Antiferroelectric Research Articles

Antiferroelectric Phase Evolution in HfxZr1-xO2 Thin Film Toward High Endurance of Non-Volatile Memory Devices

In this study, we experimentally and theoretically demonstrated a universal pathway of hysteresis evolution in polarization switching cycling in both antiferroelectric (AFE) and ferroelectric (FE) Hf xZr <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\text {1-x}}\text{O}\,\,_{{2}}$ </tex-math></inline-formula> (HZO) thin films. AFE films can achieve sufficient remnant polarization and high endurance by engineering the evolution process of double hysteresis merge. Based on this, we propose a new strategy for realizing high-endurance AFE films in non-volatile memory devices. Additionally, a record high endurance >10 12 on 6 nm AFE HZO under full polarization switching conditions at 4.5 MV/cm and 1 MHz is achieved to demonstrate the potential of this strategy.

Dielectric Layer Design of Bilayer Ferroelectric and Antiferroelectric Tunneling Junctions Toward 3D NAND-Compatible Architecture

The 3D vertical ferroelectric tunneling junction (FTJ) of bilayer antiferroelectric (AFE) <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathrm {Hf}_{1-x}Zr_{x}\text{O}$ </tex-math></inline-formula> 2(HZO) and Al2O3 has been demonstrated for NAND-compatible feasibility. A bilayer-type FTJ is explored for the designs of the dielectric interlayer Al2O3 0 nm to 4 nm and the ferroelectric type, while the current mechanism is revealed. The multilevel AFE-FTJ is exhibited for both the Program and Erase operations and realizes a synaptic device. High-density emerging memory and computing-in-memory (CiM) are in high demanded for the future era and can be feasible by the proposed vertical FTJ.

Phase and polarization modulation in two-dimensional In2Se3 via in situ transmission electron microscopy.

Phase transitions in two-dimensional (2D) materials promise reversible modulation of material physical and chemical properties in a wide range of applications. 2D van der Waals layered In2Se3 with bistable out-of-plane ferroelectric (FE) α phase and antiferroelectric (AFE) β′ phase is particularly attractive for its electronic applications. However, reversible phase transition in 2D In2Se3 remains challenging. Here, we introduce two factors, dimension (thickness) and strain, which can effectively modulate the phases of 2D In2Se3. We achieve reversible AFE and out-of-plane FE phase transition in 2D In2Se3 by delicate strain control inside a transmission electron microscope. In addition, the polarizations in 2D FE In2Se3 can also be manipulated in situ at the nanometer-sized contacts, rendering remarkable memristive behavior. Our in situ transmission electron microscopy (TEM) work paves a previously unidentified way for manipulating the correlated FE phases and highlights the great potentials of 2D ferroelectrics for nanoelectromechanical and memory device applications.

High Energy Storage Performance in La-Doped AgNbO3 Ceramics via Tape Casting.

AgNbO3-based Pb-free antiferroelectric (AFE) ceramics have attracted increasing interest owing to their excellent potential in energy storage applications. Herein, a high recoverable energy storage density (Wrec) of 7.62 J/cm3 is realized in La-doped AgNbO3 ceramics prepared via tape casting. The high Wrec is attributed to high breakdown strength Eb of 380 kV/cm induced by dense microstructure as well as fine grain size and enhanced AFE stability stemming from M2 phase and reduced tolerance factor t. The high Wrec exceeding 6 J/cm3 was maintained in a wide temperature range of 20-150 °C and exhibited frequency stability with less than 8% variation in a range of 1-200 Hz. The discharge energy density Wd exhibited temperature stability at 30-110 °C with less than 9% variation. Our research provides a good method for producing AgNbO3-based ceramics having high energy storage performances.

Unusual electric polarization behavior in elemental quasi-two-dimensional allotropes of selenium

We investigate tunable electric polarization and electronic structure of quasi-two-dimensional (quasi-2D) allotropes of selenium, which are formed from their constituent one-dimensional (1D) structures through an inter-chain interaction facilitated by the multi-valence nature of Se. Our em ab initio calculations reveal that different quasi-2D Se allotropes display different types of electric polarization, including ferroelectric (FE) polarization normal to the chain direction in alpha and delta allotropes, non-collinear ferrielectric (FiE) polarization along the chain axis in tau-Se, and anti-ferroelectric (AFE) polarization in eta-Se. The magnitude and direction of the polarization can be changed by a previously unexplored rotation of the constituent chains. In that case, an in-plane polarization direction may change to out-of-plane in alpha-Se and delta-Se, flip its direction, and even disappear in tau-Se. Also, the band gap may be reduced and changed from indirect to direct by rotating the constituent chains about their axes in these quasi-2D Se allotropes.

Realizing simultaneously excellent energy storage and discharge properties in AgNbO3 based antiferroelectric ceramics via La3+ and Ta5+ co-substitution strategy

AgNbO3 based antiferroelectric (AFE) ceramics have large maximum polarization and low remanent polarization, and thus are important candidates for fabricating dielectric capacitors. However, their energy storage performances have been still large difference with those of lead-based AFEs because of their room-temperature ferrielectric (FIE) behavior. In this study, novel La3+ and Ta5+ co-substituted AgNbO3 ceramics are designed and developed. The introduction of La3+ and Ta5+ decreases the tolerance factor, reduces the polarizability of B-site cations and increases local structure heterogeneity of AgNbO3, which enhance AFE phase stability and refine polarization-electric field (P–E) loops. Besides, adding La3+ and Ta5+ into AgNbO3 ceramics causes the decrease of the grain sizes and the increase of the band gap, which contribute to increased Eb. As a consequence, a high recoverable energy density of 6.79 J/cm3 and large efficiency of 82.1%, which exceed those of many recently reported AgNbO3 based ceramics in terms of overall energy storage properties, are obtained in (Ag0.88La0.04)(Nb0.96Ta0.04)O3 ceramics. Furthermore, the discharge properties of the ceramic with discharge time of 16 ns and power density of 145.03 MW/cm3 outperform those of many lead-free dielectric ceramics.

Energy storage properties of PLZST-based antiferroelectric ceramics with glass additives for low-temperature sintering

PLZST-based antiferroelectric (AFE) ceramics with high recoverable energy density (Wre) and efficiency (η) can be applied to pulsed power electronic devices. However, this application is constrained by the high sintering temperature (ST, 1250–1320 °C) of the ceramics per se. In this context, this study introduced a new glass phase of Ba2CO3–Al2O3–SiO2–K2CO3 (BASK) into Pb0.95La0.02Sr0.02(Zr0.50Sn0.40Ti0.10)O3 (PLSZST) AFE ceramics by using a traditional solid-state method. By doping 0.5 wt% BASK, the ST of PLSZST ceramics was significantly reduced from 1300 °C to 1020 °C and a high Wre of 3.54 J/cm3 and a high η of 86% were yield, when the electric breakdown strength increased to 230 kV/cm. In addition, a pulse discharge energy density of 2.47 J/cm3, and an extremely fast discharge speed (<0.5 μs), as well as acceptable thermal stabilities of both Wre and η within 30–110 °C temperature range, were achieved. Conclusively, this AFE ceramic composition with glass additives has a great potential to be used in base metal inner-electrode multilayer ceramic capacitors for pulse power applications.

Atomic-scale insight into the tetragonal platelets correlated with the antiferroelectricity in Na0.5Bi0.5TiO3-based materials

The structural origin of antiferroelectric (AFE)-like double P–E loops near the depolarization temperature in lead-free Na0.5Bi0.5TiO3 (NBT)-based materials remains elusive despite decades of study. Here, temperature-dependent ferroelectric properties, Raman spectra, and advanced electron microscopy reveal that the AFE-like behavior in Mn: NBT single crystals is strongly related to the tetragonal phase. The tetragonal platelets oriented along three principle directions of the pseudo-cubic cell with the typical thickness of 1–2-unit cells were visualized at the atomic scale. Special AFE-like dipoles were formed by two antiparallel-polarized tetragonal platelets with a thickness of 2-unit cells, which are separated by a thin non-polar and tilt-free transition layer. Such locally structural components vary in both volume and/or size to a certain extent as changing temperature, chemical composition, and external electric field, phenomenologically showing AFE characteristics. Our study provides the decisive atomic-scale information of tetragonal platelets and establishes a hitherto unobserved AFE-like structure existing in the NBT-based materials.

High‐performance antiferroelectric ceramics via multistage phase transition

AbstractLead‐based antiferroelectric (AFE) ceramics have attracted increasing interest in pulse power systems owing to their high‐energy storage and power densities. However, the single AFE–ferroelectric (FE) phase transition in conventional AFE materials usually leads to premature polarization saturation and low breakdown strength, which are disadvantageous to energy storage performance. In this study, high energy storage performance was achieved in Pb0.94−xLa0.04Cax[Nb0.02(Zr0.99Ti0.01)0.975]O3 (PLCNZT) AFE ceramics by constructing electric‐field‐induced multiple phase transitions. A maximum recoverable energy storage density of 12.15 J/cm3 and a high energy efficiency of 85.4% were obtained for the PLCNZT ceramic with x = 0.03 at 420 kV/cm. These excellent properties are attributed to the AFE–FE Ⅰ‐FE Ⅱ multiple phase transitions induced by Ca2+ doping, which effectively enhances the breakdown strength. This result indicates that field‐induced multiple phase transitions significantly improve the energy storage of AFE materials.

Excellent energy‐storage property and thermal stability of PLZT‐based antiferroelectric ceramics

Abstract(Pb, La)(Zr, Ti)O3 antiferroelectric (AFE) materials are promising materials due to their energy‐storage density higher than 10 J cm−3, but their low energy‐storage efficiency and poor temperature stability limit their application. In this paper, the (1 − x)(Pb0.9175La0.055)(Zr0.975Ti0.025)O3–xPb(Yb1/2Nb1/2)O3 (PLZTYN100x) AFE ceramics were prepared via two‐step sintering method and investigated thoroughly. With the doping of Yb3+ and Nb5+, the phase structure transforms from the orthorhombic phase (AFEO) to the coexistence of the orthorhombic‐and‐tetragonal phases. This structure reduces the free energy difference between the AFE and ferroelectric phases and reduces the fluctuation of energy with temperature, improving the energy storage efficiency and temperature stability. When the x = 0.05 (PLZTYN5), the AFE ceramic exhibits excellent temperature stability and ultrahigh energy storage performance, whose recoverable energy density (Wrec) is 6.8–8.2 J cm−3 at 30 kV mm−1 in the temperature range from −55 to 75°C, and efficiency (ƞ) is 78%–86.7%. In addition, the change of Wrec is less than 15%, exceeding the performance of most AFE ceramics. The results demonstrate that the PLZTYN5 ceramic has great potential in pulse power capacitors.

Revisiting the Kittel’s model of antiferroelectricity: phase diagrams, hysteresis loops and electrocaloric effect

We revisit the Kittel’s model of antiferroelectricity by extending the model to study the phase transitions, hysteresis loop behaviors and electrocaloric effect (ECE) of antiferroelectrics (AFEs). By considering both the first- and second-order AFEs, explicit expressions for the physical and staggered polarizations of AFEs in the stable states are derived. We also obtain the analytical solutions for describing the dielectric susceptibilities of AFEs in the AFE and paraelectric (PE) phases. Coercive fields in AFE are also derived and studied. To verify the usefulness of the Kittel’s model of antiferroelectricity, we apply the model to systematically investigate the phase transitions, hysteresis loops and ECEs of PbZrO3 (PZO). By adopting appropriate values of the Kittel’s parameters for first-order transition, analytical and numerical results are obtained and discussed. Our results show that PZO exhibits a complex temperature (T)—electric field (E) phase diagram, consisting of the AFE, ferroelectrics, ferrielectric, PE and mixed phases. The T-E phase diagram is qualitatively agreed with the new AFE model that was derived based on symmetry by Tolédano and Khalyavin (2019 Phys. Rev. B 99 024105). We found that the calculated zero-field dielectric susceptibility is qualitatively and quantitatively agreed with experimental results. We show that the polarizations and dielectric susceptibilities of PZO in heating and cooling deviate from each other, as expected for the first-order materials. Our calculated results also reveal that the ECE in PZO has an electro-heating of ΔT ≈ +6.5 °C and an electro-cooling of ΔT ≈ −4.0 °C, respectively, which are comparable to the experimental results.

Investigation on antiferroelectricity of Pb0.97La0.02(Hf1−xTix)O3ceramics with low Ti content (0 ≤ x ≤ 0.1)

AbstractPbHfO3was found with antiferroelectricity early and identical to PbZrO3in many aspects but much less attention was received. In the present work, the PbHfO3‐based ceramics with compositions of Pb0.97La0.02(Hf1−xTix)O3(PLHT, 0 ≤ x≤ 0.1) were fabricated, and their antiferroelectricity was investigated. All the compositions have an initially antiferroelectric (AFE) phase and by introducing Ti content, the AFE phase is destabilized. Typical AFE‐like double polarization‐electric field (P–E) loop was observed in compositions with 0 ≤ x≤ 0.08. Whenx= 0.10, the composition is initially AFE but remains ferroelectric (FE) phase after the removal of the external electric field, resulting in an FE‐like singleP–Eloop. The temperature dependence of phase transition and multiple phase transition behavior in PLHT was also studied. This work revealed the antiferroelectricity in PLHT with low Ti content. In addition, the potential application of PLHT for energy storage and conversion was also discussed. A recoverable energy density of 7.1 J/cm3and efficiency of 78.5% were achieved in Pb0.97La0.02HfO3at 300 kV/cm.

Improved anti-ferroelectric properties enabled by high pressure annealing for eDRAM applications

The non-ideal characteristics at the interfaces of anti-ferroelectric (AFE) film and electrodes will greatly affect the potential performance in the way to embedded dynamic random-access memory applications. In this paper, we have proposed a high-performance AFE TiN/HfxZr1−xO2/TiN capacitor fabricated by fully atomic layer deposition grown and alcohol-thermal high-pressure annealing methods that have been employed to avoid exposure to the ambient atmosphere and cure the interface defects induced by the inevitable oxidization of electrodes. Due to the high improvement of the interface quality, the capacitors based on ultra-thin (∼6 nm) AFE film show competitive memory performances, such as low operating voltage (−0.6/1.8 V), high speed (10 ns), long retention time (103 s), and high endurance (1012). The final benchmark demonstrates that the proposed AFE TiN/HfxZr1−xO2/TiN capacitor is a promising candidate toward the next generation high-speed and high-density embedded memory.

A 3D Vertical-Channel Ferroelectric/Anti-Ferroelectric FET With Indium Oxide

A vertical channel ferroelectric-FET (FeFET) with HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -based ferroelectric (Fe-HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) and atomic layer deposition (ALD) Indium oxide (InOx) channel has been developed and demonstrated for 3D high-density memory applications. Reliable memory operation has been confirmed with memory window (MW) >1V in gate length (L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> ) = 50nm short channel FeFETs. Polar-axis transition of Fe-HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> from in- plane in the initial film to out-of-plane after electrical cycling has been verified by both experimental and theoretical studies. A vertical channel anti-ferroelectric (AFe) FET (AFeFET) with ZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> has been also demonstrated by making use of half-loop hysteresis in AFe, which can be a new solution for the weak erase problem seen in oxide semiconductor channel FeFETs.

Study of Structural and Electrical Properties of Li and Nb Modified BNT Thin Film and Observation of Enhanced Electrocaloric Effect near Room Temperature

A detailed investigation was done on Li and Nb modified Bi0.5Na0.5TiO3 (BNT) thin films where structural, dielectric, ferroelectric and electrocaloric properties were studied. All thin films were synthesized using pulsed laser deposition. Structural investigation revealed that addition of Li and Nb do not alter the parent rhombohedral structure and all compositions were observed to have rhombohedral structure. However Ferroelectric and dielectric analysis clearly revealed that addition of Li and Nb affect the Ferroelectric (FE) -Antiferroelectric (AFE) phase transition temperature (T d , depolarization temperature) and bring it down towards the room temperature and consequently a mixed phase of FE and AFE was observed near room temperature for composition x = 0.06. A sudden change in polarization in x = 0.06 composition with increasing temperature, subsequently leading to significantly high (∂P/∂T) E along with FE-AFE transition contributed to large electrocaloric (ΔT) = − 4.32 K in composition x = 0.06 ∼ 35 °C.

Diffuse dielectric behaviors in non-stoichiometric sodium niobate-based ceramics via Bi-substitution

Systematic investigation on the phase transition, dielectric behavior, and ferroelectric property of non-stoichiometric sodium niobate-based antiferroelectric (AFE) ceramics is carried out via Bi-substitution. Doping Bi3+ is capable of adjusting phase transition temperature meanwhile accelerating the formation of polar nanoregions instead of the long-range order structure. The phase transition is identified by the structural Rietveld refinement from the orthorhombic P phase to the pseudo-cubic phase consisting of the P and orthorhombic R phase as Bi3+ dopant increases. The composition regulation shifts the dielectric anomaly to a lower temperature and effectively enhances the relaxor nature. Specifically, associated with the diffuse dielectric relaxation aroused by oxygen vacancy defect, excellent thermal stability is achieved in a wide temperature range from −82 °C to 408 °C. Additionally, the simultaneously significant improvement of the recoverable energy density and efficiency is gained at moderate electric fields. This work makes it an alternative AFE strategy for the application of high-temperature capacitor.

Phase identification and structural evolution in BMT modified NN anti-ferroelectric ceramics

It has been an enormous challenge to obtain double P-E loops and identify structure evolution in NaNbO3 based ceramics. BiMg2/3Ta1/3O3(BMT) modified NaNbO3 ceramics were fabricated by solid-state methods, showing slimmer double P-E loops compared with other reported work. Combined with the Raman and refined XRD results, we confirmed that the coexistence of anti-ferroelectric (AFE) P (Pbma) and ferroelectric (FE) Q (P21ma) phases gradually transformed into the coexistence of AFE R (Pnma) and AFE P phases by adding BMT, and thus, the relaxor behavior and reversible phase transition can be enhanced. TEM analysis demonstrated the coexistence of the P and Q phases in pure NN, verified by the characteristic ¼ and ½ (010) type reflections in the selected area electron diffraction patterns, respectively. The characteristic antiphase boundaries are observed as well-parallel lines with a 6-fold modulation, interrupting the 4-fold P phase. After BMT modification, the high-temperature R phase was stabilized, evidenced by the 1/6 (001) type reflections. Moreover, the domain morphology changes dramatically, illustrated by the complicated network of APBs and the elongated band morphology comprising orientational nanodomains, which indicate a strong structural heterogeneity in the NN-BMT ceramics.

Li+ and Sm3+ co-doped AgNbO3-based antiferroelectric ceramics for high-power energy storage

Ag1-x-3yLixSmyNbO3 (x≤0.05, y≤0.05) (ALSN) antiferroelectric ceramics were successfully prepared via conventional solid-state reaction and sinter routes in oxygen atmosphere for improving the energy storage characteristic of pure AgNbO3. The results indicate that all of the studied compositions display a pure orthorhombic antiferroelectric (AFE) perovskite structure, while their key parameters of electric-field-induced antiferroelectric-ferroelectric transition can be affected by Li+ or/and Sm3+ doping contents. The Sm3+ doping can enhance the stability of antiferroelectric state, giving rise to higher antiferroelectric-ferroelectric transition electric-field (EF and EB), while Li+ doping can reduce EF and EB for Sm3+ doped AgNbO3 with low Sm3+ content (y≤0.03). When co-doping the same amounts of Li+ and Sm3+ at x=y≤0.03, both EF and EB almost remain unchanged. At x=y=0.05, the diffuse phase transition (DPT) behavior of antiferroelectric-paraelectric (AFE-PE) phase transition occurred, resulting in a “slim-like” double-polarization hysteresis with significantly enhanced EF. Due to these features, both Wrec and η are improved compared with pure AgNbO3. The Wrec and η with composition at x=y=0.05 is 2.33 J/cm3 and 58% under applying electric field of 240 kV/cm, respectively. The results suggest that building DPT behavior of AFE-PE phase transition could be an alternative strategy to improve the energy storage characteristic of AgNbO3.

Spark plasma sintered PBLZST ceramics modified by BN nanosheets with significant energy storage density

The progress of antiferroelectric (AFE) ceramics exhibiting outstanding energy storage performance has attracted widespread attention. Nevertheless, for a single material, the energy storage density cannot satisfy the needs for integration and miniaturization of electronic devices. Herein, PBLZST ceramics modified by BN nanosheets via the SPS method are designed. As a result, when 0.1 wt% PB nanosheets are added, 7.9 J/cm3 of excellent recoverable energy storage density (Wrec) can be gathered, and the breakdown strength (BDS) is increased to 318 kV/cm, while that of pure PBLZST ceramics is 202 kV/cm. This outstanding energy storage property is associated with an increase in BDS, which is due to a certain number of insulating second phases with wide bandgaps and low dielectric constants being compounded. Additionally, superior charge–discharge performance can be obtained, including a 5.37-μs discharge rate and 6.81-J/cm3 discharge energy density (Wdis). The experimental outcomes suggest that this study provides in-depth systematic research and an innovative strategy for the further development of energy storage ceramics.

High energy-storage density and efficiency in PbZrO3-based antiferroelectric multilayer ceramic capacitors

The utilization of antiferroelectric (AFE) materials is commonly believed as an effective strategy to improve the energy-storage density of multilayer ceramic capacitors (MLCCs). Unfortunately, the inferior energy conversion efficiency (η) leads to high energy dissipation, which severely restricts the broader applications of MLCCs due to the increased probability of materials and/or devices failure. Herein, AFEs featuring large polarization response and small hysteresis loss are proposed to make up for deficiencies. Guided by this proposal, (Pb0.94La0.04)(Zr0.69Sn0.30Ti0.01)O3 AFE MLCC (abbreviated as M2) are manufactured. An ultrahigh Wrec of 16.1 J/cm3 and an excellent η of 90.9% are achieved simultaneously. Additionally, a great discharge energy density (Wdis) of 8.8 J/cm3 and a large power density (PD) of 165.6 MW/cm3 are obtained synchronously. Noticeably, M2 exhibits excellent frequency-insensitive, temperature-bearable, and fatigue cycle-endurable energy-storage performances and/or charge-discharge properties. These results indicate that M2 has a promising prospect in advanced power electronic and/or pulsed power systems.