Ferroelectric HfO_(2)has attracted much attention owing to its superior ferroelectricity at an ultra-thin thickness and good compatibility with Si-based complementary metal-oxide-semiconductor(CMOS)technology.However,...Ferroelectric HfO_(2)has attracted much attention owing to its superior ferroelectricity at an ultra-thin thickness and good compatibility with Si-based complementary metal-oxide-semiconductor(CMOS)technology.However,the crystallization of polar orthorhombic phase(o-phase)HfO_(2)is less competitive,which greatly limits the ferroelectricity of the as-obtained ferroelectric HfO_(2)thin films.Fortunately,the crystallization of o-phase HfO_(2)can be thermodynamically modulated via interfacial stress engineering.In this paper,the growth of improved ferroelectric Al doped HfO_(2)(HfO_(2):Al)thin films on(111)-oriented Si substrate has been reported.Structural analysis has suggested that nonpolar monoclinic HfO_(2):Al grown on(111)-oriented Si substrate suffered from a strong compressive strain,which promoted the crystallization of(111)-oriented o-phase HfO_(2)in the as-grown HfO_(2):Al thin films.In addition,the in-plane lattice of(111)-oriented Si substrate matches well with that of(111)-oriented o-phase HfO_(2),which further thermally stabilizes the o-phase HfO_(2).Accordingly,an improved ferroelectricity with a remnant polarization(2P_(r))of 26.7C/cm^(2) has been obtained.The results shown in this work provide a simple way toward the preparation of improved ferroelectric HfO_(2)thin films.展开更多
The performance and reliability of ferroelectric thin films at temperatures around a few Kelvin are critical for their application in cryo-electronics.In this work,TiN/Hf_(0.5)Zr_(0.5)O_(2)/TiN capacitors that are fre...The performance and reliability of ferroelectric thin films at temperatures around a few Kelvin are critical for their application in cryo-electronics.In this work,TiN/Hf_(0.5)Zr_(0.5)O_(2)/TiN capacitors that are free from the wake-up effect are investigated systematically from room temperature(300 K)to cryogenic temperature(30 K).We observe a consistent decrease in permittivity(εr)and a progressive increase in coercive electric field(Ec)as temperatures decrease.Our investigation reveals exceptional stability in the double remnant polarization(2P_(r))of our ferroelectric thin films across a wide temperature range.Specifically,at 30 K,a 2P_(r)of 36μC/cm^(2)under an applied electric field of 3.0 MV/cm is achieved.Moreover,we observed a reduced fatigue effect at 30 K in comparison to 300 K.The stable ferroelectric properties and endurance characteristics demonstrate the feasibility of utilizing HfO_(2)based ferroelectric thin films for cryo-electronics applications.展开更多
The 0.98(K_(0.5)Na_(0.5))NbO_(3)-0.02Ba(Nb_(0.5)Co_(0.5))O_(3-δ) ceramics with doped Ba^(2+) and Co^(2+) ions are fabricated,and the impacts of the thermal process are studied.Compared with the rapidly cooled (RC) sa...The 0.98(K_(0.5)Na_(0.5))NbO_(3)-0.02Ba(Nb_(0.5)Co_(0.5))O_(3-δ) ceramics with doped Ba^(2+) and Co^(2+) ions are fabricated,and the impacts of the thermal process are studied.Compared with the rapidly cooled (RC) sample,the slowly cooled (SC) sample possesses superior dielectric and ferroelectric properties,and an 11 K higher ferroelectricparaelectric phase transition temperature,which can be attributed to the structural characteristics such as the grain size and the degree of anisotropy.Heat treatment can reversibly modulate the content of the oxygen vacancies,and in turn the ferroelectric hysteresis loops of the samples.Finally,robust and tunable ferroelectric property is achieved in SC samples with good structural integrity.展开更多
Rhombohedral phase Hf_(x)Zr_(1.x)O_(2)(HZO,x from 0 to 1)films are promising for achieving robust ferroelectric polarization without the need for an initial wake-up pre-cycling,as is normally the case for the more com...Rhombohedral phase Hf_(x)Zr_(1.x)O_(2)(HZO,x from 0 to 1)films are promising for achieving robust ferroelectric polarization without the need for an initial wake-up pre-cycling,as is normally the case for the more commonly studied orthorhombic phase.However,a large spontaneous polarization observed in rhombohedral films is not fully understood,and there are also large discrepancies between experimental and theoretical predictions.In this work,in rhombohedral ZrO_(2)thin films,we show that oxygen vacancies are not only a key factor for stabilizing the phase,but they are also a source of ferroelectric polarization in the films.This is shown experimentally through the investigation of the structural properties,chemical composition and the ferroelectric properties of the films before and after an annealing at moderate temperature(400℃)in an oxygen environment to reduce the V_(o)concentration compared.The experimental work is supported by density functional theory(DFT)calculations which show that the rhombohedral phase is the most stable one in highly oxygen defective ZrO_(2)films.The DFT calculations also show that V_(o)contribute to the ferroelectric polarization.Our findings reveal the importance of V_(o)for stabilizing rhombohedral ZrO_(2)thin films with superior ferroelectric properties.展开更多
The finding of the robust ferroelectricity in HfO_(2)-based thin films is fantastic from the view point of both the fundamentals and the applications.In this review article,the current research status of the future pr...The finding of the robust ferroelectricity in HfO_(2)-based thin films is fantastic from the view point of both the fundamentals and the applications.In this review article,the current research status of the future prospects for the ferroelectric HfO_(2)-based thin films and devices are presented from fundamentals to applications.The related issues are discussed,which include:1)The ferroelectric characteristics observed in HfO_(2)-based films and devices associated with the factors of dopant,strain,interface,thickness,defect,fabrication condition,and more;2)physical understanding on the observed ferroelectric behaviors by the density functional theory(DFT)-based theory calculations;3)the characterizations of microscopic and macroscopic features by transmission electron microscopes-based and electrical properties-based techniques;4)modeling and simulations,5)the performance optimizations,and 6)the applications of some ferroelectric-based devices such as ferroelectric random access memory,ferroelectric-based field effect transistors,and the ferroelectric tunnel junction for the novel information processing systems.展开更多
We study the ferroelectricity in a one-dimensional(1D)system composed of a double helix SnIP with absorbing water molecules.Our ab initio calculations reveal two factors that are critical to the electrical polarizatio...We study the ferroelectricity in a one-dimensional(1D)system composed of a double helix SnIP with absorbing water molecules.Our ab initio calculations reveal two factors that are critical to the electrical polarization.The first one is the orientation of polarized water molecules staying in the R2 region of SnIP.The second one is the displacement of I atom which roots from subtle interaction with absorbed water molecules.A reasonable scenario of polarization flipping is proposed in this study.In the scenario,the water molecule is rolling-up with keeping the magnitude of its electrical dipole and changing its direction,meanwhile,the displacement of I atoms is also reversed.Highly tunable polarization can be achieved by applying strain,with 26.5%of polarization enhancement by applying tensile strain,with only 4%degradation is observed with 4%compressive strain.Finally,the direct band gap is also found to be correlated with strain.展开更多
Hafnium-based ferroelectric films,remaining their ferroelectricity down to nanoscale thickness,present a promising application for low-power logic devices and nonvolatile memories.It has been appealing for researchers...Hafnium-based ferroelectric films,remaining their ferroelectricity down to nanoscale thickness,present a promising application for low-power logic devices and nonvolatile memories.It has been appealing for researchers to reduce the required temperature to obtain the ferroelectric phase in hafnium-based ferroelectric films for applications such as flexible and wearable electronics.This work demonstrates that a remanent polarization(P_(r))value of>5μC/cm^(2)can be obtained in asdeposited Hf_(0.5)Zr_(0.5)O_(2)(HZO)films that are fabricated by thermal atomic layer deposition(TALD)under low temperature of 250℃.The ferroelectric orthorhombic phase(o-phase)in the as-deposited HZO films is detected by scanning transmission electron microscopy(STEM).This low fabrication temperature further extends the compatibility of ferroelectric HZO films to flexible electronics and avoids the cost imposed by following high-temperature annealing treatments.展开更多
Two-dimensional(2D)ferroelectric(FE)systems are promising candidates for non-volatile nanodevices.Previous studies mainly focused on 2D compounds.Though counter-intuitive,here we propose several new phases of telluriu...Two-dimensional(2D)ferroelectric(FE)systems are promising candidates for non-volatile nanodevices.Previous studies mainly focused on 2D compounds.Though counter-intuitive,here we propose several new phases of tellurium with(anti)ferroelectricity.Two-dimensional films can be viewed as a collection of one-dimensional chains,and lone-pair instability is responsible for the(anti)ferroelectricity.The total polarization is determined to be 0.34×10^(-10)C/m for the FE ground state.Due to the local polarization field in the FE film,we show a large Rashba splitting(α_(R)~2 eV·?)with nonzero spin Hall conductivity for experimental detection.Furthermore,a dipole-like distribution of Berry curvature is verified,which may facilitate a nonlinear Hall effect.Because Rashba-splitting/Berry-curvature distributions are fully coupled with a polarization field,they can be reversed through FE phase transition.Our results not only broaden the elemental FE materials,but also shed light on their intriguing transport phenomena.展开更多
Moiré superlattices have emerged as a highly controllable quantum platform for exploration of various fascinating phenomena,such as Mott insulator states,ferroelectric order,unconventional superconductivity and o...Moiré superlattices have emerged as a highly controllable quantum platform for exploration of various fascinating phenomena,such as Mott insulator states,ferroelectric order,unconventional superconductivity and orbital ferromagnetism.Although remarkable progress has been achieved,current research in moiré physics has mainly focused on the single species properties,while the coupling between distinct moiré quantum phenomena remains elusive.Here we demonstrate,for the first time,the strong coupling between ferroelectricity and correlated states in a twisted quadrilayer MoS2moiré superlattice,where the twist angles are controlled in sequence to be ~57°,~0°,and ~-57°.Correlated insulator states are unambiguously established at moiré band filling factors v = 1,2,3 of twisted quadrilayer MoS_(2).Remarkably,ferroelectric order can occur at correlated insulator states and disappears quickly as the moiré band filling deviates from the integer fillings,providing smoking gun evidences of the coupling between ferroelectricity and correlated states.Our results demonstrate the coupling between different moiré quantum properties and will hold great promise for new moiré physics and applications.展开更多
Two-dimensional(2D)ferroelectric compounds are a special class of materials that meet the need for devices miniaturization,which can lead to a wide range of applications.Here,we investigate ferroelectric properties of...Two-dimensional(2D)ferroelectric compounds are a special class of materials that meet the need for devices miniaturization,which can lead to a wide range of applications.Here,we investigate ferroelectric properties of monolayer group-IV monochalcogenides MX(M=Sn,Ge;X=Se,Te,S)via strain engineering,and their effects with contaminated hydrogen are also discussed.GeSe,GeTe,and GeS do not go through transition up to the compressive strain of-5%,and consequently have good ferroelectric parameters for device applications that can be further improved by applying strain.According to the calculated ferroelectric properties and the band gaps of these materials,we find that their band gap can be adjusted by strain for excellent photovoltaic applications.In addition,we have determined the most stable hydrogen occupancy location in the monolayer SnS and SnTe.It reveals that H prefers to absorb on SnS and SnTe monolayers as molecules rather than atomic H.As a result,hydrogen molecules have little effect on the polarization and electronic structure of monolayer SnTe and SnS.展开更多
The group-V monolayers(MLs)have been studied intensively after the experimental fabrication of two-dimensional(2D)graphene and black phosphorus.The observation of novel quantum phenomena,such as quantum spin Hall effe...The group-V monolayers(MLs)have been studied intensively after the experimental fabrication of two-dimensional(2D)graphene and black phosphorus.The observation of novel quantum phenomena,such as quantum spin Hall effect and ferroelectricity in group-V elemental layers,has attracted tremendous attention because of the novel physics and promising applications for nanoelectronics in the 2D limit.In this review,we comprehensively review recent research progress in engineering of topology and ferroelectricity,and several effective methods to control the quantum phase transition are discussed.We then introduce the coupling between topological orders and ferroelectric orders.The research directions and outlooks are discussed at the end of the perspective.It is expected that the comprehensive overview of topology and ferroelectricity in 2D group-V materials can provide guidelines for researchers in the area and inspire further explorations of interplay between multiple quantum phenomena in low-dimensional systems.展开更多
In this paper we report the leakage current, ferroelectric and piezoelectric properties of the YFe O3 film with hexagonal structure, which was fabricated on Si（111） substrate by a simple sol-gel method. The leakage ...In this paper we report the leakage current, ferroelectric and piezoelectric properties of the YFe O3 film with hexagonal structure, which was fabricated on Si（111） substrate by a simple sol-gel method. The leakage current test shows good characteristics as the leakage current density is 5.4 × 10^-6A/cm^2 under 5 V. The dominant leakage mechanism is found to be an Ohmic behavior at low electric field and space-charge-limited conduction at high electric field region. The P–E measurements show ferroelectric hysteresis loops with small remnant polarization and coercive field at room temperature.The distinct and switchable domain structures on the nanometer scale are observed by piezoresponse force microscopy,which testifies to the ferroelectricity of the YFe O3 film further.展开更多
5-at% Mn-doped and undoped BaTiO3 thin films have been grown under different oxygen partial pressures by Pulsed Laser Deposition （PLD） on platinum-coated sapphire substrates. X-ray diffraction （XRD） measurements f...5-at% Mn-doped and undoped BaTiO3 thin films have been grown under different oxygen partial pressures by Pulsed Laser Deposition （PLD） on platinum-coated sapphire substrates. X-ray diffraction （XRD） measurements for all the thin films reveal a similar polycrystalline single-phase perovskite structure. Ferroelectricity is observed in the Mn-doped and undoped BaTiO3 thin films grown under relatively high oxygen partial pressure. Ferromagnetic coupling of the Mn dopant ions, on the other hand, is only seen in Mn-doped BaTiO3 thin films prepared under low oxygen partial pressure in a wide temperature range from 5 K to 300 K, and is attributed to the enhanced exchange coupling between Mn dopants and electrons at oxygen vacancies. Our results show that the leakage current is decreased with the doped Mn, but increases the dielectric loss and decreases the dielectric constant, and the ferroelectricity is impaired. To produce ferromagnetism, oxygen vacancies are necessary, which unfortunately increase the leakage current. This confirms that the mutual interplay between the ferroelectricity and ferromagnetism can be tuned by exchange coupling of the doped-Mn and oxygen vacancies in the BaTiO3 thin films.展开更多
Multiferroic materials,showing the coexistence and coupling of ferroelectric and magnetic orders,are of great technological and fundamental importance.However,the limitation of single phase multiferroics with robust m...Multiferroic materials,showing the coexistence and coupling of ferroelectric and magnetic orders,are of great technological and fundamental importance.However,the limitation of single phase multiferroics with robust magnetization and polarization hinders the magnetoelectric effect from being applied practically.Magnetic frustration,which can induce ferroelectricity,gives rise to multiferroic behavior.In this paper,we attempt to construct an artificial magnetically frustrated structure comprised of manganites to induce ferroelectricity.A disordered stacking of manganites is expected to result in frustration at interfaces.We report here that a tri-color multilayer structure comprised of non-ferroelectric La;Ca;MnO;（A）/Pr;Ca;MnO;（B）/Pr;Sr;MnO;（C） layers with the disordered arrangement of ABC-ACBCAB-CBA-BAC-BCA is prepared to form magnetoelectric multiferroics.The multilayer film exhibits evidence of ferroelectricity at room temperature,thus presenting a candidate for multiferroics.展开更多
Ferroelectric and magnetic properties of Fe1-xMnxV2O4 （0 ≤ x ≤ 0.5） spinels are investigated on the basis of dielectric, polarization, and susceptibility measurements. Ferroeleetric polarization is discovered in c...Ferroelectric and magnetic properties of Fe1-xMnxV2O4 （0 ≤ x ≤ 0.5） spinels are investigated on the basis of dielectric, polarization, and susceptibility measurements. Ferroeleetric polarization is discovered in collinear ferrimagnetic and Yafet-Kittel magnetic phases for 0.1 ≤ x ≤ 0.4, which can be tuned by a magnetic field. As orbital-active FJ＋ is substituted with Mn2＋, ferroeleetric polarization decreases for 0 ≤ x ≤ 0.4 and disappears for x=0.5. We propose that the two polar components in ferroelectric polarization originate from the exchange striction mechanism and the spin-current model, respectively.展开更多
Nanoscale PbxLa1-,Ti1-x/4O3 （PLT） thin film has been fabricated on Pt／Ti／SiO2／Si substrates by chemical solution deposition （CSD） method. Ferroelectricity of the fresh-made PLT thin film has been clearly detect...Nanoscale PbxLa1-,Ti1-x/4O3 （PLT） thin film has been fabricated on Pt／Ti／SiO2／Si substrates by chemical solution deposition （CSD） method. Ferroelectricity of the fresh-made PLT thin film has been clearly detected through piezoelectric force microscopy （PFM） by writing reversible ferroelectric domains. However, PLT thin film also shows off-standard ferroelectric hysteresis loops highly dependent on frequency, indicating large amount of mobile space charges in the film. Subsequent current-voltage （C-V） studies show that sandwich-like Pt／PLT／Pt structure exhibits notable bipolar resistive switching （BRS） characteristics with high stability （〉 103 switching cycles）. It is found that the C-V curves of both high- and low-resistance states have the feature of space-charge-limited current （SCLC） conduction, indicating important roles of defects in the conduction. X-ray photoelectron spectroscopy measurement further verifies that oxygen vacancies based conductive filament mechanism is likely responsible for the observed RS effect. Our demonstration of stable RS effect in the PLT thin film and its possible coupling with ferroelectricity is promising in device development and applications, such as development of ferroelectric-tunable RS memories.展开更多
The instability of thin ferroelectric films is discussed based on the close similarity of dielectric properties between bulk Bi-layered perovskites and thin BaTiO<sub>3</sub> films. The dielectric properti...The instability of thin ferroelectric films is discussed based on the close similarity of dielectric properties between bulk Bi-layered perovskites and thin BaTiO<sub>3</sub> films. The dielectric properties of pseudo-two-dimensional layered perovskites suggest that the bulk layered ferroelectric is a good model of ultra-thin ferroelectric film with a few perovskite units, free from any misfit lattice strain. It seems plausible that the ferroelectric interaction is still prominent but shows a crossover from ferroelectric to antiferroelectric along the unique c-axis (perpendicular to the film plane);with decreasing thickness, the ferroelectricity appears within the plane, which results in so-called “canted ferroelectricity”. An extra relaxation mode induced by surface effect of thin films correlates with soft mode, which results in a new intermediate phase between the paraelectric and ferroelectric phases. These evidences may indicate no critical thickness even for ferroelectric ultra- thin films.展开更多
Ba（Zr, Ti）O3is a lead-free relaxor ferroelectric. Using the first-principles method, the ferroelectric dipole moments for pure BaTiO3 and Ba（Zr, Ti）O3supercells are studied. All possible ion configurations of Ba Z...Ba（Zr, Ti）O3is a lead-free relaxor ferroelectric. Using the first-principles method, the ferroelectric dipole moments for pure BaTiO3 and Ba（Zr, Ti）O3supercells are studied. All possible ion configurations of Ba Zr0.5Ti0.5O3 and Ba Zr0.25Ti0.75O3 are constructed in a 2 × 2 × 2 supercell. For the half-substituted case, divergence of ferroelectric properties is found from these structures, which greatly depends on the arrangements of Ti and Zr ions. Thus our results provide a reasonable explanation to the relaxor behavior of Ba（Zr, Ti）O3. In addition, a model based on the thermal statistics gives the averaged polarization for Ba（Zr, Ti）O3, which depends on the temperature of synthesis. Our result is helpful to understand and tune the relaxor ferroelectricity of lead-free Ba（Zr, Ti）O3.展开更多
Sr-doped Ba_(0.7)La_(0.3)TiO_(3)(BSLTO)thin films are deposited by pulsed laser deposition,and their microstructure,conductivity,carrier transport mechanism,and ferroelectricity are systematically investigated.The x-r...Sr-doped Ba_(0.7)La_(0.3)TiO_(3)(BSLTO)thin films are deposited by pulsed laser deposition,and their microstructure,conductivity,carrier transport mechanism,and ferroelectricity are systematically investigated.The x-ray diffraction measurements demonstrate that Sr-doping reduces the lattice constant of BSLTO thin films,resulting in the enhanced phonon energy in the films as evidenced by the Raman measurements.Resistivity-temperature and Hall effect measurements demonstrate that Sr can gradually reduce electrical resistivity while the electron concentration remains almost unchanged at high temperatures.For the films with semiconducting behavior,the charge transport model transforms from variable range hopping to small polaron hopping as the measurement temperature increases.The metalic conductive behaviors in the films with Sr=0.30,0.40 conform to thermal phonon scattering mode.The difference in charge transport behavior dependent on the A-site cation doping,is clarified.It is revealed that the increasing of phonon energy by Sr doping is responsible for lower activation energy of small polaron hopping,higher carrier mobility,and lower electrical resistivity.Interestingly,the piezoelectric force microscopy(PFM)results demonstrate that all the BSLTO films can exhibit ferroelectricity,especially for the room temperature metallic conduction film with Sr=0.40.These results imply that Sr-doping could be a potential way to explore ferroelectric metal materials for other perovskite oxides.展开更多
We investigate the resistive switching and ferroelectric polarization properties of high-quality epitaxial BiFeO3 thin films in various temperature ranges. The room temperature current-voltage（I-V） curve exhibits a ...We investigate the resistive switching and ferroelectric polarization properties of high-quality epitaxial BiFeO3 thin films in various temperature ranges. The room temperature current-voltage（I-V） curve exhibits a well-established polarization-modulated memristor behavior. At low temperatures（〈 253 K）, the I-V curve shows an open circuit voltage（OCV）, which possibly originates from the dielectric relaxation effects, accompanied with a current hump due to the polarization reversal displacement current. While at relative higher temperatures（〉 253 K）, the I-V behaviors are governed by both space-charge-limited conduction（SCLC） and Ohmic behavior. The polarization reversal is able to trigger the conduction switching from Ohmic to SCLC behavior, leading to the observed ferroelectric resistive switching. At a temperature of〉 298 K, there occurs a new resistive switching hysteresis at high bias voltages, which may be related to defect-mediated effects.展开更多
基金Research Fund of Guangdong-Hong Kong-Macao Joint Laboratory for Intelligent Micro-Nano Optoelectronic Tech-nology,China(Grant No.2020B1212030010)Project of Faculty of Agricultural Equipment of Jiangsu University (Grant No. NZXB20210202) are acknowledged。
文摘Ferroelectric HfO_(2)has attracted much attention owing to its superior ferroelectricity at an ultra-thin thickness and good compatibility with Si-based complementary metal-oxide-semiconductor(CMOS)technology.However,the crystallization of polar orthorhombic phase(o-phase)HfO_(2)is less competitive,which greatly limits the ferroelectricity of the as-obtained ferroelectric HfO_(2)thin films.Fortunately,the crystallization of o-phase HfO_(2)can be thermodynamically modulated via interfacial stress engineering.In this paper,the growth of improved ferroelectric Al doped HfO_(2)(HfO_(2):Al)thin films on(111)-oriented Si substrate has been reported.Structural analysis has suggested that nonpolar monoclinic HfO_(2):Al grown on(111)-oriented Si substrate suffered from a strong compressive strain,which promoted the crystallization of(111)-oriented o-phase HfO_(2)in the as-grown HfO_(2):Al thin films.In addition,the in-plane lattice of(111)-oriented Si substrate matches well with that of(111)-oriented o-phase HfO_(2),which further thermally stabilizes the o-phase HfO_(2).Accordingly,an improved ferroelectricity with a remnant polarization(2P_(r))of 26.7C/cm^(2) has been obtained.The results shown in this work provide a simple way toward the preparation of improved ferroelectric HfO_(2)thin films.
基金supported by the National Key R&D Program of China under Grant No.2022YFB3608400National Natural Science Foundation of China under Grant Nos.61825404,61888102,and 62104044the Strategic Priority Research Program of the Chinese Academy of Sciences under Grant No.XDB44000000 and the project of MOE innovation platform.
文摘The performance and reliability of ferroelectric thin films at temperatures around a few Kelvin are critical for their application in cryo-electronics.In this work,TiN/Hf_(0.5)Zr_(0.5)O_(2)/TiN capacitors that are free from the wake-up effect are investigated systematically from room temperature(300 K)to cryogenic temperature(30 K).We observe a consistent decrease in permittivity(εr)and a progressive increase in coercive electric field(Ec)as temperatures decrease.Our investigation reveals exceptional stability in the double remnant polarization(2P_(r))of our ferroelectric thin films across a wide temperature range.Specifically,at 30 K,a 2P_(r)of 36μC/cm^(2)under an applied electric field of 3.0 MV/cm is achieved.Moreover,we observed a reduced fatigue effect at 30 K in comparison to 300 K.The stable ferroelectric properties and endurance characteristics demonstrate the feasibility of utilizing HfO_(2)based ferroelectric thin films for cryo-electronics applications.
基金supported by the National Key R&D Program of China (Grant No.2022YFA1402903)the National Natural Science Foundation of China (Grant Nos.52172116 and 62171214)the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD)。
文摘The 0.98(K_(0.5)Na_(0.5))NbO_(3)-0.02Ba(Nb_(0.5)Co_(0.5))O_(3-δ) ceramics with doped Ba^(2+) and Co^(2+) ions are fabricated,and the impacts of the thermal process are studied.Compared with the rapidly cooled (RC) sample,the slowly cooled (SC) sample possesses superior dielectric and ferroelectric properties,and an 11 K higher ferroelectricparaelectric phase transition temperature,which can be attributed to the structural characteristics such as the grain size and the degree of anisotropy.Heat treatment can reversibly modulate the content of the oxygen vacancies,and in turn the ferroelectric hysteresis loops of the samples.Finally,robust and tunable ferroelectric property is achieved in SC samples with good structural integrity.
基金supported by the Portuguese Foundation for Science and Technology(FCT)in the framework of the Strategic Funding Contract UIDB/04650/2020 and by M-ERA.NET NanOx4EStor Contract no.M-ERA-NET3/0003/2021the Oblivion Supercomputer at university ofévora,funded by the ENGAGE SKA Research Infrastructure(reference POCI-01-0145-FEDER022217-COMPETE 2020 and FCT)+4 种基金by the BigData@UE project(reference ALT20-03-0246-FEDER-000033-FEDER and the Alentejo 2020 Regional Operational Program),for providing HPC resources in the framework of the advanced computing project CPCA/A1/415075/2021 awarded by FCT IPthe financial support through the contract FEDR-POC No.332/390008/29.122020-SMIS 109522the CERIC-ERIC Consortium for access to experimental facilities and financial support under proposals 20202037,20202038 and 20192055supported by the COST Action CA20116-European Network for Innovative and Advanced Epitaxy(OPERA)the Royal Academy of Engineering grant,CIET1819_24,for funding and the ERC grant,EU-H2020-ERC-ADG#882929,EROS
文摘Rhombohedral phase Hf_(x)Zr_(1.x)O_(2)(HZO,x from 0 to 1)films are promising for achieving robust ferroelectric polarization without the need for an initial wake-up pre-cycling,as is normally the case for the more commonly studied orthorhombic phase.However,a large spontaneous polarization observed in rhombohedral films is not fully understood,and there are also large discrepancies between experimental and theoretical predictions.In this work,in rhombohedral ZrO_(2)thin films,we show that oxygen vacancies are not only a key factor for stabilizing the phase,but they are also a source of ferroelectric polarization in the films.This is shown experimentally through the investigation of the structural properties,chemical composition and the ferroelectric properties of the films before and after an annealing at moderate temperature(400℃)in an oxygen environment to reduce the V_(o)concentration compared.The experimental work is supported by density functional theory(DFT)calculations which show that the rhombohedral phase is the most stable one in highly oxygen defective ZrO_(2)films.The DFT calculations also show that V_(o)contribute to the ferroelectric polarization.Our findings reveal the importance of V_(o)for stabilizing rhombohedral ZrO_(2)thin films with superior ferroelectric properties.
基金supported by National Key Research and Development Program(grant 2019YFB2205100)National Science Foundation of China(grant 92064001)。
文摘The finding of the robust ferroelectricity in HfO_(2)-based thin films is fantastic from the view point of both the fundamentals and the applications.In this review article,the current research status of the future prospects for the ferroelectric HfO_(2)-based thin films and devices are presented from fundamentals to applications.The related issues are discussed,which include:1)The ferroelectric characteristics observed in HfO_(2)-based films and devices associated with the factors of dopant,strain,interface,thickness,defect,fabrication condition,and more;2)physical understanding on the observed ferroelectric behaviors by the density functional theory(DFT)-based theory calculations;3)the characterizations of microscopic and macroscopic features by transmission electron microscopes-based and electrical properties-based techniques;4)modeling and simulations,5)the performance optimizations,and 6)the applications of some ferroelectric-based devices such as ferroelectric random access memory,ferroelectric-based field effect transistors,and the ferroelectric tunnel junction for the novel information processing systems.
基金the Natural Science Foundation of Jiangsu Province,China(Grant No.BK20210198)the National Natural Science Foundation of China(Grant No.12204095)+1 种基金the Fundamental Research Funds for the Central Universities(Grant No.2242022R10197)the National Natural Science Foundation of China(Grant No.11834002).
文摘We study the ferroelectricity in a one-dimensional(1D)system composed of a double helix SnIP with absorbing water molecules.Our ab initio calculations reveal two factors that are critical to the electrical polarization.The first one is the orientation of polarized water molecules staying in the R2 region of SnIP.The second one is the displacement of I atom which roots from subtle interaction with absorbed water molecules.A reasonable scenario of polarization flipping is proposed in this study.In the scenario,the water molecule is rolling-up with keeping the magnitude of its electrical dipole and changing its direction,meanwhile,the displacement of I atoms is also reversed.Highly tunable polarization can be achieved by applying strain,with 26.5%of polarization enhancement by applying tensile strain,with only 4%degradation is observed with 4%compressive strain.Finally,the direct band gap is also found to be correlated with strain.
基金Project supported by the National Key Research and Development Program of China(Grant No.2021YFA1200700)the National Natural Science Foundation of China(Grant Nos.T2222025 and 62174053)+5 种基金the Open Research Projects of Zhejiang Laboratory(Grant No.2021MD0AB03)the Shanghai Science and Technology Innovation Action Plan(Grant Nos.21JC1402000 and 21520714100)the Guangdong Provincial Key Laboratory Program(Grant No.2021B1212040001)the Fundamental Research Funds for the Central Universitiessupport from the Zuckerman STEM Leadership ProgramPazy Research Foundation(Grant No.149-2020)。
文摘Hafnium-based ferroelectric films,remaining their ferroelectricity down to nanoscale thickness,present a promising application for low-power logic devices and nonvolatile memories.It has been appealing for researchers to reduce the required temperature to obtain the ferroelectric phase in hafnium-based ferroelectric films for applications such as flexible and wearable electronics.This work demonstrates that a remanent polarization(P_(r))value of>5μC/cm^(2)can be obtained in asdeposited Hf_(0.5)Zr_(0.5)O_(2)(HZO)films that are fabricated by thermal atomic layer deposition(TALD)under low temperature of 250℃.The ferroelectric orthorhombic phase(o-phase)in the as-deposited HZO films is detected by scanning transmission electron microscopy(STEM).This low fabrication temperature further extends the compatibility of ferroelectric HZO films to flexible electronics and avoids the cost imposed by following high-temperature annealing treatments.
基金supported by the National Natural Science Foundation of China(Grant Nos.11904317 and 12204029)the Funding of Leading Innovative and Entrepreneur Team Introduction Program of Zhejiang(Grant No.2020R01002)the Natural Science Foundation of Zhejiang Province(Grant Nos.LY23E020010 and LQ23A040013)。
文摘Two-dimensional(2D)ferroelectric(FE)systems are promising candidates for non-volatile nanodevices.Previous studies mainly focused on 2D compounds.Though counter-intuitive,here we propose several new phases of tellurium with(anti)ferroelectricity.Two-dimensional films can be viewed as a collection of one-dimensional chains,and lone-pair instability is responsible for the(anti)ferroelectricity.The total polarization is determined to be 0.34×10^(-10)C/m for the FE ground state.Due to the local polarization field in the FE film,we show a large Rashba splitting(α_(R)~2 eV·?)with nonzero spin Hall conductivity for experimental detection.Furthermore,a dipole-like distribution of Berry curvature is verified,which may facilitate a nonlinear Hall effect.Because Rashba-splitting/Berry-curvature distributions are fully coupled with a polarization field,they can be reversed through FE phase transition.Our results not only broaden the elemental FE materials,but also shed light on their intriguing transport phenomena.
基金supported by the Key-Area Research and Development Program of Guangdong Province,China (Grant No.2020B0101340001)the National Key Research and Development Program of China (Grant Nos.2021YFA1202900 and 2020YFA0309600)+4 种基金the National Science Foundation of China (Grant Nos.61888102,11834017,1207441,and 12274447)the Strategic Priority Research Program of CAS(Grant Nos.XDB30000000 and XDB33000000)the supports from the Elemental Strategy Initiative conducted by the MEXT,Japan(Grant No.JPMXP0112101001)JSPS KAKENHI(Grant Nos.19H05790,20H00354,and 21H05233)A3 Foresight by JSPS。
文摘Moiré superlattices have emerged as a highly controllable quantum platform for exploration of various fascinating phenomena,such as Mott insulator states,ferroelectric order,unconventional superconductivity and orbital ferromagnetism.Although remarkable progress has been achieved,current research in moiré physics has mainly focused on the single species properties,while the coupling between distinct moiré quantum phenomena remains elusive.Here we demonstrate,for the first time,the strong coupling between ferroelectricity and correlated states in a twisted quadrilayer MoS2moiré superlattice,where the twist angles are controlled in sequence to be ~57°,~0°,and ~-57°.Correlated insulator states are unambiguously established at moiré band filling factors v = 1,2,3 of twisted quadrilayer MoS_(2).Remarkably,ferroelectric order can occur at correlated insulator states and disappears quickly as the moiré band filling deviates from the integer fillings,providing smoking gun evidences of the coupling between ferroelectricity and correlated states.Our results demonstrate the coupling between different moiré quantum properties and will hold great promise for new moiré physics and applications.
基金the National Natural Science Foundation of China(NSFC)(Grant No.12074126)the Foundation for Innovative Research Groups of NSFC(Grant No.51621001)the Fundamental Research Funds for the Central Universities(Grant No.2020ZYGXZR076).
文摘Two-dimensional(2D)ferroelectric compounds are a special class of materials that meet the need for devices miniaturization,which can lead to a wide range of applications.Here,we investigate ferroelectric properties of monolayer group-IV monochalcogenides MX(M=Sn,Ge;X=Se,Te,S)via strain engineering,and their effects with contaminated hydrogen are also discussed.GeSe,GeTe,and GeS do not go through transition up to the compressive strain of-5%,and consequently have good ferroelectric parameters for device applications that can be further improved by applying strain.According to the calculated ferroelectric properties and the band gaps of these materials,we find that their band gap can be adjusted by strain for excellent photovoltaic applications.In addition,we have determined the most stable hydrogen occupancy location in the monolayer SnS and SnTe.It reveals that H prefers to absorb on SnS and SnTe monolayers as molecules rather than atomic H.As a result,hydrogen molecules have little effect on the polarization and electronic structure of monolayer SnTe and SnS.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11974307 and 61574123)Zhejiang Provincial Natural Science Foundation,China(Grant No.D19A040001)+1 种基金the Fundamental Research Funds for the Central Universities of Chinathe 2DMOST,Shenzhen University(Grant No.2018028).
文摘The group-V monolayers(MLs)have been studied intensively after the experimental fabrication of two-dimensional(2D)graphene and black phosphorus.The observation of novel quantum phenomena,such as quantum spin Hall effect and ferroelectricity in group-V elemental layers,has attracted tremendous attention because of the novel physics and promising applications for nanoelectronics in the 2D limit.In this review,we comprehensively review recent research progress in engineering of topology and ferroelectricity,and several effective methods to control the quantum phase transition are discussed.We then introduce the coupling between topological orders and ferroelectric orders.The research directions and outlooks are discussed at the end of the perspective.It is expected that the comprehensive overview of topology and ferroelectricity in 2D group-V materials can provide guidelines for researchers in the area and inspire further explorations of interplay between multiple quantum phenomena in low-dimensional systems.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61471301,61078057,51202195,and 511172183)the Research Fund for the Doctoral Program of Higher Education of China(Grant No.20126102110045)the NPU Foundation for Fundamental Research(Grant Nos.JC201155,JC201271,and JC20120246)
文摘In this paper we report the leakage current, ferroelectric and piezoelectric properties of the YFe O3 film with hexagonal structure, which was fabricated on Si（111） substrate by a simple sol-gel method. The leakage current test shows good characteristics as the leakage current density is 5.4 × 10^-6A/cm^2 under 5 V. The dominant leakage mechanism is found to be an Ohmic behavior at low electric field and space-charge-limited conduction at high electric field region. The P–E measurements show ferroelectric hysteresis loops with small remnant polarization and coercive field at room temperature.The distinct and switchable domain structures on the nanometer scale are observed by piezoresponse force microscopy,which testifies to the ferroelectricity of the YFe O3 film further.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 10875004 and 11005005)the National Basic Research Program of China (Grant No. 2010CB832904)
文摘5-at% Mn-doped and undoped BaTiO3 thin films have been grown under different oxygen partial pressures by Pulsed Laser Deposition （PLD） on platinum-coated sapphire substrates. X-ray diffraction （XRD） measurements for all the thin films reveal a similar polycrystalline single-phase perovskite structure. Ferroelectricity is observed in the Mn-doped and undoped BaTiO3 thin films grown under relatively high oxygen partial pressure. Ferromagnetic coupling of the Mn dopant ions, on the other hand, is only seen in Mn-doped BaTiO3 thin films prepared under low oxygen partial pressure in a wide temperature range from 5 K to 300 K, and is attributed to the enhanced exchange coupling between Mn dopants and electrons at oxygen vacancies. Our results show that the leakage current is decreased with the doped Mn, but increases the dielectric loss and decreases the dielectric constant, and the ferroelectricity is impaired. To produce ferromagnetism, oxygen vacancies are necessary, which unfortunately increase the leakage current. This confirms that the mutual interplay between the ferroelectricity and ferromagnetism can be tuned by exchange coupling of the doped-Mn and oxygen vacancies in the BaTiO3 thin films.
基金supported by the National Natural Science Foundation of China(Grant Nos.61471301,61078057,51172183,51402240,and 51471134)the Specialized Research Fund for the Doctoral Program of Higher Education,China(Grant No.20126102110045)+1 种基金the Natural Science Foundation of Shaanxi Province,China(Grant No.2015JQ5125)the Fundamental Research Funds for the Central Universities,China(Grant No.3102015ZY078)
文摘Multiferroic materials,showing the coexistence and coupling of ferroelectric and magnetic orders,are of great technological and fundamental importance.However,the limitation of single phase multiferroics with robust magnetization and polarization hinders the magnetoelectric effect from being applied practically.Magnetic frustration,which can induce ferroelectricity,gives rise to multiferroic behavior.In this paper,we attempt to construct an artificial magnetically frustrated structure comprised of manganites to induce ferroelectricity.A disordered stacking of manganites is expected to result in frustration at interfaces.We report here that a tri-color multilayer structure comprised of non-ferroelectric La;Ca;MnO;（A）/Pr;Ca;MnO;（B）/Pr;Sr;MnO;（C） layers with the disordered arrangement of ABC-ACBCAB-CBA-BAC-BCA is prepared to form magnetoelectric multiferroics.The multilayer film exhibits evidence of ferroelectricity at room temperature,thus presenting a candidate for multiferroics.
基金Supported by the National Basic Research Program of China under Grant Nos 2011CB921904 and 2012CB927402the National Natural Science Foundation of China under Grant Nos 11074142 and 11021464+1 种基金the Key Project of the Ministry of Education of China under Grant No 309003the Tsinghua TNList Cross-discipline Foundation
文摘Ferroelectric and magnetic properties of Fe1-xMnxV2O4 （0 ≤ x ≤ 0.5） spinels are investigated on the basis of dielectric, polarization, and susceptibility measurements. Ferroeleetric polarization is discovered in collinear ferrimagnetic and Yafet-Kittel magnetic phases for 0.1 ≤ x ≤ 0.4, which can be tuned by a magnetic field. As orbital-active FJ＋ is substituted with Mn2＋, ferroeleetric polarization decreases for 0 ≤ x ≤ 0.4 and disappears for x=0.5. We propose that the two polar components in ferroelectric polarization originate from the exchange striction mechanism and the spin-current model, respectively.
基金supported by the National Natural Science Foundation of China(51172291,11232015,and 11302267)the Fundamental Research Funds for the Central Universities,NCET in University+3 种基金Research Fund for the Doctoral Program of Higher EducationFok Ying Tung FoundationScience and Technology Innovation Project of Guangdong Provincial Education DepartmentGuangdong Natural Science Funds for Distinguished Young Scholar
文摘Nanoscale PbxLa1-,Ti1-x/4O3 （PLT） thin film has been fabricated on Pt／Ti／SiO2／Si substrates by chemical solution deposition （CSD） method. Ferroelectricity of the fresh-made PLT thin film has been clearly detected through piezoelectric force microscopy （PFM） by writing reversible ferroelectric domains. However, PLT thin film also shows off-standard ferroelectric hysteresis loops highly dependent on frequency, indicating large amount of mobile space charges in the film. Subsequent current-voltage （C-V） studies show that sandwich-like Pt／PLT／Pt structure exhibits notable bipolar resistive switching （BRS） characteristics with high stability （〉 103 switching cycles）. It is found that the C-V curves of both high- and low-resistance states have the feature of space-charge-limited current （SCLC） conduction, indicating important roles of defects in the conduction. X-ray photoelectron spectroscopy measurement further verifies that oxygen vacancies based conductive filament mechanism is likely responsible for the observed RS effect. Our demonstration of stable RS effect in the PLT thin film and its possible coupling with ferroelectricity is promising in device development and applications, such as development of ferroelectric-tunable RS memories.
文摘The instability of thin ferroelectric films is discussed based on the close similarity of dielectric properties between bulk Bi-layered perovskites and thin BaTiO<sub>3</sub> films. The dielectric properties of pseudo-two-dimensional layered perovskites suggest that the bulk layered ferroelectric is a good model of ultra-thin ferroelectric film with a few perovskite units, free from any misfit lattice strain. It seems plausible that the ferroelectric interaction is still prominent but shows a crossover from ferroelectric to antiferroelectric along the unique c-axis (perpendicular to the film plane);with decreasing thickness, the ferroelectricity appears within the plane, which results in so-called “canted ferroelectricity”. An extra relaxation mode induced by surface effect of thin films correlates with soft mode, which results in a new intermediate phase between the paraelectric and ferroelectric phases. These evidences may indicate no critical thickness even for ferroelectric ultra- thin films.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51322206 and 11274060)the Natural Science Foundation of Jiangsu ProvinceChina(Grant No.15KJB140009)
文摘Ba（Zr, Ti）O3is a lead-free relaxor ferroelectric. Using the first-principles method, the ferroelectric dipole moments for pure BaTiO3 and Ba（Zr, Ti）O3supercells are studied. All possible ion configurations of Ba Zr0.5Ti0.5O3 and Ba Zr0.25Ti0.75O3 are constructed in a 2 × 2 × 2 supercell. For the half-substituted case, divergence of ferroelectric properties is found from these structures, which greatly depends on the arrangements of Ti and Zr ions. Thus our results provide a reasonable explanation to the relaxor behavior of Ba（Zr, Ti）O3. In addition, a model based on the thermal statistics gives the averaged polarization for Ba（Zr, Ti）O3, which depends on the temperature of synthesis. Our result is helpful to understand and tune the relaxor ferroelectricity of lead-free Ba（Zr, Ti）O3.
基金Project supported by the National Natural Science Foundation of China(Grant No.51872099)the Science and Technology Program of Guangzhou,China(Grant No.2019050001)+2 种基金the Fund from the Guangdong Provincial Key Laboratory of Optical Information Materials and Technology,China(Grant No.2017B030301007)the 111 Projec,Chinasponsored by the Project for Guangdong Province Universities and Colleges Pearl River Scholar Funded Scheme,China(2016)。
文摘Sr-doped Ba_(0.7)La_(0.3)TiO_(3)(BSLTO)thin films are deposited by pulsed laser deposition,and their microstructure,conductivity,carrier transport mechanism,and ferroelectricity are systematically investigated.The x-ray diffraction measurements demonstrate that Sr-doping reduces the lattice constant of BSLTO thin films,resulting in the enhanced phonon energy in the films as evidenced by the Raman measurements.Resistivity-temperature and Hall effect measurements demonstrate that Sr can gradually reduce electrical resistivity while the electron concentration remains almost unchanged at high temperatures.For the films with semiconducting behavior,the charge transport model transforms from variable range hopping to small polaron hopping as the measurement temperature increases.The metalic conductive behaviors in the films with Sr=0.30,0.40 conform to thermal phonon scattering mode.The difference in charge transport behavior dependent on the A-site cation doping,is clarified.It is revealed that the increasing of phonon energy by Sr doping is responsible for lower activation energy of small polaron hopping,higher carrier mobility,and lower electrical resistivity.Interestingly,the piezoelectric force microscopy(PFM)results demonstrate that all the BSLTO films can exhibit ferroelectricity,especially for the room temperature metallic conduction film with Sr=0.40.These results imply that Sr-doping could be a potential way to explore ferroelectric metal materials for other perovskite oxides.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51272078 and 51332007)the State Key Program for Basic Research of China(Grant No 2015CB921202)+2 种基金the Guangdong Provincial Universities and Colleges Pearl River Scholar Funded Scheme,China(2014)the International Science&Technology Cooperation Platform Program of Guangzhou,China(Grant No.2014J4500016)the Program for Changjiang Scholars and Innovative Research Team in University of China(Grant No.IRT1243)
文摘We investigate the resistive switching and ferroelectric polarization properties of high-quality epitaxial BiFeO3 thin films in various temperature ranges. The room temperature current-voltage（I-V） curve exhibits a well-established polarization-modulated memristor behavior. At low temperatures（〈 253 K）, the I-V curve shows an open circuit voltage（OCV）, which possibly originates from the dielectric relaxation effects, accompanied with a current hump due to the polarization reversal displacement current. While at relative higher temperatures（〉 253 K）, the I-V behaviors are governed by both space-charge-limited conduction（SCLC） and Ohmic behavior. The polarization reversal is able to trigger the conduction switching from Ohmic to SCLC behavior, leading to the observed ferroelectric resistive switching. At a temperature of〉 298 K, there occurs a new resistive switching hysteresis at high bias voltages, which may be related to defect-mediated effects.
