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Stabilization of ferroelectric Hf <sub/>x</sub> Zr <sub/>1?x</sub> O <sub/>2</sub> films using a millisecond flash lamp annealing technique
摘要： We report on the stabilization of ferroelectric HfxZr1?xO2 (HZO) films crystallized using a low thermal budget millisecond flash lamp annealing technique. Utilizing a 120 s 375 ?C preheat step combined with millisecond flash lamp pulses, ferroelectric characteristics can be obtained which are comparable to that achieved using a 300 s 650 ?C rapid thermal anneal. X-ray diffraction, capacitance voltage, and polarization hysteresis analysis consistently point to the formation of the ferroelectric phase of HZO. A remanent polarization (Pr) of ～21 μC/cm2 and a coercive field (Ec) of ～1.1 MV/cm are achieved in 10 nm thick HZO layers. Such a technique promises a new alternative solution for low thermal budget formation of ferroelectric HZO films.
关键词： low thermal budget,ferroelectric HfxZr1?xO2 films,remanent polarization,ferroelectric phase,millisecond flash lamp annealing,coercive field
更新于2025-09-04 15:30:14
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Improved Retention Performance in Graphene-Ferroelectric Memory Device Through Mitigation of the Surface Roughness of the Ferroelectric Layer
摘要： A ferroelectric-gated graphene field-effect transistor was fabricated with a bottom-gate structure. A ferroelectric gate dielectric was formed using the spin-coating method. Two samples were made, one with a single coating and the other with a double coating. It was observed that the data retention times of the two samples were significantly different. When comparing the surface roughness, the surface of the thin film produced by the double coating was much flatter. Based on the observation of the surface morphology, an interfacial layer composed of air was deduced as the origin of both the depolarization and short retention time. That is, when fabricating the graphene-ferroelectric memory device, the importance of the interface treatment could be confirmed. Based on these results, it is expected that a much more reliable device can be realized through surface engineering via a graphene-ferroelectric device process.
关键词： Surface Roughness,Graphene,Ferroelectric,Interface
更新于2025-09-04 15:30:14
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[Ceramic Transactions Series] Proceedings of the 12th Pacific Rim Conference on Ceramic and Glass Technology (Ceramic Transactions) || Recent Topics in the Field of Ferroelectric Materials for BME-MLCCs
摘要： The present paper focuses on the recent direction of materials technology for Base Metal Electrode (BME)-Multilayer Ceramic Capacitors (MLCCs). Recently, technologies are accelerating in the area of miniaturization, high capacitance, and reduction of production cost of MLCCs, in order to meet the requirements of the electronics market. In order to maintain high capacitance values with smaller case sizes, reduction in thickness and the multiplication of the dielectric layers have been advancing. Thinning dielectric layers, however, has a deleterious effect on the dielectric performance and it is considered getting closer to dimensional limit. So far, temperature stable MLCCs of high capacitance such as X7R, X7S, and X7T specifications in EIA-STD have been employing BaTiO3 based ferroelectric materials. In the case of BaTiO3 based ferroelectrics, X8R characteristics may be a limit for temperature stable MLCCs, because Curie temperature of BaTiO3 is around 120-130oC. Under these circumstances, numerous studies have been devoted to ferroelectric materials such as giant dielectric constant (K) materials, high TC materials of high K, and high withstanding voltage materials. In this paper, these challenges in the field of dielectric materials for MLCCs are reviewed, and a potential of filled tungsten-bronze-type ferroelectrics for high capacitance BME-MLCCs of X9R specification (ΔC/C25 ±15%, -55~200oC) are proposed.
关键词： BME-MLCCs,X9R specification,ferroelectric materials,tungsten-bronze-type ferroelectrics,BaTiO3
更新于2025-09-04 15:30:14
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Constitutive modeling of polarization relaxation behavior in ferroelectrics
摘要： A thermodynamically consistent model is formulated to depict the polarization hysteresis and the rate-dependent behavior of relaxation in ferroelectric materials. On the relaxation condition, the polarization gradually changes with time while the applied electric field is kept constant. The present model introduces internal state variables to represent such irreversible dissipation processes. Based on the first and second laws of thermodynamics, the evolution laws of the internal state variables consisting of constitutive equations are then derived through the definitions of the Helmholtz free energy and a dissipation potential. To verify the applicability of the constitutive model, numerical simulations are compared with experiment in the literature.
关键词： Constitutive model,Polarization relaxation,Ferroelectric material,Hysteresis
更新于2025-09-04 15:30:14
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Nucleation-Limited Ferroelectric Orthorhombic Phase Formation in Hf <sub/>0.5</sub> Zr <sub/>0.5</sub> O <sub/>2</sub> Thin Films
摘要： Various possibilities have been proposed as the cause of the doped- or undoped-HfO2 thin film materials showing unusual ferroelectricity. These assumptions are based on empirical results, yet finding the origin of the unprecedented ferroelectricity within HfO2 has suffered from a serious gap between its theoretical calculation, mostly based on thermodynamic approach and the actual experimental results. To fill the gap, this study proposes to consider the kinetic energy, providing the evidence of the kinetic energy barrier upon a phase transformation from the tetragonal phase to the monoclinic phase affected by the TiN top electrode (capping layer). 10 nm thick Hf0.5Zr0.5O2 thin films are deposited and annealed with or without the TiN capping layer with subsequent annealing at different time and temperature. Arrhenius plot is constructed to obtain the activation energy for the tetragonal-to-monoclinic phase transformation by calculating the amount of the transformed phase using X-ray diffraction pattern. Johnson–Mehl–Avrami and nucleation-limited transformation models are utilized to describe the characteristic nucleation and growth time and calculate the activation energy for the monoclinic phase transformation of the Hf0.5Zr0.5O2 thin film. Both models demonstrate that the TiN capping layer provides a kinetic energy barrier for tetragonal-to-monoclinic phase transformation and enhances the ferroelectric property.
关键词： ferroelectric thin films,hafnium zirconium oxide,activation energy,nucleation-limited transformation,nucleation and growth transformation kinetics
更新于2025-09-04 15:30:14
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Influence of compositional ratio K/Na on structure and piezoelectric properties in [(Na1?xKx)0.5Bi0.5]Ti0.985Ta0.015O3 ceramics
摘要： [(Na1-xKx)0.5Bi0.5]Ti0.985Ta0.015O3 (abbreviated as Ta-NK100x) lead-free ceramics with good piezoelectric properties were prepared using a solid-state reaction method. The structure and electrical properties of Ta-NK100x had been systemically investigated. The highest bipolar strain of 0.458% and the unipolar strain 0.448% are achieved at x = 0.18 at 60 kV/cm. Meanwhile, the corresponding normalized strain d*33 reaches 747 pm/V. In addition, the unipolar strain of the poled Ta-NK18 increases to 0.537%, and corresponding d*33 increases slightly to 894.5 pm/V at 60 kV/cm. The electric-field-induced phase transition between ferroelectric and relaxor is found to play a dominant role in the origin of the large strain. Moreover, the strain behavior remains stable within 105 switching cycles which indicating the prepared ceramics are promising candidates for actuators and stress sensors.
关键词： ferroelectric,relaxor,solid-state reaction,piezoelectric properties,lead-free ceramics
更新于2025-09-04 15:30:14
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Identification of the nature of traps involved in the field cycling of Hf0.5Zr0.5O2 -based ferroelectric thin films
摘要： The discovery of ferroelectricity in hafnium oxide has revived the interest in ferroelectric memories as a viable option for low power non-volatile memories. However, due to the high coercive field of ferroelectric hafnium oxide, instabilities in the field cycling process are commonly observed and explained by the defect movement, defect generation and field induced phase transitions. In this work, the optical and transport experiments are combined with ab-initio simulations and transport modeling to validate that the defects which act as charge traps in ferroelectric active layers are oxygen vacancies. A new oxygen vacancy generation leads to a fast growth of leakage currents and a consequent degradation of the ferroelectric response in Hf0.5Zr0.5O2 films. Two possible pathways of the Hf0.5Zr0.5O2 ferroelectric property degradation are discussed.
关键词： leakage currents,oxygen vacancies,defects,luminescence,ferroelectric Hf0.5Zr0.5O2
更新于2025-09-04 15:30:14
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Structural, piezoelectric and high-density energy storage properties of lead-free BNKT-BCZT solid solution
摘要： A solid solution of lead-free piezoelectric ceramic (1-x)Bi0.50(Na0.80K0.20)0.50TiO3-xBa0.90Ca0.10Ti0.90Zr0.10O3 (with x=0.00, 0.02, 0.04, 0.06, 0.08) was synthesized by conventional solid-state reaction route. The effect of addition of BCZT on BNKT was investigated on structural, microstructural, dielectric, ferroelectric, piezoelectric and high-density energy storage properties experimentally. Modified Curie Weiss law and Vogel-Fulcher law were employed to study the diffusivity and activation energy. The dielectric dispersion with frequency reveals the relaxor behavior for all compositions. The value of Tv (calculated from Vogel-Fulcher relation) decreases while the corresponding value of Ea increases with the BCZT composition. The unipolar curve shows the increased strain of 0.15% and corresponding ? (Smax/Emax =311 pm/V) for x = 0.02 composition among all studied compositions. Furthermore, compositions x = 0.02 and x = 0.04 shows the improved energy storage efficiency ～50% with respect to pure BNKT.
关键词： Relaxor,Ferroelectric,Vogel-Fulcher,Piezoelectric
更新于2025-09-04 15:30:14
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Structural Aspects at Phase Transitions in Ferroelectric Copolymers of Vinylidenefluoride and Tetrafluoroethylene
摘要： low-voltage Permittivity and conductivity temperature dependences of a ferroelectric copolymer of vinylidenefluoride VDF with tetrafluoroethylene TFE in the ferroelectric to paraelectric phase transition range were investigated. The as received films obtained by crystallization from a solution had the metastable structure shown in particular in coexistence of ferroelectric and paraelectric phases below a Curie point. Temperature dependences of electrical characteristics in the first and second cycles of heating differ. Low glass transition (?40 oC) facilitate intensive micro-Brownian chains mobility in the amorphous phase at ambient temperatures and above. As per the x-ray and spectroscopic data, the first heating cycle will result in a recrystallization process for molecular structure improvement. Asymmetry of temperature dependence of a dielectric susceptibility in a vicinity of “order-disorder” phase change is found out. For the first time paid attention to the fact that for crystalline polymer ferroelectrics interpretation of the parameters of the temperature dependences of the dielectric susceptibility in the cycle of heating near the phase transition point should take into account the possibility of the premelt processes. First the method of IR spectroscopy shows that the melting of ordered structures, emerging secondary crystallization is accompanied by a change of the basic parameters (frequency position, the integral intensity and half-width) component of the doublet of valence vibrations of С-Н groups. Such structural changes lead to the emergence of “anomalies” on the temperature dependences of conductivity.
关键词： conductivity,IR-spectroscopy,phase transitions,Ferroelectric polymers,structure
更新于2025-09-04 15:30:14
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High-resolution angle-resolved lateral piezoresponse force microscopy: Visualization of in-plane piezoresponse vectors
摘要： Piezoresponse force microscopy (PFM) is a widely used tool for ferroelectric domain imaging. Lateral PFM (LPFM) utilizes the torsional vibration mode of a probe cantilever; it can distinguish ferroelectric domains having different polarizations with respect to the axis perpendicular to the cantilever, but it is blind to the parallel axis innately. We introduce a high-resolution angle-resolved-LPFM technique that is capable of visualizing full two-dimensional in-plane piezoresponse vector fields. The LPFM signal is analyzed for each pixel with respect to the sample-probe orientation angle with the aid of an image registration technique, and the corresponding local in-plane piezoresponse vector is deduced from the amplitude and phase of the trigonometric curve fitting. This technique provides a pathway for the visualization of complicated ferroelectric and piezoelectric structures.
关键词： Piezoresponse force microscopy,image registration technique,ferroelectric domain imaging,in-plane piezoresponse vector fields
更新于2025-09-04 15:30:14