Ferroelectric Layer Research Articles

Improvement of ferroelectric and dielectric properties in BaTiO3/LaNiO3 superlattices by regulating the ferroelectric layer thickness

Ferroelectric superlattices exhibit rich functional characteristics. Yet, the ferroelectric properties are always unsatisfactory due to the presence of depolarization field resulting from the polarization discontinuities between the component materials, which has become a bottleneck problem hindering the improvement of ferroelectric properties and further industrial applications. Here, the BTO/LNO superlattices composed of ferroelectric (BaTiO3, BTO) and metallic (LaNiO3, LNO) materials were prepared by pulsed laser deposition (PLD). The periodic thickness of the LNO layers was fixed to 2 unit cells, while the periodic thickness of the BTO layers was changed. We demonstrate experimentally that by regulating the BTO periodic thickness, BTO/LNO superlattices exhibit excellent and adjustable ferroelectric and dielectric properties. The enhancement of electrical properties is closely related to the increase of tetragonality (c/a) combined with the effect of the ultra-thin LNO layers and the accumulation of oxygen vacancies at superlattice interfaces on reducing the depolarization field. We hope this work will provide an effective strategy for optimizing the ferroelectric properties of ferroelectric superlattices based on the component material and periodic structure regulation.

Improved Energy Storage Performance of Composite Films Based on Linear/Ferroelectric Polarization Characteristics.

The development and integration of high-performance electronic devices are critical in advancing energy storage with dielectric capacitors. Poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) (PVTC), as an energy storage polymer, exhibits high-intensity polarization in low electric strength fields. However, a hysteresis effect can result in significant residual polarization, leading to a severe energy loss, which impacts the resultant energy storage density and charge/discharge efficiency. In order to modify the polarization properties of the polymer, a biaxially oriented polypropylene (BOPP) film with linear characteristics has been selected as an insulating layer and combined with the PVTC ferroelectric polarization layer to construct PVTC/BOPP bilayer films. The hetero-structure and polarization characteristics of the bilayer film have been systematically studied. Adjusting the BOPP volume content to 67% resulted in a discharge energy density of 10.1 J/cm3 and an energy storage efficiency of 80.9%. The results of this study have established the mechanism for a composite structure regulation of macroscopic energy storage performance. These findings can provide a basis for the effective application of ferroelectric polymer-based composites in dielectric energy storage.

Impact of Dual-Gate Configuration on the Endurance of Ferroelectric Thin-Film Transistors With Nanosheet Polycrystalline-Silicon Channel Film

This work explores the characteristics of ferroelectric thin-film transistors (FeTFTs) utilizing an asymmetric dual-gate (DG) structure in both single-gate (SG) and DG operation modes. In the transfer characteristics, DG mode exhibits a memory window (MW) of 1.075 V, smaller than SG mode’s MW of 1.402 V, attributed to the back-gate bias effect causing a reduction in the device’s threshold voltage. However, DG mode demonstrates superior endurance characteristics with 106 cycles compared to SG mode’s 105 cycles. Additionally, the increase in erase pulse voltage (VERS) exacerbates the polycrystalline-silicon channel lattice damage of FeTFT, resulting in subthreshold swing (SS) degradation. Nevertheless, the extent of SS degradation from DG mode operation is significantly lower than that of SG mode, contributing to the superior endurance of DG mode. The elevation of program pulse voltage (VPRG) induces imprint and charge-trapping effects in the top-gate ferroelectric dielectric, leading to reduced endurance. Due to the use of SiO2 as the back-gate dielectric in FeTFT, DG mode exhibits lower impacts of charge-trapping effects from the top-gate ferroelectric dielectric layer, resulting in better endurance compared to SG mode. The asymmetric DG structure provides greater tolerance in the selection of VPRG and VERS.

Multi-level storage in cleaved-gate ferroelectric FETs investigated by 3D phase-field-based quantum transport simulation

In this work, we investigate the feasibility of cleaved-gate ferroelectric FET (CG-FeFET) as multi-level cell (MLC) memory devices, by conducting 3-dimensional quantum transport simulations based on time-dependent-Ginzburg–Landau equation, and the non-equilibrium Green’s function method. Our results indicate that CG-FeFET can achieve multi-level operations by utilizing different thicknesses of the ferroelectric layer. We analyze the influence of electron–phonon interaction and also verify that CG-FeFET is robust to noise. Furthermore, we identify the critical role of the spacing between two ferroelectric layers in determining the memory window, considering the effects of polarization cancellation and electrostatic coupling. These findings provide valuable insights into designing stable and reliable nonvolatile memory technologies, which could offer potential solutions for high-density memory requirements.

Computing in-memory reconfigurable (accurate/approximate) adder design with negative capacitance FET 6T-SRAM for energy efficient AI edge devices

Computing in-memory (CiM) is an alternative to von-Neumann architectures for energy efficient AI edge computing architectures with CMOS scaling. Approximate computing in-memory (ACiM) techniques have also been recently proposed to further increase the energy efficiency of such architectures. In the first part of the work, a negative capacitance FET (NCFET) based 6T-SRAM CiM accurate full adder has been proposed, designed and performance benchmarked with equivalent baseline 40 nm CMOS design. Due to the steep slope characteristics of NCFET, at an increased ferroelectric layer thickness, T fe of 3 nm, the energy consumption of the proposed accurate NCFET based CiM design is ∼82.48% lower in comparison to the conventional/Non CiM full adder design and ∼85.27% lower energy consumption in comparison to the equivalent baseline CMOS CiM accurate full adder design at V DD = 0.5 V. This work further proposes a reconfigurable computing in-memory NCFET 6T-SRAM full adder design (the design which can operate both in accurate and approximate modes of operation). NCFET 6T-SRAM reconfigurable full adder design in accurate mode has ∼4.19x lower energy consumption and ∼4.47x lower energy consumption in approximation mode when compared to the baseline 40 nm CMOS design at V DD = 0.5 V, making NCFET based approximate CiM adder designs preferable for energy efficient AI edge CiM based computing architectures for DNN processing.

Neuromorphic Vision Sensor driven by Ferroelectric HfAlO

The rapid progress in bioinspired machine vision supported by intelligent computing has attracted attention of the modern electronics due to their wide applications in image recognition, artificial intelligence, and medical applications. The ferroelectric materials are considered as most reliable for the fabrication of these devices due to their nonvolatile and dense memory capacity as well as stability. Here, we report the neuromorphic vision sensor (NVS) based on a self-grown ferroelectric interfacial HfAlO layer. The unique properties of graphene (Gr) and silicon are integrated through the ferroelectric layer to fabricate the NVS, which can mimic the human eye system. The sensor efficiently demonstrates the basic neural functions including pair-pulsed facilitation, depression, inhibition, and excitation under electric as well as optical stimuli. The optical spike rate (2 Hz–10 Hz) as well as the amplitude (0.5 μW/cm2-1.5 μW/cm2) dependent plasticity, exhibited excellent facilitation and depression index of 1.62% and −1.86% with the minimum energy consumption of only 3.5 fJ per spike. The high endurance of 1 × 107 cycles confirm its reliability and data security. Our device with excellent features of optical signal detection, information processing, and data storage with its simple structure can be efficiently utilized as an image sensor for robotics and intelligent machine vision systems.

Effects of the remnant polarization on the electrical characteristics of steeper sub-threshold swing Fe-GeFinFET

In this article, a ferroelectric material is used in the gate stack of germanium FinFET to enhance the electrical performance of transistor, viz. subthreshold swing (SS), switching ratio (ION/IOFF), threshold voltage (Vth), transconductance (gm), and improve the short channel effects (SCEs). The extent of the improvement depends on the capacitance matching between the ferroelectric (FE) capacitance (Cferro) and baseline FinFET capacitance (Cmos). The variation of ferroelectric parameters like ferrothickness (tferro) and remnant polarization (Pr) on electrical characteristics of ferro-germanium FinFET (Fe-GeFinFET) have been investigated. The non-linear relationship between Cferro and Cmos over a voltage range circumvents the acceptable capacitance congruence between the two capacitances. With the incorporation of FE layer, the SS has been obtained as 8 mV/decade and the ION enhanced by 12 %. The device yields a transconductance (gm) of 20 mS at Vgs = Vds = 0.7 V. The results have been investigated using Sentaurus 3-D TCAD simulations.

In-situ electric field-tailored exchange bias in the manganite/ferroelectric multiferroic heterostructures

The application of electric field-induced magnetic structure changes has significantly advanced nonvolatile data storage with ultralow energy consumption, as well as spintronics and quantum computing processes. In artificial perovskite oxide multiferroic structures composed of ferromagnetic and ferroelectric layers, the evolution of magnetic phases and ferroelectric domains often contribute to the magnetoelectric coupling. To fully understand the mechanisms behind electric field-induced changes in magnetic structures and enable the miniaturization of magnetoelectric devices, it is crucial to achieve local ferroelectric domain-triggered ferromagnetic evolution. In this study, we have fabricated La0.7Ca0.3MnO3/Pb(Zr0.52Ti0.48)O3 (LCMO/PZT) heterostructures, where the magnetic phase separation of LCMO and the ferroelectric domain of PZT can be modulated by substrates and piezoelectric force microscopy, respectively. Our experiments demonstrate that by switching the polarization states of PZT, we can observe electric field control of the magnetic exchange bias effect through changes in the phase separation of the LCMO layer. These results contribute to the development of magnetoelectric devices with enhanced properties and offer valuable insights for future design strategies.

Ideal Photodetector Based on WS2/CuInP2S6 Heterostructure by Combining Band Engineering and Ferroelectric Modulation.

Two-dimensional van der Waals (2D vdW) heterostructure photodetectors have garnered significant attention for their potential applications in next-generation optoelectronic systems. However, current 2D vdW photodetectors inevitably encounter compromises between responsivity, detectivity, and response time due to the absence of multilevel regulation for free and photoexcited carriers, thereby restricting their widespread applications. To address this challenge, we propose an efficient 2D WS2/CuInP2S6 vdW heterostructure photodetector by combining band engineering and ferroelectric modulation. In this device, the asymmetric conduction and valence band offsets effectively block the majority carriers (free electrons), while photoexcited holes are efficiently tunneled and rapidly collected by the bottom electrode. Additionally, the ferroelectric CuInP2S6 layer generates polarization states that reconfigure the built-in electric field, reducing dark current and facilitating the separation of photocarriers. Moreover, photoelectrons are trapped during long-distance lateral transport, resulting in a high photoconductivity gain. Consequently, the device achieves an impressive responsivity of 88 A W-1, an outstanding specific detectivity of 3.4 × 1013 Jones, and a fast response time of 37.6/371.3 μs. Moreover, the capability of high-resolution imaging under various wavelengths and fast optical communication has been successfully demonstrated using this device, highlighting its promising application prospects in future optoelectronic systems.

Impact of HfO2 Dielectric Layer Placement in Hf0.5Zr0.5O2‐Based Ferroelectric Tunnel Junctions for Neuromorphic Applications

AbstractThe use of Hf0.5Zr0.5O2 (HZO) films within hafnia‐based ferroelectric tunnel junctions (FTJ) presents a promising avenue for next‐generation non‐volatile memory devices. HZO exhibits excellent ferroelectric properties, ultra‐thinness, low power consumption, nondestructive readout, and compatibility with silicon devices. In this study, Mo/HZO/n+ Si devices are investigated, incorporating a 1 nm HfO2 dielectric layer at the top and bottom of the HZO ferroelectric layer. Comparing the FTJ device configurations, it is observed that the metal‐ferroelectric‐dielectric‐semiconductor (MFIS) outperforms the metal‐dielectric‐ferroelectric‐semiconductor (MIFS) in terms of ferroelectricity, displaying a high 2Pr value of ≈69 µC cm−2. Additionally, MFIS exhibits lower leakage current, higher tunneling electro‐resistance ratio, and a thin dead layer during short pulse switching, as confirmed through DC double sweeping of I−V characteristics. The modified half‐bias scheme demonstrates a maximum array size of 191 for MFIS, showcasing its superior performance over MIFS. Synaptic characteristics, including potentiation, depression, paired‐pulse facilitation, spike‐rate‐dependent plasticity, and excitatory postsynaptic current, are measured using MFIS, highlighting its outstanding ferroelectric properties. As a physical reservoir, the FTJ device implements 16 states of 4 bits in reservoir computing. Finally, pattern recognition using a deep learning neural network achieves high accuracy with using the Modified National Institute of Standards and Technology dataset.

Unveiling the reliability of negative capacitance FinFET with confrontation of different HfO2-ferroelectric dopants

The CMOS compatibility of Negative Capacitance (NC) FETs has been enhanced tremendously after introducing a thin film-doped HfO2 as a ferroelectric (FE) layer. For a given FE layer, the NC property is governed by specific HfO2 dopants (e.g., La, Zr, Al, Sr, Gd, Y, and Si). Thus, the TCAD simulation considerably depends on the dopant-specific Landau parameters (αx,βx,γx,ρx,gx), and its solidity needs proper attention. Further, the reliability of the NC devices is severely affected by process variations, i.e., interface trap charges, work function variation, random dopant fluctuation, and ambient temperature (external), which modulates the device threshold voltage (Vth); in turn, the device aging. In this paper, using well-calibrated TCAD models, we investigated reliability for the different dopant-specific NC-FinFET, in terms of Vth, ON current (ION), and OFF current (IOFF) modulation induced by: (i) the interface trap variability (ITV) considering the different trap concentration and energy location; (ii) the work function variability (WFV) considering different metal grain sizes (Gr); (iii) the random dopant fluctuations (RDF); and (iv) the ambient temperature. In this way, the device aging is calculated by inspecting Vth shift by ±50mV. These investigations pave the path for realizing a reliable NC-FinFET design.

The physical origin of inhomogeneous field within HfO2-based ferroelectric capacitor

In this work, the origins of the inhomogeneous field within the HfO2-based ferroelectric (FE) capacitor are investigated. We propose a model to simulate the relationship between the reversed polarization and the applied pulses with different amplitudes and durations. The electric field distribution is considered to be influenced by the ferroelectric layer thickness (tFE) and the built-in field (Eb). Then, the distribution parameters of both two physical factors and the Merz law, which define the switching dynamics, could be obtained by fitting the experimental results. Comparing with the results of high-resolution transmission electron microscope and first-order reversal curve measurements, it can be reasonably concluded that the physical origin of the inhomogeneous field in HfO2-based ferroelectrics is the random distribution of tFE and Eb. This work improves the understanding of the switching dynamics by providing the origins of the inhomogeneous field in an FE film.

Negative capacitance FET based dual-split control 6T-SRAM cell design for energy efficient and robust computing-in memory architectures

A Negative Capacitance Field effet transistor (NCFET) based Dual split control (DSC) 6T-SRAM cell has been designed and explored with Computing-in memory (CiM) architecture for energy efficient demonstration of Deep neural networks (DNN) basic operation such as Input-Weight (Dot) Product. The impact of ferro electric layer thickness (Tfe) on the SRAM cell perfomance metrics such as read noise margin (RNM), write noise margin (WNM) and energy efficiency for read and write operations have been analyzed at supply voltages of 0.3 V and 0.5 V. It has been observed that due to the steep slope characteristics, the NCFET based DSC 6T-SRAM cell design exhibits better RM, WM, and energy efficiency as compared to the baseline CMOS DSC SRAM cell design at VDD = 0.3 V and 0.5 V respectively (with Tfe range of 1 nm to 3 nm). Further, NCFET dual split control scheme for 6T-SRAM cell demonstrate improved read stability and write ability when compared with NCFET 6 T-SRAM cell design along with improved energy efficiency. NCFET based DSC 6T-SRAM CiM cell design has ∼22.77× and 12.41× lower energy consumption compared to the équivalent baseline 40 nm CMOS/baseline SRAM CiM design and ∼ 25.80× and 22.76× lower energy consumption compared to the NCFET based SRAM CiM at VDD = 0.3 V and 0.5 V respectively. NCFETs have improved steep subthreshold slope characteristics at an optimal Tfe value and NCFET SRAM based CiM circuits are expected to have higher noise margins and lower energy consumption compared to the baseline CMOS designs and are effective for NCFET based computing in-memory architectures with reduced read disturb issues in combination with DSC concept.

Photon upconversion assisted ferroelectric photovoltaics: Device configuration with multifaceted influence in augmenting the photovoltaic response of BiFeO3 thin‐film solar cells

AbstractThis 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.

Ferroelectric Control of Band Alignments in In2Se3/h‐BN and CuInP2S6/h‐BN van der Waals Heterostructures

Recently, 2D ferroelectric (FE) heterostructures have become a subject of great interest due to their potential device applications and the underlying physics involved. In this study, the first‐principles calculations are employed to examine the FE control of electronic structures in 2D FE heterostructures, specifically In2Se3/h‐BN and CuInP2S6 (CIPS)/h‐BN. In these results, it is demonstrated that by reversing the polarization of the FE layers, the band alignment of the heterostructures can be interconverted between type II and type I. For In2Se3/h‐BN, the variation of out‐of‐plane polarization can be attributed to the hindrance and facilitation of charge transfer from h‐BN to In2Se3 by the intrinsic electric field of the In2Se3 monolayer. For CIPS/h‐BN heterostructures, the higher transferred charge in the Cdn configuration due to the presence of built‐in electric fields and the stronger interfacial interaction in the Cdn configuration result in a higher polarization value compared to the Cdn configuration. Moreover, the carrier mobility of the heterostructures can also be effectively modulated by the FE polarization. In these findings, the potential significance of FE heterostructures with tunable band alignment and bandgap is highlighted in the development of nanoscale optoelectronic devices.

Artificial Optoelectronic Synapses Based on Light‐Controllable Ferroelectric Semiconductor Memristor

AbstractNumerous synaptic devices have been explored for the next generation of energy‐efficient computing techniques. Among them, optoelectronic synaptic devices based on semiconductor/ferroelectric heterostructures have received a lot of attention lately due to their amazing parallelism, efficiency, and fault tolerance properties. However, polarizing the ferroelectric layer or gating the dielectric layer is necessary to achieve tunable synaptic functions, which generally causes an increase in energy consumption and complex manufacturing processes. Here, a simple and efficient method is demonstrated to develop a tunable optoelectronic synaptic device based on a single ferroelectric semiconductor, BiFeO3‐BaTiO3 (BF‐BT). Multi‐essential synaptic functions including short‐term plasticity, paired‐pulse facilitation, and long‐term plasticity are all satisfactorily replicated by the memristor device. More significantly, light‐controllable synaptic behaviors are realized by altering the ferroelectric polarization state of BF‐BT. Synaptic devices’ relaxation characteristics enable simulation of the effects of positive/negative emotions on learning and forgetting processes. This study highlights the potential of the ferroelectric semiconductor memristor in constructing the efficient optoelectronic synapses for future neuromorphic electronics with the ability to learn and sense optical information.

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.

Impact of deposition temperature on electrical properties of HZO-based FeRAM

This study presents a comprehensive investigation of the impact of the deposition temperature on the HfxZr1−xO2 (HZO) ferroelectric layer of ferroelectric random access memory with TaN electrodes. This investigation mainly focuses on its electrical characteristics and compares the differences. It is revealed that the deposition temperature plays a crucial role in determining the crystal structure of HZO, which can exhibit a combination of tetragonal and orthorhombic phases or exist solely in one of the two phases. Furthermore, the grain size of HZO varies with the deposition temperature. These findings correspond well to the electrical measurement results, including leakage current, polarization, capacitance, and reliability tests. The study tracks the phase transition process during the operation of switching cycles when the phase transition process can be monitored as well. To better understand the observed differences, physical models that shed light on the underlying mechanisms affected by deposition temperature are proposed at the end of the article.

Nonvolatile Multistate Manipulation of Topological Magnetism in Monolayer CrI3 through Quadruple-Well Ferroelectric Materials.

Nonvolatile multistate manipulation of two-dimensional (2D) magnetic materials holds promise for low dissipation, highly integrated, and versatile spintronic devices. Here, utilizing density functional theory calculations and Monte Carlo simulations, we report the realization of nonvolatile and multistate control of topological magnetism in monolayer CrI3 by constructing multiferroic heterojunctions with quadruple-well ferroelectric (FE) materials. The Pt2Sn2Te6/CrI3 heterojunction exhibits multiple magnetic phases upon modulating FE polarization states of FE layers and interlayer sliding. These magnetic phases include Bloch-type skyrmions and ferromagnetism, as well as a newly discovered topological magnetic structure. We reveal that the Dzyaloshinskii-Moriya interaction (DMI) induced by interfacial coupling plays a crucial role in magnetic skyrmion manipulation, which aligns with the Fert-Levy mechanism. Moreover, a regular magnetic skyrmion lattice survives when removing a magnetic field, demonstrating its robustness. The work sheds light on an effective approach to nonvolatile and multistate control of 2D magnetic materials.

A proof of concept for reliability aware analysis of junctionless negative capacitance FinFET-based hydrogen sensor

This work demonstrates the reliability-aware analysis of the Junctionless negative capacitance (NC) FinFET employed as a hydrogen (H2) gas sensor. Gate stacking of the ferroelectric (FE) layer induces internal voltage amplification owing to the NC property, thus, improving the sensitivity of the baseline junctionless FinFET. A well-calibrated TCAD model is used to investigate the sensing characteristics of the proposed FinFET-based H2 sensor by employing the palladium (Pd) metallic gate as a sensing element. The mechanism involves the transduction of H2 gas molecules over the metal gate; due to the diffusion process, some atomic hydrogen diffuses into the metal. The H2 gas absorption at the metal surface causes a dipole layer formation at the gate and oxide interface, which changes the metal gate work function. As a result, this change in the work function can be used as a sensing parameter of the proposed gas sensor. Further, the threshold voltage and other electrical characteristics, such as output conductance, transconductance, and drain current are examined for sensitivity analysis for both NC and without NC JL FinFET at different pressure ranges, keeping the temperature constant (i.e. 300 K). The device variation, i.e. Fin thickness, Fin height, doping and thickness of HfO2 ferroelectric layer, etc, on sensor sensitivity has been evaluated through extensive simulation. This paper also presents a detailed investigation of the sensor’s reliability in terms of work function variation, random dopant fluctuation, trap charges, and device aging, i.e. end of a lifetime. At last, the acquired results are compared with earlier reported data, which justifies the profound significance of the proposed junctionless negative capacitance FinFET-based H2 gas sensor.