Ferroelectric Polarization Effect Research Articles

Comprehensive empirical modeling of ScAlN/AlGaN/GaN ferroelectric HEMT

This correspondence introduces a concise depiction of a high electron mobility transistor (HEMT) utilizing a model that incorporates the effect of ferroelectric (FE) polarization on the empirical expression for drain current. This is accomplished by modifying the basic Shockley equation (S.E) for MESFET. The model employed in this investigation is particularly geared towards investigating the impact of the counterclockwise hysteresis effect due to the use of dielectric ScAlN on the transfer characteristics ( Id−Vgs ), which is mainly attributed to trapping and de-trapping of charge carriers at the dielectric/semiconductor interface. Modifying the S.E. made it possible to replicate the behavior observed in experimental HEMT accurately. We reported the modified drain current empirical expressions for the ScAlN/AlGaN/GaN HEMT that considers the FE polarization. The results of this study showed good agreement between the Id−Vgs characteristics obtained from the analytical and experimental data, with a root mean square deviation (RMSD) error of 0.97% and a mean squared error error of 0.94%. This analytical drain current model, presented herein for the first time, incorporates a limited number of fitting parameters. Therefore, enhancing the computational efficiency to assess the performance of FE GaN HEMTs for usage in wide-area electronics.

Piezoelectric Polymer Solid Electrolyte Integrating Electromechanical Coupling and Ferroelectric Polarization Effects.

The unsatisfactory lithium-ion conductivity (σ) and limited mechanical strength of polymer solid electrolytes hinder their wide applications in solid-state lithium metal batteries (SSLMBs). Here, a thin piezoelectric polymer solid electrolyte integrating electromechanical coupling and ferroelectric polarization effects has been designed and prepared to achieve long-term stable cycling of SSLMBs. The ferroelectric Bi4 Ti3 O12 nanoparticle (BIT NPs) loaded poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) piezoelectric nanofibers (B-P NFs) membranes are introduced into the poly(ethylene oxide) (PEO) matrix, endowing the composite electrolyte with unique polarization and piezoelectric effects. The piezoelectric nanofiber membrane with a 3D network structure not only promotes the dissociation of lithium (Li) salts through the polarization effect but also cleverly utilizes the coupling effect of a mechanical stress-local electric field to achieve dynamic regulation of the Li electroplating process. Through the corresponding experimental tests and density functional theory calculations, the intrinsic mechanism of piezoelectric electrolytes improving σ and suppressing Li dendrites is fully revealed. The obtained piezoelectric electrolyte has achieved stable cycling of LiFePO4 batteries over 2000 cycles and has also shown good practical application potential in flexible pouch batteries.

Effect of ferroelectric polarization on the oxygen evolution reaction: a theoretical study of MIrSn2S6 (M = Bi, Mn, and Sb)

The roles of ferroelectric polarization in catalysis, which include affecting adsorption configuration, adsorption energy, bonding morphology, kinetics, etc., are systematically investigated based on MIrSn2S6.

Synergistic effect of interface engineering and bulk photovoltaic effect enhanced self-powered Ta2NiS5/ α -In2Se3/WSe2 van der Waals heterojunction for photodetection

The discovery of van der Waals ferroelectric materials with narrow bandgaps has opened up opportunities for the extensive adoption of self-powered ferroelectric devices that rely on the bulk photovoltaic effect. However, it still needs to overcome the challenges related to the weak ferroelectric polarization and bulk photovoltaic effect in ultrathin van der Waals ferroelectric materials. In this report, we present a synergistic effect of interface engineering and bulk photovoltaic effect in the Ta2NiS5/α-In2Se3/WSe2 van der Waals heterojunction for photodetection. The heterojunction can detect the light with a wide range of wavelengths from near-ultraviolet to near-infrared without requiring external power sources. The output current density of the self-powered heterojunction shows a linear relationship with the optical power intensity at a specific wavelength. Moreover, it accurately identifies the wavelength of light at the same optical power intensity. The on/off ratio is 1.1 × 104, 3.9 × 104, 1 × 104, and 17, respectively, when the optical power density is 100 mW/cm2 for 405, 660, 808, and 1064 nm light. The self-powered Ta2NiS5/α-In2Se3/WSe2 van der Waals photodetector exhibits high specific detectivity of 1.56 × 1011, 1.79 × 1012, 9.16 × 1010, and 1.26 × 105 Jones for wavelengths of 405, 660, 808, and 1064 nm, respectively. These results validate our strategy for enhancing the detection performance in self-powered ferroelectric van der Waals photodetectors, thus opening up possibilities for future self-powered photodetection technologies.

Ab Initio Characterization of Magnetoelectric Coupling in Fe/BaTiO3, Fe/SrTiO3, Co/BaTiO3 and Co/SrTiO3 Heterostructures

Magneto-electric coupling is a desirable property for a material used in modern electronic devices to possess due to the favorable possibilities of tuning the electronic properties using a magnetic field and vice versa. However, such materials are rare in nature. That is why the so-called superlattice approach to creating such materials is receiving so much attention. In the superlattice approach, the functionality of a combined heterostructure depends on the interacting components and can be adjusted depending on the desired property. In the present paper, we present supercells of ferromagnetic thin films of Fe and Co deposited on ferroelectric and piezoelectric substrates of BaTiO3 and SrTiO3 that exhibit magnetism, ferroelectric polarization and piezoelectric effects. Within the structures under investigation, magnetic moments can be tuned by an external electric field via the ferroelectric dipoles. We investigate the effect of magnetoelectric coupling by means of ab initio spin-polarized and spin–orbit calculations. We study the structural, electronic and magnetic properties of heterostructures, and show that electrostriction can reduce the magnitude of the magnetization vector of a ferromagnet. This approach can become the basis for controlling the properties of one of the ferromagnetic layers of a superconducting spin valve, and thus the superconducting properties of the valve.

Enhanced memristor performance via coupling effect of oxygen vacancy and ferroelectric polarization

As a new type of nonvolatile memory, the resistive memristor has broad application prospects in information storage and neural computing based on its excellent resistive switching (RS) performance. At present, it is still a great challenge to improve both ferroelectric polarization and leakage current to achieve a high RS on/off ratio of ferroelectric memristors. Herein, epitaxial Pb(Zr0.40Ti0.60)O3 (PZT) thin films with low content Ca doping were deposited on the Nb:SrTiO3 substrate to prepare PCZT/NSTO heterostructures and their RS behaviors were studied. The research findings show that compared with pure PZT film, the ferroelectric polarization of 1-mol%-Ca-doped PZT film is slightly improved, while the leakage current is increased by three orders of magnitude. Therefore, the RS on/off ratio reaches 2.5 × 105, about three orders of magnitude higher than pure PZT films. The theoretical analysis reveals that the RS behavior of PCZT/NSTO heterostructures is controlled by the PCZT/NSTO interfacial barrier and the space charge-limited current mechanism. Our results demonstrate that the ferroelectricity and electricity of ferroelectric thin films can be improved simultaneously by doping low-content Ca ions to increase the RS performance, which provides a good reference for the development of high-performance ferroelectric memristor devices.

Doped HfO2-based ferroelectric-aided charge-trapping effect in MFIS gate stack of FeFET

The ferroelectric field effect transistor (FeFET) is a very promising candidate for low-power and non-volatile memory. However, the co-existing effect of ferroelectric polarization and interface charge trapping in the FeFETs is demonstrated and many efforts have been made to eliminate this charge-trapping effect, which is usually treated as a deleterious effect. In contrast, we have found that the charge-trapping effect can play a dominant role in ferroelectric gates. In this work, we have verified that the charge-trapping effect of the ferroelectric/insulator interface could induce a memory window as the main physical mechanism in the TiN/Hf0.5Zr0.5O2/SiO2/p-Si (MFIS) structure, in which the ferroelectric characteristics of HZO thin films was verified through a reverse-grown MFIS structure. We also demonstrated that 2.5 nm SiO2 is optimal for the charge tunneling effect and the device has the largest memory window. Moreover, in order to enlarge the memory window of MFIS capacitors, we utilized the stress-enhanced ferroelectric polarization characteristics of Hf0.5Zr0.5O2 to improve the charge-trapping effect. Such a finding demonstrates that the ferroelectric-aided charge-trapping devices are potential to be used in non-volatile memories.

Ferroelectric polarization promoted electrocatalytic hydrogen evolution on Bi2Fe4O9 nanoplates

Unconventional ferroelectricity exhibited by Bi-based nanosheets presents potential opportunities in catalytic fields, whereas the polarization characteristic remains controversial in electrocatalysis. Herein, we report a novel ferroelectric catalyst of polarized Bi2Fe4O9 nanoplates through the corona poling method after hydrothermal and calcination processes, exhibiting super catalytic activity for water splitting controlled by ferroelectric switching and special two-dimensional (2D) structure. The ferroelectric polarization depending on high voltage greatly enhances the activity of polarized Bi2Fe4O9 nanoplates for hydrogen evolution reaction (HER) with a 98 mV positive shift of overpotential compared to the unpolarized Bi2Fe4O9 nanoplates in alkaline conditions. And after long-term stability tests, the polarized Bi2Fe4O9 nanoplates exhibit excellent durability for hydrogen production. Our results show that the effect of ferroelectric polarization of Bi2Fe4O9 nanoplates enhances the electrocatalytic hydrogen evolution, which provide a new strategy for broad the application of ferroelectric materials.

Light-Controlled Magnetoelastic Effects in Ni/BaTiO3 Heterostructures

Magnetoelastic and magnetoelectric coupling in the artificial multiferroic heterostructures facilitate valuable features for device applications such as magnetic field sensors and electric-write magnetic-read memory devices. In ferromagnetic/ferroelectric heterostructures, the intertwined physical properties can be manipulated by an external perturbation, such as an electric field, temperature, or a magnetic field. Here, we demonstrate the remote-controlled tunability of these effects under visible, coherent, and polarized light. The combined surface and bulk magnetic study of domain-correlated Ni/BaTiO3 heterostructures reveals that the system shows strong sensitivity to the light illumination via the combined effect of piezoelectricity, ferroelectric polarization, spin imbalance, magnetostriction, and magnetoelectric coupling. A well-defined ferroelastic domain structure is fully transferred from a ferroelectric substrate to the magnetostrictive layer via interface strain transfer. The visible light illumination is used to manipulate the original ferromagnetic microstructure by the light-induced domain wall motion in ferroelectric substrates and consequently the domain wall motion in the ferromagnetic layer. Our findings mimic the attractive remote-controlled ferroelectric random-access memory write and magnetic random-access memory read application scenarios, hence facilitating a perspective for room temperature spintronic device applications.

Ferroelectric-polarization modulation of charge-to-spin conversion in Pb(Mg1/3Nb2/3)O3–Pb0.7Ti0.3O3/La0.67Sr0.33MnO3 system

Modulation of charge-to-spin conversion through active control is supposed to manipulate efficiency in a wide range for future spintronic devices. Despite its great significance, passive control still dominates the manipulation while the active control of charge-to-spin conversion is still challenging. Here we experimentally observe spin pumping-type charge-to-spin conversion besides Rashba-type one in La0.67Sr0.33MnO3 thin films deposited on ferroelectric Pb(Mg1/3Nb2/3)O3–Pb0.7Ti0.3O3 (PMN-PT) substrate. We exhibit that both two types of charge-to-spin conversion efficiency give rise to a variety of sign under positive and negative remnant polarized states of PMN-PT, which can be ascribed to the effect of ferroelectric polarization. The possibility of modulating charge-spin conversion opens a route for designing low-energy spintronics.

Composition-Related Dielectric, Ferroelectric and Electrocaloric Properties of Pb5Ge3O11 Single Crystals Modified by Ba Ions

In this paper, we studied some ferroelectric properties of archetypal oxide uniaxial ferroelectric single crystals of Pb5Ge3O11 modified by Ba ions. They include dielectric, DSC, ferroelectric polarization, and electrocaloric effect (ECE) measurements. The measurements show that increasing Ba doping considerably influences all the measured parameters, mainly by lowering the Curie temperature, gradually diffusing the phase transition, and decreasing values of polarization as well as the coercive field. The decrease in overall ECE is influenced by decreasing polarization. Compared with the pure PGO single crystals, this decrease is from 1.2 K to 0.2 K. However, the effect of diffusing the phase transition increases the range of its occurrence (up to 30 K), which might be beneficial in applications.

Stability of oxygen vacancies at metal/oxide interfaces.

We investigated the influence of work function and charge doping on the formation of oxygen vacancies in metal/oxide heterojunctions by first-principles calculations. SrTiO3 is used as a typical oxide. Simple metals Pt, Au and Ag are used as electrodes. We show that electron doping could improve the formation energy of oxygen vacancies. In such a heterojunction, we found that the work function of the metal electrode affects the stability of oxygen vacancies in SrTiO3. For an electrode with a smaller work function, more electrons are induced and accumulated in the oxides near the interface and improve the formation energy of oxygen vacancies. We also studied the effect of ferroelectric polarization in a heterojunction of metal/BaTiO3 and found similar properties. We hope that our work could help in the design of complex-oxide-based electronic devices.

Engineering Polarization in the Ferroelectric Electrocatalysts to Boost Water Electrolysis

AbstractWater splitting is the most important process for making green hydrogen. The positive effects of ferroelectric polarization in various kinds of water splitting are well recognized, but the study of electrocatalytic water splitting is still in its infancy. Herein, a family of intrinsic ferroelectrics with a flexible tetragonal tungsten bronze structure is chosen to accommodate oxygen evolution reaction (OER) active sites together with its freedom for tuning the ferroelectric polarization. It is found that the OER performance is positively correlated with the ferroelectric polarization, with a significant reduction in the overpotential of ≈40 mV at 10 mA cm−2, coming from two trade‐off effects, i.e., enhancement of the surface adsorption and band tilting for fast electron transfer. This study not only fills the gap between electrocatalytic water splitting and the band structure but also proposes ferroelectric polarization as a powerful tool to enhance water splitting for clean hydrogen in several ways.

Synergy-Compensation Effect of Ferroelectric Polarization and Cationic Vacancy Collaboratively Promoting CO2 Photoreduction.

Photocatalytic CO2 reduction is severely limited by the rapid recombination of photo-generated charges and insufficient reactive sites. Creating electric field and defects are effective strategies to inhibit charge recombination and enrich catalytic sites, respectively. Herein, a coupled strategy of ferroelectric poling and cationic vacancy is developed to achieve high-performance CO2 photoreduction on ferroelectric Bi2 MoO6 , and their interesting synergy-compensation relationship is first disclosed. Corona poling increases the remnant polarization of Bi2 MoO6 to enhance the intrinsic electric field for promoting charge separation, while it decreases the CO2 adsorption. The introduced Mo vacancy (VMo ) facilitates the adsorption and activation of CO2 , and surface charge separation by creating local electric field. Unfortunately, VMo largely reduces the remnant polarization intensity. Coupling poling and VMo not only integrate their advantages, resulting in an approximately sevenfold increased surface charge transfer efficiency, but also compensate for their shortcomings, for example, VMo largely alleviates the negative effects of ferroelectric poling on CO2 adsorption. In the absence of co-catalyst or sacrificial agent, the poled Bi2 MoO6 with VMo exhibits a superior CO2 -to-CO evolution rate of 19.75µmol g-1 h-1 , ≈8.4 times higher than the Bi2 MoO6 nanosheets. This work provides new ideas for exploring the role of polarization and defects in photocatalysis.

Search for Magnetoelectric Coupling at the 57Fe/Hf0.5Zr0.5O2 Interface Using Operando Synchrotron Mössbauer Spectroscopy

AbstractMultiferroic materials with coexisting ferroelectric and ferromagnetic orders have attracted much attention due to the magnetoelectric coupling opening alternative prospects for electronic devices. Composite multiferroics containing separate ferroelectric and ferromagnetic components are a promising alternative to the single‐phase counterparts. Composite multiferroic structures comprising HfO2‐based ferroelectrics are potentially feasible for technological applications. Here, this study reports on the experiments aiming at the manifestation of magnetoelectric coupling at Fe/Hf0.5Zr0.5O2 (HZO) interface. Using synchrotron based 57Fe Mössbauer spectroscopy technique in operando, this study probes element‐selectively the local magnetic properties of a nanometer‐thick enriched 57Fe marker layer in functional Pt/57Fe/HZO/TiN capacitors and demonstrates the evidence of the ferroelectric polarization effect on the α‐Fe magnetic response. Besides α‐Fe exhibiting a magnetoelectric coupling, both ferromagnetic and superparamagnetic Fe3O4 components are found in the Mössbauer spectra, apparently originating from the oxygen or OH− ions penetrating ultrathin Pt overlayer during crystallization annealing of HZO. The observed effect as well as the electronic band lineup of the Fe/HZO interface elucidated from synchrotron based hard X‐ray photoemission spectroscopy measurements are interpreted in terms of charge‐mediated magnetoelectric coupling at the Fe/HfO2 interface driven by ferroelectric HZO polarization reversal.

Ferroelectric Polarization and Oxygen Vacancy Synergistically Induced an Ultrasensitive and Fast Humidity Sensor for Multifunctional Applications.

With the arrival of the Internet of Things and artificial intelligence, humidity sensors monitoring water emissions from human metabolism have attracted great attention in the fields of smart wearable devices and noncontact human-machine interaction. However, their application is seriously limited by the trade-off between the sensitivity and response speed for traditional humidity sensors. Herein, to overcome it, a self-powered high performance humidity sensor is developed on the basis of the electric-poled and oxygen vacancy-rich BiFeO3 (BFO) ferroelectric material. The synergistic effect of ferroelectric polarization and oxygen vacancy provides a strong driving force and active adsorption sites for an abundance of OH/H2O adsorption, resulting in an ultrahigh response (∼104) and ultrafast response/recovery speed (∼84/376 ms). Benefiting from its promising advantages, the wearable humidity sensor can accurately record the respiration rate/depth and recognize different human respiratory behaviors in real-time. Importantly, by utilizing the moisture from mouth-blowing and skin, the sensors are successfully applied to noncontact control of a robotic car, noncontact switch, and noncontact interface for visualization applications. This work provides an effective strategy for developing excellent humidity sensors that meet the requirement of noncontact interaction for next-generation intelligent electronics.

Tuning of photovoltaic response in multiferroic heterojunction photodiodes by a built-in electric field and carrier transport: Effect of magnetization and ferroelectric polarization

Photovoltaic devices consisting of multiferroic thin films have been studied extensively for carrier separation regulated by a built-in electric field and the above bandgap. Here, a novel photodiode with photoelectric conversion efficiency (PCE) of 3.70% by introducing TiO2 and NiOx:5%Cu as the electron and the hole transport layers (ETL/HTL) on both sides of multiferroic bismuth layered perovskite oxide Bi2FeCrO6/Bi6Fe1.6Co0.2Ni0.2Ti3O18 (BFCO/BFCNT) heterojunction with the appropriate band gap were reported based on our recent studies. The results showed that BFCNT displays an Aurivillius structure, but BFCO is of a double perovskite, the bandgaps are ∼1.62 eV and 1.74 eV, respectively. The open-circuit voltage, short-circuit current density, and fill factor of the devices are 0.73 V, 10.5 mA·cm-2, and 48.3% separately under the illumination of 100 mW·cm-2 simulated AM 1.5 G solar light. Investigations of the effects of both external electric and magnetic fields on the photovoltaic responses delivered that the magnetization and ferroelectric polarization can effectively tune the built-in electric field and the carrier transport in multiferroics, thus offering an experimental and theoretical basis for further improving the performance of multiferroic photovoltaic devices.

Ion Drift and Polarization in Thin SiO2 and HfO2 Layers Inserted in Silicon on Sapphire.

To reduce the built-in positive charge value at the silicon-on-sapphire (SOS) phase border obtained by bonding and a hydrogen transfer, thermal silicon oxide (SiO2) layers with a thickness of 50–310 nm and HfO2 layers with a thickness of 20 nm were inserted between silicon and sapphire by plasma-enhanced atomic layer deposition (PEALD). After high-temperature annealing at 1100 °C, these layers led to a hysteresis in the drain current–gate voltage curves and a field-induced switching of threshold voltage in the SOS pseudo-MOSFET. For the inserted SiO2 with a thickness of 310 nm, the transfer transistor characteristics measured in the temperature ranging from 25 to 300 °C demonstrated a triple increase in the hysteresis window with the increasing temperature. It was associated with the ion drift and the formation of electric dipoles at the silicon dioxide boundaries. A much slower increase in the window with temperature for the inserted HfO2 layer was explained by the dominant ferroelectric polarization switching in the inserted HfO2 layer. Thus, the experiments allowed for a separation of the effects of mobile ions and ferroelectric polarization on the observed transfer characteristics of hysteresis in structures of Si/HfO2/sapphire and Si/SiO2/sapphire.

Artificially induced ferroelectric-like behavior in an antiferroelectric sandwich structure by interface engineering

Interface engineering is essential for achieving fascinating interfacial functionalities in a single all-oxide-interface-based device. In the present work, a sandwich structure (Pb0.94La0.06(Zr0.95Ti0.05)O3 (PLZT)/HfO2/ Pb0.94La0.06(Zr0.95Ti0.05)O3) was fabricated via a chemical solution approach. A distinct “ferroelectricity-like” behavior with high Pmax (∼ 80 μC/cm2) and Pr (∼ 36 μC/cm2) is demonstrated. The dielectric HfO2 thin layer presents a tetragonal symmetry structure, which stabilizes a slight distorted structure of the upper PLZT layer (PLZT(T)) with a= 4.19(9) Å, b= 4.10(6) Å, β ∼ 91.04˚. In PLZT(T), the ferroelectric (FE) phase is identified as the matrix embedded with a small amount of AFE nanodomains, while the bottom PLZT layer (PLZT(B)) exhibits typical AFE incommensurately modulated structures. The near-interface structures in both PLZT layers are characterized by ferroelectric polarizations with head-to-tail configuration across the heterointerface. Such discontinuous, downward polarizations support the accumulation of oxygen vacancies at the heterointerface that facilitate the local polarization enhancement. It is the combination effect of stable ferroelectric polarization in the PLZT(T) layer, interfacial oxygen vacancies and large surface to volume ratio that leads to the superior polarization performance of the antiferroelectric sandwich structure. It indicates that interface engineering is a feasible approach to manipulate the ferroic behavior.

Enhanced photovoltaic performance via polarization in Bi/Co co‐doped KN‐based ferroelectric ceramics

AbstractA bandgap‐tunable KNbO3 ferroelectric ceramic was prepared by introducing Bi/Co ion. The existence of mixed valence states of Co2+/Co3+ in the system induced the bandgap reduction and its tunable behavior. KNbO3–BiCoO3 solid solutions showed a typical orthogonal perovskite structure and maintained good ferroelectricity (Ps = 15.13 µC/cm2) and high‐field polarization ability. The devices based on the .98KNbO3–.02BiCoO3 sample exhibited an improved short‐circuit photocurrent density (Jsc) of 19.2 nA/cm2 under simulated solar radiation, and this was further enhanced to 79.8 nA/cm2 after a 60‐kV/cm polarizing. The structural analysis of the samples after polarization reveals the effect of ferroelectric polarization on photovoltaic performance. This work provides new insights into the effects of ferroelectric polarization on photovoltaic performance.