Ferroelectric Pb Zr Research Articles

High-performance self-powered visible-blind ultraviolet photodetection achieved by ferroelectric PbZr0.52Ti0.48O3 thin films

Self-powered visible-blind ultraviolet (UV) photodetection has been generally achieved based on the built-in electric field formed within the complicated devices such as pn or Schottky junctions, which involves a complicated device fabrication process. In contrast, employing the ferroelectric materials featured with unique bulk photovoltaic effect as absorbers will simplify the device structure and the subsequent device fabrication process without losing the performance of self-powered photodetection. In the current work, the fabrication of high-performance self-powered visible-blind UV photodetectors based on ferroelectric PbZr0.52Ti0.48O3 (PZT) thin films has been reported. The results showed that the spin-coated PZT thin films exhibited superior ferroelectric properties. On this basis, an efficient, stable, and repeatable self-powered UV photodetection has been achieved in the Au/PZT/FTO (fluorine-doped tin oxide) structured devices with the responsivity and detectivity as high as 0.092 A/W and 1.2 × 1012 Jones, respectively. More interestingly, the self-powered photocurrent has been further enhanced when downward polarizing the PZT thin film. The results reported in this work highlight the superiorities of ferroelectric PZT-based self-powered visible-blind UV photodetectors and provide valuable strategies for the fabrication of high-performance self-powered photodetectors with a simplified device structure in the future.

Significant Modulation of Ferroelectric Photovoltaic Behavior by a Giant Macroscopic Flexoelectric Effect Induced by Strain‐Relaxed Epitaxy

AbstractFlexoelectricity has become an emerging tool to tailor the material properties. The flexoelectric modulation of ferroelectric photovoltaic (FEPV) properties is of particular interest, because it offers an opportunity to boost the photovoltaic efficiency. In most previous studies, the flexoelectric effect is generated by local pressing or macroscopic bending, which, however, results in a local or weak modulation of the FEPV behavior. Here, a significant modulation of the FEPV effect by the strain‐relaxed epitaxy (SRE)‐induced giant macroscopic flexoelectric effect is demonstrated. Using SRE, giant strain gradients (>107 m−1) are generated and tuned in ferroelectric Pb(Zr0.2Ti0.8)O3 epitaxial films. Tuning the giant strain gradient can significantly modify the switchable FEPV properties. Particularly, a photovoltage enhancement as large as ≈0.5 V is achieved. It is suggested that the flexoelectric modulation of FEPV behavior may originate from the flexoelectric polarization‐induced depolarization field. This study highlights the immense application potential of the SRE‐induced flexoelectricity in the engineering of functional thin‐film devices.

Local and correlated studies of humidity-mediated ferroelectric thin film surface charge dynamics

Electrochemical phenomena in ferroelectrics are of particular interest for catalysis and sensing applications, with recent studies highlighting the combined role of the ferroelectric polarisation, applied surface voltage and overall switching history. Here, we present a systematic Kelvin probe microscopy study of the effect of relative humidity and polarisation switching history on the surface charge dissipation in ferroelectric Pb(Zr0.2Ti0.8)O3 thin films. We analyse the interaction of surface charges with ferroelectric domains through the framework of physically constrained unsupervised machine learning matrix factorisation, Dictionary Learning, and reveal a complex interplay of voltage-mediated physical processes underlying the observed signal decays. Additional insight into the observed behaviours is given by a Fitzhugh–Nagumo reaction–diffusion model, highlighting the lateral spread and charge passivation process contributors within the Dictionary Learning analysis.

Bipolar Resistive Switching in Magnetostrictive Ni/PZT/Pt Structure for Non-Volatile Memory Applications

Resistive switching (RS) has significant potential for the forthcoming generation in logical and non-volatile memory devices. Owing to their switchable spontaneous polarization ferroelectric materials can be utilized for non-volatile memory applications, e.g., FeRAM, but their destructive readout scheme limits applications. The spontaneous electrical polarization of ferroelectric materials enhances the tuning charge properties at the ferroelectric/metal interface making them appropriate for RS applications. Here, the resistive switching performance of ferroelectric Pb(Zr0.6Ti0.4)O3 (PZT) thin film grown on flexible Ni substrate using pulsed laser deposition were investigated. The PZT film showed both entrenched P-E ferroelectric hysteresis loop and reversible resistive switching behaviors with DC voltage sweep. Bipolar switching between a low resistance state to a high resistance state with a large ON/OFF ratio of 102 and resistance retention potential up to 1010 cycles was observed. The current conduction mechanism can be understood by dual logarithm I-V curve fitting. The obtained results encourage the utilization of prepared Ni/PZT/Pt widget for the non-volatile memory applications.

Size-dependent electromechanical response and ferroelectric behavior of engineered morphotropic phase boundary PbZr1−xTixO3 nano-heterostructures

An enhancement of electromechanical performance in ferroelectric materials commonly requires a delicate control of compositions to the proximity of morphotropic phase boundary. Here, we demonstrate an alternative design strategy for enhanced electromechanical responses by engineering ferroelectric PbZr1−xTixO3 nano-heterostructures, where the overall composition is near the morphotropic phase boundary yet compositions of constitutive layers are far from the boundary. Effects of layer thickness on the ferroelectric and piezoelectric properties of such engineered heterostructures are investigated by using phase field model. The obtained results reveal unusual behaviors of domain structures according to the reduction of film thickness. Importantly, piezoelectricity can be enhanced significantly due to the strong interaction among polarization phases near the interfaces when the layer thickness reduces. In addition, the coercive electric field also decreases, which facilitates the polarization switching. Ultimately, this study paves a route for artificial heterostructure design to enhance electrical and electromechanical performances.

Прямой магнитоэлектрический эффект в двухслойных керамических композитах на основе ферримагнетика Mn-=SUB=-0.4-=/SUB=-Zn-=SUB=-0.6-=/SUB=-Fe-=SUB=-2-=/SUB=-O-=SUB=-4-=/SUB=- и сегнетоэлектрика PbZr-=SUB=-0.53-=/SUB=-Ti-=SUB=-0.47-=/SUB=-O-=SUB=-3-=/SUB=-

Under different experimental conditions, the direct magnetoelectric effect was studied in two-layer composites prepared both by joint sintering of layers of powders of ferrimagnet Mn0.4Zn0.6Fe2O4 and ferroelectric PbZr0.53Ti0.47O3 and by gluing plates pre-sintered from powder materials of Mn0.4Zn0.6Fe2O4 and PbZr0.53Ti0.47O3. It was found that sintered composites show greater values of the magnetoelectric effect than composites prepared by gluing sintered plates together. The revealed regularities are in good agreement with the conclusions from the theoreti-cal model of the effective parameters of the heterogeneous environment.

Understanding nanoscale structural distortions in Pb(Zr0.2Ti0.8)O3 by utilizing X-ray nanodiffraction and clustering algorithm analysis.

Hard X-ray nanodiffraction provides a unique nondestructive technique to quantify local strain and structural inhomogeneities at nanometer length scales. However, sample mosaicity and phase separation can result in a complex diffraction pattern that can make it challenging to quantify nanoscale structural distortions. In this work, a k-means clustering algorithm was utilized to identify local maxima of intensity by partitioning diffraction data in a three-dimensional feature space of detector coordinates and intensity. This technique has been applied to X-ray nanodiffraction measurements of a patterned ferroelectric PbZr0.2Ti0.8O3 sample. The analysis reveals the presence of two phases in the sample with different lattice parameters. A highly heterogeneous distribution of lattice parameters with a variation of 0.02 Å was also observed within one ferroelectric domain. This approach provides a nanoscale survey of subtle structural distortions as well as phase separation in ferroelectric domains in a patterned sample.

Injection charge dynamics on the Pb(Zr0.52Ti0.48)O3 surface by scanning probe microscopy

The origin of an injected charge and its temperature dependence in ferroelectric Pb(Zr0.52Ti0.48)O3 (PZT) thin films is studied by multimode scanning probe microscopy. During the poling process in scanning probe microscope (SPM) measurement, which is a local bias applied by using a conductive tip on a film’s surface to induce polarization orientation, a strong charge injection is always observed in oxide ferroelectric films; therefore, the surface potential is dominated by injection charge rather than polarization and screening charge. The surface potential shows an increase with the increase in the applied bias and saturation at a higher bias, which is much higher than the coercive field in PZT films. The positive surface potential shows a clear increase after oxygen plasma treatment, suggesting that the injection behavior is significantly enhanced. Subsequent heating could recover the surface condition to the initial state. Charge injection could be weakened but could not be completely eliminated by heat treatment. The current results suggest that charge injection behavior could not be easily relaxed, and a careful control of the localized poling process using an SPM conductive tip is required especially for studying the charge state on the surfaces of ferroelectric thin films.

Unexpected band-bending of donor-doped PbZr[formula omitted]Ti[formula omitted]O[formula omitted] films

We present a study of the correlation between doping induced band shifts in ferroelectric PbZr0.52Ti0.48O3 (PZT) and the electrical characteristics of PZT-based capacitors. Sol-gel grown 220 nm PZT thin films were doped with 1 to 4% La or Nb donors at A and B-sites, respectively. The peak surface capacitance and breakdown field values are obtained for 2% La and Nb. The breakdown field decreases significantly for higher doping suggesting the formation of new conduction paths. Film chemistry is unchanged by La or Nb doping but band shifts are observed. La and Nb doping results in band bending towards the Fermi level, with a maximum shift also at 2% and La doping softens the ferroelectric state as seen from the reduction in the coercive field. The results are consistent with initial compensation of oxygen vacancies by La and Nb doping following thermal activation of defects.

Low‐Pressure Mechanical Switching of Ferroelectric Domains in PbZr0.48Ti0.52O3

AbstractLow‐energy switching of ferroelectrics is currently being investigated for energy‐efficient nanoelectronics. While conventional methods employ electrical fields to switch the polarization state, mechanical switching is investigated as an interesting alternative low‐energy switching concept, if low enough pressures could be achieved. Here, the thickness‐dependent mechanical and electrical switching behavior of ferroelectric PbZr0.48Ti0.52O3/YBa2Cu3O7−δ (PZT/YBCO) epitaxial heterostructures grown on single crystalline LaAlO3‐(001)pseudo‐cubic (LAO) substrate is reported. Mechanical switching is found under relatively low force (600 nN; estimated pressure ≈0.21 GPa) in atomic force microscopy‐based measurements. Mechanically switched domains can be erased by small electric fields and, interestingly, exhibit a surface potential change similar to electrically poled areas. The feasibility of switching these heterostructures with very low pressure makes them promising candidates for nanoscale electromechanical devices.

{001}-textured Pb(Zr, Ti)O3 thin films on stainless steel by pulsed laser deposition

In this work, we report nearly single oriented {001}-textured ferroelectric PbZr0.52Ti0.48O3 thin films grown by pulsed laser deposition onto AISI 304 stainless steel substrates. Pt, Al2O3, and LaNiO3 buffer layers promote the PbZr0.52Ti0.48O3 {001} texture and protect the substrate against oxidation during deposition. The dominant {001} texture of the PbZr0.52Ti0.48O3 layer was confirmed using x-ray and electron backscatter diffraction. Before poling, the films exhibit a permittivity of about 350 at 1 kHz and a dielectric loss below 5%. The films display a remanent polarization of about 16.5μCcm−2 and a high coercive field of up to Ec=135.9kVcm−1. The properties of these PbZr0.52Ti0.48O3 thin films on stainless steel are promising for various MEMS applications such as transducers or energy harvesters.

Gamma Radiation Detection Response of Pt/PZT/SRO Based Capacitor for Dosimetry Application

Radiation induced changes in the electrical properties of PbZrTiO3 (PZT) thin films have been studied for dosimetry application. The radiation detection was based on radiation induced changes in the electrical properties under the influence of gamma radiation. Epitaxial heterostructure of ferroelectric PbZr0.52 Ti0.48O3 (001)/SrRuO3 (SRO) were grown on single crystal SrTiO3 (001) substrates by pulsed laser deposition and platinum (Pt) electrode was deposited on top of the PZT film. The maximum capacitance of the heteroepitaxial capacitor devices was $\approx ~25$ pF with a corresponding small leakage current. The effect of gamma ( $\gamma $ -ray) irradiation on the intrinsic electrical behavior of the Lead Zirconate Titanate (PZT) capacitor devices were explored in form of the current–voltage (I–V) and capacitance–voltage (C–V) properties. The PZT devices were exposed to a 60Co Gamma source with 2.8 kGy/h dose rate from 0 kGy to 400 kGy doses. Gamma radiation induced broadening was observed in full width half maxima (FWHM) of the x-ray diffraction (00l) peak with the increasing gamma doses. All devices showed a consistence changes in conductance and capacitance with increasing gamma doses. The results demonstrated linear relationship in electrical response of PZT thin-film capacitors as a function of gamma doses. The device showed significant changes in the values of current and capacitance with the increase in dose up to 400 kGy and are therefore suitable for high-dose dosimetry applications.

New method to measure domain-wall motion contribution to piezoelectricity: the case of PbZr0.65Ti0.35O3 ferroelectric

A new data analysis routine is introduced to reconstruct the change in lattice parameters in individual ferroelastic domains and the role of domain-wall motion in the piezoelectric effect. Using special electronics for the synchronization of a PILATUS X-ray area detector with a voltage signal generator, the X-ray diffraction intensity distribution was measured around seven split Bragg peaks as a function of external electric field. The new data analysis algorithm allows the calculation of `extrinsic' (related to domain-wall motion) and `intrinsic' (related to the change in lattice parameters) contributions to the electric-field-induced deformation. Compared with previously existing approaches, the new method benefits from the availability of a three-dimensional diffraction intensity distribution, which enables the separation of Bragg peaks diffracted from differently oriented domain sets. The new technique is applied to calculate the extrinsic and intrinsic contributions to the piezoelectricity in a single crystal of the ferroelectric PbZr1−x Ti x O3 (x = 0.35). The root-mean-square value of the piezoelectric coefficient was obtained as 112 pC N−1. The contribution of the domain-wall motion is estimated as 99 pC N−1. The contribution of electric-field-induced changes to the lattice parameters averaged over all the domains is 71 pC N−1. The equivalent value corresponding to the change in lattice parameters in individual domains may reach up to 189 pC N−1.

Interfacial dielectric layer as an origin of polarization fatigue in ferroelectric capacitors

Origins of polarization fatigue in ferroelectric capacitors under electric field cycling still remain unclear. Here, we experimentally identify origins of polarization fatigue in ferroelectric PbZr0.52Ti0.48O3 (PZT) thin-film capacitors by investigating their fatigue behaviours and interface structures. The PZT layers are epitaxially grown on SrRuO3-buffered SrTiO3 substrates by a pulsed laser deposition (PLD), and the capacitor top-electrodes are various, including SrRuO3 (SRO) made by in-situ PLD, Pt by in-situ PLD (Pt-inPLD) and ex-situ sputtering (Pt-sputtered). We found that fatigue behaviour of the capacitor is directly related to the top-electrode/PZT interface structure. The Pt-sputtered/PZT/SRO capacitor has a thin defective layer at the top interface and shows early fatigue while the Pt-inPLD/PZT/SRO and SRO/PZT/SRO capacitor have clean top-interfaces and show much more fatigue resistance. The defective dielectric layer at the Pt-sputtered/PZT interface mainly contains carbon contaminants, which form during the capacitor ex-situ fabrication. Removal of this dielectric layer significantly delays the fatigue onset. Our results clearly indicate that dielectric layer at ferroelectric capacitor interfaces is the main origin of polarization fatigue, as previously proposed in the charge injection model.

High nonvolatile modulation of resistance on a ferroelectric PbZr0·2Ti0·8O3 /Nd0.3Sm0.25Sr0·45MnO3 liquid-gated electric-double-layer transistors

Abstracts A ferroelectric polarization field electric-double-layer transistor based on the PbZr0·2Ti0·8O3 (PZT)/Nd0.3Sm0.25Sr0·45MnO3 (NSSMO) structure gated by ionic-liquid was established. The electrostatic modulation on the NSSMO channel was performed by applying electric field, while the respective non-volatile field effect upon the polarization field of PZT was investigated. Interestingly, a nonvolatile modulation on the resistance of NSSMO channel was observed, depending on the ferroelectric polarization field from PZT layer. Moreover, a large modulation of electrical conductivity of the NSSMO channel was achieved when applying a bias voltage of +3 V. This result indicates that a high nonvolatile electrostatic effect can be achieved in complex oxides devices under ferroelectric polarization field.

Activity of Sub‐Band Gap States in Ferroelectric Pb(Zr0.2Ti0.8)O3 Thin Films

AbstractDefect or intermediate states within the band gap of ferroelectric oxides are known to impact functional characteristics such as saturated polarization. However, depending upon their respective position, such levels can also induce a substantial photoelectrical response under appropriate illumination and severely impact the conduction mechanism of an otherwise highly insulating material system. Sub‐band‐gap illumination is used to highlight the activity of these levels in epitaxially grown and ferroelectric Pb(Zr0.2Ti0.8)O3 thin films. Large transient effects are observed in relation to ferroelectric polarization and conductivity after illumination. In the case of polarization, light induces a “leaky” character, which eventually decays over a period of nearly 1.5 h. In conjunction, persistent photoconductivity is observed as the enhanced conductivity attained under illumination gradually decays over several minutes after removal of illumination. Thermally stimulated currents are measured to probe the presence of sub‐band gap states and analyze their effect over a wide range of temperature. The trapping nature of the states and their role in the conduction is found to be the underlying origin.

Comparative study of piezoelectric response and energy-storage performance in normal ferroelectric, antiferroelectric and relaxor-ferroelectric thin films

The energy-storage performance and piezoelectric properties were determined for epitaxial antiferroelectric (AFE) PbZrO3 (PZ), ferroelectric (FE) PbZr0.52Ti0.48O3 (PZT), and relaxor ferroelectric (RFE) Pb0.9La0.1Zr0.52Ti0.48O3 (PLZT) thin films that were deposited on to SrTiO3 buffered Si substrates. The films were investigated by directly measuring the polarization hysteresis loops and piezoelectric strain curves. The square polarization loop with a high remanent polarization and a large piezoelectric coefficient obtained in PZT thin films allow them to be useful for various applications in ferroelectric field effect transistors and/or in MEMS actuators. Meanwhile, there is a jump of about 0.9% in the strain curve of PZ thin films around the field-induced AFE-FE phase transition, which is useful in digital displacement transducers due to a good ON/OFF strain state. The large recoverable energy-storage density, excellent energy-storage efficiency, and low strain hysteresis due to a slim hysteresis loop combine to make PLZT thin films as a potential candidate for a broad range of applications from energy storage to nano-positioning precision systems.

Impact of fatigue behavior on energy storage performance in dielectric thin-film capacitors

The polarization hysteresis loops and the dynamics of domain switching in ferroelectric Pb(Zr0.52Ti0.48)O3 (PZT), antiferroelectric PbZrO3 (PZ) and relaxor-ferroelectric Pb0.9La0.1(Zr0.52Ti0.48)O3 (PLZT) thin films deposited on Pt/Ti/SiO2/Si substrates were investigated under various bipolar electric fields during repetitive switching cycles. Fatigue behavior was observed in PZT thin films and was accelerated at higher bipolar electric fields. Degradation of energy storage performance observed in PZ thin films corresponds to the appearance of a ferroelectric state just under a high bipolar electric field, which could be related to the nonuniform strain buildup in some regions within bulk PZ. Meanwhile, PLZT thin films demonstrated fatigue-free in both polarization and energy storage performance and independent bipolar electric fields, which are probably related to the highly dynamic polar nanodomains. More importantly, PLZT thin films also exhibited excellent recoverable energy-storage density and energy efficiency, extracted from the polarization hysteresis loops, making them promising dielectric capacitors for energy-storage applications.

Artificial Optoelectronic Synapses Based on Ferroelectric Field-Effect Enabled 2D Transition Metal Dichalcogenide Memristive Transistors.

Neuromorphic visual sensory and memory systems, which can perceive, process, and memorize optical information, represent core technology for artificial intelligence and robotics with autonomous navigation. An optoelectronic synapse with an elegant integration of biometric optical sensing and synaptic learning functions can be a fundamental element for the hardware-implementation of such systems. Here, we report a class of ferroelectric field-effect memristive transistors made of a two-dimensional WS2 semiconductor atop a ferroelectric PbZr0.2Ti0.8O3 (PZT) thin film for optoelectronic synaptic devices. The WS2 channel exhibits voltage- and light-controllable memristive switching, dependent on the optically and electrically tunable ferroelectric domain patterns in the underlying PZT layer. These devices consequently show the emulation of optically driven synaptic functionalities including both short- and long-term plasticity as well as the implementation of brainlike learning rules. Integration of these rich synaptic functionalities into one single artificial optoelectronic device could allow the development of future neuromorphic electronics capable of optical information sensing and learning.

Structural characterization of PZT and CFO/PZT films on (001) SrTiO3 by the pulsed laser deposition (PLD)

In this work, we investigated the structural properties of ferroelectric PbZr0.2Ti0.8O3 (PZT) and ferrimagnetic/ferroelectric [CoFe2O4(CFO)/PZT] bilayers grown on (001)SrTiO3 (STO) substrates with 50 nm thick LaNiO3 bottom electrodes via X-ray diffraction by θ-2θ scan, reciprocal space mapping (RSM), rocking curve, and phi-scan modes. Interestingly, structural properties of the PZT layer exhibited remarkable changes after the top-layer CFO deposition. Both the c- and a-domains exist in the PZT layer by the data acquired and the tetragonality of the PZT decreases after the CFO top-layer deposition.