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Ferroelectric thin-film transistors (Fe-TFTs) have promising potential for flexible electronics, memory, and neuromorphic computing applications. Here, we report on a physics-based efficient device model for Fe-TFTs that effectively describes memory switching and device I–V characteristics. This model combines a stochastic multi-domain description of FE switching dynamics with a virtual source treatment of TFT device characteristics. It demonstrates that the memory window of Fe-TFTs depends on the amplitude and duration of the applied voltage pulses, thus suggesting quantitative means of programming and control. Additionally, we introduce a machine-learning-enabled method to automatically generate optimal voltage pulses for accurately programming multiple intermediate FE states, which is crucial for multi-bit memory and neuromorphic computing applications. To showcase the model's applications, we simulate a 4 × 4 crossbar array circuit based on Fe-TFTs, highlighting its utility in performing multiply-accumulate computing operations. This small array can achieve a high speed of ∼ 1.28 tera operations per second (OPS) and a power efficiency of ∼ 0.43 W/PetaOPS. The model developed here is valuable for exploring the capabilities of Fe-TFTs in future flexible memory and computing technologies. [ABSTRACT FROM AUTHOR]

The continuous effort in making artificial neural networks more alike to human brain calls for the hardware elements to implement biological synapse-like functionalities. The recent experimental demonstration of ferroelectric-like FETs promises low-power operation as compared to the conventional ferroelectric switching devices. This work presents an in-house numerical tool, which self-consistently solves the electrostatics and time-dependent electronic and ionic transport. The tool is exploited to analyze the effect that various physical parameters such as mobility and ion concentration could have on the design of the ferroelectric-like FETs. Their suitability in emulating different functions of the biological synapses is also demonstrated. [ABSTRACT FROM AUTHOR]

Efficient data processing is heavily reliant on prioritizing specific stimuli and categorizing incoming information. Within human biological systems, dorsal root ganglions (particularly nociceptors situated in the skin) perform a pivotal role in detecting external stimuli. These neurons send warnings to our brain, priming it to anticipate potential harm and prevent injury. In this study, we explore the potential of using a ferroelectric memristor device structured as a metal–ferroelectric–insulator–semiconductor as an artificial nociceptor. The aim of this device is to electrically receive external damage and interpret signals of danger. The TiN/HfAlOx (HAO)/HfSiOx (HSO)/n+ Si configuration of this device replicates the key functions of a biological nociceptor. The emulation includes crucial aspects, such as threshold reactivity, relaxation, no adaptation, and sensitization phenomena known as "allodynia" and "hyperalgesia." Moreover, we propose establishing a connection between nociceptors and synapses by training the Hebbian learning rule. This involves exposing the device to injurious stimuli and using this experience to enhance its responsiveness, replicating synaptic plasticity. [ABSTRACT FROM AUTHOR]

The generation of above-bandgap photovoltage, referred to as the anomalous photovoltaic effect (APV), is an extraordinary characteristic sought after property in bulk ferroelectric photovoltaic devices. Despite the fact that the relatively narrow bandgap of BiFeO3 (BFO) (2.7 eV) induces a comparatively larger generation of photocurrent than other ferroelectric photovoltaic, it falls short in producing an anomalous photovoltage (Eg ≪ Voc) and exhibits leaky ferroelectric hysteresis due to unavoidable oxygen vacancies. This work revealed a reduction in oxygen vacancies through the substitution of Ba(Fe1/2Nb1/2)O3 in BFO, leading to improved structural, morphological, synchrotron XPS, and electrical properties. This reduction in oxygen vacancies has resulted in an impressive above-bandgap photovoltage (APV) of 4.41 V for 80BFO–20BFN with greater ferroelectric polarization (Pr = 20.45 μC/cm2) observed at the co-existence of polar and non-polar phases. Moreover, both theoretical and experimental optical analyses have demonstrated a significant decrease in the bandgap to 1.92 eV, effectively extending the visible region close to 653 nm. As a result, a larger population of photoexcited charge carriers is generated, enabling the attainment of a high current density (Jsc) of 0.75 μA/cm2 under 100 mW/cm2 light irradiation. [ABSTRACT FROM AUTHOR]

To meet commercialization requirements, the distributions of materials in hafnium-based ferroelectric devices—including their phase and orientation—need to be controlled. This article presents a method for improving the ferroelectric phase ratio and orientation by adjusting the stress distribution of the annealing structure in a three-dimensional capacitor. In such a structure, stress can be applied in three directions: tangential, axial, and radial; there are, thus, more ways to regulate stress in three-dimensional structures than in two-dimensional structures. This work sought to clarify the role of the stress direction on the proportions and orientations of ferroelectric phases. The results of stress simulations show that a structure with an internal TiN electrode, but no filling provides greater axial and tangential stresses in the hafnium-oxide layer. In comparison with the case of the hole being filled with tungsten, the proportion of the O phase is increased by approximately 20%, and in experiments, the projection of the polarization direction onto the normal was found to be increased by 5%. Axial and tangential stresses are regarded to be beneficial for the formation of the O phase and for improving the orientation of the polarization direction. This work provides a theoretical basis and guidance for the three-dimensional integration of hafnium-based ferroelectric materials. [ABSTRACT FROM AUTHOR]

Ferroelectric materials are widely used in actuators, exciters, and memory devices due to their excellent electromechanical properties. However, the instinctive brittleness of ferroelectric materials makes them easy to fracture under external load. Since giant strain gradient can be easily generated near the crack tip, the flexoelectric effect is indispensable in the research of fracture properties of ferroelectric materials. With the combination of time-dependent Ginzburg–Landau theory and phase-field model, the electromechanical behavior of PbTiO 3 in the vicinity of the crack tip is determined in this work. The simulation results demonstrate that the domain structure near the crack tip becomes asymmetric with the flexoelectric effect. The polarization switching-induced toughening, which is characterized by the J -integral, depends on the direction of the crack relative to the original polarization orientation. Furthermore, the longitude flexoelectric coefficient f 11 has more significant impact on the fracture toughness than that of the transverse flexoelectric coefficient f 12 and the shear flexoelectric coefficient f 44. The results of the present work suggest that the flexoelectric effect must be considered in the reliable design of ferroelectric devices. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) ferroelectric tunnel junctions (FTJs) have great potential in the design of non-volatile memory devices due to the tunneling electroresistance (TER) effect and the fact that it is not constrained by critical thickness. Incorporation of 2D ferroelectric materials in realistic FTJs inevitably involves the contacts to the traditional three-dimensional (3D) metals. However, how to design the FTJs by combining the 2D ferroelectric materials with the 3D metals still needs to be studied. In this work, we design a vertical 3D FTJ by adopting the 3D metal Au as the left and right electrodes and the 2D ferroelectric material In2Se3 together with h-BN as the central scattering region. By density functional theory combined with the non-equilibrium Green's function (NEGF) method, we demonstrate that the h-BN intercalation with a large bandgap plays the role of good "insulator," which breaks the symmetry of the left and right electrodes. As a result, we obtain the TER ratio of about 170%, and it can be further improved to about 1200% if two layers of In2Se3 (2L-In2Se3) are adopted as the tunneling barrier layer. Our results provide another way for the design and application of ferroelectric memory devices based on 2D ferroelectric materials. [ABSTRACT FROM AUTHOR]

High ScN fraction ScxAl1−xN has promise in important application areas including wide bandwidth RF resonators and filters, and ferroelectric devices such as non-volatile memory, but demands high crystal quality. In this work, the role of the nucleation layer (NL), ScxAl1−xN growth temperature, and strain management to preserve the wurtzite crystal structure are investigated to maximize both acoustoelectric and ferroelectric material properties for high ScN fraction ScxAl1−xN grown on SiC substrates. A 5 nm AlN nucleation layer reduces the x-ray diffraction 0002 reflection full width at half maximum (FWHM) for a Sc0.32Al0.68N film by almost a factor of 2, and reducing the growth temperature to 430 °C enables a Sc0.40Al0.60N film with a FWHM of 4100 arcsec (1.1°) while being only 150 nm thick. Grading the initial ScxAl1−xN layer from x = 0.32 to 0.40 suppresses the formation of rock-salt grain nucleation at the Sc0.40Al0.60N lower interface and reduces the anomalously oriented grain density by an order of magnitude. Increasing the total ScxAl1−xN growth thickness to 500 nm produces an average x = 0.39 ScxAl1−xN layer with a FWHM of 3190 arcsec (0.89°) and an anomalously oriented grain areal fill factor of 1.0%. These methods enable the lowest heteroepitaxial ScxAl1−xN FWHM reported for x ∼ 0.4, with layer thicknesses and defect densities appropriate for high frequency (>10 GHz) filter applications. [ABSTRACT FROM AUTHOR]

Neuromorphic devices can emulate the human brain to process information, which receives lots of attention in the field of artificial intelligence. Synaptic devices based on ferroelectric thin films feature low-power consumption, multifunctionality, and scalability. Among them, ferroelectric charged domain wall (CDW) devices have attracted intensive interest for the implementation of memristive devices due to their ultrahigh integration ability inherited from the nanoscale domain wall thickness. In particular, the preparation of wafer-scale single-crystalline ferroelectric thin films via ion-sliced heterogeneous wafer bonding lays a good foundation for large-scale integration of ferroelectric devices with functional circuits. However, the biomimic synaptic characteristics and the systematic demonstration of synaptic devices are largely unexplored for this material system. Here, we demonstrate a model synaptic device based on a single-crystal ferroelectric LiNbO3 thin film, which provides the desired characteristics for neuromorphic computing. The conductance modulation demonstrates good linearity for efficient neuromorphic computing applications. Simulations using the Modified National Institute of Standards and Technology handwritten recognition dataset prove that LiNbO3-based synaptic devices can operate with an online learning accuracy of 95.1%. The injection and annihilation of the CDW are proposed as the basis of the conductivity modulation by combining with the piezoresponse force microscopy and conductive atomic force microscopy mapping measurements. With the mature fabrication process of the ultrathin high-quality ferroelectric thin films, LiNbO3-based synaptic devices have an extensive application prospect for future neuromorphic computing systems. [ABSTRACT FROM AUTHOR]

Ferroelectric photoelectric devices show promising applications in artificial vision systems. However, this type of devices used in artificial vision systems exhibits low photoresponsivity and this limited cyclability of photocurrents, which hinders the progress of artificial vision systems. In this study, an artificial vision system is constructed with high photoresponsivity, fast photoresponse speed, and high read/write speed based on the Pd/PbZr0.4Ti0.6O3/La0.3Sr0.7MnO3/LaAlO3 ferroelectric photomemristor. The high optical response (18.86 nanoamperes) and read/write speeds (50 nanoseconds) of the device significantly improve the robustness and speed of the neuromorphic visual system while reducing power consumption for recognition. The artificial vision system developed in this study provides excellent real‐time image processing capabilities, including edge detection and classification with 100% accuracy for musical key patterns, and it is expected to offer great potential for the development of high‐performance self‐powered artificial vision systems. [ABSTRACT FROM AUTHOR]

Multiferroic BiFeO3 exhibits a morphotropic phase boundary at large compressive strain that merges metastable phases of tetragonal (T) and rhombohedral (R) character resulting in giant ferroelectric and electromechanical responses. To utilize this functionality in devices, it is essential to understand the response of these ferroelectric phases to the environment of a nanoscale heterostructure. Here, the emergence of ferroelectricity near the morphotropic phase boundary in BiFeO3 is explored directly during thin‐film growth, using optical second harmonic generation. It is found that the epitaxial films form at the growth temperature purely in the T phase with zero critical thickness for the spontaneous polarization. Signatures of monoclinic T‐like and R‐like phases only appear upon sample cooling. The robustness of a single‐domain configuration in the high‐temperature T phase is furthermore demonstrated during growth of capacitor‐like metal | ferroelectric | metal heterostructures. Here, a reduction in tetragonality, rather than multidomain formation, lowers the electrostatic energy in the few‐unit‐cell thickness regime. For this lower tetragonality, density‐functional calculations and scanning transmission electron microscopy point to the stabilization of a novel metastable monoclinic structure upon cooling toward room temperature. The synergistic combination of strain and electrostatic phase stabilization in BiFeO3 heterostructures hence provides a basis for designing new ferroelectric phases and ultrathin ferroelectric devices. [ABSTRACT FROM AUTHOR]

Hafnium oxide (HfO2)-based ferroelectrics are being explored as potential candidates for ferroelectric memory devices due to their highly compatibility with complementary metal-oxide-semiconductor (CMOS) technology. Enhancing the remanent polarization and investigating the underlying mechanism are crucial tasks. In the present study, tantalum (Ta) was introduced as a dopant to induce ferroelectric properties in HfO2, a large portion of orthorhombic phase was recognized in the as-grown Ta:HfO2 without further thermal treatment. The remanent polarization of Ta:HfO2 thin films can be optimized by adjusting the oxygen flow rates during the sputtering process. The influencing factors for enhanced ferroelectric performance include the control of Ta concentration, its valence state, and the presence of singly ionized oxygen vacancies, which are influenced by oxygen addition. Furthermore, the resistive switching behavior showing non-zero crossing current–voltage (I–V) hysteresis is associated with ferroelectricity and the presence of oxygen vacancies. A model has been proposed to explain the ferroelectric resistive switching with non-zero crossing I–V characteristics by considering the role of oxygen vacancies and polarization effects. This model suggests that the oxygen vacancies at the surface layer, along with ferroelectric polarization, play a crucial role in electron transport. [ABSTRACT FROM AUTHOR]

BiFeO3 (BFO) application in flexible wearable devices is garnering interest because of its unique ferroelectric and magnetic properties. However, the integration of high-quality BFO films onto flexible substrates presents significant technical challenges. Here, we successfully fabricated high-quality BFO films on mica substrates by using pulsed laser deposition, and report the fatigue characteristics of BFO films on flexible substrates for the first time. The results demonstrated that, after 108 bipolar switching cycles, the polarization only degraded by 0.28%, indicating superior fatigue characteristics compared to previously reported BFO films. Additionally, the device ferroelectric properties remained largely unchanged, with a bending radius of 3.5 mm. The fabricated flexible Pt/BFO/La0.65Sr0.35MnO3(LSMO)/SrTiO3(STO)/mica non-volatile memory devices exhibited mechanical flexibility and fatigue resistance. These findings not only highlight the potential of flexible BFO films for wearable electronic devices and flexible memory devices, they also provide valuable insight for the future development of high-performance flexible ferroelectric materials. [ABSTRACT FROM AUTHOR]

Reducing the reversal barrier of Al1−xScxN ferroelectric alloy is critical for improving the coercive voltage and power consumption of ferroelectric devices. Here, the synergistic effect of alloy composition and strain is introduced to optimize the ferroelectric properties of Al1−xScxN alloys. Because of the increased Al–N ionic bond character and the contribution of Sc-d orbitals, the spontaneous polarization, reversal barrier, and bandgap all reduce as the Sc concentration increases. Strain engineering improves the electron's electric dipole moment, resulting in a significant increase in spontaneous polarization (145.93 μC/cm2 for Al0.625Sc0.375N alloy). Meanwhile, the horizontal tension and vertical compression lower the reversal barrier of Al0.625Sc0.375N alloy to 95.45 meV/f.u., significantly lower than that of orthorhombic HfO2. Interestingly, the bandgap of Al1−xScxN alloy with low Sc concentration rises initially and then decreases as horizontal strain varies from compression to tension, whereas that of Al1−xScxN alloy with high Sc concentration monotonically decreases. The Al1−xScxN alloy exhibits the opposite tendency under vertical strain. These findings provide a thorough understanding of Al1−xScxN ferroelectric alloys and a guideline for designing high-performance Al1−xScxN ferroelectric alloys. [ABSTRACT FROM AUTHOR]

Ferroelectric materials hold significant potential for ultralow-energy-consuming oxide electronics and have recently been pointed out as a suitable platform for next-generation neuromorphic and reservoir computing schemes. We provide a brief overview of the progress in engineering electric dipole textures of epitaxial ferroelectric oxide thin films, with an emphasis on the technologically relevant ultrathin regime. In epitaxial films that are only a few unit-cells thick, surface chemistry and interfacial electrostatics are commonly considered limiting factors in ferroelectric device integration, as they may suppress the net ferroelectric behavior. Here, we highlight how nanoscale lattice chemistry control, including off-stoichiometry and layer polarization in oxides, can, in fact, emerge as powerful tools for engineering ferroelectricity in thin films. We also discuss the potential of such an approach in the context of recent trends in the field, such as the design of ferroelectric freestanding membranes and the optical control of polarization in thin films. Hence, with our Perspective article, we aim to provide key insights on the use of lattice chemistry for ferroelectricity engineering in thin films to facilitate exciting developments in ferroelectric-based applications. [ABSTRACT FROM AUTHOR]

The ferroelectric tunneling junction, with a metal-ferroelectric ultra-thin film-metal structure, has different tunneling resistance states through polarization manipulation, leading to potential applications in next-generation information storage devices with low-power consumption, fast reading/writing speed, high storage density, and non-volatility. However, the ferroelectric thin films still experience high-temperature rises with reduced stability due to high driving fields, and reducing the driving electric field is crucial for designing ferroelectric tunneling devices. The ferroelectric thin films with coexisting domains have lowered barriers and decreased driving electric fields for domain switching, which are achieved through substrate manipulation. Herein the substrate effects on the driving field, the tunneling resistance switching ratio and the tunneling properties, were studied based on the WKB approximation combined with the Landau phenomenological theory. The results show that, the ferroelectric tunnel junction with coexisting domains exhibits 3 resistive states corresponding to out-of-plane and in-plane polarizations. The effective driving electric field can be reduced to 25 MV/m, which is 76% lower than that with 2 resistive single domains. The proposed theoretical framework provides a fundamental understanding of the formation of multi-state and reduction of the driving field for low-energy, multi-resistance ferroelectric storage devices. [ABSTRACT FROM AUTHOR]

Neuromorphic devices capable of emulating biological synaptic behaviors are crucial for implementing brain‐like information processing and computing. Emerging 2D ferroelectric neuromorphic devices provide an effective means of updating synaptic weight aside from conventional electrical/optical modulations. Here, by further synergizing with an energy‐efficient synaptic plasticity strategy, a multimodal mechano‐photonic synaptic memory device based on 2D asymmetric ferroelectric heterostructure is presented, which can be modulated by external mechanical behavior and light illumination. By integrating the asymmetric ferroelectric heterostructured field‐effect transistor and a triboelectric nanogenerator, the mechanical displacement‐derived triboelectric potential is ready for gating, programming, and plasticizing the synaptic device, resulting in superior electrical properties of high on/off ratios (> 107), large storage windows (equivalent to ≈95 V), excellent charge retention capability (> 104 s), good endurance (> 103 cycles), and primary synaptic behaviors. Besides, optical illumination can effectively synergize with mechanoplasticity to implement multimodal spatiotemporally correlated dynamic logic. The demonstrated multimodal memory synapse provides a facile and promising strategy for multifunctional sensory memory, interactive neuromorphic devices, and future brain‐like electronics embodying artificial intelligence. [ABSTRACT FROM AUTHOR]

HfO2-based ferroelectric materials as the most promising candidate for the ferroelectric memories, have been widely studied for more than a decade due to their excellent ferroelectric properties and CMOS compatibility. In order to realize its industrialization as soon as possible, researchers have been devoted to improving the reliability performance, such as wake up, imprint, limited endurance, et al. Among them, the breakdown characteristic is one of main failure mechanisms of HfO2-based ferroelectric devices, which limits the write/read reliability of the devices. Based on this, we systematically studied the effect of thickness on the time-dependent dielectric breakdown (TDDB) tolerate capability of HfO2–ZrO2 (HZO) FE films under both forward and reverse electrical stress conditions. The thickness of HZO FE film ranged from 6 to 20 nm. Our findings reveal that decreasing the thickness of the HZO FE film leads to an improvement in TDDB tolerance capability which is attributed to the fact that higher density of oxygen vacancies in thinner HZO FE films can effectively inhibit the generation of new oxygen vacancies and the growth of conductive filaments, thus effectively improving the TDDB characteristics. These results provide a potential solution for mitigating breakdown characteristics of HfO2-based ferroelectric devices in memory applications. [ABSTRACT FROM AUTHOR]

In recent years, the emergence of numerous applications of artificial intelligence (AI) has sparked a new technological revolution. These applications include facial recognition, autonomous driving, intelligent robotics, and image restoration. However, the data processing and storage procedures in the conventional von Neumann architecture are discrete, which leads to the "memory wall" problem. As a result, such architecture is incompatible with AI requirements for efficient and sustainable processing. Exploring new computing architectures and material bases is therefore imperative. Inspired by neurobiological systems, in-memory and in-sensor computing techniques provide a new means of overcoming the limitations inherent in the von Neumann architecture. The basis of neural morphological computation is a crossbar array of high-density, high-efficiency non-volatile memory devices. Among the numerous candidate memory devices, ferroelectric memory devices with non-volatile polarization states, low power consumption and strong endurance are expected to be ideal candidates for neuromorphic computing. Further research on the complementary metal-oxide-semiconductor (CMOS) compatibility for these devices is underway and has yielded favorable results. Herein, we first introduce the development of ferroelectric materials as well as their mechanisms of polarization reversal and detail the applications of ferroelectric synaptic devices in artificial neural networks. Subsequently, we introduce the latest developments in ferroelectrics-based in-memory and in-sensor computing. Finally, we review recent works on hafnium-based ferroelectric memory devices with CMOS process compatibility and give a perspective for future developments. [ABSTRACT FROM AUTHOR]

Ferroelectric charged domain walls offer a revolutionary path for next-generation ferroelectric devices due to their exceptional conductivity within an otherwise insulating matrix. However, quantitative understanding of this "giant conductivity" has remained elusive due to the lack of robust models describing carrier behavior within CDWs. The current paper bridges this critical knowledge gap by employing a first-principles approach that incorporates Boltzmann transport theory and the relaxation time approximation. This strategy enables the calculation of carrier concentration, mobility, and conductivity for both head-to-head and tail-to-tail domain wall configurations within a stabilized periodic structure. The comprehensive transport analysis given here reveals that the accumulation of charge carriers, particularly their concentration, is the dominant factor governing domain wall conductance. Interestingly, observed conductance differences between head-to-head and tail-to-tail walls primarily arise from variations in carrier mobility. Additionally, this study demonstrates a significantly reduced domain wall width compared to previous reports. This miniaturization is attributed to the presence of compressive strain, which lowers the energy barrier for electron–hole pair generation. Furthermore, the findings here suggest that reducing the band gap presents a viable strategy for stabilizing charged domain walls. These results pave the way for the optimization and development of domain wall devices across a spectrum of ferroelectric materials. [ABSTRACT FROM AUTHOR]

Oxygen vacancies play a crucial role in stabilizing the ferroelectric phase in hafnium (Hf) oxide-based thin films and in shaping the evolution of their ferroelectric properties. In this study, we directly manipulated the oxygen vacancy concentration in Hf0.5Zr0.5O2−x (HZO) ferroelectric thin films in situ using oxygen plasma treatment. We scrutinized the variations in the ferroelectric properties of HZO films across different oxygen vacancy concentrations by integrating the findings from ferroelectric performance tests. Additionally, we elucidated the mechanism underlying the influence of oxygen vacancies on the coercive field and polarization properties of HZO ferroelectric films through the first-principles density functional theory (DFT) calculations. Finally, to study the impact of oxygen vacancies on the practical application of HZO ferroelectric synaptic devices, leveraging the plasticity of the ferroelectric polarization, we constructed a multilayer perceptron (MLP) network. We simulated its recognition accuracy and convergence speed under different oxygen vacancy concentrations in the MNIST recognition task. [ABSTRACT FROM AUTHOR]

HfO 2 -based thin films have raised considerable interest in ferroelectric memory devices due to their thickness scalability and process compatibility with CMOS. Stress exhibits a significant influence on ferroelectric polarization in HfO 2 -based films. However, the effect of stress has yet to be clarified despite numerous efforts, and there has been a lack of systematic review to collate and discuss this effect. This paper briefly introduces how stress is characterized in HfO 2 -based polycrystalline films as basis. Then, the process in which stress affects ferroelectricity is carefully discussed. The paper subsequently elaborates both the effects of out of plane stress and in plane stress. Furthermore, the interaction between stress and other factors is presented. Finally, the up-to-date research on the effect of stress are summarized, and several further research challenges for researchers are provided. Given the ubiquitous stress during the chip manufacturing process, a detailed summary of the stress effect has technological implications for processing and applications of HfO 2 -based thin films. [ABSTRACT FROM AUTHOR]

We present a massively parallel, 3D phase-field simulation framework for modeling ferroelectric materials based scalable logic devices. This code package, FerroX, self-consistently solves the time-dependent Ginzburg Landau (TDGL) equation for ferroelectric polarization, Poisson's equation for electric potential, and charge equation for carrier densities in semiconductor regions. The algorithm is implemented using the AMReX software framework [1], which provides effective scalability on manycore and GPU-based supercomputing architectures. We demonstrate the performance of the algorithm with excellent scaling results on NERSC multicore and GPU systems, with a significant (15×) speedup on the GPU using a node-by-node comparison. We further demonstrate the applicability of the code in simulations of ferroelectric domain-wall induced negative capacitance (NC) effect in Metal-Ferroelectric-Insulator-Metal (MFIM) and Metal-Ferroelectric-Insulator-Semiconductor-Metal (MFISM) devices. The charge (Q) v.s. voltage (V) responses for these 3D structures clearly indicate stabilized negative capacitance with multidomain formation, which is corroborated by amplification of the voltage at the interface between the ferroelectric and dielectric layers.

The recent realization of ferroelectricity in scandium‐ and boron‐substituted AlN thin films has spurred tremendous research interests. Here we established a molecular dynamics simulation framework to model the ferroelectricity of AlN thin films. Through reparameterization of Vashishta potential for AlN, the coercive field strength and the AlN polarization were found to be close to experimental values. Furthermore, we examined the effects of film thickness, temperature, in‐plane strain on polarization‐electric field hysteresis loop, and the thickness‐dependent Curie temperature. Lastly, we incorporated electrodes towards atomic‐level modeling of ferroelectric device, by considering the induced charge at the interface between electrodes and ferroelectric film. We found that low dielectric contrast significantly lowers the coercive field for switching AlN. [ABSTRACT FROM AUTHOR]

The atmospheric chemical vapor deposition (APCVD) method has been widely applied to synthesize high-quality two-dimensional materials. GeTe has many intriguing properties, such as phase transition, thermoelectric and ferroelectricity, which allow unique opportunities for functional ferroelectric devices. Here, we systematically investigated effects of various parameters during the growth of α-GeTe nanosheets on mica by APCVD. Single-crystal α-GeTe nanosheets possess a lateral size of up to ∼30 μm and a thickness as low as ∼8.6 nm. It was found that substrate pre-annealing significantly impacted the nucleation density of α-GeTe nanosheets. Furthermore, the room-temperature ferroelectric properties of α-GeTe nanosheets grown by CVD are reported for the first time. This work offers an effective accessible method for the controllable growth of large-size 2D α-GeTe to explore its fascinating multiferroic properties. [ABSTRACT FROM AUTHOR]

The demand for low‐dimensional ferroelectric devices is steadily increasing, however, the thick substrates in epitaxial films impede further size miniaturization. Freestanding films offer a potential solution by eliminating substrate constraints. Nevertheless, it remains an ongoing challenge to improve the stability in thin and fragile freestanding films under strain and temperature. In this work, the structure and ferroelectric order of freestanding PbTiO3 (PTO) films are investigated under continuous variation of the strain and temperature using nondestructive optical second harmonic generation (SHG) technique. The findings reveal that there are both out‐of‐plane and in‐plane domains with polarization along out‐of‐plane and in‐plane directions in the orthorhombic‐like freestanding PTO films, respectively. In contrast, only out‐of‐plane domains are observed in the tetragonal epitaxial PTO films. Remarkably, the ferroelectricity of freestanding PTO films is strengthened under small uniaxial tensile strain from 0% up to 1.66% and well‐maintained under larger biaxial tensile strain up to 2.76% along the [100] direction and up to 4.46% along the [010] direction. Moreover, a high Curie temperature of 630 K is identified in 50 nm thick freestanding PTO films by wide‐temperature‐range SHG. These findings provide valuable understanding for the development of the next‐generation electronic nanodevices with flexibility and thermostability. [ABSTRACT FROM AUTHOR]

Ultrathin ferroelectric tunnel junctions (FTJs) hold considerable promise for next‐generation, high‐speed, low‐power, and high‐density nonvolatile memory applications. Achieving a substantial tunneling electro‐resistance (TER) remains a challenge as the ferroelectric layer is thinned to nanoscale dimensions, often resulting in a diminished or lost polarization. An innovative interface barrier gain mechanism is introduced, employing interface electronic state modulation to precisely control the size of an additional interface barrier. This strategy lessens the dependency of the tunneling barrier on ferroelectric polarization strength, facilitating a remarkable TER even at ferroelectric thicknesses as minimal as ≈1 nm. The focus is on composite FTJs using In2Se3/MTe2 (M = Mo, W), where the inclusion of an MTe2 monolayer disrupts the asymmetric electrode configuration. The weak ferroelectric polarization reversal of the In2Se3 monolayer effectively modulates the electronic state coupling at the In2Se3/MTe2 interface. This modulation leads to variations in the width and height of the Schottky barrier at the heterojunction‐electrode interface corresponding with the ferroelectric polarization reversal, establishing a beneficial Ohmic contact in the “on” state and resulting in an exponential TER increase up to 5.4 × 106%. This work introduces a universal mechanism to overcome the thickness limitations traditionally associated with enhancing TER, marking a significant advancement in the development of ultrathin ferroelectric nonvolatile devices. [ABSTRACT FROM AUTHOR]

Potassium sodium niobate (KNN) has attracted much interest as a promising lead-free ferroelectric candidate with its excellent physical properties for potential applications to novel nano-devices such as non-volatile ferroelectric memory. However, the use of KNN films in actual devices has been limited due to concerns in operational reliability (i.e., a polarization fatigue property). In this work, we demonstrate the enhancement of a polarization fatigue behavior in KNN thin films by doping of Mn ions. Ferroelectric fatigue is significantly suppressed in 0.4 mol% Mn-doped KNN films compared with pure KNN films. The amounts of mobile charged defects (e.g., oxygen vacancies and hole carriers produced with cation vacancies) are reduced in the presence of multivalent Mn dopants resulting in a decrease of leakage current density. The reduction of charged defect density can weaken the domain wall pinning effect enabling the polarization fatigue to be suppressed in KNN films. Our work is of practical interest for realizing lead-free ferroelectric memory devices with high performance. [ABSTRACT FROM AUTHOR]

Freestanding ferroelectric thin films, free from substrate constraints, present a platform for advanced strain engineering owing to their exceptional mechanical flexibility. The strain state in freestanding ferroelectric thin films can be modulated through various mechanical deformations, enabling precise control over the physical properties and performance of the ferroelectric films. Here, we utilized phase-field simulations to explore the polarization evolution and switching behavior of freestanding BaTiO3 ferroelectric thin films under bending and shear strains. Our findings reveal that shear strain transforms flux-closure domains into a monoclinic phase, increasing the coercive field, maximum polarization, and remanent polarization, thereby broadening the ferroelectric polarization–electric field hysteresis loop. The underlying mechanism involves the competition between elastic and electrostatic energies, which becomes more pronounced with increasing shear strain. Additionally, this contrasts with the modulation of domain structures by bending strain, which causes a rightward shift in the ferroelectric polarization–electric field hysteresis loop due to the flexoelectric fields generated by bending deformation. These findings provide profound insights into the strain effects in ferroelectrics, highlighting the complex interplay between mechanical deformation and electrical response. The ability to manipulate domain structures and polarization behaviors through controlled mechanical strains paves the way for designing high-performance, flexible ferroelectric devices. [ABSTRACT FROM AUTHOR]

This work presents a novel paradigm for upconversion‐assisted ferroelectric photovoltaic devices. The system comprises a ferroelectric active layer (BiFeO3), an upconverter layer (Yb; Er‐doped ZnO), a conductive ITO‐coated glass substrate, and a reflective coating (Al) at the rear end of the glass substrate. The photovoltaic efficiency of the single‐layer BFO was found to be 0.71%. With the prescribed device model, the total solar efficiency of BiFeO3 improved significantly and touched solar conversion efficiency of 2.21%. This model's projection widens the future perspectives of device performance in emerging photovoltaic technology, mainly perovskite‐based solar cells. [ABSTRACT FROM AUTHOR]

Photonic devices based on ferroelectric domain engineering in thin film lithium niobate are key components for both classical and quantum information processing. Periodic poling of ridge waveguide can avoid the selective etching effect of lithium niobate, however, the fabrication of high-quality ferroelectric domain is still a challenge. In this work, we optimized the applied electric field distribution, and rectangular inverted domain structure was obtained in the ridge waveguide which is beneficial for efficient nonlinear frequency conversions. Second harmonic confocal microscope, piezoresponse force microscopy, and chemical selective etching were used to characterize the inverted domain in the ridge waveguide. In addition, the performance of nonlinear frequency conversion of the periodically poled nano-waveguide was investigated through second harmonic generation, and the normalized conversion efficiency was measured to be 1,720 % W−1 cm−2, which is close to 60 % that of the theoretical value. The fabrication technique described in this work will pave the way for the development of high-efficiency, low-loss lithium niobate nonlinear photonic devices. [ABSTRACT FROM AUTHOR]

The LiNbO3 (LNO) single crystal receives wide applications in nonvolatile memories, surface acoustic wave devices, and electro-optic modulators. However, engineering of antiparallel domain patterns within micrometer-sized devices generally requires a poling voltage more than a few thousands of volts. The high poling voltage could invoke dielectric breakdown. Here, we found an effective method to increase the local electric field significantly for domain nucleation at the interfaces of an etched LNO mesa in contact to two concave side electrodes, while the electric field across the protruding intra-electrode area can be lower by 10 times after the metal diffusion at the surface. Subsequent piezoresponse force microscopy mapping shows the nucleating domains to grow up through the entire intra-electrode area. This method is universal and analogous to other ferroelectric devices for the realization of low-voltage operations. [ABSTRACT FROM AUTHOR]

The metastable nature of the ferroelectric phase of HfO2 is a significant impediment to its industrial application as a functional ferroelectric material. In fact, no polar phases exist in the bulk phase diagram of HfO2, which shows a dominant non-polar monoclinic ground state. As a consequence, ferroelectric orthorhombic HfO2 is stabilized either kinetically or via epitaxial strain. Here, we propose an alternative approach, demonstrating the feasibility of thermodynamically stabilizing polar HfO2 in superlattices with other simple oxides. Using the composition and stacking direction of the superlattice as design parameters, we obtain heterostructures that can be fully polar, fully antipolar or mixed, with improved thermodynamic stability compared to the orthorhombic polar HfO2 in bulk form. Our results suggest that combining HfO2 with an oxide that does not have a monoclinic ground state generally drives the superlattice away from this non-polar phase, favoring the stability of the ferroelectric structures that minimize the elastic and electrostatic penalties. As such, these diverse and tunable superlattices hold promise for various applications in thin-film ferroelectric devices [ABSTRACT FROM AUTHOR]

Ferroelectric materials have switchable electrical polarization that is appealing for high-density nonvolatile memories. However, inevitable fatigue hinders practical applications of these materials. Fatigue-free ferroelectric switching could dramatically improve the endurance of such devices. We report a fatigue-free ferroelectric system based on the sliding ferroelectricity of bilayer 3R molybdenum disulfide (3R-MoS2). The memory performance of this ferroelectric device does not show the wake-up effect at low cycles or a substantial fatigue effect after 106 switching cycles under different pulse widths. The total stress time of the device under an electric field is up to 105 s, which is long relative to other devices. Our theoretical calculations reveal that the fatigue-free feature of sliding ferroelectricity is due to the immobile charge defects in sliding ferroelectricity. [ABSTRACT FROM AUTHOR]

Highlights: Ferroelectricity and domain dynamics of emerging ferroelectric AlScN films were discussed. The performance optimization of ferroelectric AlScN films grown by different deposition techniques was comprehensively analyzed. The challenges and perspectives regarding the commercial avenue of AlScN-based memories and in-memory computing applications were summarized. Ferroelectrics have great potential in the field of nonvolatile memory due to programmable polarization states by external electric field in nonvolatile manner. However, complementary metal oxide semiconductor compatibility and uniformity of ferroelectric performance after size scaling have always been two thorny issues hindering practical application of ferroelectric memory devices. The emerging ferroelectricity of wurtzite structure nitride offers opportunities to circumvent the dilemma. This review covers the mechanism of ferroelectricity and domain dynamics in ferroelectric AlScN films. The performance optimization of AlScN films grown by different techniques is summarized and their applications for memories and emerging in-memory computing are illustrated. Finally, the challenges and perspectives regarding the commercial avenue of ferroelectric AlScN are discussed. [ABSTRACT FROM AUTHOR]

Nano ferroelectrics holds the potential application promise in information storage, electro-mechanical transformation, and novel catalysts but encounters a huge challenge of size limitation and manufacture complexity on the creation of long-range ferroelectric ordering. Herein, as an incipient ferroelectric, nanosized SrTiO3 was indued with polarized ordering at room temperature from the nonpolar cubic structure, driven by the intrinsic three-dimensional (3D) tensile strain. The ferroelectric behavior can be confirmed by piezoelectric force microscopy and the ferroelectric TO1 soft mode was verified with the temperature stability to 500 K. Its structural origin comes from the off-center shift of Ti atom to oxygen octahedron and forms the ultrafine head-to-tail connected 90° nanodomains about 2 to 3 nm, resulting in an overall spontaneous polarization toward the short edges of nanoparticles. According to the density functional theory calculations and phase-field simulations, the 3D strain-related dipole displacement transformed from [001] to [111] and segmentation effect on the ferroelectric domain were further proved. The topological ferroelectric order induced by intrinsic 3D tensile strain shows a unique approach to get over the nanosized limitation in nanodevices and construct the strong strain-polarization coupling, paving the way for the design of high-performance and free-assembled ferroelectric devices. [ABSTRACT FROM AUTHOR]

Nano ferroelectrics holds the potential application promise in information storage, electro-mechanical transformation, and novel catalysts but encounters a huge challenge of size limitation and manufacture complexity on the creation of long-range ferroelectric ordering. Herein, as an incipient ferroelectric, nanosized SrTiO3 was indued with polarized ordering at room temperature from the nonpolar cubic structure, driven by the intrinsic three-dimensional (3D) tensile strain. The ferroelectric behavior can be confirmed by piezoelectric force microscopy and the ferroelectric TO1 soft mode was verified with the temperature stability to 500 K. Its structural origin comes from the off-center shift of Ti atom to oxygen octahedron and forms the ultrafine head-to-tail connected 90° nanodomains about 2 to 3 nm, resulting in an overall spontaneous polarization toward the short edges of nanoparticles. According to the density functional theory calculations and phase-field simulations, the 3D strain-related dipole displacement transformed from [001] to [111] and segmentation effect on the ferroelectric domain were further proved. The topological ferroelectric order induced by intrinsic 3D tensile strain shows a unique approach to get over the nanosized limitation in nanodevices and construct the strong strain-polarization coupling, paving the way for the design of high-performance and free-assembled ferroelectric devices. [ABSTRACT FROM AUTHOR]

The recent discovery of ferroelectric properties in HfO2 has sparked significant interest in the fields of nonvolatile memory and neuromorphic computing. Yet, as device scaling approaches sub-nanometer dimensions, leakage currents present a formidable challenge. While tungsten (W) electrodes are favored over traditional TiN electrodes for their superior strain and interface engineering capabilities, they are significantly hampered by leakage issues. In this study, we elucidate a positive feedback mechanism attributable to W electrodes that exacerbates oxygen vacancy defects, as evidenced by density functional theory computations. Specifically, intrinsic oxygen vacancies facilitate the diffusion of W, which, in turn, lowers the formation energy of additional oxygen vacancies. This cascade effect introduces extra defect energy levels, thereby compromising the leakage characteristics of the device. We introduce a pre-annealing method to impede W diffusion, diminishing oxygen vacancy concentration by 5%. This reduction significantly curtails leakage currents by an order of magnitude. Our findings provide a foundational understanding for developing effective leakage suppression strategies in ferroelectric devices. [ABSTRACT FROM AUTHOR]

Ferroelectric, phase-change, and magnetic materials are considered promising candidates for advanced memory devices. Under the development dilemma of traditional silicon-based memory devices, ferroelectric materials stand out due to their unique polarization properties and diverse manufacturing techniques. On the occasion of the 100th anniversary of the birth of ferroelectricity, scandium-doped aluminum nitride, which is a different wurtzite structure, was reported to be ferroelectric with a larger coercive, remanent polarization, curie temperature, and a more stable ferroelectric phase. The inherent advantages have attracted widespread attention, promising better performance when used as data storage materials and better meeting the needs of the development of the information age. In this paper, we start from the characteristics and development history of ferroelectric materials, mainly focusing on the characteristics, preparation, and applications in memory devices of ferroelectric wurtzite AlScN. It compares and analyzes the unique advantages of AlScN-based memory devices, aiming to lay a theoretical foundation for the development of advanced memory devices in the future. [ABSTRACT FROM AUTHOR]

The coupling of ferroelectric, photoelectric, semiconducting, and phase transition properties make two-dimensional (2D) In2Se3 a material platform with great application potential in the phase change memory, intelligent sensing, and in-memory computing devices. However, at present, there are unclear phase transition mechanisms and ferroelectric dynamics in 2D In2Se3, which seriously hinder the development of device applications. In this review, we mainly highlight the phase transition mechanisms and ferroelectric devices of In2Se3 beginning with the history of bulk In2Se3 and of 2D In2Se3. The phase transition relations of the four In2Se3 phases, including α-, β-, β′-, and γ-phases, under various driving forces, are summarized. The different driving forces, including temperature, laser, electric-field, vacancy, doping, and strain, are introduced and discussed. Moreover, the phase-control growth of 2D In2Se3 films and their novel ferroelectric device applications are demonstrated. Finally, a perspective on future research directions of 2D In2Se3 is provided. [ABSTRACT FROM AUTHOR]

The coupling of ferroelectric, photoelectric, semiconducting, and phase transition properties make two-dimensional (2D) In2Se3 a material platform with great application potential in the phase change memory, intelligent sensing, and in-memory computing devices. However, at present, there are unclear phase transition mechanisms and ferroelectric dynamics in 2D In2Se3, which seriously hinder the development of device applications. In this review, we mainly highlight the phase transition mechanisms and ferroelectric devices of In2Se3 beginning with the history of bulk In2Se3 and of 2D In2Se3. The phase transition relations of the four In2Se3 phases, including α-, β-, β′-, and γ-phases, under various driving forces, are summarized. The different driving forces, including temperature, laser, electric-field, vacancy, doping, and strain, are introduced and discussed. Moreover, the phase-control growth of 2D In2Se3 films and their novel ferroelectric device applications are demonstrated. Finally, a perspective on future research directions of 2D In2Se3 is provided. [ABSTRACT FROM AUTHOR]

Interfacial engineering is important for ferroelectric thin-film heterostructures because of the modulation of boundary conditions of the spontaneous polarizations and their switching behaviors, which are essential for ferroelectric electronics. In this work, we study the effects of interfacial buffering layer, 5-nm-thick SrTiO3 (STO), on the imprint and domain switching of epitaxial Pt/Pb(Zr,Ti)O3/SrRuO3 (SRO) thin-film heterostructures and capacitors. By buffering the ultrathin SrTiO3 layer at the Pb(Zr,Ti)O3 surface, the imprint effect can be dramatically alleviated as observed in the piezoresponse force microscopy (PFM)-measured domain structures and polarization–electric field hysteresis loops in thin-film capacitors. However, when the SrTiO3 layer is buffered at the Pb(Zr,Ti)O3/SrRuO3 interface, the imprint effect is slightly increased. These phenomena are explained based on the band alignments among the Pt and SrRuO3 electrodes and the Pb(Zr,Ti)O3 layer associated with the existence of oxygen vacancies in the SrTiO3 layer. With the reduction of imprint effect, the domain switching dynamics are also improved in the SrTiO3-buffered Pb(Zr,Ti)O3 capacitor, in which the switching activation field is decreased by about 45.3% in comparison with that of the pristine capacitor. These results facilitate the design and optimization of ferroelectric devices with the improvements in domain configurations, switching behaviors and band alignments. [ABSTRACT FROM AUTHOR]

In the presence of asymmetric potential barriers, such as those created by imprint fields, ferroelectric polarization can be reversed by light due to the photoinduced suppression of polarization. Both thermal effects and photocarrier-induced polarization screening may agree with this experimental observation, challenging its understanding. Here, we explore light-induced ferroelectric polarization switching in BaTiO3 thin films. Time-dependent photocurrent and photoresistance experiments at different wavelengths indicate that the optical switch of polarization is mainly driven by photocarriers rather than thermal effects. The effect of light on sample polarization is found to be relatively slow and that an illumination period as long as ≈100 s is required to achieve complete switching when using a 405 nm light wavelength and 1.4 W/cm2 power density. It is shown that this response is governed by the concentration of photo-generated charges, which is low due to the reduced light absorption of BaTiO3 films at the explored wavelengths. Our conclusions can help us to better design optically switching devices based on ferroelectric materials. [ABSTRACT FROM AUTHOR]

The recent discovery of van der Waals (vdW) ferroelectric materials has inspired their incorporation into numerous nonvolatile technologies and shown potential promise for various device applications. Here in this perspective, we evaluate the recent developments in the field of vdW ferroelectric devices, with discussions focusing on vdW heterostructure ferroelectric field-effect transistors and vdW ferroelectric memristor technologies. Additionally, we discuss some of the many open questions that persist in these technologies and possible pathways research can take to answer these questions and further advance the understanding of vdW ferroelectric materials. [ABSTRACT FROM AUTHOR]

Fundamental aspects of ferroelectric HfO 2 , a fluorite-type oxide, are not understood yet. This is evident by different theories regarding, e.g., the wake-up effect or the antiferroelectric-like behavior of HfO 2 manufactured with different doping or deposition techniques. Therefore, we focus on sputtered and undoped HfO 2 to gain deeper understanding of the ferroelectric properties of pure HfO 2. A temperature gradient on a 10 × 10 mm 2 substrate during rapid thermal annealing led to different ferroelectric device performances in terms of remnant polarization and the wake-up effect. The results from the electrical characterization are compared to observations by transmission electron microscopy, performed on pristine and trained samples in plan-view as well as in cross section. We observed that different temperature treatments caused effects at the interfaces of the TiN electrodes and also affected the microstructure and defect concentration of the HfO 2 itself. Devices from the hot corner showed wake-up free ferroelectricity with a remnant polarization below 10 μ C / cm 2 , whereas devices from the cold corner showed a strong wake-up effect with remnant polarization starting from 0 to above 20 μ C / cm 2 after 10 6 cycles. After observing a small structural transformation in trained devices, we attributed this strong wake-up effect to gradual ferroelastic switching of pristine [110] oriented grains with in-plane polarization to partially out-of-plane polarization, while the predominantly ⟨ 111 ⟩ oriented grains in the hot corner can suppress the wake-up effect. [ABSTRACT FROM AUTHOR]

Group IIIA metal chalcogenides are an auspicious material system due to their variability of properties and hence the multitude of application options, for example, in the fields of optoelectronic, thermoelectric, piezo‐, and ferroelectric devices. Indium and gallium selenide films are innovatively grown in a sequential PVD (physical vapor deposition) process starting from metal precursor layers of various thicknesses, which are then subject to chalcogenization in different selenium contents. The resulting thin films are investigated for structural and optical properties by Raman, XRD (X‐ray diffraction), and UV–Vis–NIR spectrometry, revealing that all the compounds In2Se3, InSe, In4Se3, Ga2Se3, and GaSe as well as different polytypes can be achieved depending on the metal/chalcogen ratio. Results from Raman and XRD spectroscopy are highly consistent, and also from the optical measurements changes in absorption characteristics can be correlated. The results indicate, that by fine‐tuning the selenium content, deliberately growing ultra‐thin layers of the different indium and gallium phases will be possible, thus opening up a promising route for 2D material fabrication. Given the scalability of the fabrication method, it is highly promising for large‐scale deployment of the materials. [ABSTRACT FROM AUTHOR]

Recently, the observation of ferroelectric vortex arrays has triggered the investigation of topological domain structures and their characteristics. Vortices are typical topological domain structures with chirality in nanoscale ferroelectric materials. The chirality of a single vortex in a nanodot can be easily manipulated, but the collective control of a vortex array is exceptionally difficult and has not yet been realized. This Letter proposes an effective scheme for the collective control of a vortex array and investigates it via phase-field simulations. The results indicate that the collective control of a vortex array with bidirectional switching can be realized by introducing a bending film with periodic large curvatures under alternative electric fields. Furthermore, a general rule for determining the electrically controllable chirality of ferroelectric vortices is proposed. This Letter demonstrates the feasibility of the collective control of vortex arrays and provides insights for developing ferroelectric nanoelectronic devices based on vortex arrays. [ABSTRACT FROM AUTHOR]

2D ferroelectric materials have garnered extensive attention for promising applications in next‐generation electronic devices, which provides a platform to explore ferroelectricity without the critical thickness constraint of traditional perovskite oxide‐based ferroelectric materials. Recent studies have shown that chemical vapor deposition (CVD) can synthesis the large‐area 2D ferroelectric materials, making the 2D ferroelectric materials to be compatible with scalable semiconductor devices. In this Review, the CVD‐grown 2D ferroelectric materials are summarized in terms of materials, properties to devices application view. First, the synthesis strategy and recent advances of the CVD growth of 2D ferroelectric materials are highlighted in the aspects of diverse groups of 2D materials. Second, the recent experimental progress of 2D ferroelectric devices is introduced, and the potential applications of 2D ferroelectric devices are discussed. The availability of the CVD‐grown 2D ferroelectrics provides an abundant playground for not only deep studying the ferroelectric properties, but also conceiving various device applications. Lastly, the perspectives are provided to address the current challenges in terms of materials design, physics mechanism, device, and multifunctional application. [ABSTRACT FROM AUTHOR]

Relaxor ferroelectrics have applications in transducers and capacitors owing to their dielectric relaxation. Although the existence of polar nanoregions (PNRs) inside the relaxor ferroelectrics contributes to enhancing the dielectric response, the dielectric relaxation mechanism remains unclear in the wide frequency range from kHz to THz. In this study, we investigated the frequency-dependent (103-1012 Hz) dielectric properties using ultrafast phase-field simulations. The dielectric response is divided into the matrix response, the "collinear" PNR response, and the "non-collinear" PNR response. Among them, the collinear PNR response accounts for 90% of the dielectric constant enhancement. The response behavior of collinear PNRs has a higher frequency limitation than that of non-collinear PNRs. The different relaxation times of the collinear PNR lead to a corresponding distinct rotation for the polar vectors. Finally, we investigate the different response behaviors of the polarization in the PNR from the aspect of energy barriers. This study not only promotes the understanding of wide-range frequency-dependent dielectric relaxation processes but also guides the design of ultrafast relaxor ferroelectric devices in the future. [ABSTRACT FROM AUTHOR]

Realization of higher-order multistates with mutual interstate switching in ferroelectric materials is a perpetual drive for high-density storage devices and beyond-Moore technologies. Here we demonstrate experimentally that antiferroelectric van der Waals CuInP2S6 films can be controllably stabilized into double, quadruple, and sextuple polarization states, and a system harboring polarization order of six is also reversibly tunable into order of four or two. Furthermore, for a given polarization order, mutual interstate switching can be achieved via moderate electric field modulation. First-principles studies of CuInP2S6 multilayers help to reveal that the double, quadruple, and sextuple states are attributable to the existence of respective single, double, and triple ferroelectric domains with antiferroelectric interdomain coupling and Cu ion migration. These findings offer appealing platforms for developing multistate ferroelectric devices, while the underlining mechanism is transformative to other non-volatile material systems. Materials with higher-order multistates are desired for non-Boolean high-density storage. Here the authors realized sextuple intrinsic polarization states in vdW CuInP2S6, and reversible transformation among sextuple-, quadruple-, and double-polarization orders. [ABSTRACT FROM AUTHOR]