Ferroelectric Research Articles

Ultralow Energy Consumption and Fast Neuromorphic Computing Based on La0.1Bi0.9FeO3 Ferroelectric Tunnel Junctions.

Low-power and fast artificial neural network devices represent the direction in developing analogue neural networks. Here, an ultralow power consumption (0.8 fJ) and rapid (100 ns) La0.1Bi0.9FeO3/La0.7Sr0.3MnO3 ferroelectric tunnel junction artificial synapse has been developed to emulate the biological neural networks. The visual memory and forgetting functionalities have been emulated based on long-term potentiation and depression with good linearity. Moreover, with a single device, logical operations of "AND" and "OR" are implemented, and an artificial neural network was constructed with a recognition accuracy of 96%. Especially for noisy data sets, the recognition speed is faster after preprocessing by the device in the present work. This sets the stage for highly reliable and repeatable unsupervised learning.

Polymerization-induced Chiral Self-assembly for the In situ Construction, Modulation, Amplification and Applications of Asymmetric Suprastructures.

In the polymerization-induced chiral self-assembly (PICSA) process, chiral functional monomers undergo spontaneous supramolecular self-assembly and asymmetric stacking during living polymerization, leading to the in situ generation of chiroptical polymer assemblies characterized by diverse morphologies. The PICSA strategy facilitates precise control and manipulation of both non-covalent supramolecular helices and covalent macromolecular helices within aggregated cores, thereby driving significant advancements in fields such as chiral recognition materials, asymmetric catalysts, nonlinear optical materials, and ferroelectric liquid crystals (LC). This minireview summarizes recent developments in the in situ chiroptical construction and modulation associated with the PICSA methodology. Furthermore, it seeks to elucidate emerging PICSA systems founded on various living polymerization mechanisms, exploring hierarchical chirality transfer processes and the pathway complexities in both equilibrium and non-equilibrium conditions. This minireview also presents several illustrative examples that demonstrate the practical applications of chiral polymer materials synthesized through the PICSA approach, thereby illuminating future opportunities in this innovative field.

Organic Ferroelectrics for Regulation of Electronic and Ionic Transport Toward Neuromorphic Applications

AbstractOrganic ferroelectrics (OFEs) have been of significant research interest not only for nonvolatile memory applications but also for their unique material characteristics such as mechanical softness, biocompatibility, facile processibility, and chemically tailorable functionalities that inorganic counterparts are hard to achieve. Despite these promising merits, the utilization of OFEs has mainly focused on simply demonstrating flexible nonvolatile memories wherein modulation of electronic conductance is of interest. Recent studies indicate that the applicability of OFEs can be further extensive, particularly when combined with electronic, ionic, and mixed electronic‐ionic conducting media. Herein, we discuss that OFEs can be employed for the regulation of electronic as well as ionic charges, and lead to unique device behaviors. First, we comprehensively introduce organic ferroelectric materials classified with their structures and compositions. Next, we discuss recent studies where organic ferroelectricity has been incorporated with electronic, ionic, or mixed transport system to resolve issues in devices and endow multifunctionality, which are promising for neuromorphic computing and sensory memory systems. Finally, insight into the research direction of OFEs is provided, and what hurdles shall be overcome for real‐world applications.

Nonvolatile Electro-optic Response of Graphene Driven by Ferroelectric Polarization.

Two-dimensional materials (2DMs) have exhibited remarkably tunable optical characteristics, which have been applied for significant applications in communications, sensing, and computing. However, the reported tunable optical properties of 2DMs are almost volatile, impeding them in the applications of multifarious emerging frameworks such as programmable operation and neuromorphic computing. In this work, nonvolatile electro-optic response is developed by the graphene-Al2O3-In2Se3 heterostructure integrating with microring resonators (MRRs). In such compact devices, the optical absorption coefficient of graphene is substantially tuned by the out-of-plane ferroelectric polarization in α-In2Se3, resulting in a nonvolatile optical transmission in MRRs. This work demonstrates that integrating graphene with ferroelectric materials paves the way to develop nonvolatile devices in photonic circuits for emerging applications such as optical neural networks.

High electroresistance in all-oxide ferroelectric tunnel junctions enabled by a narrow bandgap Mott insulator electrode

Ferroelectric tunnel junctions (FTJs) based on epitaxial complex oxide heterostructures are promising building blocks for developing low power nanoelectronics and neuromorphic computing. FTJs consisting of correlated oxide electrodes have distinct advantages in size scaling but only yield moderate electroresistance (ER) at room temperature due to the challenge in imposing asymmetric interfacial screening and large modulation of the tunneling potential profile. Here, we achieve large ER in all-oxide FTJs by paring a correlated metal with a narrow bandgap Mott insulator as electrodes. We fabricate epitaxial FTJs composed of 2.8 and 4 nm PbZr0.2Ti0.8O3 tunnel barriers sandwiched between correlated oxides LaNiO3 and Sr3Ir2O7 electrodes. An ER of 6500% has been observed at room temperature, which increases to over 105% at 100 K. The high ER can be attributed to ferroelectric polarization induced metal–insulator transition in interfacial Sr3Ir2O7, which enhances the potential asymmetry for the tunnel barrier. The temperature dependence of tunneling current shows that direct tunneling dominates in the on state, while the off-state conduction transitions from thermally activated behavior at high temperatures to Glazman–Matveev defect-mediated inelastic tunneling at low temperatures. Our study provides a viable material strategy for designing all-oxide FTJs with high ER, facilitating their implementation in nonvolatile memories and energy-efficient computing devices.

Wireless and Opto-Stimulated Flexible Implants: Artificial Retina Constructed by Ferroelectric BiFeO3-BaTiO3/P(VDF-TrFE) Composites.

The degeneration of retinal photoreceptors is one of the primary causes of blindness, and the implantation of retinal prostheses offers hope for vision restoration in individuals who are completely blind. Flexible bioelectronic devices present a promising avenue for the next generation of retinal prostheses owing to their soft mechanical properties and tissue friendliness. In this study, we developed flexible composite films of ferroelectric BiFeO3-BaTiO3 (BFO-BTO) particles synthesized by the hydrothermal method and ferroelectric poly(vinyldene difluoride-trifluoroethylene) (P(VDF-TrFE)) polymer and investigated their applications in artificial retinas. Owing to the coupling of the photothermal effect of BFO-BTO particles and the pyroelectric effect of the P(VDF-TrFE) polymer, the composite films demonstrate a strong photoelectric response (a maximum peak-to-peak photovoltage > 80 V under blue light of 100 mW/cm2) in a wide wavelength range of light (from visible to infrared) with the inherent flexibility and ease of preparation, making it an attractive candidate for artificial retinal applications. Experimental results showed that blind rats implanted with artificial retinas of the composites display light-responsive behavior, showcasing the effectiveness of vision restoration. This study demonstrates a novel approach for employing ferroelectric materials in vision restoration and offers insights into future artificial retina design.

A perspective on mechanoluminescence and multipiezo in ferroelectric materials

The discovery of innovative mechanoluminescence materials of SrAl2O4 and ZnS, which emit repeatable light [repeatable mechanoluminescence (ML), hereafter simply ML] even by soft touch, has trigged intense research interest in material/device/system development for applications across various fields. This perspective presents an overview of the crystal structures, mechanisms, and ML behaviors of most promising systems, namely, SrAl2O4-, ZnS-, LiNbO3-, and Sr3Sn2O7-based ferroelectric materials. These multipiezo materials, which simultaneously exhibit intrinsic piezoluminescence (true elastic deformation induced ML and no friction effect) and piezoelectricity, show distinct and valuable characteristics by integrating mechanical force, electric field, and light for stress sensing and other applications. Recent studies indicated the critical role of crystal structure, doping, and piezoelectric properties in achieving robust and reliable ML performance. These findings suggest that ML materials hold substantial promise for applications in stress/force sensing, structural health monitoring, mechanically activated lighting, and advanced imaging techniques. Further investigation and advancement of multipiezo materials could yield breakthroughs, further augmenting their usefulness across various industries and scientific domains. Exploring ferroelectric ML materials offer new prospects for developing advanced materials with unique electro-mechano-optical properties.

Ab initio insight into the physical properties of new ferroelectric perovskite oxide materials XGeO3 (X = Sr, Ca)

The investigation of structural stability, electronic, mechanical, spontanous polarization, and thermodynamic properties of simple cubic perovskite oxides XGeO3 (X =Sr, Ca) has been performed through density functional theory as introduced in Wien2K code. The tolerence factor, Born criteria, and phonon dispersion confirm the stability and the formation of both materials in the ideal cubic structure. Additionally, the application of nmBJ approach in electronic properties shows an exceptional semiconducting aspect. The strain effect on spontaneous polarization of XGeO3 (X =Sr, Ca) perovskites presents an excellent ferroelectric behavior. The thermodynamic parameters such as volume, bulk modulus, thermal expansion coefficient, Debye temperature, Gibbs free energy, enthalpy, heat capacities, and Gruneisen, have been ¨ calculated and discussed with a wide range of pressures (0−20 GPa) and temperatures (0−1000 K). Based on the exceptional semiconducting nature and significant spontaneous polarization, the studied materials can be considered as ferroelectric materials, which make them as a suitable candidates in ferroelctric devices.

Spatially Resolved Light-Induced Ferroelectric Polarization in α-In2Se3/Te Heterojunctions.

Light-induced ferroelectric polarization in 2D layered ferroelectric materials holds promise in photodetectors with multilevel current and reconfigurable capabilities. However, translating this potential into practical applications for high-density optoelectronic information storage remains challenging. In this work, an α-In2Se3/Te heterojunction design that demonstrates spatially resolved, multilevel, nonvolatile photoresponsivity is presented. Using photocurrent mapping, the spatially localized light-induced poling state (LIPS) is visualized in the junction region. This localized ferroelectric polarization induced by illumination enables the heterojunction to exhibit enhanced photoresponsivity. Unlike previous reports that observe multilevel polarization enhancement in electrical resistance, the device shows nonvolatile photoresponsivity enhancement under illumination. After polarization saturation, the photocurrent increases up to 1000 times, from 10-12 to 10-9 A under the irradiation of a 520nm laser with a power of 1.69 nW, compared to the initial state in a self-driven mode. The photodetector exhibits high detectivity of 4.6×1010 Jones, with a rise time of 27 µs and a fall time of 28 µs. Furthermore, the device's localized poling characteristics and multilevel photoresponse enable spatially multiplexed optical information storage. These results advance the understanding of LIPS in 2D ferroelectric materials, paving the way for optoelectronic information storage technologies.

Piezocatalytic effect induced by Schottky junction at interface of 0.5Ba(Zr0.2Ti0.8)O3 – 0.5(Ba0.7Sr0.3)TiO3

In water remediation applications ferroelectric materials have been shown wide applicability in catalysis due to their spontaneous polarization. 0.5Ba(Zr0.2Ti0.8)O3 – 0.5(Ba0.7Sr0.3)TiO3 (BST-BZT) pellets were examined for piezocatalysis activity by electrode effect. These samples were prepared using traditional solid-state reaction and sintering process. The samples were coated with silver paste using manual brushing resulting in Schottky junction having enhanced surface polarization and dye degradation capability. X-ray diffraction, Field emission scanning electron microscopy (FE SEM), and Raman spectroscopy were performed to confirm the phase, morphology and vibrational modes of prepared samples, respectively. Further, Diffuse reflectance spectra (DRS) and X-Ray Photoelectron spectroscopy (XPS) was done to check absorbance and chemical composition. Piezocatalysis activity on electrode sample was observed under 150W and 40kHz ultrasonication. Well dried samples showed enhanced dye degradation of 68%. It could be due to additional charges developed at the interface which act as Schottky junction along with triboelectric phenomenon. This highlights the significant impact of Schottky junction in electrode effect by enhancing the piezocatalytic activity.

Coexistence and Interplay of Two Ferroelectric Mechanisms in Zn1-xMgxO.

Ferroelectric materials promise exceptional attributes including low power dissipation, fast operational speeds, enhanced endurance, and superior retention to revolutionize information technology. However, the practical application of ferroelectric-semiconductor memory devices has been significantly challenged by the incompatibility of traditional perovskite oxide ferroelectrics with metal-oxide-semiconductor technology. Recent discoveries of ferroelectricity in binary oxides such as Zn1-xMgxO and Hf1-xZrxO have been a focal point of research in ferroelectric information technology. This work investigates the ferroelectric properties of Zn1-xMgxO utilizing automated band excitation piezoresponse force microscopy. This findings reveal the coexistence of two ferroelectric subsystems within Zn1-xMgxO. A "fringing-ridge mechanism" of polarization switching is proposed that is characterized by initial lateral expansion of nucleation without significant propagation in depth, contradicting the conventional domain growth process observed in ferroelectrics. This unique polarization dynamics in Zn1-xMgxO suggests a new understanding of ferroelectric behavior, contributing to both the fundamental science of ferroelectrics and their application in information technology.

Emulating Low-Power Synaptic Plasticity in a Solution-Processed Oxide-Based Long Retention Memory Transistor with High Learning Accuracy.

The exploration of synaptic plasticity in metal-oxide-based ferroelectric thin-film transistors has been limited. As a perovskite ferroelectric material, LiNbO3 is widely studied; but its potential use as a neuromorphic device, like synaptic transistors, has not been realized. In this study, a solution-processed ferroelectric thin-film transistor (FeTFT) with an alternating layer of LiNbO3 and Li5AlO4 as a gate dielectric has been fabricated. This configuration reduces the depolarization field by leveraging the large ionic polarization of Li+ ions in the Li5AlO4 layer, while the wide bandgap helps mitigate the leakage current. FeTFT exhibits impressive transistor performance, including a saturation mobility of 0.478 cm2V-1 s-1, an on/off ratio of 3.08 × 103, and a low trap-state density of 1.3 × 1013 cm-2. Moreover, the device demonstrates good memory retention, retaining information for nearly 1 day. It successfully emulates synaptic plasticity, specifically short-term plasticity and long-term plasticity. Besides, a 94% training accuracy has been achieved through artificial neural network simulation. Notably, the FeTFT consumes minimal power, with energy consumption of approximately 3.09 nJ per synaptic event, which is remarkably low compared to other reported solution-processed FeTFT devices.

Layer-polarized anomalous Hall effect in the MnBi[formula omitted]Te[formula omitted]/In[formula omitted]Se[formula omitted] (In[formula omitted]Te[formula omitted]) heterostructures

The layer-polarized anomalous Hall effect has emerged as a novel phenomenon in the field of condensed matter physics, holding significant promise for future applications in designing low-dissipation devices. Currently, the layer-polarized anomalous Hall effect has been theoretically predicted or experimentally demonstrated through the application of external electric fields or the utilization of sliding ferroelectricity in diverse systems. Here, through first-principles calculations, we propose a pathway to realize the layer-polarized anomalous Hall effect by constructing A-type antiferromagnetic topological insulator MnBi2Te4 based heterostructures with ferroelectric materials In2Se3/In2Te3. Our results firstly show that the sizeable band splitting (larger than 20 meV) appears in the antiferromagnetic 4 septuple layers MnBi2Te4/In2Se3 system due to broken inversion symmetry. Further calculations approve that the layer-polarized anomalous Hall conductivity with reversal signs can be observed in the antiferromagnetic 4 septuple layers MnBi2Te4/In2Se3 (In2Te3) systems by shifting the Fermi energy level. Additionally, it is also found that ferrimagnetic 4 septuple layers MnBi2Te4/In2Se3 (In2Te3) can be realized by controlling the direction of ferroelectric polarization of ferroelectric materials. Thus, the resulting layer-polarized anomalous Hall effect may be switchable in our suggested systems. This work provides feasible systems for the further experimental realization of the layer-polarized anomalous Hall effect.

Enhancement of Microwave Absorption Properties of Crystal‐Engineered Perovskite Oxide Using Cobalt Ferrite

A multiferroic composite that comprises of a non‐ferromagnetic ferroelectric material with a high dielectric constant and a non‐ferroelectric ferromagnetic material with a high magnetostriction is of tremendous interest as microwave absorption material due to its applicability in tunable microwave phase shifters, resonators, filters, absorbers, etc. In the previous work, the solid solution of strontium titanate and sodium bismuth titanate (Sr0.5(Na0.5Bi0.5)0.5TiO3, SNBT50), which is observed to possess a very high dielectric constant at room temperature (Ferroelectrics, Vol 583, 252–263 [2021]), is successfully reported. Thus, in this work, a core–shell magnetoelectric composite is prepared by coating highly ferromagnetic and magnetostrictive cobalt ferrite onto a diamagnetic but strongly ferroelectric SNBT50 to enhance its magnetic properties and to investigate the modification in microwave absorption. Detailed characterization of electric and magnetic parameters in microwave frequency range (1–20 GHz) reports substantial enhancement in the magnetic permeabilities as well as the magnetic loss of the composite system, as opposed to bare SNBT50. This results in improved impedance matching in the system and enhanced microwave absorption, with a minimum reflection loss (RL) of −20.19 dB and an increased effective absorption bandwidth of 4.56 GHz at a mere 2.7 mm absorber length. Consequently, in this investigation, a promising pathway is established for the development of multiferroic composites with favorable magnetoelectric coupling at room temperature that possesses wide absorption bandwidth and suitable RL, making them highly suitable for use in multiferroic‐based microwave components.

Emerging Multifunctionality in 2D Ferroelectrics: A Theoretical Review of the Interplay With Magnetics, Valleytronics, Mechanics, and Optics

Abstract2D ferroelectric materials present promising applications in information storage, sensor technology, and optoelectronics through their coupling with magnetics/valleytronics, mechanics, and optics, respectively. The integration of 2D ferroelectrics with magnetism enhances data storage density in memory devices by enabling electric‐field‐controlled magnetic states. Ferroelectric‐valley coupling holds promise for high‐speed, low‐energy electronics by leveraging the electrical control of valley polarization. Ferroelectric‐strain coupling results in various polar topologies, with potential applications in high‐density data storage technologies and sensor devices. Moreover, the coupling between ferroelectrics and optics facilitates the development of nonlinear photonics based on ferroelectric materials. This review summarizes the latest theoretical progress in the coupling mechanisms, including the Dzyaloshinskii‐Moriya‐interaction‐induced magnetoelectric coupling, symmetry‐linked ferroelectric‐valley coupling, ferroelectric‐strain‐coupling‐generated polar topologies, and second‐harmonic generation through ferroelectric‐light interactions. The current challenges and future opportunities in harnessing the coupling in 2D ferroelectric materials for multifunctional applications are provided.

Ferroelectric nematic fluids as spontaneous polarization field for enhanced orientational-dependent second-harmonic generation

ABSTRACT Second-order nonlinear optical effects have piqued researchers’ interest in fundamental physics and practical perspectives. The ferroelectric nematic liquid crystals (NF LCs) have recently drawn attention to LC nonlinear optical applications due to their relatively high second-harmonic generation output. Further improving the nonlinear optical properties to get closer to the performance of inorganic nonlinear optical materials is challenging. Here, we take a blending strategy to enhance the nonlinear optical response of a prototype NF LC, DIO. We mixed an organic nonlinear optical crystalline material, 3,5,5-trimethyl (cyclohex-2-enylidene) malononitrile (TCM), with DIO and investigated the effects of TCM doping at various concentrations. We quantitatively determined the second-harmonic generation and spontaneous polarization as functions of temperature and concentration. We found that, compared with the pure DIO, the second-harmonic generation performance increased by about 130% at maximum, 93% in maximum for the nonlinear optical coefficient, and 10% in maximum for spontaneous polarization.

TCAD approach for negative capacitance ferroelectric devices for radiation detection applications

Negative capacitance (NC) emerges as a promising technology for low-power, high-performance transistors. The HiEnD project intends to analyze and design high-energy efficient electronic devices based on innovative ferroelectric materials. It explores NC technology for high-resolution tracking detectors in future high-energy physics experiments. It aims to create ultra-thin, radiation-resistant devices for superior signal detection in harsh environments. This paper presents detailed modeling, simulation results, and a comparison with experimental data, highlighting the potential of the developed methodology but also of the technology for the realization of compact, high-performance detectors. Advanced Technology CAD modeling has been employed to investigate the potentiality of NC devices in unconventional application domains, such as high-energy physics experiments. Numerical simulations, capable of verifying experimental results, enhance predictive power, reducing time and cost in detector design and testing.

Constraining the value of the dielectric constant of the ferroelectric nematic phase.

Ferroelectric nematic liquid crystals are currently being subject to a plethora of investigations since they are of great fundamental interest and could potentially foster promising applications. However, many basic aspects are still poorly understood, among which the problem of the dielectric constant stands out. Ferroelectric nematics have previously been reported to exhibit giant dielectric constants whose value depends on the thickness of the measurement cell, claims that have recently been shown to be the result of an incorrect interpretation of the experimental data. The intrinsic permittivity of these materials has not been determined yet. In this work, we tackle this problem by modeling the dielectric response of the liquid crystal filled cell through an equivalent circuit proposed by Clark et al. [Phys. Rev. Res. 6, 013195 (2024)2643-156410.1103/PhysRevResearch.6.013195] accounting for polarization reorientation and the effect of insulating interfacial layers. We arrive at the conclusion that the perpendicular component of the permittivity ɛ_{⊥} is of the order of 10 in the prototypical ferroelectric nematogen DIO, while the parallel component ɛ_{∥} is of the order of 150. In this way, the dielectric tensor of DIO has been fully determined.

Mechanisms for enhanced ferroelectric properties in ultra-thin Hf0.5Zr0.5O2 film under low-temperature, long-term annealing

To gain insight into the ferroelectric mechanisms under reduced thermal budget and thickness scaling, a 4.6 nm ultra-thin ferroelectric Hf0.5Zr0.5O2 capacitor compatible with back-end-of-line (BEOL) processes (all conducted at temperatures ≤350 °C) is investigated in this work. Through O3 pretreatment at the bottom electrode (BE) interface and controlled temperature modulation of the crystalline phase, the capacitor exhibits exceptional ferroelectric (FE) properties following low-temperature (350 °C) and long-term (300 s) rapid thermal annealing (RTA). These properties include high remanent polarization (2Pr ∼ 28.53 μC/cm2), low coercive voltage (Vc ∼ 0.43 V), effective leakage suppression, robust endurance (∼1010 cycles without hard breakdown), and a desirable high dielectric constant. The main mechanisms identified include tetragonal phase nucleation under enhanced tensile stress via the oxidized BE layer (TiO2), crystalline growth controlled through RTA temperature modulation, and phase transition to the ferroelectric orthorhombic phase under electric field cycling. This research provides valuable insights for the development of BEOL-compatible nonvolatile FE memories.

Exploiting the Cationic Size Effect to Improve the Curie Temperature of Hybrid Perovskites Photoferroelectric Semiconductors.

Ferroelectric materials with Curie temperature (Tc) below room temperature severely limit their practical applications. Although research on hybrid perovskite photoferroelectrics is ongoing, effective regulation of Tc still poses significant challenges. Herein, we utilized the cationic size effect to successfully regulate the Tc of hybrid perovskite photoferroelectric semiconductors. As the perovskitizer was replaced by a smaller-sized MA+ (methylammonium) with a larger-sized EA+ (ethylammonium), not only was the ferroelectricity of the hybrid perovskite well maintained but the Tc of (PA)2(MA)2Pb3Br10 (315 K) to (PA)2(EA)2Pb3Br10 (385 K) (PA is n-propylaminium) increased by 70 K, which was mainly due to the significant increase in the energy barriers that the system needed to overcome during the phase transition. Subsequently, we achieved efficient self-powered X-ray detection through the ferroelectric-induced bulk photovoltaic effect (BPVE) in (PA)2(EA)2Pb3Br10. The devices based on (PA)2(EA)2Pb3Br10 single crystals exhibit an outstanding sensitivity of 95 μC Gy-1 cm-2 and a low detection limit of 239 nGy s-1 at 0 V bias under X-ray radiation. This study provides an effective approach for designing and constructing high-temperature multilayer photoferroelectric semiconductors in the future.