Ferroelectric Films Research Articles

Nanoscale ferroelectric domain switching and thickness scaling impact in undoped hafnium-oxide ferroelectric devices

In this work, we investigated the polarization characteristics of nanoscale undoped hafnium oxide (HfO2) ferroelectric film. The nanoscale domain switching behavior of undoped HfO2 is mainly dominated by mixed ferroelectric/nonferroelectric crystalline phases and interface domain pinning by oxygen vacancies or defect traps. Our experimental results confirm that these issues can be improved by film thickness scaling and well-controlled mechanical stress. We demonstrated a 4-nm-thick undoped HfO2 negative capacitance thin film transistor (NCFET) with an energy-efficient switch characteristic of a low overdrive voltage of -0.6 V, a steep subthreshold swing of sub-60 mV/dec and a uniform hysteresis distribution of sub-60 mV.

Dielectric ultracapacitors based on columnar nano-grained ferroelectric oxide films with gradient phases along the growth direction

Dielectric ultracapacitors based on columnar nano-grained ferroelectric oxide films with gradient phases along the growth direction

A relaxor-ferroelectric PMN-PZT thin-film-based drop-on-demand printhead for bioprinting applications with high piezoelectricity and low heat dissipation

This article presents a relaxor ferroelectric, lead magnesium niobate-lead zirconate titanate (PMN-PZT)-thin-film-based piezoelectric drop-on-demand printhead exhibiting high jetting capability and thermal stability. Unlike conventional piezoelectric materials such as lead zirconate titanate (PZT), the PMN-PZT film demonstrates high electrical responsiveness to polarization and reduced hysteresis loss due to polar nano regions, thereby improving printhead’s performance. Our research involves a comprehensive exploration of the fabrication and packaging processes for the PMN-PZT-based printhead, along with optimization of driving pulses to maximize its performance. An in-depth investigation into the dynamics of ferroelectric film’s polarization identifies the best driving conditions that minimize self-heating while maximizing the dynamic displacement of the printhead. As demonstrated in the results, the unipolar pulse, capable of maintaining a consistent polarization direction of the film, yielded twice the displacement compared to driving with a bipolar pulse. Simultaneously, it reduced the thermal dissipation of the printhead by 73.4 %. Consequently, we aim to propose a method for developing ferroelectric thin film-based print heads suitable for various biological modeling research, leveraging their high productivity and thermal stability.

Edge dislocation with [001] [formula omitted] induced positive magnetoresistance in BaTiO3/La0.66Sr0.33MnO3 heterostructure

The magnetoresistance (MR) effect holds immense potential for applications in various fields, including but not limited to storage and sensing. Manganese oxide has garnered significant attention due to its colossal magnetoresistance characteristics. Investigating the effects of the complex magnetic interactions on the magnetism and transport enables a better understanding of magnetic materials. La0.66Sr0.33MnO3 (LSMO) manganese oxides typically exhibiting negative MR as a result of magnetic field-induced spin order, while positive MR typically occurs in systems with spin-orbit coupling (SOC) or P-N junctions. In this work, the magnetic and transport properties of BaTiO3 (BTO)/LSMO heterostructure were studied. By introducing edge dislocation with [001] b→ (burgers vector) in BTO, the c-axis lattice constant is increased, resulting in positive MR in LSMO, which could be modulated by the magnetic field history and the annealing temperature. The nonlinear magnetic order induced by antiferromagnetism at the interface is proposed to cause the positive MR. Finally, the influence of ferroelectric layer on MR could be controlled by the ferroelectric BTO film. The increase in the large lattice constant and the observed variations in MR under magnetic field and annealing temperature provide valuable insights for further studies on the complex oxide.

Domain Switching Characteristics in Ga-Doped HfO2 Ferroelectric Thin Films with Low Coercive Field.

The gallium-doped hafnium oxide (Ga-HfO2) films with different Ga doping concentrations were prepared by adjusting the HfO2/Ga2O3 atomic layer deposition cycle ratio for high-speed and low-voltage operation in HfO2-based ferroelectric memory. The Ga-HfO2 ferroelectric films reveal a finely modulated coercive field (Ec) from 1.1 (HfO2/Ga2O3 = 32:1) to an exceptionally low 0.6 MV/cm (HfO2/Ga2O3 = 11:1). This modulation arises from the competition between domain nucleation and propagation speed during polarization switching, influenced by the intrinsic domain density and phase dispersion in the film with specific Ga doping concentrations. Higher Ec samples exhibit a nucleation-dominant switching mechanism, while lower Ec samples undergo a transition from a nucleation-dominant to a propagation-dominant reversal mechanism as the electric field increases. This work introduces Ga as a viable dopant for low Ec and offers insights into material design strategies for HfO2-based ferroelectric memory applications.

Control of Ferroelectricity in Solution‐Processed Hafnia Films Through Annealing Atmosphere

AbstractChemical Solution Deposition enables low‐cost fabrication of ferroelectric HfO2 films suitable for piezoelectric applications. Control of processing parameters is of utmost importance to obtain high‐quality functional films. However, the impact of the annealing atmosphere on ferroelectric properties of solution‐processed HfO2 films is not clear. In this work, the influence of annealing atmosphere and growth methods on orientation, density and electrical properties of La:HfO2 films is studied. The 45 nm‐thick films are grown by two routes, conventional (crystallization of the final 45 nm‐thick film) and layer‐by‐layer (intermediate crystallizations of 5 nm‐thick films). Annealing is performed in N2:O2 and Ar atmosphere. Films grown by layer‐by‐layer method in an oxygen‐rich atmosphere tend to have higher density (87% of theoretical density) and remanent polarization (15 µC cm–2) than the conventional films (density and remanent polarization of 80% and 7.5 µC cm‐2). Secondary ion mass spectrometry reveals higher amounts of carbon presence in the conventional films annealed in Ar. For layer‐by‐layer films, the ability to control the preferential out‐of‐plane orientation from (111) to (002) simply by changing the annealing atmosphere, is demonstrated. The results can guide the path toward high‐quality thicker films for piezoelectric applications.

Investigation of negative differential resistance on negative capacitance Germanium source vertical TFET

In this article, a systematic investigation of negative differential resistance (NDR) on a negative capacitance Germanium source vertical TFET (NC-Ge-vTFET) is presented. The implementation and increased ferroelectric (FE) film thickness (t FE) offers a significantly high current ratio, improved subthreshold slope, high transconductance with a very low hysteresis voltage. However, NDR is exhibited and is increasingly prominent at lower gate voltage and higher t FE due to the coupling of the internal gate and drain voltages. NDR is an undesired effect in analog circuits that has to be mitigated. To suppress the impacts of NDR on the device, different approaches are carried out: varying the overlap channel thickness, gate length, drain doping and gate-drain underlap. Circuit analysis is carried out with the implementation of NC-Ge-vTFET as digital inverter. When the gate-drain underlap length is increased from 0 nm to 15 nm, the propagation delay is significantly reduced by 30.98%. Benchmarking of the proposed device has also been carried out. This renders the gate-drain underlapped NC-Ge-vTFET to be a viable candidate for high performance, nanoscale, low power digital applications.

Oppositely Charged Interfacial Janus Nanoparticles Induce the Formation of Highly Ferroelectric Poling-Free PVDF Films for Piezoelectric Energy Generation

Oppositely Charged Interfacial Janus Nanoparticles Induce the Formation of Highly Ferroelectric Poling-Free PVDF Films for Piezoelectric Energy Generation

Strain-driven high energy storage in BaTiO3-based lead-free epitaxial thin films

In this work, the epitaxial 0.85BaTiO3-0.15Bi(Mg1/2Ti1/2)O3 (BT-BMT) films with large compressive strain were fabricated on SrTiO3 (001). The expansion of the unit cell volume and out-of-plane lattice parameter and the large built-in electric field (Ebi) in BT-BMT films indicate the existence of defect dipoles. It was found that the polarization and the breakdown strength can be optimized by the strain and the defects, respectively. Ultimately, a desirable energy density of 90.3 J/cm3 with efficiency of 62.3% was achieved. It suggests that strain can serve as a practical means to modulate the energy storage performance of ferroelectric epitaxial film capacitors.

Ultrahigh-temperature capacitors realized by controlling polarization behavior in relaxor ferroelectric

Dielectric film capacitors have drawn much attention in recent years due to the fast charge–discharge rate, while the energy storage performance at ultra-high temperature needs to be satisfied for the increasing demand of the market. Here, we develop an ultrahigh-temperature capacitor of relaxor ferroelectric (RFE) films via controlling polarization behavior. The (110) oriented 0.85BaTiO3-0.15Bi(Mg0.5Zr0.5)O3 (BT-BMZ) thin film, with anisotropic strain and the optimal ratio of extrinsic/intrinsic polarization, exhibits minimized hysteresis loss and maintains maximum polarization. The (110) oriented film capacitor shows giant energy storage density 104.94 J/cm3, with energy storage efficiency 75.83 % BT-BMZ at room temperature. Moreover, the BT-BMZ capacitor achieves excellent thermal stability, from −100 °C to 400 °C, with an energy density 51.61 J/cm3 at an efficiency 79.36 % due to the low leakage current and hysteresis loss. This work demonstrates that the energy storage performance can be enhanced by adjusting the ratio of intrinsic/extrinsic polarization and provides a feasible method for improving high-temperature performance of capacitors.

Evidence for reversible oxygen ion movement during electrical pulsing: enabler of emerging ferroelectricity in binary oxides

Ferroelectric HfO2-based materials and devices show promising potential for applications in information technology but face challenges with inadequate electrostatic control, degraded reliability, and serious variation in effective oxide thickness scaling. We demonstrate a novel interface-type switching strategy to realize ferroelectric characteristics in atomic-scale amorphous binary oxide films, which are formed in oxygen-deficient conditions by atomic layer deposition at low temperatures. This approach can avoid the shortcomings of reliability degradation and gate leakage increment in scaling polycrystalline doped HfO2-based films. Using theoretical modeling and experimental characterization, we show the following. (1) Emerging ferroelectricity exists in ultrathin oxide systems as a result of microscopic ion migration during the switching process. (2) These ferroelectric binary oxide films are governed by an interface-limited switching mechanism, which can be attributed to oxygen vacancy migration and surface defects related to electron (de)trapping. (3) Transistors featuring ultrathin amorphous dielectrics, used for non-volatile memory applications with an operating voltage reduced to ±1 V, have also been experimentally demonstrated. These findings suggest that this strategy is a promising approach to realizing next-generation complementary metal-oxide semiconductors with scalable ferroelectric materials.

Effect of polarization on tunnelling electroresistance in ferroelectric tunnel junctions

High-quality epitaxial BiFeO3 (BFO) films were grown on (001)-, (110)- and (111)-oriented Nb:SrTiO3 (NSTO) substrates by pulsed laser deposition. The type of domain structure can be modulated using BFO ferroelectric films with different crystalline orientations. The ON/OFF ratios obtained in (001)-, (110)- and (111)-oriented Au/BFO/NSTO ferroelectric tunnel junctions (FTJs) are 6 × 103, 3 × 104 and 2 × 105, respectively. Analysis of the I–V curves of tunnelling current and average BFO ferroelectric barrier height proves that the polarization intensity of the BFO films modulates both the ferroelectric barrier and the Schottky barrier profile, which further influences the electronic tunnelling probability in BFO FTJs. This work will be useful for further study on achieving a giant ON/OFF ratio and developing insights into the barrier profile and transport mechanism of metal/ferroelectric/semiconductor-type FTJs.

Tailoring Practical Solid Electrolyte Composites Containing Ferroelectric Ceramic Nanofibers and All-Trans Block Copolymers for All-Solid-State Lithium Metal Batteries.

Ion transport efficiency, the key to determining the cycling stability and rate capability of all-solid-state lithium metal batteries (ASSLMBs), is constrained by ionic conductivity and Li+-migration ability across the multicomponent phases and interfaces in ASSLMBs. Here, we report a robust strategy for the large-scale fabrication of a practical solid electrolyte composite with high-throughput linear Li+-transport channels by compositing an all-trans block copolymer PVDF-b-PTFE matrix with ferroelectric BaTiO3-TiO2 nanofiber films. The electrolyte shows a sustainable electromechanical-coupled deformability that enables the rapid dissociation of anions with Li+ to create more movable Li+ ions and spontaneously transform the battery internal strain into Li+-ion migration kinetic energy. The ceramic framework homogenizes the interfacial potential with electrodes, endowing the electrolyte with a high conductivity of 0.782 mS·cm-1 and stable ion transport ability in ASSLMBs at room temperature. The batteries of LiFePO4/Li can stably cycle 1000 times at 0.5 C with a high capacity retention of 96.1%, and Ah-grade pouch or high-voltage Li(Ni0.8Mn0.1Co0.1)O2/Li batteries also exhibit excellent rate capability and cycling performance.

Low-Temperature Nanosecond Laser Process of HZO-IGZO FeFETs toward Monolithic 3D System on Chip Integration.

Ferroelectric field-effect transistors (FeFETs) are increasingly important for in-memory computing and monolithic 3D (M3D) integration in system-on-chip (SoC) applications. However, the high-temperature processing required by most ferroelectric memories can lead to thermal damage to the underlying device layers, which poses significant physical limitations for 3D integration processes. To solve this problem, the study proposes using a nanosecond pulsed laser for selective annealing of hafnia-based FeFETs, enabling precise control of heat penetration depth within thin films. Sufficient thermal energy is delivered to the IGZO oxide channel and HZO ferroelectric gate oxide without causing thermal damage to the bottom layer, which has a low transition temperature (<250 °C). Using optimized laser conditions, a fast response time (<1 µs) and excellent stability (cycle >106, retention >106 s) are achieved in the ferroelectric HZO film. The resulting FeFET exhibited a wide memory window (>1.7V) with a high on/off ratio (>105). In addition, moderate ferroelectric properties (2·Pr of 14.7 µCcm-2) and pattern recognition rate-based linearity (potentiation: 1.13, depression: 1.6) are obtained. These results demonstrate compatibility in HZO FeFETs by specific laser annealing control and thin-film layer design for various structures (3D integrated, flexible) with neuromorphic applications.

Giant polarization in tetragonal-like BiFeO3 film via (Ba,Ca)TiO3 doping

BiFeO3 is a multiferroic material, its tetragonality (T) phase usually exhibits large tetragonality (c/a ratio) and strong ferroelectricity. Unlike the commonly used method of strain engineering via substrate, here we present a general and practical approach for obtaining T-like phase BiFeO3 films through (Ba,Ca)TiO3 doping (BF-BCT). The BF-BCT film coherently grows on the La0.7Sr0.3MnO3/(La0.18Sr0.82)(Al0.59Ta0.41)O3 (001) substrate even at 180 nm thick, implying a very large critical thickness, and shows a large tetragonality of 1.12. Impressively, the films exhibit a giant remanent polarization (2Pr) of 320 μC/cm2, which is higher than the corresponding values of any other lead-free ferroelectric films reported to date. Cross-sectional scanning transmission electron microscopy measurements confirm the presence of the T-like phase in BF-BCT films, where the giant polarization might be attributed to the off-center B-site atom. The BF-BCT films are structurally homogeneous without any precipitation of the second phase. The giant polarization observed in the BF-BCT films indicate their great potential for application in next-generation storage and information devices.

Polar Bloch points in strained ferroelectric films

Topological domain structures have drawn great attention as they have potential applications in future electronic devices. As an important concept linking the quantum and classical magnetism, a magnetic Bloch point, predicted in 1960s but not observed directly so far, is a singular point around which magnetization vectors orient to nearly all directions. Here we show polar Bloch points in tensile-strained ultrathin ferroelectric PbTiO3 films, which are alternatively visualized by phase-field simulations and aberration-corrected scanning transmission electron microscopic imaging. The phase-field simulations indicate local steady-state negative capacitance around the Bloch points. The observation of polar Bloch points and their emergent properties consequently implies novel applications in future integrated circuits and low power electronic devices.

A BaTiO3-based flexible ferroelectric capacitor for non-volatile memories

BaTiO3 (BTO) ferroelectric films, which are renowned for their lead-free compositions, superior stability, and absence of a wake-up effect, are promising candidate materials in the field of non-volatile memories. However, the prerequisites for high-temperature conditions in the fabrication of ferroelectric thin films impose constraints on the substrate choice, which has limited the advancement in non-volatile memories based on single-crystal flexible BTO films with robust ferroelectric properties. Herein, a technique has been developed for the fabrication of flexible devices using a pulsed laser deposition system. BTO ferroelectric films have then been deposited onto a flexible mica substrate, with SrTiO3 (STO) serving as a buffer layer. The obtained flexible BTO devices exhibited excellent ferroelectricity, with a maximum polarization (2Pmax) of up to 42.58 μC/cm2 and a remnant polarization (2Pr) of up to 21.39 μC/cm2. Furthermore, even after 1000 bending cycles, the bipolar switching endurance remained high at 1012 cycles. After 104 s, the flexible BTO device still maintained excellent polarization characteristics. These results make the flexible BTO ferroelectric thin film a potential candidate for the next generation of non-volatile memories.

Self-Assembled MXene@Fluorographene Hybrid for High Dielectric Constant and Low Loss Ferroelectric Polymer Composite Films.

Modern electrical applications urgently need flexible polymer films with a high dielectric constant (εr) and low loss. Recently, the MXene-filled percolative composite has emerged as a potential material choice because of the promised high εr. Nevertheless, the typically accompanied high dielectric loss hinders its applications. Herein, a facile and effective surface modification strategy of cladding Ti3C2Tx MXene (T = F or O; FMX) with fluorographene (FG) via self-assembly is proposed. The obtained FMX@FG hybrid yields high εr (up to 108 @1 kHz) and low loss (loss tangent tan δ = 1.16 @ 1 kHz) in a ferroelectric polymer composite at a low loading level (the equivalent of 1.5 wt % FMX), which is superior to its counterparts in our work (e.g., FMX: εr = 104, tan δ = 10.71) and other studies. It is found that the FG layer outside FMX plays a critical role in both the high dielectric constant and low loss from experimental characterizations and finite element simulations. For one thing, FG with a high F/C ratio would induce a favorable structure of high β-phase crystallinity, extensive microcapacitor networks, and abundant interfacial dipoles in polymer composites that account for the high εr. For another, FG, as a highly insulating layer, can inhibit the formation of conductive networks and inter-FMX electron tunneling, which is responsible for conduction loss. The results demonstrate the potential of a self-assembled FMX@FG hybrid for high εr and low loss polymer composite films and offer a new strategy for designing advanced polymer composite dielectrics.

Novel strategies for low-voltage NAND flash memory with negative capacitance effect

Here, we present a novel approach to employing a negative capacitance (NC) phenomenon in the blocking oxide of charge trap flash (CTF) memory. To achieve this, we developed an inversible mono-domain like ferroelectric (IMFE) film through high-pressure post-deposition annealing in a forming gas at 200 atm (FG-HPPDA). The FG-HPPDA process enables to form a uniform alignment of domains and facilitates invertible domain switching behavior in ferroelectrics, generating an internal field by the flexo-electric effect as well as interface-pinned polarization by chemical reaction. Subsequently, to stabilize the NC effect, we fabricated the IMFE/Al2O3 heterostructure, which exhibits an outstanding capacitance-boosting feature. Finally, we successfully demonstrate unprecedented CTF memory with the NC effect in a blocking oxide. Our unique CTF device shows the improved performance (maximum incremental-step-pulse-programming (ISPP) slope ∼1.05) and a large MW (>8 V), attributed to the capacitance boosting by NC phenomenon.

Large Polarization of Hf₀.₅Zr₀.₅Oₓ Ferroelectric Film on InGaAs With Electric-Field Cycling and Annealing Temperature Engineering

Large Polarization of Hf₀.₅Zr₀.₅Oₓ Ferroelectric Film on InGaAs With Electric-Field Cycling and Annealing Temperature Engineering