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Ferroelectric memory is a promising candidate for next‐generation nonvolatile memory owing to its outstanding performance such as low power consumption, fast speed, and high endurance. However, the ferroelectricity of conventional ferroelectric materials will be eliminated by the depolarization field when the size drops to the nanometer scale. As a result, the miniaturization of ferroelectric devices was hindered, which makes ferroelectric memory unable to keep up with the development of integrated‐circuit (IC) miniaturization. Recently, a two‐dimensional (2D) In2Se3 was reported to maintain stable ferroelectricity at the ultrathin scale, which is expected to break through the bottleneck of miniaturization. Soon, devices based on 2D In2Se3, including the ferroelectric field‐effect transistor, ferroelectric channel transistor, synaptic ferroelectric semiconductor junction, and ferroelectric memristor were demonstrated. However, a comprehensive understanding of the structures and the ferroelectric‐switching mechanism of 2D In2Se3 is still lacking. Here, the atomic structures of different phases, the dynamic mechanism of ferroelectric switching, and the performance/functions of the latest devices of 2D In2Se3 are reviewed. Furthermore, the correlations among the structures, the properties, and the device performance are analyzed. Finally, several crucial problems or challenges and possible research directions are put forward. We hope that this review paper can provide timely knowledge and help for the research community to develop 2D In2Se3 based ferroelectric memory and computing technology for practical industrial applications. Two‐dimensional (2D) In2Se3 is a novel ferroelectric capable of fighting against the depolarization field at nanoscale. Thus, 2D In2Se3‐based low‐power consumption, high‐density ferroelectric devices are promising candidates for data storage applications. This review summarizes the major advances in 2D In2Se3, including structures, properties, phase/switching transitions, and device performance. Prospects for its future development and research directions are also presented.

In the present hyper-scaling era, memory technology is advancing owing to the demand for high-performance computing and storage devices. As a result, continuous work on conventional semiconductor-process-compatible ferroelectric memory devices such as ferroelectric field-effect transistors, ferroelectric random-access memory, and dynamic random-access memory (DRAM) cell capacitors is ongoing. To operate high-performance computing devices, high-density, high-speed, and reliable memory devices such as DRAMs are required. Consequently, considerable attention has been devoted to the enhanced high dielectric constant and reduced equivalent oxide thickness (EOT) of DRAM cell capacitors. The advancement of ferroelectric hafnia has enabled the development of various devices, such as ferroelectric memories, piezoelectric sensors, and energy harvesters. Therefore, in this review, we focus the morphotropic phase boundary (MPB) between ferroelectric orthorhombic and tetragonal phases, where we can achieve a high dielectric constant and thereby reduce the EOT. We also present the role of the MPB in perovskite and fluorite structures as well as the history of the MPB phase. We also address the different approaches for achieving the MPB phase in a hafnia material system. Subsequently, we review the critical issues in DRAM technology using hafnia materials. Finally, we present various applications of the hafnia material system near the MPB, such as memory, sensors, and energy harvesters.

Macroscopic ferroelectric polarization switching, similar to other first-order phase transitions, is controlled by nucleation centres. Despite 50 years of extensive theoretical and experimental effort, the microstructural origins of the Landauer paradox, that is, the experimentally observed low values of coercive fields in ferroelectrics corresponding to implausibly large nucleation activation energies, are still a mystery. Here, we develop an approach to visualize the nucleation centres controlling polarization switching processes with nanometre resolution, determine their spatial and energy distribution and correlate them to local microstructure. The random-bond and random-field components of the disorder potential are extracted from positive and negative nucleation biases. Observation of enhanced nucleation activity at the 90 ∘ domain wall boundaries and intersections combined with phase-field modelling identifies them as a class of nucleation centres that control switching in structural-defect-free materials.

Ferroelectric memory devices are expected for low-power and high-speed memory applications. HfO2-based ferroelectric is attracting attention for its CMOS-compatibility and high scalability. Mesoscopic-scale grains, of which size is almost comparable to device size, are formed in HfO2-based ferroelectric poly-crystalline thin films, which largely influences electrical characteristics in memory devices. It is important to study the impact of mesoscopic-scale grain formation on the electrical characteristics. In this work, first, we have studied the thickness dependence of the polarization switching kinetics in HfO2-based ferroelectric. While static low-frequency polarization is comparable for different thickness, dynamic polarization switching speed is slower in thin Hf0.5Zr0.5O2 (HZO) capacitors. Based on the analysis using the NLS model and physical characterization, thinner HZO contains smaller grains with orientation non-uniformity and more grain boundaries than thicker HZO, which can impede macroscopic polarization switching. We have also theoretically and experimentally studied the polar-axis alignment of a HfO2-based ferroelectric thin film. While in-plane polar orientation is stable in as-grown HZO, out-of-plane polarization can be dominant by applying electric field, which indicates the transition from in-plane polar to out-of-plane polar orientation in the ferroelectric phase grains. This is confirmed by calculating kinetic pathway using ab-initio calculation.

This article presents a study on the subthreshold swing (SS) and the ON–OFF current ratio of a negative capacitance source pocket double-gate tunnel field-effect transistor (NC-SP-DGTFET). In this analysis, a novel device is developed that integrates gate and channel engineering techniques. The combination of the ferroelectric material hafnium zirconium oxide (HZO) with the dielectric material SiO2 generates a negative capacitance (NC) effect. Additionally, the incorporation of a totally depleted source pocket into the DGTFET reduces the tunneling width. The addition of NC has the potential to improve the SS through the amplification of the electric field at the tunnel junction. Moreover, it has been observed that a fully depleted source pocket within the source/channel region significantly enhances the ION current when compared to the double-gate tunnel field-effect transistor (DGTFET). Following thorough device optimization, there has been a notable enhancement in the ION/IOFF current ratio, SS, and transconductance (gm) by a factor of 1.54 × 1013, 20.8 mV/dec, and 5.102 × 10−4 S/µm, respectively. These improvements signify superior energy efficiency and enhanced performance when compared to both DGTFET and source pocket based DGTFET (SP-DGTFET) configurations. Furthermore, substantial research has been conducted on the variation in electrical properties in relation to the thickness of ferroelectric materials. The findings indicate that the proposed device exhibits considerable potential as a viable option for applications requiring both low power consumption and high operational speed.

Background The unique non-uniform polar nanoregions and complex phase structure near morphotropic phase boundaries (MPBs) in relaxor ferroelectric materials lead to rich microstructure changes (domain transition, phase transition) under external field stimulation. This not only results in the material with extremely high electromechanical properties, but also greatly affects their mechanical properties and stability. Objective This study investigated the fundamental mechanical properties of the rhombohedral phase (R-phase) and tetragonal phase (T-phase) structures of the relaxor ferroelectric single crystal PMN-PT material using the nanoindentation with different shapes of indenters. Methods The basic mechanical properties of the material were measured by nanoindentation, and the fracture caused by indentation was analyzed by scanning electron microscopy. Results The elastic modulus of R-phase relaxed ferroelectric materials showed a significant dependence on the indentation depth, and the hardness of different phases (R, T-phase) materials all show obvious indentation size effects (ISE). Under the loading of the spherical indenter, both R and T phase materials exhibited a pop-in phenomenon caused by the transition from elastic to inelastic. Under the loading of the Berkovich indenter, the R and T phase materials showed different fracture characteristics of crack propagation response with the increase of the indentation depth. Conclusions The result demonstrate that the mechanical properties of relaxor ferroelectric materials are significantly related to their phase structure, providing guidance for the design of load bearing and material selection in the practical application of related ferroelectric devices.

Ferroelectric materials, with their spontaneous electric polarization, are renewing research enthusiasm for their deployment in high-performance micro/nano energy harvesting devices such as triboelectric nanogenerators (TENGs). Here, the introduction of ferroelectric materials into the triboelectric interface not only significantly enhances the energy harvesting efficiency, but also drives TENGs into the era of intelligence and integration. The primary objective of the following paper is to tackle the newest innovations in TENGs based on ferroelectric materials. For this purpose, we begin with discussing the fundamental idea and then introduce the current progress with TENGs that are built on the base of ferroelectric materials. Various strategies, such as surface engineering, either in the micro or nano scale, are discussed, along with the environmental factors. Although our focus is on the enhancement of energy harvesting efficiency and output power density by utilizing ferroelectric materials, we also highlight their incorporation in self-powered electronics and sensing systems, where we analyze the most favorable and currently accessible options in attaining device intelligence and multifunctionality. Finally, we present a detailed outlook on TENGs that are based on ferroelectric materials.

Ferroelectric materials are characterized by a permanent electric dipole that can be reversed through the application of an external voltage, but a strong intrinsic coupling between polarization and deformation also causes all ferroelectrics to be piezoelectric, leading to applications in sensors and high-displacement actuators. A less explored property is flexoelectricity, the coupling between polarization and a strain gradient. We demonstrate that the stress gradient generated by the tip of an atomic force microscope can mechanically switch the polarization in the nanoscale volume of a ferroelectric film. Pure mechanical force can therefore be used as a dynamic tool for polarization control and may enable applications in which memory bits are written mechanically and read electrically.

Bi0.5Na0.5TiO3 (BNT)-based lead-free materials are important for piezoelectric actuator, and several researchers have studied the effect of B-site complex ion doping on strain in (Bi0.5Na0.5)TiO3–SrTiO3. In this work, a paraelectric perovskite Sr(Zn1/3Nb2/3)O3 (SZN) with B-site complex structure was introduced into 0.80(Bi0.5Na0.5)TiO3–0.20SrTiO3 (BNTST) to investigate the phase structure and electrical properties as well as the field-induced strain behavior. The results showed that SZN substitution decreases the rhombohedrality 90-γ and induces the transition from dominant ferroelectric to nonergodic relaxor by shifting its TF-R to lower temperatures. Moreover, the field-induced ferroelectric domains cannot remain stable at room temperature when SZN substitution is large than 1.0 mol%. These behaviors induced the transition between nonergodic relaxor and ergodic relaxor, which contributed to its large strain and related properties. In this work, this material gave the largest bipolar strain of 0.43% and large normalized unipolar strain of 505 pm/V at the SZN content of 2 mol% under 8 kV/mm, and showed good temperature stability up to 100 °C. The above encouraging results may be helpful for further investigation of BNTST-based ternary systems in search of a potential Pb-free piezoelectric material.

Two-dimensional (2D) ferroelectric materials, which possess electrically switchable spontaneous polarization and can be easily integrated with semiconductor technologies, is of utmost importance in the advancement of high-integration low-power nanoelectronics. Despite the experimental discovery of certain 2D ferroelectric materials such as CuInP 2 S 6 and In 2 Se 3 , achieving stable ferroelectricity at room temperature in these materials continues to present a significant challenge. Herein, stable ferroelectric order at room temperature in the 2D limit is demonstrated in van der Waals SnP 2 S 6 atom layers, which can be fabricated via mechanical exfoliation of bulk SnP 2 S 6 crystals. Switchable polarization is observed in thin SnP 2 S 6 of ∼7 nm. Importantly, a van der Waals ferroelectric field-effect transistor (Fe-FET) with ferroelectric SnP 2 S 6 as top-gate insulator and p-type WTe 0.6 Se 1.4 as the channel was designed and fabricated successfully, which exhibits a clear clockwise hysteresis loop in transfer characteristics, demonstrating ferroelectric properties of SnP 2 S 6 atomic layers. In addition, a multilayer graphene/SnP 2 S 6 /multilayer graphene van der Waals vertical heterostructure phototransistor was also fabricated successfully, exhibiting improved optoelectronic performances with a responsivity ( R ) of 2.9 A/W and a detectivity ( D ) of 1.4 × 10 12 Jones. Our results show that SnP 2 S 6 is a promising 2D ferroelectric material for ferroelectric-integrated low-power 2D devices.