Rapid progress of artificial neural network applications in recent years has led to the issue of an unprecedented energy consumption. It can be solved by the implementation of energy efficient hardware based on non-von-Neumann architectures, which requires the development of electronic components emulating the behavior of synapses and neurons. While research of synaptic elements is vast, the technology for fabrication of scalable and highly reproducible neuronal elements is far less developed. In this paper, we demonstrate an artificial neuron with multiple functionalities based on filamentary switching Ag/Hf_0.5Zr_0.5O_2 (HZO) memristors. To improve the parameters of memristors, we propose a two-step annealing method, which allows for better control of the crystallization of the functional dielectric layer (HZO) as well as of the diffusion of active electrode (Ag) atoms. Furthermore, we demonstrate the leaky integrate-and-fire (LIF) neuronal behavior in multiple spiking modes: time-to-first-spike (TTFS), number of spikes and firing rate coding. Moreover, the neuron operation does not require the additional electronic overhead and is supported solely by a Ag/HZO memristor with a current limiting resistor connected in series. The presented results pave the way for the creation of next generation energy efficient neuromorphic hardware operating on the principles of spiking neural networks.

Alloyed Hf0.5Zr0.5O2 (HZO) ultrathin layers crystallized in a metastable non-centrosymmetric phase are the leading candidate for implementation of scaled ferroelectric devices due to their excellent CMOS compatibility and demonstrated integrability with TiN in industrial process flows. One of the key problems on the route of using HZO-based capacitors as functional parts of ferroelectric memory cells is that the cyclic electrical stress required to write and read the stored information sets off a gradual increase in the leakage current, leading to eventual breakdown in the HZO layer. The breakdown in dielectric oxide layers sandwiched between two metal electrodes is generally viewed as a defect-assisted process; however, the relative contributions from the bulk and interfaces depend on the material system and are still under intense investigation. Here, we report on the dramatic effect of the polarity of constant-voltage electrical stress on the lifetime prior to breakdown in the nominally symmetric TiN/HZO/TiN ferroelectric capacitors. At the same time, we observed that pulsed stress with the same amplitude and equivalent total time under stress does not lead to the breakdown of the HZO layer. The step-recovery with multi-pulse test (SRMPT) technique was employed to quantify the energy distribution of chargeable defects in the HZO bandgap. Our analysis suggests that electrical breakdown in TiN/HZO/TiN devices is governed by the evolution of preexisting charged oxygen-vacancy-related defects associated with chemically nonequivalent TiN/HZO interfaces formed during HZO crystallization annealing.

Doping of Hf0.5Zr0.5O2 (HZO) films with rare-earth metals during atomic layer deposition growth has been found to significantly affect their structural and functional properties. Here, we report on the structural properties of Y- and La-doped polycrystalline HZO films as revealed by synchrotron-based near-edge x-ray absorption fine-structure (NEXAFS) technique, and complemented by x-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques for Y:HZO. In contrast to XRD and TEM, NEXAFS analysis taken near the O K (1s)-edge can distinguish between orthorhombic (o-) and tetragonal (t-) phases with much better accuracy and, furthermore, provides quantitative information about phase composition. In addition, the absorption spectra taken near Zr M3 (3p3/2)-edge and O K (1s)-edge also provide reliable information about the presence of the monoclinic (m-) phase, even in the case of highly textured samples. The structural data are further correlated with the electrical properties of Y: and La:HZO films sandwiched in capacitor structures, which are found to depend on the dopant concentration either, suggesting that the delicate balance of different phases in doped HZO (revealed by NEXAFS) defines the functional properties of devices. Despite the progress in the quantitative assessment of phase composition by NEXAFS, the unambiguous prediction of the electrical response in doped HZO remains challenging, and calls for the use of operando NEXAFS structural analysis in functional prototype capacitor devices to directly monitor an apparent structural evolution in this class of materials upon the electrical stress.

The transition to smart, wearable, and flexible optoelectronic devices that communicate with each other and perform neuromorphic computing at the edge, is a major goal in next‐generation optoelectronics. These devices are expected to carry out their regular tasks while being supported by energy‐efficient, in‐memory computations. In this study, a lateral flexible device based on cesium lead tribromide perovskite single crystals integrated with single‐walled carbon nanotube thin‐film electrodes is presented. It is demonstrated that the device follows the Bienenstock‐Cooper‐Munro theory of synaptic modification under hybrid optoelectronic stimuli. This biorealistic response paves the way for the development of hybrid organic–inorganic artificial visual systems.

Metallic nanoparticles are a powerful and versatile tool for various applications: catalysis and electrochemistry, chemical sensing, nonvolatile information storage, and plasmonics. Nanoparticles made of ruthenium (Ru) are particularly promising due to enhanced catalytic activity, high structural, and chemical stability. However, existing methods for Ru nanoparticle synthesis are not always favorable for applications, with major issues being proneness to aggregation at high temperature operation or functionality and performance degradation due to amorphous structure. In this work, a method to synthesize Ru nanocrystals on the SiO 2 surface using a pulsed laser deposition technique at 600 °C is presented. This study thoroughly characterizes the morphological, structural, and electronic properties of the nanocrystal arrays and shows that their size can be tuned with the number of laser pulses during the growth up to the limit of percolation threshold. The formation of Ru nanocrystals is favored by the emergence of interface dipole between Ru and SiO 2 during deposition. The high growth temperature ensures improved heating stability of the Ru nanocrystals, which can be implemented in various appropriate applications.

The relation between the structure of amorphous SiOx films of various compositions obtained by plasma-enhanced chemical vapor deposition and the characteristics of Resistive Random-Access Memory (ReRAM) devices with the active layer based on such films were investigated. The composition of the samples was studied using X-ray photoelectron spectroscopy. A comparison of the experimental Si 2p photoelectron spectrum with calculations showed that the short-range order in the arrangement of atoms in the amorphous SiOx films is defined by the content of excess silicon and can be described within the framework of different structural models. The short-range order has a decisive influence on the memristor characteristics of obtained films. Memristors based on SiOx whose active layer obeys the Random Bonding model exhibit a more pronounced hysteresis window and high stability of the resistive switching of ReRAM devices between two stable (low- and high-resistive) states.

Implementations of artificial neural networks increased power consumption by computing facilities. This can be solved by developing energy efficient neuromorphic hardware, where use of memristors is a promising route. Besides memristive synapse implementations, artificial neurons need to be created. Here, focus has been on developing threshold switches, among which perfect physical realization is yet to be found. In this work, we use gas discharge tubes (GDTs) as prototype threshold switching devices. We construct a leaky integrate-and-fire (LIF) neuristor, based on one GDT, and further extend its functionality by creating a Hodgkin–Huxley-like neuron (HH), based on two GDTs, capable of reproducing 24 neuronal modes. We exploit the light sensitivity of a GDT, caused by the photoelectric effect, and demonstrate light-induced inhibition of spiking in the LIF neuron, while in the HH-like neuron, we show the light-induced spiking threshold tuning and autonomous (without electrical input) spiking, combining photoreceptor and sensory neuron functionality. We propose the scheme to miniaturize gas discharge devices and reduce the operation voltage down to technologically relevant values. Employed approach offers an alternative path for developing modern neuromorphic electronic hardware and presents an opportunity to engage more researchers in the field by using off-the-shelf devices for neuronal circuit research.

Implementation of neuromorphic hardware is a promising way to improve the computing efficiency and decrease the energy consumption of artificial neural networks. For this purpose, electronic elements emulating the behavior of synapses and neurons have to be developed. In order to realize electronic artificial neurons, threshold resistive switches or memristors can be efficiently used. One of the most widespread materials for threshold switches is vanadium dioxide due to its property to demonstrate the metal-insulator transition at a temperature about 70 °C. However, the processes of VO_2 synthesis are quite restrictive in temperature and gas atmosphere conditions, which hinders its integration into CMOS fabrication. In this work, we propose a new method of VO_2 synthesis: reactive pulsed laser deposition from metallic V target in oxygen atmosphere at room temperature, followed by vacuum annealing. Our method enables target synthesis of an appropriate VO_2 phase in a polycrystalline thin film form by finely tuning oxygen pressure during room temperature deposition, which allows to relax the equipment demands, such as high temperature heating in oxygen. Successful targeted VO_2 synthesis under fabrication conditions close to back-end-of-line CMOS production, achieved in this work, show the way toward its large-scale microelectronic integration for neuromorphic hardware creation.

Metallic nanoparticles are a powerful and versatile tool for various applications: catalysis and electrochemistry, chemical sensing, nonvolatile information storage, and plasmonics. Nanoparticles made of ruthenium (Ru) are particularly promising due to enhanced catalytic activity, high structural, and chemical stability. However, existing methods for Ru nanoparticle synthesis are not always favorable for applications, with major issues being proneness to aggregation at high temperature operation or functionality and performance degradation due to amorphous structure. In this work, a method to synthesize Ru nanocrystals on the SiO2 surface using a pulsed laser deposition technique at 600 degrees C is presented. This study thoroughly characterizes the morphological, structural, and electronic properties of the nanocrystal arrays and shows that their size can be tuned with the number of laser pulses during the growth up to the limit of percolation threshold. The formation of Ru nanocrystals is favored by the emergence of interface dipole between Ru and SiO2 during deposition. The high growth temperature ensures improved heating stability of the Ru nanocrystals, which can be implemented in various appropriate applications.

Thin-film ferroelectric doped hafnia has emerged as a promising candidate for non-volatile computer memory devices due to its CMOS compatibility. The ferroelectricity in thin-film HfO2 is defined by the polar orthorhombic phase, whose stabilization depends on various parameters, such as doping species, stress, thickness, crystallization annealing temperature, etc. The concentration of oxygen vacancies is yet another parameter affecting the stabilization of the ferroelectric phase in HfO2 thin films. Here, we report on the effect of oxygen vacancies introduced in Y-doped HfO2 (HYO) films during reactive pulsed laser deposition on their ferroelectric properties, which we systematically study by correlating structural and electrical properties. Among different techniques, near-edge x-ray absorption fine structure analysis is successfully employed to distinguish between structurally similar ferroelectric orthorhombic and paraelectric tetragonal phases. It is shown that oxygen vacancies introduced at a certain concentration in HYO films can be used as a tool to control the phase composition as well as to decrease the formation energy (crystallization temperature) of the ferroelectric phase. Based on these results, we demonstrate a back-end-of-line compatible ferroelectric HYO capacitor device with competitive functional properties.

The transition to smart wearable and flexible optoelectronic devices communicating with each other and performing neuromorphic computing at the edge is a big goal in next-generation optoelectronics. These devices should perform their regular tasks supported by energy-efficient in-memory calculations. Here, we study the response of the CsPbBr$_3$ halide-perovskite single crystal fabricated on the flexible polymer substrate and integrated with the single-walled carbon nanotube thin film electrodes in a lateral geometry. We show both photodetection functions combined with the synaptic functionality in our device under the application of hybrid optoelectrical stimuli. Furthermore, we demonstrate that our device exhibits frequency-dependent bidirectional modification of synaptic weight with a sliding threshold similar to biologically plausible Bienenstock-Cooper-Munro learning. The demonstrated optoelectronic synaptic behavior in halide-perovskite single-crystals opens the opportunity for the development of hybrid organic-inorganic artificial visual systems.

The nanosecond speed of information writing and reading is recognized as one of the main advantages of next-generation non-volatile ferroelectric memory based on hafnium oxide thin films. However, the kinetics of polarization switching in this material have a complex nature, and despite the high speed of internal switching, the real speed can deteriorate significantly due to various external reasons. In this work, we reveal that the domain structure and the dielectric layer formed at the electrode interface contribute significantly to the polarization switching speed of 10 nm thick Hf0.5Zr0.5O2 (HZO) film. The mechanism of speed degradation is related to the generation of charged defects in the film which accompany the formation of the interfacial dielectric layer during oxidization of the electrode. Such defects are pinning centers that prevent domain propagation upon polarization switching. To clarify this issue, we fabricate two types of similar W/HZO/TiN capacitor structures, differing only in the thickness of the electrode interlayer, and compare their ferroelectric (including local ferroelectric), dielectric, structural (including microstructural), chemical, and morphological properties, which are comprehensively investigated using several advanced techniques, in particular, hard X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, and electron beam induced current technique.

Multiferroic materials with coexisting ferroelectric and ferromagnetic orders have attracted much attention due to the magnetoelectric coupling opening alternative prospects for electronic devices. Composite multiferroics containing separate ferroelectric and ferromagnetic components are a promising alternative to the single‐phase counterparts. Composite multiferroic structures comprising HfO 2 ‐based ferroelectrics are potentially feasible for technological applications. Here, this study reports on the experiments aiming at the manifestation of magnetoelectric coupling at Fe/Hf 0.5 Zr 0.5 O 2 (HZO) interface. Using synchrotron based 57 Fe Mössbauer spectroscopy technique in operando, this study probes element‐selectively the local magnetic properties of a nanometer‐thick enriched 57 Fe marker layer in functional Pt/ 57 Fe/HZO/TiN capacitors and demonstrates the evidence of the ferroelectric polarization effect on the α‐Fe magnetic response. Besides α‐Fe exhibiting a magnetoelectric coupling, both ferromagnetic and superparamagnetic Fe 3 O 4 components are found in the Mössbauer spectra, apparently originating from the oxygen or OH − ions penetrating ultrathin Pt overlayer during crystallization annealing of HZO. The observed effect as well as the electronic band lineup of the Fe/HZO interface elucidated from synchrotron based hard X‐ray photoemission spectroscopy measurements are interpreted in terms of charge‐mediated magnetoelectric coupling at the Fe/HfO 2 interface driven by ferroelectric HZO polarization reversal.

HfO2/Si interface is among the most studied heterostructure materials due to the use of HfO2 in the mainstream Si microelectronic technology. Following the discovery of new functionalities in HfO2 such as ferroelectric and reversible resistance-switching properties, we study ultrathin HfO2 films grown on highly doped (p(+) and n(+)) Si by means of synchrotron-based soft-x-ray spectroscopy techniques, such as x-ray photoelectron spectrosopy (XPS) and angle resolved photoelectron spectroscopy (ARPES). With angular resolution, we directly obtain the electronic dispersions E(k) of the single-crystalline Si substrate in contact with the HfO2 overlayer, depending on the Si doping and heat treatment, and determine the k-resolved band offset at the interface. Analysis of the Hf and Si core-level energies and line shapes as a function of photon energy yields band bending in HfO2 and Si. The evolution of the Hf 4f linewidth upon annealing points to development of a potential distribution across HfO2 due to charged defects at the surface and interface with Si. The effect of intense x-ray beam on the HfO2/Si interfaces, distorting their pristine electronic structure, is evaluated from the time evolution of line shape and position under irradiation. We propose a model explaining the effects of both heat treatment and x-ray irradiation on the HfO2/Si electronic structure in terms of oxygen vacancies generated at the surface of HfO(2)and its interface to Si, where the released O atoms react with Si to form SiOx at the interface. The knowledge of the irradiation-dependent band bending is essential for precise determination of the k-dependent band offset locally at the HfO2/Si interface.

$\mathrm{Hf}{\mathrm{O}}_{2}/\mathrm{Si}$ interface is among the most studied heterostructure materials due to the use of ${\mathrm{HfO}}_{2}$ in the mainstream Si microelectronic technology. Following the discovery of new functionalities in ${\mathrm{HfO}}_{2}$ such as ferroelectric and reversible resistance-switching properties, we study ultrathin ${\mathrm{HfO}}_{2}$ films grown on highly doped (${p}^{+}$ and ${n}^{+}$) Si by means of synchrotron-based soft-x-ray spectroscopy techniques, such as x-ray photoelectron spectrosopy (XPS) and angle resolved photoelectron spectroscopy (ARPES). With angular resolution, we directly obtain the electronic dispersions $E$(k) of the single-crystalline Si substrate in contact with the ${\mathrm{HfO}}_{2}$ overlayer, depending on the Si doping and heat treatment, and determine the k-resolved band offset at the interface. Analysis of the Hf and Si core-level energies and line shapes as a function of photon energy yields band bending in ${\mathrm{HfO}}_{2}$ and Si. The evolution of the Hf $4f$ linewidth upon annealing points to development of a potential distribution across ${\mathrm{HfO}}_{2}$ due to charged defects at the surface and interface with Si. The effect of intense x-ray beam on the $\mathrm{Hf}{\mathrm{O}}_{2}/\mathrm{Si}$ interfaces, distorting their pristine electronic structure, is evaluated from the time evolution of line shape and position under irradiation. We propose a model explaining the effects of both heat treatment and x-ray irradiation on the $\mathrm{Hf}{\mathrm{O}}_{2}/\mathrm{Si}$ electronic structure in terms of oxygen vacancies generated at the surface of ${\mathrm{HfO}}_{2}$ and its interface to Si, where the released O atoms react with Si to form ${\mathrm{SiO}}_{x}$ at the interface. The knowledge of the irradiation-dependent band bending is essential for precise determination of the k-dependent band offset locally at the $\mathrm{Hf}{\mathrm{O}}_{2}/\mathrm{Si}$ interface.

Embedded, low-power, fast nonvolatile memory is considered to be a viable approach to improving the performance of computing systems designed for real-time processing of the incoming information stream. Among of the competitive candidates because of the combination of functional properties, such as the energy per writing cycle, speed, number of switching cycles (endurance), and retention time. In this work, we explore the effect of nanopatterning of the Pt bottom electrode (BE) to control the formation, number, and size of conductive filaments in the TaOx layer in Ta/TaOx/Pt resistance switching (RS) devices integrated with field-effect transistors (the one transistor and one resistor concept). Patterning is achieved by either etching "holes" in the Pt BE or growth of Pt "pillars" on top of a flat continuous underlayer. Such nanopatterned RS devices reveal lower (similar to 1.2 vs similar to 2.5 V) electroforming voltages and similar to 102 times lower currents in the ON state compared to those with a nonpatterned Pt electrode, while exhibiting more than 105 switching cycles without any degradation as well as better device-to-device and cycle-to-cycle repeatability of electrical characteristics. The modeling of the electric-field distribution across the functional TaOx layer reveals the edge of Pt nanopillars as the most probable area for filament formation. The elemental mapping during transmission electron microscopy analysis of the patterned Ta/TaOx/Pt RS device cross section confirms that the thickness of the TaOx layer on top of the Pt "pillar" is minimal at the inclined edge. The conducting atomic force microscopy current mapping of two patterned RS devices upon electroforming and removal of the top electrode in high- and lowresistance states confirms a single conducting channel formed at the edge of the Pt electrode.

The crystallization of as‐grown amorphous Hf 0.5 Zr 0.5 O 2 (HZO) thin films to the metastable ferroelectric phase by pulsed laser annealing (PLA) is investigated. PLA experiments are conducted using a Nd:YAG laser operating in two regimes: Q ‐switched mode with a pulse duration of τ ≈ 16 ns and free‐running mode ( τ ≈ 1 ms). The crystallization of a ferroelectric orthorhombic phase in the annealed films is confirmed by X‐ray diffraction, polarization versus electric field ( P–E ) measurements, and piezoresponse force microscopy (PFM) analyses. Remnant polarization up to 2 P r ≈ 50 μC cm −2 is achieved in the TiN/HZO/W capacitor structures grown on the Si substrate and subjected to millisecond PLA. In contrast, the use of laser annealing in a 10 ns pulse duration range is found ineffective for the crystallization of any HZO phase in capacitor structures. Detailed PFM analysis across a capacitor device area reveals the effect of the local temperature on the sample surface during PLA on the resulting ferroelectric domain structure. The lower thermal impact on the substrate during PLA opens the possibility of creating local areas of the ferroelectric phase in HZO films using reflecting copper masks.

Pairing two-dimensional semiconductors with ferroelectric films may allow for the development of hybrid electronic devices that would not only exhibit a combination of the functional properties of both material groups but would also reveal unusual characteristics emerging from coupling between these properties. Here, we report the observation of a considerable (up to 103 at 0.8 V read bias) polarization-mediated tunneling electroresistance (TER) effect in Hf0.5Zr0.5O2 (HZO) ferroelectric tunnel junctions (FTJs) employing MoS2 as one of the electrodes. It was found that for this type of hybrid FTJs, a change in resistance upon polarization reversal could be described by Fowler–Nordheim tunneling. The underlying mechanism for the enhanced TER effect is a polarization-mediated accumulation or depletion of the majority carriers at the MoS2/HZO interface, which results in a change in the effective barrier shape seen by the tunneling electrons. Given the compatibility of HfO2-family ferroelectrics with CMOS technology and a possibility of large scale growth and transfer of MoS2 films, our results provide a pathway for fabrication of high-density nonvolatile memory and data storage systems based on hybrid FTJs.

Composite multiferroics containing ferroelectric and ferromagnetic components often have much larger magnetoelectric coupling compared to their single-phase counterparts. Doped or alloyed HfO2-based ferroelectrics may serve as a promising component in composite multiferroic structures potentially feasible for technological applications. Recently, a strong charge-mediated magnetoelectric coupling at the Ni/HfO2 interface has been predicted using density functional theory calculations. Here, we report on the experimental evidence of such magnetoelectric coupling at the Ni/Hf0.5Zr0.5O2(HZO) interface. Using a combination of operando XAS/XMCD and HAXPES/MCDAD techniques, we probe element-selectively the local magnetic properties at the Ni/HZO interface in functional Au/Co/Ni/HZO/W capacitors and demonstrate clear evidence of the ferroelectric polarization effect on the magnetic response of a nanometer-thick Ni marker layer. The observed magnetoelectric effect and the electronic band lineup of the Ni/HZO interface are interpreted based on the results of our theoretical modeling. It elucidates the critical role of an ultrathin NiO interlayer, which controls the sign of the magnetoelectric effect as well as provides a realistic band offset at the Ni/HZO interface, in agreement with the experiment. Our results hold promise for the use of ferroelectric HfO2-based composite multiferroics for the design of multifunctional devices compatible with modern semiconductor technology.