Antiferroelectric Thin Films Research Articles

Exploring anti-ferroelectric thin films with high energy storage performance by moderating phase transition

Anti-ferroelectric thin films are renowned for their signature double hysteresis loops and sheds light on the distinguished energy storage capabilities of dielectric capacitors in modern electronic devices. However, anti-ferroelectric capacitors are still facing the dual challenges of low energy density and efficiency to achieve state-of-the-art performance. Their large hysteresis and sharp first-order phase transition usually results in a low energy storage efficiency and easy breakdown, severely obscuring its future application. In this study, we demonstrate that anti-ferroelectric (Pb0.97La0.02)(Zr1−xSnx)O3 epitaxial thin films exhibit enhanced energy storage performance through local structural heterogeneity to moderate the first-order phase transition by calculating the corresponding polarization as a function of switching time for the first time. The films exhibit remarkable enhanced breakdown strength (∼3.47 MV/cm, ∼5 times the value for PbZrO3) and energy storage performance. Our endeavors have culminated in the ingenious formulation of a novel strategy, namely, the postponement of polarization processes, thereby elevating the breakdown strength and total energy storage performance. This landmark achievement has unveiled a fresh vista of investigative opportunities for advancing the energy storage prowess of electric dielectrics.

Superior Piezo-/Ferro-Electricity in Antiferroelectric AgxNbO3-δ Thin Films by Nanopillar Local Structure Design.

Antiferroelectrics are fundamental mother compounds critical in developing innovative lead-free piezoelectrics and ferroelectrics and hold great promise for wide-ranging applications in energy conversion and electronic devices. However, harnessing their superior properties presents a significant challenge due to the delicate balance required between their various states. In this study, through the unique design of nanopillar structures to alleviate the local polar heterogeneity, we have achieved significantly improved piezo-/ferro-electricity in classic lead-free antiferroelectric AgxNbO3-δ (x = 1, 0.9, and 0.8) epitaxial thin films. The effective piezoelectric coefficient reaches 440 pm V-1, 1 order of magnitude larger than the stoichiometric AgNbO3, rivaling classic lead zirconate titanate piezoelectrics. Atomic-scale electron microscopy investigations unravel the underlying mechanisms. The nanopillars, characterized by antisite occupancy of both Ag and Nb atoms and forming out-of-phase boundaries with the matrix, reduce the local crystal symmetry via interphase strain. This leads to the creation of flexible multinanodomain structures that significantly facilitate polarization rotation, thus substantially enhancing the piezoelectric performance. This study demonstrates the feasibility of engineering local heterogeneity through nanopillar design, offering a generally applicable method for property improvement of a wide range of antiferroelectrics.

Novel Two-Terminal Synapse/Neuron Based on an Antiferroelectric Hafnium Zirconium Oxide Device for Neuromorphic Computing.

Functionally diverse devices with artificial neuron and synapse properties are critical for neuromorphic systems. We present a two-terminal artificial leaky-integrate-fire (LIF) neuron based on 6 nm Hf0.1Zr0.9O2 (HZO) antiferroelectric (AFE) thin films and develop a synaptic device through work function (WF) engineering. LIF neuron characteristics, including integration, firing, and leakage, are achieved in W/HZO/W devices due to the accumulated polarization and spontaneous depolarization of AFE HZO films. By engineering the top electrode with asymmetric WFs, we found that Au/Ti/HZO/W devices exhibit synaptic weight plasticity, such as paired-pulse facilitation and long-term potentiation/depression, achieving >90% accuracy in digit recognition within constructed artificial neural network systems. These findings suggest that AFE HZO capacitor-based neurons and WF-engineered artificial synapses hold promise for constructing efficient spiking neuron networks and artificial neural networks, thereby advancing neuromorphic computing applications based on emerging AFE HZO devices.

Giant negative electrocaloric effect in modified PbZrO3 antiferroelectric thin films doped with Mn

Negative charge card refrigeration, as a new solid-state refrigeration technology, has garnered much interest with its broad application potential in the area of temperature control for sensors and electronic devices. In this study, antiferroelectric thin films of Pb1−xMnxZrO3 (x = 0.0%, 0.5%, 1.0%, 2.0%, abbreviated as PMZ-100x) were prepared on tin oxide doped with fluorine/glass substrates by the sol-gel method. When the variable temperature P–E loops under various applied electric fields are compared, the P–E loops gradually change from linear to typical double P–E loops. This result implies that temperature and electric field work together to induce the phase change. The negative electrocaloric effect of the PMZ-0.5 film is greatly enhanced at 50 °C, 444 kV/cm, ΔS = 16.75 J·K−1·kg−1, ΔT = −16.39 K, in comparison to the PbZrO3 film (ΔS = 11.84 J·K−1·kg−1, ΔT = −12.48 K at 75 °C, 421 kV/cm). The great cooling performance indicates that PMZ-100x films have excellent potential for use in integrated circuit solid-state cooling.

Revealing the phase transition scenario in antiferroelectric thin films by x-ray diffuse scattering

There is no consensus among researchers regarding how phase transitions occur in antiferroelectric (AFE) epitaxial heterostructures, in particular, in heterostructures based on model AFE lead zirconate. The questions about the number of phase transitions in such films and by what mechanism they occur remain controversial. This paper presents a look at the phase transition scenario in two types of epitaxial heterostructures: PbZrO3/Ba[La–Sn]O3/MgO (001) thin films with thicknesses from 25 to 1000 nm and PbZrO3/SrRuO3/SrTiO3 (001) thin film 100 nm thick using the diffuse x-ray scattering in the grazing incidence setup. We register the characteristic butterfly-shaped diffuse scattering (DS) intensity distribution in the HK pseudocubic planes, which corresponds to the anisotropic ferroelectric soft mode. No incommensurate soft mode was observed in the cuts of reciprocal space parallel to the film surface by diffuse scattering. We reproduce the shape of DS distribution at different temperatures by the model based on the dielectric stiffness and the electric polarization correlation tensor in the cubic approximation. Such modeling allows not only to characterize the DS parameters from the challengingly low signal-to-background data set, but also to extract experimentally the sensitivity of the materials with respect to inhomogeneous polarization. While the observed temperature evolution of DS is consistent with the dielectric measurements, the correlation between the DS and the phase transition sequence observed by superstructure reflections is yet to be understood better.

Antiferroelectric domain modulation enhancing energy storage performance by phase-field simulations

Antiferroelectric materials represented by PbZrO3(PZO) have excellent energy storage performance and are expected to be candidates for dielectric capacitors. It remains a challenge to further enhance the effective energy storage density and efficiency of PZO-based antiferroelectric films through domain engineering. In this work, the effects of three variables, misfit strain between the thin film and substrate, defect dipoles doping, and film thickness, on the domain structure and energy storage performance of PZO-based antiferroelectric materials are comprehensively investigated via phase-field simulations. The results show that applying tensile strain to the films can effectively increase the transition electric field from antiferroelectric to ferroelectric. In addition, the introduction of defect dipoles while applying tensile strain can significantly reduce the hysteresis and improve energy storage efficiency. Ultimately, a recoverable energy density of 38.3 J/cm3 and an energy storage efficiency of about 89.4% can be realized at 1.5% tensile strain and 2% defect dipole concentration. Our work provides a new idea for the preparation of antiferroelectric thin films with high energy storage density and efficiency by domain engineering modulation.

Clamping enables enhanced electromechanical responses in antiferroelectric thin films.

Thin-film materials with large electromechanical responses are fundamental enablers of next-generation micro-/nano-electromechanical applications. Conventional electromechanical materials (for example, ferroelectrics and relaxors), however, exhibit severely degraded responses when scaled down to submicrometre-thick films due to substrate constraints (clamping). This limitation is overcome, and substantial electromechanical responses in antiferroelectric thin films are achieved through an unconventional coupling of the field-induced antiferroelectric-to-ferroelectric phase transition and the substrate constraints. A detilting of the oxygen octahedra and lattice-volume expansion in all dimensions are observed commensurate with the phase transition using operando electron microscopy, such that the in-plane clamping further enhances the out-of-plane expansion, as rationalized using first-principles calculations. In turn, a non-traditional thickness scaling is realized wherein an electromechanical strain (1.7%) is produced from a model antiferroelectric PbZrO3 film that is just 100 nm thick. The high performance and understanding of the mechanism provide a promising pathway to develop high-performance micro-/nano-electromechanical systems.

Highly area-selective atomic layer deposition of device-quality Hf1-xZrxO2 thin films through catalytic local activation

Area-selective atomic layer deposition (AS-ALD) has garnered significant attention as a promising bottom-up patterning process for sub-10 nm scale technology, offering unmatched atomic-scale precision and pattern alignment capabilities in 3D nanofabrication. In this study, we present a groundbreaking methodology for achieving highly selective deposition of Hf1-xZrxO2 (HZO) thin films through catalytic local activation on noble metal surfaces (Ru and Pt) and TiN surfaces, without the need for surface inhibitory materials. To achieve inherent selectivity on metal surfaces, we employ O2 gas as a mildly oxidizing reactant and utilize cyclopentadienyl-tris(dimethylamido)-hafnium(zirconium) [Hf(Zr)Cp(NMe2)3] precursors, which require strong oxidizing agents, for HZO film formation. By catalytically dissociating O2 molecules, we successfully achieved area-selective deposition of HZO films greater than ∼7 nm on both blanket Ru versus Si substrates and Pt/Si-patterned substrates. Furthermore, we demonstrate the selective deposition of antiferroelectric HZO thin films with high dielectric constants of 34 and 31 on Ru and TiN substrates, respectively, using the inherent AS-ALD method combined with post-ozone treatment. Importantly, this catalytic local activation approach for achieving inherent deposition selectivity expands the potential utility of 3D bottom-up nanopatterning processes in next-generation nanoelectronic applications.

Improved energy storage properties through multilayer stacking of relaxor ferroelectric and antiferroelectric thin films

Abstract Multilayers of relaxor ferroelectric (Pb0.92La0.08Zr0.52Ti0.48O3) and antiferroelectric (Pb0.96La0.04Zr0.98Ti0.02O3) thin films were fabricated on Pt/Ti/SiO2/Si substrates by Chemical Solution Deposition (CSD) method. The properties of the independent relaxor ferroelectric (RFE denoted as R) and antiferroelectric (AFE denoted as A) thin films were compared with their various stack configurations made by alternatively coating the R and A layers in the patterns of R/A, R/A/R, R/A/R/A/R/A, A/R, A/R/A, and A/R/A/R/A/R. The crystallographic studies confirmed the coexistence of both RFE and AFE phases in the multilayer stacks which was further verified by electrical characterizations. The multilayer stack showed improved power density (PD), energy efficiency (η), and reduced dielectric loss compared to individual R and A films. Among all the multilayer configurations, the stack with A/R/A/R/A/R layer exhibited significant improvement in energy efficiency (94%) which is higher than the reported results so far on multilayer structures.

The differences in phase transition characteristics of antiferroelectric PbZrO3 thin films via grain size engineering

PbZrO3 (PZO) possesses a unique antiferroelectric-ferroelectric (AFE-FE) phase transition under an external electric field and engages more attention in understanding and regulating the phase transition behavior. In this work, changing annealing temperature (600–750 °C) and ultralow content (5‰) ions doping are used to optimize the phase transition of PZO films via grain size engineering. As annealing temperature increases, the maximum polarization Pmax increases but forward/backward switching fields EF/EA reduce accompanied by the average grain size enhances from 622 to 686 nm. Following, 5‰ mol aliovalent ion La3+ or K+ doped PZO-650 films both enhance Pmax and EF/EA indicating the strengthened antiferroelectricity, and meanwhile the grain size enhances to ∼800 nm. A high discharge density of 31 J/cm3 is achieved for 5‰ mol La-doped PZO films at a low electric field of 1 MV/cm, which is ∼100 % higher than those of pure PZO films at different annealing temperatures. This work compares the phase transition characteristics changes in PZO films by changing annealing temperature and ultra-low content ion doping strategy, which would provide new thinking in grain size-engineered antiferroelectric materials for energy storage applications.

Ultralow operating voltage for energy conversion performance in Hf1–xZrxO2 thin films

Emerging ferroelectric and antiferroelectric HfO2-based thin films are attractive candidates for energy conversion and storage applications. In this work, the polar phase transformation between tetragonal and orthorhombic phases associated with ferroelectric or antiferroelectric behaviors is utilized to manipulate the electrocaloric cooling and energy storage performances in Zr-doped, woken up HfO2 ultrathin films. A giant electrocaloric temperature change of up to 11.85 K in Hf0.5Zr0.5O2 with the morphotropic phase boundary (MPB) state and a high energy storage density of 39.34 J/cm3 in the tetragonal phase-dominant Hf0.25Zr0.75O2 system are obtained. More interestingly, contrary to overdoping and excessive electric fields, an appropriate Zr concentration of 0.5 and an applicable driving field of 1.91 MV/cm are desired for the electrocaloric effect, resulting in an ultralow operating voltage as low as 1.3 V in this 6.8 nm thick Hf0.5Zr0.5O2 film. These findings illustrate that the structural design strategy is a visible method for achieving optimal energy-related behaviors and highlight the great possibilities for building future energy-related devices.

High‐Throughput Exploration of Phase Evolution in (Pb1−XBaX)ZrO3 Thin Films

AbstractAntiferroelectric thin films hold significant potential for bringing novel physics phenomena and fascinating properties. Their applications are often intertwined with the antiferroelectric‐ferroelectric phase transition, which is contingent on the chemical compositions of the constituent material. Nevertheless, the prevailing trial‐and‐error‐based research methodology is ill‐suited for the exploration of the relationship between chemical compositions and the antiferroelectric‐ferroelectric phase transition. To address this challenge, a high‐throughput synthesis strategy for antiferroelectric thin films is presented, which is enabled by an advanced high‐throughput pulsed laser deposition technology. The effectiveness of this synthesis strategy using (Pb1−XBaX)ZrO3 and achieving precise control over the parameter X is showcased. This approach allows for the deposition of (Pb1−XBaX)ZrO3 thin films encompassing nine chemical compositions ranging from X = 0 to X = 0.08. Based on this high‐throughput method, the composition that corresponds to the phase transition of (Pb1−XBaX)ZrO3, falling within the range of X = 0.04 to X = 0.06 is pinpointed. Furthermore, a temperature‐dependent correlation between the phase transition and chemical composition is established. This work not only presents a practical routine for establishing a comprehensive map of material chemical composition in relation to the properties of antiferroelectric thin films but also offers a method for the high‐throughput exploration of complex oxide thin films.

Energy storage performance and piezoelectric response of silver niobate antiferroelectric thin film

AgNbO3-based antiferroelectric materials have attracted extensive attention in energy storage due to their double polarization-electric field hysteresis loops, but they always suffer from low breakdown strength (Eb). Films with few defects and small thickness exhibit high breakdown strength, which helps to improve energy storage performance. In the present work, an AgNbO3 film with a small thickness of ∼200 nm is prepared via pulsed laser deposition, which has a dense microstructure and a small average grain size of ∼34.5 nm. The AgNbO3 film displays an antiferroelectric nature, as confirmed by the double polarization-electric field hysteresis loops at room temperature. The room temperature phase structure of the AgNbO3 film determined by the dielectric behaviour is the antiferroelectric M2 phase. Due to the small thickness and fine grain size, a high Eb of 1200 kV/cm is obtained, which boosts a recoverable energy storage density (Wrec) of 9.3 J/cm3 and an energy efficiency (η) of 63.7 % in the AgNbO3 film. In addition, Wrec exhibits good temperature stability at 30–120 °C. The AgNbO3 film shows an obvious piezoelectric response after the electric field-induced antiferroelectric-ferroelectric phase transition as confirmed by piezoresponse force microscopy. These results provide guidance for the development of AgNbO3 antiferroelectric films and devices with good energy storage performance.

Improved energy storage density in La-doped PbZr0.95Ti0.05O3 films with stress regulation

The Pb1–1.5xLaxZr0.95Ti0.05O3 films with different La3+ contents were successfully prepared on the LaNiO3/SiO2/Si substrates by sol-gel method. The effect of La3+ doping on the microstructure, electrical properties, and energy storage performance of the films are systematically investigated. It is found that the introducing of La3+ with a smaller tolerance factor could enhance the lattice distortion and compressive stresses, leading to smaller grain size, slimmer electric hysteresis loops, and lower phase transition field hysteresis. As a result, a relatively high energy storage density of 30.2 J/cm3 together with the energy storage efficiency of 62.2% has been achieved in Pb0.82La0.12Zr0.95Ti0.05 antiferroelectric thin films with the optimum doping content. This improvement is largely attributed to the enhanced breakdown field strength from 1442 kV/cm to 1564 kV/cm as a result of grain size reduction. Our results demonstrate the crucial role of decreased tolerance factor in stabilizing the antiferroelectric phase and enhancing the phase transition electric field, and provide an effective route to enhance the energy storage performance of antiferroelectric thin films.

High energy storage of PbZrO3 antiferroelectric thin films via constructing phase composition

In this paper, we fabricated PbZrO3 (PZ) thin films by the way of sol–gel spin on LaNiO3 buffered SiO2/Si substrates, and annealed them at different given temperatures by rapid thermal annealing (RTA). By controlling annealing temperature, PZ thin films showed different microstructures and phase compositions, whose impact of electrical properties and energy storage performance were researched. According to the research findings, the phase composition of film presents a general rule with the decrease of annealing temperature: PZ thin films crystallize into perovskite phase, pyrochlore phase, and amorphous phase. The films annealed at 620 °C crystallized into a state of coexistence of pyrochlore phase and perovskite phases, which also show moderate recoverable energy density and the highest energy storage efficiency (8.7 J cm−3 and 93.1%). This energy storage performance can be attributed to the synergistic effect of high electric breakdown strength of dense pyrochlore phase structure and high maximum polarization of perovskite phase. The findings of this paper help to explain the influence of pyrochlore phase on the energy storge performance of thin films. Thus, it is useful way to improve the energy storage performance of thin films.

Low voltage–driven high-performance thermal switching in antiferroelectric PbZrO 3 thin films

Effective control of heat transfer is vital for energy saving and carbon emission reduction. In contrast to achievements in electrical conduction, active control of heat transfer is much more challenging. Ferroelectrics are promising candidates for thermal switching as a result of their tunable domain structures. However, switching ratios in ferroelectrics are low (<1.2). We report that high-quality antiferroelectric PbZrO 3 epitaxial thin films exhibit high-contrast (>2.2), fast-speed (<150 nanoseconds), and long-lifetime (>10 7 ) thermal switching under a small voltage (<10 V). In situ reciprocal space mapping and atomistic modelings reveal that the field-driven antiferroelectric-ferroelectric phase transition induces a substantial change of primitive cell size, which modulates phonon-phonon scattering phase space drastically and results in high switching ratio. These results advance the concept of thermal transport control in ferroic materials.

Phase stability and energy storage properties of polycrystalline antiferroelectric BaTiO3-substituted NaNbO3 thin films

Lead-free sodium niobate (NN) thin films with varying barium titanate (BT) content and 1 mol% manganese were deposited on platinized silicon substrates by chemical solution deposition. Microstructural analysis reveals a change in nucleation mechanism, and X-ray diffraction and Raman spectroscopy confirmed a composition-driven antiferroelectric (AFE) to ferroelectric (FE) phase transition at 0.01 < x < 0.03, providing a stability interval for the AFE phase despite increasing the tolerance factor. The thin films show well-shaped ferroelectric response under applied electric field, indicating an irreversible field-induced phase transition. The composition with 7 mol% BaTiO3 showed the most promising energy storage properties (Wrec ∼5.7 J/cm3 and 68% efficiency (η)), along with excellent thermal stability up to 120 °C and largely improved cyclic stability up to 5 * 106 bipolar cycles. These findings highlight the potential of NN-based thin films as lead-free candidates for energy storage, emphasizing the importance of stabilizing the AFE phase under electric fields for practical applications.

Effect of Sn4+ doping on antiferroelectric and energy storage properties of PbHfO3 thin films prepared by a sol-gel process

Antiferroelectric materials possess excellent energy storage capacity, fatigue resistance, and high thermal stability. This study successfully prepared PbHf1-xSnxO3 (x = 0.5%, 1.0%, 1.5%, 2.0%, abbreviated as PHS-100x) antiferroelectric thin films on fluorine-doped tin oxide (FTO)/glass substrates using the sol-gel method. The polarization-electric field hysteresis (P–E) loops were utilized to reflect the AFE characteristics. These findings demonstrate that the PHS-1.0 thin film exhibited exceptional energy storage performance with a recoverable energy storage density (Wrec) of 30.91 J/cm3 and an energy storage efficiency (η) of 75.8% at room temperature (RT) and an electric field of 1670 kV/cm. P–E loops tests (30–130 °C) indicated that the PHS-1.0 film possessed good temperature stability. Additionally, the PHS-1.0 film displayed outstanding fatigue resistance under 880 kV/cm, with a minor decrease in Wrec from 23.93 to 20.20 J/cm3 and in η from 72.93 to 71.21% after 108 cycles of testing. These results suggest that PHS-100x films hold great potential for use in pulsed power systems.

Highly compatible and reliable ZrN interfacial layer between TiN top electrode and antiferroelectric ZrO2 thin film to boost the electrocaloric behavior

A highly compatible and reliable ZrN interfacial layer with different cycles of atomic layer deposition was inserted between the TiN top electrode and antiferroelectric (AFE) ZrO2 thin film to achieve low oxygen vacancies and high crystallinity of the ZrO2 thin film, boosting the AFE and electrocaloric (EC) characteristics of TiN/ZrO2/TiN metal–insulator–metal (MIM) capacitors. An outstanding adiabatic temperature change (ΔT) of − 21 K was realized for devices with a ZrN interfacial layer of nine cycles, which can be ascribed to the reduction in redox between the TiN and ZrO2 for the suppression of interfacial dead layer during annealing as confirmed via high-angle annular dark field images and interfacial capacitance measurement. Hence, the reliability of ZrO2 MIM capacitors with a nine-cycle ZrN interfacial layer was examined with a negligible change in AFE and EC behaviors after a cycling endurance test of 106 cycles, exhibiting great potential for future applications in solid-state cooling.

Curvature-dependent strain-induced photoluminescence modulations in flexible Er-doped Pb0.98La0.02Zr0.95Ti0.05O3 antiferroelectric thin films prepared by the sol-gel method

Tunable photoluminescence (PL) has wide applications in optical waveguides and communication. Since the PL intensity is strongly dependent on the crystal field symmetry, curvature-dependent strain-induced PL modulation is expected in flexible antiferroelectric (AFE) thin film materials. Here, flexible Er-doped Pb0.98La0.02Zr0.95Ti0.05O3 (PLZT) AFE thin films were prepared via the sol-gel method. A giant and reversible PL intensity modulation (482%) was achieved during the bending process. Based on density functional theory (DFT) calculations and Raman spectra measurements, the relationship amongst the curvature-dependent strains, crystal structure, and PL modulation was discussed. The induced strain leads to lattice distortion and even a phase transition, both of which contribute to the reduction in crystal symmetry and thus significantly enhance the PL intensity.