Emerging Robust Polymer Materials for High-Performance Two-Terminal Resistive Switching Memory

Facing the era of information explosion and the advent of artificial intelligence, there is a growing demand for information technologies with huge storage capacity and efficient computer processing. However, traditional silicon-based storage and computing technology will reach their limits and cannot meet the post-Moore information storage requirements of ultrasmall size, ultrahigh density, flexibility, biocompatibility, and recyclability. As a response to these concerns, polymer-based resistive memory materials have emerged as promising candidates for next-generation information storage and neuromorphic computing applications, with the advantages of easy molecular design, volatile and non-volatile storage, flexibility, and facile fabrication. Herein, we first summarize the memory device structures, memory effects, and memory mechanisms of polymers. Then, the recent advances in polymer resistive switching materials, including single-component polymers, polymer mixtures, 2D covalent polymers, and biomacromolecules for resistive memory devices, are highlighted. Finally, the challenges and future prospects of polymer memory materials and devices are discussed. Advances in polymer-based memristors will open new avenues in the design and integration of high-performance switching devices and facilitate their application in future information technology.

Novel ternary organic resistive switching memory doped with bipolar materials

Organic resistive switching memory (ORSM) shows great potential for neotype memory devices due to the preponderances of simple architecture, low power consumption, high switching speed and feasibility of large-area fabrication. Herein, solution-processed ternary ORSM devices doped with bipolar materials were achieved with high ON/OFF ratio and outstanding device stability. The resistive switching performance was effectively ameliorated by doping two bipolar materials (DpAn-InAc and DpAn-5BzAc) in different blending concentration into the PVK:OXD-7 donor-accepter system. Compared with the binary system (PVK: 30 wt% OXD-7), the ON/OFF ratios of the ternary devices doped with 6 wt% DpAn-5BzAc were greatly increased from 7.91 × 10²to 4.98 × 10⁴, with the operating voltage (∣V_set-V_reset∣) declined from 4.90 V to 2.25 V, respectively. Additionally, the stability of resistance state and uniformity of operating voltage were also significantly optimized for the ternary devices. For comparison, ternary devices doped with DpAn-InAc have been explored, which also achieved improved resistive switching behavior. A detailed analysis of electrical characteristics and the internal charge transfer properties of ORSM was performed to unveil the performance enhancement in ternary devices. Results indicate that the use of bipolar materials favors the efficient operation of OSRMs with proper energy level alignment and effective charge transfer.

Inorganic Halide Perovskite Quantum Dots: A Versatile Nanomaterial Platform for Electronic Applications

Metal halide perovskites have generated significant attention in recent years because of their extraordinary physical properties and photovoltaic performance. Among these, inorganic perovskite quantum dots (QDs) stand out for their prominent merits, such as quantum confinement effects, high photoluminescence quantum yield, and defect-tolerant structures. Additionally, ligand engineering and an all-inorganic composition lead to a robust platform for ambient-stable QD devices. This review presents the state-of-the-art research progress on inorganic perovskite QDs, emphasizing their electronic applications. In detail, the physical properties of inorganic perovskite QDs will be introduced first, followed by a discussion of synthesis methods and growth control. Afterwards, the emerging applications of inorganic perovskite QDs in electronics, including transistors and memories, will be presented. Finally, this review will provide an outlook on potential strategies for advancing inorganic perovskite QD technologies.

All Solution-Processed Inorganic, Multilevel Memristors Utilizing Liquid Metals Electrodes Suitable for Analog Computing

Herein, we report a solution-processable memristive device based on bismuth vanadate (BiVO₄) and titanium dioxide (TiO₂) with gallium-based eutectic gallium-indium (EGaIn) and gallium-indium-tin alloy (GaInSn) liquid metal as the top electrode. Scanning electron microscopy (SEM) shows the formation of a nonporous structure of BiVO₄ and TiO₂ for efficient resistive switching. Additionally, the gallium-based liquid metal (GLM)-contacted memristors exhibit stable memristor behavior over a wide temperature range from -10 to +90 °C. Gallium atoms in the liquid metal play an important role in the conductive filament formation as well as the device's operation stability as elucidated by I-V characteristics. The synaptic behavior of the GLM-memristors was characterized, with excellent long-term potentiation (LTP) and long-term depression (LTD) linearity. Using the performance of our device in a multilayer perceptron (MLP) network, a ∼90% accuracy in the handwriting recognition of modified national institute of standards and technology database (MNIST) was achieved. Our findings pave a path for solution-processed/GLM-based memristors which can be used in neuromorphic applications on flexible substrates in a harsh environment.

Low-Dimensional Metal-Halide Perovskites as High-Performance Materials for Memory Applications

Metal-halide perovskites have drawn profuse attention during the past decade, owing to their excellent electrical and optical properties, facile synthesis, efficient energy conversion, and so on. Meanwhile, the development of information storage technologies and digital communications has fueled the demand for novel semiconductor materials. Low-dimensional perovskites have offered a new force to propel the developments of the memory field due to the excellent physical and electrical properties associated with the reduced dimensionality. In this review, the mechanisms, properties, as well as stability and performance of low-dimensional perovskite memories, involving both molecular-level perovskites and structure-level nanostructures, are comprehensively reviewed. The property-performance correlation is discussed in-depth, aiming to present effective strategies for designing memory devices based on this new class of high-performance materials. Finally, the existing challenges and future opportunities are presented.

New Lead-free Organic-Inorganic Hybrid Semiconductor Single Crystals for a UV-Vis-NIR Broadband Photodetector

Organic-inorganic hybrid semiconducting (OIHS) materials, which can detect broader spectral regions, are highly desired in several applications including biomedical imaging, night vision, and optical communications. Although lead (Pb)-halide perovskites have reached a mature research stage, high toxicity of Pb hinders their large-scale viability. Tin (Sn)-based perovskites are the most common OIHS broadband light absorbers that replace toxic Pb; however, they are extremely unstable due to the notorious Sn2+ oxidation. Herein, a novel, non-toxic, and solution-processed millimeter-sized OIHS single crystal [Ga(C3H7NO)6](I3)3 has been grown at room temperature. Both the absorption measurement and density functional theory calculations have confirmed a narrow indirect band gap of 1.32 eV. The corresponding photodetector based on this single crystal demonstrated excellent performance including an ultraviolet-visible-near infrared (UV-vis-NIR) response between 325 and 1064 nm, fast response time (trise/tdecay = 3.8 ms/5.4 ms), and profound air storage stability (41 h), thus outperforming most common photodetectors based on Sn-based perovskites. This work not only provides a profound understanding of this novel organic-inorganic single-crystal material but also demonstrates its great potential to realize the high-performance UV-vis-NIR broadband photodetectors.

Electrode Engineering in Halide Perovskite Electronics: Plenty of Room at the Interfaces

Contact engineering is a prerequisite for achieving desirable functionality and performance of semiconductor electronics, which is particularly critical for organic-inorganic hybrid halide perovskites due to their ionic nature and highly reactive interfaces. Although the interfaces between perovskites and charge-transporting layers have attracted lots of attention due to the photovoltaic and light-emitting diode applications, achieving reliable perovskite/electrode contacts for electronic devices, such as transistors and memories, remains as a bottleneck. Herein, a critical review on the elusive nature of perovskite/electrode interfaces with a focus on the interfacial electrochemistry effects is presented. The basic guidelines of electrode selection are given for establishing non-polarized interfaces and optimal energy level alignment for perovskite materials. Furthermore, state-of-the-art strategies on interface-related electrode engineering are reviewed and discussed, which aim at achieving ohmic transport and eliminating hysteresis in perovskite devices. The role and multiple functionalities of self-assembled monolayers that offer a unique approach toward improving perovskite/electrode contacts are also discussed. The insights on electrode engineering pave the way to advancing stable and reliable perovskite devices in diverse electronic applications.

A purely ionic voltage effect soft triode

We report on the construction and characterization of an ionic soft triode intended to be based on interfacial ion adsorption and redox oxidizer depletion. The soft triode was built in a simple manner with no need for sophisticated or expensive materials. It does not utilize the control of a semiconducting channel, but an electrolyte. In different electrical circuit configurations, it can show amplification or memory effects. The device had an electrical current amplification reaching 52 and memory effects in the electrical resistance lasting for up to 6 h. These values were achieved by tuning the electrode interface, the electrolyte and diffusion properties. They are promising for neuromorphic applications.

Nanofiber Architecture Engineering Implemented by Electrophoretic-Induced Self-Assembly Deposition Technology for Flash-Type Memristors

Electrophoretic deposition (EPD) has been recognized as a promising large-scale film preparation technology for industrial application. Inspired by the conventional EPD method and the crystal diffusion growth strategy, we propose a modified electrophoretic-induced self-assembly deposition (EPAD) technique to control the morphologies of organic functional materials. Here, an ionic-type dye with a conjugated skeleton and strong noncovalent interactions, celestine blue (CB), is chosen as a module molecule for EPAD investigation. As expected, CB molecules can assemble into different nanostructures, dominated by applied voltage, concentration effect, and duration. Compared to a nanopillar layered packing structure formed by the traditional spin-coating method, the EPAD approach can produce a nanofiber structure under a fixed condition of 10 V/10 min. Intriguingly, a memristor device based on a pillar-like nanostructure exhibits WORM-type behavior, while a device based on nanofibers presents Flash memory performance. The assemble process and the memory mechanism are uncovered by molecular dynamics simulations and density-functional theory (DFT) calculations. This work endows the typical EPD technique with a fresh application scenario, where an in-depth study on the growth mechanism of nanofibers and the positive effect of unique morphologies on memristor performance are offered.

High Temperature CsPbBrxI3-x Memristors Based on Hybrid Electrical and Optical Resistive Switching Effects

The emergence of perovskite-based memristors associated with the migration of ions has attracted attention for use in overcoming the limitations of the von Neumann computing architecture and removing the bottleneck of storage density. However, systematic research on the temperature dependence of halide perovskite-based memristors is still required due to the unavoidable thermal stability limits. In this work, mixed halide CsPbBr_xI_3-x-based (X = 0, 1, 2) memristors with unique electrical and optical resistive switching properties in an ambient atmosphere from room temperature to a 240 °C maximum have been successfully achieved. At room temperature, the CsPbBr_xI_3-x-based memristors exhibit outstanding resistive switching behaviors such as ultralow operating voltage (∼0.81, ∼0.64, and ∼0.54 V for different devices, respectively), moderate ON/OFF ratio (∼10²), stable endurance (10³ cycles), and long retention time (10⁴ s). The CsPbBr_xI_3-x-based memristors maintain excellent repeatability and stability at high temperature. Endurance failures of CsPbI₃, CsPbBrI₂, and CsPbBr₂I memristors occur at 90, 150, and 270 °C, respectively. Finally, nonvolatile imaging employing CsPbBr₂I-based memristor arrays based on the electrical-write and optical-erase operation at 100 °C has been demonstrated. This study provides utilization potentiality in the high temperature scenarios for perovskite wearable and large-scale information devices.

Resistive Switching in HfO2-x/La0.67Sr0.33MnO3 Heterostructures: An Intriguing Case of Low H-Field Susceptibility of an E-Field Controlled Active Interface

High-performance nonvolatile resistive random access memories (ReRAMs) and their small stimuli control are of immense interest for high-speed computation and big-data processing in the emerging Internet of Things (IoT) arena. Here, we examine the resistive switching (RS) behavior in growth-controlled HfO₂/La_0.67Sr_0.33MnO₃ (LSMO) heterostructures and their tunability in a low magnetic field. It is demonstrated that oxygen-deficient HfO₂ films show bipolar switching with a high on/off ratio, stable retention, as well as good endurance owing to the orthorhombic-rich phase constitution and charge (de)trapping-enabled Schottky-type conduction. Most importantly, we have demonstrated that RS can be tuned by a very low externally applied magnetic field (∼0-30 mT). Remarkably, application of a magnetic field of 30 mT causes RS to be fully quenched and frozen in the high resistive state (HRS) even after the removal of the magnetic field. However, the quenched state could be resurrected by applying a higher bias voltage than the one for initial switching. This is argued to be a consequence of the electronically and ionically "active" nature of the HfO_2-x/LSMO interface on both sides and its susceptibility to the electric and low magnetic field effects. This result could pave the way for new designs of interface-engineered high-performance oxitronic ReRAM devices.

Oxide Passivation of Halide Perovskite Resistive Memory Device: A Strategy for Overcoming Endurance Problem

Owing to a low operation voltage, high on/off ratio, and tunable band gap, halide perovskites (HPs) are being conceived as an alternative to oxide or chalcogenide materials in resistive-switching (RS) memory devices. However, the HP-based RS memory devices face problems such as short endurance, low retention, and device stability. Herein, the oxide-passivated HP devices were fabricated by hybridizing the oxide sol-gel and halide adduct methods. The silicon oxide (SiO₂)-passivation enhanced the device properties with an endurance of 6000 cycles and retention of 1.8 × 10⁴ s. The study of activation energy using ionic conductivity and time-of-flight secondary-ion mass spectroscopy demonstrated that the migration path of the Ag ions is well-controlled by the SiO₂ passivation layer. Various oxides were used as passivation materials. Especially, the zirconium oxide-passivated devices exhibit excellent properties with an endurance of 57 000 cycles and retention of 7.8 × 10⁴ s. The high cohesive energy of oxides effectively increased the formation voltage by retarding the Ag-ion migration, leading to the improved endurance properties of the devices. This paper proposes a strategy for significantly improving the low endurance property of HP-based RS memory devices using the oxide passivation technology.

Tunable Synaptic Characteristics of a Ti/TiO2/Si Memory Device for Reservoir Computing

In this study, we fabricate and characterize a Ti/TiO₂/Si device with different dopant concentrations on a silicon surface for neuromorphic systems. We verify the device stack using transmission electron microscopy (TEM). The Ti/TiO₂/p⁺⁺Si device exhibits interface-type bipolar resistive switching with long-term memory. The potentiation and depression by the pulses of various amplitudes are demonstrated using gradual resistive switching. Moreover, pattern-recognition accuracy (>85%) is obtained in the neuromorphic system simulation when conductance is used as the weight in the network. Next, we investigate the short-term memory characteristics of the Ti/TiO₂/p⁺Si device. The dynamic range is well-controlled by the pulse amplitude, and the conductance decay depends on the interval between the pulses. Finally, we build a reservoir computing system using the short-term effect of the Ti/TiO₂/p⁺Si device, in which 4 bits (16 states) are differentiated by various pulse streams through the device that can be used for pattern recognition.

Halide Perovskites: A New Era of Solution-Processed Electronics

Organic-inorganic mixed halide perovskites have emerged as an excellent class of materials with a unique combination of optoelectronic properties, suitable for a plethora of applications ranging from solar cells to light-emitting diodes and photoelectrochemical devices. Recent works have showcased hybrid perovskites for electronic applications through improvements in materials design, processing, and device stability. Herein, a comprehensive up-to-date review is presented on hybrid perovskite electronics with a focus on transistors and memories. These applications are supported by the fundamental material properties of hybrid perovskite semiconductors such as tunable bandgap, ambipolar charge transport, reasonable mobility, defect characteristics, and solution processability, which are highlighted first. Then, recent progresses on perovskite-based transistors are reviewed, covering aspects of fabrication process, patterning techniques, contact engineering, 2D versus 3D material selection, and device performance. Furthermore, applications of perovskites in nonvolatile memories and artificial synaptic devices are presented. The ambient instability of hybrid perovskites and the strategies to tackle this bottleneck are also discussed. Finally, an outlook and opportunities to develop perovskite-based electronics as a competitive and feasible technology are highlighted.

Insights into Microscopic Crystal Growth Dynamics of CH3NH3PbI3 under a Laser Deposition Process Revealed by In Situ X-ray Diffraction

The process dynamics for the vacuum deposition of methylammonium lead iodide (MAPbI₃) perovskite was analyzed by in situ X-ray diffraction using synchrotron radiation. MAPbI₃ was fabricated by alternatingly supplying PbI₂ and methylammonium iodide via a laser deposition system installed at the synchrotron beamline BL46XU at SPring-8, and in situ crystallization analysis was conducted. Microscopic insights into the crystallization were obtained, including observation of Laue oscillation during the PbI₂ growth and octahedral unit (PbI₆) rotation during the transformation into perovskite. On the basis of this analysis, conditions that favor the construction of atomically flat MAPbI₃ perovskite films were deduced.

Nonlinear Photonics Using Low-Dimensional Metal-Halide Perovskites: Recent Advances and Future Challenges

Low-dimensional metal-halide perovskites have exhibited significantly superior nonlinear optical properties compared to traditional semiconductor counterparts, thanks to their peculiar physical and electronic structures. Their exceptional nonlinear optical characteristics make them excellent candidates for revolutionizing widespread applications. However, the research of nonlinear photonics based on low-dimensional metal-halide perovskites is in its infancy. There is a lack of comprehensive and in-depth summary of this research realm. Here, the state-of-the-art research progress related to third-and higher-order nonlinear optical properties of low-dimensional metal-halide perovskites with diverse crystal structures from 3D down to 0D, together with their practical applications, is summarized comprehensively. Critical discussions are offered on the fundamental mechanisms beneath their exceptional nonlinear optical performance from the physics viewpoint, attempting to disclose the role of intrinsic attributes (e.g., composition, bandgap, size, shape, and structure) and external modulation strategies (e.g., developing core-shell structures, transition metal ion doping, and hybridization with dielectric microspheres) in tuning the response. Additionally, their potential applications in nonlinear photonics, nonlinear optoelectronics, and biophotonics are systematically and thoroughly summed up and categorized. Lastly, insights into the current technical challenges and future research opportunities of nonlinear photonics based on low-dimensional metal-halide perovskites are provided.

Solution-processed electronics for artificial synapses

Artificial synaptic devices and systems have become hot topics due to parallel computing, high plasticity, integration of storage, and processing to meet the challenges of the traditional Von Neumann computers. Currently, two-terminal memristors and three-terminal transistors have been mainly developed for high-density storage with high switching speed and high reliability because of the adjustable resistivity, controllable ion migration, and abundant choices of functional materials and fabrication processes. To achieve the low-cost, large-scale, and easy-process fabrication, solution-processed techniques have been extensively employed to develop synaptic electronics towards flexible and highly integrated three-dimensional (3D) neural networks. Herein, we have summarized and discussed solution-processed techniques in the fabrication of two-terminal memristors and three-terminal transistors for the application of artificial synaptic electronics mainly reported in the recent five years from the view of fabrication processes, functional materials, electronic operating mechanisms, and system applications. Furthermore, the challenges and prospects were discussed in depth to promote solution-processed techniques in the future development of artificial synapse with high performance and high integration.

Bifunctional Silver-Doped ZnO for Reliable and Stable Organic-Inorganic Hybrid Perovskite Memory

Halide perovskites (HPs) have possible uses as an active layer for emerging memory devices due to their low operation voltage and high on/off ratio. However, HP-based memory devices, which are operated by the formation of a conductive filament, still suffer from reliability issues such as limited endurance and stability. To solve the problems, it is essential to control filament formation in the active layer. Here, we present nanoscale HP-based memory devices that have a Ag-doped ZnO (AZO) layer on HP. The AZO layer is used as a Ag ion reservoir for filament formation in HP, and this reservoir enables control of filament formation. By adjusting the Ag concentration in the AZO layer, the controlled filament composed of Ag can be formed; as a result, the memory device has excellent endurance (3 × 10⁴ cycles) compared to the device that uses a Ag electrode instead of an AZO layer (4 × 10² cycles). Also, an AZO layer can passivate HP, so the device operates stably in ambient air for 15 days with a high on/off ratio (10⁶). These results demonstrate that the introduction of the AZO layer can improve the reliability of HP-based memory devices for high-density applications.

Nonvolatile Multistates Memories for High-Density Data Storage

In the current information age, the realization of memory devices with energy efficient design, high storage density, nonvolatility, fast access, and low cost is still a great challenge. As a promising technology to meet these stringent requirements, nonvolatile multistates memory (NMSM) has attracted lots of attention over the past years. Owing to the capability to store data in more than a single bit (0 or 1), the storage density is dramatically enhanced without scaling down the memory cell, making memory devices more efficient and less expensive. Multistates in a single cell also provide an unconventional in-memory computing platform beyond the Von Neumann architecture and enable neuromorphic computing with low power consumption. In this review, an in-depth perspective is presented on the recent progress and challenges on the device architectures, material innovation, working mechanisms of various types of NMSMs, including flash, magnetic random-access memory (MRAM), resistive random-access memory (RRAM), ferroelectric random-access memory (FeRAM), and phase-change memory (PCM). The intriguing properties and performance of these NMSMs, which are the key to realizing highly integrated memory hierarchy, are discussed and compared.

Synaptic Characteristics of Amorphous Boron Nitride-Based Memristors on a Highly Doped Silicon Substrate for Neuromorphic Engineering

In this study, the resistive switching and synaptic properties of a complementary metal-oxide semiconductor-compatible Ti/a-BN/Si device are investigated for neuromorphic systems. A gradual change in resistance is observed in a positive SET operation in which Ti diffusion is involved in the conducting path. This operation is extremely suitable for synaptic devices in hardware-based neuromorphic systems. The isosurface charge density plots and experimental results confirm that boron vacancies can help generate a conducting path, whereas the conducting path generated by a Ti cation from interdiffusion forms is limited. A negative SET operation causes a considerable decrease in the formation energy of only boron vacancies, thereby increasing the conductivity in the low-resistance state, which may be related to RESET failure and poor endurance. The pulse transient characteristics, potentiation and depression characteristics, and good retention property of eight multilevel cells also indicate that the positive SET operation is more suitable for a synaptic device owing to the gradual modulation of conductance. Moreover, pattern recognition accuracy is examined by considering the conductance values of the measured data in the Ti/a-BN/Si device as the synaptic part of a neural network. The linear and symmetric synaptic weight update in a positive SET operation with an incremental voltage pulse scheme ensures higher pattern recognition accuracy.

Controlled Growth of Fine Multifilaments in Polymer-Based Memristive Devices Via the Conduction Control

Solid polymer electrolyte (SPE) is one of the choices for many ionic devices, including organic transistors, ion batteries, memristors, and more. However, uncontrollable conductive filament formation seriously affects the performance of the device. In this paper, the PEDOT:PSS was doped to improve the electronic and ionic conductivity of amorphous polymer electrolyte poly(vinylpyrrolidone) (PVP), realizing the transition of the filaments growth from cathode to anode in atomic switch memristors. Based on the difference in ion and electron mobility and scanning electron microscope observation, the in situ reductions of metal ions inside the dielectric layer can effectively prevent the formation of uncontrollable filaments. The formation of uniformly distributed metal particles in the dielectric layer is similar to co-sputter doping technology, which enables the device to exhibit excellent performance, such as smaller set/reset bias distribution, endurance, and retention. Obviously, this innovative way improves the conductive mechanism of ionic devices.

Multilevel Resistive Switching Memory Based on a CH3NH3PbI 3-xClx Film with Potassium Chloride Additives

High-quality CH3NH3PbI 3-xClx (MAPIC) films were prepared using potassium chloride (KCl) as an additive on indium tin oxide (ITO)-coated glass substrates using a simple one-step and low-temperature solution reaction. The Au/KCl-MAPIC/ITO/glass devices exhibited obvious multilevel resistive switching behavior, moderate endurance, and good retention performance. Electrical conduction analysis indicated that the resistive switching behavior of the KCl-doped MAPIC films was primarily attributed to the trap-controlled space-charge-limited current conduction that was caused by the iodine vacancies in the films. Moreover, the modulations of the barrier in the Au/KCl-MAPIC interface under bias voltages were thought to be responsible for the resistive switching in the carrier injection trapping/detrapping process.

Tailored 2D/3D Halide Perovskite Heterointerface for Substantially Enhanced Endurance in Conducting Bridge Resistive Switching Memory

Hybrid organic-inorganic halide perovskites (HPs) have garnered significant attention for use in resistive switching (RS) memory devices due to their low cost, low operation voltage, high on/off ratio, and excellent mechanical properties. However, the HP-based RS memory devices continue to face several challenges owing to the short endurance and stability of the HP film. Herein, two-dimensional/three-dimensional (2D/3D) perovskite heterojunction films were prepared via a low-temperature all-solution process and their RS behavior was investigated for the first time. The 2D/3D perovskite RS devices exhibited excellent performance with an endurance of 2700 cycles, a high on/off ratio of 10⁶, and an operation speed of 640 μs. The calculated thermally assisted ion hopping activation energy and the results of the time-of-flight secondary ion mass spectroscopy demonstrated that the 2D perovskite layer could efficiently prevent the Ag ion migration into the 3D perovskite film. Moreover, we found that owing to its high thermal conductivity, the 2D perovskite can control the rupture of the Ag conductive filament. Thus, the 2D perovskite layer enhances endurance by controlling both Ag migration and filament rupture. Hence, this study provides an alternate strategy for improving endurance of HP-based RS memory devices.

Formation of p-n junctions in nanoparticle cerium oxide electrolytic cells displaying memristive switching behaviour

A macro-scale metal-semiconductor-metal device comprising CeO₂ nanoparticles cast from a suspension of cerium dioxide formed by a novel synthetic method was fabricated. Thin CeO₂ films of 40 nm thickness placed between panels of aluminium and/or copper displayed memristive-like resistive switching behaviour upon the application of potential sweeps ranging between -0.6 V and 0.6 V. A mechanism is proposed based on the notion that an electrolytic cell operates under such conditions with the initial formation of p and n-type regions within the central semiconductive thin film. Evidence is presented for the existence of numerous point defects in these nanosized CeO₂ films, which are also likely to play a role in the device's operation acting as internal dopants. Steady currents were observed upon the imposition of constant potentials, most notably at higher potential values (both anodic and cathodic). It is suggested that electrons and holes act as charge carriers in these devices rather than ionic species as proposed in some other mechanisms.