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Investigating the promising chalcogenide materials for the development of memory and advanced neuromorphic computing applications is a critical step in realizing electronic memory and synaptic devices that can efficiently emulate biological synaptic functions. However, the assessment of monochalcogenide materials for the fabrication of highly scalable memory and electronic synaptic devices that can accurately mimic synaptic functions remain limited. In the present study, we investigated the thickness-dependent resistive switching (RS) behavior of conductive bridge random access memory (CBRAM) based on a monochalcogenide GeSe switching medium for its possible application in high-performance memory and electronic synapses. GeSe thin films of different thicknesses (6, 13, 24, 35, 47, and 56 nm) were deposited via sputtering to fabricate CBRAM devices with a stacking sequence of Ag/GeSe/Pt/Ti/SiO 2 . The devices exhibited compliance current (CC)-free and electroforming-free RS with highly stable endurance and retention characteristics with no major degradation. All devices with a thickness of 6 nm had a low-resistance state (LRS), which required an initial reset to ensure reliable switching cycles. The devices with a thickness of 47 nm and above exhibited the co-existence of unipolar resistive switching (U-RS) and bipolar resistive switching (B-RS) with the CC-controlled transition between the two switching behaviors. Multilevel resistance states in the 24-nm device between a highresistance state (HRS) and an LRS were achieved by controlling the set-CC (from 5 mA to CC-free) and the reset stop voltage (from −0.5 to −1.0 V) during the set and reset processes, respectively. The analog RS behavior of the device was further investigated with appropriate pulse measurements to emulate vital synaptic functions, including long-term potentiation (LTP), long-term depression (LTD), spike-rate-dependent plasticity (SRDP), spike-timing-dependent plasticity (STDP), paired-pulse facilitation (PPF), paired-pulse depression (PPD) and post-tetanic potentiation (PTP). Overall, the detailed investigation of thickness-dependent GeSe monochalcogenide material indicates that it is a highly suitable candidate for use in highly scalable memory devices and electronic synapses for neuromorphic computing applications.

This article reviews recent progress in understanding the resistive switching (RS) behavior and improvements in device performance of RS metal oxide (MO) thin-film systems and devices. The diverse RS MO materials are classified according to their switching mechanisms and characteristics. For each category, some representative materials are selected, and their characteristics are discussed. In addition, other factors such as the device structure, which also plays a crucial role in determining the device properties, are discussed as well. When applied in a real circuit (e.g., in a crossbar structure), there are device features/characteristics that need to be considered, including the bias polarity for switching, the current-voltage relationship, reliability, and scaling issues. Since nonvolatile RS in many MO materials is primarily associated with localized conduction channels, understanding the nature and the dynamic change of the current path structure is crucial and therefore is reviewed at length here. Guidelines for the choice of materials and access devices and their fabrication methods will also be provided. Finally, this review concludes with the outlook and challenges of MO-based resistance change devices for semiconductor memories.

The phenomenon of electron tunneling has been known since the advent of quantum mechanics, but continues to enrich our understanding of many fields of physics, as well as creating sub-fields on its own. Spin-dependent tunneling in magnetic tunnel junctions has aroused considerable interest and development. In parallel with this endeavor, recent advances in thin-film ferroelectrics have demonstrated the possibility of achieving stable and switchable ferroelectric polarization in nanometer-thick films. This discovery opened the possibility of using thin-film ferroelectrics as barriers in magnetic tunnel junctions, thus merging the fields of magnetism, ferroelectricity, and spin-polarized transport into an exciting and promising area of novel research. Nowadays, this research has become an important constituent of a broader effort in multiferroic materials and heterostructures that involves rich fundamental science and offers a potential for applications in novel multifunctional devices. The purpose of this article is to review recent developments in ferroelectric and multiferroic tunnel junctions. Starting from the concept of electron tunneling, we first discuss the key properties of magnetic tunnel junctions and then assess key functional characteristics of ferroelectric and multiferroic tunnel junctions. We discuss the recent demonstrations of giant resistive switching observed in ferroelectric tunnel junctions and the new concept of electrically controlling the spin polarization in magnetic tunnel junctions with a ferroelectric tunnel barrier.

Memristors are regarded as promising candidates for breaking the problems including high off‐chip memory access delays and the hash rate cost of frequent data moving induced by algorithms for data‐intensive applications of existing computational systems. Recently, organic–inorganic halide perovskites (OIHPs) have been recognized as exceptionally favorable materials for memristors due to ease of preparation, excellent electrical conductivity, and structural flexibility. However, research on OIHP‐based memristors focuses on modulating resistive switching (RS) performance through electric fields, resulting in difficulties in moving away from complex external circuits and wire connections. Here, a multilayer memristor has been constructed with eutectic gallium and indium (EGaIn)/ MAPbI3/poly(3,4‐ethylenedioxythiophene): poly(4‐styrenesulphonate) (PEDOT: PSS)/indium tin oxide (ITO) structure, which exhibits reproducible and reliable bipolar RS with low SET/RESET voltages, stable endurance, ultrahigh average ON/OFF ratio, and excellent retention. Importantly, based on ion migration activated by sound‐driven piezoelectric effects, the device exhibits a stable acoustic response with an average ON/OFF ratio greater than 103, thus realizing non‐contact, multi‐signal, and far‐field control in RS modulation. This study provides a single‐structure multifunctional memristor as an integrated architecture for sensing, data storage, and computing. The memristors with EGaIn/MAPbI3/PEDOT:PSS/ITO structure are successfully fabricated. The devices present reproducible electrical RS behavior. Importantly, the devices exhibit piezo‐acoustic RS behaviors, enabling non‐contact, multi‐signal, and far‐field control. This phenomenon is strongly dependent on different frequencies and SPL. A physical model is proposed to enhance understanding. This work introduces a single‐structure multifunctional memristor for sensing, data storage, and computing.

Resistive switching, the reversible modulation of electronic conductivity in thin films under electrical stress, has been observed in a wide range of material systems and is attributed to diverse physical mechanisms. Research activity in this area has been traditionally fueled by the search for a perfect electronic memory candidate but recently received additional attention due to a number of other promising applications, such as reconfigurable and neuromorphic computing. This issue of MRS Bulletin is devoted to current state-of-the-art understanding of the physics behind resistive switching in several major classes of material systems and their intrinsic scaling prospects in the context of electronic circuit applications. In particular, the goal of this introductory article is to review the most promising applications of thin-film devices and outline some of the major requirements for their performance.

The mechanism of resistive switching in Pt/HfO 2 (8 nm)/HfO X N Y (4 nm)/TiN structures, in which there are two resistive switching modes: bipolar resistive switching and complementary resistive switching. We demonstrate that resistive switching without external current compliance is possible. It is shown experimentally that the conductivity in the low-resistance state corresponds to the space-charge-limited current. A qualitative model is proposed that describes the transition from bipolar resistive switching to complementary resistive switching using Schottky barrier modulation at the metal-insulator interface. Based on this model, an explanation is given for the degradation of the low-resistance state during endurance measurements.

A range of material systems exist in which nanoscale ionic transport and redox reactions provide the essential mechanisms for memristive switching. One class relies on mobile cations, which are easily created by electrochemical oxidation of the corresponding electrode metal, transported in the insulating layer, and reduced at the inert counterelectrode. These devices are termed electrochemical metallization (ECM) memories, also called conductive bridge random access memories. The memristive characteristics of the ECM cells provide opportunities for circuit design and computational concepts that go beyond those in traditional complementary metal oxide semiconductor (CMOS) technology. Passive memory arrays open up paths toward ultradense and 3D stackable memory and logic gate arrays. Furthermore, the multivalued conductance characteristics allow for potential exploitation of the cells as synapses in neuromorphic circuits in future energy efficient high-performance computer architectures. Despite exciting results obtained in recent years, many challenges have to be met before these physical effects can be turned into competitive industrial technology. Here, we briefly review the basic working principle, the different possible and potential material combinations, and the fundamental electrochemical processes in ECM cells and their implications for device operations. The prospects of ECM-based resistive random access memory as an emerging memory technology are also reviewed in terms of switching speed and scalability.

In this work, we examined the irregular resistive switching behaviors of a complementary metal–oxide–semiconductor (CMOS)-compatible Cu/Al2O3/Si resistor device. X-ray photoelectron spectroscopy (XPS) analysis confirmed the chemical and material compositions of a Al2O3 thin film layer and Si substrate. Bipolar resistive switching occurred in a more stable manner than the unipolar resistive switching in the device did. Five cells were verified over 50 endurance cycles in terms of bipolar resistive switching, and a good retention was confirmed for 10,000 s in the high-resistance state (HRS) and the low-resistance state (LRS). Both high reset current (~10 mA) and low reset current (<100 μA) coexisted in the bipolar resistive switching. We investigated nonideal resistive switching behaviors such as negative-set and current overshoot, which could lead to resistive switching failure.

Resistive memory devices based on organic materials that can be configured to two or more stable resistance states have been extensively explored as information storage media due to their advantages, which include simple device structures, low fabrication costs, and flexibility. Various organic-based materials such as small molecules, polymers, and composite materials have been observed to show bistability. This review provides a general summary about the materials, structures, characteristics, and mechanisms of organic resistive memory devices. Several critical strategies for device fabrication, performance enhancement, and integrated circuit architectures are also discussed.

Polycrystalline SnO2-HfO2 nanolaminated thin films were grown by atomic layer deposition (ALD) on SiO2/Si(100) and TiN substrates at 300 °C. The samples, when evaluated electrically, exhibited bipolar resistive switching. The sample object with a stacked oxide layer structure of SnO2 | HfO2 | SnO2 | HfO2 additionally exhibited bidirectional threshold resistive switching properties. The sample with an oxide layer structure of HfO2 | SnO2 | HfO2 displayed bipolar resistive switching with a ratio of high and low resistance states of three orders of magnitude. Endurance tests revealed distinguishable differences between low and high resistance states after 2500 switching cycles.