarization and the coercive field with increasing the tensile stress.

Preparation of ferroelectric Pb(Zr0.52 Ti0.48)O3 thin films by sol-gel processing

Ferroelectric Pb(Zr0.52 Ti0.48)O3 thin films were prepared by sol-gel processing on the Pt/Ti/SiO2/Si(100) substrates. Effects of the concentration (0.2–0.8 M) of the starting solution (Pb/Zr/Ti= 1.1/0.52/0.48) and the sintering temperature (500–700 ‡C) on crystallinity, microstructure and electrical properties of PZT thin films were investigated. For the thin film prepared at 0.4 M starting solution, the highest crystallinity appeared at a sintering temperature of 650 ‡C. The average grain size of the PZT thin films was about 0.17 Μm. The film thickness was about 0.2 Μm. The relative dielectric constant and the dissipation factor of the film measured at 1 kHz were about 750 and 4.3%, respectively. The remnant polarization (Pr) and coercive field (Ec) of the film measured at the applied voltage of 5 V were about 49 ΜC/cm2 and 134 kV/cm, respectively.

Effects of lead concentration on dielectric properties of ferroelectric Ni/PZT/Pt thin films at low and infralow frequencies

Results of the studies of dielectric properties of PZT thin films of different excess lead concentrations are reported. Samples of excess lead concentration x = 0, 30, and 50 mol % are examined. The observed relaxation of polarization at infralow frequencies is interpreted on the basis of Cole-Cole relaxation. Polarization loops of samples with x = 0 and 50 mol % are compared and the reasons of their asymmetric view and displacement in the direction of negative field are discussed.

Enhanced Fatigue and Data Retention Characteristics of Pb(Zr, Ti)O3 Thin Films by the Selectively Nucleated Lateral Crystallization Method

Fatigue and data retention characteristics of Pb(Zr, Ti)O3 (PZT) thin films by the selectively nucleated lateral crystallization (SNLC) method were investigated. By placing the top Pt electrode inside the grain and directly on the grain boundary, we measured and compared the electrical properties of PZT thin films based on the grain boundary. When there was no grain boundary underneath the top electrode, no loss in switched polarization up to 2×1011 cycles and no data loss after 30000 s of memory retention at room temperature with the Pt/PZT/Pt structure were observed. However, serious degradation of the fatigue and data retention characteristics of PZT thin films occurred when there was a grain boundary in the area studied. In this study, we show that when there is no grain boundary in the area measured, no degradation such as fatigue and retention occurs, thus the main source of degradation is the grain boundary in PZT thin films.

Ultralow-frequency dielectric relaxation and fatigue properties of PZT thin film

Temperature and frequency dispersion of the dielectric constant was investigated on the ferroelectric Pb(Zr0.53 Ti0.47)TiO3[PZT] thin films, which prepared by sol-gel spin on process using 0.4 M PZT solution. The virgin PZT and fatigued PZT films exhibited a marked dielectric dispersion over the temperature range from room temperature to 300°C and over the frequency range from 10−2 Hz to 100 kHz. The dielectric relaxation was observed below 10 kHz, which was interpreted based on a dipole relaxation of the Cole-Cole type. Low-frequency dielectric relaxation is attributed to the lead and oxygen vacancies complex dipoles in PZT film. The thermal activation energy for the relaxation process of ionized space-charge carriers in the virgin and fatigued PZT film were 1.61 eV and 0.96 eV, respectively.

PZT thin films produced by oxide precursors and crystallized by conventional and RTA process

Abstract Physical properties of ferroelectric thin films can be dependent on the preparation and crystallization process. This work reports studies on crystallinity, ferroelectric and dielectric properties of PZT thin films produced by an oxide precursor method and crystallized by conventional and RTA process. Grain sizes were estimated by scanning electron microscopy (SEM) to be around 100 nm. Films were deposited on Si and Pt/Si substrates and crystallized at 700°C for different times. For film crystallized by conventional furnace the remanent polarization ( P r ) was about 7.8 μC/cm 2 and the coercive field (E c ) was 99 kV/cm. On the other hand, for PZT film crystallized at the same temperature by the RTA method, the remanent polarization and coercive field were about 16 μC/cm 2 and 73 kV/cm, respectively.

Preparation and Ferroelectric Properties of PZT Thin Films Using a Chemical Solution Deposition Process.

Lead zirconate titanate (PZT) thin films with various compositions near the morphotropic phase boundary were prepared on Pt (111)/Ti/SiO2/Si substrates using a chemical solution deposition (CSD) process. The formation conditions of the thin films with a single-phase perovskite were systematically investigated by varying the processing parameters. It was found that the PZT thin films pyrolyzed at 350-500°C and then fired at 700 and 750°C consisted of a single-phase perovskite, whereas a microcrystalline pyrochlore phase remained in the perovskite matrix when the thin films were fired at 600 and 650°C. No appreciable improvement in the dielectric and the ferroelectric properties was found by increasing firing temperature from 700 to 750°C, but the leakage current density of the thin film fired at 750°C is about three orders of magnitude higher than that of the thin film fired at 700°C. The optimal firing temperature was determined to be 700°C, single-phase perovskite being obtained with optimum dielectric and ferroelectric properties as well as a low leakage current. The Pr are around 38-46, 30-40 and 25-30μC/cm2 and the coercive field to 141-192, 119-136 and 80-95kV/cm, respectively, for the Pb(ZrxTi1-x)O3 (x=0.45, 0.53 and 0.6) pyrolyzed at 350-500°C for 3min and then fired at 700°C. The orientation of the PZT thin film can be controlled by a pyrolysis process rather than by the firing temperature and the composition of the precursor solution. The PZT pyrolyzed at 400°C tends to take ‹100› orientation, whereas the counterpart pyrolyzed at 350, 450 and 500°C have a strong ‹111› dominating orientation.

Effect of temperature and frequency on dielectric and ferroelectric properties of PZT thin films

This work reports the effect of annealing temperature and frequency on dielectric and ferroelectric properties of PZT thin films produced by oxide precursor method. The properties reported include dielectric constant and dissipation factor and hysteresis loops as a function of annealing temperature and frequency. Dielectric constant and dissipation factor were measured to be, respectively, 517 and 0.04, at 100 kHz frequency, for film crystallized at 700°C for 1 h. Ferroelectricity was confirmed by P– E hysteresis loops. Films annealed at 700°C for 1 h presented higher remanent polarization compared with films annealed at 600°C for 1 h over frequency range from 300 Hz to 300 kHz. However, coercive field increases for films annealed at 700°C and decreases for films annealed at 600°C for 1 h over the same frequency range.

Effect of Pb Content in Target on Electrical Properties of Laser Ablation Derived Lead Zirconate Titanate Thin Films

Thin films of Pb(Zr0.52Ti0.48)O3(PZT) 1.8–2.0 µm thick on a Pt/Ti/SiO2/Si substrate were prepared by excimer laser ablation and were crystallized by subsequent annealing. 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 effect of the Pb content of the target on electrical properties of PZT thin films was investigated. The PZT films with a well-crystallized perovskite phase were obtained by adding 20 wt.% excess PbO to the target and annealing at 750°C for 90 min. The remanent polarization and the coercive field of this 0.8 µm think film were 23.6 µC/cm2 and 60.0 kV/cm, while the dielectric constant and loss values measured at 1 kHz were approximately 935 and 0.04, respectively.

Preparation and Characterization of Pb(Zr, Ti)O3Thin Films by Metalorganic Chemical vapor Deposition Using a Solid Delivery System

Pb(Zr, Ti)O3(PZT) thin films were deposited on Pt/SiO2/Si substrates by metalorganic chemical vapor deposition using solid delivery system. The effects of deposition parameters such as the substrate temperature, the concentration of Pb precursor in the precursor mixtures, and the reactor pressure on the structural and electrical properties of PZT thin films were investigated. To obtain single-phase PZT thin films, the optimal range of the substrate temperature should be between 600 and 650 °C. The PbO content in PZT thin films was proportional to the fraction of Pb in the precursor mixture below 550 °C, but it was independent of the fraction of Pb in the mixture above 600 °C. With the increment of the reactor pressure, Zr contents in PZT thin films were increased, and the Pb/(Zr + Ti) ratio became more stoichiometric so that the ferroelectric properties were improved.

Structural and electrical properties of highly oriented Pb(Zr,Ti)O 3 thin films deposited by facing target sputtering

The Pb(Zr,Ti)O 3 thin films with single (111) oriented perovskite phase and excellent electrical properties have been prepared by annealing the as-deposited samples. The orientation of crystals depends strongly on both the deposition temperature and annealing temperature. The sample annealed at 606°C has the best (111) orientation. When the sample is annealed at lower temperature, the relative content of (111) oriented perovskite phase decreases quickly with increase of deposition temperature. The deposition temperature has little effects on the orientation when the sample is annealed at higher temperature. The effects of deposition temperature and annealing temperature on the crystallographic structures and electrical properties of PZT thin films were investigated in this paper. The sample deposited at 285°C and annealed at 606°C has the maximum value of polarization, which displays excellent ferroelectric properties. The typical P r and P s values are 57 and 101 μC/cm 2, respectively.

Piezoelectric properties of PZT thin films on metallic substrates

The piezoelectric properties of PZT thin films on metallic substrates prepared by sol-gel processing were investigated. The films show a high remanent polarization of about 40 μC/cm2 and a coercive field strength of about 10 V/μm. The direct piezoelectric effect was used for measuring the electrical charge generated by an applied strain. The generated charge depends linearly on the strain up to a strain of about 0.1 %. A charge per area of about 0.1 μC/cm2 was measured for a strain of 0.1 %. From these measurements the piezomodulus d31 was calculated. The values of d31 were about 29 pC/N and have been compared with former measurements of the piezomodulus d33. The time dependence and the mechanical fatigue of the piezomodulus were investigated. The piezomoduli remain nearly constant up to 105 mechanical or electrical cycles, after this the piezomoduli decrease.

Transient Behavior of the Polarization in Ferroelectric Thin Film Capacitors

AbstractThe understanding of the polarization switching process of ferroelectric capacitors is highly relevant for the development and optimization of FeRAM devices. We report on the characterization of Pb(Zr,Ti)O3 thin films which have been studied by means of dedicated rectangle pulse measurements. Decreasing the voltage level of the excitation pulses decelerates the polarization switching significantly to the range of milliseconds and reduces the switchable polarization. In this work the influence of niobium (Nb) doping on the switching properties of PZT thin films prepared by CSD are investigated to reach the aspired conditions of low voltage operation, read and write access pulses in the range of nanoseconds. For the implementation of the transient behavior of ferroelectric capacitors in circuit design and simulation tools it is necessary to develop a model which precisely describes the polarization hysteresis, the pulse switching behavior as well as the small signal capacitance. The fundamental considerations for this model are presented, based on an ideal ferroelectric capacitor, taking into account the Curie-von Schweidler behavior. The latter is observed in non-ferroelectric high-K materials as well as in ferroelectric thin films.

Sol-gel derived PZT/RuO2 multilayer films on stainless steel substrates

The structural and electric properties of PZT thin films deposited by the sol-gel process on RuO2 coated stainless steel as well as on bare stainless steel were studied and compared. As-deposited amorphous RuO2 thin films on stainless steel were transformed to pure rutile-type RuO2 at temperatures ranging from 400°C to 600°C, the resistivity of which had a value less than 200 μΩ ° cm. The PZT films processed on RuO2 needed slightly higher temperature (610°C) in order to be completely transformed into the perovskite phase than PZT on stainless steel (600°C). The films showed best ferroelectric properties when depositing it on the 100 nm thick RuO2 bottom electrodes fired at 400°C for 10 minutes. The hysteresis loops of the PZT films were more slim when being processed on RuO2 coated stainless steel than on bare stainless steel. For the RuO2 bottom electrodes the values of coercive field decreased to about 55% of those without a RuO2 layer.

The Microstructure, Phase and Ferroelectric Properties of PZT Thin Films on Oriented Multilayer Electrodes

AbstractThree kinds of oriented electrodes of Pt, Ir and Pt/Ir electrodes were prepared using electron beam evaporation techniques for deposition of PZT thin films. An oxide MOCVD reactor with liquid delivery system was used for the growth of PZT thin films. [Pb(thd)2], Zr(TMHD)4 and Ti(IPO)4 were dissolved in a mixed solvent of tetrahydrofuran or butyl ether, isopropanol and tetraglyme to form a precursor source. The deposition temperature and pressure were 500 - 650°C and 5 - 10 Torr, respectively. The experimental results showed PZT thin film deposited on various electrodes had different phase formation, microstructure and ferroelectric property. The X-ray patterns showed the perovskite phase of PZT was formed on both Ir and Pt/Ir electrodes at 550°C. The grain size of the PZT thin film increases after a further, higher temperature annealing. The as-deposited PZT thin film on Pt electrode exhibits pyrochlore phase at 550°C. The phase is transformed to perovskite phase after 650°C annealing. The experimental results also indicated that the MOCVD PZT thin film on Pt/Ir exhibits better ferroelectric and electrical properties compared to those deposited on Pt and Ir electrodes. A 300 nm thick PZT thin film on Pt/Ir electrode has a square, well saturated, and symmetrical hysteresis loop with 2Pr value of 40 μC/cm2 and 2Ec of 73 kV/cm at an applied voltage of 5 V. The hysteresis loop of the PZT thin film is almost saturated at 2 V. The leakage current of the film is 6.16 × 10−7 A/cm2 at 100 KV/cm. The electrode effects on ferroelectric properties of PZT thin films also have been investigated.

Characterization of lead zirconate titanate thin film deposition onto Pt/Ti/SiO2/Si substrates

Lead zirconate titanate, (Pb(Zr0.52Ti0.48)O3PZT) thin films were deposited onto a Pt/Ti/SiO2/Si substrate using radio frequency (r.f.) planar magnetron sputtering in this study. The deposited PZT thin films were almost amorphous before the annealing processes and developed a perovskite structure after the annealing process. If the annealing temperature was too low or annealing time too short, pyrochlore would form. However, if the annealing temperature was too high or annealing time too long, the thin film structure would degrade due to the volatilization of PbO. The significant finding in this experiment is that high quality perovskite PZT thin films on Pt/Ti/SiO2/Si substrates can be obtained by adjusting the annealing temperature to a range of 650 °C to 850 °C and annealing time to a range from 5 to 80 min. In this experiment, the optimal annealing condition was an annealing temperature of 650 °C and time of 20 min. The properties of PZT thin film annealed at 650 °C for 20 min were dielectric constant ɛr = 869 free dielectric constant ɛT33 = 893 piezoelectric constant d33 = 2.03p m V-1 piezoelectric constant g33 = 2.57 x 10-4 V m N-1, remanent polarization P1 = 112.5 nC cm-2 and coercive field Ec= 0.061 kV cm-1.

Effect of substrate characteristics on dielectric properties of PZT thin films obtained from oxide precursors

Effect of substrate characteristics on dielectric properties of PZT thin films obtained from oxide precursors

Influence of the Purity of Source Precursors on the Electrical Properties of Pb(Zr, Ti)O3 Thin Films Prepared by Metalorganic Chemical Vapor Deposition

Pb(Zr, Ti)O3 (PZT) thin films were prepared by metalorganic chemical vapor deposition (MOCVD) using two types of Pb precursors (tetra-ethyl lead: TEL) with different purities and the influence of the purity of TEL on the electrical properties of PZT thin films was investigated. While the difference in the purity of TEL did not affect the crystalline properties and surface morphology of PZT films, it influenced the electrical properties of PZT films. Relative dielectric constants and D-E hysteresis loops of PZT thin films were influenced slightly by the difference in the purity of TEL. PZT films grown using high purity TEL showed lower current densities and higher breakdown fields than those grown using low purity TEL. High source purity PZT films also had higher endurance against polarization fatigue than low source purity films. From these results, it was concluded that the purification of source materials led to the improvement of the electrical properties of ferroelectric thin films.

Electrical properties of PZT thin films grown on Ir/IrO2 bottom electrodes by MOCVD

Electrical properties of Ir/IrO2/PZT/Ir/IrO2 and IrO2/Ir/PZT/Ir/IrO2 capacitors were investigated. SIMS analysis showed that the Ir/IrO2 bottom electrode acted as a good barrier layer of the interdiffusion. Ir/IrO2/PZT/Ir/IrO2 capacitors did not show good electrical properties due to plasma damage during top electrode sputtering. On the other hand, IrO2/Ir/PZT/Ir/IrO2 capacitors showed no fatigue up to 109 cycles, when annealing after top electrode deposition was performed. Electrical properties of IrO2/Ir/PZT/Ir/IrO2 capacitors were dependent on the thickness of Ir/IrO2 bottom electrode. These experimental results suggested that electrical properties of PZT capacitors were influenced by the interdiffusion at the bottom interface and the plasma damage at the upper interface.