BFO Layer Research Articles

Resistive switching in tetragonal tungsten bronze Sr0.6Ba0.4Nb2O6 thin films and control of Schottky barrier by insertion of BiFeO3 layer

Tetragonal tungsten bronze Sr0.6Ba0.4Nb2O6 (SBNO) has exceptional electro-optical, piezoelectric, and thermoelectric properties. Its potential as an electronic device is, furthermore, also relay on the good insulation and multiple-channels structural. However, the transport behavior in SBNO films remains poorly researched. Here, a Pt/SBNO/LSMO capacitor was prepared using the magnetron sputtering method on STO (001) substrates, and its transport behavior was measured. Interestingly, an ultra-high resistive-switching ratio over 103 was obtained in SBNO film. The read voltage when the switch ratio is ∼103 drops from 2 V to 0.5 V by inserting a BFO-layer between the interface of SBNO and LSMO. The findings demonstrate that the interface barrier in SBNO/BFO/LSMO devices between the SBNO and BFO layers is essential for maintaining a high switching ratio at low voltage. As a result, the SBNO/BFO/LSMO demonstrates a method for reducing read voltage and offers an approach for future resistive-switching applications.

Photocarrier transport of ferroelectric photovoltaic thin films detected by the magnetic dynamics of adjacent ferromagnetic layers

We have observed photocarrier transport behaviors in ${\mathrm{BiFeO}}_{3}/{\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{MnO}}_{3}$ (BFO/LSMO) heterostructures by using time-resolved synchrotron x-ray magnetic circular dichroism in reflectivity. The magnetization of LSMO layers was used as a probe of photo-induced carrier dynamics in the photovoltaic BFO layers. During the photo-induced demagnetization process, the decay time of LSMO ($x$=0.2) magnetization strongly depends on the ferroelectric polarization direction of the BFO layer. The variation of decay time should be attributed to the different sign of accumulated photocarriers at the BFO/LSMO interface induced by the photovoltaic effect of the BFO layer. The photocarriers can reach the BFO/LSMO interface and influence the magnetization distribution in the LSMO layers within the timescale of $\ensuremath{\sim}100$ ps. Our results provide a novel strategy to investigate carrier dynamics and mechanisms of optical control of magnetization in thin film heterostructures.

Increased Magnetoelectric Coupling in Porous Nanocomposites of CoFe2O4 and BiFeO3 with Residual Porosity for Switchable Magnetic Devices

In this work, multiferroic thin-film nanocomposites were synthesized by coating the inside of mesoporous, cobalt ferrite (CoFe2O4 or CFO) with varying thicknesses of piezoelectric bismuth ferrite (BiFeO3 or BFO) grown by atomic layer deposition (ALD). Since ALD allows for precise control of the BFO layer thickness, the amount of residual porosity inside the pores can be controlled. Upon electrical poling, the piezoelectric BFO strains to be under out-of-plane tension, and since BFO is covalently bound to CFO, this tensile stress is transferred from BFO to CFO. CFO is a negative magnetostrictive material, meaning its magnetization should decrease in the direction of tension. This decrease in magnetization was observed in out-of-plane magnetometry experiments. Interestingly, the magnetization changes were found to be largest in the samples with the most residual porosity, despite the fact that they contained the smallest volume of BFO. Indeed, while the fully filled samples had a similar magnetoelectric coefficient to other dense nanostructured BFO-CFO composites reported in the literature, composites with the most residual porosity showed an exceptionally large converse magnetoelectric coefficient of 1.2 × 10–6 s m–1, an order of magnitude higher than dense composites. Strain transfer was confirmed using high-resolution X-ray diffraction. Samples with more residual porosity showed larger strain changes, corroborating the magnetization data. This suggests that magnetoelectric coupling can be optimized by engineering residual porosity into multiferroic composites. Such systems have profound effects for a broad range of switchable magnetic devices, particularly in the microwave and spintronic space.

Effect of BFO layer position on energy storage properties of STO/BFO thin films

Effect of BFO layer position on energy storage properties of STO/BFO thin films

Achieving high energy storage performance in BiFeO3@TiO2 filled PVDF-based composites with opposite double heterojunction via electric field tailoring

Polymer-based dielectric capacitors are well recognized for high energy density and efficiency. However, the energy density is restricted by the deterioration of breakdown strength with excessive addition of inorganic fillers. Herein, an innovative design of the lamellar-structured BiFeO3@TiO2 (BFO@TO) fillers is proposed and a small amount of BFO@TO is added into P(VDF-HFP)/PMMA blended polymer to fabricate BFO@TO-P(VDF-HFP)/PMMA composites, which delivers an outstanding energy density of 19.3 J cm−3 at 549.2 kV mm−1. The filler possesses a BFO/TO/BFO triple-layered structure. Due to the different Fermi level, electrons are injected from TO into BFO to form electron accumulation layer and construct the heterojunction electric fields between TO and BFO layers. Heterojunction electric fields at two interfaces produced by the triple-layered structure are opposite. The opposite double heterojunction can withstand larger external electric field and improve the breakdown strength. Besides, BFO, as a narrow bandgap semiconductor, is easier for electrons and holes to separate, which further widens the width of the built-in electric field and reduces the dielectric breakdown. Electric field distribution simulations intuitively confirm the enhancement of the breakdown strength. The results provide an effective strategy to address the critical issue of improving the breakdown strength for high energy storage capability.

Study on ferroelectric polarization induced resistive switching characteristics of neodymium-doped bismuth ferrite thin films for random access memory applications

The present work reports on resistive switching (RS) characteristics of Neodymium (Nd)-doped bismuth ferrite (BFO) layers. The Nd (2–10 at%) doped BFO thin film layers were deposited using a spray pyrolysis method. The structural analysis reveals that a higher Nd doping concentration in BFO leads to significant distortion of the prepared Nd:BFO thin films from rhombohedral to tetragonal characteristics. The morphological analysis shows that all the deposited Nd:BFO thin films have regularly arranged grains. The X-ray photoelectron spectroscopy (XPS) analysis reveals that the prepared Nd:BFO thin films have a higher Fe 3+/Fe 2+ratio and less oxygen vacancy (VO) defects which enriches the ferroelectric characteristics in Nd:BFO layers. The polarization-electric field (P-E) and RS characteristics of the fabricated Nd:BFO-based RS device were examined. It was observed that the Nd (7 at%) doped BFO RS device shows large remnant polarization (P r) of 0.21 μC/cm2 and stable RS characteristics.

Evaluating the Performances of the Ultralow Power Magnetoelectric Random Access Memory With a Physics-Based Compact Model of the Antiferromagnet/Ferromagnet Bilayer

Voltage-controlled spintronic devices are considered promising candidates for low-power applications due to the nonvolatility and the elimination of the Joule heating energy. Recently, experiments have demonstrated the voltage-controlled magnetization switching in the bismuth ferrite (BFO)/CoFe heterojunction that can achieve 180° switching at room temperature. In addition, it has been demonstrated that the ferroelectric coercive voltage of the La-doped BFO can be as low as 0.2 V by tuning the doping concentration of La and choosing a thinner BFO layer. To evaluate the potential performance of the magnetoelectric magnetic random access memory (ME-MRAM) using the BFO/CoFe heterojunction, we first build a physics-based compact model of the antiferromagnet/ferromagnet (AFM/FM) bilayer. The results from our circuit-compatible model match well with the micromagnetic simulations on the dynamics of the order parameters in both the AFM and FM layers. Next, we simulate the read and write performances of ME-MRAM using the compact model we have developed. Our results show that the write energy of the ME-MRAM can be as low as a few fJ per bit and the layout area is ~20 F², which is more energy and area efficient compared to SRAM and other spintronic memory candidates.

Studies on energy storage properties of BFO/WO3 bilayer thin film capacitor

AbstractPresent work reports the growth of BFO/WO3 bilayer thin film structures over Silicon, corning and ITO coated glass substrates. BFO layer in BFO/WO3 bilayer structure was deposited using Pulsed Laser deposition (PLD) technique at optimized laser energy (200 mJ) while WO3 nanostructured layer was deposited using rf‐magnetron sputtering technique at varying glancing angle from 65° to 80°. For the realization of MBM (metal‐bilayer‐metal) device, top Gold (Au) electrodes have been deposited using thermal evaporation technique. The BFO/WO3 bilayer structure fabricated at 70° glancing angle exhibited the saturation (Ps) and remnant (Pr) polarization as 45.45 μC/cm2 and 21.52 μC/cm2 respectively, which are appreciably higher than the earlier reports for pure BFO thin films. Enhanced energy storage characteristics were obtained in Au/BFO/WO3/ITO structure fabricated at 70° glancing angle with charge‐discharge efficiency (63%) and enlarged recoverable energy density (467 mJ/cm3). Achieved results indicate the utilization of fabricated Au/BFO/WO3/ITO structures towards high energy storage applications.

Interface engineering to optimize polarization and electric breakdown strength of Ba2Bi3.97Pr0.03Ti5O18/BiFeO3 ferroelectric thin-film for high-performance capacitors

Electrostatic capacitors based on dielectrics are ubiquitous components for applications in modern electronics and electric power systems. However, the relatively low energy density of electrostatic capacitors, which is one or two orders of magnitude lower than that of the batteries, has greatly hindered the implementation of its in energy storage devices. Here, we propose a strategy to overcome the tradeoff between high polarizability and breakdown electric field, and attain great enhancement energy storage density in the lead-free (Ba2Bi3.97Pr0.03Ti5O18/BiFeO3)N (BBPT/BFO)N multilayer ferroelectric thin films with different BFO layers through interface engineering. The interface engineering could be utilized to concurrently modify both polarization and local electric field strength caused by the synergistic effect of multiple polar structures and electric field amplifying effect. Accordingly, the discharged energy density of the optimized (BBPT/BFO)1 ferroelectric thin-film capacitors as high as ∼ 79.3 J/cm3 with discharged efficiency exceeding ∼ 75 % are achieved. Combined with its fatigue-free, favorable temperature and frequency stabilities, the multilayer ferroelectric thin films of BBPT/BFO could be a promising dielectric material for practical energy storage applications.

Исследование оптических свойств гетероструктуры BiFeO-=SUB=-3-=/SUB=-SrTiO-=SUB=-3-=/SUB=-, выращенной на подложке Al-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=-(0001) методом высокочастотного катодного распыления

The phase composition, structure, and optical properties of the BiFeO3/SrTiO3/Al2O3 (c-cut) heterostructure have been studied using XRD analysis, spectrophotometry, and multi-angle ellipsometry. BFO/STO/Al2O3 heterostructures have been obtained by high-frequency cathode sputtering in an oxygen atmosphere using the intermittent deposition technology. It was found that the BiFeO3 and SrTiO3 layers grew with an orientation in the direction of the [111] crystallographic axis parallel to the normal to the Al2O3 substrate. It has been shown that the damaged layer on the surface of the heterostructure does not exceed 2–3 nm, and no signs of the presence of boundary layers at the Al2O3– SrTiO3 and SrTiO3– BiFeO3 interfaces have been identified. The dispersion dependences of the refractive indices of BFO and STO layers are calculated. The reasons for the revealed regularities are discussed.

Investigation of the optical properties of a BiFeO-=SUB=-3-=/SUB=-/SrTiO-=SUB=-3-=/SUB=- heterostructure grown on an Al-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=-(0001) substrate by RF cathode sputtering

The phase composition, structure, and optical properties of the BiFeO3/SrTiO3/Al2O3 (c-cut) heterostructure have been studied using XRD analysis, spectrophotometry, and multi-angle ellipsometry. BFO/STO/Al2O3 heterostructures have been obtained by high-frequency cathode sputtering in an oxygen atmosphere using the intermittent deposition technology. It was found that the BiFeO3 and SrTiO3 layers grew with an orientation in the direction of the [111] crystallographic axis parallel to the normal to the Al2O3 substrate. It has been shown that the damaged layer on the surface of the heterostructure does not exceed 2-3 nm, and no signs of the presence of boundary layers at the Al2O3-SrTiO3 and SrTiO3-BiFeO3 interfaces have been identified. The dispersion dependences of the refractive indices of BFO and STO layers are calculated. The reasons for the revealed regularities are discussed. Keywords: thin films, multiferroic, optical properties, ellipsometry, bismuth ferrite.

HfO2‐Based Memristor as an Artificial Synapse for Neuromorphic Computing with Tri‐Layer HfO2/BiFeO3/HfO2 Design

AbstractNeuromorphic devices are among the most emerging electronic components to realize artificial neural systems and replace traditional complementary metal–oxide semiconductor devices in recent times. In this work, tri‐layer HfO2/BiFeO3(BFO)/HfO2 memristors are designed by inserting traditional ferroelectric BFO layers measuring ≈4 nm after thickness optimization. The novel designed memristor shows excellent resistive switching (RS) performance such as a storage window of 104 and multi‐level storage ability. Remarkably, essential synaptic functions can be successfully realized on the basis of the linearity of conductance modulation. The pattern recognition simulation based on neuromorphic network is conducted with 91.2% high recognition accuracy. To explore the RS performance enhancement and artificial synaptic behaviors, conductive filaments (CFs) composed of Hafnium (Hf) single crystal with a hexaganal lattice structure are observed using high‐resolution transmission electron microscopy. It is reasonable to believe that the sufficient oxygen vacancies in the inserting BFO thin film play a crucial role in adjusting the morphology and growth of Hf CFs, which leads to the promising synaptic and enhanced RS behavior, thus demonstrating the potential of this memristor for use in neuromorphic computing.

Enhanced photovoltaic-pyroelectric coupled effect of BiFeO3/Au/ZnO heterostructures

The photovoltaic properties of ferroelectric films and ferroelectric-semiconductor heterostructures have been extensively studied due to their application prospects in photodetection, energy conversion and nonvolatile storage. However, light-induced pyroelectric effect accompanied by the photovoltaic effect of ferroelectric-semiconductor heterostructures lacks sufficient attention. Herein, BiFeO 3 (BFO)/Au/ZnO heterostructures are constructed by controlling sputtering time of Au nanoparticles and the regulation mechanism of integrating pyroelectric and photovoltaic effects is explored. The short-circuit photocurrent density of the optimal BFO/Au/ZnO heterostructures is nearly 1.4 times that of BFO/ZnO heterostructures under 405 nm light illumination. Moreover, BFO/Au/ZnO heterostructures broaden the response wavelength from 360 nm to 1060 nm light beyond the bandgap limitation. Compared with merely the photovoltaic effect found in BFO films and BFO/ZnO heterostructures, BFO/Au/ZnO heterostructures display the photovoltaic-pyroelectric coupled effect that is associated with light-induced temperature variation rate and band alignment by introducing Au nanoparticles into BFO and ZnO layers. The implementation of the photovoltaic-pyroelectric coupled effect endows BFO/Au/ZnO heterostructures with outstanding photoelectric performances modulated by self-polarization phenomenon and band bending. This work not only provides in-depth understanding about the photovoltaic-pyroelectric coupled effect of ferroelectric-metal-semiconductor heterostructures, but also provides an effective and facile route to design high-performance photoelectric related devices with wideband response. The improvement in photovoltaic performances of ferroelectric-semiconductor heterojunctions is ascribed to the construction of energy band structure tuning, whereas ferroelectric-semiconductor heterojunctions have negligible light-induced pyroelectric effect. In this work, the introduction of Au nanoparticles into BFO and ZnO layers not only endows the BFO/Au/ZnO heterostructures with broadened response wavelength from 360 nm to 1060 nm light beyond the bandgap limitation, but also integrates light-induced pyroelectric effect and photovoltaic effect. BFO/20 s Au/ZnO heterostructures display the optimal photoelectric performances and appreciable pyroelectric effect governed by self-polarization phenomenon and band bending. • Au nanoparticles modified BiFeO 3 /Au/ZnO heterostructures display improved photoelectric properties and broadband response. • The integration of light-induced pyroelectric and photovoltaic effects of BiFeO 3 /Au/ZnO heterostructures is manipulated. • The photoelectric properties of BiFeO 3 /Au/ZnO heterostructures are governed by self-polarization phenomenon and band bending.

Ferroelectric polarization induced memristive behavior in bismuth ferrite (BiFeO3) based memory devices

Bismuth ferrite (BiFeO 3 , BFO) thin films of various thickness were deposited using spray pyrolysis technique at 673 K. The structural studies of the prepared BFO thin films show a rhombohedral structure with R3c space group. The morphological analysis reveals that prepared BFO thin film samples exhibit a uniform and less porous grains. Different thickness of BFO thin films (174–808 nm) was stacked as an active layer between aluminum (Al) and indium doped tin oxide (ITO) electrodes . With the optimum thickness of the BFO intermediate layer, the polarization-electric field (P-E) loop analysis of the ITO/BFO/Al device showed a hysteresis loop with remnant polarization (P r ) of 0.21 μC/cm 2 and coercive field (E c ) of 33.4 kV/cm respectively. The impact of the BFO switching layers with varying thickness towards control of oxygen vacancy (V O ) defects and the effective role of polarization induced resistive switching (RS) characteristics were explored. • Realization of BFO resistive switching layers by cost-effective spray pyrolysis technique. • XPS analysis of different thickness of BFO layers to study the control of oxygen vacancy (V O ) defects. • The effective role of polarization in BFO layers towards resistive switching (RS) characteristics were explored.

The Investigation for Thickness-Dependent Electrical Performance on BaTiO3/BiFeO3 Bilayer Ferromagnetic Capacitors

Bilayer barium titanate (BaTiO3, BTO)/bismuth ferrite (BiFeO3, BFO) capacitive devices were fabricated and systematically analyzed from the aspects of thin-film material crystallography and electrical characterization. The tetragonal phase (T) of BTO with the reducing thickness (150 nm) was demonstrated through carefully adjusting the conditions of sputtering process and post-thermal treatments. The thickness dependence of polarization, energy density, permittivity, and leakage current was investigated in the BTO/BFO bilayer system. It showed that 150-nm BFO film is an optimal thickness, which led to the substantial increase in energy density up to 920 mJ/cm3 with the charge/discharge efficiency of 79.7% at 10 V. The permittivity of 150-nm BFO bilayer device was found to be 258, which is much higher than the single -layer BFO and other BTO/BFO devices with different BFO thicknesses. Leakage current could be reduced by three orders with the increasing thickness of BFO layer from 30 to 225 nm. In addition, the leakage current of BTO/BFO bilayer capacitors was 102 times lower than BFO single layer with the same total thickness. The result showed that the leakage current of BFO material could be significantly reduced in the bilayer system. The performance of BTO/BFO bilayer capacitors indicates that it is a promising technique for the implementation of nanoscale, lead-free, and nonelectrochemical thin-film energy storage-related applications.

Influence of BiFeO3 crystallographic phase on the enhanced interfacial magnetization in BiFeO3/La2/3Sr1/3MnO3 heterostructures

Large induced magnetization is observed in rhombohedral-like BiFeO3 (RBFO) when grown on a ferromagnetic La2/3Sr1/3MnO3 layer. This magnetization survives up to room temperature and is strongly influenced by the deposition conditions and crystallographic phase of BiFeO3. The magnetization in RBFO is induced by the Fe–O–Mn ferromagnetic (FM) superexchange (SE) interaction, after a strong hybridization between Fe and Mn orbitals mediate through oxygen orbitals, which enhances the spin canting in a BFO layer near the interface. The reduction in the magnetization of BFO due to change in its growth conditions is caused by the altered oxygen content in the interfacial region, which has a direct impact on the FM SE Fe–O–Mn coupling at the interface. In marked contrast, the induced magnetization in the super-tetragonal phase (TBFO) of BFO, in which the canting of Fe spins is forbidden by the symmetry, shows a comparatively very small moment, which vanishes below the room temperature (∼200 K). We propose that the ferromagnetic ordering induced in TBFO is limited to the adjoined section only, whereas it extended to a certain degree of bulk in RBFO. A spin-glass like state is also observed in BiFeO3/La2/3Sr1/3MnO3 heterostructure with irreversible temperature ∼100 K.

Built-in electric field induces polarization rotation in bilayer BiFeO3/(Ba,Sr)TiO3 thin films

The crystal structure of BiFeO3/BaxSr1-xTiO3 (BFO/BST) heterostructures with x = 0.2, 0.6 and 0.8, grown on single-crystal MgO (001) substrate was investigated by x-ray diffraction and Raman spectroscopy in order to determine the influence of mismatch-induced strains and spontaneous polarization in BST buffer layers on BFO layers. The lattice parameter of the BFO layers was shown to decrease with increasing concentration of Ba ions, despite the increasing in-plain lattice parameters of tetragonal unit cells of BST layers. The rhombohedral angle of the crystal structure of BFO layers demonstrates an increase towards the ideal cubic perovskite structure with the appearance of the built-in electric field, induced by the spontaneous polarization in buffer layers. This result provides a remarkable tool for the control of polarization in BFO layers and other ferroelectric films in general, by changing the built-in electric field from ferroelectric buffer layer without changing a single crystal substrate.

Effect of non-$$180^{\circ }$$ polarization invariants on the exchange bias of tetragonal $$\langle 001\rangle $$ and rhombohedral $$\langle 111\rangle $$ orientations of bismuth ferrite epitaxial thin films

\(\hbox {BiFeO}_{3}\) (BFO) is the only room temperature multiferroic material that has been extensively studied due to its multifunctional properties. BFO with a canted G-type antiferromagnetic (AFM) ordering exhibits strong exchange bias characteristics with NiFe which offers the potential to design and utilize devices working based on multiferroic features. In the past, it was known that the presence of \(180^{\circ }\) domain walls of BFO hinders a plausible exchange bias interaction. To understand the role of the strain-induced effects on such \(180^{\circ }\) domain walls and its effect on the exchange bias, NiFe, a soft ferromagnetic layer, was grown on the epitaxial BFO AFM layers. An approximately 80 nm BFO layer was grown epitaxially in both the tetragonal (001) phase on the \(\hbox {LaAlO}_{3}\) (001) substrate and the rhombohedral (111) phase on the \(\hbox {SrTiO}_{3}\) (111) substrate, with a thin (10 nm) layer of \(\hbox {Ni}_{80}\hbox {Fe}_{20}\) on top of it. An exchange bias of 510 Oe was observed in the tetragonal phase of BFO with a c / a ratio of 1.22, which is comparable with the exchange bias shown by the (111) oriented rhombohedral phase (360 Oe). Both the tetragonal (001) and rhombohedral (111) layers possess ferroelectric polarization normal to the sample surface and so the domain walls are mostly \(180^{\circ }\) oriented which is expected to have a minimum effect on the exchange bias. However, the weak strain-induced structural variants in the (111) oriented rhombohedral BFO and the monoclinic distortion present in the tetragonal BFO introduce non-\(180^{\circ }\) domain walls in the system. These variants arising due to the structural distortion are expected to play a key role in defining the ferroelectric domain wall nature, thereby exhibiting exchange bias characteristics.

First-principles investigation on tunable electronic properties and magnetism by polarization in PbTiO3/BiFeO3 2D ferroelectric heterostructures

The magnetism and 2D electron gas in a BFO layer are manipulated by PTO polarization in PTO/BFO heterostructures.

Influence of Thickness on Optical Properties of Bismuth Ferrite Layers Grown on Quartz Substrates by Chemical Solution Deposition

Bismuth ferrite (BFO) is very promising as ferroelectric material for perovskite solar cell application. This study deals with the influence of thickness on optical properties of BFO layers grown on the quartz substrates by chemical solution deposition. XRD analyses revealed that all BFO samples have a dominant peak at (110) with rhombohedral perovskite structure. The optical bandgaps remained about 2.61 eV as the increasing of the thickness. However, the diffraction angle did not shift with increasing of the thickness. It can be concluded that structural distortion at both Fe sites and Bi sites in BFO layers does not occur