Polarization Switching Properties Research Articles

Changing the polarization and mechanical response of flexible PVDF-nickel ferrite films with nickel ferrite additives

Polymer-based flexible nanocomposite films, of nickel ferrite nanoparticles in a polyvinylidene fluoride (PVDF) polymer matrix, were fabricated using a blade coating technique. A two-step process is used to prepare nanocomposite films. The first process involves the synthesis of nickel ferrite (NiFe2O4) nanoparticles using sonochemical method, and then incorporation of various weight percentage (5, 10, 20, and 30%) of nickel ferrite nanoparticles into the PVDF to form polymer nanocomposites. Nickel ferrite nanoparticles demonstrated a magnetization of 37.3 emu/g at magnetic field of 5 kOe while 30% Nickel-ferrite-PVDF nanocomposite shows 23.8 emu/g. Finally, the ferroelectric and local polarization switching properties of pure PVDF and nanocomposite films were investigated via piezoresponse force microscopy (PFM) measurements. The pure PVDF film demonstrates a negative piezoelectric coefficient from the PFM hysteresis loop measurement whereas the nanocomposite film shows a positive piezoelectric coefficient with an opposite PFM signal.

Identification of Ferroelectricity in a Capacitor With Ultra-Thin (1.5-nm) Hf0.5Zr0.5O2 Film

The characterization of ferroelectricity in ultra-thin ferroelectric (FE) films is highly challenging due to enlarged leakage current and resistive switching (RS) effect. In this study, we investigated the polarization switching properties of 1.5-nm thick Hf <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> Zr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (HZO) films via direct hysteresis remnant polarization/voltage (P-V) loop measurement. To reduce the leakage current and eliminate the RS effect, positive-up-negative-down (PUND) measurement was implemented on back-to-back connected complementary cells. Rational hysteresis loops, with remnant polarization of approximately 2 μC/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , were successfully obtained by directly measuring the polarization switching currents. In this study, we provide direct evidence of the stable ferroelectric property in 1.5-nm thick HZO films, and thereby show a potential prospect of ultimate scalability of HZO films.

Effects of strain on the electronic, optical, and ferroelectric transition properties of HfO2: ab initio simulation study

The amazing ferroelectricity observed in Hafnium oxide (HfO2) thin films is due to the existence of non-centrosymmetric orthorhombic Pca21 phase. In this study, the structural, electronic, optical, and polarization switching properties of the orthorhombic Pca21 phase with various strains are investigated by employing density functional theory (DFT) calculations based on the DFT. Out-of-plane and in-plane strains are taken into consideration. The results indicate that the band-gap values of orthorhombic HfO2 increase at first and then decrease from compressive strain to tensile strain due to the variation of the valence band maximum and the conduction band minimum. Moreover, orthorhombic HfO2 transforms into a direct bandgap material when compressive strain along the z direction is larger than or equal to 5%. A red-shift occurs under both tensile and compressive strains in the absorption edge compared with instinct HfO2 in the absorption spectra. The absorption intensity of the strained HfO2 is enhanced with the energy below 5.5 eV. The energy barriers of path A and path B of the polarization switching mediated by non-polar tetragonal phase are 116.8 and 91.2 meV per formula unit (meV/f.u.), respectively. In polarization switching without mediated by non-polar phase, the energy barriers decrease with the increasing of out-of-plane compressive strain along the x direction and tensile strain along the y direction compared with strain free structures.

Enhanced ferroelectric polarization in epitaxial superconducting–ferroelectric heterostructure for non-volatile memory cell

We report the growth and polarization switching properties of epitaxial ferroelectric–superconducting heterostructure PbZr0.52Ti0.48O3 (PZT) (100 nm)/YBa2Cu3O7−δ (YBCO) (100 nm) thin films for non-volatile ferroelectric random access memory elements. The epitaxial nature of the heterostructure is verified using the reciprocal space mapping data with the superconducting phase transition temperature (Tc) of nearly 25 K far below the Tc of as-grown YBCO under the same condition. The significant remanent polarization (Pr) ∼ 45 µC/cm2 at 1 kHz can switch from one state to another using 1 μs pulse. The devices meet the basic criteria of memory elements, such as high resistance ∼10 GΩ at 8 V, a butterfly-like capacitance–voltage (C/V) loop, significant polarization, a sharp change in the displacement current, long-time charge retention, and small fatigue at room temperature.

Ferroelectricity in CaBaCo4O7 by light non magnetic Zn doping

CaBaCo4O7 (CBCO) cobaltite shows a giant spin driven pyroelectric polarization below its ferrimagnetic transition temperature at 64 K. In the present study, we have investigated the structural, magnetic and electric polarization properties of light nonmagnetic Zn doped polycrystalline CaBaCo3.97Zn0.03O7 (CBCZO) cobaltite. Neutron powder diffraction studies on the CBCZO show that the Zn occupies the Co2 sites which lowers the strength of the magnetic interactions between the bitetrahedral cobalt c-axis chains. Further, we show that these chains act as magnetic clusters and causes the switching of the electric polarization. This study specifies that the ferrimagnetic–pyroelectric ground state of CBCO is very sensitive to the light non-magnetic doping and the results can be used to further understand the pyroelectric polarization switching properties of CBCO.

Diffused phase transition, ionic conduction mechanisms and electric-field dependent ferroelectricity of Nb/Ce co-doped Pb(Zr0.52Ti0.48)O3 ceramics

In this work, polycrystalline ceramics of the Pb(Zr0.52Ti0.48)0.95Nb0.05O3 + 0.2 wt% CeO2 (PZT-NC) compound were fabricated by the conventional solid-state reaction process from oxide precursors. Firstly, XRD analysis and SEM observation associated with EDS mapping were used for characterizing the phase structure, grain morphology and element composition of the specimens, respectively. And then, the temperature dependence of the dielectric properties were studied for the specimens in a wide frequency range of 1 kHz–1 MHz. The diffused phase transition behavior were comprehensively characterized in terms of the modified Curie-Weiss law involved in diffuseness and diffusivity. The dielectric loss mechanisms were explained by space charge conduction and domain wall relaxation. Further, the temperature dependent AC conductivity of the specimens were analyzed at a low frequency of 1 kHz. The electrical conduction mechanisms in three temperature regions: room temperature∼250 °C, 250∼400 °C, and 400∼500 °C, were associated with three different kinds of charge carriers. Finally, the polarization switching properties of the specimens were measured with the applied electric field of 30–50 kV/cm. The linear variation of coercive field, remanent polarization and maximum polarization with the electric-field amplitude demonstrated the field dependent ferroelectricity. As profited from the co-doping effect of Nb/Ce applied in the B-/A-site of the perovskite structure, the PZT-NC ceramics achieved many optimized electrical properties, including a high d33 (443 pC/N) and Tc (312 °C), a large g33 (35 × 10−3 Vm/N) and Pr (∼24 μC/cm2), as well as a low Ec (∼10 kV/cm), which make it possible for prospective applications in piezoelectric/ferroelectric devices.

Polarization driven self-biased and enhanced UV–visible photodetector characteristics of ferroelectric thin film

BiFeO3 is a promising multifunctional material in terms of its intriguing physics and diverse application potential. In this work, self-powered UV–visible photodetector characteristics of the polycrystalline BiFeO3 thin film exhibiting pronounced photo-response under both UV and visible light are demonstrated. Interestingly, the film displays switchable photodetector characteristics in accordance with the polarization switching properties and thereby confirms the role of polarization driven depolarization field on the observed properties. Importantly, the photodetector performance parameters such as responsivity , detectivity , photoconductive gain , and external quantum efficiency (5.3 %) observed under UV light are 2 to 4 order of magnitude higher than the values reported in similar oxide ferroelectric systems. These studies establish the application of polycrystalline BiFeO3 film as a self-powered UV–visible photodetector.

Switching Dynamics Analysis by Various Models of Hf0.5Zr0.5O2 Ferroelectric Thin Films

Recent discoveries of ferroelectric properties in ultrathin doped hafnium oxide (HfO2) have led to the expectation that HfO2 could overcome the shortcomings of perovskite materials and be applied to electron devices such as Fe-Random access memory (RAM), ferroelectric tunnel junction (FTJ) and negative capacitance field effect transistor (NC-FET) device. As research on hafnium oxide ferroelectrics accelerates, several models to analyze the polarization switching characteristics of hafnium oxide ferroelectrics have been proposed from the domain or energy point of view. However, there is still a lack of in-depth consideration of models that can fully express the polarization switching properties of ferroelectrics. In this paper, a Zr-doped HfO2 thin film based metal-ferroelectric-metal (MFM) capacitor was implemented and the polarization switching dynamics, along with the ferroelectric characteristics, of the device were analyzed. In addition, a study was conducted to propose an applicable model of HfO2-based MFM capacitors by applying various ferroelectric switching characteristics models.

Polarization and switching processes in multicomponent piezoceramic based on PZT with a highly diffuse phase transition

It is known that in a multicomponent piezoceramics with a certain ratio of the components of the solid solution and modifying impurities, the phase transition from the ferroelectric phase to the paraelectric phase occurs in several stages. The temperature interval of structural and polarization changes can reach hundreds of degrees. In the present work polarization switching processes and properties of a piezoceramic material based on PZT studied.

Structures and local ferroelectric polarization switching properties of orthorhombic YFeO3 thin film prepared by a sol–gel method**Project supported by the National Natural Science Foundation of China (Grant No. 61471301), Natural Science Basic Research Program of Shaanxi, China (Grant No. 2017JQ5083), and PhD Research Startup Foundation of Xi’an University of Science and Technology, China (Grant No. 2017QDJ044).

Orthorhombic YFeO3 thin film was prepared on La0.67Sr0.33MnO3/LaAlO3 substrate by a sol–gel spin-coating method. The structures of the YFeO3/La0.67Sr0.33MnO3/LaAlO3 (YFO/LSMO/LAO) sample were detected by x-ray diffraction pattern, Raman spectrometer, scanning electron microscopy, and atomic force microscope. The local ferroelectric polarization switching properties of the orthorhombic YFO film were confirmed by piezoresponse force microscopy (PFM) for the first time. The results show that the YFO film deposited on LSMO/LAO possesses orthorhombic structure, with ultra-fine crystal grains and flat surface. The leakage current of the YFO film is 8.39 × 10−4 A⋅cm−2 at 2 V, with its leakage mechanism found to be an ohmic behavior. PFM measurements indicate that the YFO film reveals weak ferroelectricity at room temperature and the local switching behavior of ferroelectric domains has been identified. By local poling experiment, polarization reversal in the orthorhombic YFO film at room temperature was further observed.

Polarization switching, dielectric, structural and elastic properties of 2-Methylbenzimidazole crystals and films

Single crystals and films of 2-methylbenzimidazole were grown from ethanol solution by slow cooling and evaporation method. 3D XRD study confirms pseudo tetragonal structure of MBI crystals. MBI films have a texture formed by spherulite type blocks with in-plane orientation of pseudo-tetragonal [001] axis. MBI crystals and films surface were studied by atomic force microscopy to evaluate Young’s modulus and surface potential distributions related to small charge of domain walls. Dielectric hysteresis loops were simulated in frames of particular case of KAI model. Strong decrease of activation field with temperature increase indicates a potential ferroelectric transition above melting point.

Local ferroelectric polarization switching properties of BiFeO3 nanodots and thin films depending on the ferroelectric polarization nanobit diameter

We investigated the local ferroelectric polarization switching characteristics of an epitaxial (001) BiFeO3 (BFO) thin film and BFO nanodots having 100–300-nm diameters. The 30-nm-thick BFO thin films were deposited on (100) Nb-doped SrTiO3 (Nb:STO) substrates via pulsed laser deposition. This large switching voltage of the BFO thin film originates from the neighboring domains that stabilize the ferroelectric polarization nanobit against the switching electric field induced by the external bias. The coercive voltages of the piezoelectric d33 hysteresis loops, which depend on the diameters of the BFO nanodots, were saturated to that of the BFO thin film, indicating that the influence of the neighboring domains is limited to within a diameter of approximately 300 nm.

Polarization Switching Dependence of VCSEL on Variable Polarization Optical Feedback

In this paper, the influence of variable-angle polarization-rotated optical feedback on the polarization switching properties of vertical-cavity surface-emitting lasers (VCSELs) is investigated theoretically and experimentally. The optical feedback (OF) level and the rotated polarization angle $\theta _{p}$ of OF are considered. Two configurations of OF are used to re-injected parallel and orthogonal polarization modes back into the VCSEL. For the parallel OF, it is shown that polarization switching (PS) of VCSELs’ modes can occur at a fixed feedback level and bias current with variable $\theta _{p}$ . However, in case of orthogonal optical feedback, PS occurs only at certain values of $\theta _{p}$ , particularly when the intensities of two polarization modes become comparable with each other. In the theoretical model for both OF conditions, there is good agreement between the experimental measurements and recent theoretical results reported in the literature.

Piezoelectric softening by Nb substitution in (Ba,Pb)ZrO3 ceramics

AbstractDonor doping is commonly applied for softening of the piezoelectric and dielectric properties and facilitation of polarization switching in the ubiquitous Pb(Zr,Ti)O3 [PZT] ceramics. The origin of the donor‐dopant effects is not entirely clear. (Pb,Ba)ZrO3 [PBZ] is a related ferroelectric material, its perovskite A‐site being partially occupied by the larger Ba+2 cation, less prone to evaporation than Pb+2, and the B‐site is occupied entirely by the valency‐stable Zr+4. Here we report on our studies of Nb+5 doping effects in (Pb,Ba)ZrO3. Similarly, to past observations on La+3 and Nb+5 doped PZT, we find a strong reduction in relative density of PBZ when the doping is &lt;0.5 atomic %. This is accompanied by lattice parameter reduction, enhanced PbO loss, smaller grain size and deterioration of dielectric, piezoelectric and polarization switching properties, the latter being opposite of expected softening effect. All those observations can be interpreted in terms of the Nb entering A‐site at small concentrations. This is supported by ab‐inito calculations and analysis of the possible defect reaction equations. The structure and microstructure of PBZ with Nb&gt;0.2% are consistent with Nb+5 entering the B‐site and softening effects are observed. The study supports the scenario of hardening due to domain walls pinning by VPb‐VO divacancies and softening upon decrease in their concentration.

Polarization switching and fatigue characteristics of highly (117)-oriented Bi3.15Nd0.85Ti2.99Mn0.01O12 ferroelectric thin films at both low and elevated temperatures

Polarization switching and fatigue properties of BNTM ferroelectric thin films were studied from 100 to 475 K. A combination of impedance spectra and PFM techniques was used to analyze the mechanisms of the dependence on temperature from 200 to 475 K.

Size-effect in layered ferrielectric CuInP2S6

We report on polarization switching properties of thin flakes of van der Waals ferrielectric CuInP2S6. We observe mesoscale polarization domains, ferroelectric switching, and the Curie temperature above 299 K down to a thickness of ∼50 nm. However, the electromechanical response is progressively suppressed below 50 nm, and vanishes at room temperature at a thickness of ∼10 nm. Though larger than a single layer, 10 nm is still a very small value compared to the expectations for an intrinsic ferroelectric semiconductor. We therefore propose a model for a doped surface layer that screens spontaneous polarization in this material. The charges in the screening layer may also participate in secondary chemical reactions, which may explain domain pinning observed in thermal cycling of the flakes above the Curie temperature. At the same time, ferroelectric switching is intertwined with ionic diffusion, resulting in erratic and damaging switching at room temperature. Owing to much stronger temperature dependence of ionic diffusion, the two phenomena can be decoupled allowing more reliable switching to be obtained at low temperatures.

Ferroic phase transitions and switching properties of modified BiFeO3–SrTiO3 multiferroic perovskites

Ferroelectric (FE), ferromagnetic (FM), and multiferroic phases are low-temperature lattice-deformed or/and spin-ordering phase through structural phase transition. Here, relaxor-FE and parasitic FM structural phase transitions with both ordering temperatures above 180 °C were observed in the A(Zn1/2Ti1/2)O3-modified BiFeO3–SrTiO3 (A = Bi, La) perovskite-structured ternary solid solution ceramics. Their ferroic polarization and magnetization switching properties were also observed at room temperature and demonstrated to be multiferroic compound.

Effect of bottom electrodes on polarization switching and energy storage properties in Pb0.97La0.02(Zr0.95Ti0.05)O3 antiferroelectric thin films

Abstract Polarization switching and energy storage properties of a series of Pb 0.97 La 0.02 Zr 0.95 Ti 0.05 O 3 (PLZT) thin films deposited on (100)-textured LaNiO 3 (LNO)-buffered Si substrates and (111)-textured Pt/Ti/SiO 2 /Si substrates were investigated. It was revealed that the PLZT films deposited on the (100)-textured LNO-buffered Si substrates prefer the (100) textured structure, while the orientation of the films deposited on the (111)-textured Pt-coated Si substrates is random. With respect to the films on the Pt-coated Si substrates, the (100) textured PLZT films have bigger compressive residual stress, larger electrical polarization, better dielectric properties, and better energy storage performances. For the (100)-orientated PLZT films, the energy density ( W s ) and efficiency ( η ) measured at room temperature are about 15.3 J/cm 3 and 56% respectively. Moreover, the better frequency stability in the range from 20 Hz to 10 kHz, and temperature stability in the range from 25 to 270 °C are demonstrated in the (100)-orientated PLZT films. These results indicate that the PLZT films with LNO bottom electrode could be potential candidate for applications in high energy storage density capacitors.

Influence of Variable-Polarization Optical Feedback on Polarization Switching Properties of Mutually Coupled VCSELs

The polarization switching (PS) properties of mutually coupled vertical-cavity surface-emitting lasers (VCSELs) subject to variable-polarization optical feedback (VPOF) are investigated numerically. Two injection schemes, parallel-polarization optical injection (PPOI), and orthogonal-polarization optical injection (OPOI) are considered. The effects of VPOF on PS properties are focused on, and the roles of feedback strength, injection strength, and frequency detuning are also discussed. The outputs in the time domain and the polarization evolution through the representation on the Poincare sphere are further presented to explain the dynamics during the PS process. For PPOI, both VCSELs exhibit similar PS properties, abrupt PS can be observed with the variation of polarizer angle, and are hardly affected by frequency detuning. For OPOI, both VCSELs exhibit mixed polarization for all polarizer angles when without frequency detuning. In particular, frequency detuning induced PS can also be observed for a given polarizer angle, and are affected by the leader-lagged relationship in terms of injection locking effect in mutually coupled VCSELs. These results provide an effective tool to obtain controllable PS in mutually coupled VCSELs, and give more insight into the polarization dynamics.

Enhanced polarization switching and energy storage properties of Pb0.97La0.02(Zr0.95Ti0.05)O3 antiferroelectric thin films with LaNiO3 oxide top electrodes

Polarization switching and energy storage properties of highly (100) oriented antiferroelectric (AFE) (Pb,La)(Zr,Ti)O3 thin films (≤250 nm) deposited via a sol-gel process with both LaNiO3 and Pt top electrodes were investigated. By using LaNiO3 top electrodes, the energy density as well as energy efficiency can be enhanced by 4.6 J/cm3 and 11%, respectively. Furthermore, the films with LaNiO3 top electrodes are more capable of providing high energy density over a wide temperature regime above room temperature compared to Pt. This work clearly highlights that oxide top electrodes can greatly improve the energy storage performance of antiferroelectric thin film capacitors.