Ferroelectric Thin Films Research Articles

A phase-field simulation of easily switchable vortex structure for multilevel low-power ferroelectric memory

Ferroelectric materials with multi-directional polarization orders can form a variety of special domain structures, which have a wide range of applications. In this work, lead-free potassium sodium niobate ferroelectric thin films were simulated by solving the Time-Dependent-Landau-Ginzburg (TDLG) equation. Based on vortex topological structure characteristic of perovskite-type ferroelectric, domain types are simplified from 26 to 9 through virtual polarization vectors. By temperature selection, we accomplished a large easily switchable vortex structure with 20% side length. Based on this, as low as 0.04V/nm electric-field pulse was applied to explore vortex domain structures change. Under different low external electric-field pulses, conductance states change in vortex have been calculated and discussed systematically. Free energy computation results reveal that the domain wall (DW) conductance states primarily originate from the competition between electrostatic energy, gradient energy, and elastic energy. Finally, we propose the multilevel data ferroelectric memory through easily switchable vortex topological structures for the first time. Under electric-field pulses, diverse storage states were presented through 0/1 measurement of 8 positions. By achieving an easy-to-distinguish and robust-to-switch data map at the vortex structure, this work might provide a significant idea of vortex structure on low-power ferroelectric memory applications.

Lead-free BaTiO3-based relaxor ferroelectric thin film rendering rapid discharge rate for pulsed power energy application

Ferroelectric thin film capacitors have large application potential in pulsed-power electronic and electrical systems due to their high-power density and rapid discharge capabilities. Although lead-based dielectrics are promising, the pursuit of eco-friendly, lead-free alternatives is gaining research attention. Here, the Bi and Li co-doped BaTiO3 thin film exhibiting relaxor ferroelectric properties was investigated for its energy storage properties. The fabricated polycrystalline Ba0.85(Bi0.5Li0.5)0.15TiO3 thin film by pulsed laser deposition revealed good breakdown strength (∼4 MV cm−1), a slim ferroelectric loop, and low leakage characteristics suitable for energy storage applications. The film exhibits a significant value of recoverable energy density (∼70 J cm−3) with better frequency and thermal stability. Notably, the better overall performance parameters of the film, including a sizable power density (261 MW cm−3) and a fast discharge rate (150 ns), along with good energy density and breakdown strength, make the material suitable for pulsed-power energy applications.

Improving the endurance for ferroelectric Hf0.5Zr0.5O2 thin films by interface and defect engineering

Improving the endurance performance for hafnia-based ferroelectric thin films and devices is of considerable significance from both scientific and technological perspectives. Here, we obtained robust ferroelectricity in Hf0.5Zr0.5O2 (HZO) thin films without the need of the confinement from top electrodes by systematically optimizing the conditions and parameters for the post-deposition annealing (PDA) process. Compared with the post-metallization annealing (PMA) process, PDA is found to markedly improve the ferroelectric endurance performance. In particular, wake-up-free ferroelectric HZO thin films with an exceptional endurance performance (∼3 × 1010 cycles) are obtained by PDA processing conducted under an oxygen atmosphere, which is attributed to the suppression of oxygen deficiency in the HZO thin films and the inhibition of interfacial reaction layer that inevitably forms during annealing treatment for PMA processing. Our work offers insight into improving ferroelectricity and endurance for hafnia-based ferroelectric materials and devices.

Engineering crystal structure transformation from layered perovskite-like to pyrochlore for electrostatic energy storage

The pyrochlore phase in ferroelectric materials has long been unaccepted as a negative factor. Therefore, every effort was made to eliminate it. Here, based on electrostatic energy storage capacitors, we provide a counter view to evaluate its effects on ferroelectric properties, i.e., the electrostatic energy storage properties of ferroelectric thin films can be significantly improved by a deliberately designed pyrochlore phase. By adjusting the components and annealing temperature to control crystal structure transformation, an energy storage density of 69 J/cm3 and an efficiency of 70.1% were achieved as a pyrochlore-dominated film, along with good temperature and fatigue stability. It is attribute to its relatively low loss and linear ferroelectric polarization behavior, which enhances the breakdown field while reducing the remnant polarization. These results will provide a versatile strategy for the development of ferroelectric thin film energy storage capacitors with high energy storage density, high efficiency, and good fatigue resistance based on crystal structure transformation.

Structure, ferroelectric, and enhanced fatigue properties of sol–gel-processed new Bi-based perovskite thin films of Bi(Cu1/2Ti1/2)O3–PbTiO3

Bi-based perovskite ferroelectric thin films have wide applications in electronic devices due to their excellent ferroelectric properties. New Bi-based perovskite thin films Bi(Cu1/2Ti1/2)O3–PbTiO3 (BCT–PT) are deposited on Pt(111)/Ti/SiO2/Si substrates in the present study by the traditional sol–gel method. Their structures and related ferroelectric and fatigue characteristics are studied in-depth. The BCT–PT thin films exhibit good crystallization within the phase-pure perovskite structure, besides, they have a predominant (100) orientation together with a dense and homogeneous microstructure. The remnant polarization (2P r) values at 30 μC/cm2 and 16 μC/cm2 are observed in 0.1BCT–0.9PT and 0.2BCT–0.8PT thin films, respectively. More intriguingly, although the polarization values are not so high, 0.2BCT–0.8PT thin films show outstanding polarization fatigue properties, with a high switchable polarization of 93.6% of the starting values after 108 cycles, indicating promising applications in ferroelectric memories.

A 2D ferroelectric vortex pattern in twisted BaTiO3 freestanding layers

The wealth of complex polar topologies1–10 recently found in nanoscale ferroelectrics results from a delicate balance between the intrinsic tendency of the materials to develop a homogeneous polarization and the electric and mechanical boundary conditions imposed on them. Ferroelectric–dielectric interfaces are model systems in which polarization curling originates from open circuit-like electric boundary conditions, to avoid the build-up of polarization charges through the formation of flux-closure11–14 domains that evolve into vortex-like structures at the nanoscale15–17 level. Although ferroelectricity is known to couple strongly with strain (both homogeneous18 and inhomogeneous19,20), the effect of mechanical constraints21 on thin-film nanoscale ferroelectrics has been comparatively less explored because of the relative paucity of strain patterns that can be implemented experimentally. Here we show that the stacking of freestanding ferroelectric perovskite layers with controlled twist angles provides an opportunity to tailor these topological nanostructures in a way determined by the lateral strain modulation associated with the twisting. Furthermore, we find that a peculiar pattern of polarization vortices and antivortices emerges from the flexoelectric coupling of polarization to strain gradients. This finding provides opportunities to create two-dimensional high-density vortex crystals that would enable us to explore previously unknown physical effects and functionalities.

Bulk photovoltaic effect of ferroelectric Sc-doped GaN thin films toward self-powered light detection

Gallium nitride (GaN), one of the most popular optoelectronic materials in the semiconductor industry, has gained renewed interest as a ferroelectric material when alloyed with scandium. However, the inherent bulk photovoltaic effect (BPE) of GaN-based ferroelectrics has yet to be fully exploited. In this work, a BPE-driven self-powered photodetector based on ferroelectric Sc-doped GaN thin film was fabricated without the usage of a p-n contact. At zero bias, this device features a high responsivity of 45.9 mA/W, a high detectivity of 2.27 × 1011 Jones, a fast response speed of sub-ms-level, a high UV selectivity of 91.3, and an imaging capacity. This work demonstrates the potential of GaN-based ferroelectric thin films in energy-efficient optoelectronic devices.

Extended contributions to the pyroelectric effect in ferroelectric thin films

Pyroelectric properties of dielectrics have been occupying the agenda of relevant scientific research groups owing to a number of device designs tailoring this effect, such as energy harvesting and caloric devices. Ferroelectrics come forward probably as the most important class of dielectrics in this regard due to their spontaneous polarization that is strongly dependent on temperature as well as strain and electric field. Here, we rigorously formulate and identify the connection between the experimentally accessible pyroelectric coefficient of a perovskite type ferroelectric and contributions arising from strain and clamping conditions. Secondary pyroelectric coefficient under partial clamping reminiscing a thin film is formulated so as to separate it from the primary coefficient that is conventionally defined at constant volume. The formulation is then applied to a number of ferroelectric compositions to reveal the extent of the variations in the secondary pyroelectric effect. The secondary effect reinforces the primary pyroelectric coefficient for the PMN-PT system, whereas it diminishes the total coefficient for PbZr0.4Ti0.6O3 and BaTiO3 systems. The role of thermal expansion coefficients in these variations is discussed.

A dynamic Bayesian optimized active recommender system for curiosity-driven partially Human-in-the-loop automated experiments

Optimization of experimental materials synthesis and characterization through active learning methods has been growing over the last decade, with examples ranging from measurements of diffraction on combinatorial alloys at synchrotrons, to searches through chemical space with automated synthesis robots for perovskites. In virtually all cases, the target property of interest for optimization is defined a priori with the ability to shift the trajectory of the optimization based on human-identified findings during the experiment is lacking. Thus, to highlight the best of both human operators and AI-driven experiments, here we present the development of a human–AI collaborated experimental workflow, via a Bayesian optimized active recommender system (BOARS), to shape targets on the fly with human real-time feedback. Here, the human guidance overpowers AI at early iteration when prior knowledge (uncertainty) is minimal (higher), while the AI overpowers the human during later iterations to accelerate the process with the human-assessed goal. We showcase examples of this framework applied to pre-acquired piezoresponse force spectroscopy of a ferroelectric thin film, and in real-time on an atomic force microscope, with human assessment to find symmetric hysteresis loops. It is found that such features appear more affected by subsurface defects than the local domain structure. This work shows the utility of human–AI approaches for curiosity driven exploration of systems across experimental domains.

A low power memristor based on Lu doped HfO2 ferroelectric thin films and its multifunctional realization

Next-generation non-volatile memories with low power consumption and multiple functions are highly desired in the era of big data. Here, we report a high-performance ferroelectric memristor Pd/Lu:HfO2/La0.7Sr0.3MnO3/SrTiO3/Si, which has low average set and reset powers of 4.28 nW and 0.75 nW, respectively. It can successfully simulate biological synaptic functions, such as the refractory period, spike-timing-dependent plasticity, and paired pulse facilitation. Moreover, the device realizes the simulation of decimal addition and multiplication. In particular, the device can be combined with the threshold device to form a neuromorphic network, which not only realizes multi-value data storage, data decryption and encryption, but also intensity modulation of peak frequency. These results may throw light on the way for the future research of low-power multifunctional neuro morphology chips.

Preface

The 2023 3rd International Conference on Advanced Materials and Chemical Engineering (AMCE 2023) was motivated to bridge the scientists, experts, practitioners, and students in the scientific forum through sharing ideas and issues about theoretical and practical knowledge in Advanced Materials and Chemical Engineering.This Conference took place from October 20th to 22nd, 2023 in Changsha, China, bringing together about 130 attendees worldwide. As an annual conference, AMCE has been and will be held in China every year starting from 2021, attracting more than 300 attendees from various countries all around the world. With strong organization team, dependable reputation and wide sponsors globally, AMCE 2023 was even more successful than previous ones.The keynote speeches were provided especially to show the contributions of scholars and experts around the world working in the fields related to advanced materials and chemical engineering towards research experience and professional knowledge sharing. We had more than ten keynote speakers coming mainly from Xiangtan University, China, Hunan University, China, University of South China, China, Wuhan Textile University, China, Yunnan University, China, Central South University, China, Changzhou University, China, Guangdong University of Petrochemical Technology, China, Yunnan Normal University, China, Kunming University of Science and Technology, China, Firat University, Elazig, Turkey, and Harbin Institute of Technology, China. These experts shared remarkable academic achievements in fields related to advanced materials and chemical engineering, and discussed critical challenges and research directions within these domains, triggering heated discussion during the Conference and even in the break.The Proceedings of AMCE 2023 involves various accepted excellent papers around topics including New Semiconductor Materials, Nano Materials and Technology, Dielectric, Ferroelectric Thin Films and Integrated Devices, High-performance Computing in Material Design, Colloid and Interface Chemistry, etc. The selected papers were checked through a rigorous peer review process, and are published in the present volume. Reviews were conducted by expert referees to the professional and scientific standards expected of Journal of Physics: Conference Series.We would like to thank the Conference Committee members for their great support and suggestion provided in every aspect to make the Conference successful and the expert reviewers for their kind assistance in reviewing the manuscripts submitted. We would also extend our best gratitude to the keynote speakers for their invaluable contribution and worthwhile ideas shared in the Conference. Last but not the least is our appreciation to Journal of Physics: Conference Series for every process its members conducted to make this volume published.List of Committee Member is available in this pdf.

Fabrication and photonic applications of Si-integrated LiNbO3 and BaTiO3 ferroelectric thin films

Silicon, renowned for its applications in electronic circuits, also offers significant advantages in the realm of integrated optics. While silicon does have inherent limitations in fabricating active devices, these challenges can be overcome through heterogeneous integration with other materials. Ferroelectric materials like lithium niobate (LN) and barium titanate (BTO) exhibit exceptional electrical and nonlinear optical properties, making them ideal candidates for integrated silicon photonics. Over the past few decades, the LN platform has made substantial progress, surmounting obstacles such as manufacturing difficulties, high waveguide losses, and low modulation bandwidth caused by wide electrode spacing. Consequently, LN-based devices have found widespread application in various fields. With the advent of high-quality, large-size LN on insulator wafers, LN photonics has become a burgeoning research area. At the same time, the ferroelectric material BTO, with its tremendous electro-optic response, shows promise for the next generation of integrated photonics. Recent studies have highlighted the remarkable performance of BTO-based modulators, which offer smaller device sizes compared to LN by achieving lower half-wave voltages. This comprehensive review presents various fabrication methods for integrating LN and BTO thin films on silicon, focusing on recent advancements. We discuss their electro-optic responses and provide an overview of the diverse applications enabled by these platforms. Finally, we summarize the current state of integrated LN and BTO photonics research and offer insights into future directions.

Texture in atomic layer deposited Hf0.5Zr0.5O2 ferroelectric thin films

HfO2-based ferroelectric materials have excellent CMOS compatibility and polarization even in ultrathin films, which is regarded as promising candidate material for memory devices and related electronic devices. However, as the ferroelectric layer thickness scaling down, the consistency of device performance is inevitably affected by the complex polyphase and polycrystalline nature of HfO2-based ferroelectric thin films. Therefore, obtaining and controlling the texture of HfO2-based ferroelectric thin films is extremely important for regulating polarization orientation and improving ferroelectric polarization. In this work, 10 nm Hf0.5Zr0.5O2 (HZO) films were prepared by atomic layer deposition (ALD) on Nb-doped SrTiO3 (NSTO) single crystal substrates. The texture and orientation of HZO films were analyzed through the state-of-the-art spherical aberration corrected transmission electron microscope (Cs-TEM) technique. The domain matching epitaxy between HZO films and NSTO substrate helps eliminate lattice mismatch and residual misfit strain, and ultimately leads to the formation of <112> texture in HZO ferroelectric films. The obtained results represent lattice and interface play an extremely important role in regulating the ferroelectricity of HfO2-based films, which provides a way to design ultra-thin HfO2-based materials with excellent ferroelectric polarization by controlling the crystal structure and orientation.

Sm and Mn doped enhancing the electrical properties of .68PMN–.32PT relaxor ferroelectric thin films

Abstract(1−x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 (PMN–PT) has attracted attention due to its excellent electrical properties as a typical relaxor ferroelectric material. High‐quality Mn–Sm co‐doped 0.68PMN–0.32PT thin films were synthesized on the Pt/Ti/SiO2/Si substrates by sol–gel based on spin coating method. The results show that 1 mol% Mn–2 mol% Sm co‐doped PMN–PT thin films have high dielectric constant (εr ∼ 1895) and relatively low dielectric loss (tanδ ∼ .039) at 1 kHz. They also show superior ferroelectric polarization (Pmax ∼ 53.71 μC/cm2, Pr ∼ 30.85 μC/cm2) and high dielectric breakdown strength (∼1656.6 kV/cm), which are primarily due to the low leakage current density (∼10−7 A/cm2). This work suggests a practical approach to enhance the dielectricity, piezoelectricity, and ferroelectricity of PMN–PT thin films.

An Adaptation of the Split-Cylinder Resonator Method for Measuring the Microwave Properties of Thin Ferroelectric Films in a “Thin Film—Substrate” Structure

The split-cylinder resonator method was adapted to measure the microwave properties (dielectric permittivity and loss tangent) of thin ferroelectric films on a dielectric substrate. The mathematical model for calculating the resonance frequency of the split-cylinder resonator was adjusted for the “ferroelectric film—substrate” structure. An approach for correcting the gap effect based on calibrating with a single-layer dielectric was introduced and used to study two-layer dielectrics. The prototype of a split-cylinder resonator designed to measure single-layer dielectric plates at a frequency of 10 GHz was presented. The resonator calibration was performed using dielectric PTFE samples and fused silica, and an example of the correction function was suggested. The measurement error was estimated, and recommendations on the acceptable parameter range for the material under investigation were provided. The method was demonstrated to measure the microwave properties of a ferroelectric film on a fused silica substrate.

Non-volatile memory field effect transistor composed of ferroelectric Mn-doped InP thin films and single-layer MoS2 channel

Ferroelectric properties can be generated by doping semiconductor thin films of ZnO and InP with a transition metal such as Mn. Furthermore, ferroelectric thin films exhibiting ferroelectric properties can be utilized as non-volatile memory components, potentially replacing conventional flash memory. In this study, we investigated non-volatile memory properties using field-effect transistors (NVMFET) fabricated from Mn-doped InP (MIP) thin films and single-layer MoS2 sheets. The 5 % Mn-doped MIP thin films exhibited a larger remanent polarization of 8.2 μC/cm2 compared to the 3 % Mn-doped films with 5.1 μC/cm2. The NVMFET devices, operating as non-volatile memory devices, demonstrated a distinct memory window for current changes. Notably, enhancing the remanent polarization of the 5 % Mn-doped MIP thin film further improved the memory window of the corresponding NVMFET.

Ultralow operating voltage for energy conversion performance in Hf1–xZrxO2 thin films

Emerging ferroelectric and antiferroelectric HfO2-based thin films are attractive candidates for energy conversion and storage applications. In this work, the polar phase transformation between tetragonal and orthorhombic phases associated with ferroelectric or antiferroelectric behaviors is utilized to manipulate the electrocaloric cooling and energy storage performances in Zr-doped, woken up HfO2 ultrathin films. A giant electrocaloric temperature change of up to 11.85 K in Hf0.5Zr0.5O2 with the morphotropic phase boundary (MPB) state and a high energy storage density of 39.34 J/cm3 in the tetragonal phase-dominant Hf0.25Zr0.75O2 system are obtained. More interestingly, contrary to overdoping and excessive electric fields, an appropriate Zr concentration of 0.5 and an applicable driving field of 1.91 MV/cm are desired for the electrocaloric effect, resulting in an ultralow operating voltage as low as 1.3 V in this 6.8 nm thick Hf0.5Zr0.5O2 film. These findings illustrate that the structural design strategy is a visible method for achieving optimal energy-related behaviors and highlight the great possibilities for building future energy-related devices.

Exploring the role of TiN electrodes in the formation of ferroelectric HfxZr1-xO2 thin films through transmission electron microscopy

Exploring the role of TiN electrodes in the formation of ferroelectric HfxZr1-xO2 thin films through transmission electron microscopy

Domain structures of PbTiO3 and Pb(Zr,Ti)O3 thin films controlled by tensile strain induced by a Sr(Zr,Ti)O3 buffer layer

Thin films of Sr(Zr,Ti)O3 were investigated as buffer layers to induce tensile strain in ferroelectric thin films such as PbTiO3 and Pb(Zr,Ti)O3 to control the domain structure. By tuning the composition of Sr(Zr,Ti)O3, (100)-oriented PbTiO3 and Pb(Zr,Ti)O3 films were obtained, revealing that tensile strain was introduced into the thin films by the lattice of the buffer layer. We propose a methodology for the successive control of tensile stress, which is useful for understanding and controlling the domain structures of ferroelectric films that result in the ferroelectric and piezoelectric properties of ferroelectric thin films.

A Self-Powered Broadband Photodetector with High Photocurrent Based on Ferroelectric Thin Film Using Energy Band Structure Design

Self-powered photodetectors have the advantages of high sensitivity, sustainability, and small size and have become a research hotspot in advanced optoelectronic systems. However, the low output photocurrent density seriously hinders the practical application of ferroelectric self-powered photodetectors. Herein, the high-efficiency photoelectric detection performance of the Bi1-xHoxFeO3 ferroelectric self-powered photodetector is realized by doping Ho. The responsivity (R) and detectivity (D*) can reach 0.0159 A/W and 1.94 × 1011 Jones under monochromatic light with a wavelength of 900 nm. Meanwhile, the R and D* can reach 0.022 A/W and 2.65 × 1011 Jones under sunlight. These excellent photodetection performances are attributed to the high short-circuit current density (Jsc). When the Ho content is 6%, the output photocurrent reaches up to 0.81 mA/cm2. The systematic structure and photo-electric characteristic analysis suggest that the decrease in the band gap leads to the generation of a larger photocurrent while the ferroelectric polarization is reduced slightly. This work provides a new way to obtain high-performance self-powered photodetectors.