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The ferroelectric properties of Pt/Pb(Zr0.6Ti0.4)O3/Pt/TiO2/SiO2/Si thin-film capacitors with different thicknesses are investigated. According to the literature data, tilting of the hysteresis loops and marked increase of the coercive fields are observed when the thickness of the film is reduced. The degradation of the switching properties is fully reproduced by simulations including nonferroelectric space-charge layers at both ferroelectric/electrode interfaces. Based on the theoretical results, a converse model is constructed from which the overall interface capacitance, the total interface built-in potential, and both dielectric permittivity and polarization of the bulk ferroelectric layer are determined for each film. Remarkably the polarization loop due to the switching domains, calculated for each Pb(Zr,Ti)O3 (PZT) capacitor, exhibited a squarelike shape with coercive fields in agreement with the bulk value. Moreover, a unique set of parameters was found whatever the film thickness. From our results it is concluded that the degradation of the ferroelectric properties of metal-PZT thin-film-metal capacitors, often encountered when their thickness is reduced, probably arises from a mechanism of modulation of density and sign of the space charge at both interfaces. [ABSTRACT FROM AUTHOR]

An epitaxial oxygen deficient Pb(Zr0.25,Ti0.75)O3 (PZT) thin film, which presented hysteresis loop with significant shift along the electric field axis and apparent polarization suppression, is investigated. Loop deformations are studied and entirely explained, both qualitatively and quantitatively by simulations including the effect of an ultrathin interfacial layer uniformly charged. The method developed in this paper is suitable to calculate not only the polarization due to the switching domains, but also all the characteristics of the space charge layer. The determination of the linear dielectric constant of the bulk ferroelectric layer does not require preparation of films with different thicknesses, unlike most of the methods proposed to date. Linear dielectric constant and thickness of the interfacial layer are in the range [variant_greek_epsilon]il=80–130 and dil=8–12 nm, respectively. On the other hand, a very large interfacial charge concentration (Nil of few 1026 m-3) is obtained. For the studied PZT sample, hysteresis deformations are not attributable to pinning of domain walls, despite the large value of Nil, but rather to the interfacial space charge layer that screens the applied electric field and prevents the full switching of the ferroelectric domains. [ABSTRACT FROM AUTHOR]

Experimental data on fatigue in the Metal/Ferroelectric/Metal thin film structures are reported. A model is proposed based on the trapping and the releasing of the free carriers in the band-gap states located at the interfaces between the electrodes and the ferroelectric film. Fits of the experimental data with the plots calculated from the model show very good agreement. In particular, the fatigue dependence on both the frequency and the magnitude of the applied voltage is well reproduced by the model. Saturation of fatigue for a large number of cycles is also predicted. [ABSTRACT FROM AUTHOR]

Switching Spectroscopy Piezoresponse Force Microscopy (SSPFM) stands out as a powerful method for probing ferroelectric properties within materials subjected to incremental polarization induced by an external electric field. However, the dense data processing linked to this technique is a critical factor influencing the quality of obtained results. Furthermore, meticulous exploration of various artifacts, such as electrostatics, which may considerably influence the signal, is a key factor in obtaining quantitative results. In this paper, we present a global methodology for SSPFM data processing, accessible in open-source with a user-friendly Python application called PySSPFM. A ferroelectric thin film sample of potassium sodium niobate has been probed to illustrate the different aspects of our methodology. Our approach enables the reconstruction of hysteresis nano-loops by determining the PR as a function of applied electric field. These hysteresis loops are then fitted to extract characteristic parameters that serve as measures of the ferroelectric properties of the sample. Various artifact decorrelation methods are employed to enhance measurement accuracy, and additional material properties can be assessed. Performing this procedure on a grid of points across the surface of the sample enables the creation of spatial maps. Furthermore, different techniques have been proposed to facilitate post-treatment analysis, incorporating algorithms for machine learning (K-means), phase separation, and mapping cross correlation, among others. Additionally, PySSPFM enables a more in-depth investigation of the material by studying the nanomechanical properties during poling, through the measurement of the resonance properties of the cantilever–tip–sample surface system. [ABSTRACT FROM AUTHOR]

Pyroelectric Pb(Zr 0.52 Ti 0.48 )O 3 films have been grown by sol–gel process on Si(001). Intrinsic pyroelectric coefficient has been measured through ferroelectric loops recorded at different temperatures and is about − 300 μC/m 2 K. Corresponding converted pyroelectric power density is estimated to be ~ 1 mW/cm 3 for a temperature variation of 10 °C every 6 s. Pyroelectric response of these films has been confirmed by direct measurements of the pyroelectric current with temperature variations at zero electric field. These results are of high interest for integrated thermally-sensitive devices. [ABSTRACT FROM AUTHOR]

We present a study of the chemistry of the nanostructured phase at the surface of lead zirconium titanate PbZr 0.52 Ti 0.48 O 3 (PZT) films synthesized by sol–gel method. In sol–gel synthesis, excess lead precursor is used to maintain the target stoichiometry. Surface nanostructures appear at 10% excess whereas 30% excess inhibits their formation. Using the surface-sensitive, quantitative X-ray photoelectron spectroscopy and glancing angle X-ray diffraction we have shown that the chemical composition of the nanostructures is ZrO 1.82−1.89 rather than pyrochlore often described in the literature. The presence of a possibly discontinuous layer of wide band gap ZrO 1.82−1.89 could be of importance in determining the electrical properties of PZT-based metal-insulator-metal heterostructures. [ABSTRACT FROM AUTHOR]

Abstract: A model based on trapping and releasing of free carriers in band gap states located at the interfaces between electrodes and the ferroelectric film is used to explain the restoration of polarization which is sometimes observed. Experimental data on two kinds of polarization restoration in metal/ferroelectric/metal thin film structures are reported. The increase of polarization, which may be observed at the early stage of fatigue test, is attributed to the release of carriers which are trapped in interfacial states at the virgin state, before fatigue test. On the other hand, the previously reported “self recovery effect” is attributed to a competition between the strength of a trapped carrier–ferroelectric dipole interaction and the applied voltage which acts on the dipole orientation. [Copyright &y& Elsevier]

The existence of threading dislocations in ferroelectric heterostructures has been frequently reported. However, their origin and impact on the ferroelectric properties are not sufficiently understood. PbZr 0.2 Ti 0.8 O 3 /SrRuO 3 heterostructures were epitaxially grown by pulsed-laser deposition (PLD) onto vicinal SrTiO 3 (001) substrates. The threading dislocations exhibited by the PbZr 0.2 Ti 0.8 O 3 films were investigated by cross-sectional and plan-view (high-resolution) transmission electron microscopy. Many threading dislocations were dissociated into dipoles spanning a, most probably lead-rich, stacking fault. It is likely that these dislocations are able to pin 180° ferroelectric domains, as suggested by a comparison between piezo-force microscope and transmission electron micrographs obtained on identical samples. Local backswitching of the polarization was observed in the vicinity of such threading dislocations. [ABSTRACT FROM AUTHOR]

Shifts of hysteresis loops along polarization axis are observed on non graded Pb(Zrx,Ti1-x)O3 ferroelectric films using a Sawyer-Tower circuit. The offsets become significant providing that the sense capacitor is large enough and the input resistance of the measurement set up is artificially increased. The offsets, consisting in DC voltages rather than DC polarizations, are thus not the exclusive feature of graded ferroelectric devices (GFD's). Our observations are consistent with the charging up of the sense capacitor by asymmetrical leakage currents in the film and strongly suggest that rectifying effects are probably involved in most of the vertical offsets observed on ferroelectric thin film capacitors. Assuming blocking contacts at the electrode—ferroelectric interfaces, we propose that the composition gradient in GFD's produces a variation of the band gap energy leading to potential barrier with different heights at the two interfaces. Such asymmetry of the energy band diagram is consistent with our hypothesis of asymmetrical leakage currents. [ABSTRACT FROM AUTHOR]

Highly [111]- and [100]-oriented compositionally graded PZT thin films have been grown at 500 °C on platinized silicon substrates by in situ RF sputtering. Electrical measurements will be presented in links with the layers structural properties. We show that the graded nature of the film alone does not seem to be sufficient to observe a polarization offset. We suggest that asymmetrical leakage currents may be at the origin of this offset. [Copyright &y& Elsevier]

Highly (1 0 0) oriented Pb(Zr, Ti)O3 (PZT) thin films have been grown in situ at 500 °C on Pt electrode by rf magnetron sputtering. The Pt bottom electrode has been sputtered in situ and influence of Pt deposition temperature on structural and electrical properties of PZT films have been investigated. The effect of preparation conditions of Pt top electrodes has also been examined. It was found that properties of PZT thin films were strongly dependent on the deposition temperature of the bottom electrode and on both the rf power and plasma composition during the sputtering of the top electrode. [Copyright &y& Elsevier]

Piezoelectric response hysteresis curves of Pb(Zr0.2Ti0.8)O3-based capacitors have been measured by piezoresponse force microscopy. The piezoelectric coefficient d33 was found to vary considerably depending on the position of the probing tip on the top electrode for films possessing a c/a/c domain structure. d33 values up to 125 pm/V, which is twice the theoretical value for a clamped film, have been measured. The spatial variations of the piezoelectric response amplitude is explained by a local movement of ferroelastic 90° a domains. This work experimentally proves the local enhancement of the polarization near the 90° wall boundaries, as predicted by Ishibashi et al. [Jpn. J. Appl. Phys. 44, 7512 (2005)]. [ABSTRACT FROM AUTHOR]

Photovoltaic properties of the metal-ferroelectric-metal structures, having SrRuO3 metal oxide electrodes and Pb(Zr,Ti)O3 (PZT) as ferroelectric layer, are investigated by the short-circuit photocurrent (SC-PHC) in the 200–800 nm wavelength domain. The band-gap dependence on the Zr content was determined from the spectral distribution of the SC-PHC signal. It was found that the band-gap value increases linearly with the Zr content, from about 3.9 eV to about 4.4 eV. It is shown that the sign and the magnitude of the signal depend on the internal bias and on the spontaneous polarization direction and value. The photocurrent describes a hysteresis loop similar to that of the ferroelectric polarization and can be used as a nondestructive readout of the nonvolatile memories based on PZT films. The existence of a significant SC-PHC signal at wavelengths corresponding to subgap energies is attributed to the presence of charged, deep levels in the forbidden band. It is also shown that the epitaxial PZT films have the potential for solid-state UV detectors, with current responsivity as high as 1 mA/W. The results are not entirely consistent with a bulk photovoltaic effect and are discussed in the frame of a Schottky barrier model for the metal-ferroelectric interface. [ABSTRACT FROM AUTHOR]

We present a method to perform elastic measurements on a thin-film as a function of frequency between a few GHz and a few hundred GHz. The technique is mainly based on Picosecond Acoustics (PA), which is an ultrafast optical technique that realizes pulse-echo measurements in the hypersonic range. Here, we combine gold layers serving as transducers and several opto-acoustic detection mechanisms to extend the PA technique to the lowest accessible frequencies (a few GHz) up to hundreds of GHz. We can therefore use the same technique on the same material to explore its elastic properties at a certain frequency over a very large frequency range. We have then applied this technique to explore the elastic properties of a lead zirconate titanate thin film from 3 to 80 GHz. We report a 9% increase in the longitudinal sound velocity above 20 GHz, which corresponds to a 19% increase in the C33 elastic modulus. We interpret such an observation as a direct evidence of ferroelastic domain wall relaxation. [ABSTRACT FROM AUTHOR]

We observed that electric field induces phase transition from tetragonal to rhombohedral in polycrystalline morphotropic lead zirconate titanate (PZT) films, as reported in 2011 for bulk PZT. Moreover, we evidenced that this field-induced phase transition is strongly correlated with PZT film piezoelectric properties, that is to say the larger the phase transition, the larger the longitudinal piezoelectric coefficient d33.eff. Although d33.eff already reaches 130 - 150 pm/V, our observation suggests that one could obtain larger d33.eff values, namely 250 pm /V , by optimizing the field-induced phase transition thanks to composition fine tuning as close as possible to the morphotropic phase boundary. [ABSTRACT FROM AUTHOR]

A direct quantification of a structural in-depth composition in the lead zirconate titanate Pb(Zr,Ti)O3 thin films of morphotropic composition has been conducted using the newly available X-ray nano-pencil beam (i.e., beam size of 100 nm ×1 μm) diffraction approach. We tested two samples with different Zr/Ti chemical gradients. Here, we demonstrate the presence of a significant microstructural gradient between the rhombohedral and tetragonal phases through PbZrxTi1-xO3 (PZT) films with a 100 nm in-depth resolution. The phase gradient extends over around 350 nm, and it is repeated through the PZT film three times, which corresponds to the number of thermal annealings. Moreover, this microstructural gradient is in agreement with the Zr/Ti chemical gradient observed by the secondary ion mass spectroscopy (SIMS). Indeed, the quantity of tetragonal phases rises in the Ti-rich zones as revealed by SIMS, and the quantity of rhombohedral phases rises in the Zr-rich zones. We also demonstrated a huge difference in the in-depth phase variation between the two tested samples. The gradient free sample still contains 4.7% of phase variation through the film and the amplified gradient contains 9.6% of phase variation through the film. Knowing that the gradient free sample shows better electric and piezoelectric coefficients, one can draw a correlation between the chemical composition, crystallographic homogeneity, and electromechanical properties of the film. The more close the film is to the morphotropic composition and the more it is crystallographically homogeneous, the higher the piezoelectric coefficients of the PZT are. Finally, the adequate knowledge of phase variation and its relation to the fabrication technique are crucial for the enhancement of the PZT electro-mechanical properties. Our methodology and findings open up new perspectives in establishing a relevant quantitative feedback to reach an ultimate electro-mechanical coupling in the sol-gel PZT thin films. [ABSTRACT FROM AUTHOR]

Abstract: In this study, a self-sensitive piezoelectric cantilever with a new design for sensing is presented. Micro-cantilevers were actuated by a 120nm-thick Lead Zirconate Titanate Oxide (PZT) layer. Detection was done by measuring the resistance of a metallic gauge integrated on the surface of the micro-piezoelectric cantilevers. Some metallic gauges were embedded in a Wheatstone bridge to improve the measured resistance accuracy. Devices with direct resistance measurement were also realized. Gauge resistance responses were compared with an optical measurement by a White Light Interferometer. By biasing the PZT between −5V and 5V, cyclic deflection of the cantilever was detected with both optical and metallic gauge resistance systems. The two measurements fit. This self-sensitive piezoelectric cantilever can be used for fatigue test with packaged devices. [Copyright &y& Elsevier]

We have performed Sawyer–Tower hysteresis measurements on micron sized Pb(Zr,Ti)O[sub 3] (PZT) capacitors prepared on Pt/Ti/SiO[sub 2]/Si substrates and patterned with a focused ion beam. Owing to a numerical compensating technique, we show that the increase of both linear dielectric constant [variant_greek_epsilon][sub r] and maximum polarization P[sub max], when decreasing the size of the capacitors, is artificial and mainly due to the parasitic effect of the probing setup. Moreover, a suitable method is proposed to accurately determine and correct for the additional parasitic capacitance in parallel with the standard capacitor. Under these conditions, the dielectric and ferroelectric properties of micron sized PZT capacitors are found to be quite similar to those measured on a large contact, i.e., the device properties are area independent. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We present a technique to measure the temperature dependence of the transverse piezoelectric coefficient e31, f of thin films of lead zirconate titanate (PZT), aluminum nitride, and BaTiO3 deposited on Si wafers. It is based on the collection of electric charges induced by the deflection of a Si cantilever coated with the piezoelectric film. The aim of this work is to assess the role of temperature in the decay of the remnant polarization of these materials, in particular, in optimized gradient-free PZT with composition PbZr0.52Ti0.48O3. It is found that in contrast to theoretical predictions, 31, f decreases with temperature because of the dominance of relaxation effects. The observation of steps in the logarithmic aging decay law is reminiscent of memory effects seen in frustrated spin glasses. [ABSTRACT FROM AUTHOR]

Offsets of hysteresis loops along the polarization axis have been observed on a step graded Pb(Zr,Ti)O[sub 3] (PZT) thin film using a Sawyer–Tower (ST) circuit. However, the same effect may be artificially reproduced by adding adequate resistors and diodes in parallel with a nongraded PZT thin film. The hypothesis that the offsets were mainly due to the asymmetrical charging up of the standard capacitor used in the ST circuit, allows us to establish that the graded ferroelectric sample behaves as a kind of rectifying device. It is concluded that the presence of asymmetrical leakage currents in compositionally graded devices may allow the elucidation of the origin of the offsets often observed in these structures. Correlatively, it is demonstrated that such offsets do not represent an abnormal static polarization but a dc voltage. The E[sub m][sup 4] power law dependence of the offsets (where E[sub m] is the amplitude of the electric field) was found to be attributable to the nonlinear increase of the net leakage current. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

An 85 nm-thick morphotropic PbZr0.52Ti0.48O3 (PZT) film grown epitaxially and [001]-oriented onto a SrTiO3-buffered Si-wafer is investigated using temperature dependent X-ray diffraction. Two phase transitions, at Trt~500K and Tc~685 K, are evidenced and are attributed to structural phase transitions from monoclinic-like to tetragonal-like phase and from tetragonal to paraelectric phase, respectively. The stronger upper shift of Trt value with respect to the bulk one and the weakly affected Tc (Tc bulk~665 K) are explained assuming misfit strain changes when crossing Trt. This finding opens new perspectives for piezoelectric PZT films in harsh applications. [ABSTRACT FROM AUTHOR]

Abstract: We report in this work the epitaxial growth and the electrical characteristics of single crystalline Pb(Zr0.52Ti0.48)O3 (PZT) thin film on SrTiO3(STO)-buffered Si(001) substrate. The STO buffer layer deposited by molecular beam epitaxy allows a coherent oxide/Si interface leading enhanced PZT crystalline quality. 70nm-thick PZT (52:48) layer was then grown on STO/Si(001) by sol–gel method. X-ray diffraction demonstrates the single crystalline PZT film on Si substrate in the following epitaxial relationship: [110] PZT (001)//[110] STO (001)//[100] Si (001). The macroscopic electrical measurements show a hysteresis loop with memory window of 2.5V at ±7V sweeping range and current density less than 1μA/cm2 at 750kV/cm. The artificial domains created by piezoresponse force microscopy with high contrast and non-volatile properties provide further evidence for the excellent piezoelectric properties of the single crystalline PZT thin film. [Copyright &y& Elsevier]

Abstract: Ba0.7Sr0.3TiO3 (BST) thin films 500nm in thickness were prepared on technologically desirable Pt/TiO2/SiO2/Si(100) substrates by ion beam sputtering (IBS) and post-deposition annealing method. The effect of annealing temperature on the structural and dielectric properties of BST thin films was systematically investigated. A sharp transition in their tunable dielectric behaviours was observed in good agreement with the evolution of crystal structure from amorphous to crystalline phase. It was demonstrated that the perovskite phase could crystallize in BST films at a very low temperature, around 450°C. The lowering of perovskite crystallization temperature in the BST films was explained in terms of the high energetic process nature of IBS technique. A high dielectric tunability of 42% at E (electric field intensity)=500kV/cm and a low loss tangent of 0.013 at zero bias were both obtained in the 450°C-annealed film, thereby resulting in the highest figure-of-merit factor among all the different temperature annealed films. Moreover, the 450°C-annealed film showed superior leakage current characteristics with a low leakage current density of about 10−4 A/cm2 at E =800kV/cm. [Copyright &y& Elsevier]

We demonstrate piezoelectrically actuated, electrically tunable nanomechanical resonators based on multilayers containing a 100-nm-thin aluminum nitride (AlN) layer. Efficient piezoelectric actuation of very high frequency fundamental flexural modes up to ∼80 MHz is demonstrated at room temperature. Thermomechanical fluctuations of AlN cantilevers measured by optical interferometry enable calibration of the transduction responsivity and displacement sensitivities of the resonators. Measurements and analyses show that the 100 nm AlN layer employed has an excellent piezoelectric coefficient, d31=2.4 pm/V. Doubly clamped AlN beams exhibit significant frequency tuning behavior with applied dc voltage. [ABSTRACT FROM AUTHOR]

Hysteresis measurements performed on graded Pt/lead zirconate titanate (PZT)/Pt structures with well oxygenated PZT films do not display any shift along the polarization axis (V[sub offset]) as previously reported. On the other hand, when the PZT graded films were grown under low oxygen pressure, an offset voltage was measured. This shift was systematically enhanced after cycling the film as for fatigue measurements. It was also observed that the V[sub offset] is independent of the value of the reference capacitor used in the Sawyer-Tower circuit. We propose an asymmetry in the leakage current of the structure to be at the origin of the shift along the polarization axis. [ABSTRACT FROM AUTHOR]

Focuses on the hypothesis on the origin of the shift along the polarization axis exhibited by graded structures. Accounts on the symmetries in leakage currents; Increase of the input resistance of the measurement set-up; Offsets of the hysteresis loops of graded ferroelectric films.