Flexible Hybrid Organic-Inorganic Perovskite Memory

Enhancing simulation feasibility for multi-layer 2D MoS2 RRAM devices: reliability performance learnings from a passive network model

While two-dimensional (2D) MoS2 has recently shown promise as a material for resistive random-access memory (RRAM) devices due to its demonstrated resistive switching (RS) characteristics, its practical application faces a significant challenge in industry regarding its limited yield and endurance. Our earlier work introduced an effective switching layer model to understand RS behavior in both mono- and multi-layered MoS2. However, functioning as a phenomenological percolation modeling tool, it lacks the capability to accurately simulate the intricate current-voltage (I-V) characteristics of the device, thereby hindering its practical applicability in 2D RRAM research. In contrast to the established conductive filament model for oxide-based RRAM, the RS mechanism in 2D RRAM remains elusive. This paper presents a novel simulator aimed at providing an intuitive, visual representation of the stochastic behaviors involved in the RS process of multi-layer 2D MoS2 RRAM devices. Building upon the previously proposed phenomenological simulator for 2D RRAM, users can now simulate both the I-V characteristics and the resistive switching behaviors of the RRAM devices. Through comparison with experimental data, it was observed that yield and endurance characteristics are linked to defect distributions in MoS2.

Resistive switching memories with enhanced durability enabled by mixed-dimensional perfluoroarene perovskite heterostructures

Hybrid halide perovskites are attractive candidates for resistive switching memories in neuromorphic computing applications due to their mixed ionic-electronic conductivity. Moreover, their exceptional optoelectronic characteristics make them effective as semiconductors in photovoltaics, opening perspectives for self-powered memory elements. These devices, however, remain unexploited, which is related to the variability in their switching characteristics, weak endurance, and retention, which limit their performance and practical use. To address this challenge, we applied low-dimensional perovskite capping layers onto 3D mixed halide perovskites using two perfluoroarene organic cations, namely (perfluorobenzyl)ammonium and (perfluoro-1,4-phenylene)dimethylammonium iodide, forming Ruddlesden-Popper and Dion-Jacobson 2D perovskite phases, respectively. The corresponding mixed-dimensional perovskite heterostructures were used to fabricate resistive switching memories based on perovskite solar cell architectures, showing that the devices based on perfluoroarene heterostructures exhibited enhanced performance and stability in inert and ambient air atmosphere. This opens perspectives for multidimensional perovskite materials in durable self-powered memory elements in the future.

High-performance one-dimensional halide perovskite crossbar memristors and synapses for neuromorphic computing

Despite impressive demonstrations of memristive behavior with halide perovskites, no clear pathway for material and device design exists for their applications in neuromorphic computing. Present approaches are limited to single element structures, fall behind in terms of switching reliability and scalability, and fail to map out the analog programming window of such devices. Here, we systematically design and evaluate robust pyridinium-templated one-dimensional halide perovskites as crossbar memristive materials for artificial neural networks. We compare two halide perovskite 1D inorganic lattices, namely (propyl)pyridinium and (benzyl)pyridinium lead iodide. The absence of conjugated, electron-rich substituents in PrPyr+ prevents edge-to-face type π-stacking, leading to enhanced electronic isolation of the 1D iodoplumbate chains in (PrPyr)[PbI3], and hence, superior resistive switching performance compared to (BnzPyr)[PbI3]. We report outstanding resistive switching behaviours in (PrPyr)[PbI3] on the largest flexible crossbar implementation (16 × 16) to date - on/off ratio (>105), long term retention (105 s) and high endurance (2000 cycles). Finally, we put forth a universal approach to comprehensively map the analog programming window of halide perovskite memristive devices - a critical prerequisite for weighted synaptic connections in artificial neural networks. This consequently facilitates the demonstration of accurate handwritten digit recognition from the MNIST database based on spike-timing-dependent plasticity of halide perovskite memristive synapses.

Self-Assembly of Delta-Formamidinium Lead Iodide Nanoparticles to Nanorods: Study of Memristor Properties and Resistive Switching Mechanism

In the quest for advanced memristor technologies, this study introduces the synthesis of delta-formamidinium lead iodide (δ-FAPbI3) nanoparticles (NPs) and their self-assembly into nanorods (NRs). The formation of these NRs is facilitated by iodide vacancies, promoting the fusion of individual NPs at higher concentrations. Notably, these NRs exhibit robust stability under ambient conditions, a distinctive advantage attributed to the presence of capping ligands and a crystal lattice structured around face-sharing octahedra. When employed as the active layer in resistive random-access memory devices, these NRs demonstrate exceptional bipolar switching properties. A remarkable on/off ratio (105) is achieved, surpassing the performances of previously reported low-dimensional perovskite derivatives and α-FAPbI3 NP-based devices. This enhanced performance is attributed to the low off-state current owing to the reduced number of halide vacancies, intrinsic low dimensionality, and the parallel alignment of NRs on the FTO substrate. This study not only provides significant insights into the development of superior materials for memristor applications but also opens new avenues for exploring low-dimensional perovskite derivatives in advanced electronic devices.

Piezo-Acoustic Resistive Switching Behaviors in High-Performance Organic-Inorganic Hybrid Perovskite Memristors

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.

Light and voltage dual-modulated volatile resistive switching in single ZnO nanowires

A single ZnO nanowire device with volatile resistive switching behavior has been prepared. Different from traditional resistive switching devices, such ZnO nanowire devices do not exhibit resistive switching behaviors under a single bias voltage, and appear resistive switching behavior under the combined action of light stimuli and bias voltage. Through the demonstration of the time-dependent hysteresis curve and atmosphere-dependent hysteresis loop of the resistive switching devices, it is believed that under the resistive switching process, ultraviolet illumination can increase the carrier concentration and modulate the barrier depletion structure, and external bias voltage can ionize the surface state. They work together to modulate the switching process of the devices. Such light stimuli and bias voltage dual-modulated resistive switching device enables optical control and may thus be considered for sensory applications or optically tunable memories.

Attaining inhibition of sneak current and versatile logic operations in a singular halide perovskite memristive device by introducing appropriate interface barriers

Emerging resistive switching devices hold the potential to realize densely packed passive nanocrossbar arrays, suitable for deployment as random access memory devices (ReRAMs) in both embedded and high-capacity storage applications. In this study, we have engineered ReRAMs comprising ITO/(UVO-treated) amorphous ZnO (a-ZnO)/MAPbI3/Ag which effectively mitigate cross-talk currents without additional components. Significantly, we successfully executed a comprehensive set of 12 distinct 2-input sequential logic functions in a single halide perovskite ReRAM unit for the first time. Furthermore, these logic functions are devoid of any dependency on external light sources, entail merely 1 or 2 logic steps, and showcase symmetrical operability. A superior resistive switching behavior was achieved by harmonizing the charge transport within the bulk MAPbI3 and the tunneling barriers at the interfaces. The outcomes indicate progress in mitigating cross-talk and executing multiple logic functions within a single halide perovskite ReRAM unit, offering a new perspective for the advancement of halide perovskite ReRAMs.

MAPbBr3 Halide Perovskite-Based Resistive Random-Access Memories Using Electron Transport Layers for Long Endurance Cycles and Retention Time

Recent studies have focused on exploring the potential of resistive random-access memory (ReRAM) utilizing halide perovskites as novel data storage devices. This interest stems from its notable attributes, including a high ON/OFF ratio, low operating voltages, and exceptional mechanical properties. Nevertheless, there have been reports indicating that memory systems utilizing halide perovskites encounter certain obstacles pertaining to their stability and dependability, mostly assessed through endurance and retention time. Moreover, the presence of these problems can potentially restrict their practical applicability. This study explores a resistive switching memory device utilizing MAPbBr3 perovskite, which demonstrates bipolar switching characteristics. The device fabrication procedure involves a low-temperature, all-solution process. For the purpose of enhancing the device's reliability, the utilization of TPBI(2,2',2″-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) as an electron transfer material on the MAPbBr3 switching layer was implemented for the first time. The formation and rupture of Ag filaments in the MAPbBr3 perovskite switching layer are attributed to reduction-oxidation reactions. The TPBI is involved in the regulation of filaments during the SET and RESET processes. Hence, it can be shown that the MAPbBr3 device incorporating TPBI exhibited about 1000 endurance cycles when subjected to continuous voltage pulses. Moreover, the device consistently maintained ON/OFF ratios above 107. In contrast, the original MAPbBr3 device without TPBI demonstrated a significantly lower endurance with only 90 cycles observed. In addition, the MAPbBr3 device integrated with TPBI exhibited a retention time exceeding 3 × 103 s. The findings of this research provide compelling evidence to support the notion that electron transfer materials have promise for the development of halide perovskite memory systems owing to their favorable attributes of dependability and stability.

Novel Semiconductive Ternary Hybrid Heterostructures for Artificial Optoelectronic Synapses

Synaptic devices that mimic biological synapses are considered as promising candidates for brain-inspired devices, offering the functionalities in neuromorphic computing. However, modulation of emerging optoelectronic synaptic devices has rarely been reported. Herein, a semiconductive ternary hybrid heterostructure is prepared with a D-D'-A configuration by introducing polyoxometalate (POM) as an additional electroactive donor (D') into a metalloviologen-based D-A framework. The obtained material features an unprecedented porous 8-connected bcu-net that accommodates nanoscale [α-SiW12 O40 ]4- counterions, displaying uncommon optoelectronic responses. Besides, the fabricated synaptic device based on this material can achieve dual-modulation of synaptic plasticity due to the synergetic effect of electron reservoir POM and photoinduced electron transfer. And it can successfully simulate learning and memory processes similar to those in biological systems. The result provides a facile and effective strategy to customize multi-modality artificial synapses in the field of crystal engineering, which opens a new direction for developing high-performance neuromorphic devices.

Solution-Processed Hydrogen-Bonded Organic Framework Nanofilms for High-Performance Resistive Memory Devices

The integration of hydrogen-bonded organic frameworks (HOFs) into electronic devices holds great promise due to their high crystallinity, intrinsic porosity, and easy regeneration. However, despite their potential, the utilization of HOFs in electronic devices remains largely unexplored, primarily due to the challenges associated with fabricating high-quality films. Herein, a controlled synthesis of HOF nanofilms with smooth surface, good crystallinity, and high orientation is achieved using a solution-processed approach. The memristors exhibit outstanding bipolar switching performance with a low set voltage of 0.86 V, excellent retention of 1.64 × 104 s, and operational endurance of 60 cycles. Additionally, these robust memristors display remarkable thermal stability, maintaining their performance even at elevated temperatures of up to 200 °C. More strikingly, scratched HOF films can be readily regenerated through a simple solvent rinsing process, enabling their reuse for the fabrication of new memristors, which is difficult to achieve with traditional resistive switching materials. Additionally, a switching mechanism based on the reversible formation and annihilation of conductive filaments is revealed. This work provides novel and invaluable insights that have a significant impact on advancing the widespread adoption of HOFs as active layers in electronic devices.

Thermal/Water-Induced Phase Transformation and Photoluminescence of Hybrid Manganese(II)-Based Chloride Single Crystals

Mn(II)-based hybrid halides have attracted great attention from the optoelectronic fields due to their nontoxicity, special luminescent properties, and structural diversity. Here, two novel organic-inorganic hybrid Mn(II)-based halide single crystals (1-mpip)MnCl4·3H2O and (1-mpip)2MnCl6 (1-mpip = 1-methylpiperazinium, C5H14N2+) were grown by a slow evaporation method in ambient atmosphere. Interestingly, (1-mpip)2MnCl6 single crystals exhibit the green emission with a PL peak at 522 nm and photoluminescence quantum yields (PLQYs) of ≈5.4%, whereas (1-mpip)MnCl4·3H2O single crystals exhibit no emission characteristics. More importantly, there exists a thermal-induced phase transformation from (1-mpip)MnCl4·3H2O to emissive (1-mpip)2MnCl6 at 372 K. Moreover, a reversible luminescent conversion between (1-mpip)MnCl4·3H2O and (1-mpip)2MnCl6 was simply achieved when heated to 383 K and placed in a humid environment or sprayed with water. This work not only deepens the understanding of the thermal-induced phase transformation and humidity-sensitive luminescent conversion of hybrid Mn(II)-based halides, but also provides a guidance for thermal and humidity sensing and anticounterfeiting applications of these hybrid materials.

Tuned Transport Path of Perovskite MAPbI3 -based Memristor Structure

In this study, the features of resistive random access memory (RRAM) employing a straightforward Cr/MAPbI3 /FTO three-layer structure have been examined and clarified. The device displays various resistance switching (RS) behavior at various sweep voltages between 0.5 and 5 V. The RS effect has a conversion in the direction of the SET and RESET processes during sweeping for a number of cycles at a specific voltage. The directional change of the RS processes corresponds to the dominant transition between the generation/recombination of iodide ion and vacancy in the MAPbI3 perovskite layer and the electrochemical metallization of the Cr electrode under the influence of an electric field, which results in the conductive filament (CF) formation/rupture. At each stage, these processes are controlled by specific charge conduction mechanisms, including Ohmic conduction, space-charge-limited conduction (SCLC), and variable-range hopping (VRH). By identifying the biased voltage and the quantity of voltage sweep cycles, one can take a new approach to control or modulate the pathways for effective charge transport. This new approach is made possible by an understanding of the RS characteristics and the corresponding mechanisms causing the variation of RS behavior in the structure.

Polyacrylonitrile Passivation for Enhancing the Optoelectronic Switching Performance of Halide Perovskite Memristor for Image Boolean Logic Applications

For the CH3NH3PbI3-based optoelectronic memristor, the high ion-migration randomness induces high fluctuation in the resistive switching (RS) parameters. Grain boundaries (GBs) are well known as the ion-migration sites due to their low energy barrier. Herein, a polyacrylonitrile (PAN) passivation method is developed to reduce GBs of the CH3NH3PbI3 film and improve the switching uniformity of the memristor. The crystal grain size of CH3NH3PbI3 increases with the addition of PAN, and the corresponding number of GBs is consequently reduced. The fluctuations of the RS parameters of the memristor device are significantly reduced. With the memristor, nonvolatile image sensing, image memory, and image Boolean operations are demonstrated. This work proposes a strategy for developing high-performance CH3NH3PbI3 optoelectronic memristors.

Low power highly flexible BiFeO3-based resistive random access memory (RRAM) with the coexistence of negative differential resistance (NDR)

We demonstrated the resistive random access memory characteristics for Cu (top contact)/BFO/PMMA (active layer)/ITO (bottom electrode)/PET sheet as a flexible substrate device configuration. The device showed non-volatile bipolar resistive switching characteristics with good repeatability and the coexistence of NDR for 100 cycles or more with 0.28/3.43 mW power consumption for 1^st/100^th cycles. The device retains its read state for 10⁴ s or more and switches from LRS to HRS or vice versa for 10³ cycles with a pulse width of 100 ms for a write-read-erase-read pulse without affecting the memory characteristics. The Weibull distribution suggests that a set state is more stable than the reset state with shape factor β = 25.20. The device follows Ohmic behavior for the lower applied external field and Child square and Schottky emission for the higher external fields. The Joule heating, Sorets, and Fick's forces are responsible for the formation and rupturing of ionic filament. The coexistence of resistive switching and flexible strength of the device sustains the bending curvature of infinity, 0.2 cm, 1 cm, 1.7 cm, and 2.2 cm. The memory characteristics are retained under tensile conditions for 100 cycles or more. More interestingly, the power consumption for sustaining the NDR region with bending (19 μW) is much lower than without bending (0.19 mW). Thus, this study provides the possibility of integrating BFO with flexible substrates suitable for hybrid organic/inorganic memory structures.

Effects of drying time on the formation of merged and soft MAPbI3 grains and their photovoltaic responses

The grain sizes of soft CH₃NH₃PbI₃ (MAPbI₃) thin films and the atomic contact strength at the MAPbI₃/P3CT-Na interface are manipulated by varying the drying time of the saturated MAPbI₃ precursor solutions, which influences the device performance and lifespan of the resultant inverted perovskite photovoltaic cells. The atomic-force microscopy images, cross-sectional scanning electron microscopy images, photoluminescence spectra and absorbance spectra show that the increased short-circuit current density (J _SC) and increased fill factor (FF) are mainly due to the formation of merged MAPbI₃ grains. Besides, the open-circuit voltage (V _OC) of the encapsulated photovoltaic cells largely increases from 1.01 V to 1.15 V, thereby increasing the power conversion efficiency from 17.89% to 19.55% after 30 days, which can be explained as due to the increased carrier density of the MAPbI₃ crystalline thin film. It is noted that the use of the optimized drying time during the spin coating process results in the formation of merged MAPbI₃ grains while keeping the contact quality at the MAPbI₃/P3CT-Na interface, which boosts the device performance and lifespan of the resultant perovskite photovoltaic cells.

Simultaneously elevating the resistive switching level and ambient-air-stability of 3D perovskite (TAZ-H)PbBr3-based memory device by encapsulating into polyvinylpyrrolidone

The study about simultaneously enhancing the resistive switching level and ambient-air-stability of perovskite-based memorizers will promote its commercialization. Here, a new 3D perovskite (TAZ-H)PbBr₃ (TAZ-H⁺ = protonated thiazole) has been fabricated as FTO/(TAZ-H)PbBr₃/Ag device, which only exhibits binary memory performance with the high tolerant temperature of 170 °C. After encapsulating by polyvinylpyrrolidone (PVP), the (TAZ-H)PbBr₃@PVP composite-based device can demonstrate ternary resistive switching behavior with considerable ON2/ON1/OFF ratio (10^5.9: 10^3.9:1) and high ternary yield (68 %). Specially, this device presents good ambient-air stability at RH 80 % and thermal tolerance of 100 °C. The binary resistive switching mechanism can be ascribed to the halogen ion migration induced by bromine defects in the (PbBr₃)_n^n- framework. But the ternary resistive switching phenomenon in the (TAZ-H)PbBr₃@PVP-based device could be depicted as the carrier transport from filled traps of PVP to (PbBr₃)_n^n- framework (ON1 state) and then carriers flowing in the re-arranged (TAZ-H)_nⁿ⁺ chain in 3D channels (ON2 state). The PVP treatment can not only modify the grain boundary defects, but also facilitate the transport of injected carriers to the perovskite films via Pb-O coordinated bonds and inhibition of order-disorder transformation. This facial strategy for implementing ternary perovskite-based memorizers with good ambient-air-stability is quite meaningful for high-density memory in harsh environments.

Flexible Organic-Inorganic Halide Perovskite-Based Diffusive Memristor for Artificial Nociceptors

With the current evolution in the artificial intelligence technology, more biomimetic functions are essential to execute increasingly complicated tasks and respond to challenging work environments. Therefore, an artificial nociceptor plays a significant role in the advancement of humanoid robots. Organic-inorganic halide perovskites (OHPs) have the potential to mimic the biological neurons due to their inherent ion migration. Herein, a versatile and reliable diffusive memristor built on an OHP is reported as an artificial nociceptor. This OHP diffusive memristor showed threshold switching properties with excellent uniformity, forming-free behavior, a high I_ON/I_OFF ratio (10⁴), and bending endurance over >10² cycles. To emulate the biological nociceptor functionalities, four significant characteristics of the artificial nociceptor, such as threshold, no adaptation, relaxation, and sensitization, are demonstrated. Further, the feasibility of OHP nociceptors in artificial intelligence is being investigated by fabricating a thermoreceptor system. These findings suggest a prospective application of an OHP-based diffusive memristor in the future neuromorphic intelligence platform.

Halide perovskite photoelectric artificial synapses: materials, devices, and applications

In recent years, there has been a research boom on halide perovskites (HPs) whose outstanding performance in photovoltaic and optoelectronic fields is obvious to all. In particular, HP materials find application in the development of artificial synapses. HP-based synapses have great potential for artificial neuromorphic systems, which is due to their outstanding optoelectronic properties, femtojoule-level energy consumption, and simple fabrication process. In this review, we present the physical properties of HPs and describe two types of synaptic devices including two-terminal (2T) memristors and three-terminal (3T) transistors. The HP layer in 2T memristors can realize the change in the device conductance through physical mechanisms dominated by ion migration. On the other hand, HPs in 3T transistors can be used as efficient light-absorbing layers and rely on some special device structures to provide reliable current changes. In the final section of the article, we discuss some of the existing applications of HP-based synapses and bottlenecks to be solved.

Resistive random access memory: introduction to device mechanism, materials and application to neuromorphic computing

The modern-day computing technologies are continuously undergoing a rapid changing landscape; thus, the demands of new memory types are growing that will be fast, energy efficient and durable. The limited scaling capabilities of the conventional memory technologies are pushing the limits of data-intense applications beyond the scope of silicon-based complementary metal oxide semiconductors (CMOS). Resistive random access memory (RRAM) is one of the most suitable emerging memory technologies candidates that have demonstrated potential to replace state-of-the-art integrated electronic devices for advanced computing and digital and analog circuit applications including neuromorphic networks. RRAM has grown in prominence in the recent years due to its simple structure, long retention, high operating speed, ultra-low-power operation capabilities, ability to scale to lower dimensions without affecting the device performance and the possibility of three-dimensional integration for high-density applications. Over the past few years, research has shown RRAM as one of the most suitable candidates for designing efficient, intelligent and secure computing system in the post-CMOS era. In this manuscript, the journey and the device engineering of RRAM with a special focus on the resistive switching mechanism are detailed. This review also focuses on the RRAM based on two-dimensional (2D) materials, as 2D materials offer unique electrical, chemical, mechanical and physical properties owing to their ultrathin, flexible and multilayer structure. Finally, the applications of RRAM in the field of neuromorphic computing are presented.

Supramolecular Framework Constructed by Dendritic Nanopolymer for Stable Flexible Perovskite Resistive Random-Access Memory

The 3D supramolecular framework (3D-SF) is constructed in this work through the hydrogen bond assisted self-assembly of spherical dendritic nanopolymer to regulate the flexibility, stability, and resistive switching (RS) performance of perovskite resistive random-access memory (RRAM). Herein, the 3D-SF network acts as the perovskite crystallization template to regulate the perovskite crystallization process due to its coordination interaction of functional groups with the perovskite grains, presenting the uniform, pinhole-free, and compact perovskite morphology for stable flexible RRAM. The 3D-SF network in situ stays at the perovskite intergranular boundaries to crosslink the perovskite grains. The RS performance of 3D-SF-modified perovskite RRAM device is evidently improved to the ON/OFF ratio of 10⁵ , the cycle number of 500 times, and the data retention time of 10⁴ s. The 50-days exposure of unencapsulated RRAM device at ambient environment still makes the ON/OFF ratio to be kept at ≈10⁴ , indicating the potential of long-term stable multilevel storage in the high-density data storage. The bending action under different radius also does not change the RS performance due to the excellent bending-resistant ability of 3D-SF-modified perovskite film. This work explores a novel polymer additive strategy to construct the 3D supramolecular framework for stable flexible perovskite optoelectronic devices.

2D Organic Materials: Status and Challenges

In the past few decades, 2D layer materials have gradually become a central focus in materials science owing to their uniquely layered structural qualities and good optoelectronic properties. However, in the development of 2D materials, several disadvantages, such as limited types of materials and the inability to synthesize large-scale materials, severely confine their application. Therefore, further exploration of new materials and preparation methods is necessary to meet technological developmental needs. Organic molecular materials have the advantage of being customizable. Therefore, if organic molecular and 2D materials are combined, the resulting 2D organic materials would have excellent optical and electrical properties. In addition, through this combination, the free design and large-scale synthesis of 2D materials can be realized in principle. Furthermore, 2D organic materials exhibit excellent properties and unique functionalities along with great potential for developing sensors, biomedicine, and electronics. In this review, 2D organic materials are divided into five categories. The preparation methods and material properties of each class of materials are also described in detail. Notably, to comprehensively understand each material's advantages, the latest research applications for each material are presented in detail and summarized. Finally, the future development and application prospects of 2D organic materials are briefly discussed.

The Role of Polymers in Halide Perovskite Resistive Switching Devices

Currently, halide perovskites (HPs) are gaining traction in multiple applications, such as photovoltaics and resistive switching (RS) devices. In RS devices, the high electrical conductivity, tunable bandgap, good stability, and low-cost synthesis and processing make HPs promising as active layers. Additionally, the use of polymers in improving the RS properties of lead (Pb) and Pb-free HP devices was described in several recent reports. Thus, this review explored the in-depth role of polymers in optimizing HP RS devices. In this review, the effect of polymers on the ON/OFF ratio, retention, and endurance properties was successfully investigated. The polymers were discovered to be commonly utilized as passivation layers, charge transfer enhancement, and composite materials. Hence, further HP RS improvement integrated with polymers revealed promising approaches to delivering efficient memory devices. Based on the review, detailed insights into the significance of polymers in producing high-performance RS device technology were effectively understood.

Mechanistic and Kinetic Analysis of Perovskite Memristors with Buffer Layers: The Case of a Two-Step Set Process

With the increasing demand for artificially intelligent hardware systems for brain-inspired in-memory and neuromorphic computing, understanding the underlying mechanisms in the resistive switching of memristor devices is of paramount importance. Here, we demonstrate a two-step resistive switching set process involving a complex interplay among mobile halide ions/vacancies (I^-/V_I⁺) and silver ions (Ag⁺) in perovskite-based memristors with thin undoped buffer layers. The resistive switching involves an initial gradual increase in current associated with a drift-related halide migration within the perovskite bulk layer followed by an abrupt resistive switching associated with diffusion of mobile Ag⁺ conductive filamentary formation. Furthermore, we develop a dynamical model that explains the characteristic I-V curve that helps to untangle and quantify the switching regimes consistent with the experimental memristive response. This further insight into the two-step set process provides another degree of freedom in device design for versatile applications with varying levels of complexity.

Two metal-free perovskite molecules with different 3D frameworks show reversible phase transition, dielectric anomaly and SHG effect

Three-dimensional (3D) hybrid organic-inorganic perovskites (HOIPs) have attracted tremendous research interest due to their unique structure and promising applications. However, research on the design, synthesis and properties of this kind of metal-free crystalline material is still in the exploratory stage. Herein, two 3D perovskite molecules [1,4-3.2.2-dabcn]NH₄Br₃ (1) and [1,4-3.2.2-dabcn]NH₄I₃·0.5H₂O (2) were obtained by reacting 1,4-diazabicyclo[3.2.2]nonane (1,4-3.2.2-dabcn) with NH₄X (X = Br and I) in the corresponding concentrated halogen acids. The single X-ray diffraction results demonstrated that the inorganic framework structures in compounds 1 and 2 constructed with NH₄Br and NH₄I are completely different, caused by the radius of the bromide ion being smaller than that of the iodide ion. The 3D framework of compound 1 is constructed with a coplanar dimer [(NH₄)₂Br₆]^2- as the basic building unit, leading to the expanded 3D perovskite framework structure with a larger cavity to accommodate the 1,4-3.2.2-dabcn molecule. Nevertheless, compound 2 adopts a familiar 3D crystal framework structure with corner-sharing [(NH₄)I₆] octahedra, where the [1,4-3.2.2-dabcn] cations and water solvent molecule are confined in the cavities enclosed by the octahedra. Notably, both compounds exhibit reversible phase transition, dielectric anomaly and the second harmonic generation (SHG) effect. From the perspective of molecular design, this work is of great significance to guide the construction of new 3D metal-free perovskite molecular materials with reversible properties.

Polyoxometalate-Viologen Thermochromic Hybrids for Organic Amine Detectors and Memristors with Temperature-Regulating Resistance Switching Characteristics

There are relatively few reports on the combination of viologen and polyoxometalates (POMs). Herein, we successfully synthesized three viologen-POM-based compounds by in situ transformation of ligands under hydrothermal conditions, namely, {M^II(1,4-cby)₂[H₂(γ-Mo₈O₂₆)]}·nH₂O (1: M = Ni, n = 4; 2: M = Co, n = 6), and [Ni^II(1,3-cby)(H₂O)₄(β-Mo₈O₂₆)_0.5]·2H₂O (3) (1,4-cby·Cl = 1-(4-carboxy-benzyl)-[4,4']bipyridinyl-1-ium, 1,3-cby·Cl = 1-(3-carboxy-benzyl)-[4,4']bipyridinyl-1-ium). Isostructural compounds 1 and 2 exhibit two-dimensional (2D) layer structures with POMs as linking nodes, while compound 3 shows a one-dimensional (1D) metal-organic chain with dissociative POM anions. When the temperature increases, compounds 1-3 show good reversible thermochromism properties and also have a fluorescence quenching effect. Moreover, compounds 1-3 can also be used as detectors for organic amines, especially in the atmosphere of ammonia, ethylenediamine, and diethylamine with an obvious discoloration effect. In addition, compound 1 was used as a material for the preparation of memristors with superior properties (distinct temperature-adjusted resistive switching properties). It shows bipolar resistive switching (RS) behavior at different temperatures of 20, 50, and 100 °C. The results show that the 1-based memristor has good thermal stability, which is important for high-temperature environment applications. It also shows that crystalline viologen-POM-based compounds are ideal candidates for making memristors.

Dual Resistive Switching Performance Derived from Ionic Migration in Halide Perovskite Based Memory

Herein, we report an environmentally stable and friendly halide perovskite based resistive random access memory device with an Ag/PMMA/(PMA)₂CuBr₄/FTO (PMMA = poly(methyl methacrylate); PMA = C₆H₅CH₂NH₃) architecture. The device exhibits the coexistence of two bipolar resistive switching modes, including counterclockwise and clockwise switching characteristics. The devices with both switching modes show stable endurance (>100 cycles) and long retention performance (>10⁴ s). By applying a suitable electrical stimulation, the counterclockwise and clockwise switching behaviors are interconvertible. Furthermore, the Au/PMMA/(PMA)₂CuBr₄/FTO and Ag/(PMA)₂CuBr₄/FTO devices were fabricated to verify the origin of dual resistive switching behaviors. The similar dual resistive switching behaviors after electroforming processes of three types of memory devices suggest that the interconvertible dual resistive switching characteristics could be attributed to the ionic migration in the (PMA)₂CuBr₄ perovskite layer.

Flexible Memristor Devices Using Hybrid Polymer/Electrodeposited GeSbTe Nanoscale Thin Films

We report on the development of hybrid organic-inorganic material-based flexible memristor devices made by a fast and simple electrochemical fabrication method. The devices consist of a bilayer of poly(methyl methacrylate) (PMMA) and Te-rich GeSbTe chalcogenide nanoscale thin films sandwiched between Ag top and TiN bottom electrodes on both Si and flexible polyimide substrates. These hybrid memristors require no electroforming process and exhibit reliable and reproducible bipolar resistive switching at low switching voltages under both flat and bending conditions. Multistate switching behavior can also be achieved by controlling the compliance current (CC). We attribute the switching between the high resistance state (HRS) and low resistance state (LRS) in the devices to the formation and rupture of conductive Ag filaments within the hybrid PMMA/GeSbTe matrix. This work provides a promising route to fabricate flexible memory devices through an electrodeposition process for application in flexible electronics.

Metal Halide Perovskite/Electrode Contacts in Charge-Transporting-Layer-Free Devices

Metal halide perovskites have drawn substantial interest in optoelectronic devices in the past decade. Perovskite/electrode contacts are crucial for constructing high-performance charge-transporting-layer-free perovskite devices, such as solar cells, field-effect transistors, artificial synapses, memories, etc. Many studies have evidenced that the perovskite layer can directly contact the electrodes, showing abundant physicochemical, electronic, and photoelectric properties in charge-transporting-layer-free perovskite devices. Meanwhile, for perovskite/metal contacts, some critical interfacial physical and chemical processes are reported, including band bending, interface dipoles, metal halogenation, and perovskite decomposition induced by metal electrodes. Thus, a systematic summary of the role of metal halide perovskite/electrode contacts on device performance is essential. This review summarizes and discusses charge carrier dynamics, electronic band engineering, electrode corrosion, electrochemical metallization and dissolution, perovskite decomposition, and interface engineering in perovskite/electrode contacts-based electronic devices for a comprehensive understanding of the contacts. The physicochemical, electronic, and morphological properties of various perovskite/electrode contacts, as well as relevant engineering techniques, are presented. Finally, the current challenges are analyzed, and appropriate recommendations are put forward. It can be expected that further research will lead to significant breakthroughs in their application and promote reforms and innovations in future solid-state physics and materials science.

Improved Performance of the Al2O3-Protected HfO2-TiO2 Base Layer with a Self-Assembled CH3NH3PbI3 Heterostructure for Extremely Low Operating Voltage and Stable Filament Formation in Nonvolatile Resistive Switching Memory

Herein, we report intriguing observations of an extremely stable nonvolatile bipolar resistive switching (NVBRS) memory device fabricated using HfO₂-TiO₂ topologically protected by Al₂O₃ as a stacked base layer for a CH₃NH₃PbI₃ (MAPI) electrolyte layer sandwiched between Ag and fluorine-doped tin oxide (FTO) electrodes. MAPI has been successfully synthesized by a rapid microwave-solvothermal (MW-ST) method within 10 min at 120 °C without requiring any inert gas atmosphere using low-cost precursors and solvents. Subsequently, MAPI powders are dissolved in aprotic solvents (DMF/DMSO = 8:2), and a spin-coated thin film is allowed to recrystallize upon annealing at 120 °C via a solution-based nanoscale self-assembly process. The fabricated memory device with the Ag/MAPI/Al₂O₃/TiO₂-HfO₂/FTO configuration shows an enhanced resistance ratio of 10⁵ for >10⁴ s at an extremely lower operating voltage (SET +0.2 V, RESET -0.2 V) when compared to that of the pristine MAPI device (±1 V, 10², 10⁴ s). We show that the memory device also exhibits a remarkable endurance of ≥3500 cycles due to the Al₂O₃ robust coating on the HfO₂-TiO₂ layer, facilitating prompt heterojunction formation. Thus, the adopted innovative strategies to prepare structurally and optically stable (∼1.5 years) MAPI under high-humid conditions could offer enhanced performance of NVBRS memory devices for medical, security, internet of things (IoT), and artificial intelligence (AI) applications.

A Polyanionic Strategy to Modify the Perovskite Grain Boundary for a Larger Switching Ratio in Flexible Woven Resistive Random-Access Memories

The intergranular interface modification of organic-inorganic hybrid perovskites (OHP) is an important issue to regulate the flexibility, stability, and resistive switching (RS) performance of resistive random-access memories (RRAMs). A novel strategy of polymer additives for OHP intergranular interface modification is explored in this work with the polyanionic backbone to improve the distribution of cage-shaped cavity molecules at the perovskite grain boundaries. Specifically speaking, poly(1-adamantylammonium acrylate) (PADAm) is first synthesized through the acid-base reaction of polyacrylic acid with 1-adamantylamine to simultaneously realize the introduction of a cage-shaped cavity molecule and the polyanionic backbone. Herein, organic ammonium cations 1-adamantylammonium (ADNH₃⁺) in PADAm are applied as the cage-shaped cavity molecules to tune the dielectric property by being anchored at the perovskite grain boundaries. Meanwhile, polyacrylic anions in PADAm play the role of the polyanionic backbone to produce the more uniform distribution of ADNH₃⁺. Simultaneously, the flexibility and stability of OHP RRAM devices are also improved due to the introduction of the polyanionic backbone. Consequently, the 4% ADNH₃I-modified planar device exhibits the stable nonvolatile RS behavior with an on/off ratio of ∼10⁴, even with one-month exposure under an ambient environment. Importantly, the introduction of PADAm in the flexible fibrous crosspoint of functional fiber Al@MAPbI₃:PADAm and bare Al fiber further increases the on/off ratio to 10⁸ due to the effectively improved distribution of hollow cage-shaped ADNH₃⁺ at the perovskite intergranular interfaces together with the application of the fibrous crosspoint device configuration. Especially, these excellent crosspoint RRAM devices can be integrated into the woven fibrous RRAM array in the thermal plastic packaging configuration. In addition, the excellent multilevel RS behavior can also be realized in the woven fibrous RRAM array, indicating potential high-density data storage. This work provides a novel strategy of polymer additives bearing the polyanionic backbone to improve the flexibility, stability, and RS performance of perovskite RRAM devices.

Advances in Emerging Photonic Memristive and Memristive-Like Devices

Possessing the merits of high efficiency, low consumption, and versatility, emerging photonic memristive and memristive-like devices exhibit an attractive future in constructing novel neuromorphic computing and miniaturized bionic electronic system. Recently, the potential of various emerging materials and structures for photonic memristive and memristive-like devices has attracted tremendous research efforts, generating various novel theories, mechanisms, and applications. Limited by the ambiguity of the mechanism and the reliability of the material, the development and commercialization of such devices are still rare and in their infancy. Therefore, a detailed and systematic review of photonic memristive and memristive-like devices is needed to further promote its development. In this review, the resistive switching mechanisms of photonic memristive and memristive-like devices are first elaborated. Then, a systematic investigation of the active materials, which induce a pivotal influence in the overall performance of photonic memristive and memristive-like devices, is highlighted and evaluated in various indicators. Finally, the recent advanced applications are summarized and discussed. In a word, it is believed that this review provides an extensive impact on many fields of photonic memristive and memristive-like devices, and lay a foundation for academic research and commercial applications.

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.

Actual origin and precise control of asymmetrical hysteresis in an individual CH3NH3PbI3 micro/nanowire for optical memory and logic operation

Although CH₃NH₃PbI₃ can present an excellent photoresponse to visible light, its application in solar cells and photodetectors is seriously hindered due to hysteresis behaviour. Moreover, for its origin, there exist different opinions. Herein, we demonstrate a route to realize precise control for the electrical transport of a single CH₃NH₃PbI₃ micro/nanowire by constructing a two-terminal device with asymmetric Ag and C electrodes, and its hysteresis can be clearly identified as a synergistic effect of the redox reaction at the interface of the Ag electrode and the injection and ejection of holes in the interfacial traps of the C electrode rather than its bulk effect. The device can show superior bias amplitude and illumination intensity dependence of hysteresis loops with typical bipolar resistive switching features. Thus, an excellent multilevel nonvolatile optical memory can be effectively realized by the modulation of the illumination and bias, and moreover a logic OR gate operation can be successfully implemented with voltage and illumination as input signals as well. This work clearly reveals and provides a new insight of hysteresis origin that can be attributed to a synergistic effect of two asymmetrical electrode interfaces, and therefore precisely controlling its electrical transport to realize an outstanding application potential in multifunctional devices integrated with optical nonvolatile memory and logic OR gate operation.

Transparent, Flexible, and Low-Operating-Voltage Resistive Switching Memory Based on Al2O3/IZO Multilayer

In this study, a different number of indium zinc oxide (IZO) interlayers are fabricated into Al₂O₃-based transparent resistive switching memory on a transparent indium tin oxide (ITO)/glass substrate at room temperature. Al₂O₃/IZO multilayer transparent memory has a transmittance of at least 65% in the wavelength range of 400-900 nm. In addition, the Al₂O₃/IZO multilayer transparent memory can achieve an electroforming voltage that is 35.7% lower than that of ITO/pure-Al₂O₃/IZO transparent memory. The fabricated Al₂O₃/IZO multilayer transparent memory exhibits typical bipolar resistive switching behavior, regardless of the number of IZO interlayers. Also, the fabricated Al₂O₃/IZO multilayer transparent memory has a low operating voltage within ±1.5 V. In addition, a flexible Al₂O₃/IZO multilayer transparent memory is fabricated using the same process on ITO-coated polyethylene terephthalate. The fabricated flexible transparent memory also maintains the resistive switching characteristics during the bending state.

Metal Halide Perovskite-Based Memristors for Emerging Memory Applications

There is an increased demand for next-generation memory devices with high density and fast operation speed to replace conventional memory devices. Memristors are promising candidates for next-generation memory devices because of their scalability, stable data retention, low power consumption, and fast operation. Among the various types of memristors, halide perovskites exhibit potential as emerging materials for memristors by using hysteresis based on the movement of defects or ions in halide perovskites. However, research on the implementation of perovskite materials as memristors is in its early stages; some challenges and problems must be solved to enable the practical application of halide perovskites for next-generation memory devices. From this perspective, we highlight the recent progress in memristors that use halide perovskites. Moreover, we introduce a strategy to enhance the performance and analyze the operation mechanism of memory devices that use halide perovskites. Finally, we summarize the challenges in the development of device technology to use halide perovskites in next-generation memory devices.

Back Interface Passivation for Efficient Low-Bandgap Perovskite Solar Cells and Photodetectors

Low-bandgap (E_g~1.25 eV) mixed tin-lead (Sn-Pb) perovskites are promising candidates for efficient solar cells and self-powered photodetectors; however, they suffer from huge amounts of defects due to the unintentional p-type self-doping. In this work, the synergistic effects of maltol and phenyl-C61-butyric acid methyl ester (PCBM) were achieved to improve the performance of low-bandgap perovskite solar cells (PSCs) and unbiased perovskite photodetectors (PPDs) by passivating the defects and tuning charge transfer dynamics. Maltol eliminated the Sn-related traps in perovskite films through a strong metal chelating effect, whereas PCBM elevated the built-in electric potential and thus improved voltage through the spike energy alignment. Combining both advantages of maltol and PCBM, high-quality perovskite films were obtained, enabling low-bandgap PSCs with the best efficiency of 20.62%. Moreover, the optimized PSCs were further applied as self-powered PPDs in a visible light communication system with a response time of 0.736 μs, presenting a satisfactory audio transmission capability.

Metal-Free Perovskite Piezoelectric Nanogenerators for Human-Machine Interfaces and Self-Powered Electrical Stimulation Applications

Single crystal metal-free halide perovskites have received great attention in recent years owing to their excellent piezoelectric and ferroelectric properties. However, the nanotoxicity and piezoelectricity within the nanoscale of such materials have yet been reported for the demonstration of practical applications. In this work, the observation of intrinsic piezoelectricity in metal-free perovskite (MDABCO-NH₄ I₃ ) films using piezoresponse force microscopy (PFM) is reported. A cytotoxicity test is also performed on MDABCO-NH₄ I₃ to evaluate its low-toxic nature. The as-synthesized MDABCO-NH₄ I₃ is further integrated into a piezoelectric nanogenerator (PENG). The MDABCO-NH₄ I₃ -based PENG (MN-PENG) exhibits optimal output voltage and current of 15.9 V and 54.5 nA, respectively. In addition, the MN-PENG can serve as a self-powered strain sensor for human-machine interface applications or be adopted in in vitro electrical stimulation devices. This work demonstrates a path of perovskite-based PENG with high performance, low toxicity, and multifunctionality for future advanced wearable sensors and portable therapeutic systems.

Novel charm of 2D materials engineering in memristor: when electronics encounter layered morphology

The family of two-dimensional (2D) materials composed of atomically thin layers connected via van der Waals interactions has attracted much curiosity due to a variety of intriguing physical, optical, and electrical characteristics. The significance of analyzing statistics on electrical devices and circuits based on 2D materials is seldom underestimated. Certain requirements must be met to deliver scientific knowledge that is beneficial in the field of 2D electronics: synthesis and fabrication must occur at the wafer level, variations in morphology and lattice alterations must be visible and statistically verified, and device dimensions must be appropriate. The authors discussed the most recent significant concerns of 2D materials in the provided prose and attempted to highlight the prerequisites for synthesis, yield, and mechanism behind device-to-device variability, reliability, and durability benchmarking under memristors characteristics; they also indexed some useful approaches that have already been reported to be advantageous in large-scale production. Commercial applications, on the other hand, will necessitate further effort.

Ion Migration in Organic-Inorganic Hybrid Perovskite Solar Cells: Current Understanding and Perspectives

Organic-inorganic hybrid perovskite (OIHPs) solar cells are the most promising alternatives to traditional silicon solar cells, with a certified power conversion efficiency beyond 25%. However, the poor stability of OHIPs is one of the thorniest obstacles that hinder its commercial development. Among all the factors affecting stability, ion migration is prominent because it is unavoidable and intrinsic in OHIPs. Therefore, it is important to understand the mechanism for ion migration and regulation strategies. Herein, the types of ions that may migrate in OHIPs are first discussed; afterward, the migrating channels are demonstrated. The effects of ion migration are further elaborated. While ion migration can facilitate the p-i-n structure in some cases, the current hysteresis and other adverse effects such as phase segregation in OHIPs attract widespread attention. Based on these, several recent strategies to suppress the ion migration are enumerated, including the introduction of alkali cations, organic additives, grain boundaries passivation, and employment of low-dimensional perovskites. Finally, the prospect for further modulating the ion migration and more stable perovskite solar cells is proposed.

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.

Flexible SnO Optoelectronic Memory Based on Light-Dependent Ionic Migration in Ruddlesden-Popper Perovskite

Nonvolatile optoelectronic memories based on organic-inorganic hybrid perovskites have appeared as powerful candidates for next-generation soft electronics. Here, ambipolar SnO transistor-based nonvolatile memories with multibit memory behavior (11 storage states, 120 nC state^-1) and ultralong retention time (>10⁵ s) are demonstrated for which an Al₂O₃/two-dimensional Ruddlesden-Popper perovskite (2D PVK) heterostructure dielectric architecture is employed. The unique storage features are attributed to suppressed gate leakage by Al₂O₃ layer and hopping-like ionic transport in 2D PVK with varying activation energy under different light intensities. The photoinduced field-effect mechanism enables top-gated transistor operation under illumination, which would not be achieved under dark. As a result, the device exhibits remarkable photoresponsive characteristics, including ultrahigh specific detectivity (2.7 × 10¹⁵ Jones) and broadband spectrum distinction capacity (375-1064 nm). This study offers valuable insight on the PVK-based dielectric engineering for information storage and paves the way toward multilevel broadband-response optoelectronic memories.

Flexible and Stretchable Memristive Arrays for in-Memory Computing

With the tremendous progress of Internet of Things (IoT) and artificial intelligence (AI) technologies, the demand for flexible and stretchable electronic systems is rapidly increasing. As the vital component of a system, existing computing units are usually rigid and brittle, which are incompatible with flexible and stretchable electronics. Emerging memristive devices with flexibility and stretchability as well as direct processing-in-memory ability are promising candidates to perform data computing in flexible and stretchable electronics. To execute the in-memory computing paradigm including digital and analogue computing, the array configuration of memristive devices is usually required. Herein, the recent progress on flexible and stretchable memristive arrays for in-memory computing is reviewed. The common materials used for flexible memristive arrays, including inorganic, organic and two-dimensional (2D) materials, will be highlighted, and effective strategies used for stretchable memristive arrays, including material innovation and structural design, will be discussed in detail. The current challenges and future perspectives of the in-memory computing utilizing flexible and stretchable memristive arrays are presented. These efforts aim to accelerate the development of flexible and stretchable memristive arrays for data computing in advanced intelligent systems, such as electronic skin, soft robotics, and wearable devices.

Solution-Processed Light Induced Multilevel Non-volatile Wearable Memory Device Based on CsPb2Br5 Perovskite

Despite of the recent advancements on memory devices, quest for the building materials having low-power consumption is still on with the ultimate focus over durability of system and reliability and...

Single Crystal Halide Perovskite Film for Nonlinear Resistive Memory with Ultrahigh Switching Ratio

Morre's law is coming to an end only if the memory industry can keep stuffing the devices with new functionality. Halide perovskite acts as a promising candidate for application in next-generation nonvolatile memory. As is well known, the switching ratio is the key device requirement of resistive memory to improve recognition accuracy. Here, the authors introduce an all-inorganic halide perovskite CsPbBr₃ single crystal film (SCF) into resistive memory as an active layer. The Ag/CsPbBr₃ /Ag memory cells exhibit reproducible resistive switching with an ultrahigh switching ratio (over 10⁹ ) and a fast switching speed (1.8 µs). It is studied that the Schottky barrier of metal/CsPbBr₃ SCF contact follows the tendency of Schottky-Mott theory, and the Fermi level pinning effect is effectively reduced. The interface S parameter of metal/CsPbBr₃ SCF contact is 0.50, suggesting a great interface contact is formed. The great interface contact contributes to the steady high resistance state (HRS), and then the steady HRS leads to an ultrahigh resistive switching ratio. This work demonstrates high performance from halide perovskite SCF-based memory. The introduction of halide perovskite SCF in resistive random access memory provides great potential as an alternative in future computing systems.

Light-activated Multilevel Resistive Switching Storage in Pt/Cs2AgBiBr6/ITO/Glass Devices

High-density Cs₂AgBiBr₆ films with uniform grains were prepared by a simple one-step and low-temperature sol-gel method on indium tin oxide (ITO) substrates. An explicit tristate bipolar resistance switching behavior was observed in the Pt/Cs₂ AgBiBr₆/ITO/glass devices under irradiation of 10 mW/cm² (445 nm). This behavior was stable over 1200 s. The maximum ratio of the high and low resistance states was about 500. Based on the analysis of electric properties, valence variation and absorption spectra, the resistive switching characteristics were attributed to the trap-controlled space charge-limited current mechanism due to the bromine vacancies in the Cs₂AgBiBr₆ layer. On the other hand, it is suggested that the ordering of the Schottky-like barrier located at Pt/Cs₂AgBiBr₆ affects the three-state resistance switching behavior under light irradiation. The ability to adjust the photoelectrical properties of Cs₂AgBiBr₆-based resistive switching memory devices is a promising strategy to develop high-density memory.

Halide Perovskites for Resistive Switching Memory

Resistive switching random access memory (RRAM), also known as memristor, is regarded as an emerging nonvolatile memory and computing-in-memory technology to address the intrinsic physical limitations of conventional memory and the bottleneck of von Neumann architecture. In particular, halide perovskite RRAMs have attracted widespread attention in recent years because of their ionic migration nature and excellent photoelectric properties. This Perspective first provides a condensed overview of halide perovskite RRAMs based on materials, device performance, switching mechanism, and potential applications. Moreover, this Perspective attempts to detail the challenges, such as the quality of halide perovskite films, the compatible processing of device fabrication, the reliability of memory performance, and clarification of the switching mechanism, and further discusses how the outstanding challenges of halide perovskite RRAMs could be met in future research.