Cyclic Electric Field Research Articles

Electric Field Cycling of Physisorbed Antibodies Reduces Biolayer Polarization Dispersion

AbstractThe electric dipoles of proteins in a biolayer determine their dielectric properties through the polarization density P. Hence, its reproducibility is crucial for applications, particularly in bioelectronics. Biolayers encompassing capturing antibodies covalently bound at a biosensing interface are generally preferred for their assumed higher stability. However, surface physisorption is shown to offer advantages like easily scalable fabrication processes and high stability. The present study investigates the effects of electric‐field (EF)‐cycling of anti‐Immunoglobulin M (anti‐IgM) biolayers physisorbed on Au. The impact of EF‐cycling on the dielectric, optical, and mechanical properties of anti‐IgM biolayer is investigated. A reduction of the dispersion (standard deviation over a set of 31 samples) of the measured P values is observed, while the set median stays almost constant. Hence, physisorption combined with EF cycling, results in a biolayer with highly reproducible bioelectronic properties. Additionally, the study provides important insights into the mechanisms of dielectric rearrangement of dipole moments in capturing biolayers after EF‐cycling. Notably, EF‐cycling acts as an annealing process, driving the proteins in the biolayer into a statistically more probable and stable conformational state. Understanding these phenomena enhances the knowledge of the properties of physisorbed biolayers and can inform design strategies for bioelectronic devices.

Mechanisms for enhanced ferroelectric properties in ultra-thin Hf0.5Zr0.5O2 film under low-temperature, long-term annealing

To gain insight into the ferroelectric mechanisms under reduced thermal budget and thickness scaling, a 4.6 nm ultra-thin ferroelectric Hf0.5Zr0.5O2 capacitor compatible with back-end-of-line (BEOL) processes (all conducted at temperatures ≤350 °C) is investigated in this work. Through O3 pretreatment at the bottom electrode (BE) interface and controlled temperature modulation of the crystalline phase, the capacitor exhibits exceptional ferroelectric (FE) properties following low-temperature (350 °C) and long-term (300 s) rapid thermal annealing (RTA). These properties include high remanent polarization (2Pr ∼ 28.53 μC/cm2), low coercive voltage (Vc ∼ 0.43 V), effective leakage suppression, robust endurance (∼1010 cycles without hard breakdown), and a desirable high dielectric constant. The main mechanisms identified include tetragonal phase nucleation under enhanced tensile stress via the oxidized BE layer (TiO2), crystalline growth controlled through RTA temperature modulation, and phase transition to the ferroelectric orthorhombic phase under electric field cycling. This research provides valuable insights for the development of BEOL-compatible nonvolatile FE memories.

Lead-free ferroelectrics with giant unipolar strain for high-precision actuators

The trade-off between electrostrain and strain hysteresis for piezo/ferroelectric materials largely restrains the development of high precision actuators and remains unresolved over the past few decades. Here, a simple composition of (Bi0.5Na0.5)1-x/100Srx/100TiO3 in the ergodic relaxor state is collaboratively designed through the segregated domain structure with the ferroelectric core, local polarization heterogeneity, and defect engineering. The ferroelectric core can act as a seed to facilitate the field-induced nonpolar-to-polar transition. Together with the internal bias field caused by defect dipoles and adjusted through electric field cycling and heat treatment technology, a giant unipolar strain of 1.03% is achieved in the x = 30 ceramic with a low hysteresis of 27%, while the electric-field-independent large-signal piezoelectric strain coefficient of ~1000 pm/V and ultralow hysteresis of <10% can be obtained in the x = 35 ceramic. Intriguingly, the low-hysteresis high strain also exhibits near-zero remnant strain, excellent temperature and cycling stability.

Effects of quenching on domain switching and electric field-induced phase transformations in Na0.5Bi0.5TiO3-NaNbO3 ceramics

Quenching from high temperatures has been identified as a useful means to enhance the piezoelectric properties and thermal stability of bismuth-based perovskite ferroelectrics. In the present work, it is demonstrated that quenching leads to improvement of depolarization temperature, ferroelectric and piezoelectric properties in Na0.5Bi0.5TiO3-NaNbO3 (NBT-0.1NN) ceramics. In-situ synchrotron x-ray diffraction measurements indicated an irreversible transformation from cubic to coexisting cubic and rhombohedral phases during the application of a high electric field, for both as-sintered and quenched ceramics. These results confirm the non-ergodic relaxor ferroelectric nature of the materials. DC poling induced a transformation to single-phase rhombohedral structure in both cases, with highly textured domain configurations. These well-oriented ferroelectric domain states were relatively stable under subsequent bipolar electric field cycling. For the pre-poled NBT-0.1NN ceramics, the quenched samples were found to exhibit the highest intrinsic (lattice strain) and extrinsic (domain switching) contributions to electrostrain, due to the increased rhombohedral distortion.

In situ grazing incidence synchrotron x-ray diffraction studies on the wakeup effect in ferroelectric Hf0.5Zr0.5O2 thin films

The discovery of ferroelectricity in HfO2 ultrathin films has gathered considerable interest from the microelectronic industry owing to their compatibility with complementary metal oxide semiconductor technology. However, a significant challenge in utilizing HfO2 thin films for commercial devices is the wakeup effect, which is an increase in polarization with the number of electric field cycles in HfO2-based capacitors. Despite efforts to develop wakeup-free HfO2 thin films, the root cause of this effect remains elusive. Some studies attribute it to the tetragonal (T) to orthorhombic (O) phase transformation, while others suggest it is due to the redistribution of oxygen vacancies within the HfO2 layer during electric field cycling. This study investigated the phase transformation dynamics and oxygen vacancy distributions in TiN/Hf0.5Zr0.5O2/TiN capacitors subjected to electric field cycling using in situ grazing incidence synchrotron x-ray diffraction and ex situ x-ray photoelectron spectroscopy. The as-grown HZO films were crystallized in a mixed phase consisting of monoclinic (M), tetragonal, and orthorhombic fractions. The T-phase volume fraction decreased continuously up to 10k electric field cycles. In contrast, the O-phase fraction increased within the first 100 cycles and then stabilized with further cycling. The redistribution of oxygen vacancies occurred continuously throughout the cycling process. The results revealed that continuous oxygen vacancy redistribution during electric field cycling resulted in phase transformation between the T-, O-, and M-phases. The study provides insight into the phase transformation dynamics and oxygen vacancy redistribution in TiN/Hf0.5Zr0.5O2/TiN capacitors during electric field cycling, shedding light on the underlying mechanisms of the wakeup effect.

Large Polarization of Hf₀.₅Zr₀.₅Oₓ Ferroelectric Film on InGaAs With Electric-Field Cycling and Annealing Temperature Engineering

Large Polarization of Hf₀.₅Zr₀.₅Oₓ Ferroelectric Film on InGaAs With Electric-Field Cycling and Annealing Temperature Engineering

Pure ZrO2 Ferroelectric Thin Film for Nonvolatile Memory and Neural Network Computing.

The recent discovery of ferroelectricity in pure ZrO2 has drawn much attention, but the information storage and processing performances of ferroelectric ZrO2-based nonvolatile devices remain open for further exploration. Here, a ZrO2 (∼8 nm)-based ferroelectric capacitor using RuO2 oxide electrodes is fabricated, and the ferroelectric orthorhombic phase evolution under electric field cycling is studied. A ferroelectric remnant polarization (2Pr) of >30 μC/cm2, leakage current density of ∼2.79 × 10-8 A/cm2 at 1 MV/cm, and estimated polarization retention of >10 years are achieved. When the ferroelectric capacitor is connected with a transistor, a memory window of ∼0.8 V and eight distinct states can be obtained in such a ferroelectric field-effect transistor (FeFET). Through the conductance manipulation of the FeFET, a high object image recognition accuracy of ∼93.32% is achieved on the basis of the CIFAR-10 dataset in the convolutional neural network (CNN) simulation, which is close to the result of ∼94.20% obtained by floating-point-based CNN software. These results demonstrate the potential of ferroelectric ZrO2 devices for nonvolatile memory and artificial neural network computing.

Ferroelectric and electric field cycling properties of un-doped HfO2 films

As the most promising candidate material for nonvolatile memories, premature occurrence of fatigue phenomenon for ferroelectric HfO2 film has no appropriate solution method. In this paper, HfO2/Y/HfO2 films were deposited with reactive magnetron sputtering and realized ferroelectric property after wake-up process even if without doping and post-metallization annealing (PMA). Different with uniform or symmetrical distribution, oxygen vacancies concentrated in the film middle, resulting in a longer migration path and tardy fatigue. Fatigue appeared after the electric field cycling of 109 in HfO2 film inserted with 0.6 nm metal Y, which is obviously higher than films deposited by other methods. The remanent polarization of un-doped HfO2 films inserted with 0.6 and 1.5 nm metal Y interlayer is 11.8 and 14.8 μC/cm2, respectively. The results provide a method for to improve cycling property and confirm the important role of oxygen vacancies in wake-up and fatigue phenomenon for HfO2 films.

Investigation of the large-signal electromechanical behavior of ferroelectric HfO2–CeO2 thin films prepared by chemical solution deposition

Investigation of the large-signal electromechanical behavior of ferroelectric HfO2–CeO2 thin films prepared by chemical solution deposition

Evaluation of ferroelectric profile of poly(vinylidene fluoride‐co‐trifluoroethylene) (P(VDF‐TrFE)) thin films by positive‐up–negative‐down and fatigue measurement

Organic polymers are of interest due to their numerous promising potential applications in the area of energy harvesting and sensing. In this context, piezoelectric and ferroelectric polymers are subject to intense research; however, it is challenging to understand polarization switching in such systems. The focus of the present study is to thoroughly evaluate the finer details of polarization reversal in poly(vinylidene fluoride‐co‐trifluoroethylene) (P(VDF‐TrFE)) thin films. The intrinsic features arising from the true values of (switching) polarization and extrinsic features associated with the presence of non‐switching contributions, i.e. leakage current and linear dielectric component, have been investigated using the positive‐up–negative‐down technique. These contributions are quantified and discussed. Furthermore, fatigue endurance has been examined by repeated switching cycles. Increase in polarization increases is associated with the improved crystallinity and enhancement of the β‐phase. However, a higher degree of crystallinity, for extended numbers of repeated cycles of the bipolar electric field, resulted in degradation of the (switching) polarization. Fatigue significantly affects the leakage and ferroelectric components while the paraelectric contribution remains almost constant. The underlying mechanism of such trends are discussed in terms of hysteresis losses. © 2023 Society of Industrial Chemistry.

P(VDF-TrFE-CFE) polymer based electrocaloric device design for battery cooling

Electrocaloric (EC) cooling has the potential to be an alternative to traditional cooling methods. The polyvinylidene fluoride-trifluoro ethylene-chlorofluoroethylene terpolymer (P(VDF-TrFE-CFE) is used as electrocaloric material. A 3D equation-based modeling and finite element simulations are performed for EC cooling, where the battery's heat generation is considered a heat source for analysis. The electric field waveform has been varied to obtain the maximum possible ECE. Electric field cycles with 0.3 sec holding provide the maximum EC temperature change. The magnitude of the electric field is also varied and a maximum adiabatic temperature change of 5.41 K is achieved under 100 MV/m. The EC effect shows that the heat transfer from the source (battery surface) to the sink (environment) is faster than without EC.

Examining the ferroelectric characteristics of aluminum nitride‐based thin films

AbstractThe discovery of ferroelectricity in AlN‐based thin films, including Al1‐xScxN and Al1‐xBxN, over the past few years has spurred great research interests worldwide. In this review, we carefully examined the latest developments for these ferroelectric films with respect to alloy composition, temperature, film thickness, deposition condition, and fatigue endurance by electric field cycling. Looking ahead, there is an urgent need to resolve the challenge of large current leakage faced by these films, which necessitates a combined efforts from both simulations and experiments to identify the root cause and eventually come up with engineering strategies to suppress such leakage. In addition, overcoming the thickness scaling challenge to push ferroelectric thin film down to a few nanometers for better device miniaturization will also be of great interest. Considering the somewhat unexpected discovery of AlN‐based thin films with potential ferroelectric application, we believe that it will be also rewarding to further explore other III‐V‐based semiconductor materials.

Enhanced Switching Reliability of Hf0.5Zr0.5O2 Ferroelectric Films Induced by Interface Engineering.

Ferroelectric materials have been widely researched for applications in memory and energy storage. Among these materials and benefiting from their excellent chemical compatibility with complementary metal-oxide-semiconductor (CMOS) devices, hafnia-based ferroelectric thin films hold great promise for highly scaled semiconductor memories, including nonvolatile ferroelectric capacitors and transistors. However, variation in the switched polarization of this material during field cycling and a limited understanding of the responsible mechanisms have impeded their implementation in technology. Here, we show that ferroelectric Hf0.5Zr0.5O2 (HZO) capacitors that are nearly free of polarization "wake-up"─a gradual increase in switched polarization as a function of the number of switching cycles─can be achieved by introducing ultrathin HfO2 buffer layers at the HZO/electrodes interface. High-resolution transmission electron microscopy (HRTEM) reveals crystallite sizes substantially greater than the film thickness for the buffer layer capacitors, indicating that the presence of the buffer layers influences the crystallization of the film (e.g., a lower ratio of nucleation rate to growth rate) during postdeposition annealing. This evidently promotes the formation of a polar orthorhombic (O) phase in the as-fabricated buffer layer samples. Synchrotron X-ray diffraction (XRD) reveals the conversion of the nonpolar tetragonal (T) phase to the polar orthorhombic (O) phase during electric field cycling in the control (no buffer) devices, consistent with the polarization wake-up observed for these capacitors. The extent of T-O transformation in the nonbuffer samples is directly dependent on the duration over which the field is applied. These results provide insight into the role of the HZO/electrodes interface in the performance of hafnia-based ferroelectrics and the mechanisms driving the polarization wake-up effect.

Evolving electromechanical properties of defect engineered Pb(Zr,Ti)O3-based piezoceramics

Chemical modification is the frequently-adopted strategy to enhance the electromechanical properties of piezoelectric ceramics. However, chemically modified piezoelectric materials will inevitably produce point defects, such as dopant ions, oxygen vacancies, etc. In this study, we investigated the properties of defect-engineered Pb(Zr,Ti)O3 (denoted by PSZT–Fe) polycrystals after aging, quenching, poling, and de-aging processes. At the same time, a general mechanism on the strength of defect dipole is also put forward to explain the corresponding changes. After aging, the spontaneous polarization of PSZT-Fe can be changed instantly upon application of external electric field, but the defect dipole and its defect symmetry can’t change simultaneously. Therefore, after the external electric field is removed, the defective dipole would drive the electric domain back to its original state, resulting in restorable strain effect and macroscopic pinch polarization. Bipolar electric field cycling can effectively redistribute oxygen vacancies to a random state, so that the aged PSZT-Fe can recover the electrical properties of typical ferroelectrics, similar to quenched samples. The spontaneous polarization and defect dipole in the poled PSZT-Fe ceramics are driven by an external electric field parallel to each other, which results in the emergence of internal bias field, accounting for the asymmetric hysteresis loop.

Structural origin of excellent fatigue resistance in KNN-based ceramics with multiphase coexistence

By constructing polymorphic multiphase coexistence, excellent piezoelectric properties and fatigue resistance have been obtained in potassium sodium niobate (KNN)-based ceramics, which was considered with great potential to replace lead-based ceramics. However, the potential structural origin and physical mechanism for the improvement of fatigue resistance are worth further exploration. Here, two kinds of KNN ceramics with orthorhombic phase and rhombohedral-orthorhombic-tetragonal mixed-phase were designed to investigate the fatigue behavior as well as the behind contributing factors. Excellent fatigue resistance under cyclic electric field was found in ceramic with multi-phase coexistence, but the ceramic with orthorhombic phase shows obvious electrical fatigue. Through analyzing the macro-meso-micro structure before and after fatigue, the multiphase coexistence state, stable microstructure and easily rotated miniaturized domains synergistic contributed to the enhancement of fatigue stability. On the contrary, the performance degradation of orthorhombic one is due to the blocked and pinned large size domains during the fatigue process as well as the microstructure damage.

Polarity effects on wake‐up behavior of Al0.94B0.06N ferroelectrics

AbstractWurtzite ferroelectric materials are promising candidates for energy‐efficient memory technologies, particularly for applications requiring high operating temperatures. Asymmetric wake‐up behaviors, in which the polarization reversal depends both on polarity and cycle number for the first few dozen cycles, must be better understood for reliable device operation. Here, the detailed analysis of the asymmetric wake‐up behavior of thin film Al0.94B0.06N was performed combining time‐resolved switching measurements with Rayleigh analysis, piezoelectric measurements, and etching experiments of progressively switched samples. The analysis shows that the gradual opening of the polarization hysteresis loops associated with wake‐up is driven by a gradual increase in the domain‐wall density and/or domain‐wall mobility with electric field cycle to the polarity opposite to the growth polarity. The insights of this discovery will help to guide interface and polarity design in the eventual deployment of reliable devices based on these materials.

Computational simulations of spatio—temporal plasma dynamics in a very high frequency capacitively coupled reactor

Abstract The standing wave effect in Very High Frequency Capacitively Coupled Plasma (VHF CCP) reactors is a major cause of plasma non-uniformity. The nonlinearly excited higher harmonics exacerbate this non-uniformity. In this work we analyze the physical mechanisms of plasma—electromagnetic wave coupling in detail for a single RF cycle of the input electric field. We consider a simplified CCP reactor geometry operated at 100 mTorr and computationally simulate three cases where the bulk electron density increases from order 1015 m−3 to 1017 m−3. We see the appearance of higher harmonics in the B-dot signal with increasing bulk electron density in accordance with recent experimental measurements. By looking at the spatio-temporal variations of different quantities at a periodic steady state, we observe significant changes in the dynamics of current flow, electromagnetic power deposition and ionization rates within the reactor. In particular, as the electron density increases, we see that the current profile in the bulk plasma exhibits a re-circulation pattern that is correlated with the appearance of structural features in the B-dot signal seen in the measurements.

Role of Defects in the Breakdown Phenomenon of Al1-xScxN: From Ferroelectric to Filamentary Resistive Switching.

Aluminum scandium nitride (Al1-xScxN), with its large remanent polarization, is an attractive material for high-density ferroelectric random-access memories. However, the cycling endurance of Al1-xScxN ferroelectric capacitors is far below what can be achieved in other ferroelectric materials. Understanding the nature and dynamics of the breakdown mechanism is of the utmost importance for improving memory reliability. The breakdown phenomenon in ferroelectric Al1-xScxN is proposed to be an impulse thermal filamentary-driven process along preferential defective pathways. For the first time, stable and robust bipolar filamentary resistive switching in ferroelectric Al1-xScxN is reported. A hot atom damage defect generation model illustrates how filament formation and ferroelectric switching are connected. The model reveals the tendency of the ferroelectric wurtzite-type Al1-xScxN system to reach internal symmetry with bipolar electric field cycling. Defects generated from bipolar electric field cycling influence both the energy barrier between the polarization states and that required for the filament formation.

High-κ Hf0.3Zr0.7O2 film with morphotropic phase boundary for DRAM capacitor by controlling H2O dose

For the miniaturization of dynamic random-access memory (DRAM), it is necessary to obtain low equivalent oxide thickness (EOT) and low leakage capacitor materials with complementary metal-oxide semiconductor (CMOS) process compatibility. Herein, we explore the influence of the dose of H2O reactants on the phase structure and electrical characteristics of Hf0.3Zr0.7O2 (HZO) thin films during the atomic layer deposition (ALD). By controlling the H2O dose as well as other conditions including inserting alumina, adjusting annealing temperature and electric field cycling, a high dielectric constant of ∼45 (EOT ∼ 0.54 nm) and low leakage current density (<7.7 × 10−8 A/cm2 at ±0.5 V) are achieved in the TiN/Al2O3 (∼0.3 nm)/Hf0.3Zr0.7O2 (∼6 nm)/TiN capacitor near the morphotropic phase boundary (MPB). Furthermore, the dielectric constant remains above 40 with endurance >1012 cycles (even extrapolated to 1015 cycles under voltage pulse of 0.5 V @10 MHz) at both room temperature and 85 °C. These results are helpful for achieving a high dielectric constant and low leakage for future generation DRAM capacitor materials.

Pinched hysteresis loop and internal bias field in Ba4(La0.2Nd0.2Sm0.2Eu0.2Y0.2)2Ti4Nb6O30 tungsten bronze ceramics

A-site high entropy Ba4(La0.2Nd0.2Sm0.2Eu0.2Y0.2)2Ti4Nb6O30 tungsten bronze ceramics were designed and prepared by a standard solid state sintering process. First-order ferroelectric transition occurs around 240 °C on heating, while around 136 °C on cooling. Pinched and asymmetric P–E hysteresis loops were observed within and below the thermal hysteresis temperature range of the ferroelectric transition. Pinched P–E hysteresis loops were attributed to the coupling between the ferroelectric transition and the commensurate/incommensurate modulation transition. The reason for the asymmetry of the hysteresis loop was the presence of an internal bias electric field. Different measuring procedures were designed to clarify the evolution of hysteresis loop asymmetry. The existence of oxygen vacancy and Eu3+/Eu2+ was identified by x-ray photoemission spectroscopy. The electric field cycling with elevated temperatures caused defect dipoles incline to align along the direction of spontaneous polarization leading to the internal bias electric field. Due to the A-site high entropy effect, dielectric strength of Ba4(La0.2Nd0.2Sm0.2Eu0.2Y0.2)2Ti4Nb6O30 ceramics is up to 300 kV/cm, which is increased by more than 50% than that with the single element in the A1-site.