Fe-doped PZT Research Articles

Effect of Mg-doping and Fe-doping in lead zirconate titanate (PZT) thin films on electrical reliability

Uniformly acceptor doped Pb(Zr0.48Ti0.52)O3 (PZT) films with 2 mol. % Mg or Fe prepared by chemical solution deposition exhibited decreased dielectric constants and remanent polarizations relative to undoped PZT. For highly accelerated lifetime testing (HALT) at 200 °C and an electric field of 300 kV/cm in the field up direction, the HALT lifetimes (t50) for undoped, Mg-doped, and Fe-doped PZT films were shortened from 2.81 ± 0.1 to 0.21 ± 0.1 and 0.54 ± 0.04 h, respectively. Through thermally stimulated depolarization current measurement, significant VO∙∙ electromigration was found in homogeneously Mg-doped PZT thin films, a major factor in their short HALT lifetime. Because the concentration of oxygen vacancies increases with uniform acceptor doping, the lifetime decreases. In contrast, when a thin layer of Mg-doped or Fe-doped PZT was deposited on undoped PZT or Nb-doped PZT (PNZT), the HALT lifetimes were longer than those of pure PZT or PNZT films. This confirms prior work on PNZT films with a Mn-doped top layer, demonstrating that the HALT lifetime increases for composite films when a layer with multivalent acceptors is present near the negative electrode during HALT. In that case, the compensating electrons are trapped, presumably on the multivalent acceptors, thus increasing the lifetime.

Controlling polarization direction in epitaxial Pb(Zr0.2Ti0.8)O3 films through Nb (n-type) and Fe (p-type) doping

Fe (acceptor) and Nb (donor) doped epitaxial Pb(Zr0.2Ti0.8)O3 (PZT) films were grown on single crystal SrTiO3 substrates and their electric properties were compared to those of un-doped PZT layers deposited in similar conditions. All the films were grown from targets produced from high purity precursor oxides and the doping was in the limit of 1% atomic in both cases. The remnant polarization, the coercive field and the potential barriers at electrode interfaces are different, with lowest values for Fe doping and highest values for Nb doping, with un-doped PZT in between. The dielectric constant is larger in the doped films, while the effective density of charge carriers is of the same order of magnitude. An interesting result was obtained from piezoelectric force microscopy (PFM) investigations. It was found that the as-grown Nb-doped PZT has polarization orientated upward, while the Fe-doped PZT has polarization oriented mostly downward. This difference is explained by the change in the conduction type, thus in the sign of the carriers involved in the compensation of the depolarization field during the growth. In the Nb-doped film the majority carriers are electrons, which tend to accumulate to the growing surface, leaving positively charged ions at the interface with the bottom SrRuO3 electrode, thus favouring an upward orientation of polarization. For Fe-doped film the dominant carriers are holes, thus the sign of charges is opposite at the growing surface and the bottom electrode interface, favouring downward orientation of polarization. These findings open the way to obtain p-n ferroelectric homojunctions and suggest that PFM can be used to identify the type of conduction in PZT upon the dominant direction of polarization in the as-grown films.

Origin of defect dipoles in Fe doped Pb(ZrxTi1−x)O3 thin film

We report the formation and the role of defect dipoles in Fe doped Pb(Zr0.52Ti0.48)O3 (PZT) epitaxial thin film grown on SRO/LSAT substrate by pulsed laser deposition. The observed enhancement of spontaneous polarization in Nb-doped PZT thin film is found to be due to easy orientation and mobility of domain walls. The presence of defect complexes in Fe doped PZT film is responsible for the voltage offset or asymmetric polarization versus electric field hysteresis loop. Topography and nanoscale polarization switching of pure and doped PZT films are investigated by piezo force microscopy. X-ray photoelectron spectroscopy (XPS) study is used to confirm the presence of defect dipoles in Fe-doped PZT thin film. Detailed analysis of the XPS spectra also revealed that the defect dipoles are only formed in the Fe doped system and is absent in Nb- modified PZT thin film.

Multifunctional behavior of acceptor-cation substitution at higher doping concentration in PZT ceramics

Abstract The Fe-doped PZT, Pb (Zr, Ti)1-xFexO3, ceramics have gathered plenty of attention because of the interplay of ferroelectric and ferromagnetic properties. In the present study, we report the properties of Pb(Zr0.52Ti0.48)1-xFexO3 prepared by conventional solid-state reaction route with varying Fe3+ doping concentrations, x = 0, 0.05, 0.10, 0.15 and 0.20. Study of X-ray diffraction patterns confirmed the tetragonal crystal structure along with reduction in tetragonality and unit-cell size with doping. It also showed formation of secondary magneto-plumbite phase at higher doping concentrations. The SEM micrographs exhibited decrease in grain size with increase in doping concentration (for x > 0.05). The increase in oxygen vacancies and the formation of secondary magneto-plumbite phase and Fe3+–VO2−–Fe3+ defect dipole complexes introduced with the acceptor (Fe3+) doping, caused clamping of the domain walls and hence reduced the room temperature dielectric constant as the doping concentration was increased. The coexistence of electrical polarization and magnetic moment at room temperature in all PFZT compositions confirmed the multiferroic characteristic in the ceramic samples. Electric polarization (Pr) and coercive fields (Ec) decreased with increase in Fe3+ concentration in PFZT sample. However, magnetization (M) and magnetic coercive fields (Ec) increased with the increasing Fe3+ concentration due to the dominant effect of F-center exchange mechanism in Fe3+–VO2−–Fe3+ and formation of ferromagnetic secondary magneto-plumbite phase.

Synthesizing nanostructured crack-free thick films of Fe-doped lead zirconate titanate by sol–gel dip coating method

Lead zirconate titanate is one of the most well-known ferroelectric oxides and has been widely used in nano/micro-electromechanical systems and piezoelectric industries. Doping the lead zirconate titanate thick films by Fe3+ as an acceptor dopant leads to hard lead zirconate titanate piezoelectrics for specific applications including high frequency transducers. In this article, Fe-doped lead zirconate titanate thick films with the thickness of 27 µm are synthesized by using a modified acetic acid/alcoholic based sol–gel method and applying diethanolamine as a complexing agent. Crystallographic measurements are performed considering lattice constants and lattice distortion of the films by means of X-ray diffraction. Pure perovskite phase is obtained by adding the dopant up to 5 at. % Fe. The tetragonal lattice distortion and lattice parameters decrease by adding Fe and reach to its minimum level of c t = 4.024 A and a t = 3.966 A at 3 at. % Fe. The surface morphology and grain size are surveyed using field emission scanning electron microscopy, which shows the reduction in grain size by adding the dopant. Polarization-voltage loops and dielectric constants of the films are calculated by electrical measurement and illustrate reduction in the polarization by increasing Fe dopant. The highest value of coercive voltage is achieved at 3 at. % Fe. Moreover, the lowest dielectric constant of 318 is obtained at 5 at. % Fe. Nanostructured crack-free Fe-doped PZT thick films are successfully prepared by using modified sol–gel route with different Fe dopant percentages (a) surface morphology of PF(3 %)ZT, (b) cross section of PZT thick film.

Fabrication and characterization of fast response pyroelectric sensors based on Fe-doped PZT thin films

Pyroelectric IR-detectors based on Pb(1−y)Fey(Zrx,Ti(1−x))O3 thin film have been successfully fabricated via ex situ oxidization annealing of DC magnetron sputtered conductive Fe doped lead-zirconium-titanium thin film on Au/SiO2/Si substrates. Structural as well as electro-optical properties were characterized. The results indicate that Fe-doping has had a remarkable structural effect namely, grain-size reduction, enhanced device voltage responsivity, 67.23 mV/mJ, and current-sensitivity, 5.16 × 10−6 mA/mJ. Moreover the pyroelectric coefficient, 609 μC m−2 °C−1, and merit figure, 1.43 × 10−6 μC m J−1, were significantly enhanced in comparison to previous reports on composite thick and thin film PZT and non-PZT based device structures.

Effect of dopants on ferroelectric and piezoelectric properties of lead zirconate titanate thin films on Si substrates

Lead zirconate titanate Pb(Zr0.52Ti0.48)O3 (undoped PZT) and doped PZT thin films with thickness of about 500 nm were grown on Pt/Ti/SiO2/Si substrates by pulsed laser deposition (PLD). In this study, 1.0 mol% Nb-doping (at Zr/Ti site) as donor, 1.0 mol% Fe-doping (at Zr/Ti) as acceptor and 10 mol% Ba-doping (at Pb site) as isovalence were used. The effects of the introduction of these dopants on the ferroelectric and piezoelectric properties were investigated and compared to the undoped PZT film. A noticeable improvement of the dielectric constant (ε) and effective piezoelectric coefficient (d33,f) are obtained. The maximum values of these parameters vary from 1280 and 126 pm/V for undoped PZT film to 1520 and 164 pm/V for Nb-doped PZT film. The largest remnant polarization (Pr) and coercive field (Ec) are obtained for Fe-doped PZT film, equal to 22.6 µC/cm2 and 35.3 kV/cm, as compared to 17.3 µC/cm2 and 31.2 kV/cm respectively for undoped PZT film. The Ba-doping decreases the dielectric constant but enhances the breakdown field of the film, reaching 800 kV/cm while it was only 660 kV/cm for undoped PZT film. The crystalline structure of Ba-doped film has a dominating (110) orientation instead of (100) in case of undoped, Nb-, and Fe-doped PZT films. The obtained results are important for the applications of doped PZT films in piezoMEMS devices.

Effect of Fe-doping concentration on microstructure, electrical, and magnetic properties of Pb(Zr0.5Ti0.5)O3 thin films prepared by chemical solution deposition

The highly (l00) oriented Pb(Zr0.5Ti0.5)O3 thin films with different Fe3+ doping concentrations were fabricated on LaNiO3-coated silicon substrates by chemical solution deposition. And the microstructure, ferroelectric, leakage, and magnetic properties were investigated. The results indicate that incorporation of Fe3+ into PZT thin films can promote the degree of the lattice distortion and greatly improve the surface roughness. In comparison with the pure PZT sample, the ferroelectric hysteresis loops of Fe-doped PZT samples demonstrate larger and larger polarizations and coercive fields with the increase in Fe3+ doping amount. Moreover, leakage mechanism of present films evolves from the space charge limited conduction to the “modified” space charge limited conduction, and then returns to the space charge limited conduction with increasing Fe3+ doping concentration. The occurrence of exchange bias in these Fe-doped PZT samples implies that the magnetic exchange interaction can be explained by the bound magnetic polaron model.

Effect of acceptor and donor dopants on polarization components of lead zirconate titanate thin films

We have compared the magnitudes of reversible and irreversible polarization components of sol–gel-derived Nd3+- and Fe3+-doped PZT (53/47) thin films on platinized silicon substrates. Beyond the switching field, it was found that the reversible component of the polarization remains almost constant both for donor- (Nd3+) and acceptor- (Fe3+) doped PZT films. The irreversible polarization component reduces with the increase in Nd3+ content, whereas it increases until 3 at. % Fe3+-doped PZT thin films. The dielectric behavior of these films at subswitching fields was analyzed in terms of Rayleigh law. The inverse of the Raleigh coefficient (υ) was considered as a measure of the obstacle for the domain-wall motion. In the case of Fe-doped PZT, the inverse of the Raleigh coefficient (υ) shows a declining linearity with Fe content, which may be found exactly opposite to that observed for Nd-doped PZT. The observed results are explained in terms of the nature of the defect-domain-wall interaction of acceptor-and-donor-doped PZT thin films. Studies indicated that in the case of Fe-doped PZT films, the possible defect interaction initiates only above 2 at. % and it was found to be much lower in magnitude in comparison with the Nd doping.

Schottky barrier effects in the electronic conduction of sol–gel derived lead zirconate titanate thin film capacitors

Pure and Fe-doped Pb(Zr0.53Ti0.47)O3 (PZT) thin film capacitors were fabricated by the sol–gel method and the leakage current versus voltage characteristics of these films were investigated at several temperatures and initial polarization states. After the initial poling of ferroelectric thin films, we measured two kinds of leakage current: (i) the full-switching current measured against an initial polarization direction and (ii) the nonswitching current measured toward an initial polarization direction. In the case of the full-switching current measurement, the anomaly of leakage current due to the switching of space charges was observed, which we suggest to be accumulated at a Schottky barrier region near an electrode or a gain boundary. In the case of the nonswitching current measurement, the Schottky diode rectifier current and the field-enhanced Schottky (ES) emission current came out without the switching current. The Poole–Frenkel emission process was dominant over ES emission for a Fe-doped PZT thin film having a large amount of space charge and traps. The height of the Schottky barrier in a Au/PZT film/Pt capacitor was measured to be 0.64 eV.

Analysis of Fatigue Characteristics in Fe-doped Pb(Zr 0.52Ti 0.48)O 3 Thin Films by Switching Currents

The polarization fatigue for ferroelectric Pb(Zr0.52Ti0.48)O3 (PZT) thin films has a known relation with oxygen vacancies occurring in the films during fabrication processes. Fe-doped PZT thin films were intentionally deposited with consideration for the effects of oxygen vacancies regarding fatigue using rf-magnetron sputtering. The remanent polarization is suppressed to half its initial value after 109 bipolar switching cycles. From the observance of the switching currents with consideration to applied voltages, switching characteristics in the films were studied by fitting using the Kolmogorov-Avrami (K-A) theory. It was revealed from the switching currents as a function of fatigue cycles that the quantity of switched charges decreased with increasing switching cycles, but the dimensionality with respect to domain growth was unchanged as compared to its initial value. The velocities of domain wall motions before and after fatigue were also unchanged, indicating that the motion of the domain walls by applied pulse voltages was not an additional obstacle concerning fatigue processes. Therefore, in the case of polarization fatigue by subjecting to electric cycles, the domain states in these films may not be affected by the fatigue.

Domain wall and volume contributions to material properties of PZT ceramics

Abstract A set of complex dielectric, piezoelectric and elastic constants has been measured in a temperature range between 4.2 K and the Curie point on undoped and Fe-doped PZT samples. All samples show a pronounced relaxation below 400 K which is attributed to domain wall vibrations according to an earlier developed model. A separation procedure allows to distinguish between the domain wall and the volume parts of the material constants. The relaxation peak in the losses and therefore the domain wall parts are shifted to higher temperatures by increasing the Zr content and they exhibit maximum values at the MPB. The volume contributions show a maximum at the MPB too. By increasing the Fe content the relaxation peak is shifted to lower temperatures and it decreases. This behaviour and the frequency dependence can be fitted by distributed thermally activated relaxation processes.

90°-domain wall relaxation in tetragonally distorted ferroelectric ceramics

A phenomenological model of a vibrating 90°-domain wall in an electric and mechanic stress field is presented. The model allows to separate the domain wall and the volume contribution to the complex dielectric, piezoelectric and elastic constants. The results are compared with representative measurements of the above mentioned six material parameters on a Fe-doped PZT sample. It turns out that the absolute values and the temperature dependencies of the intrinsic contributions are comparable to those obtained by a thermodynamical treatment. The ratio S0/P0 (spontaneous deformation/spontaneous polarization) which can also be derived in our model from the measured losses, is in good agreement with other measuring methods. It follows that, although there is as yet no physical interpretation for the loss mechanism, the conception of a vibrating 90°-domain wall under the above described conditions is a useful path towards a better insight into the material properties of ferroelectric ceramics.

Aging of fe-doped pzt ceramics and the domain wall contribution to the dielectric constant

Abstract The time dependence of the complex dielectric constant e of ferroelectric ceramics is well known as aging which is ascribed by most authors to a modification of the 90°-domain walls. Measurement of aging of Fe-doped PZT ceramic (rhombohedral) and Cr-doped BT ceramic (tetragonal), show that aging in these ceramics can be understood as a reduction of vibrating 90°-domain wall areas. This reduction of the domain wall contribution to the dielectric constant can be due either by pinning of parts of 90°-domain walls having high activation energies and/or by an increase in domain sue in time which reduces the total domain wall area. The increase of the domain sue during aging is ascribed to a thermally activated relief of internal stresses just by rearrangement of the domain configuration. The stress relaxes in a logarithmic time law which results from uniformly distributed activation energies between an upper and a lower limit. The measurements allow to distinguish clearly the bulk contribution and the...