Ferroelectric Research Articles

Bulk photovoltaic effect in ferroelectric nematic liquid crystals

Bulk photovoltaic effect in ferroelectric nematic liquid crystals

Oxygen vacancy engineering in Si-doped, HfO2 ferroelectric capacitors using Ti oxygen scavenging layers

In this paper, the ferroelectric properties of TiN/Ti/Si:HfO2/TiN stacks are shown to be modulated by the Ti oxygen scavenging layer, leading to improved remanent polarization and wake-up at low switching fields. Hard x-ray photoelectron spectroscopy is used to measure the oxygen vacancy (VO) concentration in Si-doped HfO2 based capacitors. This VO engineered ferroelectric stack is then assessed at the wafer scale within 16 kbit 1T-1C FeRAM arrays integrated into 130 nm CMOS. The introduction of a Ti oxygen scavenging layer at the top interface of Si:HfO2-based BEOL-integrated metal/ferroelectric/metal capacitors enhances their ferroelectric (FE) behavior (+100% remanent polarization 2.Pr), confirming the positive role of modest concentrations of VO in orthorhombic phase crystallization at low thermal budgets. It is statistically demonstrated at 16 kbit array level that VO-rich FE Si:HfO2 facilitates 2.5 V FeRAM array operation with improved memory window. The field cycling dependence of the memory window is correlated with the VO concentration, and an endurance of 108 cycles is measured at the array level.

Maximizing the Synaptic Efficiency of Ferroelectric Tunnel Junction Devices Using a Switching Mechanism Hidden in an Identical Pulse Programming Learning Scheme

Memristors play a pivotal role in advanced computing, with memristor‐based crossbar arrays showing promise for various artificial neural networks. Among these, HfO2‐based ferroelectric tunnel junctions (FTJs) stand out as ideal synaptic devices for neuromorphic computing. Their compatibility with the complementary metal oxide semiconductor process and intrinsic energy efficiency make them particularly appealing. While an increasing number of studies adopt identical pulse programming (IPP) with short width to update the conductance of HfO2‐based FTJs synaptic devices, conventional ferroelectric switching models fall short in describing updates the conductance with the IPP scheme. Consequently, studies achieving conductance updates via IPP lack an underlying mechanism explanation, potentially limiting the application of HfO2‐based FTJs as synaptic devices. This study explores the potential of ferroelectric Zr‐doped HfO2 (HZO) FTJs to undergo learning through the IPP scheme. Synaptic characteristics, including the number of conductance states, symmetry, linearity, write energy, and latency by modulating IPP scheme conditions are optimized. Finally, the applicability of HZO FTJ as a synaptic device by assessing learning accuracy in pattern recognition through artificial neural network simulation based on the optimized synaptic characteristics is evaluated.

Ferroelectric proximity effects in two-dimensional FeSeTe

Recent studies have shown that proximity effects are able to substantially modulate the superconducting properties of various quasi-two-dimensional layered materials such as FeSe, FeSeTe, NbSe2, and NbS2. Due to their high surface charge concentration and high dielectric constants, ferroelectric materials provide an interesting avenue for inducing proximity effects in layered superconductors. In this study, we explore the interactions between FeSeTe and the two-dimensional ferroelectrics CuInP2S6 and CuInP2Se6. We found that contrary to the normal behavior of FeSeTe, FeSeTe/CuInP2S6, and FeSeTe/CuInP2Se6 heterostructures display a peculiar two-step superconducting transition. Further testing revealed a hysteresis loop in the IV curves of these samples when measured below the critical temperature indicating the presence of disorder and domains within FeSeTe. We conclude that these domains are responsible for the two-step transition in FeSeTe and hypothesize that they are induced by the domain structure of the aforementioned ferroelectric materials.

An energy efficient way for quantitative magnetization switching

Recent advancements in electrically controlled spin devices have been made possible through the use of multiferroic systems comprising ferroelectric (FE) and ferromagnetic (FM) materials. This progress provides a promising avenue for developing energy-efficient devices that allow for electrically controlled magnetization switching. In this study, we fabricated spin orbit torque (SOT) devices using multiferroic composites and examined the angular dependence of SOT effects on localized in-plane strain induced by an out-of-plane electric field applied to the piezoelectric substrate. The induced strain precisely modulates magnetization switching via the SOT effect in multiferroic heterostructures, which also exhibit remarkable capability to modulate strain along different orientations – a feature with great potential for future applications in logic device arrays. To investigate the influence of electric fields on magnetization switching, harmonic Hall measurements, synchrotron-powered x-ray magnetic circular dichroism-photoemission electron microscopy (XMCD-PEEM), x-ray diffraction (XRD), magnetic force microscopy (MFM), and micromagnetic simulation were conducted. The results demonstrate that electric-field-induced strain enables precise control of SOT-induced magnetization switching with significantly reduced energy consumption, making it highly suitable for next-generation spin logic devices.

Fast selective edge-enhanced imaging with topological chiral lamellar superstructures

Abstract Edge detection is a fundamental operation for feature extraction in the image processing. All-optical method arouses growing interest owing to its ultra-fast speed, low energy consumption and parallel computation. However, current optical edge detection is generally limited to static devices and fixed functionality. Herein, we propose a fast-switchable scheme based on a ferroelectric liquid crystal topological structure. The self-assembled chiral lamellar superstructure, directed by the azimuthally-variant photo-alignment agent, can be dynamically controlled by the polarity of external electric field, and respectively generates the vector beams with nearly orthogonal polarization distribution. Even after thousands of cycles, horizontal and vertical edges of the object are selectively enhanced with an ultra-fast switching time of about 57 μs. Broadband edge-enhanced imaging is efficiently demonstrated. This work extends the ingenious building of topological heliconical superstructures, and offers an important glimpse into their potentials in the emerging frontiers of optical computing for artificial intelligence.

Mapping Ferroelectric Fields Reveals the Origins of the Coercivity Distribution.

Better techniques for imaging ferroelectric polarization would aid the development of new ferroelectrics and the refinement of old ones. Here we show how scanning transmission electron microscope (STEM) electron beam-induced current (EBIC) imaging reveals ferroelectric polarization with obvious, simply interpretable contrast. Planar imaging of an entire ferroelectric hafnium zirconium oxide (Hf0.5Zr0.5O2, HZO) capacitor shows an EBIC response that is linearly related to the polarization determined in situ with the positive-up, negative-down (PUND) method. The contrast is easily calibrated in MV/cm. The underlying mechanism is magnification-independent, operating equally well on micrometer-sized devices and individual nanoscale domains. Coercive-field mapping reveals that individual domains are biased "positive" and "negative", as opposed to being "easy" and "hard" to switch. The remanent background E-fields generating this bias can be isolated and mapped. Coupled with STEM's native capabilities for structural identification, STEM EBIC imaging provides a revolutionary tool for characterizing ferroelectric materials and devices.

New Solitary Waves for Thin-Film Ferroelectric Material Equation Arising in Dielectric Materials

Abstract In this paper, the thin-film ferroelectric material equation (TFFME), which enables the propagation of solitary polarisation in thin-film ferroelectric materials is investigated, will be expressed through the non-linear evolution models. Ferroelectrics are dielectric materials that explain wave propagation non-linear demeanors. The non-linear wave propagation form is administrated by TFFME. To investigate the characterisations of new waves and solitonic properties of the TFFME, the modified exponential Jacobi technique and rational exp(−ϕ(η))-expansion technique are used. Plenty of alternative responses may be achieved by employing individual formulas; each of these solutions is offered by some plain graphs. The validity of such schemes and solutions may be exhibited by assessing how well the relevant schemes and solutions match up. The effect of the free variables on the manner of acting of reached plots to a few solutions in the exact forms was also explored depending upon the nature of non-linearities. The descriptive characteristics of the reached results are presented and analysed by some density, two- and three-dimensional figures. We believe that our results would pave the way for future research generating optical memories based on non-linear solitons.

First-principles predictions of HfO2-based ferroelectric superlattices

The metastable nature of the ferroelectric phase of HfO2 is a significant impediment to its industrial application as a functional ferroelectric material. In fact, no polar phases exist in the bulk phase diagram of HfO2, which shows a dominant non-polar monoclinic ground state. As a consequence, ferroelectric orthorhombic HfO2 is stabilized either kinetically or via epitaxial strain. Here, we propose an alternative approach, demonstrating the feasibility of thermodynamically stabilizing polar HfO2 in superlattices with other simple oxides. Using the composition and stacking direction of the superlattice as design parameters, we obtain heterostructures that can be fully polar, fully antipolar or mixed, with improved thermodynamic stability compared to the orthorhombic polar HfO2 in bulk form. Our results suggest that combining HfO2 with an oxide that does not have a monoclinic ground state generally drives the superlattice away from this non-polar phase, favoring the stability of the ferroelectric structures that minimize the elastic and electrostatic penalties. As such, these diverse and tunable superlattices hold promise for various applications in thin-film ferroelectric devices

Superfine Nanodomain Engineering Unleashing Ferroelectricity in Incipient Ferroelectrics.

Incipient ferroelectrics have emerged as an attractive class of functional materials owing to their potential to be engineered for exotic ferroelectric behavior, holding great promise for expanding the ferroelectric family. However, thus far, their artificially engineered ferroelectricity has fallen far short of rivaling classic ferroelectrics. In this study, we address this challenge by developing a superfine nanodomain engineering strategy. By applying this approach to representative incipient ferroelectric of SrTiO3-based films, we achieve unprecedentedly strong ferroelectricity, not only surpassing previous records for incipient ferroelectrics but also being comparable to classic ferroelectrics. The remanent polarization of the thin film reaches up to 17.0 μC cm-2 with an ultrahigh Curie temperature of 973 K. Atomic-scale investigations elucidate the origin of this robust ferroelectricity in the emergent high-density superfine nanodomains spanning merely 3-10 unit cells. Combining experimental results with theoretical assessments, we unveil the underlying mechanism, where the intentionally introduced diluted foreign Fe element creates a deeper Landau energy well and promotes a short-range ordering of polarization. Our developed strategy significantly streamlines the design of unconventional ferroelectrics, providing a versatile pathway for exploring new and superior ferroelectric materials.

Spin Hall effect in doped ferroelectric HfO2

The spin Hall effect (SHE) enables charge-to-spin conversion by electrical means and is promising for spintronic applications. Here, we report on the intrinsic spin Hall effect in the prototypical ferroelectric material HfO2 with charge doping using density functional theory calculations and theoretical analysis. We show that ferroelectric displacements are insensitive to charge doping and are sustained up to a large doping concentration of 0.4 electrons or holes per unit cell volume. In addition, the large spin Hall conductivity in the vicinity of the band edges is well preserved. Intriguingly, we demonstrate the giant spin Hall efficiency characterized by the sizable spin Hall angle of ∼0.1 in doped HfO2. These results add unexplored functionality to ferroelectric HfO2 and open opportunities for potential device applications.

Design of polar boundaries enhancing negative electrocaloric performance by antiferroelectric phase-field simulations

Electrocaloric refrigeration which is environmentally benign has attracted considerable attention. In distinction to ferroelectric materials, which exhibit an extremely high positive electrocaloric effect near the Curie temperature, antiferroelectric materials represented by PbZrO3 have a specific negative electrocaloric effect, i.e., electric field decreases the temperature of the materials. However, the explanation of the microscopic mechanism of the negative electrocaloric effect is still unclear, and further research is still needed to provide a theoretical basis for the negative electrocaloric effect enhancement. Herein, the antiferroelectric phase-field model has been proposed to design polar boundaries enhancing antiferroelectric negative electrocaloric performance in PbZrO3-based materials. Based on this, we have simulated the polarization response and domain switching process of the temperature and electric field-induced antiferroelectric—ferroelectric phase transition. It is shown that the temperature range tends to increase as the density of polar boundaries increases from the antiferroelectric stripe domain, polymorphic domain to the nanodomain. Among them, the peak adiabatic temperature change of antiferroelectric nanodomains can reach −13.05 K at 84 kV/cm, and a wide temperature range of about 75 K can be realized at 42 kV/cm. We expect these discoveries to spur further interest in the potential applications of antiferroelectric materials for next-generation refrigeration devices.

Hybrid mechanism of electrical breakdown in ferroelectric materials under high-pressure shock loading

The unique ability of ferroelectrics to generate high voltage under shock loading is limited by electrical breakdown within the shock-compressed ferroelectric material. Breakdown is a hybrid process of initiation and growth. The possible mechanisms of electrical breakdown in ferroelectric films and bulk ceramics subjected to high-pressure shock loading are discussed and experiments designed to elucidate which mechanisms govern breakdown. Gigapascal shock loading experiments were performed on poled Pb0.99(Zr0.95Ti0.05)0.98Nb0.02O3 ferroelectric film specimens in the range of 32–156 μm thickness to determine the dependence of the breakdown field on thickness and on film specimens in the range of 4–16 mm length to determine the dependence of the breakdown field on the duration of shock compression. The resulting breakdown-field vs thickness and breakdown-field vs shock transit time dependencies are consistent with a hybrid electron emission initiation and Joule heating microchannel growth mechanism. Further analysis of data previously obtained on shock-compressed 0.27Pb(In1/2Nb1/2)O3–0.47Pb(Mg1/3Nb2/3)O3–0.26PbTiO3 ferrvoelectric single crystals and Pb(Zr0.65Ti0.35)O3, Pb0.99(Zr0.52Ti0.48)0.99Nb0.01O3, Pb0.99(Zr0.95Ti0.05)0.98Nb0.02O3 bulk ceramics is consistent with this dual mechanism. It appears that neither chemical composition nor microstructure (single crystal vs polycrystalline) of the ferroelectric material has a significant effect on the breakdown mechanism in shocked ferroelectrics.

Enhanced Performance of Self-Powered Ga2O3/ZnO:V Heterojunction Solar-Blind Ultraviolet Photodetectors by Coupling Ferroelectricity and Piezoelectricity.

Ferroelectric materials have aroused increasing interest in the field of self-powered ultraviolet (UV) photodetectors (PDs) for their switchable spontaneous polarization. However, the utilization of ferroelectric materials to modulate the built-in electric field and energy band at the junction interface has rarely been investigated. Herein, we design and fabricate self-powered solar-blind UV PDs based on a Ga2O3/ZnO:V heterojunction. The performance of the Ga2O3/ZnO:V PD is significantly enhanced through the reasonable coupling of ferroelectricity and piezoelectricity within the ZnO:V film. The device at 260 nm exhibits excellent photoelectric properties with high peak responsivity of 64.5 mA/W, a specific detectivity of 3.8 × 1010 Jones, and a rise/decay time of 1.9/45.2 μs, together with reproducibility and stability. Systematical energy band diagram analysis reveals that the excellent performance of Ga2O3/ZnO:V PD can be attributed to the driving forces arising from the addition of the depolarization field and piezoelectric field, which increases the intensity of built-in electric field and promotes the separation and transport of photogenerated carriers at the heterojunction interface. The findings of our research provide a novel avenue and valuable guidance for the design of high-performance self-powered photodetectors.

Accelerating ferroelectric materials discovery through high-throughput first-principles screening and experimental validation

Abstract We conducted high-throughput screening of ferroelectrics using first-principles calculations based on an existing crystal structure database. We focused on nonpolar structures with polar instability, to efficiently screen materials for their potential to undergo ferroelectric phase transitions from oxide materials in crystal structure databases. Our screening criteria included computational feasibility (excluding partial occupation), the absence of hazardous elements, and a maximum of 250 atoms in the conventional cell. Through this screening, we identified 47 ferroelectric candidates, 8 of which have already been reported as ferroelectrics. To validate our screening approach, we synthesized and evaluated several candidate materials with Dion-Jacobson-type structures and measured their dielectric and ferroelectric properties. Although the ferroelectric behavior was not initially identified in these materials, our experiments confirmed their properties. 
Finally, we discovered a new ferroelectric material, CsCa2Nb3O10, which exhibited a ferroelectric phase transition at 28 K, clearly demonstrating the effectiveness of our screening strategy.

Accelerating ferroelectric materials discovery through high-throughput first-principles screening and experimental validation

Abstract We conducted high-throughput screening of ferroelectrics using first-principles calculations based on an existing crystal structure database. We focused on nonpolar structures with polar instability, to efficiently screen materials for their potential to undergo ferroelectric phase transitions from oxide materials in crystal structure databases. Our screening criteria included computational feasibility (excluding partial occupation), the absence of hazardous elements, and a maximum of 250 atoms in the conventional cell. Through this screening, we identified 47 ferroelectric candidates, 8 of which have already been reported as ferroelectrics. To validate our screening approach, we synthesized and evaluated several candidate materials with Dion-Jacobson-type structures and measured their dielectric and ferroelectric properties. Although the ferroelectric behavior was not initially identified in these materials, our experiments confirmed their properties. 
Finally, we discovered a new ferroelectric material, CsCa2Nb3O10, which exhibited a ferroelectric phase transition at 28 K, clearly demonstrating the effectiveness of our screening strategy.

Comparative study on the stability of ferroelectric polarization of HfZrO2 and AlScN thin films over the depolarization effect

This study investigates the stability of the (Hf,Zr)O2 (HZO) and AlScN thin films against the depolarization effect. In order to adversely interfere with the polarization screening of ferroelectric (FE) film and induce the depolarization effect, an Al2O3 film was inserted between the TiN bottom electrode and the FE film. Subsequently, to minimize charge injection through Al2O3 films, the double remanent polarization–voltage (2Pr–V) curve was measured employing voltage pulses with 1 μs-length. As the thickness of the Al2O3 film increased, the charge injection through the Al2O3 film decreased, leading to a decrease in the slope of the 2Pr–V curve. The magnitude of the depolarization field applied to the FE film was determined by simulating the 2Pr–V curve using an equivalent circuit model. Subsequently, the proportion of reversed domains during the delay period due to the depolarization effect was measured. It was revealed that HZO films exhibited vulnerability to the depolarization effect, with 16% of domains being reversed. On the other hand, AlScN films demonstrated superior stability, with polarization loss of less than 1%. Ultimately, it was revealed that AlScN films demonstrated superior stability against the depolarization effect compared to HZO films due to their higher coercive field and more uniform polarization distribution across the film area.

Comparative study on the stability of ferroelectric polarization of HfZrO2 and AlScN thin films over the depolarization effect

This study investigates the stability of the (Hf,Zr)O2 (HZO) and AlScN thin films against the depolarization effect. In order to adversely interfere with the polarization screening of ferroelectric (FE) film and induce the depolarization effect, an Al2O3 film was inserted between the TiN bottom electrode and the FE film. Subsequently, to minimize charge injection through Al2O3 films, the double remanent polarization–voltage (2Pr–V) curve was measured employing voltage pulses with 1 μs-length. As the thickness of the Al2O3 film increased, the charge injection through the Al2O3 film decreased, leading to a decrease in the slope of the 2Pr–V curve. The magnitude of the depolarization field applied to the FE film was determined by simulating the 2Pr–V curve using an equivalent circuit model. Subsequently, the proportion of reversed domains during the delay period due to the depolarization effect was measured. It was revealed that HZO films exhibited vulnerability to the depolarization effect, with 16% of domains being reversed. On the other hand, AlScN films demonstrated superior stability, with polarization loss of less than 1%. Ultimately, it was revealed that AlScN films demonstrated superior stability against the depolarization effect compared to HZO films due to their higher coercive field and more uniform polarization distribution across the film area.

Nonlinear Optical Effects in Europium Melilite Eu2MgSi2O7

Crystals of the family of tetragonal, non‐centrosymmetric melilites have attracted interest as nonlinear optical, piezoelectric, and ferroelectric materials. This work presents an ab initio study of the optical properties of europium melilite, Eu2MgSi2O7. The study includes the calculation of refractive and absorption spectra, with respect to the density of states of the system. The obtained results demonstrate the correlation between the electronic structure of europium melilite and its optical characteristics.

Nonlinear Optical Effects in Europium Melilite Eu2MgSi2O7

Crystals of the family of tetragonal, non‐centrosymmetric melilites have attracted interest as nonlinear optical, piezoelectric, and ferroelectric materials. This work presents an ab initio study of the optical properties of europium melilite, Eu2MgSi2O7. The study includes the calculation of refractive and absorption spectra, with respect to the density of states of the system. The obtained results demonstrate the correlation between the electronic structure of europium melilite and its optical characteristics.