Ferroelectric Hafnium Oxide Research Articles

Unveiling pyroelectricity in ferroelectric planar capacitors with area-selective wet etched hafnium zirconium oxide: from ab initio and multiphysics simulations to experiments

Abstract In this work, a systematic approach aimed at investigating and validating a novel way of realizing pyroelectric harvesting is presented. Generating a direct-current (dc) signal through a temperature gradient within a less than 7 nm-thick ferroelectric zirconium-doped hafnium oxide (HZO) nano-film, embedded in planar interdigitated capacitors on high-resistivity silicon, is a new, simple, effective, and reproducible solution. Temperature-related structural modifications in HZO are first simulated using advanced ab initio calculations. Then, rigorous multiphysics simulations of the final devices provide insight into the expected performance of the pyroelectric harvester, as a function of temperature, contact area, and crystal orientation, showing a maximum open-circuit voltage of up to 900 mV. The fabrication of the harvesters involves the area-selective wet etching of the HZO layer to retain it exclusively in between the fingers of each capacitor. This choice maximizes the pyroelectric effect (which strongly depends on the area) and represents a new paradigm in the development of HZO-based electronics, which are conventionally built on ferroelectric continuous films. Experimental validation at both low frequencies and microwaves confirms the pyroelectric effect, exhibiting a significant increase in the output current for higher temperature gradients, and a generated dc voltage of several hundred millivolts.

A design methodology for highly reliable operation for 2T0C dynamic random access memory application based on IGZO channel-all-around ferroelectric field-effect transistors

In this paper, the memory characteristics of In-Ga-Zn-O (IGZO)-channel ferroelectric FETs (FeFETs) with stackable vertical channel-all-around structure are investigated by technology computer-aided design (TCAD) simulation. The simulated drain current–gate voltage (I DS–V GS) curves of the IGZO FeFET show an on–off ratio of up to 107 and a memory window of 1.76 V, proving that ferroelectric hafnium oxide (FE-HfO2) is suitable for a 2T0C transistor. To solve the potential current-sharing problem of the 2T0C dynamic random access memory (DRAM) array, an advanced operation design methodology is proposed, which utilizes the bipolar polarization characteristics of FE-HfO2. This solution shows a remarkable current ratio between data “1” and data “0”, not only demonstrating the feasibility of the IGZO-based FeFET on 2T0C DRAM memory cells, but also providing an array design guideline for highly reliable 2T0C memory applications.

Superflexible and Stretchable Ferroelectric Memory on a Biocompatible Platform

AbstractNext‐generation flexible electronics for healthcare applications require biocompatible flexible non‐volatile memory for data storage. Ultra‐thin ferroelectric hafnium oxide films offer great potential for flexible memories due to their potential flexibility and perfect compatibility with modern technologies. This study presents ultra‐flexible and stretchable memory devices based on 10‐nm‐thick Hf0.5Zr0.5O2 film fabricated by an innovative technology involving encapsulation of the devices in a biocompatible organic package. They exhibit high memory functionality (remanent polarization of 27 µC cm−2) and withstand extreme mechanical conditions, including folding in half, multiple bending up to 150 000 bending cycles as well as tension with loads up to 1.5 kg. Further, flexible devices are employed as a platform to elucidate the fundamental role of mechanical stress in ferroelectricity of hafnia both experimentally and theoretically. Direct in situ experiment demonstrates that in‐plane tension causes changes in spontaneous polarization, coercive voltage, permittivity, and conductivity. First‐principle calculations explain the role of mechanical stress in ferroelectric and dielectric properties of hafnia. In applications, this work establishes a foundation for the implementation of biocompatible, high‐performance flexible ferroelectric memory, and in the field of ferroelectric materials fundamentals, it provides insight into the critical role of the residual mechanical stress that is inevitably present in thin films.

Oxygen vacancies stabilized 180° charged domain walls in ferroelectric hafnium oxide

Ferroelectric domain walls (DWs) are spatial interfaces separating domains with distinct polarization orientations. Among these DWs, some can carry bound charges and display metallic-like conductivity. The feature is highly of interest for future nanoelectronics. However, the inherent instability of charged domain walls (CDWs) has posed a critical challenge for their experimental exploration. This Letter reports the head-to-head (HH) and tail-to-tail (TT) 180° CDWs within the context of ferroelectric hafnium oxide. We proposed that oxygen vacancy is a crucial factor stabilizing the periodic CDWs. Through meticulous first-principles calculations, we elaborated on the intricate properties of these CDWs, including their polarization profiles, and potential and charge distributions. Furthermore, we calculated the energy barrier for layer-by-layer propagation of a HH wall and carefully discussed the migration of a TT wall with oxygen vacancy. Our study can shed more light onto the characteristics of CDWs and their implications to hafnia-based ferroelectric devices.

Investigation of wet etching technique for selective patterning of ferroelectric zirconium-doped hafnium oxide thin films for high-frequency electronic applications

This paper presents the area-selective wet etching (ASWE) method as a novel approach to have a selective patterning of a 6.8 nm-thick zirconium-doped hafnium oxide (HZO) thin film, to improve the performance of a metal ferroelectric metal (MFM)-like structure. According to the electromagnetic simulations of microwave phase shifters with patterned HZO thin films, it is underlined the importance to have selectively targeted areas covered with HZO instead of full-coverage wafers, to gain a further increase in the microwave performance of low-voltage tunable high-frequency components. The impact of the ASWE method on the morpho-structural properties was studied using various investigation tools in a non-destructive manner. X-ray reflectivity (XRR) has been employed at different immersion times, up to 120 s. Based on the extended Fast Fourier Transform (FFT) analysis, as well as from the simulation of the experimental curves in the framework of parallel-tempering algorithm, the determination of the etching rate became possible. X-ray diffraction (XRD), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) clearly indicated the complete removal of HZO after etching processes at 180 s. The method is fast, reliable, and low-cost, thus filling the actual gap in providing the necessary ferroelectric thin films exclusively in selected areas of interest.

Evidence for ferroelastic switching and nanoscopic domains in polycrystalline Si-doped hafnium oxide films

The mechanism of nanoscopic domain switching in ferroelectric hafnium oxide and its implications for antiferroelectric-like behavior as well as for the wake-up effect is still widely discussed. Understanding this mechanism is of vital importance for a multitude of applications like piezoelectric actuators, pyroelectric sensors, and nonvolatile memory devices. In this article, electrical and physical analysis methods are used to characterize ferroelectric hafnium oxide on the nanoscopic as well as the macroscopic length scale. Evidence for nanoscopic domains is found using transmission Kikuchi diffraction. In combination with macroscopic Preisach density measurements, strong evidence is found that antiferroelectric-like behavior and wake-up are governed by ferroelastic switching, i.e., a 90° domain wall motion. Based on these insights, the material stack can be optimized to further improve microelectronic applications based on HfO2.

Neural network approach for ferroelectric hafnium oxide phase identification at the atomistic scale

Neural network approach for ferroelectric hafnium oxide phase identification at the atomistic scale

Molecular layer modulation of two-dimensional organic ferroelectric transistors

Ferroelectric transistors hold great potential in low consumption devices. Due to the high film quality and clean system, two dimensional organic semiconductors are widely employed to fabricate high performance organic electronic devices and explore the modulation mechanism of the molecular packing on device performance. Here, we combine the ferroelectric hafnium oxide HfZrO x and two-dimensional molecular crystal 2,9-didecyldinaphtho[2,3-b:2′,3′-f]thieno[3,2b]thiophene (C10-DNTT) with controllable layers to study the molecular layer modulation of ferroelectric organic thin-film transistors (OTFTs). The contact resistance, driving current and transconductance are directly affected by the additional access resistance across the upper molecular layers at the source/drain contact region. Simultaneously, the capacitance of Schottky junction related to the molecular layer thickness could effectively adjust the gate potential acting on the organic channel, further controlling the devices’ subthreshold swing and transconductance efficiency. This work would promote the development of low voltage and high performance OTFTs.

Recent Progress and Applications of HfO2-Based Ferroelectric Memory

The discovery of ferroelectricity in hafnium oxide (HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) based thin films in 2011 renewed the interest in ferroelectrics. These new ferroelectrics possess completely different crystal morphology with conventional perovskite ferroelectrics, and present more robust ferroelectric properties upon aggressive scaling and compatibility with standard integrated circuit fabrication processes. In this article, we give a brief introduction to the conventional ferroelectric memories, then review the basic properties, recent progress, and memory applications of these HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -based ferroelectrics.

A Study on Imprint Behavior of Ferroelectric Hafnium Oxide Caused by High‐Temperature Annealing

Hafnium oxide is found to be a favorable material for ferroelectric nonvolatile memory devices. Its compatibility with complementary metal–oxide–semiconductor processes, the relatively low crystallization temperature when zirconium‐doped, and the thickness scaling are among the advantageous properties of hafnium oxide. Different requirements must be fulfilled for different applications of hafnium oxide. Herein, high‐temperature annealing and operation conditions are analyzed in order to investigate nonvolatile memories for automotive applications. A strong imprint behavior (shift in coercive voltages) is observed after annealing hafnium–zirconium–oxide thin films at temperatures varied between 100 and 200 °C. The imprint behavior is a significant challenge in many applications. Therefore, to reduce/recover the undesirable imprint behavior caused by high‐temperature treatment, two different ways are successfully examined and delineated here: endurance cycling and applying high electric fields.

From Ferroelectric Material Optimization to Neuromorphic Devices.

Due to the voltage driven switching at low voltages combined with nonvolatility of the achieved polarization state, ferroelectric materials have a unique potential for low power nonvolatile electronic devices. The competitivity of such devices is hindered by compatibility issues of well-known ferroelectrics with established semiconductor technology. The discovery of ferroelectricity in hafnium oxide changed this situation. The natural application of nonvolatile devices is as a memory cell. Nonvolatile memory devices also built the basis for other applications like in-memory or neuromorphic computing. Three different basic ferroelectric devices can be constructed: ferroelectric capacitors, ferroelectric field effect transistors and ferroelectric tunneling junctions. In this article first the material science of the ferroelectricity in hafnium oxide will be summarized with a special focus on tailoring the switching characteristics towards different applications.The current status of nonvolatile ferroelectric memories then lays the ground for looking into applications like in-memory computing. Finally, a special focus will be given to showcase how the basic building blocks of spiking neural networks, the neuron and the synapse, can be realized and how they can be combined to realize neuromorphic computing systems. A summary, comparison with other technologies like resistive switching devices and an outlook completes the paper.

Publisher's Note: “A Perspective on ferroelectricity in hafnium oxide: Mechanisms and considerations regarding its stability and performance” [Appl. Phys. Lett. 121, 240502 (2022)

Publisher's Note: “A Perspective on ferroelectricity in hafnium oxide: Mechanisms and considerations regarding its stability and performance” [Appl. Phys. Lett. <b>121</b>, 240502 (2022)

Retention Model and Express Retention Test of Ferroelectric HfO2 -Based Memory

Ferroelectric hafnium oxide films are one of the most promising functional materials for a new generation of nonvolatile memory for data storage because of a number of excellent performance features, including nanosecond speed, high endurance, low power consumption, full scalability, and perfect compatibility with Si technology. However, the commercialization of this memory is hindered by its limited retention time, which still does not meet the 10-year electronics-industry standard. To date, much effort has been focused on the improvement of retention via material and interface engineering. Meanwhile, the evaluation and comparison of engineering results have been hampered, since there is still no unified retention test. Indeed, a specific feature of the retention performance is that it cannot be measured directly, because 10 years is required to measure the actual polarization loss. In this paper, we present a physical model that predicts the retention loss in ${\mathrm{Hf}\mathrm{O}}_{2}$-based memory during long-term information storage. The time-dependent polarization loss originates from the phenomenon of polarization imprint, which consists in the temporal development of a preferential polarization state in a poled ferroelectric. For high reliability of the retention calculation, the model takes into account the specific features of imprint evolution in the ferroelectric material ${\mathrm{Hf}\mathrm{O}}_{2}$. Among these is the origin of the imprint in this material, which consists in the interplay of two physical mechanisms, specifically, charge injection into interface traps and migration of mobile charged defects across the functional layer. The second property of ${\mathrm{Hf}\mathrm{O}}_{2}$ taken into account is the different rates of imprint evolution in two types of ${\mathrm{Hf}\mathrm{O}}_{2}$ film that exist within each memory cell. These two types of film originate from two populations of domains that appear during crystallization of the ${\mathrm{Hf}\mathrm{O}}_{2}$ and persist during the whole lifetime of the memory cell. The high accuracy of the retention model makes it possible to implement an express retention test, i.e., to predict the retention time in record short time (1 h) for any particular sample, whereas usually a retention test takes at least several days. For ${\mathrm{Hf}}_{0.5}{\mathrm{Zr}}_{0.5}{\mathrm{O}}_{2}$-based capacitors, the retention model shows excellent agreement with experimental results. The proposed model can serve not only for the implementation of this express retention test, but also as a tool for intelligent material engineering in the field of nonvolatile ferroelectric memory.

A Perspective on ferroelectricity in hafnium oxide: Mechanisms and considerations regarding its stability and performance

Ferroelectric hafnium oxides are poised to impact a wide range of microelectronic applications owing to their superior thickness scaling of ferroelectric stability and compatibility with mainstream semiconductors and fabrication processes. For broad-scale impact, long-term performance and reliability of devices using hafnia will require knowledge of the phases present and how they vary with time and use. In this Perspective article, the importance of phases present on device performance is discussed, including the extent to which specific classes of devices can tolerate phase impurities. Following, the factors and mechanisms that are known to influence phase stability, including substituents, crystallite size, oxygen point defects, electrode chemistry, biaxial stress, and electrode capping layers, are highlighted. Discussions will focus on the importance of considering both neutral and charged oxygen vacancies as stabilizing agents, the limited biaxial strain imparted to a hafnia layer by adjacent electrodes, and the strong correlation of biaxial stress with resulting polarization response. Areas needing additional research, such as the necessity for a more quantitative means to distinguish the metastable tetragonal and orthorhombic phases, quantification of oxygen vacancies, and calculation of band structures, including defect energy levels for pure hafnia and stabilized with substituents, are emphasized.

Heavy ion irradiation induced phase transitions and their impact on the switching behavior of ferroelectric hafnia

The discovery of ferroelectric hafnium oxide enabled a variety of non-volatile memory devices, like ferroelectric tunnel junctions or field-effect transistors. Reliable application of hafnium oxide based electronics in space or other high-dose environments requires an understanding of how these devices respond to highly ionizing radiation. Here, the effect of 1.6 GeV Au ion irradiation on these devices is explored, revealing a reversible phase transition, as well as a grain fragmentation process. The collected data demonstrate that non-volatile memory devices based on ferroelectric hafnia layers are ideal for applications where excellent radiation hardness is mandatory.

Effect of Al2O3 interlayers on the microstructure and electrical response of ferroelectric doped HfO2 thin films

Novel devices based on ferroelectric hafnium oxide comply with the increasing demand for highly scalable embedded non-volatile memory devices, especially for in-memory computing applications. However, due to the polycrystalline nature of these hafnium oxide films, highly scaled devices face variability concerns. In order to enable smaller grains to circumvent the current limitations, the introduction of Al2O3 interlayers to interrupt the columnar grain growth is presented herein. Transmission Kikuchi diffraction is utilized to investigate influences of the Al2O3 layer on the microstructure of hafnium oxide. Moreover, electrical analysis indicates how the interlayer affects the wake-up phenomena as well as the electric field distribution within the stack. These results provide evidence on how to control grain size, electric behavior, and crystallization temperature by the insertion of Al2O3 interlayers.

Pyroelectric and Ferroelectric Properties of Hafnium Oxide Doped with Si via Plasma Enhanced ALD

Devices based on ferroelectric hafnium oxide are of major interest for sensor and memory applications. In particular, Si-doped hafnium oxide layers are investigated for the application in the front-end-of-line due to their resilience to high thermal treatments. Due to its very confined doping concentration range, Si:HfO2 layers based on thermal atomic layer deposition often exhibited a crossflow pattern across 300 mm wafer. Here, plasma enhanced atomic layer deposition is explored as an alternative method for producing Si-doped HfO2 layers, and their ferroelectric and pyroelectric properties are compared.

One Nanometer HfO2‐Based Ferroelectric Tunnel Junctions on Silicon (Adv. Electron. Mater. 6/2022)

Low-Power Memory Ferroelectric Si-compatible hafnium oxide is attractive for emerging low-power memory considering its voltage-switchable electric polarization, exemplified in article number 2100499 by Suraj S. Cheema, Sayeef Salahuddin, and co-workers by 1 nm ferroelectric tunnel junctions on Si that overcome a key traditional trade-off: simulatenous ultrahigh read current and electroresistance.

Nanoscale Doping and Its Impact on the Ferroelectric and Piezoelectric Properties of Hf0.5Zr0.5O2.

Ferroelectric hafnium oxide thin films—the most promising materials in microelectronics’ non-volatile memory—exhibit both unconventional ferroelectricity and unconventional piezoelectricity. Their exact origin remains controversial, and the relationship between ferroelectric and piezoelectric properties remains unclear. We introduce a new method to investigate this issue, which consists in a local controlled modification of the ferroelectric and piezoelectric properties within a single Hf0.5Zr0.5O2 capacitor device through local doping and a further comparative nanoscopic analysis of the modified regions. By comparing the ferroelectric properties of Ga-doped Hf0.5Zr0.5O2 thin films with the results of piezoresponse force microscopy and their simulation, as well as with the results of in situ synchrotron X-ray microdiffractometry, we demonstrate that, depending on the doping concentration, ferroelectric Hf0.5Zr0.5O2 has either a negative or a positive longitudinal piezoelectric coefficient, and its maximal value is −0.3 pm/V. This is several hundreds or thousands of times less than those of classical ferroelectrics. These changes in piezoelectric properties are accompanied by either improved or decreased remnant polarization, as well as partial or complete domain switching. We conclude that various ferroelectric and piezoelectric properties, and the relationships between them, can be designed for Hf0.5Zr0.5O2 via oxygen vacancies and mechanical-strain engineering, e.g., by doping ferroelectric films.

High-Performing Self-Powered Photosensing and Reconfigurable Pyro-photoelectric Memory with Ferroelectric Hafnium Oxide.

With highly diverse multifunctional properties, hafnium oxide (HfO2 ) has attracted considerable attention not only because of its potential to address fundamental questions about material behaviors, but also its potential for applied perspectives like ferroelectric memory, transistors, and pyroelectric sensors.However, effective harvesting of the pyro-photoelectric effect of HfO2 to develop high-performing self-biased photosensors and electric writable and optical readable memory has yet to be developed. Here, a proof-of-concept HfO2 -based self-powered and ultrafast (response time ≈ 60 µs) infrared pyroelectric sensor with a responsivity of up to 68 µA W-1 is developed. In particular, temporal infrared light illumination induced surface heating and, in turn, change in spontaneous polarization are attributed to robust pyro-photocurrent generation. Further, controllable suspension and reestablishment of the self-biased pyro-photocurrent response with a short electric pulse are demonstrated, which offers a conceptually new kind of photoreadable memory. Potentially, the novel approach opens a new avenue for designing on-demand pyro-phototronic response over a desired area and offers the opportunity to utilize it for various applications, including memory storage, neuromorphic vision sensors, classification, and emergency alert systems.