Ferroelectric Capacitors Research Articles

Cross-Point Ferroelectric Hf0.5Zr0.5O2 Capacitors for Remanent Polarization-Driven In-Memory Computing.

Ferroelectric Hf0.5Zr0.5O2 (HZO) capacitors have been extensively explored for in-memory computing (IMC) applications due to their nonvolatility and back-end-of-line (BEOL) compatible process. Several IMC approaches using resistance and capacitance states in ferroelectric HZO have been proposed for vector-matrix multiplication (VMM), but previous approaches suffer from limited accuracy and reliability. In this work, we propose a promising approach centered on the remanent polarization (Pr) switching of binary ferroelectric HZO capacitor synapses. We experimentally demonstrate a simple pattern recognition task showing that the voltage readout of Pr switching provides excellent accuracy due to its high on/off ratio and consequent reliability. We also performed large-scale simulations on a complex inference task, achieving high accuracy and immunity to device variations. We therefore believe that our proposed paradigm is promising for near-term neuromorphic IMC.

Electro-optic tuning in ferroelectric capacitor with photonic crystal nanobeam cavity

Electro-optic tuning in ferroelectric capacitor with photonic crystal nanobeam cavity

3D Vertical Ferroelectric Capacitors with Excellent Scalability.

Three-dimensional vertically stacked memory is more cost-effective than two-dimensional stacked memory. Vertically stacked memory using ferroelectric materials has great potential not only in high-density memory but also in neuromorphic fields because it secures low voltage and fast operation speed. This paper presents the implementation of a ferroelectric capacitor comprising a vertical two-layer stacked structure composed of a titanium nitride (TiN)/aluminum-doped hafnium oxide/TiN configuration. To enhance the ferroelectric properties influenced by the active area, we propose a structure in which multiple small holes share a common pillar electrode. Comprehensive analyses using transmission electron microscopy and energy-dispersive X-ray spectroscopy were conducted to confirm the chemical composition and physical structure of the device. This newly engineered architecture demonstrated promising characteristics, including a sufficient remnant polarization, small device-to-device variations, high endurance, and excellent retention in 3D vertical structures. Moreover, this structure can be applied to one-transistor n-capacitor ferroelectric random access memory with a vertical transistor.

Geometric effects in the measurement of the remanent ferroelectric polarization at the nanoscale

A resurgence of research on ferroelectric materials has recently occurred due to their potential to enhance the performance of memory and logic. For the design and commercialization of such technologies, it is important to understand the physical behavior of ferroelectrics and the interplay with device size, geometry, and fabrication processes. Here, we report a study of geometric factors that can influence the measurement of the remanent ferroelectric polarization, an important measurement for understanding wakeup, retention, and endurance in ferroelectric technologies. The areal size scaling of W/Hf0.5Zr0.5O2/W capacitors is compared in two typical structures: an island top electrode with a continuous ferroelectric layer and an island top electrode/ferroelectric layer (etched ferroelectric layer). Error in the evaluation of the switched area leads to anomalous scaling trends and increasing apparent remanent polarization as capacitor sizes decrease, most strongly in continuous ferroelectric layer capacitors. Using TEM and electric field simulations, this is attributed to two effects: a processing artifact from ion milling that creates a foot on the top electrode and a fringe electric field penetrating outside of the capacitor area. With the correction of the switching area, the 2Pr for both samples agree (∼32 μC cm−2) and is invariant in the capacitor sizes used (down to 400 nm diameter). Our work demonstrates that the determination of the actual capacitor structure and local electric field is needed to evaluate the intrinsic ferroelectric behavior at the nanoscale.

A comprehensive study on the sandwich stacking structures of antiferroelectric/ferroelectric doped hafnium oxide

In this paper, the combinations of sandwich stacking structures of antiferroelectric/ferroelectric doped hafnium oxide are systematically explored. The sandwich stacking ferroelectric capacitors with the optimal structure (2 nm ferroelectric HZO/4 nm antiferroelectric HZO/2 nm ferroelectric HZO) exhibit high remanent polarization (2Pr = 48 μC/cm2), low coercive field (1.15 MV/cm), and excellent retention ability (8% degraded Pr after 105 s) at a low operating voltage of 1.8 V. The endurance of this structure has also been enhanced to over 1010 cycles, compared with the control group of 8 nm ferroelectric HZO (∼109 cycles). This study provides a promising solution for the application of the embedded FeRAM and advanced silicon technology nodes with low-power consumption.

Global-optimized energy storage performance in multilayer ferroelectric ceramic capacitors

Multilayer ceramic capacitor as a vital core-component for various applications is always in the spotlight. Next-generation electrical and electronic systems elaborate further requirements of multilayer ceramic capacitors in terms of higher energy storage capabilities, better stabilities, environmental-friendly lead-free, etc., where these major obstacles may restrict each other. An effective strategy for energy storage performance global optimization is put up here by constructing local polymorphic polarization configuration integrated with prototype device manufacturing. A large energy density of 20.0 J·cm−3 along with a high efficiency of 86.5%, and remarkable high-temperature stability, are achieved in lead-free multilayer ceramic capacitors. The strategy provides a feasible routine from nano, micro to macro regions in manipulating local polarizations, domain-switching barriers and breakdown strength, illustrating its great potential to be generally applicable in the design of high-performance energy storage multilayer ceramic capacitors.

Conductive filament formation in the failure of Hf0.5Zr0.5O2 ferroelectric capacitors

Ferroelectric materials provide pathways to higher performance logic and memory technologies, with Hf0.5Zr0.5O2 being the most popular among them. However, critical challenges exist in understanding the material’s failure mechanisms to design long endurance lifetimes. In this work, dielectric failure due to repeated switching cycles, occurring through oxygen vacancy motion and leading to the formation of a conductive filament, is demonstrated. A field modified hopping barrier of ∼150–400 meV is observed, indicating a vacancy charge of 0.4–0.6e markedly different from the charge states predicted in the literature. After failure, the capacitor leakage current is high (∼25 mA) and constant with capacitor area, consistent with filament formation. Conductive atomic force microscopy measurements and field distribution simulations suggest a local failure mechanism consistent with filament formation along the boundary of the island capacitor due to an enhanced electric field.

Enhanced Energy Storage Performance in La-Doped CaBi4Ti4O15 Films Through the Formation of a Weakly Coupled Relaxor.

Relaxor ferroelectric film capacitors exhibit high power density with ultra-fast charge and discharge rates, making them highly advantageous for consumer electronics and advanced pulse power supplies. The Aurivillius-phase bismuth layered ferroelectric films can effectively achieve a high breakdown electric field due to their unique insulating layer ((Bi2O2)2+ layer)). However, designing and fabricating Aurivillius-phase bismuth layer relaxor ferroelectric films with optimal energy storage characteristics is challenging due to their inherently stable ferroelectric properties. In this work, lead-free CaBi4-xLaxTi4O15 films were synthesized using the sol-gel technique and a weakly coupled relaxor design. On one hand, the introduction of La3+ ions weaken the dipole-dipole interactions, thereby enhancing the relaxor behavior. Alternatively, the expansion of grain size is restricted to enhance the number of grain boundaries, which possess improved insulating properties. This leads to a higher breakdown electric field. The results indicate that CaBi4-xLaxTi4O15 (x = 1.0) films exhibit excellent recoverable energy storage density (70 J/cm3) and high energy efficiency (73%). Moreover, the film exhibited good temperature stability and frequency stability. This study not only identifies a promising material for dielectric film capacitors but also demonstrates that the energy storage capabilities of Aurivillius-phase bismuth layer ferroelectric films can be effectively modulated through a design incorporating weakly coupled relaxor characteristics.

Passive control strategy of inductive power transfer to microimplants based on ferroelectric dielectrics

Abstract In this study, a passive control strategy of inductive power transfer (IPT) using ferroelectric multilayer ceramic chip capacitors (MLCCs) is presented. The required system parameters, i.e., ferroelectric hysteresis, frequency of the IPT, and voltage range across the MLCCs are reported. The receiver circuit consists only of a parallel resonant circuit, a halfwave rectifier and a load; the passive control of the IPT is achieved exclusively by the nonlinear properties of the ferroelectric MLCCs. The stabilization of the secondary output voltage ULoad at constant load is experimentally evaluated for an inductive coupling factor k between 10 % and 30 % for three nonlinear MLCCs #1, #2 and #3. With our proposed passive control strategy ULoad is maintained at -1.2 % and +0.6 % around a median value of 17.3 V (17.1 - 17.4 V) for k ∈ [20 %, 30 %] using MLCC #1, ±0.9 % around a median value of 11.2 V (11.1 - 11.3 V) for k ∈ [10 %, 18 %] using MLCC #2, and -1.6% and +2.6 % around a median value of 5.03 V (4.95 - 5.16 V) for k ∈ [16 %, 30 %] using MLCC #3. The proposed control principle is particularly advantageous for highly miniaturized microimplants, as it allows IPT control without additional semiconductors, sensors and vulnerable communication channels.

Interface Engineering on Ferroelectricity of Transparent Hf₀.₅Zr₀.₅O₂ Ferroelectric Capacitors

Interface Engineering on Ferroelectricity of Transparent Hf₀.₅Zr₀.₅O₂ Ferroelectric Capacitors

Polarization-rotation-driven modulation of second harmonic generation in van der Waals layered ferroelectric CuInP2S6

Two-dimensional van der Waals (vdW) ferroelectrics, renowned for their spontaneous breaking of inversion symmetry and finite electric polarization, are pivotal in nonlinear optics and low-power nanoelectronics. Prior studies primarily focused on materials exhibiting out-of-plane or in-plane ferroelectric polarization, whose rotational degrees of freedom are commonly overlooked. Herein, we experimentally validate the existence of a weak yet symmetry-allowed in-plane polarization in the low-symmetry vdW ferroelectric CuInP2S6 by rigorous structural analysis and vectorial property characterizations. Remarkably, the magnitude of this in-plane polarization is tunable via an interface-induced electric field, leading to a significant contrast in second harmonic generation between oppositely polarized domains. Based on this unique rotational capability of electric polarization, we demonstrate an electrically tunable second-order optical emission in a fabricated vdW ferroelectric capacitor. Our findings highlight the intricate interplay between crystal symmetry and tensorial physical properties, providing a novel pathway for manipulating nonlinear optical functionalities in vdW layered ferroelectrics.

Direct Imaging of Asymmetric Interfaces and Electrostatic Potentials inside a Hafnia-Zirconia Ferroelectric Nanocapacitor.

In hafnia-based thin-film ferroelectric devices, chemical phenomena during growth and processing, such as oxygen vacancy formation and interfacial reactions, appear to strongly affect device performance. However, the correlation between the structure, chemistry, and electrical potentials at the nanoscale in these devices is not fully known, making it difficult to understand their influence on device properties. Here, we directly image the composition and electrostatic potential with nanometer resolution in the cross section of a nanocrystalline W/Hf0.5Zr0.5O2-δ (HZO)/W ferroelectric capacitor using multimodal electron microscopy. This reveals a 1.4 nm wide tungsten suboxide interfacial layer formed at the bottom interface during fabrication, which introduces a potential dip and leads to asymmetric switching fields. Additionally, we compare the measured potentials to DFT calculations and find it is nearly 3 V lower than expected in the HZO, which appears to be caused by oxygen vacancies and a resulting negative built-in potential. These chemical and electrostatic details are important to characterize and tune to achieve high-performance ferroelectric devices.

Ultra-tunable dielectric capacitors enhanced by coupling ferroelectric field effect and semiconductor field effect

Tunable ferroelectric film capacitors play an important role in tunable microwave devices and filter systems due to their high dielectric constant, low loss, and high dielectric tunability. However, there is a trade-off between low loss and high tunability, which limits further enhancement of dielectric performance. Here, we propose an ultra-tunable capacitor by designing a Ba0.7Sr0.3TiO3 (BST)–semiconductor heterostructure. In the tunable capacitor, the BST film is fabricated directly on p-type silicon substrates by magnetron sputtering, and a heterostructure layer is constructed. The coupling effects between the semiconductor depletion layer capacitance and the BST capacitance produce higher capacitance tunability than a traditional sandwich BST capacitor. Based on the coupling effects, a metal–ferroelectric–semiconductor–ferroelectric–metal capacitor is developed, which enables the capacitor to operate under both negative and positive biases, which has an n value (n=Cmax/Cmin) of 90 with 40 V bias voltage and a maximum Q of 1000. The results offer a potential approach to designing high-performance tunable capacitors on silicon with BST film that could build tunable filters for information processing in communication systems.

Oxygen reservoir effect of Tungsten trioxide electrode on endurance performance of ferroelectric capacitors for FeRAM applications

The effect of W and WO3 electrodes on the ferroelectric characteristics of HZO (Zr-doped HfO2)-based MFM (metal-ferroelectric-metal) capacitors was investigated. During the deposition of tungsten, the W electrode was formed using only Ar gas, while the WO3 electrode was formed using a mixture of Ar and O2 gases. The W-based MFM capacitors exhibited superior remnant polarization (2Pr of 107.9 µC/cm2 at 700 oC) compared to the WO3-based capacitors; however, their endurance performance was degraded. In contrast, the WO3-based capacitors showed endurance performance enhanced by three orders of magnitude due to the oxygen-rich reservoir effect. The oxygen introduced during the deposition of WO3 prevented the oxygen scavenging effect of tungsten. Consequently, excessive generation of oxygen vacancies in the HZO layer was suppressed, resulting in improved endurance performance. These results were quantitatively confirmed through TEM, XPS, and XRD analyses.

Temperature-Dependent Ferroelectric Behaviors of AlScN-Based Ferroelectric Capacitors with a Thin HfO2 Interlayer for Improved Endurance and Leakage Current

The ferroelectric switching behavior of a metal–ferroelectric AlScN–HfO2 interlayer–metal (MFIM) capacitor was investigated at variable temperatures and compared with an MFM capacitor. Although the MFIM capacitor demonstrated an inferior remnant polarization (2Pr value of 74 µC/cm2), it exhibited a reduced leakage current (×1/100) and higher breakdown field. The MFIM showed a stable change in 2Pr from room temperature to 200 °C and an enhanced endurance of ~104 cycles at 200 °C; moreover, the leakage current was less degraded after the cycling tests. Thus, the ferroelectric AlScN with a thin HfO2 interlayer can enhance the reliability of ferroelectric switching.

Performance and Characterization of Additively Manufactured BST Varactor Enhanced by Photonic Thermal Processing

The demand for reconfigurable devices for emerging RF and microwave applications has been growing in recent years, with additive manufacturing and photonic thermal treatment presenting new possibilities to supplement conventional fabrication processes to meet this demand. In this paper, we present the realization and analysis of barium–strontium–titanate-(Ba0.5Sr0.5TiO3)-based ferroelectric variable capacitors (varactors), which are additively deposited on top of conventionally fabricated interdigitated capacitors and enhanced by photonic thermal processing. The ferroelectric solution with suspended BST nanoparticles is deposited on the device using an ambient spray pyrolysis method and is sintered at low temperatures using photonic thermal processing by leveraging the high surface-to-volume ratio of the BST nanoparticles. The deposited film is qualitatively characterized using SEM imaging and XRD measurements, while the varactor devices are quantitatively characterized by using high-frequency RF measurements from 300 MHz to 10 GHz under an applied DC bias voltage ranging from 0 V to 50 V. We observe a maximum tunability of 60.6% at 1 GHz under an applied electric field of 25 kV/mm (25 V/μm). These results show promise for the implementation of photonic thermal processing and additive manufacturing as a means to integrate reconfigurable ferroelectric varactors in flexible electronics or tightly packaged on-chip applications, where a limited thermal budget hinders the conventional thermal processing.

Novel Topology for Modified Boost Series and Parallel Switching Capacitor DC-DC Converter

Theoretical and experimental work for a novel topology of DC-DC boost switching capacitor converter is introduced in this paper. This new design is an adjustment for boost series and parallel topology developed by Makowski. Thus, a comparison between the two designs presented in this paper aims to highlight the improvement in the conversion rate of the boost converter’s output voltage while using the same number and size of capacitors. Converter analyses for both with and without load are presented. Also, a boost converter with a nonlinear ferroelectric capacitor is presented to further increase the boost converter conversion rate using advantages of the ferroelectric capacitors, such as their big dielectric constant and polarization reversal.

High performance and nearly wake-up free Hf0.5Zr0.5O2 ferroelectric capacitor realized by middle layer strategy with BEOL compatibility

Hf0.5Zr0.5O2(HZO) has drawn great attention owing to its excellent ferroelectricity, sub-10 nm scalability, and CMOS compatibility. With regard to increasingly restrict thermal budget and power consumption, conventional HZO films need further optimization to meet these demands. Here, we propose a middle layer (ML) strategy aiming to enhance ferroelectricity and inhibit wake-up effect of ferroelectric (FE) capacitors compatible with back-end of line under the low operating electric field. ZrO2, HfO2, and Al2O3were integrated into HZO film as different MLs. Among them, the device with ZrO2ML achieves the excellent double remnant polarization (2Pr) of 41.7μC cm-2under the operating electric field of 2 MV cm-1. Moreover, ultralow wake-up ratios of around 0.08 and 0.05 were observed under 2 MV cm-1and 3 MV cm-1, respectively. Additionally, the FE capacitor with ZrO2ML demonstrated an enhanced reliability characterizations, including a stable 2Prof 40.7μC cm-2after 4.3 × 109cycles. This work provides the perspective to optimize both the ferroelectricity and reliability, while maintains the ultralow wake-up ratio in HfO2-based FE through ML engineering.

A ferroelectric capacitor with an asymmetric double-layered ferroelectric structure comprising a liquid-delivery MOCVD Pb(Zr, Ti)O3 layer and a sputter-deposited La-doped Pb(Zr, Ti)O3 for highly reliable FeRAM

We have developed a double-layered ferroelectric capacitor comprising a liquid-delivery metal–organic chemical vapor deposition-based Pb(Zr, Ti)O3 (PZT) lower layer and a sputter-deposited La-doped Pb(Zr, Ti)O3 (PLZT) upper layer. This structure is designed to achieve a large polarization in the stacked-type capacitor of FeRAM. Ferroelectric capacitors with noble metal electrodes, which are patterned by sputter-etching due to the difficulty of standard chemical reactive etching typically exhibit sloped sidewalls. Consequently, their polarization values, determined by the actual capacitor area, depend on their geometric shape. Our developed capacitor exhibits a 35% increase in polarization compared to an all-sputter-deposited PLZT capacitor. This improvement is due to the reduced total thickness of the developed capacitor achieved by simplifying the bottom electrode structure, which results in steeper capacitor sidewalls. Furthermore, our developed capacitor demonstrates excellent retention margin even after 3000 h of baking at 150 °C, and with a potential endurance of 1014 cycles as predicted by voltage acceleration measurements.

Oxygen-Atom Incorporated Ferroelectric AlScN Capacitors for Multi-Level Operation

Oxygen-Atom Incorporated Ferroelectric AlScN Capacitors for Multi-Level Operation